Year 9 Biology
Photograph by Noha El Naggar
Name:________________
Form: ________________
Teacher:______________
Table of Contents
Command Terms and definitions
3
Unit 1: Characteristics of living organisms and cells
7
•
•
•
•
•
•
Characteristics of life
Cells and levels of organisation
Specialised Cells
Microscope
Biological Drawings
Dichotomous Keys
Unit 2: Classification and adaptation
•
•
•
•
•
•
Binomial system
DNA
5 Kingdoms of life
Viruses, bacteria, and Fungi
Plants
Animals
26
26
28
29
32
38
41
Unit 3: The movement of molecules
• Diffusion
• Osmosis
• Active Transport
49
49
51
55
Unit 4: Enzymes
56
• Features
• Factors that affect enzymes
56
57
Unit 5: Nutrition
59
• Seven food groups plus one
▪ Carbohydrates
▪ Fats
7
9
13
16
18
21
59
▪ Proteins
▪ Vitamins
▪ Minerals
▪ Water
1
▪ Fibre
▪ Additives
• 6 Food tests and the energy test
• Nutrition and malnutrition
Unit 6: Plant Nutrition
• Plant and leaf structure
• Photosynthesis
• Photosynthesis Experiments
 Chlorophyll
 Carbon Dioxide
 Light
• Rate of photosynthesis and limiting factors
• Carbon Dioxide
• Light
• Temperature
• Stomatal Number
• Greenhouses
Unit 7: Animal Nutrition
• Ingestion: Mouth

Teeth

Care of teeth

Tooth Decay

Animal Dentition
• Swallowing
• Digestion: Stomach and small intestine
• Absorption: Small and large intestine
• Egestion: Anus
Unit 8: Ecology
•
•
•
•
•
•
•
Energy Loss
Food chains
Food web
Pyramids numbers, biomass and energy
Food chain efficiency
Invasive Species
Population Size
72
78
83
84
87
88
 Water
 Mineral Ion Requirements
 Oxygen Production
96
101
102
104
108
109
110
115
117
118
121
123
126
131
133
134
2
Command terms
Exam questions will ask you to do any of the following. Lots of marked can be lost if
you do not understand the command terms, so go and learn them!
1. Define (the term(s) … ) is intended literally, only a formal statement or
equivalent paraphrase being
required.
2. What do you understand by/What is meant by (the term(s) … ) normally
implies that a definition should be given, together with some relevant comment on
the significance or context of the term(s) concerned, especially where two or more
terms are included in the question. The amount of supplementary comment intended
should be interpreted in the light of the indicated mark value.
3. State implies a concise answer with little or no supporting argument (e.g. a
numerical answer that can
readily be obtained ‘by inspection’).
4. List requires a number of points, generally each of one word, with no
elaboration. Where a given
number of points is specified this should not be exceeded.
5. (a) Explain may imply reasoning or some reference to theory, depending on the
context. It is another
way of asking candidates to give reasons. The candidate needs to leave the
examiner in no doubt
why something happens.
(b) Give a reason/Give reasons is another way of asking candidates to explain
why something happens.
6. Describe requires the candidate to state in words (using diagrams where
appropriate) the main points.
Describe and explain may be coupled, as may state and explain.
7. Discuss requires the candidate to give a critical account of the points involved.
8. Outline implies brevity (i.e. restricting the answer to giving essentials).
9. Predict implies that the candidate is expected to make a prediction not by recall
but by making a logical
connection between other pieces of information.
10. Deduce implies that the candidate is not expected to produce the required
answer by recall but by
making a logical connection between other pieces of information.
11. Suggest is used in two main contexts, i.e. either to imply that there is no
unique answer (e.g. in biology
there are a variety of factors that might limit the rate of photosynthesis of a plant in a
greenhouse), or to
imply that candidates are expected to apply their general knowledge of the subject
to a ‘novel’ situation,
one that may be formally ‘not in the syllabus’ – many data response and problemsolving questions are
3
of this type.
12. Find is a general term that may variously be interpreted as calculate, measure,
determine, etc.
13. Calculate is used when a numerical answer is required. In general, working
should be shown, especially where two or more steps are involved.
14. Measure implies that the quantity concerned can be directly obtained from a
suitable measuring
instrument (e.g. length using a rule, or mass using a balance).
15. Determine often implies that the quantity concerned cannot be measured
directly but is obtained from a graph or by calculation.
16. Estimate implies a reasoned order of magnitude statement or calculation of the
quantity concerned,
making such simplifying assumptions as may be necessary about points of principle
and about the
values of quantities not otherwise included in the question.
17. Sketch, when applied to graph work, implies that the shape and/or position of
the curve need only be qualitatively correct, but candidates should be aware that,
depending on the context, some quantitative aspects may be looked for (e.g.
passing through the origin, having an intercept).
In diagrams, sketch implies that simple, freehand drawing is acceptable;
nevertheless, care should be taken over proportions and the clear exposition of
important details
4
Definitions
You need to learn these, no ifs/buts maybe....learn em! These come up all the time
on exams
Movement - An action by an organism or part of an organism causing a change of
position or place.
Respiration - The chemical reactions in cells that break down nutrient molecules
and release energy for metabolism.
Sensitivity - The ability to detect or sense stimuli in the internal or external
environment and to make appropriate responses.
Growth - A permanent increase in size and dry mass by an increase in cell number
or cell size or both.
Excretion - Removal from organisms of the waste products of metabolism
(chemical reactions in cells including respiration), toxic materials, and substances in
excess of requirements.
Nutrition - Taking in of materials for energy, growth and development; plants
require light, carbon dioxide, water and ions; animals need organic compounds and
ions and usually need water.
Species - A group of organisms that can reproduce to produce fertile offspring.
Binomial system of naming species - An internationally agreed system in which
the scientific name of an organism is made up of two parts showing the genus and
species.
Tissue - A group of cells with similar structures, working together to perform a
shared function.
Organ - A structure made up of a group of tissues, working together to perform
specific functions.
Organ System - A group of organs with related functions, working together to
perform body functions.
Diffusion - The net movement of particles from a region of their higher
concentration to a region of their lower concentration down a concentration gradient,
as a result of their random movement.
Osmosis - The net movement of water molecules from a region of higher water
potential (dilute solution) to a region of lower water potential (concentrated solution),
through a partially permeable membrane.
Active transport - The movement of particles through a cell membrane from a
region of lower concentration to a region of higher concentration using energy from
respiration.
Catalyst - A substance that increases the rate of a chemical reaction and is not
changed by the reaction.
Enzymes - Proteins that function as biological catalysts.
-Amylase breaks down Starch to Maltose.
-Maltose is broken down by Maltase to Glucose.
-Protease breaks down Protein to Amino Acids.
-Lipase breaks down Fats to Fatty Acids and Glycerol.
5
Photosynthesis - The process by which plants manufacture carbohydrates from
raw materials using energy from light.
Limiting Factor - Something present in the environment in such short supply that it
restricts life processes.
Mechanical digestion - The breakdown of food into smaller pieces without
chemical change to the food molecules.
Chemical digestion - The breakdown of large, insoluble molecules into small,
soluble molecules.
Absorption - The movement of small food molecules and ions through the wall of
the intestine into the blood.
Assimilation - The movement of digested food molecules into the cells of the body
where they are used, becoming part of the cells.
Egestion - The passing out of food that has not been digested or absorbed, as
faeces, through the anus.
Food Chain - Show the transfer of energy from one organism to the next, beginning
with a producer.
Food Web - A network of interconnected food chains.
Producer - An organism that makes its own organic nutrients, usually using energy
from sunlight, through photosynthesis.
Consumer - An organism that gets its energy by feeding on other organisms.
Herbivore - An animal that gets its energy by eating plants.
Carnivore - An animal that gets its energy by eating other animals.
Decomposer - An organism that gets its energy from dead or waste organic
material.
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Unit 1: Characteristics of living organisms and cells
Biology ~ the study of Life
So how do we define what it is to be alive?
What’s living and what’s non-living?
Look at the list below and decide whether the things are alive or not.
Living or
not?
•
•
•
Living or
not?
How did you decide?
What characteristics do they have in common?
What life processes do all living things carry out?
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Scientists have identified the key characteristics that all living
things have in common which are collectively known as the
Seven Life Processes.
M
Movement:
R
Respiration:
an action by an organism or part of an organism
that causes a change in position.
the chemical reactions that break down nutrient
molecules in living cells to release energy.
Sensitivity:
S
the ability to detect or sense changes in the
environment (stimuli) and to make responses.
G
Growth:
R
Reproduction:
E
Excretion:
N
Nutrition:
a permanent increase in size and dry mass by an
increase in cell number or cell size.
the processes that make more of the same kind of
organism.
the removal of toxic materials, the waste products
of metabolism, and substances in excess from an
organism.
the taking in of nutrients which are organic
substances and mineral ions, containing raw
materials or energy for growth and tissue repair,
absorbing and assimilating them.
* Please note: Viruses are not considered alive as they only carry out
reproduction and even that they must do inside a host cell.
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Cells – the basic units
of life
❖ All living organisms are made up of cells.
❖ Living things can either be unicellular (one cell only) or are multicellular
(made up of many cells).
❖ Unicellular organisms carry out all seven life processes in a single cell.
❖ Larger, more complex organisms, which are made up of many cells, have
different cells to carry out different functions. These cells are said to be
specialised.
❖ Multicellular organisms are made up of many cells.
Levels of organisation in a multicellular organism
Simple
More
complex
•
A cell is the basic unit of life.
•
These cells are organised into groups of similar shaped cells
working together to perform a particular function known as a
TISSUE.
e.g. muscle cells form a muscle used for movement
•
Tissues which work together to form a structure and perform
a specific function, are known as an ORGAN
e.g. muscle cells form the heart which beats as a result of all
muscle cells contracting at the same time.
•
Organs with related functions which work together to perform
specific body functions are known as an ORGAN SYSTEM.
e.g. the circulatory system made of the heart and blood vessels.
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Levels of organisation in a multicellular organism
Cells
Tissue
Organ
Organ System
On the diagrams below, write the names of the organs on the lines provided. Use
the words in the box.
Brain
Leaf
Root
Flower
Liver
Stem
Intestines
Stomach
Lungs
Fill in the correct word in each of the sentences. Use the words in the
box.
Circulatory
a
A group of organs working together is called an
Digestive
organ ____________________.
Leaves
b
Plants take water in through their___________.
Nervous
The water travels up the _________________.
Photosynthesis
Some of the water is used to make food using
Roots
__________________. A lot of the water is lost
Stem
System
by the ______________.
c
Food is digested in the ____________ system.
d
The heart is part of the ____________________ system.
e
The brain is part of the ____________________ system.
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Animal and Plant Cells
Structure
Found in
Function
Cell membrane
Animal and
Plant
▪
▪
▪
▪
Cytoplasm
Animal and
Plant
▪ jelly-like substance
▪ contains enzymes which control all
the chemical reactions of the cell
(metabolism)
▪ Respiration to release energy
occurs here with the help of the
mitochondria.
Nucleus
Animal and
Plant
▪ Contains the genetic information
of the cell in the form of DNA.
▪ DNA codes for proteins and
physical characteristics. It is
considered to be the ‘blueprint’ of
the cell and organism.
▪ DNA condenses during mitosis
and forms packets known as
chromosomes.
Glycogen Granules
Animal
▪ Extra glucose is converted to
glycogen especially in the
cytoplasm of liver and muscles
cells
▪ Glycogen granules can be broken
down to release glucose (sugar)
for when quick energy is needed.
▪ Glycogen is a polysaccharide
(made from many subunits of
sugar)
0.00001 mm thick, very thin
Made of fats, proteins and sugars
maintains cell shape
partially permeable membrane
which controls what can
enter/leave the cell
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Cell Wall
Vacuoles
Plant
▪ Made of cellulose
(polysaccharide)
▪ It’s a tough, inflexible wall that
encloses the plant cell
▪ It provides support and rigidity
to the cells and to the plant as a
whole.
▪ Fully permeable
Plants
have
permanent
ones.
▪ It contains cell sap
▪ It is a storage organelle and holds
salts, sugars, amino acids and
other nutrients needed by the cell.
* Animals may have temporary ones
for movement of molecules into/out
of cells.
Chloroplast
Plants
▪ contain chlorophyll (a green
pigment)
▪ site of photosynthesis and
where the cell is able to produce
sugar using sunlight.
▪ only found in aerial parts of a
plant not in the roots.
Starch Granules
Plants
▪ found inside chloroplasts
▪ Extra glucose is converted to
starch (polysaccharide) for
storage.
▪ It can be converted back to
glucose for respiration or sucrose
for transport.
Mitochondria
Animals
and Plants
▪ Extremely small (only visible with
an electron microscope)
▪ Site of respiration and energy
for the cell.
❖ Construct a table to show the differences and similarities
between plant and animal cells using a light microscope.
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Specialised Cells
❖ In multicellular organisms, there are cells which have become adapted
to perform their function better.
❖ Cells with features that enable them to perform their specific functions
better are said to be SPECIALISED.
❖ Always relate structure to function, e.g reb blood cells have no nucleus
which allows them to carry more haemoglobin.
Animal Cells
1. Red blood cell – Biconcave disc
shaped. They have no nucleus
which allows them to pack more
haemoglobin into their cells. Haemoglobin helps to carry oxygen by
forming oxyhaemoglobin. Also in the centre of the cell is an area of thin
cytoplasm which allows rapid diffusion of gases. The function of the red
blood cell is to transport oxygen around the body.
