ISS BOOK _ 7
International
Secondary
Science
Ann Fullick
Philippa Gardom Hulme
Catherine Jones
Second Edition
Contents
Introduction
Thinking and working scientifically
1
Asking questions
iii
3.5
Using science to prevent disease
56
3.6
Strengthening the immune system
58
v
3.7
Microorganisms and disease
60
2
Planning and carrying out investigations
vii
3.8
Infectious diseases: Hepatitis
62
3
Collecting and recording data
ix
3.9
Infectious diseases: Covid-19
64
4
Drawing graphs
xi
3.10
Infectious diseases: Typhoid
66
5
Analysis
xiii
3.11
Infectious diseases: Dengue
68
6
Evaluation
xv
3.12
Review
70
1
Plant Systems
1.1
Plants system
2
4.1
The Periodic Table
72
1.2
Photosynthesis
4
4.2
The periodic table: Group 1
74
1.3
Evidence for photosynthesis: testing for starch 6
4.3
Inside atoms
76
1.4
Evidence of photosynthesis: oxygen bubbles
8
4.4
Atomic number and the Periodic Table
78
1.5
Respiration and Photosynthesis
10
4.5
Mass number
80
1.6
The need for minerals
12
4.6
Electrons in atoms
82
1.7
The use of fertilisers
14
4.7
Review
84
1.8
Water and mineral transport in plants
16
5
1.9
Factors affecting transpiration
18
5.1
Making ions
86
1.10
Xylem, phloem and plant pests
20
5.2
Inside ionic compounds
88
1.11
Review
22
5.3
Covalent bonding
90
5.4:
Covalent structures
92
5.5
Valency and chemical formulae
94
Review
96
2
4
Transport Systems in Humans
Structure of an Atom
Chemical Bonds
2.1
Human respiratory system
24
2.2
Aerobic and anaerobic respiration
26
5.6
2.3
The lungs and gas exchange
28
6
2.4
Investigating respiration
30
6.1
Chemical and physical changes
2.5
Breathing
32
6.2
Physical and chemical properties
100
2.6
The structure of the alveoli
34
6.3
Using materials: Thermal conductivity
102
2.7
Asthma
36
6.4
Using materials: Bicycles
104
2.8
The human heart and circulatory system
38
6.5
Using materials: Rusting
106
2.9
Arteries, veins and capillaries
40
6.6
Preventing rusting
108
2.10
Transport in the blood
42
6.7
Using materials: Combustion
110
2.11
The effect of exercise on pulse rate
44
6.8
112
Review
Review
2.12
46
3
Immunity and Diseases
3.1
Microorganisms
48
3.2
Pathogens and infectious diseases
50
3.3
Body defences against pathogens
52
3.4
The adaptive immune system
54
i
7
Physical and Chemical Changes
98
Solutions
7.1
Speeding up dissolving – 1
114
7.2
Speeding up dissolving – 2
116
7.3
Solutions and concentration
118
7.4
How much salt is in the sea?
120
7.5
Chlorine and water
122
Contents
7.6
Solubility
7.7
Investigating solubility and temperature – 1 126
7.8
Investigating temperature and solubility – 2 128
7.9
Factors affecting solubility
130
7.10
Review
132
8
124
Heat and Temperature
12
Earth and Space
12.1
The force of gravity
194
12.2
Orbits
196
12.3
How ‘old’ is gravity?
198
12.4
The Moon
200
12.5
Our planet: Day and night
202
8.1
Hot and cold
134
12.6
Our planet: Seasons
204
8.2
Thermal expansion and contraction
136
12.7
Using planetary data
206
8.3
Energy transfer: Conduction
138
12.8
Review
208
8.4
Energy transfer: Convection
140
8.5
Energy transfer: Radiation
142
1
Choosing apparatus
210
8.6
Insulating homes
144
2
Working accurately and safely
212
8.7
Cooling by evaporation
146
Glossary
8.8
Review
148
9
Waves and energy
9.1
Introducing waves
150
9.2
Describing waves
152
9.3
Sound waves and how they travel
154
9.4
Detecting sounds
156
9.5
Observing sound
158
9.6
Hearing, decibels, and risk
160
9.7
Review
162
10
Reference
214
Forces and Motion
10.1
Introduction to forces
164
10.2
Action and reaction pairs
166
10.3
Air resistance
168
10.4
Changing ideas about motion
170
10.5
Planning fair tests: Streamlining
172
10.6
Speed
174
10.7
Precision and accuracy: What’s the difference?
176
10.8
Distance–time graphs
178
10.9
Acceleration and speed–time graphs
180
10.10 Presenting data from racing
182
10.11 Review
184
11
Technology in Everyday Life
11.1
Making a simple stethoscope
186
11.2
Preserving food
188
11.3
Irrigation system
190
11.4
Making hand sanitizer
192
ii
Introduction
How to use your Student Book
Welcome to your International Secondary Science Student Book. This book
has been written to help you study science at all three secondary stages in
accordance with the National Curriculum of Pakistan.
Most of the units in this book work like this:
y
y
Every page starts with the learning objectives for the unit.
y
At the end of each unit there are questions to test that you understand
what you have learned. The first question is straightforward and later
questions are more challenging.
Answers are available in the Teacher Handbook
y
The key points to remember from the unit are also summarised here.
Keywords are marked in bold. You can check the meaning of these words
in the glossary at the back of the book.
In addition, many of the units help you think and work scientifically, put science
in context, prepare for the next level, and test your knowledge.
Thinking and working scientifically
Thinking and working scientifically is an important component of the
curriculum framework.
The Thinking and working scientifically units and features will help you learn:
y
iii
how to understand and apply models and representations
Introduction
y
the importance of asking scientific questions and planning how to answer
them
y
y
how to carry out enquiries such as fair test investigations and field work
how to analyse data, draw conclusions, and evaluate your enquiry.
Questions which test your Thinking and working scientifically skills and
TWS knowledge are marked with this icon.
You will find next a dedicated Thinking and working scientifically chapter which
introduces essential skills which will be useful throughout every stage of the
curriculum framework.
Science in context
Science in context units will also help you learn:
y
how scientists throughout history and from around the globe developed
theories, carried out research, and drew conclusions about the world around
them
y
y
how science is applied in everyday life
how issues involving our daily life are evaluated
Extension
Throughout this book there are lots of opportunities to learn even more about
physics, beyond the curriculum framework. These units are called Extension
because they extend and develop your science skills further.
You can tell when a question or part of a unit is Extension because it is
marked with a dashed line, like the one on the left.
Review
At the end of every chapter and every stage there are review questions.
These questions are written in the style of the Cambridge Checkpoint test. They are
there to help you review what you have learned in that chapter or stage. Answers
to these questions are available in the Teacher Handbook.
Reference
At the end of this book, there are reference pages providing further information
that will help you while you study.
They include information on:
y
y
y
how to choose suitable apparatus
how to work accurately and safely
key terms you have studied (Glossary)
iv
Thinking
and working
scientifically
1
Asking questions
How do scientists answer questions?
We can ask lots of different questions about the world. Why does the battery
last longer in some mobile phones than others? What might mobile phones
be like in the future? Which mobile phone is best?
Objectives
y There are questions that science can answer
y There are questions that science cannot answer.
y
What makes a question ‘scientific’?
y
y
Recognise that there are
many ways to find answers
to questions in science.
Understand how to
decide on a question to
investigate.
Understand that there
are some questions that
science cannot answer.
Part of making a prediction
is to think about what
might happen if your
hypothesis is wrong. Your
investigation should be
able to show the difference
between a correct and
an incorrect hypothesis.
Your conclusion will say
whether the evidence
supports, or does not
support, your hypothesis.
How does the type of
games I play affect the
battery life of my mobile
phone?
Scientists make observations and ask questions such as, ‘How do fossil
fuels form?’ or ‘Why are there are so many different animals on Earth?’
These are scientific questions.
A scientific question is a question that you can answer by collecting and
thinking about data. Data can be numbers from measurements, or words
from observations.
Hypotheses and predictions
When they have a question, scientists may produce a hypothesis. A
hypothesis is a scientific theory or proposed explanation made on the basis
of evidence that can be further tested. A prediction is what you think will
happen in the future. Scientists base their predictions on a hypothesis. Then
they do an investigation or make further observations to collect data to see
if their prediction is correct.
A hypothesis is testable if you can:
y write a prediction based on the hypothesis
y collect data to see whether your prediction is correct.
Types of investigation
Scientists do investigations to collect data. There are lots of different types
of investigation, for example:
y a fair test
y making a model
y a field study
y a survey or set of
observations over time.
Fair testing
In science, anything that might change during an experiment is called a
variable. The thing that you deliberately change to see whether it affects
the outcome of the experiment is a variable. Anything that is affected as a
result of your change is also a variable.
Saima's question can be
answered by doing a fair
test.
v
Thinking and working scientifically
In some situations, scientists design an experiment to try to answer their
question. To be sure of the answer, they must make it a fair test. In a fair
test, the scientists change one variable to find out what effect it has, and
they are careful to keep all the other variables the same.
The quantity that you change is the independent variable. A quantity that
changes as a result is called a dependent variable.
Making a model
Sometimes it is not possible to do a practical investigation to answer a
question – maybe what you are looking at is too big or small or dangerous
to experiment on. Scientists can also make models. As well as helping to
answer the question, a model can also be used to predict or to explain. Two
types of model are a physical model and a computer model.
In a fair test, you change
the independent variable,
measure the dependent
variable, and keep all the
other variables the same.
The other variables are
called control variables.
What types of food
do chimpanzees
eat?
y A physical model is useful for very large-scale or small-scale systems. You
y
may have used a physical model of the Earth and the Sun to explain why
we have day and night.
A computer model uses a computer program to find answers.
Field study
A field study is an investigation into plants or animals in their natural
habitat. When doing fieldwork, it is important that you make observations
without affecting what you are looking at.
A survey or regular observations or measurements
To answer some questions, a scientist might make lots of observations or
measurements, or do a survey. They might do this over a long time, or all
at the same time but in different locations. Sometimes a scientist uses data
that other scientists have collected before.
Tahir’s question can be
answered by making
lots of observations of
chimpanzees in their natural
habitat. She would collect
data and then choose the
best way to display it.
Which country uses the
most fuel?
Questions that science can’t answer
Scientists cannot answer every question. They cannot answer questions
about opinions, or questions for which the answer does not depend on
data.
Science cannot answer Sanaa’s question.
It could tell you:
y which phone battery lasts longest
y which phone can access web pages fastest.
But an investigation, a field study, observations, or a model will not tell you
which phone is best. This is because different people will have different
opinions about what is important: some people want a big screen, some
people want a good camera, some people want a tough case.
Moin’s question could be
answered by collecting
data from lots of different
countries and comparing
them.
Which phone should
I buy?
Science cannot answer
Sanaa’s question.
vi
Thinking
and working
scientifically
2
Planning and carrying out
investigations
How do scientists get the data they need to find the answer to a scientific
question? They need to make a plan to collect accurate and precise data.
Planning fair tests
Objectives
y
Describe how to plan a
fair test.
y
Describe how to plan other
types of investigation.
Before carrying out a fair test, you should make a plan. This helps to make
sure that you have all the equipment you need to get useful results, and that
you do not forget to do something, or do anything dangerous.
Selecting equipment
You need to select equipment that enables you to make measurements of
your independent and dependent variables. You may also need equipment
that will help you to control the other variables.
You should think about which equipment is most appropriate and how
to use it appropriately. For example, you may need to decide whether a
measuring cylinder or a beaker is better for measuring volume, or how to
measure length accurately.
Accurate and precise data
1
2
3
4
5
6
7
8
9
10
You should look straight at
a scale to make an accurate
measurement.
The measurements you make in an investigation are called data.
It is important to collect data that is accurate and precise.
Accurate data are close to the true value of what you are trying to measure.
Precise data give similar results if you repeat the measurements. The repeat
measurements in each set are grouped closely together. Precision is also
determined by the smallest division of the measuring instrument you are using.
Reliability
not accurate
not precise
accurate
not precise
You need to be confident that your data is reliable when you make a
conclusion. Data is reliable if you have taken enough measurements. How
many are enough?
y You need to have a big enough range of values of the independent
not accurate
precise
accurate
precise
Readings can be precise but
still not accurate.
y
y
vii
variable. The range is the difference between the biggest and smallest
values. If your range is not large enough you may realise after the
investigation that you cannot be confident in your conclusion.
You need to repeat your measurements. We usually make three repeat
measurements for every value of the independent variable. You can do
fewer, or more.
You need to deal with anomalous results. An anomalous result is a
measurement that is very different from the others in a set of repeat
measurements and might be a mistake.
Thinking and working scientifically
Risk assessments
A plan should also include a risk assessment. This explains how you will
reduce the chances of:
y damage to equipment
y injury to people.
Risk depends on the probability of the damage or injury happening, and the
consequence if it did. You can reduce risk by:
y reducing the probability of something going
wrong (e.g. keeping glass objects away from the
edge of the desk)
y reducing the consequence if something goes
wrong (e.g. wearing safety goggles).
Sometimes risks appear very small. You should still note them and say that
they are not significant when you write your plan.
You should know the meaning of any hazard symbols, and consider them
when you are planning your investigation.
What should a plan include?
Your plan should include:
Hazard symbols for
flammable (left) and
corrosive substances (right).
y the scientific question that you are trying to answer y your prediction: what you think will happen
y why you have chosen to do a fair test
y the list of the equipment you will need
the
independent
and
dependent
variables
y
y how you will use the equipment, step by step, to
collect accurate and precise data
y a list of variables to control, how you will do that,
and the values each control variable will have
y how you will record your results
y your hypothesis: the scientific reason on which to y a risk assessment, even if the risk is very low.
base your conclusion
Planning other investigations
Not all investigations are fair tests. Some questions are better
answered using a field study, making observations, or using
secondary data.
Secondary data have been collected by other people. If you are
planning to use secondary data you need to be confident that:
y the information is reliable
y the observations are accurate.
