NATIONAL QUALIFICATIONS CURRICULUM SUPPORT
Chemistry
Unit 3: Chemistry and Life
1. Photosynthesis and respiration
2. The effects of chemicals on the
growth of plants
[ACCESS 3]
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Acknowledgement
Learning and Teaching Scotland gratefully acknowledges this contribution to the National
Qualifications support programme for Chemistry.
© Learning and Teaching Scotland 2009
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2
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
Contents
Student material
4
Summary notes
29
Revision exercises
37
Revision exercise answers
45
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
3
STUDENT MATERIAL
Student material
3.1.1
Respiration
Respiration is the correct scientific term for breathing, something we
all do from the moment we are born until we die.
Respiration is the reaction of glucose, in plants and animals, with
oxygen to produce water and carbon dioxide.
The energy from respiration is used in many ways:
 movement
 heat
 growth.
Animals get energy by respiration.
We use energy even when we are sleeping.
Your teacher will show you two experiments to:
 show that energy is given out when food burns
 find out about the gases in exhaled air.
3 cm 3 of limewater
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
STUDENT MATERIAL
Fill in
(a)
Animals get energy by ___________.
G ______ and ______ react.
(b)
What do you see when exhaled air is blown into limewater?
______________________________________________________
Which gas must be present in exhaled air?
______________________________________________________
(c)
What did you see when you breathed onto a mirror?
______________________________________________________
Which gas must be present in exhaled air?
______________________________________________________
(d)
Water and ______ _______ are produced by respiration.
(e)
Complete the word equation for respiration:
glucose + ______  _____ + carbon _______.
(f)
List three ways in which you use energy.
__________________________________________________
__________________________________________________
__________________________________________________
Now check your answers with
the person beside you. Can you
add anything else?
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
5
STUDENT MATERIAL
3.1.2
Plants for food
Animals can get glucose by eating food that comes from plants, for
example:



fruit
vegetables
any food made from grain.
If we eat meat, the food for the animal is plant material or comes from
plants.Look at the foods in the display. What plant source does each
food come from?
Fill in the table below.
Food
Plant source
Now check your answers with
the person beside you. Can you
add anything else?
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
STUDENT MATERIAL
3.1.3
Photosynthesis (i)
Photosynthesis is the most important chemical reaction on earth, for
humans and all animals. This reaction gives humans and animals the
oxygen needed for breathing.
Plants make glucose by taking in substances from the environment. This
is called photosynthesis.
Investigating photosynthesis
Your teacher will show you two experiments to find out more about
the reactants in photosynthesis.
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
7
STUDENT MATERIAL
What are the chemicals needed?
Fill in
(a)
1.
Draw a diagram of the stem of the plant at the end of experiment
Use a coloured pen to show how the water has risen up the plant.
(a)
In the experiment the water went straight into the stem of the
plant. In a growing plant, how is the water taken in?
______________________________________________________
(b)
Your teacher will remind you how to write a report.
(c)
The two substances taken in during photosynthesis are:
_________________ and ___________________
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
STUDENT MATERIAL
3.1.4
Photosynthesis (ii)
‘Synthesis’
tells us that new chemicals are made
in the reaction
During photosynthesis, carbon dioxide and water react in plants to
make glucose.
‘Photo’
tells us that that light energy is needed
for the process to take place
Chlorophyll
the chemical that
gives plants their
green colour
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
9
STUDENT MATERIAL
The chlorophyll in the leaves absorbs the light energy for
photosynthesis.
Your teacher will show you two experiments:
 to test that a leaf makes its own food
 to show the effect of light on the growth of plants.
Fill in
(a)
Your teacher will remind you how to write a report for the
experiments.
Draw a coloured diagram of the variegated leaf.
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
STUDENT MATERIAL
3.1.5
Photosynthesis (iii)
During photosynthesis, carbon dioxide and water react in plants to
make glucose.
Oxygen, which is released through the leaves, is produced.
Fill in
1.
Where does the carbon dioxide come from?
______________________________________________________
2.
Where does the water come from?
______________________________________________________
3.
Where does the light come from?
______________________________________________________
4.
What gives the chlorophyll?
______________________________________________________
5.
What do we use the oxygen for?
______________________________________________________
6.
What is the glucose used for?
______________________________________________________
Now check your answers with
the person beside you. Can you
add anything else?
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
11
STUDENT MATERIAL
Your teacher will show you an experiment to identify the gas
produced by photosynthesis.
Water
Photosynthesis is taking place. A gas (oxygen) is produced. The gas is
collected in the test-tube.
