Topic 3: Homeostasis

Trace the loop in order: the change, the receptor, the control centre, the effector and the response that reverses the change.

A lesson for this topic

Quick checks: multiple choice

Question 1

Which statement describes an organism's tolerance limits for an environmental factor?

Question 2

Which sequence shows the stimulus-response model in the correct order?

Question 3

During a game of netball, a player's blood carbon dioxide concentration rises. Chemoreceptors in the carotid arteries detect the change and send impulses to the breathing centre in the medulla, which increases the rate and depth of breathing. Which structures are the effectors in this response?

Question 4

What makes a homeostatic response an example of negative feedback?

Question 5

Survival of a small fish species from the southern Coorong after 96 hours at different salinities
Salinity (g L⁻¹)	Fish surviving after 96 hours (%)
10	100
30	100
50	100
70	95
90	60
110	10
130	0

In a laboratory investigation, groups of 20 fish of a small species collected from the southern Coorong were kept at seven salinities for 96 hours. Based on the table, between which salinities does the upper tolerance limit of this species lie?

Question 6

A person's core body temperature rises well above its upper tolerance limit during heat stroke. Which effect at the cellular level is most likely?

Question 7

Which pair correctly matches a receptor with the change it detects?

Question 8

A student in a Mount Gambier school laboratory counted her breathing rate at rest as 14 breaths per minute. After two minutes of step-ups it was 35 breaths per minute. What is the percentage increase in her breathing rate?

Question 9

Survival of two saltmarsh plant species grown for 8 weeks at five soil salinities
Soil salinity (g L⁻¹)	Species X surviving (%)	Species Y surviving (%)
10	100	20
25	95	70
40	60	95
55	5	90
70	0	80

Students grew two saltmarsh plant species in a greenhouse at five soil salinities. On a salt flat near Port Augusta, soil salinity is about 25 g L⁻¹ at the edge and about 70 g L⁻¹ in the centre. Based on the table, which prediction is best supported?

Question 10

Which of these is an example of negative feedback?

Question 11

A student measured the heart rate of water fleas (Daphnia) at five water temperatures. At each temperature she counted the heart rate of 5 different water fleas and calculated the mean. What is the main reason for using several water fleas at each temperature?

Question 12

A diver at Port Noarlunga reef holds her breath underwater for 50 seconds. Which row describes the change her body detects during the breath hold, and the response when she surfaces?

Question 13

Which structures make up the central nervous system?

Question 14

Which type of neuron carries impulses from a receptor to the central nervous system?

Question 15

Which part of a neuron carries nerve impulses away from the cell body?

Question 16

A student in a Barossa café touches a hot kettle and pulls her hand away before she feels any pain. Which pathway does the impulse follow in this reflex?

Question 17

Why is a spinal reflex response faster than a voluntary response to the same stimulus?

Question 18

After pulling her hand from a hot pan, a cook feels the pain a moment later. Which statement explains this?

Question 19

In an Adelaide hospital laboratory, a nerve impulse took 12 milliseconds to travel along a sensory neuron 0.96 m long, from the foot to the spinal cord. What was the speed of the impulse?

Question 20

After an accident, a cyclist can feel a pin touching the sole of his left foot but cannot move the foot away. His brain and the rest of his spinal cord work normally. Which neurons are most likely damaged?

Question 21

Which of these responses is a reflex?

Question 22

Where are interneurons found, and what do they do?

Question 23

How does a nerve impulse pass from one neuron to the next at a synapse?

Question 24

Students in a Mount Gambier school laboratory tested whether listening to music affects reaction time. Each of 10 students caught a falling ruler five times in silence and five times while listening to music, and the distance the ruler fell before it was caught was recorded. Which is a controlled variable in this investigation?

Question 25

Which statement describes a hormone?

Question 26

Insulin reaches almost every cell in the body, but only some cells respond to it. Why?

Question 27

Which statement about how hormones act on target cells is correct?

Question 28

An hour after eating a bowl of pasta, a student's insulin secretion rises. What does the insulin cause?

Question 29

Which cells secrete glucagon when blood glucose is low?

Question 30

In an Adelaide hospital laboratory, a patient's blood glucose was 9.6 mmol L⁻¹ one hour after a meal and 5.4 mmol L⁻¹ two hours later. What was the percentage decrease in blood glucose, to the nearest whole number?

Question 31

Which row correctly describes the main cause of high blood glucose in each type of diabetes mellitus?

Question 32

Blood thyroxine rises above its normal range. Which change follows as a result of negative feedback?

Question 33

A surfer at Victor Harbor sees a large wave about to break on him and releases adrenaline. Which pair of effects does adrenaline cause?

Question 34

Which gland secretes adrenaline?

Question 35

A person with untreated diabetes mellitus has glucose in their urine. Which explanation is correct?