What should a plan for other investigations include?
There are some similarities in the plans for fair tests and other
investigations. You should include:
y the scientific question that you are trying to answer y your hypothesis: the scientific reason on which to
base your conclusion
y why you are using this type of investigation
y how you are collecting precise and reliable data or y your prediction: what you think your data will show
observations
y the list of the equipment you will need, if you are
doing it yourself
y the sources of secondary information, if you are
using it
y a risk assessment, even if the risk is very low.
viii
Thinking
and working
scientifically
3
Collecting and recording data
How do scientists collect and record the data that they need to answer
scientific questions?
Using tables
Measurements are easier to understand if they are in a clear table.
Objectives
y
Describe how to record
data from a range of
investigations.
y
Describe how to deal with
anomalous results.
y
Describe how to calculate
the mean (average).
Write the name of the
variable you change
or compare in box X. If
it is something you can
measure, add its units.
x
(units)
y
(units)
Write the name of the
variable you observe
or measure in box Y.
If you are measuring
it, add the right units.
Use one line for each
test you plan to do.
I kept these variables the
same to make it a fair test:
Write the names of any
variables you control
under the table, and
add their values.
e.g. volume of water = 50 cm3
Using the correct units
If you use the wrong units for your measurements, your calculations will be
wrong.
°C
cm3
100
90
80
degrees
Celsius
70
60
50
M S
minutes
and seconds
cubic
centimetres
grams
40
30
centimetres
1
2
3
4
5
10
20
30
40
50
20
10
millimetres
The units of
temperature include
degrees celsius (ºC).
The units of
time include
seconds (s),
minutes (min),
and hours (h).
The units of
volume include
cubic centimetres (cm3)
and
cubic decimetres (dm3).
The units of
mass include
grams (g),
kilograms (kg),
and tonnes (t).
The units of
length include
millimetres (mm),
centimetres (cm),
metres (m),
and kilometres (km).
Recording repeat measurements and calculating the
mean
In most fair tests you should find the value of the dependent variable more
than once, and usually three times. This is a repeat measurement. You
ix
Thinking and working scientifically
should record all your repeat measurements in your results table, always to
the same number of decimal places.
When you have finished the repeated measurements, you should:
y Check for any anomalous results. Do not erase them.
y You can repeat the measurement, and if one is very different from
y
y
the other two put a line through it and ignore it. Use your new
measurements.
When you are confident that you do not have any anomalous results,
calculate the average (mean) of the measurements.
To calculate the mean you add up all the repeats and divide by the
number of repeats.
For example, three students find the time it takes to draw a table. Jamil
takes 75 seconds, Abeer takes 35 seconds, and Kamran takes 73 seconds.
Abeer’s result is anomalous because it is very different from the others. Jamil
and Kamran find out why. Abeer’s table is very messy. She did not use a ruler.
They decide to leave it out of the mean. The mean is (75 s +73 s)/2 = 74 s.
x
(units)
y
(units)
1
2
3
Average
Draw boxes for three
results for each test,
and an average value.
If a result looks
anomalous, repeat it.
Your average should be rounded up to the same number of decimal places
as in the data.
Recording measurements and calculated quantities
x
(units)
Result 1 Result 2
(units)
(units)
y
(units)
Average
(units)
Draw boxes for three
sets of measurements,
three calculated values,
and an average. If a
result looks anomalous,
repeat it.
There are some experiments where you will need to calculate quantities using the measurements you have
made.
In this situation, you should make another column in your table.
Recording observations
In investigations where you are recording your observations, you need to adapt your table. In some cases, you
may want to include images or diagrams, so the boxes in your table should be large enough to include them.
x
Thinking
and working
scientifically
4
How do you know which type of graph to plot? What is the best way to plot
graphs? The way that you display the results of your investigation depends
on the type of data that you have collected.
Types of data
Objectives
y
Describe how to decide
which graph to plot
y
Describe how to draw a bar
chart, a line graph and a
scatter graph
Describe how to draw a line
of best fit
If the values of the variable you change (x) are words, then x is a categoric
variable. There is no logical order, like size, for the categories. Names are
one example.
Variables like shoe size are discrete variables. They are numbers, but there
are no in-between sizes. The number of paper clips in a pot or people in a
room are discrete variables.
You can only draw a bar chart or a pie chart for data that include categoric
or discrete variables.
Other variables are continuous variables. Their values can be any number.
Height, temperature, and time are continuous variables.
If the variables you change and measure are both continuous variables,
display the results on a line graph or scatter graph.
Pie charts and bar charts
Student
Daniyal
Nida
Qasim
Time spent on poster
(minutes)
24
54
12
Time spent on
homework (hours)
2.5
4.5
2.0
Daniyal, NIda, and Qasim research and design a poster together.
Daniyal
Nida
Qasim
Time spent on homework.
The table shows the time that each of them spends. The pie chart drawn
from the results helps you to see who did the most work on their project.
Pie charts are useful for showing fractions of a whole. When you want to
show data that do not add together, a bar chart is better.
Write the name of
the variable you observe
or measure on the y-axis,
and add the correct units.
Write the y values on
the lines, evenly spaced.
Only start at zero if your
values are close to zero.
Time spent producing a
poster together.
xi
time spent on
homework (hours)
y
Drawing graphs
6
Put the bars in
order of height
4
Leave gaps
between the bars.
2
0
Qasim Daniyal
students
Write the x values
in the spaces.
Nida
Write the name of the
variable you change
or compare on the x-axis
Thinking and working scientifically
Line graphs and scatter graphs
Drawing a line graph
A line graph makes it easier to see the link between two continuous
variables – the independent variable and the dependent variable.
Write the name of
the dependent variable
(the variable you observe
or measure) on the y-axis,
and add the correct units.
height of plant (cm)
The number of points
above and below the line of
best fit should be equal.
100
Make sure the
numbers on each axis
are evenly spaced.
Draw a smooth line of best fit.
It could be straight or curved.
80
60
40
Use a neat pencil
cross for each point.
20
0
0
2
8
4
6
time (weeks)
10
Write the x values
on the lines.
Write the name of
the independent variable
(the variable you change
or compare) on the x-axis,
and add the correct units.
Use a line graph for continuous variables when you think there is a link
between them.
Drawing a scatter graph
A scatter graph shows whether there is a correlation between two
continuous variables. In the graph below, all the points lie close to a
straight line. That means there is a correlation between them. If there is no
correlation between the variables, then the points would be scattered all
over the graph.
60
arm length (cm)
58
Make sure the numbers
are evenly spaced.
Add a straight
line of best fit.
56
54
Use a neat pencil
cross for each point.
52
50
48
140
Start just below
your lowest value.
150
160
height (cm)
170
Choose intervals that make
the graph easy to plot.
A scatter graph will show you if there is a correlation between two continuous variables.
If you collect continuous
data in a fair test
investigation, you are trying
to find out how one variable
affects the other. You will
usually plot a line graph.
In other investigations, you
may be trying to see if there
is a relationship between
two variables. You will
usually plot a scatter graph.
A line graph shows the link
between two variables. You
should draw a line of best
fit. This is a line that goes
through as many points
as possible with roughly
equal numbers of points
either side of the line.
A correlation does not
mean that one variable
affects the other one.
Something else could
make them both increase
or decrease at the same
time. For example, if you
plotted the number of
ice creams sold in a town
each day against the
number of people going to
the town swimming pool
that day, you would see
a correlation. This does
not mean that getting
wet makes people eat ice
cream, or that eating ice
cream makes people go
swimming. It probably
means that on hot days
more people want to go
swimming and to eat ice
cream.
xii
Thinking
and working
scientifically
5
y describe the trends or patterns that you have worked out from the
y
Describe how to do
an analysis of an
investigation.
y
Describe the relationship
shown by different lines of
best fit on graphs.
mass of sugar that
dissolves in 1 minute (g)
Analysing the evidence
When you analyse the evidence that you have collected (yourself or from
secondary sources) you should:
Objectives
35
30
25
20
15
10
5
0
Analysis
y
y
y
y
y
display of your data (a graph, chart, or other display)
identify any anomalous results, and suggest reasons for them
make a conclusion by interpreting the results
say whether there are any limitations to your conclusion
say whether your prediction was correct
use your hypothesis or other scientific knowledge to explain your
conclusion.
Finding trends or patterns in graphs and charts
The bar chart shows how much sugar dissolves in water at different
temperatures in a certain time. We only have descriptions of the
temperature, not numbers, so the results are categoric.
You can describe the trend by saying:
‘As the temperature of the water increases, the mass of sugar that dissolves
B
increases.’
This is sometimes called the relationship between the variables.
cold
warm
hot
water temperature
ass of sugar which
M
dissolves in water at
different temperatures.
Line or scatter graphs show relationships between continuous
variables. When
A
thesedraw
graphs,
if Aof best fit.
you have plotted the points on a line or scatter In
graph,
a line
increases then B increases.
In the graphs below the line of best fit is shown, but not the points.
B
A
In
these
graphs,
In these graphs, if Aif A
increases
increasesthen
thenBBincreases.
increases
B
xiii
A
In these graphs, if A
increases then B decreases.
B
A
In these
graphs,
In these
graphs,
if Aif A
increases
then
B
decreases.
increases then B decreases
B
A
In this graph, if A increases
B does not change.
Line or scatter graphs will be different if there is no relationship or
correlation between the variables.
A
A
Inand
these
graphs,
if A
Thinking
working
scientifically
In
these
graphs,
if A
increases then B decreases.
increases then B increases.
You may get a horizontal line in a fair test investigation if changing the
independent variable has no effect on the dependent variable.
B
B
Identifying anomalous results
When you recorded your data, you may have identified points that did not
fit the pattern. You may have ignored them, or repeated the measurement.
y You should identify these points now.
y You might see points that are not close to your line of best fit. They too
y
A
A
InInthis
thisgraph,
graph,ifif AA increases
increases B
In
these
graphs,
if A
B not
does
not
change.
does
change.
increases then B decreases.
are anomalous results.
You should think of possible reasons why they might have occurred.
B
Writing your conclusion
A conclusion states what you have found out. You should also think about
the limitations to your conclusion. Your conclusion may be limited if:
y you had lots of anomalous results
y the line of best fit is not clear
y your data is limited in terms of the range of variables that you
y
investigated
your data was limited in terms of the number of results that you
collected.
Checking your prediction
When you have found the pattern, you need to check the prediction you
made and say whether it was correct. You should look carefully at the
extent to which the evidence (data and observations) supports or refutes
(disproves) your prediction.
A
In
this
graph,
thereisisnono
In this graph, there
correlation
correlationbetween
betweenA Aand
andB.B.
If points are scattered
everywhere on a graph
of two variables, it shows
that they do not affect
each other.
Explaining your conclusion
Finally, suggest scientific reasons for any relationship or correlation
differences that you have found. You could refer back to your hypothesis, or
other scientific knowledge.
I think that the shoe on the carpet
needed a bigger force to move it than
the shoe on the wooden floor because
there was more friction between the shoe
and the carpet.
I think that the powdered
sugar dissolved faster than
the normal sugar because
the pieces were much
smaller.
I think that the plant near the
window grew more quickly than
the plant away from the window
because there was more sunlight
there.
xiv
Thinking
and working
scientifically
6
Objectives
y
Describe how to evaluate
data that you have
collected.
y
Describe how to evaluate
methods that you have
used.
y
Describe improvements
that you can make to
improve the quality of the
data.
Evaluation
After you have collected your data, plotted a graph, written a conclusion,
and explained what happened using scientific knowledge, you need to
evaluate your investigation.
An evaluation is done in three stages:
y evaluate the quality of the data
y evaluate the methods you used
y suggest improvements to the method.
If you were to do the investigation again, the improvements should make
you more confident in your conclusion.
Evaluating the data
Are there anomalous results?
When you look at your data tables and graphs, you can see how many
anomalous results you had. This is why you do not erase the anomalous
results in your results tables.
Anomalous results can limit your conclusions. They can also reduce the
confidence that you have in your conclusion.
What is the spread?
The spread is between the smallest and the biggest values of repeated
measurements. When you repeated the experiment, were the results close
together (small spread) or far apart (large spread)? A smaller spread means
that you can have more confidence in any conclusion based on your data.
Evaluating means working
out what is good and what is
not so good.
What is the range and number of values?
The range of the variables that you have investigated is the difference
between the smallest and the largest values. If the range is large, then you
can be more confident of your conclusion.
You should collect enough data points to feel confident that you have
correctly identified the trend or pattern. Two would not be enough.
Were there systematic or random errors?
There is uncertainty in any measurement that you make. This is one of the
reasons why there is usually a spread in experimental data.
You should think about possible errors, as well as any anomalous
results and the spread, to help you to decide how confident you are in
your conclusion. There are two types of error that can affect scientific
measurements.
xv
Thinking and working scientifically
y Random errors – these can affect the spread, or cause anomalous
y
results. An example is the temperature of the room suddenly changing
because someone opens a door.
Systematic errors – these can make your measurements less accurate.
An example is a newtonmeter reading 1 N even when there is nothing
attached to it.
Evaluating the methods
When you planned your investigation, you chose the measuring instruments
and the methods of using them to collect your data. You should look back at
those choices and describe:
I don’t think I took the
measurements of the volume
very accurately because I did
not look directly at the scale.
y the extent to which the equipment enabled you to collect data that was
y
accurate and precise
the extent to which the methods enabled you to collect data that was
accurate and precise
Suggesting improvements
Suggesting improvements is not about making the experiment easier or
quicker.
Any improvements that you suggest should be designed to improve the
quality of your data, because that would mean:
y there are fewer limitations to your conclusion
y you would be more confident in your conclusion.
How do I get better data with the same equipment?
I think we could have videoed
the falling object so we could
have played the video to see
where it was.
You may improve the quality of the data by:
y eliminating systematic errors
y reducing the effect of any random errors
y including a bigger range
y doing more repeat readings
y repeating any measurements that gave anomalous results.
What other equipment would help?