Fill in
(a)
The name of the process by which plants make glucose is:
______________________________________________________
(b)
The gas produced relights a glowing splint and is (circle one):
carbon dioxide
oxygen
nitrogen.
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
STUDENT MATERIAL
The test for this gas is (tick one):
Turns lime water milky
Relights a glowing splint
Puts out a glowing splint
Turns lime water clear
(c)
Why did you use a bright light?
______________________________________________________
(d)
Complete the word equation for the process of photosynthesis.
__________ dioxide + water
light
carbohydrate + ____________ + chlorophyll
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
13
STUDENT MATERIAL
3.1.6
Respiration and photosynthesis – a pair of
opposites
Respiration is the reverse of photosynthesis.
Photosynthesis and respiration keep constant amounts of oxygen and
carbon dioxide in the air.
The oxygen used up in respiration is produced by photosynthesis.
The carbon dioxide produced by respiration is used up by photosynthesis.
(a)
Fill in the table
Substances taken in
Photosynthesis
Respiration
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
Substances given out
STUDENT MATERIAL
(b)
Fill in the diagram to show photosynthesis and respiration.
Use the wordbank to help.
+
+
oxygen
carbon dioxide
photosynthesis
respiration
water
glucose
Now check your answers with
the person beside you. Can you
add anything else?
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
15
STUDENT MATERIAL
3.1.7
The greenhouse effect
Most people have heard about the greenhouse effect.
The earth is getting warmer. Carbon dioxide in the atmosphere causes
the greenhouse effect.
Use resources to find out about the greenhouse effect and answer the
questions below.
Fill in
(a)
What gas in the atmosphere causes the greenhouse effect?
______________________________________________________
(b)
How would life on Earth be affected if the greenhouse effect did
not exist?
______________________________________________________
______________________________________________________
(c)
Draw a diagram of how the greenhouse effect works.
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
STUDENT MATERIAL
3.1.8
Increased carbon dioxide levels
Facts
 Carbon dioxide is taken out of the atmosphere by photosynthesis.
 Clearing of forests reduces the carbon dioxide removed in this way.
 Combustion of fuels produces carbon dioxide.
 Increased levels of carbon dioxide in the air may also be due to
increased combustion of fuels.
 An increase in the level of carbon dioxide in the atmosphere could
cause the atmosphere to retain more of the Sun’s energy as heat. This
process is known as global warming.
Use resources to find out about global warming and answer the
following questions.
What I found out ………..
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
17
STUDENT MATERIAL
Fill in
(a)
What does cutting down trees do to the level of carbon dioxide in
the air?
___________________________________________
(b)
What else can increase the levels of carbon dioxide in th e air?
______________________________________________________
(c)
What is global warming?
______________________________________________________
______________________________________________________
What causes global warming?
______________________________________________________
______________________________________________________
How could life on Earth be affected by global warming?
______________________________________________________
______________________________________________________
______________________________________________________
Now check your answers with
the person beside you. Can you
add anything else?
18
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
STUDENT MATERIAL
Section 2: The effects of chemicals on the growth of plants
3.2.1.
Healthy crops
Farmers and gardeners use chemicals to make crops grow well.
 Pesticides – used to control pests; pests
eat the crops.
 Fungicides – prevent diseases caused by
bacteria and fungi; diseases cause poor
growth in plants.
 Herbicides – used to kill weeds; weeds
can stop growth in plants by using up
essential substances in the soil.
Pesticides, fungicides and herbicides are
toxic and so must be used with care.
Natural predators can also be used to safely
control pests.
Look at the labels on the gardens products in the room.
Arrange the garden products into:
 pesticides
 fungicides
 herbicides
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
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STUDENT MATERIAL
Fill in
(a)
Type of chemical
What the chemical does
1.
2.
3.
4.
5.
6.
(b)
Garden product
1.
2.
3.
4.
5.
6.
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
‘Active’ chemical
Stops
STUDENT MATERIAL
(c)
List three pests that can be controlled by pesticides.
1.
______________
2.
______________
3.
______________
(d)
Circle or draw the hazard symbol found on a bottle of pesticide.
(e)
What are natural predators?
___________________________________
___________________________________
___________________________________
___________________________________
How can they be used to control pests?
___________________________________
___________________________________
___________________________________
Now check your answers with
the person beside you. Can you
add anything else?
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
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STUDENT MATERIAL
3.2.2
Essential elements for plant growth
Potassium
Phosphorus
Nitrogen
These elements are taken in from the soil through the roots of plants.