* When haemoglobin binds with carbon monoxide (found in cigarette smoke) it
binds permanently with it forming carboxyhaemoglobin and it will no longer
be able to transport oxygen.
2. Ciliated cells – have projections known as cilia
which are able to beat in unison to move mucus
(with dirt and bacteria trapped in it)
3. Muscle cells – contain protein fibres which slide
between each other causing the cell to contract
(shorten) and so as a tissue allow movement in an
organism.
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Other animal cells that you should know are sperm cells, egg
cells (ova) and nerve cells. You will study these later in the
course (Year 10 and 11) but ask you teacher to show you
them and draw and label them in the spaces below.
Sperm cell
Egg Cell
Nerve cell
14
Plant Cells
1. Xylem vessels – these cells have
been lignified which allows them to
hold water. Lignin is not
permeable to water and so the
cells die.
This structure become part of the
plant’s transport system and allows
conduction of water and mineral
ions within the plant and provides
support.
Pits are non-lignified parts of cell walls
that
allow sideways (lateral) movement of water
2. Root hair cells – have a long projection which increases surface area
for the absorption of water and mineral ions such as magnesium and
nitrates.
❖ Water and mineral ions are absorbed into the root hair cell.
Water is drawn in by the lowering of the pressure at the top of the plant by
water vapour leaving the leaf via stomata by the transpiration stream.
Water and mineral ions are transported in the stem of the plant in the xylem
vessels.
15
The Microscope
1. Using the words in the box below label the parts of the microscope.
mirror
objective lens
eyepiece
clip
stage
focusing knob
2. Here are some instructions on using a microscope. Put the number ‘1’
next to the instruction you should do first. Put the number ‘2’ next to
the instruction you should do next and so on.
_____
Look into the eyepiece lens.
_____
Place the smallest objective lens over the hole in the
stage.
_____
Place the slide on the stage.
_____
Turn the coarse focusing wheel until what you see is clear.
_____
Turn the coarse focusing wheel to make the objective lens
as close to the stage as possible.
_____
Adjust the light source.
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You are given a microscope which has three objective lenses: X10,
X20 and X40. The microscope has two eyepiece lenses: X5 and
X7.5. Make a table like the one below to show all the possible
magnifications you could get.
Magnification of
eyepiece lens
Magnification of
objective lens
Total magnification
You will need to be able to label a plant and animal cell as viewed under a
microscope. Look at the photographs of the cells below and label using label
lines all the visible features of the cells.
When a diagram is made, or a photograph taken, it may not be easy to directly
show the correct-size, such as, when a structure is really small or very large. The
true size of an organism can be calculated using a combination of actual
measurement and a known magnification.
Magnification = drawing measurement
Actual length
* Using the formula above, calculate what is
the actual size of the plant and animal cell shown.
D
MxA
17
Biological Drawings.
❖ Required for Paper 6 (alternative to practical)
❖ The drawing is a simple outline of the organism listing any key features
that allow it to be identified.
❖ No shading. It is not a test of your artistic talent and so it is not allowed.
The examiners will award marks under the following criteria:
•
•
•
•
•
O (outline)
S (scale)
P (proportion)
A (accuracy)
L (labelling)
Outline
You should use an HB pencil as mechanical pencils tend to scar the page and so
make it difficult to rub out if you make mistakes.
The outline must be a continuous line with no breaks or shading, so it is
recommended you draw the outline lightly at first then go over it again darker once
you are satisfied with it.
Scale
The size of diagram must take up at least half of the space provided and if they
ask for a large diagram it must be as large as or larger than the photograph in the
question
Proportion
When enlarging your diagram all parts of the diagram must be equally enlarged.
Therefore, all parts of the diagram have been magnified by the same amount.
You should include the magnification of your diagram. i.e. X2 or X3
Accuracy
When completing your diagram you must include the same number of features as
shown in the photograph.
e.g. If a flower has 5 five petals, you must draw five
If a fruit has 20 seeds, you must draw twenty
If an invertebrate has 8 legs, you must draw eight.
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Labelling
Labels are done in PENCIL too. You should draw a
straight horizontal line with a ruler clearly to the
centre of the object being named.
Remember you should label key features that
distinguish it from other living organisms.
i.e.
fish include gills, fins
insects include waxy exoskeleton, limbs, wings, antennae
flowers include petals, sepals, stigma, anthers
*To learn key features for Paper 6 you should refer to Unit 2.
There are two main methods to draw biological drawings:
1. Draw grid lines.
* Draw a cross through the centre of the photograph.
* Draw a new grid lightly (so its easy to rub off later) in
the space provided for your drawing then draw one part
of the picture (section of the grid) at a time.
* Draw using light, smooth lines with no shading.
1. The grid has been drawn for you, now you must complete it for the
flower shown as the example.
19
2. Graph Grid
• Draw graph grid lines over your photograph 10mm X 10mm.
• Next draw graph grid lines 20mmX20mm in very light pencil in the
space provided for your diagram.
• Then fill in squares accordingly.
Complete the drawing below.
20
Dichotomous Keys
❖ Another useful skill in biology is making and using keys to identify
organisms based on key features that are visible.
❖ Dichotomous means that you are given two descriptions at a time to
choose from and each choice leads you to another pair of descriptions until
you reach the final stage where you are given the name of your organism.
❖ There are two main types:
 Branching keys
 Statement keys
Branching Keys
21
Branching keys
Use this branching key to identify these two breeds of cow.
Cow 1 is _______________. Cow 2 is ____________________.
2
Use this branching key to identify these two dinosaurs.
Dinosaur 1 is __________________. Dinosaur 2 is __________.
22
Statement Keys
Use this statement key to identify the birds below.
Write the names in the lines underneath each picture.
1
Feet are webbed
Feet are not webbed
go to 2
go to 5
2
Neck feathers are all white
Neck feathers are not all white
go to 3
go to 4
3
Hooked beak
Straight beak
Great Black-backed Gull
Whooper Swan
4
Long, slender beak
Short beak
Avocet
Brent Goose
5
Underside feathers mostly white go to 6
Few or no white underside feathers go to 8
6
Long, thin beak
Short beak
7
Some sticking up feathers on head Lapwing
All feathers are flat
Ringed Plover
8
Head feathers all one colour
go to 9
Head feathers have different colours go to 10
9
Hooked beak and sharp talons
Golden Eagle
Straight beak and no sharp talons Carrion Crow
10
All feathers on back are black
Feathers on back are speckled
Bird 1 is ______________
Bird 2 is ______________
Oyster Catcher
go to 7
Bird 3 is ______________
Coot
Grey Plover
Bird 4 is ______________
23
Statement Keys
Use this statement key to identify which plants the leaves below came from. Write
the names of the leaves in your book.
1
Leaf edges are jagged
leaf edges are smooth
go to 2
go to 8
2
Leaf edges do not have hard spines
Leaf edges have sharp hard spines
go to 3
Holly
3
Leaves are not arranged in opposite pairs go to 4
Leaves arranged in opposite pairs
go to 5
4
Leaves are long and narrow
Leaves are not long and narrow
Crack Willow
go to 6
5
Leaves nearer branch are small
Leaves are roughly the same size
Common Ash
Rowan
6
5–7 leaves grow from a central point
Horse Chestnut
Leaves do not grow from a central point go to 7
7
Leaf has many lobes
Leaf has no lobes and a pointed tip
Sycamore
Lime
8
Leaf has no lobes
Leaf has lobes
go to 9
go to 10
9
Leaves grow in opposite pairs
Three leaves grow from a central point
go to 11
Laburnum
10
Each leaf has five lobes
Each leaf has more than five lobes
Field Maple
English Oak
11
Stem ends in a pair of leaves
Stem ends in a single leaf
Box
False Acacia
Leaf 1 is _______________
2
3
Leaf 2 is _______________
Leaf 3 is ___________
Using the key, write down the features of False Acacia leaves. You will need to work through the key
backwards.
Draw pictures of what you think Rowan, Sycamore and False Acacia leaves might look like on a stem.
24
A Key to Life
25
Unit 2: Classification and Adaptation
Classification and diversity of living organisms
Once you have learned to distinguish between living and non-living, you then
need to learn how to classify living things.
Carl Linnaeus of Sweden in 1735 introduced the basis of modern taxonomy
(classification).This groups organisms according to how closely related they
are).
With this in mind he invented the Binomial System.
Binomial System
All living organisms are given two names in Latin to show how closely related
they are to each other.
1 Genus name, written first and starts with a capital letter, e.g. Homo (same)
2 species name, written second and starts with a small letter, e.g. sapien
(modern)
So Homo sapiens is modern man when printed, it’s typed in Italics
When handwritten it is Homo sapien - it’s simply underlined
In the past organisms, were grouped together based on several factors:
•
•
•
•
Physical Features i.e. teeth, wings, scales
Habitat
Methods of Nutrition
Methods of reproduction, including if organisms were capable of
interbreeding
• Life cycle
Nowadays, the techniques used to organise living things is more scientific and uses
genetic information such as RNA and DNA sequencing to show how closely
related organisms are to each other and the rest of living world.
This method of study is known as cladistics. Cladistics shows us how we are
related on a biochemical level (DNA/RNA), while taxonomic classification is based
26
on visible, physical features. Cladistics is a more accurate, scientific way of
classification.
Organisims which share a more recent ancestor are more closely related and have
base sequences in DNA that are more similar, as opposed to a more distant
ancestor.
Every living thing, or organism has got at least one thing in common, that one thing
is DNA. How closely related the organisms are, the more similar their DNA is.
Here is how a “clade” or “cladogram” looks like
27
DNA (Deoxyribonucleic Acid)
• DNA is a polymer made up of nucleotides.
• The structure of DNA consists of two strands coiled together to form a double
helix.
• Each strand contains chemicals called bases.
• There are cross-links between the strands which are formed by pairs of bases.
• The bases always pair up in the same way: A with T, and C with G, there full
names are Adenine, Thymine, Cytosine and Guanine, but you only need to
know the letters.
Nucleotide
DNA
Use this space for additional notes
____________________________________
____________________________________
____________________________________
____________________________________
____________________________________
____________________________________
____________________________________
____________________________________
28
The Living World
There are 5 major groups of living organisms known as Kingdoms.
Kingdom
Prokaryotes
Protoctista
Fungi
Plantae
Angiosperm
Phylum
Algae
Protozoans
Monocotyledons
Class
Eudicotyledons
Living Things
Order
Family
Genus
Species
Living things are organised from the largest group
(Kingdom) down to the smallest group (species) of
closely related organisms.
So organisms of the same species may interbreed
as they are so closely related which is why ALL dogs, even
though they may look remarkably different, are still able to
produce puppies.
However, when organisms belonging to the same
genus try to interbreed they produce infertile offspring
which are unable to reproduce.
For example, when a female horse and male donkey
interbreed a mule is born. It has characteristics of both
parents which make it good for farming but it is unable to
produce more of itself.
Organisms are rarely able to interbreed beyond such
groupings as they are related but so distantly that it is no
longer possible either physiologically or behaviourally.
29
The Living World
Animalia
Kingdom
Vertebrate
s
Invertebrates
Chordate
Phylum
Molluscs
Nematodes
Annelids
Arthropods
Class
Fish
Amphibian
s
Insects
Order
Family
Genus
Species
Birds
Crustaceans
Reptiles
Mammals
Arachnids
Myriapods
❖ One easy way to remember a list is to use
mnemonics, where you take the first letter of
each word from the list and make a sentence
with words beginning with the same first
letters.
i.e.
Kingdom
Phylum
Class
Order
Family
Genus
Species
Kuwait
Produces
Crude
Oil
For
General
Sale
30
The Variety of Life
Let’s begin with the simplest organisms such as the unicellular organisms which
are made up of only one cell and yet still carry out all seven of the life processes
known collectively as MRS GREN.
They made be small but they each have their own kingdom. They are
the:
• Viruses (included only due to size but remember they are not
truly alive and so have no Kingdom)
• Prokaryotes (Bacteria)
• Protoctista (Algae and Protozoans)
• Fungi (Yeast are unicellular but Fungi do have some multicellular
organisms such as mushrooms)
❖ As most of these are unicellular, they are incredibly small and
so a microscope must be used to see them, they are referred
to as microscopic. Only Fungi (and a few Protoctista but they
are not on the syllabus) have individuals which are large
enough to be seen without a microscope. Mushrooms are
macroscopic and can be viewed with the naked eye.
31
• Viruses
❖ Extremely small and can only be seen with an electron microscope
at a magnification of X30 000. They are 50X smaller than bacteria.
❖ The electron microscope was only invented in 1931 by Ernst Ruska
and Max Knoll so we had no way of knowing what these tiny particles
looked like but we knew they caused disease.
❖ Not alive. Their only true living quality is their ability to reproduce but
they can only do this when they have infected a host cell.
❖ They are made up of a central core of genetic information which can
be either RNA or DNA surrounded by a protein coat known as a
capsid, made up of subunits of capsomeres.
❖ They have NO
 Cytoplasm
 Nucleus
 Organelles
 Cell membrane.
membrane from previous
host cell
32
• Prokaryotes or Bacteria
❖ Larger than viruses and can be seen with an ordinary light microscope.
They range in size from 0.5-5μm
*(1μm = 1∕1000mm)
❖ They are living and as such carry out all seven life processes within the
one cell.