Some types of equipment produce more precise and accurate data than
others. You may need to do some research to find out.
y Using light gates to measure speed produces more accurate
y
y
measurements than clicking a stopwatch by hand.
Using a measuring cylinder to measure volume produces more accurate
measurements than using a beaker.
Using a balance that measures to more decimal places produces a more
precise measurement.
xvi
1.1
Plants system
Plants are everywhere – they are even visible on the Earth from space.
Plant biology is one of the most important areas of scientific study today.
Objectives
Why are plants important?
y
Plants make carbohydrates using energy from the Sun and carbon dioxide
from the atmosphere. in a process called photosynthesis.
y
Explain the root and shoot
system in plants and label
different parts of leaf, stem
and root (external and
internal structure).
Predict the role of xylem
and phloem in the
transport of water and food
in plants by observing the
cross section of the stem.
y
y
y
y
Plants are the producers for food chains and food webs all over
the world.
Plant crops are the source of most human food, both directly and
as animal feed.
Plants are part of the water cycle.
Materials from plants are used for medicines, clothing, building,
biofuels and more.
Why do we study plants?
Biologists study plants for many different reasons. They want to find out
about the world around them. Understanding plants also helps us make
better use of them. Scientists look at plant structures, plant breeding and
the genetic material of plants. They use this knowledge to develop plants
with useful characteristics such as big leaves or large fruits. They study
the nutrients plants need to grow as fast and as large as possible, so
they can help farmers get the best crops. Scientists also investigate plant
pests and diseases, to develop ways of protecting our plants from attack.
Flower
The structure of a plant
Before you look in detail at plants, remind yourself of the main plant
structures you learned about in grade 6.
Stem
Leaf
Roots
The main structures of a plant.
2
y
Roots: the roots anchor the plant in the ground . They absorb water
and mineral nutrients from the soil to be used by the rest of the plant.
The centre of the root contains xylem tissue which transports water
and phloem tissue which carries dissolved food from the leaves to the
root cells. Roots do not have any green chloroplasts because they are
underground and do not capture light.
y
Stems: stems support the leaves, holding them out to capture the
sunlight they need for photosynthesis. They also support the flowers
and fruit. The stems contain the transport tissues xylem and phloem to
carry water and dissolved food around the plants. The transport tissues
are found in bundles around to add to the support given by the stem. The
phloem is on the outside of the bundles on the stem, and this is where
insect pests feed, taking food from the plant.
The particle
model
Plant system
y
Leaves: leaves capture energy from the Sun using the green colour
chlorophyll. They use this energy to make carbohydrates by
photosynthesis. The structure of the leaves is adapted so as much
photosynthesis takes place as possible. The leaves are thin and flat to
capture as much light as possible. The cells at the top of the leaf are
packed with chloroplasts; there are air spaces and special openings in
the leaf for the exchange of the gases that are needed, and there are
bundles of transport tissues called veins to bring water to the leaf cells
and carry food away from the leaf to the rest of the plant.
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The transport tissues xylem and phloem are arranged in different places in the
stem and root of a plant.
Questions
Key points
y
The main structures
in plants are the roots,
stems, and leaves.
y
The external and
internal structures of
plant stems, roots and
leaves are adapted for
their functions.
1. State three reasons why plants are important to people.
2. Draw a diagram of a plant and label the roots, stem, leaves and
flowers. Describe the function of each structure you label.
3. Draw and label a diagram of a plant, showing details of the
internal structure of the stem, roots and leaves. Annotate your
diagram to show how the different structures of the plant are
adapted to their functions.
3
1.2
Objective
y
Define the process of
photosynthesis and derive
word equation for it .
Photosynthesis
For many people, plants are just a green background to their lives, in
the countryside or in their homes. To biologists, plants are important
organisms. The health of our planet, our own food and wellbeing, and the
great diversity of life on Earth all depend on plants. In fact, they all depend
on one vital process – photosynthesis.
What is photosynthesis?
Biomass is the material living organisms are made of, and much of the
biomass on Earth comes from plants. Animals have to eat plants to get
the biomass they need. Plants do not need to feed. They make their own
biomass using sunlight, air and water in a process called photosynthesis.
From wood to cereal crops to flowers – all of the biomass in plants comes from
photosynthesis.
The process of photosynthesis
Plants need two small molecules to make
carbohydrates in photosynthesis:
light energy
IN
y carbon dioxide, which they get from the air, and also
water
IN
glucose
OUT
carbon
dioxide
IN
oxygen
OUT
This section through a leaf shows you the movements into
and out of a leaf during photosynthesis.
make during aerobic respiration
y water, which they get from the soils.
They also need energy from light, usually the Sun.
Plants capture light energy using the green pigment
chlorophyll. They use it in a reaction between carbon
dioxide and water to make a molecule of glucose,
a simple carbohydrate. Oxygen is also produced
in the reaction. The oxygen made by plants during
photosynthesis is used for aerobic respiration in the
cells of most living things.
Photosynthesis involves many different reactions,
but we represent the process as a simple summary
word equation:
carbon dioxide + water
(reactants)
Sunlight
chlorophyll
glucose + oxygen
(products)
Photosynthesis in plants uses energy from the Sun to combine carbon dioxide and
water to make glucose and oxygen.
4
The particle
model
Plant system
Why are chloroplasts important?
As you know, from grade 6, chloroplasts contain the green chlorophyll
needed to capture light for photosynthesis. Most of the reactions of
photosynthesis also take place inside the chloroplasts. If a plant cell does
not have any chloroplasts, it cannot carry out photosynthesis. The number
of chloroplasts in a plant cell tells you how much photosynthesis it carries
out.
How do plants use the glucose they make in
photosynthesis?
▲ Photosynthesis takes place in the
chloroplasts in plant cells.
Plants use the glucose they make during photosynthesis in several ways:
y
y
y
For aerobic respiration: about half of the glucose a plant makes is used
in cellular respiration, making energy available for all the other reactions
going on in the cells.
As a starch store: small, soluble glucose molecules cannot be stored,
but plant cells need glucose to respire in the dark, when photosynthesis
stops. Glucose molecules join together to form big molecules of starch,
which are stored in the leaves. A leaf stores enough starch to last several
days without any light. Starch is also stored in special areas such as root
tubers – for example, potatoes are full of plant starch.
To make other molecules: plant cells need other carbohydrates, proteins,
lipids and molecules like chlorophyll. Glucose molecules made during
photosynthesis are the building blocks for all of these other compounds.
Key points
y
y
y
y
Photosynthesis is the process by which plants make carbohydrates, using
the energy from light.
Chloroplasts contain chlorophyll which traps the light energy needed for
photosynthesis.
The reactions of photosynthesis take place in the chloroplasts.
The summary word equation for photosynthesis is:
light
carbon dioxide + water
glucose + oxygen
(reactants)
chlorophyll
(products)
Questions
1. a. What is photosynthesis?
b. Give the summary equation for the process of photosynthesis.
2. Describe the function of chloroplasts in photosynthesis.
3. Describe three ways in which plants use the glucose made during
photosynthesis.
4. ‘Most of the biomass on Earth has come from photosynthesis’.
Discuss this statement.
5
Thinking
and working
scientifically
1.3
Objectives
y Define the process of
photosynthesis.
y Explain that the structure
of a leaf is adapted for
photosynthesis.
Evidence for photosynthesis:
testing for starch
Salma, Dua and Aslam know that some of the glucose made in a leaf by
photosynthesis is turned into starch to be stored. Their teacher describes a
method of showing there is starch in a leaf using iodine solution, a yellow–
brown liquid which turns blue–black in starch.
How do you test a leaf for starch?
Leaves are covered in a waxy, waterproof layer and leaf cells have tough cell
walls, so iodine cannot reach the starch in a living leaf. You must prepare a
leaf carefully before testing it for starch.
1. Take a leaf from a plant. To demonstrate photosynthesis it must have
been in the light for at least 12 hours.
2. Drop the leaf into boiling water to remove the waterproof layer and
break open the cells. Turn off the Bunsen burner. Use forceps to take the
leaf from the boiling water.
3. Place the leaf in a test tube of ethanol and put the test tube into the hot
water. The ethanol will boil and the green colour will come out of the leaf.
4. Remove the white leaf from the ethanol. It will be stiff. Dip it into the hot
water to soften it.
5. Spread the leaf on a white tile and add a few drops of iodine solution.
If starch is present, the leaf will turn blue–black. This shows it contains
starch and has been photosynthesising.
remove
leaf
kill in boiling water
(30 seconds)
forceps
remove colour in
boiling ethanol
TURN OFF
BUNSEN
BURNER
HEAT
acid iodine solution
dip in the hot
water to soften
Using iodine to test a leaf for starch. Take care with hot water and hot
ethanol.
6
Plant systems
Investigating photosynthesis
Now Salma, Dua and Aslam must use the iodine test to investigate
photosynthesis. Their teacher reminds them that a leaf uses its starch stores
for respiration when it is in the dark. It has enough starch to keep respiring for
2–3 days. If you are going to investigate photosynthesis by looking for starch,
always start with a plant that has been in the dark for at least 3 days, so that
you know it has not got any starch left.
Here are their plans:
Salma
Do plants need chlorophyll to
photosynthesise?
Take a plant with two-coloured
leaves that has been in a dark
cupboard for at least 3 days. Place
it in the light for 24 hours. Test
a leaf from the plant for starch,
using the iodine test we have
learned.
Dua
Do plants need light for
photosynthesis?
Take a plant that has been in a
dark cupboard for at least 3 days.
Make a foil cover and put it on a
leaf of a plant. Make sure the foil
blocks the light. Leave the plant
in the light for 24 hours. Use the
iodine test to test the foil-covered
leaf for starch.
test 1
before
test 2
after
before
after
light blocked
with silver foil
Questions
1. Make a flow diagram showing how to test a leaf for starch.
Aslam
Do plants need carbon dioxide to
photosynthesise?
Take a plant that has been in a
dark cupboard for at least 3 days.
Place a bag containing a chemical
that absorbs carbon dioxide
around one leaf. Leave the plant
in the light for 24 hours. Take the
leaf out of the bag and test it for
starch, using the iodine test. Test
a leaf that was in the air for a
test 3
control.
before
after
carbon dioxide
removed from air
around leaf
Key points
y
Photosynthesis occurs
in the chloroplasts,
and is the process by
which plants make
carbohydrates, using
light.
y
A range of investigations
can test different
hypotheses about
the requirements for
photosynthesis.
2. a. Explain why the students use plants kept in the dark for three days
in their planned investigations.
b. For each investigation:
i.
State what they are investigating.
ii. State the conclusion you can draw from their results.
iii. Give two examples of good science in their plan.
iv. Suggest one way the investigation could be made better.
7
Thinking
and working
scientifically
1.4
Objective
y Define the process of
photosynthesis and derive
word equations for it.
Evidence of photosynthesis: oxygen
bubbles
Evidence for photosynthesis
Recall the summary equation for photosynthesis:
Sunlight
carbon dioxide + water
glucose + oxygen.
chlorophyll
(reactants)
(products)
Some of the glucose made during photosynthesis is turned into starch to
be stored. You know how to use the starch made in leaves as evidence that
photosynthesis has taken place.
Oxygen is also produced during photosynthesis. Some of the oxygen is used
by plant cells for aerobic respiration. Some of it is lost from the leaves. It
is difficult to use the oxygen produced from the leaves of land plants as
evidence for photosynthesis because it diffuses into the air. Plants that live
in water are different. The oxygen they make when they photosynthesise
is released from the leaves and from cut stems as bubbles in the water.
Shining a light on a water plant allows you to:
y collect the gas and show that it is oxygen, as evidence of photosynthesis
taking place
y count the number of bubbles produced in a given amount of time to
show how quickly photosynthesis is taking place.
Does light intensity affect the rate of photosynthesis?
Daniyal and Ijaz set out to investigate the effect of light intensity on the
rate of photosynthesis of a water plant using the apparatus shown in below
What do you predict will happen as the plant is moved further away from
the lamp?
pondweed
test tube
light source
thermometer
beaker
water
Bubbles of oxygen-rich gas
produced by waterweed as it
photosynthesis.
0
1
2
3
4
5
6
7
8
9
Apparatus used to measure the effect of light intensity on photosynthesis.
8
10
ruler
Plant systems
Method
1. Place a piece of pondweed in a tube, cut end up, and cover with water.
2. Place the tube in a beaker of water and position it on a ruler so the plant
is 0 cm from the lamp.
3. Give the plant a few minutes to adjust to the light intensity.
4. Count the number of bubbles escaping from the cut end per minute and
record your data.
5. Repeat your count at least once more.
6. Repeat the experiment, moving the plant 2 cm further away from the
lamp each time.
Key points
Results
Daniyal and Ijaz recorded their results in a table:
Lamp distance
from plant (cm)
0
2
4
6
8
10
Number of bubbles per minute
Test 1
Test 2
Average
110
104
107
92
94
93
86
84
85
75
69
72
62
58
60
50
46
48
y
Photosynthesis occurs in
the chloroplasts. It is the
process by which plants
make carbohydrates,
using the energy from
light. Oxygen is also
produced during
photosynthesis.
y
The reliability of
the results of these
investigations would be
improved using a wider
range of measurements
and by repeating each
reading more often.
y
The results show a clear
trend which can be
described both from the
table and from a graph
of the data.
y
We can draw
conclusions from
these results about the
relationship between
the light intensity
and the amount of
photosynthesis that
takes place, although
the conclusions are
limited by the quantity
and reliability of
the data.
Their teacher noticed that the second reading was often lower than the first.
Daniyal suggests that the plant is still adjusting to the lower light intensity.
Perhaps they should give it longer to adjust each time.
Ijaz thinks that the cut end of the plant might be healing over, so fewer
bubbles escape. Perhaps they should cut the stem after every measurement
to keep it open.
What do you think?
Questions
1. Plot a graph of Daniyal and Ijaz’s results.
2. Describe what you see on the graph.
3. Give the conclusions you draw from this investigation.
4. Suggest a reason for the thermometer in the beaker of water shown
on the diagram and explain why it is important.
