Interactive Science (Second Edition) 2A

Textbook Solutions

Chapter 7 LIVING THINGS AND AIR

Experiment 7.1A p.6-8

Part A

Observation	Test results
Observation	Oxygen	Carbon dioxide
1: colour of gas	colourless	colourless
2: smell of gas	odourless	odourless
3: change of burning splint	burns more brightly	goes out
4: change of glowing splint	relights	goes out
5: colour change of hydrogencarbonate indicator	no observable changes	changes from red to yellow
6: colour change of lime water	no observable changes	changes from colourless to milky

Part B

	Gas X	Gas Y
Test 1 (Using a glowing splint)	Result: (Answer depends on the gas and the test.)	Result: (Answer depends on the gas and test.)
Test 2 (Using hydrogencarbonate indicator / lime water)	Result: (Answer depends on the gas and test.)	Result: (Answer depends on the gas and test.)
The gas is identified as	(Answer depends on the gas in the test tube.)	(Answer depends on the gas in the test tube.)

Experiment 7.1B p.8-9

1. The paper is blue / light blue in colour.

2. (a) (i) blue / light blue

(ii) pink

(b) water

3. (a) The colour of the cobalt chloride paper changes from blue to pink.

(b) water (water vapour)

Experiment 7.1C p.9-11

Part B

	Breathed air	Unbreathed air
Time taken for burning splint to go out (s)	(Answer depends on the size of the gas jar and other conditions in the experiment.)	(Answer depends on the size of the gas jar and other conditions in the experiment.)

(a) less

(b) The splint burns for a longer time in the jar which contains more oxygen. (or other reasonable answers)

Part C

	Breathed air	Unbreathed air
Colour of hydrogencarbonate indicator after shaking	yellow	red

n Breathed air contains more carbon dioxide than unbreathed air.

Experiment 7.1D p.12

	Breathed air	Unbreathed air
Temperature (°C)	(Answer depends on the room temperature during the experiment.)	(Answer depends on the size of the gas jar and other conditions in the experiment.)

n The temperature of breathed air is higher than that of unbreathed air.

Experiment 7.1E p.13

1. (a) small droplets / moisture / a misty appearance

(b) changes from blue to pink

2. Yes, the change occurs more slowly than that in step 1.

n Breathed air contains more water vapour than unbreathed air.

SKILL Development 7.1 p.14

Discussion

1. Ben is correct and Betty is wrong, because both breathed air and unbreathed air contains more oxygen than carbon dioxide, although the oxygen content decreases and the carbon content increases in breathing.

2. Betty’s idea should be ‘breathed air contains more carbon dioxide and less oxygen than unbreathed air’.

Checkpoint 7.1 p.15

1. (a) glowing splint

(b) The glowing splints relights.

(d) The colour of the indicator changes from red to yellow.

(e) lime water

(f) dry cobalt chloride paper

(g) The colour of the paper changes from blue to pink.

2. (a) (i) more

(ii) less

E (iii) less

(iv) lower

(b) (i) less

(ii) more

E (iii) more

(iv) higher

Experiment 7.2A p.16-17

3. (a) warm

(b) heat

4. (a) A layer of mist

(b) (i) changes from blue to pink

(ii) water vapour

5. (a) changes from red to yellow

(b) carbon dioxide

Experiment 7.2B p.18-19

Part A

(a) goes out

(b) (i) liquid fuel

(ii) water

(iii) goes out

Part B

(a) goes out

(b) (i) sinks

(ii) goes out

Part C

(a) does not burn

(b) (i) heat

(ii) not high

nConclusion:

(a) fuel

(b) oxygen

Activity 7.2A p.21

1. oxygen

2. (a) Trees

(b) fuel

3. (a) heat

(b) temperature

Activity 7.2B p.22

Checkpoint 7.2 p.23

1. turning off the gas tap

2. pouring water on it

3. using a fire blanket

Experiment 7.3A p.26-27

3. (Answer depends on experimental conditions.)

7. (a) (Answer depends on experimental conditions.)

(b) (i) increases

(ii) heat

(iii) light

Experiment 7.3B p.29-30

Designing the experiment

Variable to be changed: type of snack

Variable(s) to be kept constant: initial temperature of water, volume of water, type of boiling tube, type of burning spoon

others: position and distance of burning food from the boiling tube of water (or other reasonable answers)

What to compare: increase in water temperature per gram of snack used

The results in the table:

(Answers depend on the snacks used and the experimental conditions.)

The greater the increase in water temperature per gram of snack burnt, the higher the energy content of the snack.

nConclusion:

(Answer depends on the snacks used.)

