7
Living things and air
7.1
Gases in the air (Book 2A, p. 3)
A
What is air made up of? (Book 2A, p. 3)
B
Identifying gases in the air (Book 2A, p. 3)

The Earth is surrounded by a layer of air called the (1) ____________________.

Air is a mixture of gases. The table below lists the methods for identifying the gases in the air:
Gas in the air
Method to identify the gas
Nitrogen
No simple test as it is (2) __________________.
Oxygen
It (3) __________________ a glowing splint.
Carbon dioxide
It turns hydrogencarbonate indicator (4) __________________.
It turns (5) __________________ milky.
Water vapour
Dry cobalt chloride paper changes from (6) _______________
to (7) _______________.
Noble gases
No simple test as they are (8) __________________.
Other gases

---
Differences between the composition of unbreathed air and breathed air:

Breathed air contains (9) ______________________ (more / less) oxygen than unbreathed
air.

Breathed air contains (10) ______________________ (more / less) carbon dioxide than
unbreathed air.

The amount of water vapour in breathed air is (11) __________________ (variable /
saturated) while that in unbreathed air is (12) __________________ (variable / saturated).
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Lesson Worksheet 2A
7.2
Air and burning (Book 2A, p. 15)
A
What is burning? (Book 2A, p. 15)

Burning is a (1) __________________ reaction between a fuel and oxygen.

Oxygen supports burning. During burning, the chemical energy stored in the fuel is changed to
(2) __________________ energy and (3) __________________ energy.

The word equation of the process of burning:
fuel + (4) __________________
B

high temperature
(5) _______________________ + water
+ energy (heat and light)
Conditions for burning (Book 2A, p. 18)
The three conditions for burning can be represented by the fire triangle.
(6) __________________
(7) __________________
(8) __________________
C

Putting out a fire (Book 2A, p. 19)
To put out a fire, we can remove the (9) _______________, cut off the (10) _______________
supply, and/or lower the (11) __________________ of the fire.

Carbon dioxide-type (12) ____________________________ put out a fire by releasing carbon
dioxide to displace the oxygen-containing air surrounding the object on fire.
D

Preventing and surviving fire accidents (Book 2A, p. 19)
In case of a fire accident, keep calm, act quickly and protect ourselves from (13) ___________.
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Lesson Worksheet 2A
7.3
How humans obtain energy (Book 2A, p. 26)
A
Obtaining energy from food (Book 2A, p. 26)

Food stores (1) ________________ energy. It is the source of energy for supporting our daily
activities.
B
Amounts of energy in different foods (Book 2A, p. 28)

The (2) ____________________ of food shows the amount of energy provided
Extension
by a certain quantity of the food. It is measured in (3) ________________ (kJ)
or (4) ________________ (kcal).

Taking in more energy than we need may cause health problems.
7.4
How green plants obtain energy (Book 2A, p. 31)
A
Photosynthesis (Book 2A, p. 31)

Green plants can make their own food by (1) ________________________.

Complete the paragraph by referring to the diagram below:
(5) energy
absorbed
by (6)
(4)
(2)
oxygen is released
(3)
Green plants take in (2) ________________________ and (3) __________________ from the
surroundings. The plants then build them into (4) __________________ (in the form of starch)
using (5) __________________ energy absorbed by (6) __________________ inside the
chloroplasts in green plant cells. Oxygen is released as a (7) ____________________.
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Lesson Worksheet 2A

The word equation of photosynthesis:
(8) _____________________
+ water
B

light energy
chlorophyll
(9) _____________________
+ oxygen
Test for the products of photosynthesis (Book 2A, p. 32)
We can carry out the (10) ______________________ to test for the presence of starch in green
leaves. Iodine solution changes from (11) __________________ to (12) __________________
when starch is present.

The purposes of the steps in testing for starch in a green leaf:
Step
1 Boil the leaf in water.
Purpose
Destroy the
boiling
water
(13) _____________________
of the cells.
Remove the chlorophyll from
2 Soak the leaf in
(14) ___________________.
alcohol
hot water
the leaf.
Wash away the alcohol and
3 Wash the leaf in hot water.
(15) _________________ the
hot water
leaf.
Test for the presence of starch.
4 Add iodine solution to the
leaf.
iodine
solution
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Lesson Worksheet 2A

Hydrilla undergoes photosynthesis under light. We can test the gas
produced by the Hydrilla with a (16) _______________________.
It relights when it is put over the mouth of the bottle. This shows
that (17) __________________ is a product of photosynthesis.
C
Hydrilla
Necessary conditions for photosynthesis (Book 2A, p. 36)
Extension
We can carry out the following experiments to find out the necessary conditions for photosynthesis.
Before conducting the experiments, we have to (18) __________________ the plant by putting it in
the dark for at least 24 hours.

To show that chlorophyll is needed for photosynthesis:

Use a potted plant with (19) __________________ leaves
in the experiment.