5. Evaluate this investigation.
a. Describe two examples of good science in this investigation.
b. Suggest three ways in which the investigation could be made better.
9
1.5
Objective
y
Respiration and Photosynthesis
All the animals and plants around you, including human beings, have many
things in common. They grow, reproduce and move at least part of their
bodies. They excrete, getting rid of their waste products, replace worn out
cells, and heal damaged tissues. Energy is needed to carry out all of these
processes. Where does that energy come from?
Describe the process of
respiration and write word
equations for it. Compare
and contrast the processes
of photosynthesis and
respiration.
Animals and plants all need energy from their food to carry out the processes of life.
Energy from food
All living organisms need food. Plants make their own food. Animals eat
plants or other animals. Why is food so important? Food provides the energy
needed by the cells to carry out the chemical reactions that are part of all
the processes of life.
If you burn sugar in oxygen, energy is released in an uncontrolled way – see. You
see the flame and feel the surroundings get hotter. Releasing energy like this
is no use to cells! They need a controlled way of releasing the energy stored in
food so that they can use it to grow, move and reproduce.
Cells cannot use the energy in their food directly. They use oxygen to
break down food molecules such as glucose in a process called aerobic
respiration. Aerobic respiration releases the energy they need in a
controlled way. Aerobic means ‘using oxygen’. When glucose is broken down
during aerobic respiration, waste products form. These waste products are
carbon dioxide and water.
When sugar burns in air, energy is
released in an uncontrolled way.
We can show what happens during aerobic respiration using a summary
word equation which you can see in below. It is important to learn and
remember this equation. Remember we do not usually include energy in
equations as it is not a substance.
glucose + oxygen
(reactants)
respiration
carbon dioxide + water + energy
(products)
Aerobic respiration uses oxygen to break down glucose into carbon dioxide and water,
releasing energy in a controlled way so that it can be used by the cell.
10
The particle
model
Plant system
Where does aerobic respiration happen?
Aerobic respiration is a very important process. It takes place in specialised
structures in cells called mitochondria. Mitochondria are found in both
animal and plant cells, because both animals and plants need to release the
energy stored in their food molecules in a controlled way.
nucleus
mitochondria
cell membrane
cell wall
cell membrane
chloroplast
sap vacuole
cytoplasm
cytoplasm
mitochondria
nucleus
Both animal cells and plant cells contain mitochondria where aerobic respiration happens.
Comparing photosynthesis and respiration
Look at the word equation for respiration in Now look back to the word
equation for photosynthesis on page 4. What do you observe?
y
In photosynthesis, plants use energy to combine carbon dioxide and water
to make glucose and oxygen.
y
In respiration, plant and animal cells break down glucose using oxygen to
release useful energy producing waste carbon dioxide and water.
Key points
y
Aerobic respiration takes place in the mitochondria of animal and plant cells. It gives a controlled
release of energy.
y
The summary word equation for aerobic respiration is:
glucose + oxygen
y
carbon dioxide + water (+ energy)
Photosynthesis takes place in the chloroplasts of plant cells. In photosynthesis, carbon dioxide and
water are combined using energy to produce glucose and oxygen.
Questions
1. Name the reaction that gives a controlled release of energy inside cells.
2. State the structures inside cells where the controlled release of energy
takes place.
3. a. Write a summary word equation for the process of respiration in cells.
4. b. Write a summary word equation for the process of photosynthesis in
plant cells.
5. Make a table to compare and contrast the processes of photosynthesis
and respiration.
11
1.6
Objective
y
Know that plants need
minerals to maintain
healthy growth and life
processes.
The need for minerals
If you put a plant in a jar of water and leave it in the air and sun, will it live?
For a time, it will do well. It has light, water and carbon dioxide – everything
it needs for photosynthesis.
Sadly, in time your plant will look sickly and eventually it will die. What
goes wrong?
The need for minerals
In Grade 6, you learned that humans need a balanced diet to stay healthy.
A balanced diet for people includes small amounts of minerals such as
calcium and iron.
Photosynthesis provides plants with glucose, which they use in aerobic
respiration or build into bigger carbohydrate molecules like starch or
cellulose for their cell walls. Plant cells also use carbohydrates to make
fats and oils. But there are some substances which cannot be made from
carbohydrates alone.
Plants need minerals too. Minerals are water-soluble substances that cells
can absorb. Two of the most important minerals for plants are:
y
y
Photosynthesis is amazing – but
plants need more than light,
water and carbon dioxide to
grow, and to produce flowers
and fruits.
12
Nitrates: Nitrates contain nitrogen. They are produced by decomposers
breaking down the waste material and dead bodies from other plants
and animals.
Plants must have nitrates to make the proteins they need. Proteins
control many reactions in plant cells, including photosynthesis. They are
also part of the structure of the plant cell itself. Without nitrates to make
proteins, a plant cannot survive for long.
Magnesium: Chlorophyll, the green molecule which traps light in
photosynthesis, contains magnesium. Plants must have enough
magnesium to make chlorophyll for the chloroplasts of new cells,
and to replace the chlorophyll when chloroplasts get worn out
or damaged.
Mineral deficiencies in plants
If a plant does not get the minerals it needs, it does not grow well. This
is called a mineral deficiency. Different mineral deficiencies in plants
have different symptoms. We can recognise which mineral is missing
by the appearance of the plant – very like mineral deficiency diseases
in people.
The particle
model
Plant system
Mineral deficiency
Nitrate
Magnesium
Symptoms
Poor growth, and
older leaves turn
yellow
Plant leaves are pale
or yellow
Where do plants get their minerals from?
Plants get most of the minerals they need, such as magnesium, from the
soil. The minerals are dissolved in the water in the soil. They are taken into
the plant with water through the plant roots and carried around in the plant
transport systems.
Most plants get all the nitrates they need from the soil, just like the other
minerals. Some plants, called legumes (peas, beans and clover), do not get
their nitrates from the soil. They have root nodules full of special bacteria
that make nitrates from the nitrogen in the air. The plants get some of these
nitrates in return for sugar from photosynthesis. Legumes grow very well in
nitrate-poor soil. They even add nitrates to the soil and make it more fertile.
Farmers often grow them to improve the soil for other crops that need lots
of nitrogen.
Peas and beans are successful
because of their root nodules.
The nodules are full of bacteria
that make nitrates for the plant.
Questions
Key points
1. Plants need minerals to grow well. What are minerals?
2. Name two minerals that plants need for healthy growth. For each,
explain the importance of the mineral in the plant.
y
3. A gardener grows fruit and vegetables in her garden to help feed her
family. This year, many of her crops do not grow well. As the plants
get bigger, the older leaves turn yellow. In one part of the garden the
plants are doing well. Her peas and beans are growing strongly.
Plants need minerals to
maintain healthy growth
and life processes.
y
Minerals are watersoluble substances that
plants can absorb from
the soil.
y
Plants need nitrates to
make proteins.
y
Plants need magnesium
to make chlorophyll for
photosynthesis.
a. Suggest why many of the plants are not growing well and explain
how you know this.
b. Explain why the peas and beans are growing well when the other
plants are not.
c. Suggest how the gardener could improve her crops next year
without buying fertiliser.
13
Science
in context
1.7
Objective
y
Plants need minerals to
maintain healthy growth
and life processes.
The use of fertilisers
In a wild ecosystem, plants grow, flower, fruit and eventually die. They are
broken down by decomposers returning nutrients to the soil, for the next
generation of plants.
On a farm the plants also grow, flower and fruit, taking minerals from the
soil. Then we harvest the crop and grow more plants in the same soil the
next year. Each crop takes more minerals from the soil. How can we keep
our soil fertile?
What are fertilisers?
Fertilisers are substances that replace minerals such as nitrates in the soil.
Using fertilisers increases the yield of crops. There are two main types of
fertilisers.
Natural fertilisers include
manure.
y
For thousands of years people have used natural fertilisers such as
manure, made from decomposed animal droppings, and compost, from
decomposed plant material. These fertilisers are cheap and improve the
structure of the soil but they release their nutrients slowly and there is a
limited supply.
y
e have only had artificial fertilisers for around 100 years. They are made
in huge quantities in industrial processes. They work fast and are always
available. Farmers control the amount of nitrate added to the soil. But
artificial fertilisers are also expensive, and they do not improve the
structure of the soil.
Scientists estimate that almost 50% of the world population now rely on
food grown with the help of artificial fertilisers!
Nitrate fertilisers – applying science to industry
The air is 78% nitrogen, but most plants can’t use it. They have to get their
nitrates from the soil.
By applying science to industry, we have developed artificial nitrate
fertilisers. This has saved billions of lives by helping us grow the food we
need to feed the increasing world population.
Nitrate fertilisers help us grow
the food we need.
In the early 20th century, a German chemist called Fritz Haber developed
a way of making a compound called ammonia from the nitrogen in the air.
Ammonia acts as a nitrate-rich fertiliser. Haber’s laboratory method only
made small amounts of ammonia, so it was not much use to farmers!
Then Carl Bosch, a chemist and engineer, developed a way to use Haber’s
reaction on an industrial scale. This Haber–Bosch process is still used today
to produce around 120 million tonnes of nitrate fertiliser for farmers all over
the world.
14
Plant systems
Through the industrial production of nitrate
fertilisers, science has changed the world. More
people have enough food to live and to raise children
– nitrate fertilisers have saved billions of lives.
Show examples of the impact of nitrate fertilisers on
the yield of two important crops. Canola oil is widely
used for cooking and wheat is one of the staple food
crops of the world.
A fertiliser factory – science applied to industry.
12
3500
10
3000
relative yield
canola yield (kg/hectare)
4000
2500
2000
1500
1000
6
4
2
500
0
8
0
0
45
90
mass of nitrate fertiliser (kg/ha)
Effect of nitrate fertiliser on the yield of canola.
0 20 40 60 80 100 120 140 160 180 200 220
mass of nitrate fertiliser (kg/ha)
Effect of nitrate fertiliser on the yield of wheat.
Questions
1. a. Define a fertiliser.
b. Explain why we need fertilisers to grow our food.
2. Give two advantages and two disadvantages of improving crop
yield by using:
a. natural fertilisers.
Key points
y
Plants need minerals to
maintain healthy growth
and life processes.
y
Scientific understanding
is applied to industrial
processes in the
production of nitrate
fertilisers. This has
increased crop yields
and so a big impact on
global society, saving
billions of lives.
b. artificial fertilisers.
3. The use of artificial fertilisers is an example of the impact of
science applied to industry. Explain this statement.
4. a. Use the graphs to calculate the percentage increase in yield of
canola using.
TWS
i. 45 kg/hectare nitrate fertiliser.
ii. 90 kg/hectare nitrate fertiliser.
b. Use the graphs above and make a table to compare the impact of
nitrate fertiliser on canola and wheat crops.
TWS
15
1.8
Objective
y
Predict the role of xylem
and phloem in the
transport of water and food
in plants by observing the
cross section of the stem.
Water and mineral transport
in plants
Plants need water for
photosynthesis, for support
and to carry substances to the
different parts of the plant body.
If a plant doesn’t get enough
water, its stems and leaves
droop. How does a plant get the
water it needs?
Without water, a plant wilts.
Moving water through plants
large
vacuole
mitochondria
long
microscopic
hair
cell wall
nucleus
cell
membrane
Root hair cells are specialised for the absorption of
water and minerals from the soil.
Water moves through plants from the roots to the leaves in
the transpiration stream
Getting water into the plant
he roots of a plant absorb water from the soil. The water
T
moves from the soil into the root hair cells by diffusion. As
you know, plants have specialised root hair cells on the
outside of their roots. Root hair cells have long, microscopic
hairs that give them a big surface area. This allows a lot of
water to move by diffusion through the surface into the root
of the plant. Remind yourself of their structure in Minerals
such as nitrates are also absorbed into plant roots through
the root hair cells. They are transported dissolved in the
water.
Transporting water and minerals around
the plant
Xylem is a specialised plant tissue. Xylem tubes
run up through the stems of a plant from the roots
to the leaves. They are part of the plant transport
system. Water moves up the plant in the xylem,
carrying dissolved minerals to the cells where they
are needed.
stomata closed
Stomata on the bottom of a
leaf, magnified 1000 times
16
stomata open
The particle
model
Plant system
Moving out of the plant
The leaves are very important plant organs. This is where most
photosynthesis takes place. The leaves are also where gas exchange takes
place in a plant. On the underside of leaves there are lots of tiny holes
called stomata (singular = stoma). Each stoma is surrounded by special
cells which open and close it. The carbon dioxide the plant needs for
photosynthesis moves in through the stomata; any spare oxygen made
during photosynthesis moves out. Whenever the stomata are open,
water evaporates from the cells of the leaves, and moves out through the
stomata by diffusion. This process is called transpiration. As water vapour
evaporates from the leaves, more water is pulled up through the plant
– rather like sucking on a drinking straw. When it is hot or windy, more
transpiration takes place because more water evaporates from the leaves.
Thinking and working scientifically
water evaporates
from leaves
travels in
xylem tubes
Does water move up the xylem?
Amir and Haya plan to show that
water moves up the xylem in
plant stems. They get some celery
stems. Celery stems have many
xylem tubes. The students stand
their stems in water mixed with
food colourings and leave them
for several hours. Describe what
you see. What conclusions can
you draw from these results?
water diffuses into
root hair cells
Amir and Haya are pleased with their
results. What do they show you?
Haya dips the end of a celery stem
in wax and repeats the experiment. She puts the wax-covered end in the
coloured water. What useful information does this give the students?
Water enters the plant through
the roots, moves up the xylem
in the stem and evaporates out
through the leaves.
Key points
y
The pathway of water
and mineral salts from
the roots to the leaves
in flowering plants
involves absorption in
root hair cells, transport
through the xylem and
transpiration from the
surface of the leaves.
y
Looking at the results of
investigations enables
you to apply your
scientific understanding
and draw conclusions.
Questions
1. Explain how water moves into the roots of a plant.
2. Describe how the mineral salts that plants need reach the cells of
the leaves.