SKILL Development 7.3B p.31

1. No, Ben’s calculations and analysis are incorrect because the initial temperature is not considered.

2. In fact, C has the highest energy content and B has the lowest energy content.

The calculations are as follows:

Snack	Weight of snack used (g)	Initial water temperature (°C)	Highest water temperature reached in burning (°C)	Increase in water temperature (°C)	Increase in water temperature per gram of snack used (°C)
A	5.0	15	50	50-15=35	35/5.0=7.0
B	4.0	15	42	42-15=27	27/4.0=6.75
C	6.0	15	60	60-15=45	45/6.0=7.5

Activity 7.3 p.31-33

1. kilojoules (kJ) and kilocalories (kcal)

2. (a) 35

(b) 63

(d) 384

(e) 520

(f) 109.8

(g) 250

(h) 314.3

3. instant noodles, cakes, potato chips, sausages

4. when we have to do physical activities for a long time (or other reasonable answers)

5. We may become overweight and have greater risks of suffering from coronary heart disease, high blood pressure, diabetes, strokes, etc. (or other reasonable answers)

Checkpoint 7.3 p.34

1. (a) chemical

(b) respiration

E 2. No, he is wrong because he should compare the amounts of energy provided by the same mass of different foods.

Experiment 7.4A p.36

1. brown

3. (a) dark blue

(b) brown

n (a) brown

(b) dark blue

Experiment 7.4B p.37-38

3 (a) (i) pale green

(ii) green

(b) soft

4 (a) dark blue

(b) starch

Discussion

1. c

2. d

3. b

4. a

Experiment 7.4C p.39

5. (a) The glowing splint relights.

(b) Oxygen is present in the bottle.

Experiment 7.4D p.41-45

Identifying the problem

What are the conditions necessary for photosynthesis to take place?

Making hypotheses

(a) necessary

(b) necessary

Part A

Designing the experiment

Variable to be changed: type of snack

Variable(s) to be kept constant: type of leaf used, light source, amount of light, temperature, presence of carbon dioxide, water supply, others: (any reasonable answers)

What to compare: presence of starch in the leaf

Carrying out the experiment

3. (Drawing depends on the leaf used.)

4. (a) (Drawing depends on the leaf used.)

(b) (i) present

(ii) absent

Drawing a conclusion

Chlorophyll is necessary for photosynthesis to take place.

Part B

Variable to be changed: presence of carbon dioxide

Variable(s) to be kept constant: type of the leaf used, presence of chlorophyll, light source, water supply, temperature, amount of light

What to compare: presence of starch in the leaf

Carrying out the experiment

1. Destarch

2. bright light

3. iodine

(a) Leaf A is brown in colour and leaf B is dark blue in colour.

(b) Starch is absent in leaf A but present in leaf B.

Drawing a conclusion

Carbon dioxide is necessary for photosynthesis to take place.

Part C

Designing the experiment

Variable to be changed: presence of light

Variable(s) to be kept constant: type of the leaf used, presence of chlorophyll, water supply, temperature, presence of carbon dioxide

What to compare: presence of starch in the leaf

2. (labelled drawing of any appropriate set-up with the materials and apparatus provided)

Carrying out the experiment

1. Destarch

2. bright light

3. iodine

(a) The part of the leaf exposed to light is dark blue, and the part not exposed to light is brown.

(b) Starch is present in the part exposed to light but absent in the part not exposed to light.

Drawing a conclusion

Light is necessary for photosynthesis to take place

GLOBAL & CHINA p.45

There are large areas of tropical rainforests in South America and Central Africa. They situate around the equator. The intensity of sunlight is strong and there are long periods with sunshine. Photosynthesis is carried out by plants at high rates for long durations.

Checkpoint 7.4 p.46

(a) chlorophyll

(b) light

(d) carbon dioxide

(e) starch

(f) oxygen

Let’s Think p.47

The characteristics of food chains are:

(a) The first members are green plants. They start the food chain by converting light energy from the sun into chemical energy in food synthesized through photosynthesis.

(b) The second members are animals that feed on green plants.

Experiment 7.5A p.48-50

2. (a) (i) oxygen

(ii) carbon dioxide

(iii) carbon dioxide

(iv) decreases

(v) towards

(b) (i) also

(ii) grasshoppers

3. (a) at night

(b) in the daytime

5. (a) the same as 2(a) on p.48

(b) the same as 2(b) on p.48

6. The grasshopper takes in oxygen and releases carbon dioxide in both bright and dark conditions. The gaseous exchange of the grasshopper is similar / the same day and night.

Experiment 7.5B p.51-52

1. (a) A and C

(b) B and D

Set-up	Colour of hydrogencarbonate indicator
Set-up	at the beginning	after one hour
A	red	purple
B	red	yellow
C	red	red
D	red	red

4. (a) It shows that a green leaf takes in carbon dioxide under a bright condition.

(b) It is a control experiment for set-up A. It shows that the change in set-up A is due to the leaf.

5. (a) It shows that a green leaf releases carbon dioxide under a dark condition.

(b) It is a control experiment for set-up B. It shows that the change in set-up B is due to the leaf.

Conclusion:

(a) carbon dioxide

(b) carbon dioxide

SKILL Development 7.5B p.54

1. No, because there may be a lot of micro-organisms on rotten leaves. The gaseous exchange of the micro-organisms may affect the results of the tests.

2. Use the same set-up without a leaf.

Checkpoint 7.5A p.54

1. (a) yellow

(b) grasshopper

(d) (i) die

(ii) oxygen

2 (a) The indicator changes from red to purple.

(b) The indicator changes from red to yellow.

Checkpoint 7.5B p.56

(a)

E (b) burning fuels in

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