The elements are taken in as compounds in solution.
Your teacher will show you how to find out about the effect of different
elements on plant growth.
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
STUDENT MATERIAL
Fill in
(a)
Give the three elements needed for healthy plant growth.
1.
__________________________________________________
2.
__________________________________________________
3.
__________________________________________________
How are they taken in by plants?
______________________________________________________
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
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STUDENT MATERIAL
3.2.3
Fertilisers
Crops need nitrogen, phosphorous and potassium for healthy growth.
These are taken from the soil during plant growth.
Fertilisers – added to the soil to restore the essential elements.
Natural fertilisers – produced from the breakdown of plant and animal
remains, eg compost, manure.
Artificial fertilisers – made by the chemical industry.
Increased demand for food has resulted in the use of artificial
fertilisers.
Major artificial fertilisers are:




24
ammonium
nitrate
phosphate
potassium
compounds
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
STUDENT MATERIAL
Look at the names of the compounds in the fertilisers in the display.
Your teacher will show you how to make potassium nitrate.
Fill in
(a)
Fertilisers are added to soil to:
______________________________________________________
______________________________________________________
______________________________________________________
(b)
(c)
What does NPK mean on fertilisers?
N
____________________
P
____________________
K
____________________
How do we get natural fertilisers?
______________________________________________________
______________________________________________________
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
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STUDENT MATERIAL
Give two natural fertilisers.
_______________
(d)
________________
Who makes artificial fertilisers?
______________________________________________________
Give four types of compound found in natural fertilisers.
_________________ _________________
_________________ _________________
(e)
In areas of _______ vegetation, decay of vegetable and ______
remains returns all essential ________ to the ____ .
soil
animal
natural
elements
Now check your answers with
the person beside you. Can you
add anything else?
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
STUDENT MATERIAL
Root nodules
Leguminous plants
A legume is a plant, such as clover, beans
and peas, which can use nitrogen in the air
to make nitrates.
Legumes can fix nitrogen to them since they
have small nodules on their roots which
contain nutrifying bacteria.
The nitrates can be used for plant growth.
Fill in
Give three examples of plants that change nitrogen into nitrates.
______________________________________________________
______________________________________________________
______________________________________________________
(b)
Draw the roots of the plants below.
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
27
STUDENT MATERIAL
Nitrate pollution
Using artificial fertilisers has made the levels of nitrate compounds in
some rivers and lochs higher.
High levels of nitrate compounds can leave the water without any life ,
ie no plants or fish.
Use resources to find out about nitrate solutions and the effect they
have on the environment and answer the questions below.
What causes nitrate pollution?
______________________________________________________
Why do farmers use fertilisers?
______________________________________________________
What can be done about the use of nitrates?
______________________________________________________
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
STUDENT MATERIAL
I also found out that ...
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
29
SUMMARY NOTES
Summary notes
You must know the following to help you in the end of unit
assessment.
Section 1: Photosynthesis and respiration
1.
Photosynthesis
Plants make their own foods by taking in substances from the
environment.
Plants use light energy to produce glucose from carbon
dioxide and water in a process called photosynthesis;
oxygen gas is also produced.
Test for oxygen
Oxygen relights a glowing splint.
During photosynthesis carbon dioxide is absorbed through the leaves of
plants.
Water is drawn up through the roots and oxygen gas
is released into the air through the leaves.
The light energy required for photosynthesis is absorbed by the
chlorophyll in the leaves.
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UNIT 2: EVERYDAY CHEMISTRY – SUBSTANCES
© Learning and Teaching Scotland 2009
SUMMARY NOTES
Photosynthesis
light
water
+
carbon dioxide
chlorophyll
carbohydrate
(glucose)
+
oxygen
Influencing factors
The things that affect how well plants can carry out photosynthesis are
the amounts of:




water
carbon dioxide
sunlight
temperature.
The amount of water is affected by how much is taken up through the
roots and how much is lost from the leaves. If less water is available in
the leaf then photosynthesis will occur more slowly.
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
31
SUMMARY NOTES
2.
Respiration
Animals require sources of energy for use in a number of ways,
including warmth and movement.
Animals can obtain energy by the reaction of glucose with oxygen to
produce water and carbon dioxide in a process called respiration.
What is respiration?
Respiration is the reason that we need oxygen.
Respiration is the process of releasing energy from food. You could
think of it as burning the fuel, glucose.