Put the destartched plant under sunlight.

Carry out the iodine test to test for the presence of starch in the
leaf.

The (20) __________________ part of the leaf becomes
blue-black while the (21) __________________ part remains brown.

Conclusion:
(22) __________________ is needed for photosynthesis.

To show that light is needed for photosynthesis:

Wrap a part of a green leaf on a potted plant with a piece
wrapped in aluminium foil
of aluminium foil.

Put the destartched plant under sunlight.

Test for the presence of starch in the leaf. Only the part
exposed to (23) __________________ turns blue-black
while the part covered with the foil remains (24) __________________.

Conclusion:
(25) __________________ is needed for photosynthesis.
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Lesson Worksheet 2A

To show that carbon dioxide is needed for photosynthesis:

Set up the apparatus as shown. Soda lime absorbs
light
the (26) ________________________ in the air.

Put the destarched plant under sunlight.

Test for the presence of starch in both leaves.
A
B
Only leaf (27) _________ contains starch.

Conclusion:
soda lime
(28) ________________________ is needed for
photosynthesis.
D
Importance of photosynthesis in producing food
Extension
(Book 2A, p. 41)

Green plants convert (29) _______________ energy from the sun to (30) _________________
energy stored in the food produced by photosynthesis.

The feeding relationship among living things can be represented by a (31) ________________.
Green plants are the (32) ___________________ because they make their own food. Animals
obtain food by feeding on plants or other animals. They are the
(33) ___________________.
7.5
Gaseous exchange in animals and plants (Book 2A, p. 43)
A
Respiration (Book 2A, p. 43)

Living cells use (1) __________________ to break down food and release the chemical energy
stored in them. The breaking down of food in cells produces (2) ____________________ and
(3) ____________________. This process is called (4) __________________ (呼吸作用).

The word equation of respiration:
food + (5) ____________
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(6) _______________ + (7) _______________ + energy
-6-
Lesson Worksheet 2A
B
Gaseous exchange in animals (Book 2A, p. 44)
1
The human respiratory system (Book 2A, p. 46)

Major parts of the human respiratory system:
Extension
(12)
(8)
(13)
(9)
(14)
(10)
(15)
(11)
(16)

The lungs are protected by the (17) __________________, which consists of the ribs, the
backbone and the chest bone.

The actions of the (18) __________________ muscles between the ribs and the
(19) __________________ brings about breathing.
Extension
2
Gaseous exchange in the air sac

In humans, gaseous exchange takes place at the surface of the (20) _________________ .
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(Book 2A, p.47)
Lesson Worksheet 2A

Gaseous exchange in the air sac:
carbon dioxide
oxygen
air sac
direction of
blood flow
(21) _________________
surrounding the air sac
Oxygen passes into the capillary and is
carried to body cells for carrying out
(22) _________________.
3
The carbon dioxide produced in respiration
passes into the air sac and leaves the body
when we (23) ____________________.
The breathing mechanism (Book 2A, p.48)
Extension
(a) Breathing in
1a
When we breathe in, the intercostal muscles (24) __________________ and pull the ribs
upwards and outwards.
1b At the same time, the diaphragm (25) ________________ and becomes
(26) __________________.
2
These movements (27) _________________ the volume of the chest cavity and therefore
the gas pressure inside it (28) __________________.
3
When the gas pressure inside the chest cavity becomes (29) __________________ than
the atmospheric pressure, air is drawn into the lungs.
3
1a
backbone
intercostal muscle
lung
rib
2
diaphragm
1b
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Lesson Worksheet 2A
(b) Breathing out
1a When we breathe out, the intercostal muscles (30) __________________, allowing the
ribs to move downwards and inwards.
1b At the same time, the diaphragm (31) __________________ and returns to its
(32) __________________ shape.
2 These movements (33) __________________ the volume of the chest cavity and therefore
the gas pressure inside it (34) __________________.
3 When the gas pressure inside the chest cavity becomes (35) __________________ than
the atmospheric pressure, air is forced out of the lungs.
3
1a
backbone
intercostal muscle
lung
rib
2
diaphragm
1b

The rib cage model
Which part of the respiratory system does each part of the model represent?
represents the
(36) ________________
represents the
(38) ________________
represents the
(37) ________________
represents the
(39) ________________

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demonstrates the situation
of breathing (40) _______
-9-

demonstrates the situation
of breathing (41) _______
Lesson Worksheet 2A

The balloon-bell jar model:
Which part of the respiratory system does each part of the model represent?
represents the
(42) _______________
represent the
(43) _______________
represent the
(44) _______________

C
represents the
(45) _______________

demonstrates the situation
of breathing (46) _______
demonstrates the situation
of breathing (47) _______
Gaseous exchange in plants (Book 2A, p. 54)
The rate of photosynthesis is
Stop taking in (51) ______________
for photosynthesis; respiration continues.
(48) ______________ than the rate of
respiration.
In the daytime
At night
(52) ________________
(49) ______________
(53) ________________
(50) ________________
Key:
net uptake
net release
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Lesson Worksheet 2A
D

The balance of oxygen and carbon dioxide in nature
(Book 2A, p.58)
The diagram below shows how green plants and other living things help keep a balance of
oxygen and carbon dioxide in nature:
oxygen in air
releases (55) ____________
taken up during
(54) _________________
(56) _________________
of green plants
of animals and plants
taken up during
carbon dioxide in air
releases
(57) _________________
Extension

Some gases in the atmosphere (e.g. carbon dioxide) can absorb (58) _____________________
from the sun and keep the Earth warm. This natural phenomenon is called the
(59) ____________________________.