Question 36

Which structure acts as the control centre in the regulation of human body temperature?

Question 37

On a frosty morning in the Adelaide Hills, a walker's core temperature starts to fall below its set point. Which set of responses follows?

Question 38

When a person is hot, the arterioles supplying the skin dilate. How does this cool the body?

Question 39

On a humid day in Darwin, a visitor from Adelaide sweats heavily but stays hot. Why does sweating cool the body less in humid air?

Question 40

ADH is made in the hypothalamus. From which gland is it released into the blood?

Question 41

Which parts of the nephron does ADH act on?

Question 42

Which describes the effect of an increase in ADH secretion?

Question 43

An adult's kidneys form about 180 L of filtrate a day and produce 1.5 L of urine. What percentage of the filtrate is reabsorbed?

Question 44

Which statement correctly compares the nervous and endocrine systems?

Question 45

Several responses help keep body temperature up in cold weather. Which of them is brought about by the endocrine system?

Question 46

In the mid north of South Australia, a pygmy blue-tongue lizard spends the early morning lying in the sun at the entrance of the spider burrow it lives in. Which statement best explains this behaviour?

Question 47

In an investigation of skin temperature, a student found that her digital thermometer read 0.5 °C higher than a calibrated thermometer at every temperature tested. Which statement about her readings is correct?

Question 48

Core temperature, skin temperature and oxygen use of a volunteer who moved into a cold room at 10 minutes
Time (min)	Core temperature (°C)	Skin temperature (°C)	Oxygen use (mL per min)
0	37.0	33	250
10	37.0	33	250
20	36.6	27	330
30	36.7	25	360
40	36.9	24	360
50	37.0	24	360

In a sports science laboratory in Adelaide, a volunteer sat in a warm room and then moved into a cold room at 10 minutes. Oxygen use is a measure of the rate of cellular respiration. Which conclusion is best supported by the table?

Question 49

Reaction times of one student in five trials
Trial	Reaction time (s)
1	0.22
2	0.19
3	0.23
4	0.46
5	0.20

A student's reaction time was measured in five trials. In trial 4 she was distracted by a noise outside the room. Based on the table, what is her mean reaction time once the anomalous result is excluded?

Question 50

A rider's spinal cord is cut completely in the middle of her back. Her knee-jerk reflex still works, but she cannot feel a light touch on her knee. Which explanation is correct?

Question 51

In an Adelaide hospital laboratory, two adults each had a glucose drink after fasting, and their blood glucose was measured every 30 minutes, as shown in the graph. Person Y has diabetes mellitus. Which additional measurement would best show whether person Y has type 1 or type 2 diabetes?

Question 52

Two adults each had a glucose drink after fasting, and their blood glucose was measured every 30 minutes, as shown in the graph. Which statement about person X is supported by the graph?

Question 53

Thyroxine contains iodine. A person whose diet lacks iodine develops an enlarged thyroid gland (a goitre). TSH stimulates the thyroid gland to grow as well as to secrete thyroxine. Which sequence explains the goitre?

Question 54

A tumour in a patient's lung releases ADH into the blood all the time, whatever the patient's water balance. The patient keeps drinking normally. ADH makes the collecting ducts more permeable to water. Which set of results is most likely?

Question 55

Mean urine volume produced in each 30 minutes after drinking 1 L of water or 1 L of salt solution
Time after drinking (min)	After water (mL)	After salt solution (mL)
30	60	50
60	320	60
90	380	70
120	180	60
150	70	55
180	50	50

Two groups of students each drank 1 L of liquid: one group drank water, and the other drank a salt solution with the same solute concentration as blood plasma. Based on the table, which explanation accounts for the difference between 60 and 90 minutes?

Question 56

A loud bang makes a student's heart rate rise within a second, and it stays raised for several minutes. Which statement best explains this pattern?

Question 57

Distance a falling ruler fell before it was caught by 10 students, five catches each in each condition
Condition	Mean distance (cm)	Shortest distance (cm)	Longest distance (cm)
Silence	14.2	11	18
Music	14.6	11	19

Students tested whether listening to music affects reaction time, measured as the distance a falling ruler travels before it is caught. Based on the table, which conclusion is valid?

Question 58

When a blood vessel is damaged, platelets stick to the damaged site and release chemicals that attract more platelets, which release more of the chemicals, until the wound is sealed. Which statement best describes this loop?

Question 59

A tumour of the beta cells in a patient's pancreas releases insulin all the time, whatever the blood glucose. Which results are most likely after an overnight fast?

Question 60

After a head injury, a patient's posterior pituitary gland can no longer release ADH. Which results are most likely?

Question 61

A drug blocks the nerve impulses that make the arterioles in the skin constrict. A person who has taken it sits outside on a cold night in Mount Gambier. Which outcome is most likely?