Glucose is the key molecule. It is made by plants in photosynthesis. In
animals, although lots of different molecules are absorbed after
digestion they are usually turned into glucose.
In respiration:
carbohydrate + oxygen  carbon dioxide + water + energy
Animals obtain glucose by eating food from plants.
Respiration is the opposite of photosynthesis.
The processes of
photosynthesis and
respiration maintain
constant amounts of oxygen
and carbon dioxide in the
air.
During the daytime
photosynthesis occurs more
quickly than respiration.
However, during the night
photosynthesis stops and
respiration carries on.
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
SUMMARY NOTES
Respiration and photosynthesis
Look back at the equation for respiration. How does it compare with
the one for photosynthesis?
3.
Greenhouse effect
It seems like everyone blames bad weather on the greenhouse effect.
What is the greenhouse effect?
The greenhouse effect causes the temperature of the Earth to increase.
This happens as less heat is radiated back from the Earth than is
received from the Sun.
The atmosphere becomes clogged up with greenhouse gases such as
carbon dioxide from burning fossil fuels and methane.
This lets the heat from the Sun in but stops some of it from being
radiated back out again.
Carbon dioxide in the atmosphere causes the greenhouse effect.
This is just how the glass on a greenhouse works, making the inside of
the greenhouse become warmer and warmer over time.
What might be the effects?
As the temperature of the Earth increases it is pre dicted that we will see
changes in weather patterns, including drought and flooding.
The Polar ice caps may melt and produce raised sea levels. Low-lying
areas will be flooded, including many major cities.
In the case of the Earth, the warming up has happened very slowly over
decades and centuries. However, the levels of greenhouse gases have
risen sharply recently.
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
33
SUMMARY NOTES
Extensive clearing of forests reduces the
amount of carbon dioxide removed from the
atmosphere by photosynthesis.
However, as we have cut down trees for
farming land, fuel and timber we have
reduced the number of plants that can carry
out photosynthesis. This deforestation results in less carbon dioxide
being cleared from the atmosphere.
At the same time we have burned a huge quantity of fossil fuel in the
last two centuries, ever since the start of the industrial revolution.
All this burning results in even more carbon dioxide being produced.
Levels have risen already and are still increasing – and doing so even
more quickly!
Increased levels of carbon dioxide in the air
may also be due to increased combustion of
fuels.
An increase in the level of carbon dioxide in
the atmosphere could cause the atmosphere
to retain more of the Sun’s energy as heat, a
process known as global warming.
34
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
SUMMARY NOTES
Section 2: The effects of chemicals on the growth of plants
1.
Using chemicals to save plants
The yield of healthy crops can be reduced in the following ways:
 Crops may be eaten by pests, eg insects and slugs.
 Bacteria and fungi can cause plants to become diseased.
 Weeds can stop the growth of plants by using up essential substances
in the soil.
Pesticides are used to control pests.
Fungicides prevent diseases.
Herbicides kill weeds.
Pesticides are toxic and so must be used with care.
Natural predators can also be used to safely control pests.
2.
Fertilisers
Natural fertilisers
Nitrogen, phosphorus and potassium are essential
elements for healthy plant growth.
These elements are taken in through the roots of plants as compound s
that are in solution.
In areas of natural vegetation, the decay of vegetable and animal
remains returns all essential elements to the soil.
Harvesting of crops prevents the natural return of essential elements to
the soil.
Fertilisers are added to the soil to restore essential elements.
Examples of natural fertilisers include compost and manure.
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
35
SUMMARY NOTES
Artificial fertilisers
The increased demand for food has resulted in the use of artificial
fertilisers.
Artificial fertilisers are made by the chemical industry.
To be effective, fertilisers must be soluble in water.
Nitrate pollution
The extensive use of nitrate fertilisers may have increased the levels of
nitrate in rivers and lochs, and the public water supply.
High levels of nitrate compounds can leave the water without any life,
ie no plants or fish.
The presence of large quantities of nitrates can leave the water lifeless.
36
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
REVISION EXERCISES
Revision exercises
Section 1: Photosynthesis and respiration
1.
Photosynthesis
1.
Photosynthesis is the way that plants make their food using energy
from sunlight. What is the word equation for photosynthesis?
2.
The gas produced in photosynthesis is ____________.
3.
The test for this gas is (tick one):
Turns limewater milky
Puts out a glowing splint
Relights a glowing splint
Turns pH paper blue.
4.
The green dye (or pigment) plants use to pick up energy from
sunlight is called (circle one):
chlorine
chlorophyll
chemical
fluorine
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
37
REVISION EXERCISES
5.