❖ They are composed of:
 a cell wall made of protein, sugar and fats.
 a cell membrane made of fats and proteins. (All livings things have
one)
 cell contains cytoplasm (a jelly substance where all chemical
reactions take place for the cell known as metabolism)
 No nucleus but they do have genetic information as one large
single circular strand of coiled DNA called its chromosome. And
there are some smaller DNA circular strands known as plasmids,
which are important for genetic engineering.
❖ They may have:
▪ Flagellum used for
movement or fimbria (look
like cilia).
▪ Slime capsule used for
protection from Fungi and
our antibiotics.
33
•
Bacteria
Bacteria are often classified according to their shape.
Importance of Bacteria to humans
Bacteria can be both helpful and harmful and it may even be the same bacteria
that are both.
Activity
Helpful
Harmful
Decomposing
a) Dead organisms, litter, manure are
converted into simple nutrients for
green plants to use
b) Sewage treatment, so preventing
water pollution.
a) Causes rotting of
food and leads to
wastage.
Circulating
Nitrogen
a) Nitrogen-fixing bacteria found in
root nodules of leguminous plants.
They fix nitrogen gas from air and
so improve soil quality.
b) Nitrifying bacteria convert
ammonia to nitrates
a) Denitrifying bacteria
converting useful
nitrates back to inert
nitrogen.
In Industry
a) dairy products i.e. used to make
yoghurt*and cheese
b) wine making
c) biofuel
a) causes milk to sour
b) causes wine to sour
c) may damage oil
lubricating engines
Health
a) producing antibiotics
b) producing human hormones and
enzymes by genetic engineering
a) causing disease in
humans and animals
* Yoghurt is made using Lactobacillus (converts lactose into lactic acid causing
milk to clump and curdle) and Streptococcus (makes yoghurt buttery in texture).
34
• Fungi
There are three main types: yeasts, moulds and mushrooms.
 Yeast
❖ They are unicellular.
❖ Important for alcohol production
and used in fermenters to make
SCP (Single Celled Protein used to
produce protein supplements for
vegetarians or as cattle feed)
❖ They are composed of:
 a cell wall made of chitin.
 a cell membrane made of fats and proteins.
 cytoplasm containing vacuoles, oil droplets and
glycogen granules
*These
features are
the same for
moulds and
mushrooms
 a nucleus (Double stranded
DNA) and so are eukaryotes
Moulds
 Macroscopic
 Moulds consist of
filaments known as hyphae.
 The hyphae form a mesh of
threads known as mycelium
through which they feed using
extracellular enzymes. They often feed on dead or decaying matter and
so are called saprophytic or they can be parasitic, where they feed
off living organisms and cause harm.
 Some have a nucleus, some have many nuclei (multinucleate).
 Have no true cross wall separating hyphae but instead have
Septa (supporting cross walls with many holes), this means solutes in
cytoplasm simply diffuse along the whole of the organism as it’s all connected.
35
Moulds
 Cell membrane,
cytoplasm and vacuoles are present.
 No chloroplasts and
so are heterotrophic; they
must feed off of other living
things to gain energy.
 Reproduce asexually
by producing spores either
by budding off or in a
sporangium.
 Mushrooms
 Multicellular networks of mycelium made up of many hyphae which
spread over many metres in the surface layers of the soil.
 In autumn or in the rainy season, they produce a fruiting body known
as a mushroom which releases the spores from its gills to be
carried away by air currents.
36
Complete the following table once you have reviewed the characteristics of
viruses, bacteria (prokaryotes) and fungi, to check you have understood the key
differences and similarities.
Viruses
Bacteria
Fungi
Living or not?
Size
Outer covering or cell
wall
(include what it is
made of)
Cell membrane
Genetic Material Type
and is it found in a
nucleus
Does it have
cytoplasm?
Does it have any
organelles?
Key features
Example
37
• Plants
❖ Multicellular organisms. They are
made up of many cells.
❖ Autotrophic as they are able to
photosynthesise (make sugar for
food energy using sunlight)
❖ They are composed of:





❖
a cell wall made of cellulose
a cell membrane made of fats and proteins. (All living things have one)
a nucleus and so are eukaryotes. It contains double stranded DNA.
cytoplasm, site of chemical reactions or metabolism.
organelles include vacuoles containing cell sap, chloroplast for
photosynthesis and starch granules for storage of sugar.
We will look only at the phylum angiosperms which are commonly called
the flowering plants. The two classes are listed below.
Monocotyledons
one cotyledon (food store
for its embryo plant in the
seed)
Long, narrow leaves with
parallel veins and a
smooth edge
Non-branching stem
Fibrous root
Flower parts in 3’s
Scattered vascular bundles
(plant transport system)
e.g. maize, all cereals,
grass, palm trees
Eudicotyledons
Two cotyledons (food
stores)
Broad leaves with
branching veins and a
toothed edge
Branching stem
Tap root
Flower parts in 5’s
Vascular bundles form a
ring
e.g. beans and trees
38
Label the key feature for each class and complete the leaves
for the eudicotyledons.
Monocotyledons
Eudicotyledons
39
Ferns
Over to you here, find out about ferns. You will be working on some skills here,
research and biological drawings. You need a diagram ( labelled) and some
characteristic features. Remember, no copy and paste, don’t transcribed Wikipedia,
use a few sources and write short concise notes. Only use words that you
understand, if there is a word that you don’t understand, look it up, write down the
meaning and there you go, you have learned something!.
40
Animals
 Heterotrophic so must feed on other living things for energy.
 Multicellular organisms They are made up of many cells,
 They are composed of:
 a cell membrane made of fats
and proteins. (All living things
have one)
 a nucleus and so are
eukaryotes. It contains double
stranded DNA.
 Cytoplasm containing mitochondria (respiration) and
glycogen granules (sugar storage).
❖ Animals can be divided clearly between two main branches.
 Those with backbones known as the vertebrates or
scientifically as the phylum chordata.
 And those with no backbones known collectively as the
invertebrates but are composed of many phyla.
41
 Vertebrates
All vertebrates have:
▪ a bony backbone surrounding the spinal cord
▪ two pairs of limbs
▪ a post anal tail (a tail that starts behind the anus)
Vertebrates are divided into five classes.
Vertebrates
Fish
Amphibians
Reptiles
Birds
Mammals
 Fish
-
Body consists of head, thorax∕abdomen,
and tail.
streamlined shape
damp overlapping scales
breathe through gills
fins: tail fin for locomotion, and lateral and
dorsal fins for orientation in water
Lateral line canal detects vibrations in the
water to find food and avoid predators
Jelly eggs laid in water
 Amphibians
-
Body consists of a head, thorax
and an abdomen with two pairs
of limbs.
-
Moist skin
-
Shell-less eggs which must be
laid in water.
-
Visible eardrums
42
 Vertebrates: five classes
 Reptiles
- Body consists of a head, thorax and an
abdomen with two pairs of limbs.
- Dry, scales for skin
- Leathery eggs
- sunken eardrums, visible only as a
hole on the surface
 Birds
-
Body consist of head,
thorax∕abdomen, and tail.
Feathers, beaks are key features
for them
Wings for flying
Scales on legs only
Holes leading to eardrums
Hard shelled eggs made with
calcium carbonate.
streamlined shape
 Mammals
-
Body consists of a head, thorax
and an abdomen with two pairs of
limbs.
-
hair ∕ fur covering skin, including
whiskers
Live birth with young fed on milk
from mammary glands
Eardrums with ear pinnae to
funnel sound better.
-
43
Using the above information about Vertebrates
construct a key to classify the following
RememberUse a pencil
Base your key on visible external characteristics
If you are unsure about the organisms, look them up
Why don’t you print out some pictures of the species to help
you? Glue them in. When you are finished, give the key to
your friend and see if they can make sense of it
Panda
Cobra
Whale
Salamander
Kestrel
Owl
Iguana
Shark
Barracuda
Bullfrog
44
 Invertebrates (collective name only)
❖ All invertebrates have no backbone.
❖ Their soft bodies may be without covering, or with either hard shells or waxy
exoskeletons.
❖ Their bodies consist usually of a head, thorax and abdomen.
❖ Limbs may range in number from zero pairs in molluscs to 3 pairs in insects
to 4 pairs in arachnids to 5 or more pairs in both crustaceans and myriapods.
Of all the numbers of different phyla (which is the plural of
phylum) in the invertebrates we only need to learn about 1!
Thank you Cambridge. The reason is that it would take
approximately 46.7 years to learn them all, so don’t moan
about learning these ones, remember....46.7 years....
The phylum arthropods is characterised by:
- three body parts
- exoskeleton
- jointed limbs which is the meaning of arthropods
We will look at four of the classes of arthropods only.
 Insects
- Body in 3 parts: head,
thorax and abdomen
- Waxy exoskeleton
made of chitin
- 3 pairs of limbs
- 1 pair of compound
eyes
- 1 pair of antennae
- Wings (1 or 2 pairs)
45
 Arachnids
- Body in 2 parts:
head/thorax called
encephalothorax, and
abdomen
- Waxy exoskeleton made
of chitin
- 4 pairs of limbs
- 4 pairs of simple eyes
- No wings or antennae
46
 Phylum Arthropods: 4 classes
 Crustaceans
- Body in 2 parts:
encephalothorax, and
abdomen
- Chalky exoskeleton made
of calcium carbonate
- 5 or more pairs of limbs
- 1 pair of compound eyes
and may be on stalks
- 2 pairs of antennae
- No wings
 Myriapods
- Body in many segments
begins with a head.
- Waxy exoskeleton
- Each segment may have 1
or 2 pairs of limbs
- 1 pair of simple eyes
- 1 pair of antennae
- No wings
- Cylindrical or flattened body
47
*Copy and complete the tables below to help you study.
Animal Kingdom: Vertebrate Phylum: Classes
Fish
Body
Limbs
Covering
Ears
Eggs
Extra
Feature
Scales
No ears,
instead
have a
lateral line
Surrounded
by soft jelly,
laid in water
Almost all
fish live in
water
No proper
limbs, fins
instead to
help with
swimming
and
balance
Amphibians
Reptiles
Birds
Mammals
Animal Kingdom: (invertebrates) Arthropod Phylum: Classes
Body
covering
Number
of body
parts
Number
of limbs
Eyes
Antenna
or wings
Insect
Arachnid
Crustacean
Myriapods
48
Unit 3: The movement of molecules
* The random movement of particles / molecules is brought about by Kinetic
Energy.
There are three main types:
A. Diffusion
B. Osmosis
C. Active Transport
A. Diffusion
Diffusion: is the net movement of molecules from a region of their higher
concentration to a region of their lower concentration down a
concentration gradient, as a result of their random movement.
❖ It’s PASSIVE and requires no added energy. Kinetic energy only.
❖ It occurs whenever there is a difference in concentration known as a concentration
gradient.
❖ Diffusion can occur in solids(only rarely), liquids or gases.
N.B. When dealing with liquids, remember:
Solute
+
Solvent
Solution
Concentration refers to the amount of dissolved solute in a given volume of solvent.
Concentrated but free moving
Before
Moved by Kinetic Energy until evenly
distributed
After
49
Factors affecting Diffusion
• Temperature
Increasing temperature increases heat which causes molecules to move
faster so there is more kinetic energy.
So the higher the temperature – the faster the rate of diffusion.
• Pressure
The greater the pressure, the more force is exerted on the molecules
causing them to move faster.
So the higher the pressure – the faster the rate of diffusion.
• Distance
The longer the distance, the more time it takes for the molecules to
randomly move so diffusion is slower.
So the shorter the distance – the faster the rate of diffusion.
• Concentration Gradient
The greater the difference in concentration between two regions –
the faster the rate of diffusion.
So the steeper the concentration gradient – the faster the rate of
diffusion.
• Size of the Molecule
The larger the molecule, the more energy it needs to move so the longer it
takes.
So the smaller the molecule – the faster the rate of diffusion.
• Cell Wall
The thicker the wall, the longer it will take for molecules to diffuse through.
So the thinner the wall – the faster the rate of diffusion.
50
Three main examples of diffusion in living things:
❖ Cells
The diffusion of substances, such as glucose and oxygen, into and out of cells is
done through the cell membrane, which is partially permeable.
❖ Diffusion of gases such as carbon dioxide and oxygen.
In plants, the leaf is the organ of gaseous exchange through its stomata.
In humans, the lungs are the organs of gaseous exchange through their alveoli.
❖ Diffusion of dissolved nutrient molecules
In humans, dissolved nutrient molecules like glucose pass from the small
intestine through the villi into the bloodstream.
B. Osmosis
Osmosis: is the diffusion of water molecules from a region of high water potential
to a region of low water potential, through a partially permeable membrane.
Osmosis: is the diffusion of water molecules from a region of their higher
concentration (dilute solution) to a region of their lower concentration
(concentrated solution), through a partially permeable membrane.
Important points to remember:
• concentration usually refers to dissolved solute so you must use the word
`their` if you choose to write the second definition to show you mean the
water concentration.
• Water concentration is usually referred to as water potential and deals with
the number of `free water molecules` available to move by osmosis.
• All cells are surrounded by cell membranes which are partially permeable
so osmosis primarily happens in living organisms.