Burning fossil fuels and clearing forests increase the amount of carbon dioxide in the
atmosphere. This enhances the greenhouse effect and causes (60) _______________________.
7.6
Air pollution and smoking
A
Effects of polluted air on our health (Book 2A, p.62)

(Book 2A, p. 62)
Burning fossil fuels gives out large amounts of (1) _________________________.
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Lesson Worksheet 2A

The effects of air pollutants on health:
Air pollutant
Effect on health
Sulphur dioxide,

(2) ___________________ the eyes and throats
nitrogen oxides

Irritate the lungs and causes (3) ___________________
diseases
Carbon particles

Irritate the lungs
Lead particles

Adversely affect the brain functions
Carbon monoxide

Lowers the amount of (4) ___________________ in the blood
and causes dizziness and headaches
Extension

The (5) ______________________________________ (API) ranges from 0 to 500 and is
divided into five levels. The higher the index, the (6) ___________________ the air quality.
B

Effects of smoking on our health (Book 2A, p.66)
Smoking and passive smoking largely increase the risk of developing respiratory diseases,
(7) ___________________ and (8) ___________________.

Match the harmful substances in cigarette smoke with their effects on health:
Harmful substance
Effect on health
I
Nicotine
a
Irritates the eyes, nose and skin
II
Tar
b
Lowers the oxygen content in blood
III
Carbon monoxide
c
Causes addiction
IV
Hydrogen cyanide
d
Stains the teeth and finger nails
e
Causes coughs and other respiratory diseases
f
Increases heart rate and blood pressure
g
Causes headaches and vomiting
h
Causes throat and lung cancer
i
Leads to heart diseases
I:
(9) _______, _______ and _______
II: (10) _______, _______ and _______
III: (11) _______
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IV: (12) _______ and _______
- 12 -
Lesson Worksheet 2A
Answers
7 Living things and air
7.1
1
atmosphere
2
unreactive
3
relights
4
yellow
5
lime water
6
blue
7
pink
8
unreactive
9
less
10
more
11
saturated
12
variable
chemical
2 / 3 heat / light
4
oxygen
5
carbon dioxide
fuel / oxygen / high temperature
9
fuel
10
oxygen
7.2
1
6/7/8
11
temperature
12
fire extinguishers
13
smoke
chemical
2
energy value
3
kilojoules
4
kilocalories
1
photosynthesis
2
carbon dioxide
3
water
4
food
5
light
6
chlorophyll
7
by-product
8
carbon dioxide
9
food (starch)
10
iodine test
11
brown
12
blue-black
13
cell membranes
14
hot alcohol
15
soften
16
glowing splint
17
oxygen
18
destarch
19
variegated
20
green
21
non-green
22
Chlorophyll
23
sunlight
24
brown
25
Light
26
carbon dioxide
27
B
28
Carbon dioxide
29
light
30
chemical
31
food chain
32
producers
33
consumers
7.3
1
7.4
7.5
1
oxygen
2 / 3 carbon dioxide / water
4
respiration
5
oxygen
6 / 7 carbon dioxide / water
8
bronchus
9
bronchiole
10
air sac
11
intercostal muscle
12
nasal cavity
13
trachea
14
lung
15
rib
16
diaphragm
17
rib cage
18
intercostal
19
diaphragm
20
air sacs
21
capillary
22
respiration
23
breathe out
24
contract
25
contracts
26
flattened
27
increase
28
decreases
29
lower
30
relax
31
relaxes
32
dome
33
reduce
34
increases
35
higher
36
rib
37
chest bone
38
backbone
39
intercostal muscles
40
out
41
in
42
trachea
43
bronchi
44
lungs
45
diaphragm
46
in
47
out
48
higher
49
oxygen
50
carbon dioxide
51
carbon dioxide
52
carbon dioxide
53
oxygen
54
photosynthesis
55
oxygen
56
respiration
57
carbon dioxide
58
heat energy
59
greenhouse effect
60
global warming
1
air pollutants
2
Irritate
3
respiratory
4
oxygen
5
Air Pollution Index
6
poorer
7 / 8 lung cancer / heart diseases
9
c, f, i
10
d, e, h
11
7.6
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b
12
a, g
Lesson Worksheet 2A