3. a. What are the stomata?
b. Why are the stomata important in transpiration?
4. Students observe that, on hot days, a pot plant in the classroom
often wilts. On cooler days, it does not. Using what you know about
transpiration, suggest an explanation for these observations.
17
1.9
Objectives
y
y
Investigate the phenomena
of transpiration and its
importance in a plant.
Explore natural raise
of water based on the
principle of transpiration.
Factors affecting transpiration
Transpiration – the evaporation of water from the leaves of a plant – is
affected by different conditions.
If plants transpire too quickly, they may wilt or even die from lack of water.
If plants do not transpire enough, they may suffer from over-heating. This
means that some conditions are much harder for plants to live in than
others.
Factors that affect transpiration
Factors that affect the rate of transpiration include wind, temperature, light
and humidity. Let’s look at each of them in turn.
Anything that increases the rate of evaporation from the leaf will increase
transpiration. This includes:
y Wind – windy conditions increase the rate of transpiration in two ways.
They increase the rate of evaporation AND remove water vapour from
around the leaf, increasing the concentration gradient between the leaf
and the air.
y
Temperature – hot conditions increase the rate of evaporation and
so increase the rate of transpiration from the surface of a leaf. Cool
conditions reduce the rate that water is lost by transpiration.
y
Humidity - this is a measure of the amount of water vapour in the air.
If the air is dry, the humidity is low. The rate of transpiration increases
because water vapour moves rapidly from the cell surfaces to the air
down the concentration gradient. If the humidity is high, the air contains
a lot of water vapour. There is little concentration gradient between the
inside of the leaf and the air around it so transpiration slows down.
Anything that increases the rate of photosynthesis from the leaf will
increase transpiration. This includes:
y
Light - when a plant photosynthesises, it opens up the stomata of the
leaves. Gases move into and out of the leaves rapidly and the rate at
which water evaporates and is lost goes up. The more light, the more
photosynthesis takes place, and the more water is lost by transpiration.
▲ Plants that live in hot, dry, windy deserts with lots of sun need have many
adaptations to prevent water loss by transpiration, or they would die.
18
The particle
model
Plant system
Thinking and working scientifically
Plant
Investigating the rate of transpiration
To investigate the rate of transpiration we use a
piece of apparatus called a potometer. A potometer
doesn’t actually measure the rate at which water
evaporates from the leaves of a plant – it measures
the rate at which the plant takes up water. The two
measurements are very similar.
Water
Scale
Air bubble
Observe the position of the air bubble at the start of
Capillary tube
your investigation. Observe how far the air bubble
moves each minute to indicate the approximate rate
▲ Potometer.
of transpiration of the plant.
Beaker
Using a potometer we observe the effect of changing the conditions on the rate of transpiration of a plant
shoot. For example, we may:
y
y
y
y
increase the light shining on the plant shoot
use a fan to increase the air movement over the plant
increase or decrease the temperature around the plant
change the humidity around the shoot e.g. placing it in a plastic bag increases the humidity.
Raising water above the ground
Transpiration depends on many things.
The movement of water into plant
roots, the transport of water up the
xylem tissue of the plant, the tendency
of water molecules to stick together in
a long column and the evaporation of
water from the leaves. Transpiration
has the power to raise water from
many metres below the ground to
▲ Banyan trees.
many metres above the ground. Water
rises several meters in the trees due to transpiration. Our banyan trees are
up to 30m tall – and water is pulled up through the trunk to the highest
shoots by transpiration.
Questions
1. Describe transpiration.
2. Predict how the following conditions will affect the rate of
transpiration from plant leaves and explain why:
a. windy weather.
Key points
y
The loss of water vapour
from the surface of a
plant by evaporation is
known as transpiration.
y
Factors that increase
the rate of evaporation
or increase the rate of
photosynthesis will
increase the rate of
transpiration.
y
These factors include
wind (air flow),
temperature, light and
humidity.
y
Transpiration is more
rapid in hot, dry, windy
and/or bright conditions.
y
We use a potometer to
investigate the rate of
transpiration.
b. windy weather.
c. a very humid day.
3. Describe how you would investigate the effect of wind on a plant
shoot using a potometer.
19
1.10
Xylem, phloem and plant pests
Plant pests cost people huge amounts of money and can result in food
shortages around the world. When plants get attacked, it is often their
transport systems that are affected.
Objective
y
Sugar transport in plants
Predict the role of the
xylem and phloem in
transport of food and water
by observing the cross
section of the stem.
The xylem that transports water and minerals from the soil up to the cells
of the leaves, flowers and fruit of a plant is dead tissue. The water and
dissolved mineral salts flow in one direction, from the roots upwards.
Plants have another transport system too. They make glucose in their leaves
by photosynthesis. This glucose is needed by cells all over the plant. Plants
transport water and dissolved sugars in the phloem, a living tissue. Phloem
cells use energy to move the water and dissolved sugars both up to the buds
and flowers and down to the roots.
photosynthetic / palisade tissue
Spongy
mesophyll
Guard cells
xylem
tissue
two-way flow
water and food
phloem
tissue
cells have end
walls with holes
in them
Stoma
Living phloem tubes carry dissolved sugars all around the plant.
Targeting transport
Every plant has phloem tubes full of sugar-rich liquid in their stems, leaves
and roots. Many different insects target this sugary water as easy food. This
is good for the insect but bad for the plant.
Insect pests
Insects that attack the phloem are some of the most damaging plant pests.
They include aphids, plant hoppers, leafhoppers, cicadas, spittlebugs,
scale insects and shield bugs. Each insect is small, but there are enormous
numbers of them. They destroy billions of plants every year.
Shield bugs are found all over the
world. Many of them feed from
the phloem of plants.
20
These insect pests have specialised mouth parts called stylets to get the
sugary liquid they want. Stylets are sharp, pointed, hollow tubes. The insect
sticks its stylet into the phloem of a plant and feeds on the sugary liquid
inside. Aphids are a common example of phloem feeders.
The particle
model
Plant system
aphid
stylet
xylem
plant leaf
or stem
phloem
An aphid sticks its pointed mouthparts deep into the phloem
to feed on the sugary contents.
Unwelcome visitors
Insect pests weaken plants. Some steal sugars from the phloem, others
eat parts of the plant itself. They reduce crop yields and ruin garden
plants. However, it is the visitors they bring with them that cause the
biggest problems.
Plant pests often carry plant pathogens. These are viruses, bacteria or fungi
that cause diseases in plants. When phloem-feeders stick their mouthparts
deep into the transport tissues of the plant they may also carry pathogens
into the xylem or phloem. Once these pathogens are in the transport
system, they are carried all over the plant. Some pathogens spread into all
of the cells of the plant. Some stay in the transport tissues. For example, if
pathogens block the xylem tissue of a plant, water cannot reach the stems
and leaves. The plant will wilt and die.
This beet plant is infected
with a virus that attacks the
xylem tissue and turns the
veins yellow.
Questions
1. Describe the main differences between xylem and phloem in a plant.
2. a. What is an aphid?
b. Describe two different ways in which aphids damage plants.
Key points
y
The pathway of water
and mineral salts from
the roots to the leaves
in flowering plants
involves transport
through the xylem from
the roots to the leaves.
y
Water also moves
around the plant in
the phloem, carrying
dissolved sugars from
the leaves to the cells
that need them.
3. One rose bush in a garden is covered in aphids. Another has none.
The rose bush infected with aphids produces fewer, smaller flowers.
Suggest a hypothesis to explain this observation.
4. The xylem and phloem of trees grows in a layer just under the bark.
In young trees the bark is soft. Some mammals, such as deer, eat the
bark of young trees.
a. If a complete ring of bark is eaten, the young tree dies. Explain why
this happens.
b. Suggest a way of protecting young trees from attack by animals such
as deer.
21
Review
1.11
b. Another tube of pondweed and indicator
was left in a dark cupboard for a day.
The indicator went yellow. Explain why.
1. a. What is photosynthesis?
[2]
b. Give a summary word equation for the
process of photosynthesis.
[3]
c. Explain how the reactants of
photosynthesis get into the leaf cells
and what happens to the products once
they are made.
[10]
9. Raheem carries out an investigation to see if
light intensity affects the rate of photosynthesis
in pondweed. He sets up 5 identical sets of
apparatus (see diagram) and puts each one a
different distance from a sunny window. He will
measure and record the volume of oxygen in each
set of apparatus at the end of the day.
oxygen
water
d. State and explain whether or not
photosynthesis would take place:
oxygen
bubble
i. in a root hair cell
[3]
ii. in a plant on a bright, sunny day
[2]
iii.in the same plant in the middle
of the night.
[2]
2. Hydrogen carbonate indicator is orange. When
carbon dioxide is added or removed, it changes
colour.
Carbon dioxide
added
removed
[4]
pondweed
Table of results:
Volume of oxygen
collected (cm3/day)
4.5
4.0
1.5
0.5
0.25
Colour of indicator
yellow
purple
Distance from window
(m)
0
1
2
3
4
a. Describe how Raheem measures the amount
of oxygen produced by the pondweed in his
apparatus.
[1]
orange
hydrogencarbonate
indicator
a. When some pond weed was left in a
tube of hydrogencarbonate indicator for
a day by a window, the solution went
purple. Explain why.
22
b. Sketch a graph of Raheem’s results.
[5]
c. Explain what these results show you
about the effect of light intensity on
photosynthesis.
[3]
d. Suggest two variables which Raheem must
control to make sure that his comparison
of the light intensities is a fair test.
[2]
[3]
Plant systems
4. A plant was left in the dark for two days. Then two
of its leaves were treated as shown in the figure.
At the end of a day in the sun, leaves A and B were
tested for the presence of starch.
B
vinegar with baking
soda to provide
carbon dioxide
A
ii. Suggest why plants that lack
magnesium do not grow as quickly as
plants that have plenty of magnesium. [5]
6. This diagram shows sections taken from
two celery stems that have been used in an
investigation. Stem B was placed in ink for
24 hours.
chemical that
absorbs carbon
dioxide
A
a. Suggest what question this experiment is
designed to answer.
[1]
b. Why is the plant left in the dark for two
days before the investigation begins?
[2]
B
a. Identify the part of the stem B that has turned
black.
[1]
b. Describe this tissue and its function in the
plant.
[3]
c. Describe how to carry out the iodine test for
[6]
starch on these leaves.
c. Suggest two possible explanations for the
appearance of stem A.
7. Choose the correct answer.
[2]
d. Predict which leaf would turn blue–black
with iodine and explain why.
1. Vascular bundle consists of ___________.
[1]
[5]
9. Identical seedlings were placed in pure water or
water mixed with soil.
A pure water
a. epidermis and cortex b. phloem and pith
c. xylem and phloem
d. pith and cortex
2. These are the reactants in photosynthesis.
B water mixed with soil
[1]
a. Water and carbon dioxide b. Starch and water
c. Oxygen and glucose
The table compares their appearance after 2 weeks.
Plant
A
Height of plant (cm)
9
Observations
Yellow leaves
B
15
Green leaves
d. Sunlight and water
3. Factors necessary for photosynthesis are:
[1]
a. water and carbon dioxide
b. water, minerals and sunlight
c. water, sunlight ad carbon dioxide
a. Suggest a reason for these differences.
[1]
d. water, sunlight and oxygen
b. Explain how a plant absorbs minerals and
transports them to its different parts.
[4]
4. In this process, carbon dioxide is produced as a
waste product.
[1]
c. Plants that lack magnesium have yellow leaves.
i. Explain why a lack of magnesium affects
the colour of the leaves.
[2]
a. Respiration
b. Photosynthesis
c. Photosynthesis and d. None
respiration
23
2.1
1.1
4.1
Objective
y Explain that living
organisms have a complex
transport system for the
transfer of various solids,
liquids and gases across
the body.
Transport Systems in Humans
Human respiratory system
Living things, whether they are a single cell or - like humans - made up of
billions of cells, need transport systems. They need to transport substances
such as glucose and oxygen around the body and move them into the cells
and they need to remove waste substances such as carbon dioxide and
urea. How do substances move in and out of cells? The answer is, often, by
diffusion.
As scientists, we know that matter is, whether solid, liquid or gas, is made
up of moving particles which are too small for us to see. Diffusion takes
place in gases and liquids as a result of the random movements of these
tiny particles. Diffusion is the net (overall) movement of particles from an
area where there are lots of them (a high concentration) to an area where
there are fewer of them (a lower concentration). Understanding diffusion
is important for understanding many the complex transport systems we
see in many living organisms, including transport in the human respiratory
system, transport in the blood, and the examples shown here.
Diffusion in action
Let’s do a thought experiment. You are walking home from school. Your
evening meal is cooking in the kitchen. As soon as you go into your home,
you can smell the food. You probably start to feel hungry! How did the smell
of the food reach your nose?
Particles escape from the cooking food, where they are at a high
concentration. They spread out randomly through the air by diffusion, down
a concentration gradient. You breathe in some of these particles and your
nose sends signals to your brain, which recognises the food.
Diffusion in the digestive system
What happens when you eat a meal? Your body cannot use the food you
eat until it is broken down and carried in your blood to the cells which need
it. The digested food moves into your blood from your digestive system by
diffusion down a concentration gradient.
Diffusion is important both for smelling our food and for getting nutrients to the
cells of our bodies.
24
Human respiratory system
Diffusion and pollination
All over the world people enjoy fruit, from pomegranates to bananas, and from
grapes to pineapples. Lots of other animals also like eating fruit. Fruits are
produced when flowers are pollinated. Lots of insects, birds and bats rely on
diffusion to find the flowers they pollinate. How does this work?
Many flowers produce a scent, which diffuses through the air to tell
pollinators they are there. Insects like butterflies and moths pick up the
scent and follow it up the concentration gradient until they reach the flower.
Blood and sharks
The oceans of the world are very large, but sharks still find their prey. If an
animal is injured it will bleed. The blood spreads out through the water by
diffusion. Sharks have a very good sense of smell. They smell substances
such as blood in the water, even at very low concentrations. They will swim
Flowers make scent and the scent
molecules diffuse through the
air to attract pollinators like this
beautiful butterfly.