51
Osmosis
Water
Starch
Dilute Solution
______Water Potential
Weak
Solution
Concentrated Solution
______Water Potential
Strong
Solution
Solutions are the same strength
*Only water diffuses
cm3
cm3
1000
1000
500
500
0
0
Partially
permeable
membrane
5g of sugar
10g of sugar
5g of sugar
10g of sugar
In this experiment a potato has been cut in half, and a well scooped out of it. The well has been
filled with salt solution and the whole lot placed into a dish of distilled water. The potato on the
right shows what has happened after it has been left for 30 minutes.
52
Osmosis in Cells
A. Animal Cells
In a Hypotonic solution (dilute or weak solution), such as water.
A Red Blood Cell
Water
Water
Water
The red blood cell would gain water by
osmosis as it’s more concentrated than
water and would eventually burst.
This is known as cell lysis.
Water
In a Hypertonic solution, such as a concentrated salt solution.
A Red Blood Cell
Water
Water
Water
Water
The red blood cell
would lose water
by osmosis as it’s
less concentrated
than the salt
solution and would
eventually shrivel
up. It is now
crennated.
B. Plant Cells
1
1. Cell loses water by osmosis as
it’s in a concentrated solution.
First the cell loses water pressure
and becomes flaccid. However if
untreated, the cell membrane will
pull away from the cell wall and
the cell is called plasmolysed.
*The tissue is wilting.
2
2. Cell gains water
by osmosis as it’s in
a dilute solution.
The cell membrane
lies next to the cell
wall. The cell is only
just turgid.
3
3. Cell has gained as
much water as it can
and is now fully turgid.
The pressure of the
cell walls now resists
any further osmosis.
Osmosis stops.
*The tissue is firm and
rigid.
53
Osmosis Experiments
•
Visking tubing is a partially
permeable membrane which we use to
test osmosis.
•
The sugar molecules are too large to
pass through and so only small water
molecules can move by osmosis.
•
The sugar and water molecules are
moving randomly by kinetic energy in
both the beaker and the visking tubing.
•
Water will move into the visking tubing
due to the difference concentration, or
gradient, as sugar can not get out.
•
This increases the hydrostatic
pressure in the capillary tube so water
is forced up an out of the capillary
tube.
a. The osmometer
b. Using potato tissue – this allows us to determine the concentration inside the
potato tissue and so are able to predict the concentration in its cells.
54
C. Active Transport
Active Transport: is the movement of ions in or out of a cell through the cell
membrane, from a region of their lower concentration to their higher concentration
against a concentration gradient, using energy released from respiration.
* Energy is applied
which causes the
protein carrier
molecule to
change shape
allowing the ion or
molecule to be
released inside the
cell, against its
concentration
gradient.
Important points to remember:
• Active transport is ACTIVE, it requires energy from respiration.
• As the energy comes from respiration, it takes place inside living cells.
Two main examples of active transport in living things:
❖ Root hair cell in plants.
As important ions, such as magnesium and nitrates, are often in higher
concentration inside the cells than in the soil, the root hair cell will use energy to
bring them inside as they are useful.
❖ Epithelial cells of the villi lining the gut in animals.
Once food is digested, the dissolved nutrients such as glucose and amino acids
rapidly begin diffusing into the blood. However, once equilibrium in concentration
is achieved between the lumen (the inside of a tube) of the small intestine and
the blood, diffusion slows preventing useful nutrients being absorbed. To speed
up diffusion through the villi into the blood stream, the epithelial cells of the villi
will use energy to actively transport useful nutrients into the bloodstream.
55
Unit 4: Enzymes
A catalyst speeds up a chemical reaction and is not changed by the reaction.
Enzymes are considered to be biological catalysts as they are made of
organic substances and speed up chemical reactions while remaining
unchanged.
Important Features:
❖ They are made of protein, so can be tested using the Biurets test and will turn purple.
❖ They are specific, meaning they can only speed up one chemical reaction.
amylase
i.e. Starch
maltose
catalase
i.e. Hydrogen peroxide
water +oxygen gas
* Enzymes and
catalysts are
written above the
arrow in a chemical
reaction to indicate
they are
unchanged.
Amylase can only work on starch, it is specific for starch.
❖ They can either join simple molecules into large ones or break down large molecules into
small molecules.
❖ Joining or breaking down of molecules can occur with lower activation energy than if no
enzyme was used. (*25°C to fix Nitrogen in bacteria or 750°C in the Haber process)
*The substrate fits into the enzyme’s active site like a ‛ lock and key’,
its shape is complementary to it.
56
Factors which affect enzyme rate of reaction:
❖ Temperature
❖ pH
❖ Enzyme concentration
❖ Substrate concentration
❖ Surface Area
❖ Temperature
Fig. 4.a the effect of temperature on
enzyme activity.
•
At low temperatures, enzyme action is
reduced and the rate of reaction is slow.
•
An increase of 10°C doubles the rate of
reaction.
•
Each enzyme has an optimum
temperature at which it works best. In
mammals it ranges from 37-40°C.
•
A slight increase above the optimum (up
to 50°C) will slow down the rate of the
reaction.
•
At high temperatures (above 50-60°C)
the enzyme will be destroyed and will
stop working. The enzyme is denatured,
altering its active site permanently due to
intense kinetic energy.
❖ Enzyme Concentration
The more enzyme molecules there are, the more open active sites there are to act
on the substrate molecules and as a result an increase in enzyme concentration
– increases the rate of reaction.
❖ Substrate Concentration
The more substrate molecules there are, the more likely they will ‛collide’
successfully with the enzymes’ active sites to be acted on. As a result an increase
in substrate concentration - increase the rate of reaction.
57
❖ pH
•
Each enzyme has its own
preferred pH, the pH in
which it works best is
known as its optimum
pH.
•
Fig. 4.b the effect of pH on
enzyme activity
For example,
o Pepsin works best in
acidic conditions, its
optimum pH is
_____2_____.
o Human amylase
works best in neutral
conditions, its optimum
pH is ___________ .
o Trypsin works best in
alkaline conditions, its
optimum pH is
_________ .
❖ Surface Area
The larger the surface area, the larger the area that can be acted on by enzymes.
As a result an increase in surface area - increases the rate of reaction.
* This is why chewing food helps as it increases surface area for enzyme action.
How do we measure enzyme rate of reaction?
There are two methods:
• Measure the rate substrates disappear.
• Measure the rate products form.
The enzyme amylase will break down the substrate starch and produce the
disaccharide maltose.
Now design an experiment you could do to test the effect of one of the factors that
affect enzymes i.e. temperature, pH on their rate of reaction.
*Remember you will need to be able to measure rate of reaction, which is equal
to1/time. So you must time how long it takes for the substrates to disappear or the
products to form.
*Think of what you already know about how to test for starch and sugars.
Write it in ten lines or less on a sheet of A4.
[10]
58
Unit 5 Nutrition
Nutrition: the taking in of nutrients which are organic substances and
mineral ions, containing raw materials or energy for growth and tissue
repair, absorbing and assimilating them.
❖ Organic substances are those that contain Carbon.
i.e. sugars, proteins and fats.
❖ There are Seven Natural Food Groups that make up our diet and an
eighth group of artificial foods such as additives and preservatives.
The Seven Natural Food Groups are:
1. Carbohydrates
2. Lipids (Fats/Oils)
These three are organic and provide the body
with both energy and the building blocks of raw
materials for growth and tissue repair.
3. Proteins
4. Vitamins
5. Minerals
These three are necessary for the proper
functioning of the body but do not provide
energy.
6. Water
7. Roughage/Fibre
This is not absorbed by the body but instead
exercises our intestines and keeps them
functioning healthily by promoting peristalsis
(muscular contractions) of the gut.
8. *Additives (artificial)
These are used to produce processed foods and
not needed by the body.
59
The Seven Natural Food Groups
1. Carbohydrates
❖ They are made up of three elements:
Carbon, Hydrogen, and
Oxygen.
There are three main types of Carbohydrates.
a) Simple Sugars – these are the most basic units. They are only one sugar
molecule in size and are known as monosaccharides.
i.e.
glucose
fructose
galactose
b) Complex Sugars – these are made up of two sugar molecules and are
known as disaccharides.
i.e. sucrose (glucose and fructose)
lactose (glucose and galactose)
maltose (glucose and glucose)
c) Polysaccharides – these are made up of many sugar molecules.
i.e.
starch (plants)
cellulose (plants)
glycogen (animals)
• How would you draw a polysaccharide?
• Did you notice any similarity between the names of the sugars?
60
The Seven Natural Food Groups
1. Carbohydrates
Good Food Source
Carbohydrates tend to be the staple foods in every country as they provide us
with 5/7th or the majority of our diet and are needed to give us energy.
A lack of carbohydrates (and protein) may cause the deficiency disease known
as marasmus. The symptoms include severe wasting away of body tissues and
dehydration.
Potatoes, Rice, and Maize (corn) are good staple foods. Other carbohydrates
include cereals (starch), fruit juices, or refined sugars such as those found in
desserts, soft drinks and sweets.
Function in our bodies
• Simple sugars are used to release energy by respiration and the
energy can then be used for active transport, cell division, and muscle
contraction and to build new larger molecules.
• Complex sugars are used to quickly and temporarily store energy.
Disaccharides are less reactive than monosaccharides and so the cell
needs less water to store them inside their cytoplasm.
• Polysaccharides are used to store energy long-term. Plant cells use
starch and animal cells use glycogen.
Also polysaccharides can be used as structural components of the
cell. For example, plants use cellulose to build their cell wall and animals
use polysaccharides as antigens on their cell membrane to provide
attachment and recognition by our white blood cells.
61
The Seven Natural Food Groups
2. Lipids (Fats in animals, oils in plants)
❖ They are made up of three elements: Carbon,
Hydrogen, and Oxygen.
❖ They are made up of two basic sub-units of molecules:
a) fatty acids
b) glycerol
❖ It is the type of fatty acids that determines if it’s a fat or an oil.
▪ Saturated fatty acids are found in animal cells and contain all
single bonds with carbon and hydrogen. (C-H)
▪ Unsaturated fatty acids are found in plant cells
and contain some double bonds between two
Carbons (C=C) as there is not enough Hydrogen
atoms available. This double bond causes a bend
in the fatty acid tail of the lipid molecule.
* Complete the boxes below by drawing in the first box as many saturated fatty acids
as you can fit and in the second draw as many unsaturated fatty acids. In which box
can you fit more?
Saturated fatty acids
Unsaturated fatty acids
62
The Seven Natural Food Groups
2. Lipids (Fats in animals, oils in plants)
Good Food Source
Lipids need only make up 1/7th of our diets but are important as they
provide energy and the raw materials to build new larger molecules.
A lack of lipids may contribute to the deficiency disease marasmus and
weight loss.
Red meat and dairy products contain animal fat which contains
cholesterol a “sticky fat” which forms a lining (plaque) inside the lumen of
the blood vessels, making the blood vessels narrower and can lead to heart
disease and obesity.
Margarine and cooking oils contain plant or vegetable oil.
Fish oils are also needed as they contain omega oils which are important
for brain function.
Functions in our bodies
• To build cell membranes by a making phospholipids.
• To store energy as it contains twice the energy (34KJ/g) as either
carbohydrates or proteins (17KJ/g).
• To insulate as fat deposits under the
skin (adipose tissue), for example as
blubber in whales and polar bears. It is
also used to insulate nerves so that their
electrical messages travel faster.
• For buoyancy; whales use it so that they can float.
• To make hormones such as oestrogen and testosterone
63
The Seven Natural Food Groups
3. Proteins
❖ They are made up of four elements:
Carbon, Hydrogen, Oxygen and Nitrogen.
❖ They are molecules made up of many units (polymers) of amino
acids. There are 20 commonly occurring amino acids.
❖ Two amino acids join together to form a dipeptide bond by
removing water and is known as a condensation reaction. When
many amino acids join together they are called polypeptides.
❖ Proteins may be made up one chain of amino acids or polypeptides
or may be made up of many polypeptide chains.
These are the basic units or amino acids.
When two amino acids join, a dipeptide forms.
When many amino acids join, a polypeptide forms.
Finally, a protein is made either from one
polypeptide chain or many.
*Remember it is DNA that codes for what sequence of amino acids is
joined together and how so any mutation to the DNA may alter what
protein is coded for.
64
The Seven Natural Food Groups
3. Proteins
Good Food Source
Proteins need only make up 1/7th of our diet but
are important as they provide energy and the
raw materials needed for tissue growth and repair.
A lack of protein may cause the deficiency disease known as
kwashiorkor. The symptoms include cracked lips, a swollen belly and
possibly liver and brain damage. Also lack of essential amino acids can
cause marasmus.
Lean meats such as fish and chicken are good animal sources
whereas eggs and red meats such as beef have high levels of
cholesterol which is a saturated fat that lines the blood vessels causing
high blood pressure.
Other sources of protein include peas, beans, milk and cheese.
Functions in our bodies
• To form protein carriers in the cell membrane.
• Hormones i.e. insulin
• Enzymes i.e. amylase
• Haemoglobin in red blood cells
• Antibodies produced by white blood cells
• Muscle cells
• Hair, and nails
•
Used for respiration energy when carbohydrates are low.
65
The Seven Natural Food Groups
*A recap of the first three, which are used for energy and to provide us and all
living organisms with the building blocks of life as raw organic materials.
Carbohydrates
Lipids
Proteins
What elements
are they made
of?
What is their
main use?
What are their
monomers
(basic single
units) called?
Give examples
Draw their
basic
structure.
66
The Seven Natural Food Groups
* The next three are needed for the healthy functioning of the body and its cells.
