Science questions, chapter 3
Coordination and Response
44 marks. Use Practice to check each answer as you go, or Exam to answer everything against the clock first.
Section A: objective questions
12 marksChoose the best answer for each question.
1
What is homeostasis?
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A
Homeostasis is the maintenance of the internal environment (temperature, water, pH, blood pressure) in a balanced and stable condition (textbook p. 72).
2
Which of the following is not part of the internal environment controlled by homeostasis?
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C
Homeostasis controls conditions such as temperature, water content, pH and blood pressure. Height is not kept at a balanced level by homeostasis.
3
Which pair of organs is involved in regulating the water content of the body?
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B
Water regulation involves the excretory and endocrine systems; the organs involved are the kidneys and the brain.
4
Farid played football for two hours on a hot afternoon and sweated a lot. What happens in his body to correct his water content?
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D
Water content falls when we sweat. The brain stimulates a hormone so the kidneys decrease urine production, and we feel thirsty.
5
Diagram 1 shows a section through human skin. Under which condition is the skin most likely to be?
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A
The hair stands erect, which happens when it is cold. Erect hairs trap a layer of air that acts as a heat insulator. In the cold, blood vessels constrict, not dilate.
6
What is the normal human body temperature?
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B
Normal human body temperature is 37 °C. 31 °C is a porcupine and 39 °C is a magpie.
7
How does sweating help to lower body temperature?
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D
Sweat glands produce more sweat on hot days; when the sweat evaporates it cools the skin.
8
On a hot day, a dog lies in the shade with its tongue hanging out. Why does the dog do this?
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C
Dogs have sweat glands only on their soles, so they hang their tongues out so that their temperature decreases.
9
A lizard is placed in a cold surrounding. Which change happens to the lizard?
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A
In a cold surrounding a lizard's body activities, muscles and movements become slower, and its metabolism rate and body temperature decrease.
10
What is the process in which plants lose water as water vapour through the stoma?
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B
Transpiration is the loss of water from the leaves, as water vapour, through the stoma.
11
Diagram 2 shows the stoma of a leaf at two different times, X and Y. Which statement is correct?
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D
In Y the stoma is closed. Guard cells (P) close the stoma (Q) when the temperature is too high, to reduce the water lost through transpiration. X (open) is the normal daytime state for gas exchange.
12
Why is it important for the body to keep its temperature at about 37 °C?
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C
All chemical reactions in cells are controlled by enzymes, which are sensitive to temperature. A constant 37 °C lets them work at their best.
Section B: structured questions
32 marksAnswer all questions. Write your answers in the spaces provided.
13
Diagram 3 shows a section of human skin on a hot day.
[1 mark]
(a)Name structure P.
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Sweat gland
P is the coiled sweat gland at the bottom of the sweat duct.
[1 mark]
(b)Name structure Q.
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Blood vessel
[1 mark]
(c)Name substance R, which comes out onto the skin surface.
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Sweat
[1 mark]
(d)Explain how Q helps the body to lose heat on a hot day.
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- Blood vessels dilate so more blood flows close to the skin, so more heat is lost to the surroundings1
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14
Mei Ling walks out of an air-conditioned room into a very cold, windy night. Her body temperature starts to fall below the normal range.
[1 mark]
(a)Which part of her body detects the fall in body temperature?
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- The brain / the control centre in the brain1
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[2 marks]
(b)State two corrective mechanisms that take place in her skin.
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Any 2 points
- Blood vessels constrict (less blood flows near the skin, so less heat is lost)1
- Hairs stand erect (trap a layer of air as an insulator)1
- Less sweating1
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[1 mark]
(c)Mei Ling starts to shiver. What causes the shivering?
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Skeletal muscles contract and relax actively
Shivering is the skeletal muscles contracting and relaxing actively to produce heat.
15
Diagram 4 shows how the quantity of sweat and urine produced by a person changes with the external temperature.