Many hunters who live in the sea rely on diffusion to help them find their prey.
up the concentration gradient, smelling the blood until they find their prey.
Diffusion and the lungs
In this chapter, you are going to look at how we breathe, and how gases
are exchanged in our lungs. It is important to remember what happens in
diffusion. It will help you to understand how your respiratory system works,
and what happens when it goes wrong.
Diffusion: The net movement of particles in a liquid or gas down a
concentration gradient, from a high concentration to a lower concentration.
Key points
y
Diffusion is the
net movement of
particles in a fluid
down a concentration
gradient, from a high
concentration to a
lower concentration.
y
Diffusion is very
important in many
biological systems.
Questions
1. Describe what matter is made of.
2. Give a definition of diffusion.
3. Describe how you can tell if there are some flowers in a dark room.
4. Describe how you think oxygen might get from the air in your lungs
into your blood.
25
2.2
1.1
4.1
Objective
y Differentiate between
aerobic and anaerobic
respiration.
Aerobic and anaerobic respiration
Your muscles work hard when you walk about. They work even harder when
you run. Most of the time, your body supplies your muscle cells with all the
glucose and oxygen they need to carry out aerobic respiration. The energy
stored in the glucose is released in a controlled way, so that your muscle
cells have the energy they need to contract. This situation is summed up in
the summary word equation:
glucose
oxygen
aerobic respiration
carbon
dioxide
water
(energy )
Aerobic respiration
Respiration without oxygen
Think about professional sprinters – the men and women who compete
internationally in sports such as the 100 m sprint. Runners like Usain Bolt,
who won gold medals in the 100 m and 200 m sprints in three Olympic Games,
run so fast that they don’t take a breath from the time they start the race until
the time they finish a few seconds later. Our muscles can store fuel, but they
cannot store oxygen. But our muscles keep working even though they don’t
have the oxygen they need. They use a process called anaerobic respiration
to provide the energy they need. Anaerobic means ‘without oxygen’.
Anaerobic respiration does not release as much useful energy from each
glucose molecule as aerobic respiration. The glucose molecules are not
completely broken down. The waste product of anaerobic respiration animal
cells is lactic acid, not carbon dioxide and water. But each muscle cell uses
many glucose molecules, so even a small amount of the energy they contain
is enough to keep the cell working. We all use anaerobic respiration when we
start running fast. Professional athletes train so that they can use it when they
need a sudden burst of speed, whether they are runners, footballers or tennis
players. Anaerobic respiration is very useful, but we can’t use it for long at a
time.
glucose
These athletes are sprinting for
the finish line. During a race,
their cells respire anaerobically
so they can keep moving fast
even when their muscles do not
have enough oxygen.
26
lactic acid
( energy )
Anaerobic respiration
Have you ever run so fast that you kept breathing hard even when you
stopped running? This is the result of anaerobic respiration. Lactic acid,
the waste product made in anaerobic respiration, is toxic when it builds
up. When you keep breathing fast after you have stopped exercising, your
body uses the extra oxygen you take in to break down the lactic acid in your
muscles. This helps your muscles to recover, so that your breathing can go
back to normal.
Human respiratory system
Differentiating between aerobic respiration and
anaerobic respiration.
Aerobic and anaerobic respiration have many similarities:
y
y
y
both take place in our cells.
both provide us with usable energy.
both involve the breakdown of glucose.
So how do we tell them apart? There are some clear differences between
these two processes:
y
Aerobic respiration uses oxygen to break down glucose and release
energy, but anaerobic respiration does not use oxygen.
y
Aerobic respiration takes place in the mitochondria, but anaerobic
respiration takes place in the cytoplasm of our cells.
y
Aerobic respiration releases much more energy per molecule of glucose
than anaerobic respiration, so it is much more efficient.
y
The waste products of aerobic respiration are carbon dioxide and water,
but the waste product of anaerobic respiration is lactic acid.
aerobic
respiration
anaerobic
respiration
Key points
y
Anaerobic respiration
takes place without
oxygen. It is used during
short bursts of vigorous
exercise.
y
Aerobic respiration uses
oxygen, takes place
in the mitochondria,
produces waste carbon
dioxide and water and
releases a lot of usable
energy from every
molecule of glucose
broken down.
y
Anaerobic respiration
does not use oxygen,
takes place in the
cytoplasm, produces
waste lactic acid and
release much less
usable energy than
aerobic respiration.
a lot of energy per molecule of glucose. less energy per molecule of glucose but produced
more quickly fast without the need for oxygen
Anaerobic respiration does not release as much energy as aerobic respiration from
each molecule of glucose but it can provide a quick burst of energy.
Questions
1. Name the reaction that gives a controlled release of energy inside
cells when the cells do not get enough oxygen.
2. Make a table to summarise the differences between aerobic and
anaerobic respiration.
3. Explain why anaerobic respiration is so useful.
4. Amir thinks he is late for school. He runs as fast as he can to get
there on time. When he gets to school it is several minutes before his
breathing rate slows down to normal. Explain what is happening in
Amir’s muscle cells.
27
2.3
1.1
4.1
Objectives
y Describe the role and
function of major organs
in the human respiratory
system including trachea,
lungs and alveoli (air sacs).
y Trace the path of air in and
out of the body, and how
the oxygen it contains is
used during the process of
respiration.
The lungs and gas exchange
Every cell in your body carries out aerobic respiration, releasing the energy
you need to grow, move, and carry out all the other characteristics of life.
For aerobic respiration to take place, your cells need oxygen. During
respiration they produce toxic carbon dioxide as waste. How do we get
these substances into and out of our bodies?
The human respiratory system
The answer is your respiratory system. It leads from your nose and mouth
down into your lungs. Your lungs are in your chest, protected by your ribs.
Your right lung is wider and shorter than your left lung. This makes room for
your liver which sits below your lungs in your chest. However, your left lung
is smaller overall because your heart sits behind it. When you are an adult,
your lungs have a volume of about 6000 cm3 or 6 litres!
Gas exchange takes place in your lungs. This is the process where your body
exchanges oxygen in the air for waste carbon dioxide from your blood. This is
The structures of the human respiratory system are closely related to their
why your respiratory system is sometimes called your gas exchange system.
nose
air in
air out
mouth
trachea
ribs
bronchus
lung
alveolus
(air sac)
pleura
diaphragm
The human respiratory system.
functions in your body:
y
y
28
Mouth and nose: The air moving in and out of your respiratory system
goes through your mouth and nose. Your nose makes the air warm and
moist, which makes gas exchange in the lungs easier. Your nose has hairs
and makes mucus to trap microorganisms that might cause disease.
Trachea: Your trachea is a tube carrying air from your nose down into
Human respiratory system
y
y
y
your chest, and back out again. It has rubbery cartilage rings around it,
holding the tube open so you can breathe easily.
Bronchi: The bronchi (singular: bronchus) are tubes from the trachea
leading to your lungs. They branch into smaller and smaller tubes,
carrying the air deep into your lung tissue. The cells lining the bronchi
are a good example of specialised cells. They make mucus which traps
dust and dirt from the air; it also traps harmful microorganisms which
might infect the lungs. These specialised cells are also covered in cilia,
hair-like structures which move the mucus, dirt and microorganisms
away from the lungs.
Lungs: the place where oxygen is taken into your body from the air
you breathe in, and carbon dioxide moves from the blood into the air
in the lungs to be breathed out. This exchange of gases takes place in
microscopic structures called alveoli.
Alveolus: Each alveolus (plural: alveoli) is a tiny air sac at the end of
the tubes in your lungs. This is where gas exchange takes place. The
structure of each alveolus is adapted for gas exchange. There are millions
of them, to give a big surface area and they all have a good blood supply
to take oxygen from the air, and to get rid of the waste carbon dioxide
made by the cells.
alveolus
capillaries
y
cilia
many
mitochondria
Ciliated cells lining the
bronchi help keep dirt and
microorganisms out of your
lungs.
The alveoli are where gas
exchange takes place. They form
little clusters like bunches of
grapes.
bunch
of alveoli
Diaphragm: The diaphragm is a sheet of muscle which divides your chest
from the rest of your organs. It is important for moving air in and out of
your lungs when you breathe.
Key points
y
The main parts of the
human respiratory
system are the mouth
and nose, the trachea,
the bronchi, the lungs,
the alveoli, and the
diaphragm.
y
The structure of the
parts of the respiratory
system are related to
their functions in the
body.
Questions
1. State what is meant by gas exchange.
2. Draw a diagram of the human respiratory system. Label the main parts
stating how they are adapted to their function, for example: mouth
and nose – make air warm and moist and remove microorganisms.
3. The bronchi are lined with specialised cells. Describe how these cells
help keep your lungs healthy.
29
Thinking
and working
scientifically
4.1
1.1
2.4
Objective
y Differentiate between
aerobic and anaerobic
respiration.
Investigating respiration
Three pairs of students plan investigations using
limewater to demonstrate something about
respiration. You have to judge which investigation
will be most useful to a biology teacher.
What is limewater?
Limewater is a dilute solution of calcium
hydroxide. It is a clear, colourless liquid. What
does the hazard symbol you
see on the bottle mean?
Limewater
If you bubble carbon dioxide through limewater,
it turns milky white. Limewater is often used to
indicate (show) the presence of carbon dioxide. The more carbon dioxide
there is, the
air breathed
faster the limewater will go cloudy.
out gently
Investigation 1
Nadia and Yousuf want to find out if people produce
carbon dioxide in the air they breathe out. They plan
to give each student a test tube containing some
limewater and a drinking straw. Each student takes
a deep breath and then breathes out gently and
steadily through the straw, which has one end under
the surface of the limewater.
Yousuf says that it will help students to
understand that they are carrying out aerobic
respiration if they see that the air they breathe out
of their lungs contains enough carbon dioxide to
turn the limewater milky.
Limewater turns from clear and
colourless to milky white as
carbon dioxide bubbles through
it.
30
straw
test tube
limewater
Apparatus to test the
air you breathe out for
carbon dioxide.
Investigation 2
Zain and Noor plan a similar investigation. They also have a test tube
containing limewater, and ask students to breathe gently through the
straw. But Zain and Noor have another part to their plan. Noor explains that
she expects all of the students to see their limewater turn milky because
everyone breathes out carbon dioxide. But how do they know where the
carbon dioxide comes from? Zain and Noor think the demonstration needs
a control. They suggest filling a big syringe or a plastic bottle with air – the
same air that everyone breathes into their lungs – and then bubbling it out
through limewater in a test tube. If the limewater stays clear, it will show that
the concentration of carbon dioxide in the air we breathe in is lower than the
concentration of carbon dioxide in the air we breathe out.
Human respiratory system
Here you can see the test apparatus and the
control for Investigation 2.
Investigation 3
Insia and Idris have a different idea. They want to show that plants respire
as well as animals. They plan to use seeds which have started to grow and
see whether they produce carbon dioxide as they grow. Insia and Idris show
a diagram of the equipment they plan to use.
dry seeds
rubber bung
test tube
soaked
(germinating) seeds
glass wool
lime water
A
B
C
The apparatus needed to investigate whether growing seeds respire and give off
carbon dioxide.
Idris explains that tube A is a control. It has no seeds in it so they do not
expect the lime water to go milky. Insia talks about tube B. This is another
control. The seeds in it are dry – they are dormant so they have not started
growing. Insia and Idris predict that the dry seeds will make so little carbon
dioxide that it will not affect the lime water. Tube C contains actively
growing (germinating) seeds. The students predict that they will make
enough carbon dioxide to turn the lime water milky. They plan to leave the
three tubes in the same place for a week and observe what happens.
Questions
Key points
y
It is important to make
predictions of the likely
outcome of a scientific
enquiry based on your
scientific knowledge and
understanding – in this
case, aerobic respiration
and the production of
waste carbon dioxide.
y
Always consider the
variables and make sure
that you have a control
when you plan an
investigation.
y
For everyone’s safety,
know the meaning
of different hazard
symbols.
Look at the three investigations. For each one:
1. Explain what the students are investigating.
2. Evaluate each planned investigation, looking for both strengths and
weaknesses in the design.
3. State which investigation you think is most useful for a teacher. Give
reasons for your answer.
31
2.5
1.1
4.1
Breathing
Sit quietly. What is happening in your body right now? One thing is
certain − you are breathing.
Objectives
Why do we breathe?
y Differentiate between the
processes of respiration
and breathing.
Gas exchange takes place in the alveoli of your lungs. It supplies oxygen
for respiration in your cells and removes the waste carbon dioxide they
produce. You need steep concentration gradients between the air in the
alveoli and your blood for gas exchange to take place.
y Trace the path of air in and
out of the body and how
the oxygen it contains is
used during the process of
respiration.
When you inhale (breathe in) you force air into your lungs. This air is
relatively high in oxygen and low in carbon dioxide. When you exhale
(breathe out) you force air out of your lungs. This air is relatively high in
carbon dioxide and lower in oxygen. Changing the air
in the lungs keeps the concentration gradients steep, so gas exchange
happens fast.
oxygen O 2
21%
air forced in
muscle
carbon dioxide CO2
0.04%
inhaled air
nitrogen N2
79%
oxygen O 2
16%
carbon dioxide CO2
4%
nitrogen N2
79%
exhaled air
air forced out
Pie charts showing the mix of gases in the air you inhale and exhale.
10
3
How do you breathe?
Your lungs cannot move by themselves. The intercostal muscles between your
ribs contract or relax to change the shape of your chest cavity. Your diaphragm
contracts and relaxes too. These movements force air into and out of your
lungs.
rib
diaphragm
n
air forced out
0
3
Inhaling (breathing in)
y
y
y
y
The intercostal muscles between your ribs contract, pulling your ribcage
up and out.
Your diaphragm contracts, so it moves downwards and flattens.
These movements increase the volume inside your chest.
This lowers the pressure inside your chest, so air moves into your lungs
from outside.