4. Vitamins
5. Minerals
6. Water
4. Vitamins – are a group of organic molecules that vary widely
in their chemical structure.
The features they share include:
•
•
•
•
Not digested for energy.
Essential is small quantities for normal health.
Needed for chemical reactions in our cells.
Not built into the body cells.
Nutrient
Vitamin C
• denatures
when
cooking
• watersoluble so
cannot be
stored and is
excreted
Vitamin D
Food Sources
Citrus fruits,
green
vegetables,
kiwis and
tomatoes.
Liver, oily
fish, dairy
• fat-soluble products and
margarine. It
and so is
stored in the is also made
by the skin in
body.
sunlight.
Functions in
Our Body
Deficiency Disease
Production of
connective
tissue such as
collagen fibres
in skin.
To help us
absorb iron.
Scurvy – symptoms
include bleeding gums,
wounds fail to heal.
Connective tissue fibres
fail to form. Anaemia.
Heart Failure.
Calcium
absorption and
storage.
To build bones
and teeth.
Rickets – symptoms
include weak bones
which bend under the
weight of the person and
hearing problems.
67
The Seven Natural Food Groups
5. Minerals – these are inorganic mineral ions.
There are four important mineral ions for healthy nutrition of plants and animals.
Nutrient
Food Sources
Functions in Our
Body
Deficiency
Disease
Calcium
• Needed for
animals
• Stored in bones
Dairy products,
sardines, watercress,
bread and cabbage
For healthy bones and
teeth, nerve function,
blood clotting and
muscle contraction.
Ricketts –
bones become
soft and weak.
Iron
•
Liver, kidneys, red meat, To form haemoglobin,
spinach and egg yolks.
which carries oxygen
in red blood cells.
Important for healthy
muscles.
Anaemia blood doesn’t
hold enough
oxygen so cells
can’t respire
and soon the
person
becomes tired
and short of
breath.
•
Needed for
animals
Stored in liver
Nitrogen
Protein such as red
meat, chicken, fish and
• Needed by both
plants too.
animals and
plants.
• As the gas it is
unreactive. First
bacteria convert it
to ammonia, then
to nitrites/nitrates
so both plants
and then animals
can use it.
To form amino acids
needed to build
protein. Proteins are
needed for growth and
tissue repair.
Kwashiorkor –
lack of
essential amino
acids and so
tissue are
unable to grow
or repair
themselves in
animals. May
lead to long
term brain
damage in
humans.
Magnesium
• Needed by plants
more.
To form chlorophyll,
the green pigment
found in plant cell
chloroplasts which
absorb sunlight to
make sugars in
photosynthesis.
Plants without
chlorophyll die
as they can’t
carry out
photosynthesis
to gain energy.
Plants obtain it from the
soil water that surrounds
their roots and will use
energy in active
transport to absorb it as
it’s essential.
68
The Seven Natural Food Groups
6. Water – this is considered to be one of the most important molecules as it allows life to
happen. This is why it is one of the first molecules we look for when we explore space and the
planets.
It is not used to produce energy but is important for the healthy functioning of an organism.
A lack of water in an organism can lead to dehydration.
As most living organisms are made up of water, humans up to 70%, we call this weight the Fresh
Mass.
However, the amount of water in an organism varies greatly from one organism to another. It also
varies depending on time of day, season, and temperature of their environment, among other
factors. As the amount of water in organisms varies, biologists often find the fresh mass to be a
misleading measurement and so prefer to use dry mass.
Dry mass is the weight of an organism after it has been killed and dried. It is a measurement that
is used in ecology, which is the study of how organisms interact with each other and their
environment.
Good Food Source
Water is found in drinking water, drinks, fruits and
vegetables.
Functions in living organisms
All living cells contain cytoplasm which is largely water. The cytoplasm is the site
of all chemical reactions that provide energy (metabolism) and is where larger
molecules are built up for growth and tissue repair by assimilation.
In multicellular animals like plants and animals, water allows for transport of
nutrients, gaseous exchange with the environment and heat loss.
69
The Seven Natural Food Groups
7. Roughage/Fibre – Important for multicellular animals
only.
Fibre is made up of non-digestible plant material such as cellulose found in plant cell walls and
lignin found in xylem vessels. We are unable to digest them due to a lack of the necessary
enzymes to break them down and make them soluble enough for absorption into our bloodstream.
*Note bacteria do produce cellulase the enzyme needed to break down cellulose in plant cell
walls and so are often found inside the guts of herbivores i.e. cows to eat grass and insects
i.e. termites to eat wood.
Good Food Sources
They are found in foods such as fruits, vegetables, wholegrain breads,
rice and cereals.
Functions in the body
Insoluble fibre ‘exercises’ the gut muscles by promoting peristalsis (muscular contraction) of
the intestines, especially of the large intestine.
This ensures that faeces (waste are egested through the anus) do not remain too long in the large
intestines, as faeces is full of toxins, which irritate the lining of the large intestine and can lead to
bowel cancer.
Also fibre allows water to be held in the faeces and so prevents constipation.
Soluble fibre (the kind you get in porridge oats) can help by helping to control the cholesterol
(‘sticky fat’) levels by binding with it in the small intestine and preventing the cholesterol from being
absorbed. Bacteria in the large intestine are able to metabolise the fibre which releases a
chemical into the bloodstream reducing plaques (fat deposits lining blood vessels which can lead
to heart disease). This chemical also reduces blood clots.
70
The 6 Food Tests and the Energy Test in Food Content
❖
There are several different
experiments food scientists
conduct to determine what is in
food (such as proteins, fats
and carbohydrates) and to
determine how much energy is
in a food so that they are able
to produce nutritional food
labels on packaged foods.
❖
Most food tests need to be conducted with the solid food made into a
solution.
▪
First grind one gram of the sample food with a pestle and mortar.
▪
Then add 5 cm3of water to ground sample and mix.
▪
Then filter the solution to remove any non-dissolved pieces of
food.
▪
Finally use 1 cm3 of sample solution to conduct food tests.
71
The 6 Food Tests and the Energy Test in Food Content
Do yourself a favour and learn these, you can rely on these coming up on IGCSE papers.
They are as follows:
• Iodine Test to test for starch, a polysaccharide.
• Benedict’s Test to test for carbohydrate sugars known as reducing sugars.
(sucrose is not a reducing sugar and so must be broken down first.)
• Emulsion Test to test for fats/oils in solution.
• Filter Paper Test to test for fats/oils in a solid.
• Biurets Test to test for proteins.
• DCPIP Test to test for Vitamin C.
• Energy Combustion Test or Bomb Calorimeter to test for the amount of
energy in 1g of food.
Iodine Test (To Test for Starch)
Add one to two drops of iodine solution (potassium iodide solution) to the
sample.
If the result is negative the orange/brown colour of the iodine solution stays the
same.
If the result is positive the colour changes to blue/black indicating that starch is
found in the sample.
Negative
Starch absent
Positive
Starch present
* Colour in the test tubes
to show the colours that
would be seen by these
results.
72
The 6 Food Tests and the Energy Test in Food Content
Benedict’s Test (To Test for Reducing Sugars)
• Add excess Benedict’s solution 2cm3 to 1cm3 of sample solution.
• Then add heat at 100°C in a hot water bath and observe colour change.
❖ It is important to use a hot water bath to avoid ‘spitting’ and safety
goggles should be worn.
• If the result is negative the light blue colour of the Benedict’s solution
stays
the same.
• If the result is positive the colour will change from
BLUE
BLUE
BRICK RED PRECIPITATE
GREEN
YELLOW
ORANGE
(1 mark answer)
BRICK RED
PRECIPITATE
(2 mark answer)
A precipitate is an insoluble solid that comes out of solution due to a chemical
reaction when two liquids are mixed.
A colour change indicates the presence of a reducing sugar.
*Sucrose, a disaccharide, is not a reducing sugar so must be either broken
down using the enzyme sucrase or hydrolysed using an acid and heat
followed by an alkaline to neutralise it. (not on syllabus)
73
The 6 Food Tests and the Energy Test in
Food Content
Emulsion Test (To Test for Lipids such as Fats/Oils)
• Add 4 cm3 of Ethanol to 1cm3 of sample solution.
• Then add 3-4 drops of distilled water.
• If the result is negative, the colourless solution stays the same.
• If the result is positive, the colourless solution changes colour to a cloudy
white emulsion which is best viewed against black card.
* An emulsion is a mixture formed when two normally immiscible liquids
such as water and oil are shaken together.
Filter Paper Test (To Test for Lipids in solids)
• Rub the solid food against the filter paper.
• If the result is negative, the filter paper’s white colour will stay the same.
• If the result is positive, the filter paper’s white colour will change to a clear,
translucent colour which is best viewed towards a light.
74
The 6 Food Tests and the Energy Test in Food Content
Biurets Test (To Test for Protein)
There are two methods:
a) Simple method –
• Add 1 cm3 Biurets solution to 1 cm3 of sample solution. (Equal amounts)
• If the result is negative then the colour stays blue.
• If the result is positive then the colour changes to mauve/purple indicating
that protein is found.
b) Detailed method –
• Add 1 cm3 of sodium hydroxide to 1 cm3 of sample solution. (Equal
amounts)
• Mix gently by tapping the base of test tube with your finger.
• Then add 3- 4 drops of copper (II) sulphate.
• If the result is negative then the colour stays blue.
• If the result is positive then the colour changes to mauve/purple indicating
that protein is found.
Negative
Protein absent
Positive
Protein present
* Colour in the test tubes
to show the colours that
would be seen by these
results.
75
The 6 Food Tests and the Energy Test in Food Content
DCPIP Test (To Test for Vitamin C)
*DCPIP is normally blue in colour but it will turn colourless when Vitamin C is
present.
• Add 1ml of DCPIP to a test tube.
• Fill a syringe with your sample solution and slowly drop by drop, release it
into the DCPIP filled test tube.
• Record the number of drops it takes to decolourise the DCPIP.
*The fewer drops needed to decolourise it the higher the Vitamin C content of the
sample solution.
Energy Combustion Test (To Test for the amount of energy)
▪ Fill a test tube with 20 cm3 of water and attach to
clamp stand.
▪ Record temperature of water using a
thermometer.
▪ Weigh food sample in grams.
▪ Attach food sample to mounted needle.
▪ Set the food sample alight or burn it.
▪ Place lit food sample under test tube and allow
radiant heat from burning food sample to heat the
water.
▪ Once sample is completely burnt, record the
final temperature of the water.
* Use the temperature increase to determine the amount of energy released from the sample
food.
*Remember when using a thermometer not to touch the sides of the test tube as it will measure
the temperature of the glass test tube not the contents of the tube.
76
The 6 Food Tests and the Energy Test in Food Content
Energy Combustion Test (To Test for the amount of energy)
How to calculate energy produced
Once the temperature increase has been recorded you can use the equation
below to determine the amount of energy in 1g of a food sample.
Energy (joules) =
mass of
water
(grams)
X
specific
heat
capacity of
water
X
temperature
increase
(Celsius)
Energy (J) = mass of water (g) X 4.2 J°C/g X temperature increase (°C)
*1g of water =1ml of water
Therefore the amount of energy in a given mass of food is calculated as:
Energy content (joules/g) = Energy released as calculated above (J)
Mass of sample food (g)
77
Nutrition: The process of taking in nutrients which are organic substances and
mineral ions, containing raw materials or energy for growth and tissue repair,
absorbing and assimilating them.
In other words we need to take in the 7 basic food groups to obtain energy or
building blocks of life for growth and tissue repair.
But how much of each do we need to get the correct balance?
A balanced diet consists of the seven basic food groups, such as carbohydrates,
lipids, and proteins in the correct proportions.
Guidelines:
Balance Calories
• Enjoy your food, but eat less.
• Avoid oversized portions.
Foods to Increase
• Make half your plate fruits and
vegetables.
• Switch to fat-free or low-fat (1%)
milk.
• Make at least half your grains whole
grains
Foods to Reduce
• Compare sodium (salt) in foods like
soup, bread and frozen meals, and
choose foods with lower numbers.
• Drink water instead of sugary drinks.
Carbohydrates, and lipids provide our bodies with energy, whereas proteins are
mostly used to provide raw materials for growth. Vitamins, minerals, water and
roughage are needed for the healthy functioning of our bodies.
*Refer to table on the following page for more details.
78
Constituent
Source
Importance
Carbohydrates Potatoes, beans and
Starch
peas, yams, cereals
Honey, fruit, and
candy
Sugars
Carbohydrates which are broken
down by digestion so they can
release energy in cells by
respiration.
Lipids
Red meat, dairy
products, nuts, and
egg yolk
Lipids contain more energy than
carbohydrates (2x). It’s stored in the
skin and around kidneys.
Proteins
Meat, peas and
beans, fish, nuts
Proteins are used for growth and
repair. Muscle is largely protein.
Citrus fruit, cabbage,
kiwi
Healthy gums and skin repair.
Fish liver oil, potato,
egg yolk, skin able to
make it in the sun.
To absorb calcium and deposit
ions to build strong teeth and bone
growth.
Milk and dairy
products, flour
For healthy bones and teeth, for
muscle action and blood clotting.
Liver, red meat,
spinach
For haemoglobin in red blood cells,
needed to carry oxygen.