[1 mark]
(a)What is the quantity of sweat produced at 35 °C?
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- 170 ml1
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[1 mark]
(b)Describe what happens to the quantity of urine as the external temperature increases.
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- The quantity of urine decreases (from 100 ml at 0 °C to 30 ml at 35 °C)1
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[2 marks]
(c)Explain the relationship between the quantity of sweat and the quantity of urine.
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- At higher temperature more sweat is produced to cool the body, so more water is lost through the skin1
- To keep the water content balanced, the kidneys produce less urine (the brain stimulates a hormone to decrease urine production)1
Tick each point you got.
16
A group carried out Experiment 3.2. One student from the group did each activity for 5 minutes and then counted the pulse for one minute. Diagram 5 shows the results.
[1 mark]
(a)State the manipulated variable.
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- Type of activity1
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[1 mark]
(b)Calculate the increase in pulse count from at rest to jogging.
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- 132 − 72 = 60 beats per minute1
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[1 mark]
(c)Is the hypothesis "pulse count will increase when executing heavy tasks" accepted? Give a reason.
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- Accepted — the pulse count is highest after jogging (the heaviest task) and lowest at rest1
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[1 mark]
(d)The student was sweating after jogging. Explain why.
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- Jogging produces heat that raises body temperature, so sweat is produced to cool the body (by evaporation)1
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17
Diagram 6 shows how water moves through a plant. P, Q and R are sections through different parts of the plant.
[1 mark]
(a)Through which part does water vapour leave the plant?
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P
P is a section of the leaf. Water vapour leaves the leaf through the stoma (transpiration).
[1 mark]
(b)State the function of the root hairs shown at R.
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- Absorb water and minerals from the soil1
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[1 mark]
(c)Explain how transpiration at P helps water to move up through Q.
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- Transpiration (loss of water vapour from the leaves) produces a pulling force that draws water up the stem1
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[1 mark]
(d)State one other way transpiration helps the plant on a hot day.
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- Evaporation of water from the leaves cools the plant1
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18
Khairul was given the same quantity of food and drinks each day for three days. His urine was collected and measured. Diagram 7 shows the results.
[1 mark]
(a)Why must the quantity of food and drinks be the same on all three days?
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- It is a constant (fixed) variable, so that the only cause of the change in urine is his activity / it is a fair test1
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[2 marks]
(b)Khairul's friend says he did the most vigorous activity on day one because he produced the most urine. Do you agree? Justify your answer.
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- Disagree — the most vigorous activity was on day two1
- Day two had the least urine (500 ml) because he lost a lot of water as sweat during vigorous activity, so the kidneys produced less urine1
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[1 mark]
(c)Khairul wants to keep warm on a cold night. Is it better to wear a few layers of thin clothing or one layer of thick clothing? Give a reason.
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- A few thin layers — air is trapped between the layers and acts as a heat insulator1
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19
Match each animal with the way it maintains homeostasis.
[1 mark]
(a)Bee
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Closes its spiracles between breathing movements
[1 mark]
(b)Snail
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Looks for humid places
[1 mark]
(c)Cat
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Licks its fur
20
Plan an experiment to test this hypothesis: More urine is produced when we drink a lot of water compared to when we drink less water.
[2 marks]
(a)State the manipulated variable and the responding variable.
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- Manipulated: volume of water drunk1
- Responding: volume of urine produced1
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[1 mark]
(b)State one constant variable.
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Any 1 points
- Time over which urine is collected1
- Same person / same activity level1
- Same surrounding temperature1
- Same food eaten1
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[2 marks]
(c)Describe the procedure. Include how the urine is measured.
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Any 2 points
- On one day drink a small volume of water (e.g. 1 litre); on another day drink a large volume (e.g. 3 litres), keeping food and activity the same1
- Collect all the urine over the same time (e.g. 24 hours) and measure its volume with a measuring cylinder1
- Record the results in a table and compare the two volumes1
Tick each point you got.