Exhaling (breathing out)
Changes in the pressure inside
your chest force air into and out
of your lungs.
32
y
y
y
y
The intercostal muscles relax, so your ribcage moves down and in.
Your diaphragm relaxes, so it moves upwards.
These movements reduce the volume inside your chest.
This increases the pressure inside your chest, so air is forced out of your
lungs and out of your body.
Human respiratory system
Remember!
y
y
Aerobic respiration: uses oxygen to break down glucose into carbon
dioxide and water, releasing energy in a controlled way so that it can be
used by the cells.
Breathing: moves air into and out of the lungs. It brings the oxygen
needed for respiration into the body, and removes the waste carbon
dioxide produced.
Thinking and working scientifically
Modelling breathing movements
We use a bell jar model to model what happens inside your chest when
you breathe in and out. The jar represents your chest cavity, the rubber
sheet represents your diaphragm and the balloons represent your
lungs. It is a useful model but it has many limitations (problems). Look
at the diagram below and work out what is happening.
Key points
y
Inhaling: the intercostal
muscles between the
ribs and the diaphragm
contract, increasing
the volume of the chest
cavity which lowers the
pressure, so air is forced
in through the nose and
mouth.
y
Exhaling: the intercostal
muscles and diaphragm
relax, decreasing the
volume of the chest and
increasing the pressure,
which forces air out of
the lungs.
y
Aerobic respiration uses
oxygen to break down
glucose into carbon
dioxide and water,
releasing energy in a
controlled way to be
used by the cell.
y
Breathing moves air into
and out of the lungs,
bringing oxygen into the
body for respiration and
removing waste carbon
dioxide.
y
The bell jar model
explains some of
the changes seen in
breathing but it has
many limitations.
bung
bell jar
balloon
(lung)
rubber (diaphragm)
Bell jar model of the chest to model inhaling and exhaling.
Questions
1. a. Explain the difference between aerobic respiration and
breathing.
b. Calculate the difference between the oxygen content of
inhaled and exhaled air.
2. Draw a flow to trace the path of air in and out of the body. Show clearly
what happens at each stage when you.
TWS
TWS
a. inhale (breathe in).
b. exhale (breathe out).
3. a. Explain how the bell-jar model helps to show what happens
when you breathe in and out.
b. Give 3 limitations of the bell-jar model of breathing.
33
Extension
4.1
1.1
2.6
Objectives
The structure of the alveoli
How do you imagine your lungs? They are not simple balloons like the bell-jar
model in topic 5.6. Your lungs are more like a sponge, made up of millions of
alveoli.
y Describe the role and
function of major organs
in the human respiratory
system including trachea,
lungs and alveoli (air sacs).
y Trace the path of air in and
out of the body.
Your lungs are made up of many tiny air sacs, rather like the inside of this sponge. This
gives a huge surface area for gas exchange.
Gas exchange and the structure of the alveoli
air inair
andinout
and out
oxygenated
air in and air
outin and out oxygenated
blood
blood
blood back
to back
heart to heart
blood
deoxygenated
deoxygenated
blood blood
thin walls thin walls
one alveolus
one alveolus
capillary
blood from heart
blood from heart
oxygen
oxygen
carbon dioxide
carbon dioxide
alveolus
capillaries
capillaries
The alveoli are where gas exchange happens.
red blood cells
red blood cells
The structure of each alveolus is adapted to allow as much gas exchange as
possible.
The alveoli have a good blood supply. Each tiny air sac is surrounded
by a network of blood vessels called capillaries. Oxygen from the air in
the alveoli moves into the blood in the capillaries. Waste carbon dioxide
moves from the blood into the air in the alveoli and is breathed out. The
oxygen and the carbon dioxide both move by diffusion down concentration
gradients.
Each alveolus is very small, but there are millions of them. Together the alveoli
have a huge surface area of around 100 m2 where gas exchange takes place.
34
capillary
alveolus
Human respiratory system
There is a steep concentration gradient between the oxygen in the air
you breathe in and the blood in your capillaries, and between the carbon
dioxide in the blood and the air in the lungs. These gradients mean that
diffusion takes place quickly. The diffusion gradients are made by moving
air in and out of your lungs when you breathe, and the movement of the
blood through your blood vessels.
The thin walls of the capillaries and alveoli are only one cell thick so the gases
do not have far to move and diffusion takes place easily.
COPD and the alveoli
Chronic Obstructive Pulmonary Disease (COPD) is a lung disease affecting
the structure of the alveoli. You have seen that the structure of the alveoli
is very well adapted for gas exchange. If this structure is damaged, gas
exchange does not take place so efficiently. Over 2% of adults over 40 in
Pakistan are affected by COPD, so it is a big problem.
The thin-walled alveoli under a
light microscope.
What happens in COPD? The thin walls of the alveoli break down. This leads
to fewer big air sacs instead of many tiny ones.
he alveoli break down in COPD giving big air sacs with less surface area for gas
T
exchange.
What are the symptoms of COPD? People with COPD get breathless very
easily. They cannot walk far, and it is difficult to run or climb stairs.
Why does COPD make people breathless? The big air sacs have a smaller
surface area than healthy alveoli. Less gas exchange takes place. This means
that the cells of the body do not get enough oxygen, and the waste carbon
dioxide builds up in the blood. You feel breathless, and the body reacts by
trying to get more air into the lungs.
Key points
y
The alveoli have a large
surface area for gas
exchange, the walls are
thin so gases don’t have
far to move, and they
have a rich blood supply
for gases to diffuse in
and out.
y
The movement of the
blood through the
capillaries and the
breathing movements of
the air in the lungs keep
steep concentration
gradients for diffusion.
Questions
1. Describe an alveolus.
2. Draw and label a diagram of a single alveolus.
3. Explain how the structure of an alveolus relates to its function in the
body.
4. Anything which damages the structure of the alveoli makes people
feel very breathless and can even be fatal. Explain why.
35
moking
allergies
Science
in context
4.1
1.1
2.7
Asthma
Minhaj has asthma. Minhaj uses his inhaler before he joins in any sport.
Minhaj and his teacher decided to explain asthma, and how it is treated, to
the whole class as an example of how scientific understanding has grown. It
also shows how scientific knowledge is applied to improve lives.
Objective
y Describe the role and
function of major organs
in the human respiratory
system including trachea,
lungs and alveoli (air sacs).
What is asthma?
Around the world, around 8–9% of people have asthma. In 2019 it was
estimated that asthma affects around 7.5 million adults and 15 million
children in Pakistan alone. The Ancient Greeks and Egyptians, both,
described asthma attacks, but doctors only began to understand what
was happening in the 1800s. If you have an asthma attack, you struggle to
breathe in and out. You cannot get enough oxygen or remove toxic carbon
dioxide.
y
pollen
infections
stress
smoking
food allergies
air pollution
From 1892 doctors discovered that in an asthma attack, the muscles
around the airways to the lungs contract. This makes the tubes narrower
so it is hard
to move air in or out.
exercise
mould
Almost
100
years
later, scientists discovered that the linings of the
y
bronchi swell and make extra mucus during an asthma attack, making
breathing even harder.
medicines
pets
dust mite
cold air
airway wide open
exercise
mould
Normal airway
muscles contract
lots of
extra mucus
swollen lining
airway very narrow
Airway during an asthma attack
The airways narrow during an asthma attack, making it hard to move air in or out of
the lungs.
medicines
llution
pets
dust mite
cold air
Common asthma triggers.
36
Common asthma symptoms
Without treatment, asthma may make it impossible to run, play or work.
Common symptoms include:
y
y
y
y
y
wheezing
coughing at night which disturbs your sleep
shortness of breath
a tight feeling in your chest
difficulty breathing.
Human respiratory system
What causes asthma?
People with asthma have very sensitive airways. Asthma
is triggered by environmental triggers. Some people
have asthma attacks every day, others only a few times
a year.
inhaler
delivering drug
mouth
How do we treat asthma?
trachea
Once scientists understood asthma, they developed
medicines to help people suffering from asthma.
y
y
bronchus
Relievers: Relievers were the first modern asthma
medicines. They are used when someone has
bronchiole
an asthma attack to make them feel better fast.
alveolus
Relievers relax the muscles around the bronchi.
This opens up the airways quickly, making it easy to
breathe again. Minhaj uses his reliever before he does
Arrow shows movement of drug
exercise so that his tubes don’t react.
Preventers: Preventers were developed once doctors
Inhalers allow millions of people
and scientists discovered that the airways also
with asthma to have active lives.
become inflamed in asthma. Preventers reduce inflammation, making
the airways less sensitive and so making asthma attacks much less likely.
Combining preventers and relievers means many people with asthma live
healthy, active lives. Some top sports stars have asthma, controlled by
these amazing medicines.
Getting medicines to the lungs
One problem for doctors treating asthma was getting the medicines down
to where they are needed. Engineers designed inhalers, medical devices
which work with our natural breathing to deliver medicines deep into the
airways.
Key points
y
In asthma the airways
are sensitive to
environmental triggers,
exercise or stress. The
muscles around the
bronchi contract and
the linings swell and
produce extra mucus.
This narrows the airways
making it difficult to
breathe.
y
Medicines to help
people with asthma
were not developed
until doctors understood
the causes.
y
Engineers applied
scientific knowledge to
develop inhalers that
take medicines into the
lungs.
Questions
1. Describe what happens during an asthma attack. Include 3
symptoms in your answer.
2. a. Give 3 common triggers for asthma.
b. Globally, how many people per hundred have asthma?
3. a. Explain the difference between a reliever medicine and a
preventer medicine in treating asthma.
b. Explain why it took almost a hundred years after relievers were
developed before preventers became commonly used.
4. a. Describe the main problem with asthma medicines.
b. Explain how this problem has been overcome.
37
2.8
1.1
4.1
Objectives
y Sketch and label the
human circulatory system.
y Explain how blood
circulates in the human
body through a network of
vessels (arteries, veins and
capillaries) and transports
gases, nutrients, wastes
and heat.
y Describe the structure and
function of the human
heart.
Body
The human heart and circulatory
system
Humans are big, active, multicellular animals - so big that we need
special systems to digest our food, and to bring oxygen-rich air into
our bodies. We also have a special system to carry the nutrients and
dissolved gases we need to our cells, and to remove the waste substances
we produce. This is our circulatory system. The circulatory system is
made up of the blood, the blood vessels and the heart.
A double circulatory system
Humans have a double circulatory system which is very efficient.
y
The heart pumps blood to the lungs, where it picks up oxygen and
releases carbon dioxide as you learned in. The oxygenated (oxygen-rich)
blood then returns to the heart. The movement of blood between the
heart and the lungs is one part of the double circulatory system
y
The heart pumps oxygenated blood around the body to all the organs
and tissues. They take up the oxygen they need and add waste carbon
dioxide. The blood is now deoxygenated – the oxygen has been removed.
It returns to the heart ready to be sent to the lungs. The movement of
blood between the heart and the rest of the body is the second part of
the double circulatory system.
The human heart
Heart
Lungs
The human double circulatory
system carries gases, nutrients
and wastes all around the body.
It is a complicated system but we
show the main parts quite simply
38
The heart pumps blood around your body in the blood vessels. It is the
main organ of the circulatory system. Your heart is mainly muscle, and
both sides of your heart fill and empty at the same time. It beats around
70 times a minute throughout your life.
y
y
y
veins from head and body: bring deoxygenated blood back to the heart
y
right ventricle: collects the deoxygenated blood and pumps it to the
lungs
y
artery to lungs: carries deoxygenated blood to the lungs
right atrium: collects deoxygenated blood from the body
valves: stop the blood flowing backwards through the heart - there are
four sets of valves
Human respiratory system
y
y
y
y
y
vein from lungs: carries oxygenated blood from the lungs to the heart
y
septum: keeps deoxygenated and oxygenated blood from mixing
left atrium: collects oxygenated blood
left ventricle: collects oxygenated blood and pumps it out to the body
aorta: carries oxygenated blood from the heart to the body
heart muscle: contracts to pump blood out of the heart to the lungs and
the body – and relaxes to let it fill again
Key points
y
The human circulatory
system is made up of the
blood, the blood vessels
and the heart.
y
It is a double circulatory
system, with one
circulatory system
between the heart and
the lungs and another
between the heart and
the rest of the body. This
is very efficient.
y
The heart is a muscular
pump which beats
about 70 times a minute.
y
The structure of the
heart is closely related to
its functions.
The structure of the human heart.
Questions
1 Define a circulatory system.
2 a. Sketch and label the human circulatory system.
b. Describe how the double circulatory system works.
3 Draw a diagram of the human heart and label it fully, giving the
function of each structure on your labels.
39
2.9
1.1
4.1
Arteries, veins and capillaries
Objectives
y
Explain how blood
circulates in the human
body through a network of
vessels (arteries, veins and
capillaries), and transports
gases, nutrients, wastes
and heat.
y
Compare and contrast
arteries, veins and
capillaries.
y
Calculate your pulse rate
and record your findings.
Think about the roads, tracks and paths used for transport in your
community. Whether you live in a big city like Karachi, Peshawar and
Quetta, or in a tiny village, transport routes are important to get the
water and food we need to our homes. Our blood vessels are the
transport routes of our body. There are three main types of blood
vessels in the human circulatory system. They are the arteries, veins and
capillaries.
Arteries, veins and capillaries
The three main types of blood vessels in your body look different and do
very different jobs.
y
Arteries carry the blood away from your heart. The blood they carry
is usually oxygenated (rich in oxygen) and bright red in colour. Arteries
have a pulse from the force of the heatbeat forcing the blood through
the vessels. Arteries have thick walls with lots of elastic tissue in them to
withstand the force of the blood pumping through them.
y
Veins carry blood back from the body to the heart. The blood they carry
is usually deoxygenated - it has given up its oxygen to the cells of your
body. It is purply-red in colour. Veins have no pulse, and relatively thin
walls. They have valves to stop the blood flowing backwards away from
the heart.
y
Capillaries are very tiny blood vessels that form a big network joining
arteries to veins. They have very thin walls, only one cell thick. The blood
moves quite slowly in the capillaries. Substances such as dissolved food
molecules and oxygen move by diffusion out of the blood into the cells
from the capillaries. Waste substances such as carbon dioxide and urea
move by diffusion out of the cells into the blood in the capillaries.