Vitamins
C (ascorbic
acid)
D (calciferol)
Minerals
Calcium
Iron
Fibre
Fruit, nuts vegetables, Forms bulk in the intestines. This
exercises the gut muscles used
for peristalsis by giving them
something to push against and
prevents constipation. This
lowers risk of bowel cancer. Soluble
fibre reduces absorption of fats,
especially cholesterol.
Water
Drinks, and all food
Water is the solvent in our body. It
is the medium of all chemical
reactions. We are 68% water.
79
A Balanced Diet
A balanced diet includes eating a variety of foods from the seven
food groups in the correct proportions so as to gain energy and
the raw materials needed for growth and tissue repair.
i.e. carbohydrates 5/7th,fats 1/7th, and protein 1/7th
The energy needed by a person depends on three main factors:
A. Gender – males generally need more energy than females as
they have more muscles and tend to be more active.
B. Age – energy consumption increases during our early years of
life to our twenties as we are undergoing growth and
development during this time. It then stabilises during our 30’s60’s and will eventually decrease after our 70’s.
C. Activity Levels/Lifestyle/Occupation – the more
physically active you are, the more energy you will need to
consume. Nutrients are needed to provide your muscles with
energy from respiration.
Recommended daily energy intakes for different people
Type of
person
New born baby
Child 1 year
Child 2-3
Child 5-7
Girl 12-15
Boy 12-15
KJ per day
2000
3000
6000
7500
9500
12000
Type of person
Girl 16-18
Boy 16-18
Office worker
Factory worker
Manual worker
Pregnant woman
KJ per day
12000
15000
11000
12000
15000
10000
80
Nutrition and Energy needs
However, the amount of nutrients/ energy needed by a person is affected by several
factors:
• Age
• Activities
• Sex/Gender
Using the graph below, write two simple rules for how these two factors affect
nutrient energy requirement.
• Age –
• Activity level -
A balance diet is also affected by the gender of the individual. Men have more
muscles than women. Referring to the table below how does this effect their energy
requirements?
• Gender -
81
Malnutrition
A balanced diet is all about eating the right amounts of the right nutrients.
Unfortunately, that balance is not always easy to achieve and malnutrition can
result.
Malnutrition (‘bad feeding’) is when a person’s diet either is deficient or has excess
of need.
Malnutrition can result from:
• Eating too much of all foods. (excess) This can lead to weight gain
and eventually obesity (an obese person’s fat storage is over the healthy
limit).
This is often called overnutrition and is a becoming a health issue in
developing countries as obesity is associated with diabetes, heart
disease, breathing difficulties, and arthritis.
• Eating too little food. This will result in weight loss but if certain nutrients
are not provided can result in a deficiency disease or undernutrition.
A deficiency disease develops when one of the seven food groups
is lacking and can be remedied usually once the food is provided.
(*You studied 4 deficiency diseases)
Undernutrition is a health issue in the developing world, where
drought conditions have led to poor harvests or where people have
left their homes due to civil war.
The two most extreme conditions are kwashiorkor (a lack of
essential amino acids leading to slow mental and physical
development in young children) and marasmus (caused by
starvation where the child is simply not given enough energy foods
and so body tissues waste away).
82
Unit 6: Plant Nutrition
Plants are autotrophic (self-feeding) which means they are able to take
simple substances from their environment and use light energy to build
them up into complex food compounds.
The diagram below gives a quick overview of the simple substances
plants need to build more complex compounds for energy and growth.
Plants are able to use the Sun’s light energy to fuse carbon dioxide and
water to make glucose (sugar) and releasing oxygen in the process of
photosynthesis.
This sugar can be used to provide energy by respiration, or it can be
stored as lipids. However, mineral ions need to be absorbed from the
soil to make proteins, and nucleic acids for growth and repair.
83
Plant Structure
lamina (surface
of the leaf)
Midrib or
vein
enters leaf
via stoma
Vascular
bundle made
of xylem and
phloem
xylem
phloem
spongy
mesophyll cells
lower epidermis
guard cell
▪ The leaf is the main photosynthesising organ of the plant and it is
where sugar is produced.
▪ The roots (with the help of root hair cells) absorb water and mineral
ions which are transported up the plant stem in the xylem vessels to
leaves by transpiration stream. Water is used in photosynthesis and the
mineral ions are used to build large complex substances for growth and
repair.
▪ The phloem delivers these substances (e.g. sucrose, amino acids) to
the rest of plant and is found in the throughout the stem and the root.
84
Leaf Structure
Structure
waxy cuticle
Function
This layer prevents water loss.
upper epidermis These cells contain no chloroplasts so light can easily
pass through as it’s transparent.
palisade
(mesophyll)
cells
Palisade cells are the main photosynthesising cells in
a plant. They contain many chloroplasts filled with
chlorophyll, a green pigment used to capture sunlight.
spongy
(mesophyll)
cells
Irregular shape creates air spaces in the leaf which
allows gaseous exchange and movement of water by
transpiration. They also contain chloroplasts for
photosynthesis.
lower epidermis
Most cells in this layer contain no chloroplasts except
the guard cells.
guard cells
stoma(ta)
Two guard cells surround a pore called a stoma. During
the day, guard cells bend when full of water causing the
stoma to open. At night, they lose water causing them to
deflate and so close the stoma.
Through these holes in the leaf gaseous exchange and
water movement by transpiration occurs.
85
Leaves are the main photosynthesising organ and they are
adapted (well suited) to their function.
❖
Two main purposes of the leaves are to absorb
carbon dioxide and sunlight for
photosynthesis.
Adaptations for CO2 and sunlight absorption:
• Leaves have large laminas. Their flat, broad shape provides a large surface
area for absorption of light and carbon dioxide.
• They are thin and flat to reduce diffusion distances of carbon dioxide and to
allow light to penetrate easily.
• Thin epidermal cells with no chloroplasts allows light to pass through to
palisade cells.
• Air spaces created by spongy mesophyll cells allow diffusion of carbon
dioxide within the leaf.
• The chloroplasts are moveable to maximise available light.
• Many stomata to allow entry of carbon dioxide into leaf.
• The vascular bundle in the midrib provides support for the leaf so that it
maximises its exposure to the sun.
• Leaves are arranged to prevent shading of one another to allow the most light
to be captured by the plant.
86
Photosynthesis
❖ It is the process where plants using chlorophyll in
their leaves are able to absorb the Sun’s light energy
to fuse carbon dioxide (from air) and water (from roots)
(glucose). They also release oxygen as a waste product.
to form sugar
So photosynthesis can be written as a word equation as follows:
carbon dioxide + water
Sunlight
glucose + oxygen
chlorophyll
❖ However, you must also learn the chemical equation.
Sunlight
6CO2 + 6H2O
C6H12O6 + 6O2
Chlorophyll
Chlorophyll converts light energy into chemical energy and so is called an energy
transducer.
The chemical energy is initially incorporated as glucose which can be used for
respiration by the plants’ cells to provide energy or to build new substances.
Glucose can be converted to
▪
▪
▪
▪

starch for storage.
cellulose for building cell walls
sucrose for transport in the phloem cells.
amino acids for protein synthesis with nitrate ions from the soil.
Magnesium ions from soil are needed to build the chlorophyll protein
complex.
N.B This means you must know 4 mineral ions for healthy nutrition.
• Iron and calcium for humans.
• Nitrates and magnesium for plants.
Do you remember
what each is for?
87
Photosynthesis Experiments
How do we know that the following are needed for
photosynthesis to occur?
•
•
•
•
Chlorophyll
Carbon dioxide
Light
Water
We learn this the way all scientists learn things, by conducting
experiments.
❖ The first ever experiment to show that plants were able to convert light energy
into chemical energy was by placing a plant of a known mass on a scale for a
year. This original mass included the pot and the soil it was grown in. The only
nutrient provided was water. Its mass increased so it was deduced that it
must have been gaining energy from the sun.
Next scientists wanted to prove that plants were using sunlight to make
sugar. i.e. photosynthesising.
❖ First, they had to assume that if plants produced a lot of glucose from
photosynthesis, they would have to convert it to starch otherwise too much
water would be drawn into their cells by osmosis.
❖ Also, iodine solution can be used to test for the presence of starch. If it turns
from orange/brown to blue/black then starch is present.
❖ They then had to destarch a plant by simply placing it in a dark cupboard for
at least 24 hours. This forces the plant to use its stored starch for food as it is
unable to photosynthesise.
❖ Finally, they placed their plant in the sunlight and after a
day they removed several leaves to test for starch to see
if glucose was produced using light in the process of
photosynthesis.
88
Testing a leaf for starch
1) Dip a leaf in a boiling water bath for 1 minute
•
This kills the leaf and makes it more permeable
2) Turn off bunsen burner.
• Ethanol is flammable and will
be used next. Goggles must
be worn.
3) Place leaf in a test tube filled with
ethanol and stand in a hot water
bath for 10 minutes.
• The ethanol breaks down cell
and organelle membranes and so releases chlorophyll, which can be
dissolved in alcohol.
4) Remove leaf and rinse in cold water.
• The ethanol makes the leaf brittle and so must be washed away to make
leaf supple so it can be spread out.
5) Spread leaf on white cutting tile and cover with iodine solution.
• If leaf turns blue/black starch is found, but if it remains orange/brown no
starch is present.
N.B. There are several other methods to test for rate (1/time) of
photosynthesis, such as:
• change in mass or height in a given time.
• increase in leaves or surface area in a given time.
• oxygen production in water plants in a given time.
89
Chlorophyll Experiment
❖ A variegated leaf is used. Variegated leaves have both green
(containing chlorophyll) and white (not containing chlorophyll) parts
in its surface. Geraniums are a good example.
1) Detach a variegated leaf from a plant that has been in sunlight.
2) Trace around the leaf onto graph paper, and label your diagram
indicating where green and white parts are found. No shading.
3) Test the leaf for starch and show which parts turned blue/black and
which parts stayed the same.
Example Results
Before
After
white
green
Label the above diagram to show what colour you think they will be
after testing with iodine solution.
90
Carbon Dioxide Experiment
1) Destarch two plants of equal mass, height and with leaves of equal
number and size.
2) Place one potted plant in a polythene (plastic) bag with soda lime
to absorb CO2 from air.
3) Place the other potted plant in a polythene bag with sodium
hydrogen carbonate which releases CO2.
*This will be used as the control to show if there is any differences
between the plant with carbon dioxide and the plant without it.
4) Place both plants in light for several hours.
5) Remove a leaf from each plant and test for starch.
So remember when designing experiments testing the effect of CO2 on
photosynthesis, you can use:
• Sodium hydrogen carbonate to release CO2
• Soda lime or bicarbonate to absorb CO2
91
Light Experiment
1) Destarch a plant.
2) Cut out a simple letter or design on a piece of black card and attach
it to the leaf.
3) Place plant in light for several hours.
4) Remove black card and test leaf for starch.
* Only those parts which received sunlight will have produced starch
and so turn blue/black.
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Water Experiment
1) Take two potted plants of equal size or mass.
2) One plant is provided with water daily, the other is not.
3) After a week’s time, observe plants.
Plant A with water
Plant B with no water
Plant A will still be strong and upright, as its cells are full with water
and are turgid. The water fills the plant cell walls (forming a hydrostatic
skeleton), their cytoplasm and their vacuoles so the whole plant
becomes rigid.
Plant B will be limp and the leaves will have become wilted, as its
cells lose water pressure and become flaccid.
*If left long enough without water, the plant will die.
* This experiment is not on syllabus for photosynthesis
but is useful when thinking about osmosis.
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What mineral ions are needed by the plant?
Water Culture Experiment
1) Set up several plants like diagram.
2) One plant is given all the necessary
nutrients, the others will have all but one
mineral ion removed.
For example, the nutrient solutions may lack
magnesium or nitrate ions.
❖
Magnesium is needed to build the chlorophyll
protein complex so a plant grown without it will
begin producing yellow leaves and have poor
growth due to its inability to photosynthesise.
❖
Nitrate ions are needed to convert glucose to amino acids and so produce
proteins. A plant cannot grow without proteins and so its growth will be
stunted.
Draw the results you would expect to see in the table below.
Plant grown in
complete nutrient
solution.
Plant grown in
Plant grown in
nutrient solution
nutrient solution
lacking magnesium. lacking nitrate ions.
94
Is oxygen released during photosynthesis?
Oxygen Experiment
1) Use a water plant and set up apparatus as shown.
2) Place apparatus in light and collect gas released in an inverted
measuring cylinder to determine volume.
*Use a gas syringe to measure volume if accuracy is important.
3) Use a glowing splint to test the gas collected for the presence of
oxygen. It will relight if oxygen is found.
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Rate of photosynthesis and limiting factors
A limiting factor is a something found in the environment that when in
short supply limits the rate of a process when all other factors are in
excess.
Good examples of processes that can be limited are photosynthesis,
respiration and enzyme reactions.
The rate of photosynthesis is affected or can be limited by these
main factors:
• Carbon dioxide
• Light
• Temperature
Carbon Dioxide
*Globally, it is a constant limiting factor despite time of day or year.
In summer/midday in most parts of the world carbon dioxide is a constant at 0.04%
of atmospheric air.
However, the major limiting factor in winter or dawn/dusk is temperature or light.
The graph show the daily
changes in CO2 one metre
above a plant crop.
Why do you think CO2 drops at
midday?
What process is using it up?
Why do you think levels of CO2
are high at 4am?
96
Carbon dioxide
Experiment 1: To show how increasing carbon dioxide affects the
rate of photosynthesis.