Complete the sentences on photosynthesis:
 ______ _______ is absorbed through the ______ of plants
during photosynthesis.
 _____ is drawn up through the roots.
 Oxygen ___ is released into the ___ through the leaves.
 The ___________ in the leaves absorbs the light
______ needed for photosynthesis.
gas
water
carbon dioxide
energy
chlorophyll
leaves
6.
Give four things that affect photosynthesis:
____________ _____________
____________ _____________
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
air
REVISION EXERCISES
2.
Respiration
1.
Respiration is the process of releasing energy from food. What is
the word equation for respiration?
2.
Answer true or false:
 Respiration is the same as photosynthesis.
T/F
 Animals get glucose from plants.
T/F
 Respiration produces carbon dioxide.
T/F
 Photosynthesis produces hydrogen.
T/F
 Respiration and photosynthesis keep a balance of carbon
dioxide and oxygen in the air.
T/F
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
39
REVISION EXERCISES
3.
The greenhouse effect
1.
Fill in the missing words:
 The greenhouse effect is where the temperature of the Earth
_________.
 This happens as ____ ____ is radiated back from the Earth than
is received from the Sun.
 The atmosphere becomes clogged up with greenhouse gases
such as ______ _______ from burning fossil fuels.
 This lets the heat from the ___ in but stops some of it from
going back out again.
 Carbon dioxide in the atmosphere causes the __________
______.
less heat
carbon dioxide
Sun
greenhouse effect
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
increases
REVISION EXERCISES
2.
Answer true or false.
Extensive clearing of forests reduces the amount of carbon dioxide
removed from the atmosphere by photosynthesis.
T/F
In the case of the Earth the warming up has happened quickly.
T/F
The levels of greenhouse gases have risen sharply recently.
T/F
As we have cut down trees for farming land, fuel and timber we
reduce the number of plants that can carry out photosynthesis.
T/F
This deforestation results in more carbon dioxide being put into
the atmosphere.
T/F
We have burned a huge amount of fossil fuels in the last two
centuries, ever since the start of the industrial revolution.
T/F
All this burning results in even more carbon dioxide being lost.
T/F
Increased levels of carbon dioxide in the air may also be due to
increased combustion of fuels.
T/F
Increases in the level of carbon dioxide in the atmosphere could
cause the atmosphere to retain more of the Sun’s energy as heat, a
process known as global warming.
T/F
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
41
REVISION EXERCISES
Section 2: The effects of chemicals on the growth of plants
1.
Using chemicals to save plants
1.
Use the wordbank to fill in the spaces.
Reducing the yield of healthy crops.
 Insects and _____ eat crops.
 Disease in plants is caused by ________ and _____.
 Weeds use up essential __________ in soil.
 Pests can be controlled by using _______ predators.
 Pesticides are _____.
substances
slugs
natural
fungi
bacteria
toxic
2.
Match up the words and definitions with arrows.
pesticides
fungicides
herbicides
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
kill weeds
prevent diseases
control pests
REVISION EXERCISES
2.
Fertilisers
1.
Complete.
These elements are taken in through the roots of plants.
They are essential for healthy plant growth.
Natural fertilisers
2.
Complete using the wordbank.
 Essential ________ are put back into the soil by ___________.
 Harvesting _____ prevents the natural return of essential
elements to the ____.
 Decaying _________ and animal remains put essential elements
back into the soil.
 Two natural fertilisers are _______ and ______.
vegetable
crops
fertilisers
manure
elements
compost
soil
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
43
REVISION EXERCISES
Artificial fertilisers
3.
Use an arrow to finish the sentence…….
As demand for food has gone up so has the use of
artificial
legs
artificial
fertilisers
useless
fertilisers
Shade the correct answer. True or false?
Artificial fertilisers are made by the chemical industry.
True
False
To be effective, fertilisers must not be soluble in water.
True
False
Nitrate pollution
4.
Complete the sentences using the wordbank.
 Artificial fertilisers have made nitrate levels _______.
 Lochs and rivers can be left ___________.
 Water supplies can have high levels of____________.
lifeless
44
high
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
nitrates
REVISION EXERCISE ANSWERS
Revision exercise answers
Section 1: Photosynthesis and respiration
1.
Photosynthesis
1.
Photosynthesis is the way that plants make their food using energy
from sunlight. What is the word equation for photosynthesis?
water + carbon dioxide  glucose + oxygen
2.
The gas produced in photosynthesis is oxygen.
3.