The transport system of a big
city like Faisalabad, seen here at
night, supplies the city with all
its needs.
Thick
walls
Artery
Vein
small lumen
relatively
thin walls
thick layer
of muscle
and elastic
fibres
Capillary
large lumen
often
have
valves
The three main types of blood vessels.
40
walls a
single
cell thick
tiny vessel
with narrow
lumen
Human respiratory system
How do valves work?
Valves are important structures in your heart and in your veins. The
structure of valves means that, when blood is flowing in the right
direction, they are open. But if the blood starts to move backwards, the
valves close, preventing the backflow of the blood. This makes sure blood
is returned to the heart from all around your body. The opening and
closing of valves allows the heart to function properly.
Thinking and working scientifically
Investigating your blood vessels
Arteries
Arteries run all over your body carrying
oxygenated blood to your tissues. Some run
near the surface. There is an artery in your
wrist – you cannot see it but you can feel the
pulse in it. Use this pulse to work out how
many times your heart beats in a minute.
Do not use your thumb to feel the artery in
your wrist – it also has a pulse and this is
confusing!
Once you are sure you can find your pulse
easily, sit quietly for a few minutes – then
take your pulse using a stopwatch or your
phone. Count the pulse beats you feel for 15
seconds. Then multiply the answer by 4 to
find your heart rate per minute.
E.g. 18 beats counted in 15 secs 18 x 4 = 72
beats/minute
The valves in your veins keep
the blood flowing in the right
direction.
Tip hand
slightly back
Raised bone
press lightly
A pulse is found where an
artery passes close to the
surface of your skin.
Key points
y
The blood vessels
include arteries, veins
and capillaries.
y
Arteries carry blood
away from the heart
(usually oxygenated).
They have thick, elastic
walls and a pulse.
y
Veins carry blood back
to the heart (usually
deoxygenated). They
have thinner walls, no
pulse, and valves to stop
the backflow of blood.
y
Capillaries are very
tiny with walls a single
cell thick. They link
the arteries and veins
and are the place
where substances are
exchanged between the
cells and the blood.
Veins
Open and close your fist several times. Now have a look at the back
of your hand, underside of your wrist, or the crook of your elbow. You
should be able to see veins there. You may even see the bulges that
show where the valves in the veins are found. If you cannot see veins
on your own skin, if you have grandparents you may be able to find
them on their hands, as veins are easier to see on older people.
Questions
1. Name the three main types of human blood vessels.
2. (a) Describe the main functions of the three main types of blood vessels.
(b) Name two substances that pass from the blood to the cells of
your body, and one substance that passes from your cells into the
blood.
3. Draw a diagram of the human heart and label it fully, giving the
function of each structure on your labels.
41
2.10
1.1
4.1
Our blood transports many substances around our body. It also protects us
against many diseases.
white blood cell
Human blood
Objective
y
Transport in the blood
Describe the composition
of the blood and the
functions of red cells, white
cells, platelets and plasma.
55%
plasma
platelets
You have about 5 litres of
blood in your body. Blood
is not a simple red liquid. It
is made up of many things
including:
y
y
y
red blood cells to carry
oxygen from the lungs
around the body
white blood cells to
red blood cell
fight disease
The main components
plasma to carry blood
of blood.
cells, digested food,
waste substances such
as carbon dioxide and urea, hormones, and antibodies around the body.
platelets to help the blood to clot.
1%
white blood cells
and platelets
The blood is not made up of equal proportions of these different
components.
44%
red blood cells
y
The structure and functions of the blood
The percentage volume of the
different components of blood.
Plasma
Plasma is a yellow, straw-coloured liquid making up 55% of your blood
volume. Plasma is mainly water, and it transports your blood cells and
platelets around your body. It also carries dissolved food and other
nutrients to your cells and
carries toxic carbon dioxide
digested
away from your cells to your
food
lungs. The waste product
urea is transported in the
plasma from the cells of your
small intestine
all cells
liver to your kidneys, where
it is removed from your body
carbon
in the urine.
dioxide
When your muscles are
working, they warm your
blood as it passes through
them in your blood vessels.
The heated blood is
transported around your
body, warming the other
tissues it passes through.
In this way, your blood
‘transports heat’ around
your body.
42
all cells
lungs
urea
liver
kidneys
Blood plasma transports many different
substances around your body.
Human respiratory system
Red blood cells
The red blood cells are the smallest cells in your body, but they make up
about 44% of your blood volume. You have more red blood cells than any
other type of cell. Red blood cells have a disc-like shape and no nucleus.
This makes lots of room for haemoglobin, the red-coloured molecule that
carries oxygen from the alveoli of the lungs to the cells of the body for
aerobic respiration. They squeeze through very small blood vessels one at a
time.
White blood cells
All white blood cells are big, and they all have a nucleus. They help protect
your body against pathogens, which are microorganisms that get into our
bodies and cause infectious diseases. Some types of white blood cells flow
round and digest microorganisms. Other types of white blood cells make
special proteins called antibodies. Antibodies stick to microorganisms so
that they cannot cause disease. White blood cells make up about 1% of your
blood volume.
Platelets
Platelets are tiny pieces of cells – they make up less than 1% of your blood
volume. Platelets make your blood clot if you cut yourself, so that you do
not bleed to death. Platelets help clots to form scabs, which cover damaged
tissues, allowing the body to repair itself. The scab protects the wound from
more damage, and stops microorganisms getting into your body.
In this light microscope image
of the blood (mag. 1000×), the
red blood cells look red and the
white blood cells are stained
blue. Platelets are too small to
see.
Platelets and white blood cells both help to protect you from disease.
Key points
Questions
1. Make a table to show the main components of the blood, their
percentage volume in the blood and their functions.
2. Copy and complete this table to summarise transport in the blood.
Substance
Part of the blood it is
transported in
From
y
The main components
of the blood are plasma,
red blood cells, white
blood cells and platelets.
y
Plasma transports blood
cells, platelets, nutrients,
carbon dioxide and urea
around the body.
y
Red blood cells
transport oxygen from
the lungs to the cells of
the body.
y
White blood cells
protect the body
against pathogens.
To
Oxygen
Carbon dioxide
Digested food
Urea
3. Some people say that blood is the most important tissue in the
body. Give four different functions of the blood which support this
statement.
43
Thinking
and working
scientifically
4.1
1.1
2.11
Objective
y
Hypothesize how exercises
of varying intensity would
impact the pulse rate, test
the hypothesis, calculate
the pulse rate and test the
findings.
The effect of exercise on pulse rate
Many factors affect the number of times your heart beats in a minute. These
include your age, your size, how fit you are and what you are doing.
A class is going to investigate the effect of exercise on the pulse rate.
y
y
What do you predict will happen to your heart rate after a minute of hard
exercise?
What is the scientific basis for your prediction?
Investigating the resting pulse rate
1. Each student sits still, without speaking, for 1 minute.
2. Using a stopwatch, each student records their pulse rate as shown
before. They count the heart beats for 15 seconds and multiply by 4 to
find their pulse rate per minute.
3. The students repeat this process two more times – Table 1 shows some
of their results.
Table 1
Adil’s results
Investigation
1
2
3
Beats per minute
80
76
78
Kashif’s results
Investigation
1
2
3
Beats per minute
72
68
70
4. The students use their results to work out their mean resting heart rate
per minute.
Adil: Mean resting heart rate per minute = (80 + 76 + 78) ÷ 3
= 234 ÷ 3 = 78 heartbeats/min
Kashif: Mean resting heart rate per minute = (72 + 68 + 70) ÷ 3
= 210 ÷ 3 = 70 heartbeats/min
Investigating the effect of exercise
5. Each student runs on the spot for 1 minute.
6. As soon as the exercise stops, each student starts their stopwatch and
takes their pulse, to find how many times their heart beats in a minute.
7. The students sit quietly until their heart rate returns to its resting level,
then repeat the exercise and record their heart rate twice more Table 2
shows some of their results.
Table 2
Adil’s results
Different types of stopwatch.
44
Investigation
1
2
3
Beats per minute
97
95
96
Kashif’s results
Investigation
1
2
3
Beats per minute
86
84
88
Human respiratory system
8. The students use their results to work out their mean heart rate per
minute after exercise, to the nearest whole heart beat.
Adil: Mean heart rate per minute after exercise = (97 + 95 + 96) ÷ 3
= 288 ÷ 3 = 96 heartbeats/min
Kashif: Mean heart rate per minute after exercise = (86 + 84 + 88) ÷ 3
= 258 ÷ 3 = 86 heartbeats/min
The class results
The students all record their mean heart rate at rest and after exercise in a
big table.
Table 3: The mean resting heart rate before and after exercise.
Individual mean resting
heart rate
(beats/min)
73
75
72
70
72
62
74
75
70
74
66
Individual mean heart rate
after exercise (beats/min)
96
97
92
88
90
88
90
92
96
95
75
Individual mean resting
heart rate
(beats/min)
70
80
Individual mean heart rate
after exercise (beats/min)
73
75
70
95
91
88
77
73
68
71
100
95
88
96
90
98
Questions
1. a. Suggest why students have to sit without moving or speaking for
a minute before they measure their resting heart rate.
Key points
y
You can predict
the outcome of an
investigation by
applying your scientific
knowledge.
y
The data allows you to
see a pattern, and the
more results used, the
more reliable the data.
y
You can make
conclusions by
interpreting results but
you must recognise
the limitations in the
way the investigation is
carried out.
b. Explain why students sit quietly after each session of exercise
before repeating their investigation.
2. Explain why students carry out several readings and calculate the
mean heart/pulse rate in each part of their investigation.
3. a. U
se the data in Table 3 to calculate the mean resting heart/pulse rate
per minute and the mean heart/pulse rate after exercise for the whole
class.
b. D
isplay these mean data on a bar graph to show the effect of
exercise on the heart rate.
c. E
xplain why the whole class results are more useful than the
results of each individual student.
4. Give a scientific explanation for the results observed by the students.
5. Suggest three limitations in this investigation.
45
Review
1.1
4.1
2.12
3. Name the parts of the respiratory system that
match each of these descriptions:
1. a. State the name of the reaction that gives a
controlled release of energy inside cells.
[1]
b. Write a summary word equation for the
process of controlled energy release
in cells.
[2]
c. A student looks at diagrams of three cells.
One has very few mitochondria, one has
many mitochondria, and the third has both
chloroplasts and mitochondria.
[1]
b. a reinforced tube that takes air down
to one lung
[1]
c. sheet of muscle involved in breathing
movements.
[1]
4.
air drawn in
muscle
air drawn
out
lung
[1]
i. What are mitochondria?
ii. There are four conclusions that the student
can make from the information given
[4]
here. List all four of them.
2. The diagram below shows the main structures of
the human respiratory system.
rib
diaphragm
a. Draw a flow diagram to show the sequence
of events when you breathe in (inhale).
[5]
b. Draw a flow diagram to show the sequence
of events when you breathe out (exhale). [5]
B
5. The model respiratory system in this diagram can
be used to show how air is moved into and out of
your lungs.
F
C
D
a. small air spaces where gas exchange
takes place
hollow tube
A
bung
bell jar
E
Choose the correct letter for each of these parts:
a. alveolus
[1]
b. bronchus
[1]
c. ribs
[1]
d. lung
[1]
e. diaphragm
[1]
balloon
rubber sheet
a. Which part of the human respiratory system
is represented by the hollow tube outside the
[1]
bell jar?
46
Human respiratory system
b. What does the rubber sheet represent?
c. Describe what happens when the
rubber sheet is pulled down and explain
why it happens.
[1]
[2]
d. A model is never exactly like the real thing.
Describe two ways in which this model is
different from the real respiratory system and
explain how these differences might lead to
[4]
misconceptions.
6. This diagram shows part of the lungs where gas
exchange takes place.
[1]
ii. helps to destroy microorganisms
[1]
iii. carries oxygen from the lungs to
the body tissues.
[1]
b. Blood cells are suspended in a watery
liquid. Name this liquid.
[1]
c. What percentage of the blood is made
up of this watery liquid?
[1]
d. Name three different substances
transported in this watery liquid, not
including the blood cells.
[3]
9.Make a table to compare and contrast the
structure and functions of arteries, veins and
capillaries.
[8]
X
gas B
a. i. helps form blood clots
10. The table below shows you the breathing rates
of six students at rest, and after exercise.
gas A
Y
a. Name the parts X and Y.
[2]
b. Name the gases A and B.
[2]
a. Plot a bar graph to show the mean individual
breathing rates of all the students at rest and
after a minute of hard exercise.
[8]
Individual
Individual
mean resting
breathing rate
(whole breaths
per minute)
Individual mean
breathing rate
after exercise
(whole breaths
per minute)
A
12
18
B
14
21
C
17
21
D
10
15
E
17
25
F
14
20
c. Gas exchange takes place by a
process called diffusion. Describe diffusion. [3]
d. X and Y have very thin walls. Explain
how this helps gas exchange.
[1]
e. Give another way in which these structures
are adapted to help gas exchange take place.
Explain how this adaptation works.
[3]
7. a. Sketch and label a simple diagram to show the human circulatory system.
[4]
b. State which student is least fit and which is
most fit, giving reasons.
[4]
b. Describe the functions of the following
structures of the human heart:
(i) the veins from the head and body
[1]
(ii) the left ventricle
[2]
(iii) the valves
[1]
(iv) the septum
[1]
8. The blood is a very important tissue made
up of many different components. Name the
component of the blood that:
c. Calculate the mean breathing rate at rest and
after exercise for the whole group of students.
[7]
Display the data as a bar graph.
d. Suggest one way in which this data is similar
to the effect of exercise on the heart rate
(pulse) and one way in which it is different. [2]
47