Rate of
photosyn
thesis
A
B
CO2 Concentration
A – shows that as CO2
concentration increases,
so does the rate of
photosynthesis which
tells us it was a limiting
factor.
B – shows that with
increased CO2
concentration, there is no
further increase in the
rate of photosynthesis so
something else must now
be the limiting factor.
Experiment 2: To show the effects of different concentrations of CO2
on the rate of photosynthesis.
Rate of
photosyn
thesis
A – high CO2 concentration.
B – low CO2 concentration.
Time
At B, the rate of photosynthesis
increases to its maximum level.
However, at A it can be seen that
once CO2 was increased, the rate
of photosynthesis increases to a
new maximum rate. This
indicates that although it was a
limiting factor, it is not the only
limiting factor.
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Light
Light conditions depend on several aspects:
▪ Time of day – light tends to be a limiting factor in the morning
and evening but not midday.
▪ Latitude - more light is spread over the equator than the poles.
▪ Season – less light in
autumn/winter; more
light in spring/summer.
▪ Wavelength (colour) –
Red and violet are best,
and green is the worst.
Rate of
photosyn
thesis
A
B
Using the graph, write one
sentence for what is occurring at A
and B and what may be the limiting
factor in each?
A
____________________________
____________________________
____________________________
____
Light intensity
B
____________________________
____________________________
____________________________
____
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Temperature
Temperature can be a limiting factor.
At lower temperatures (low thermal energy), the lower the kinetic energy and so the
rate of reaction slows.
Also, at high temperatures, the kinetic energy becomes so high the chemical
bonds joining molecules together break down. When enzymes break apart they are
said to be denatured and are unable to catalyse reactions.
All chemical reactions inside cells and living things are controlled by enzymes and
so directly limit them.
However, at optimum temperatures the rate of reaction is at its maximum.
Rate of
photosyn
thesis
Both plants and animals use
enzymes to control their
chemical reactions, but animals
are more metabolically active as
they need more energy for
movement.
Human body temperature is 37°C
which is slightly below optimum
temperature for reactions but still
allows reactions to work at
reasonably quick rate.
Temperature (°C)
Plants tend to work best at lower
temperatures and their optimum
temperature tends to be closer to
20-25°C.
99
Stomata Number
Stomata are pores that are usually found on the underside of the leaf that control
gaseous exchange (carbon dioxide in and oxygen out) and water movement by
transpiration.
The effect of stomata is fixed per species of plant, as the number and distribution
on a leaf will always be roughly the same and so affect the rate of photosynthesis
and gaseous exchange in the same way.
However, it can be used when comparing two different species of plant to see if they
photosynthesise at different rates due to different number of stomata.
Stomata are controlled by the two guard cells surrounding them.
Opening
Closing
Open during the day.
Closed at night.
Starch
Glucose
glucose
starch
This lowers the water potential in the
guard cells.
This raises the water potential of the
guard cells.
Water is drawn in by osmosis and the
cells become TURGID.
Water moves out by osmosis and the
cells become FLACCID.
Their guard cells walls are thickest on the
inside and so bend creating the opening.
The guard cells deflate and so cause
the pore to close.
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Greenhouses
Greenhouses are used to control limiting factors so that
optimal growth can be achieved and therefore yield can
be increased.
How are conditions controlled to improve yield (amount of crop produced):
❖
Temperature
• Sunlight heats up the inside of the glasshouse and the glass stops a lot
of this heat from escaping.
• Electric or methane burners* can be used in cold weather. (*methane
burners also release carbon dioxide)
• Ventilator flaps can be opened to cool greenhouses if its gets too hot. Or
to allow exchange of gases.
❖
Light
• The glass lets light in.
• Artificial lighting can be used to grow plants when light gets too low.
• Blinds can be used for shade when light gets too strong and could
damage chlorophyll in the leaves.
❖
Carbon dioxide
• Growers can pump carbon dioxide into greenhouses to
increase rate of photosynthesis.
• Methane burners can used to add carbon dioxide and heat.
❖
Water
• Many greenhouses have automatic watering systems.
• When needed, sprinklers and humidifiers come on.
Due to the expense, normally only cash crops are grown
with a good financial return, such as tomatoes, or spring
flowers.
101
Unit 7: Animal Nutrition
Animal nutrition begins with the process of digestion.
Nutrition: The process of taking in nutrients which are organic substances and
mineral ions, containing raw materials or energy for growth and tissue repair,
absorbing and assimilating them.
Digestion is the process that breaks down large, insoluble molecules into small,
soluble molecules by chemical or mechanical means.
Once the raw materials have been broken down into small, soluble molecules they
can be absorbed into the blood or lymph and finally used for energy or assimilated
into new tissue for growth or repair.
There are five main stages to nutrition:
1) Ingestion – the process of taking food substances into the body through the
mouth.
2) Digestion – the process of breaking large, insoluble molecules into small,
soluble molecules by chemical (i.e. enzymes) or mechanical (i.e. muscle
action) means.
3) Absorption – the process of small, soluble molecules moving into the blood or
lymph from the small intestine.
4) Assimilation – the process of using the small, soluble molecules to produce
energy by respiration or to be used as raw materials for growth and repair.
5) Egestion – the process of removing any undigested materials and waste from
the body through the anus.
102
Here’s a diagram of the human alimentary canal.
1
2
5
As you go through the main stages of nutrition, write the corresponding
number next to the place it occurs.
*The first and last one have been done for you.
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Stages of Nutrition
1) Ingestion – begins by the taking in food in the mouth.
2) Digestion – also begins in the mouth by both mechanical and chemical
means.
Mechanical digestion is carried out by the teeth and chemical digestion is
carried out by saliva (mucus, water, and the enzyme amylase).
Mastication or chewing has two important functions:
• to reduce the sizes of the pieces to be swallowed
• to increase surface area of the food for enzyme action.
Fig. Shows the lateral view of the human teeth and jaws.
Humans have two sets of teeth during their lifetime:
a) Milk teeth –appear around one and last to six years of age.
b) Permanent teeth – replace milk teeth and normally finish growing by age 26.
104
There are four main types of adult
teeth:

Incisors – Four in the front of each jaw.
They are chisel-shaped and have sharp edges.
They are used for cutting and biting.

Canines – Two in each jaw.
They are long and pointed. Their function used
be tearing meat but they are now used for
cutting and biting.
to

Pre-molars – Four at the side of each jaw.
They have flat crowns with two blunt cusps.
They are used for crushing and grinding.

Molars – Six at the back of each jaw.
They are the largest teeth and have four or more cusps in their crown or surface.
They are used for crushing and grinding.
Human teeth represent omnivores, animals that consume both plant and animal
material. Animal dentition or teeth tell scientists a lot about the type of consumer an
animal is.
Look at the examples of a carnivore and herbivore’s teeth.
• Large dagger like incisor and
canine teeth, used for holding
onto prey, as well as
ripping/tearing flesh.
• Large, heavily cusped premolars/
molars for grinding bone. One
pair may be adapted into
carnassial teeth, used for slicing
flesh off bones.
• Chisel-like incisors for cutting or
pulling off vegetation.
• Diastema may be present - a
space to store food due to long
periods of chewing
• Premolars/molars are heavily
ridged large surfaces for grinding
up tough vegetable matter.
Grinding sharpens them.
• Canines are usually absent or
small.
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The structure of the tooth
The tooth is composed of three layers:
Enamel – is the hard outer layer. It is the hardest substance in the body and its
strength comes from the mineral salt calcium.
Dentine – is the middle layer. It is also very hard and resembles bone in
composition.
Pulp cavity – is the inside layer. It contains soft connective tissue, blood
vessels and nerves. The blood vessels supply nutrients such as glucose and
oxygen for respiration. (Teeth are alive.) The nerves allow messages to be sent
to the brain if the tooth is hurting.
*If teeth are not properly cared for then dental carries or decay may
result.
Plaque
If you don’t clean your teeth, a mixture of food, saliva and bacteria collects at
the base of the tooth, near the gums. This deposit is called plaque. The acids
released by the bacteria damage the enamel of the tooth and can lead to gum
disease.
106
Tartar
If plaque is not removed then it hardens and forms tartar. Tartar forms a
solid barrier, so bacteria anaerobically respire the sugary waste left on teeth
producing lactic acid which causes tooth decay.
Care of the teeth
• Do not eat sweets or candies.
• Eat more fibre such as apples and carrots which help to
remove plaque from teeth.
• Drink milk which has calcium for strengthening enamel and
dentine.
• Vitamin D is needed for calcium absorption and Vitamin C for
healthy gums.
• Brush teeth with toothpaste twice daily.
• Use dental floss to clean between teeth.
• Visit a dentist every six months.
N.B. Toothpaste with fluoride helps to strengthen teeth enamel, kills bacteria
and neutralises acid produced by bacteria.
However, people prefer to have the choice of using it rather than having it
added directly to their water supply. The main reasons being:
 Restricts freedom of choice.
 Can cause brown patches (mottling) on teeth.
 Water may taste unpleasant.
 In industrial areas, it may already occur in high levels.
 Calculating dose levels accurately is difficult.
 Health risks such as brittle bones and bone cancer
Tooth Decay
 Food particles become stuck between teeth.
 Bacteria begin to feed on the sugary material.
 These bacteria are anaerobic and so respire sugar without
oxygen producing lactic acid. This acid slowly dissolves away
the tooth enamel.
 A hole or cavity is gradually formed catching even more sugary
foods encouraging even more bacteria to feed and respire.
 Eventually, the hole becomes so large that it reaches the living
part of the tooth – the pulp cavity. If left untreated it can lead to
an abscess which is a painful swelling filled with pus.
107
Chemical Digestion in Mouth
While the food is being chewed it is being mixed with saliva. Saliva is made of
water, mucus and the enzyme amylase and is produced by the salivary
gland.
The water provides the ideal pH for amylase to break down starch into maltose.
The mucus helps to coat the food to be swallowed down the oesophagus
forming the ‘bolus’.
Swallowing (oesophagus)
With the help of the tongue the
partially digested food is rolled
up forming the bolus and is
pushed to the back of the
mouth for swallowing.
The epiglottis closes
preventing food entering the
larynx (air passageways).
The bolus hits the pharynx
which triggers a reflex action
(automatic response) moving it
down the oesophagus by
rhythmic muscular
contractions known as peristalsis.
108
There are two sets of muscles that help with peristalsis.
Before bolus
After bolus
Circular muscles
Contract
Relax
Longitudinal
muscles
Relax
Contract
* These muscles work in opposition to each other and so are a good example
of antagonistic pairing of muscles.
N.B. there is no digestion in the oesophagus only movement to the stomach.
How do we know food is moving by muscular contractions
and not gravity?
• We can eat upside-down or in space
• Vomiting is reverse peristalsis
• Most animal have a horizontal alimentary canal but still
food is pushed through.
2) Digestion: Stomach
Cardiac sphincter
The main function of the stomach is protein digestion.
*The sphincters on either side of the stomach regulate the flow of
food through the stomach. Food may remain in the stomach for
several hours finally leaving as a semi-liquid substance called
chyme.
Pyloric sphincter
There are two means of digestion in the stomach:
A) Mechanical Digestion – the stomach walls contract by peristalsis to
churn/mix the partially digested food with stomach juices.
B) Chemical Digestion – the stomach walls release gastric juice which
contains: hydrochloric acid, pepsin (a protease enzyme), and mucus.
109
• Hydrochloric acid – kills any bacteria that may have entered with food in
the mouth with pH2 and so the optimum pH for protein digestion is acidic.
• Pepsin – a protease enzyme that breaks down large protein molecules
into polypeptides.
• Mucus – this lines the inside of the stomach to prevent the acid from
digesting the stomach
Possible stomach problems:
▪ Ulcers – where mucus lining has been worn away and gastric juice has
eaten a raw patch in the stomach wall.
▪ Heartburn – cardiac sphincter does not close properly and gastric juice
goes into oesophagus causing a burning sensation to the acidic pH. This is
common in pregnancy as alimentary canal is pushed up into woman’s
thoracic cavity to accommodate the fetus.
2) Digestion: Small Intestine
Chyme (partially digested food) enters the duodenum of the small intestine. It is
mixed with bile and pancreatic juice to help neutralise the acid and provide
enzymes to aid with digestion.
• Bile is made in the liver when red blood cells (haemoglobin) are broken
down, then stored in the gall bladder and finally released into the small
intestine through the bile duct. It contains sodium hydrogen carbonate
which neutralises the acid pH and bile salts which emulsify fats so
lipase can work on them.
110
Bile salts emulsify fats into small
fat droplets. Then surround them to
make them semi-soluble so lipase
can act on them.
lipase
Fatty acids
+ glycerol
• Pancreatic juice is made in the pancreas and is released via the
pancreatic duct. It contains sodium hydrogen carbonate to further
neutralise the acid and to help obtain the optimum pH of pH 7-8. It also
contains enzymes for protein, fat and carbohydrate digestion, such as
trypsin, lipase, and amylase.
In the duodenum (top part of the small intestine), large, complex
molecules are broken down into their simpler sub-units.
a.
Proteins
trypsin
Proteases*
Polypeptides
Amino acids
*Proteases are produced by small intestine and protein digestion finishes
in the ileum of the small intestine.
b.
amylase
Carbohydrases*
Polysaccharides
Disaccharides
Monosaccharides
i.e. Starch
i.e. maltose
i.e. glucose
*Carbohydrases such as maltase are produced by the small intestine and
carbohydrate digestion finishes in the ileum.
c.