The test for this gas is (tick one):
Turns limewater milky
Puts out a glowing splint
Relights a glowing splint
Turns pH paper blue
4.
The green dye (or pigment) plants use to pick up energy from
sunlight is called (circle one):
chlorine
chlorophyll
chemical
fluorine
45
UNIT 2: EVERYDAY CHEMISTRY – SUBSTANCES
© Learning and Teaching Scotland 2009
REVISION EXERCISE ANSWERS
5.
Complete the sentences on photosynthesis.
 Carbon dioxide is absorbed through the leaves of plants during
photosynthesis.
 Water is drawn up through the roots.
 Oxygen gas is released into the air through the leaves.
 The chlorophyll in the leaves absorbs the light energy needed
for photosynthesis.
6.
Give four things that affect photosynthesis.
water
carbon dioxide
sunlight
temperature
2.
Respiration
1.
Respiration is the process of releasing energy from food. What is
the word equation for respiration?
carbohydrate + oxygen  carbon dioxide + water + energy
2.
46
Answer true or false.
 Respiration is the same as photosynthesis.
F
 Animals get glucose from plants.
T
 Respiration produces carbon dioxide.
T
 Photosynthesis produces hydrogen.
F
 Respiration and photosynthesis keep a balance of carbon
dioxide and oxygen in the air.
T
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
REVISION EXERCISE ANSWERS
3.
The greenhouse effect
1.
Fill in the missing words.
 The greenhouse effect is where the temperature of the Earth
increases.
 This happens as less heat is radiated back from the Earth than
is received from the Sun.
 The atmosphere becomes clogged up with greenhouse gases
such as carbon dioxide from burning fossil fuels.
 This lets the heat from the Sun in but stops some of it from
going back out again.
 Carbon dioxide in the atmosphere causes the greenhouse
effect.
2.
Answer true or false.
Extensive clearing of forests reduces the amount of carbon dioxide
removed from the atmosphere by photosynthesis.
T
In the case of the Earth the warming up has happened quickly.
F
The levels of greenhouse gases have risen sharply recently.
T
As we have cut down trees for farming land, fuel and timber we have
reduced the number of plants that can carry out photosynthesis.
T
This ‘deforestation’ results in more carbon dioxide being put into the
atmosphere.
F
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
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REVISION EXERCISE ANSWERS
We have burned a huge amount of fossil fuels in the last two centuries,
ever since the start of the industrial revolution.
T
All this burning results in even more carbon dioxide being lost.
F
Increased levels of carbon dioxide in the air may also be due to
increased combustion of fuels.
T
Increases in the level of carbon dioxide in the atmosphere could cause
the atmosphere to retain more of the Sun’s energy as heat, a process
known as global warming.
T
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
REVISION EXERCISE ANSWERS
Section 2: The effects of chemicals on the growth of plants
1.
Using chemicals to save plants
1.
Use the wordbank to fill the spaces.
Reducing the yield of healthy crops.
 Insects and slugs eat crops.
 Disease in plants is caused by bacteria and fungi.
 Weeds use up essential substances in soil.
 Pests can be controlled by using natural predators.
 Pesticides are toxic.
2.
Match up the words and definitions with arrows.
pesticides
fungicides
herbicides
kill weeds
prevent diseases
control pests
UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
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REVISION EXERCISE ANSWERS
2.
Fertilisers
1.
Complete.
These elements are taken in through the roots of plants.
Nitrogen
Potassium
Phosphorus
They are essential for healthy plant growth.
Natural fertilisers
2.
Complete using the wordbank.
 Essential elements are put back into the soil by fertilisers.
 Harvesting crops prevents the natural return of essential elements to
the soil.
 Decaying vegetable and animal remains put essential elements back
into the soil.
 Two natural fertilisers are compost and manure.
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UNIT 3: CHEMISTRY AND LIFE
© Learning and Teaching Scotland 2009
REVISION EXERCISE ANSWERS
Artificial fertilisers
3.
Use an arrow to finish the sentence……..
Demand for food has gone up so has the use of
artificial
fertilisers
artificial
legs
useless
fertilisers
Shade the correct answer. True or false?
Artificial fertilisers are made by the chemical industry.
True
False
To be effective, fertilisers must not be soluble in water.
True
False
Nitrate pollution
4.
Complete the sentences using the wordbank.
(a)
Artificial fertilisers have made nitrate levels high.
(b)
Lochs and rivers can be left lifeless.
(c)
Water supplies can have high levels of nitrates.
UNIT 3: CHEMISTRY AND LIFE
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