Lipid * lipase
Fatty acids + glycerol
*Lipids can only have enzymes work on them if they have been emulsified
first. Lipid digestion is completed in the duodenum of the small intestine.
111
Once digestion has been completed, the simple monomers of each food
group are ready to be absorbed.
3) Absorption: Small Intestine: Ileum
Absorption is the movement of small, soluble food molecules and
water (5-10dm3) by diffusion through the wall of the small intestine
into the blood or lymph.
The small intestine is well designed for its job of absorption.
It is long and narrow. This increases the surface area and reduces diffusion
distance for soluble nutrient molecules.
But most importantly they have specialised structures known as villi.
Structure of villi and how they help with absorption:



Single epithelial layer of cells – short diffusion distance.
Many villi – 40/mm2 they increase surface area for diffusion.
Villi have microvilli on each epithelial cell - further increasing the
surface area for diffusion.
112



Closely Associated Capillary Network– amino acids and
monosaccharide are absorbed and quickly removed by blood to
maintain a steep diffusion gradient.
Lacteal – fatty acids and glycerol are absorbed into lymph vessel and
quickly removed to maintain steep diffusion gradient.
Muscle fibres at base of villi – allow villi to wiggle closer to soluble
molecules and so shorten diffusion distance.
*Lipids – travel in the lymph vessel and are used:
▪ To build hormones
▪ Build cell membranes
▪ As energy for muscle tissue.
4) Assimilation: Liver
Assimilation – the process of using the small, soluble molecules to produce
energy by respiration or to be used as raw materials for growth and repair.
The liver is a unique organ
in that it has two blood
vessels that bring nutrient
or oxygen rich blood to it:
▪ hepatic artery
▪ hepatic portal
vein*
*Soluble nutrient
molecules such as amino
acids and glucose are
brought to the liver for
processing.
Glucose –
▪ Respired for energy
▪ Stored as glycogen
▪ Stored as fat for insulation
Amino Acids –
▪ Used to build new proteins
113
▪ Excess are deaminated, removing the amine group of the
amino acids and producing urea to be excreted. The carboxyl
part of the amino acid can be converted into carbohydrates for
energy.
114
5) Egestion
Egestion – the process of removing any undigested materials and
waste from the body through the anus.
What remains of the food now enters the large intestine.
Composition of food residues:
•
•
•
•
•
•
•
•
Water
Cellulose and lignin (plant cell walls)
Epithelial cells
Bacteria
Dead cells
Bile salts
Mucus
Toxic residues
This is now referred to as faeces.
❖
Any useful substances such as water (0.3-0.5dm3) and salt are
absorbed back into the body and the remainder is egested through
the anus.
N.B. Fibre is important part of egestion.
Fibre is largely made up of indigestible plant material and provides the bulk of
faeces. The bulk is used to exercise intestinal walls (peristalsis) and to hold
water in faeces which avoids constipation.
If faeces are not egested regularly, the toxic residues in the faeces can irritate
the delicate lining of the intestines and can lead to bowel cancer.
Additionally, high fibre diets tend to have less sugar and fat and so reduce
obesity and even heart disease.
115
A quick overview of the human alimentary canal.
116
Unit 8: Ecology
Energy flow, energy loss
The Sun is the principal source of
energy input to biological systems.
The Earth receives 2 main types of
energy from the Sun: light (solar)
and heat. Photosynthetic plants
and some bacteria can trap light
energy
and convert it into chemical energy.
Non-cyclical nature of energy flow
Heterotrophic organisms
obtain their energy by
eating plants or animals
that have eaten plants. So
all organisms, directly or
indirectly, get their energy
from the Sun. The energy
is passed from one
organism to another in a
food chain but, unlike
water and elements such
as carbon and nitrogen,
energy does not return
in a cycle. Energy give
out by organisms is lost to
the environment.
117
Energy is lost at each level in the food chain, as in the examples below.
Energy lost through the process of respiration (as heat)
Energy used up for movement (to search for food, find a mate,
escape from
predators…).
Warm-blood animals (birds and mammals) maintain a standard
blood temperature – they lose heat to the environment.
Warm-blood animals lose heat energy in faeces and urine.
Some of the material in the organism being eaten is not used by the
consumer, for example a locust does not eat the roots of maize, and
some of the parts eaten are not digestible.
Even plants do not make use of all the light energy available to them. This
is because some light:
is reflected off shiny leaves
is the wrong wavelength for chlorophyll to trap
passes through the leaves without passing through any chloroplasts
does not fall on the leaves.
On average, about 90% of the energy is lost at each level in a food chain.
This means that in long food chains, very little of the energy entering the
chain through the producer is available to the top carnivore. So there tend
to be small numbers of top carnivores. The food chain below shows how
energy reduces through the chain. It is based on maize obtaining 100 units
of energy.
maize
locust
lizard
snake
100 units
10 units
1 unit
0.1 unit
On shorter food chains, less energy is lost.
118
Try this
Figure below shows the flow of energy through a complete food chain:
119
1. a) Which form of the Sun’s energy is trapped by the producer?
[1 mark]
b) Into which energy form is the Sun’s energy converted when it is
trapped by the producer?
[1 mark]
2. a)The first consumer has received 6000 units of energy. How many
units of energy (X on the figure) have been passed to the second
consumer? [1 mark]
b) How many units of energy (Y on the figure) are lost from the third
consumer to the decomposers.
[1 marks]
3. a) Suggest why the proportion of the energy intake which a producer
loses to the environment (20%) is smaller than that lost to the environment
by a first consumer (30%).
[2 marks]
b) Many countries have difficulty in producing enough food for their
population. How might it help to overcome this problem if humans
were always fed as first consumers, rather than second or third
consumers?
[3 marks]
Answer
1.
2.
3.
120
Food chains
Food chain is a chart showing the flow of energy (food) from
one organism to the next beginning with a producer.
Examples:
mahogany tree
maize
caterpillar
locust
song bird
lizard
hawk
snake
A food chain usually starts with a photosynthetic plant, which
gains its energy from the Sun.
The arrows used to link each organism to the next represent the
direction of energy flow. They always points towards the ‘eater’, and
away from the plant.
The feeding level is known as the trophic level.
121
Plant are producers (they make/produce food for other organisms).
Animals that eat plants are primary consumers (a consumer is an
‘eater’). They are also called carnivore
Examiner’s tips
Make sure you can write a food chain involving 3 consumers, with
the arrows in the correct direction.
Don’t include the Sun (it is not an organism).
Always start with the producer on the left of diagram.
Practice labeling each trophic level in your food chain under
the organisms (producer, primary consumer, etc.).
Don’t waste time drawing plants and animals: this will not get you
any
extra marks.
Common misconceptions
Marks are often lost when students write out food chains and webs
because they draw the arrows the wrong way round or put the chain backto-front (or both). The following example was seen in a recent paper:
jackal sheep grass
This student is suggesting that grass eats sheep and sheep eat jackals!
122
Food webs
Food web is a network of interconnected food chains showing the
energy flow through part of an ecosystem.
These are a more accurate way of showing feeding relationships than
food chains, because most animals have more than one food source.
For
example, in the food webs in figure below, the leopard feeds on baboons
and impala.
The leopard can be placed at 2 different trophic levels:
123
secondary consumer (feeding on imlala)
quaternary or fourth level consumer (feeding on baboons).
Another example of food web.
Food webs are easily unbalanced, especially if one population of
organisms in the web dies or disappears. This may happen for a number
of reasons, including:
over–predation or hunting
disease
pollution
use of pesticides
lack of food (or other resources)
emigration.
For example, in the food web here, if all the baboons were killed by
hunters the leopard would have only impala to eat. So the impala
population would decrease. The scorpion population may increase
because of less predation by baboons, but if there are more scorpions
they will eat more locusts, reducing the locust population, and so on.
124
Try this
Figure below shows a food web:
1. Select appropriate organisms form the food web to complete each
column in the table below.
[4
marks]
Consumer Producer
Carnivore
Herbivore
Organism 1
Organism 2
2. Ladybirds eat aphids. A very large number of ladybirds arrive in the
habita where these organisms live. Predict some of the possible effects
this could have on the organisms in the above food web.
[6 marks]
Answer
a)
b)
125
Food pyramids of numbers, biomass and energy
A food pyramid shows the relative sizes of different
components at the various trophic levels of a food
chain. There are three types of ecological pyramid
we use: numbers, biomass and energy.
In a food pyramid, each trophic level in a food chain is represented by a
horizontal bar, with the width of the bar representing the number of
organisms, the amount of biomass or the amount of energy available
at that level. The base of the pyramid represents the producer; the
second level is the primary consumer; and so non.
1. Pyramids of numbers
A pyramid of numbers shows the relative number of organisms at each
stage of a food chain.
Example 1: clover → snail → thrush → hawk
Clover is a plant and it is the
producer in this food chain. Its bar
goes at the bottom of the pyramid.
Energy is lost to the surroundings as
we go from one level to the next, so
there are fewer organisms at each
level in this food chain. A lot of clover
is needed to support the snail
population. A thrush eats lots of
snails, and a hawk eats lots of
thrushes, so the population of hawks
is very small.
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Other pyramid shapes
Sometimes the pyramid of numbers doesn't look like a pyramid at all. This
could happen if the producer is a large plant such as a tree, or if one of
the animals is very small. Remember, though, that whatever the situation,
the producer still goes at the bottom of the pyramid.
Here are two examples like this:
Example 2: Oak tree → Insects → Woodpecker
An oak tree is very large so many insects can feed on
it.
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Example 3: Grass → Rabbit → Flea
Fleas are very small and lots of them can feed on a
rabbit.
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2. Pyramids of biomass
Sometimes a pyramid of numbers is not the best way to represent a food
chain. In this case a pyramid of biomass (the dry mass of an organism) is
a better diagram to use. It shows the total mass of organisms at each
stage of a food chain.
In general, all producers have a higher biomass than the primary
consumer, so a pyramid will always be produced.
The total energy (and biomass) present at a lower tier of the pyramid, must
be greater than the higher tiers in order to support the energy requirements
of the subsequent organisms.
Pyramid of numbers and pyramid of biomass
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3. Pyramids of energy
Pyramid of energy shows amount of energy trapped
per unit time and area at each stage of a food chain.
A normal-shaped pyramid is always produced because there is a
reduced amount of energy at each successive level.
* Most of information in this post is taken from BBCBitesize
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Food chains and energy efficiency
In term of conversations of energy, there is an increased efficiency in
supplying green plants as human food and a relative inefficiency in
feeding crop plants to animals.
Short food chains are more efficient than long ones in providing energy
to the top consumer. Below are two food chains and energy values for
each level in them. Both food chains have a human being as the top
consumer.
maize → cow →
human unit of energy
100
10
1
maize →
human unit of energy
100
10
Ten times more energy is available to the human in the second food chain
than in the first. In the second food chain, the human is a herbivore
(vegetarian). But eating parts of a cow provide humans with other nutrients,
as well as those we gain energy from – it would be very difficult to
persuade everyone to become vegetarian for the sake of energy efficiency.
Some farmers try to maximize meat production by reducing movement of
their animals (keeping them in pens or cages with a food supply) and
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keeping them warm in winter. This means less stored energy is wasted by
the animals.
Why food chains usually have fewer than 5 trophic levels?
As the energy is passed along the chain, each organism uses some of it. So
the further along the chain you go, the less energy there is. The loose of
energy along the food chain limits the length of it. There rarely more than 5
links in a chain, because there is not enough energy left to supply the next
link. Many food chains only have 3 links.
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Invasive species
An invasive species is a plant or animal that has been introduced to an
ecosystem intentionally or by accident. It is not native to the ecosystem and
this, usually, leads to problems. As it is not native, it is going to disrupt the
food web. One of the main problems is that there are no natural predators
for the species, nothing to keep its numbers down. So, if the new species
finds a source of food and begins to reproduce its population will get out of
control very quickly. This affects all other members of the food web.
Invasive species are a fascinating area of study in biology. Most countries
have problems with at least one. Some of the reasons that they have been
introduced vary from accidental- zebra mussels in the Great Lakes and the
brown tree snake in Guam, to intentional- cane toad and rabbit in Australia.
Look up the four invasive species mentioned above and look up a few
more. Investigate why the species were introduced in the first place and
also what damage they are doing.
Invasive species research.
1. Name of species and countrySpecies sufferingActions being done to control the invasive species2. Name of species and countrySpecies sufferingActions being done to control the invasive species-
3. Name of species and countrySpecies sufferingActions being done to control the invasive species
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Population Size
Population size depends on birth rates, death rates, immigration and
emigration.
Immigration - IN
Emigration - EXIT
The factors influencing birth and death rates are the limiting factors on
population growth. The biggest population that a given area can support is
called its carrying capacity.
The three factors that affect population size are:
• Food Supply
• Disease
• Predation (being eaten)
Growth can be shown using the sigmoid growth curve which is shown
below:
The phases a-e are shown below:
A = Lag phase (population settling in)
B = Exponential growth (Log) phase
C = Population growth slows down
D = Stationary phase (zero growth)
E = Death phase
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Human Population Growth Curves
Globally, the human growth curve is still in the log phase, This is mainly due
to:
• Increased health care:
- reduced mortality (death rate of children).
- less disease.
• More efficient agriculture:
- better food supply.
- better nutrition.
• Decreased predation - substituted to a degree by military conflict.
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