Question 62

A student with type 1 diabetes injects her usual dose of insulin before lunch, then skips lunch and plays an hour of netball. Which outcome is most likely?

Question 63

Percentage of brine shrimp eggs hatching after 48 hours in four tanks
Tank	Salinity (g L⁻¹)	Water temperature (°C)	Eggs hatched (%)
1	20	22	88
2	40	22	84
3	60	29	41
4	80	29	30

Students put 200 brine shrimp eggs into each of four tanks. Tanks 3 and 4 were on a sunny windowsill and tanks 1 and 2 were on a bench. The students concluded that salinities above 40 g L⁻¹ are beyond the shrimps' tolerance range for hatching. Based on the table, which evaluation of the conclusion is best?

Question 64

Blood calcium is controlled by a feedback loop. When blood calcium falls, cells of the parathyroid glands detect the change and release parathyroid hormone (PTH). PTH causes bone to release calcium into the blood. A patient's parathyroid glands are removed during surgery. Which outcome is most likely?

Question 65

A knee-jerk reflex took 0.035 s from the stimulus to the start of muscle contraction. The impulses travelled 1.6 m in total along the sensory and motor neurons, at 80 m s⁻¹. How much of the 0.035 s was not spent travelling along the neurons?

Question 66

A tumour of the alpha cells in a patient's pancreas releases glucagon all the time, whatever the blood glucose. The patient's beta cells work normally. Which set of results is most likely?

Question 67

Blood glucose and insulin of three adults at 0, 60 and 120 minutes after a glucose drink
Person	Glucose at 0, 60, 120 min (mmol L⁻¹)	Insulin at 0, 60, 120 min (arbitrary units)
P	5.0, 7.2, 5.3	8, 45, 12
Q	7.4, 13.8, 12.1	22, 88, 70
R	7.6, 14.5, 13.9	2, 3, 2

Three adults, P, Q and R, each had a glucose drink after fasting overnight. One has no diabetes, one has type 1 diabetes and one has type 2 diabetes. Based on the table, which row identifies them correctly?

Question 68

A patient's thyroid cells have faulty TSH receptors, so TSH cannot bind to them. Her hypothalamus and pituitary work normally. Which set of results is most likely?

Question 69

A patient's hypothalamus is damaged so it no longer receives impulses from thermoreceptors. Her sweat glands and skin arterioles are undamaged. On a 42 °C day in Port Augusta, which outcome is most likely?

Written questions

Water flea heart rate and temperatureWritten question · 8 marks

A student in a Mount Gambier school laboratory investigated the effect of water temperature on the heart rate of water fleas (Daphnia), which are ectotherms. She placed each water flea in a cavity slide of water at the test temperature, waited two minutes, then counted its heartbeats for 15 seconds under a microscope. She tested five water fleas at each temperature and calculated the mean (table).

Mean heart rate of five water fleas at each water temperature
Water temperature (°C)	Mean heart rate (beats per minute)
10	130
15	168
20	208
25	246
30	275
35	152

(a) Identify the independent variable, the dependent variable and one controlled variable in this investigation. [3]

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(b) Calculate the percentage increase in mean heart rate from 15 °C to 30 °C. [2]

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Two adults and a glucose drinkWritten question · 9 marks

In an Adelaide hospital laboratory, two adults who had fasted overnight each drank a solution containing 75 g of glucose at 0 minutes. Their blood glucose and insulin were measured every 30 minutes (table).

Blood glucose and insulin of two adults after a glucose drink at 0 minutes
Time (min)	Person X glucose (mmol L⁻¹)	Person Y glucose (mmol L⁻¹)	Person X insulin (arbitrary units)	Person Y insulin (arbitrary units)
0	4.9	6.8	7	2
30	8.1	11.9	48	3
60	6.8	15.2	35	3
90	5.6	16.0	18	2
120	5.0	15.1	9	2

(a) Describe how insulin brings person X's blood glucose back towards normal after 30 minutes. [3]

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(b) Identify the type of diabetes person Y most likely has, and give the evidence for it from the table. [2]

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Setting a thyroxine doseWritten question · 6 marks

A woman in Whyalla had her thyroid gland removed because of a tumour. She now takes a thyroxine tablet each morning. Every few months her doctor measures her blood TSH and uses the result to adjust her dose.

(a) Describe how negative feedback normally keeps blood thyroxine within a narrow range. [3]

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(b) Her latest test shows TSH well below the normal range. Explain what this suggests about her dose. [3]

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A hot oven trayWritten question · 6 marks

A boy in a Port Lincoln kitchen touches a hot oven tray. His hand pulls away before he feels any pain, and a moment later his fingers start to hurt.

(a) Describe the pathway of the nerve impulse that pulls his hand away. [3]

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(b) Explain why his hand moves before he feels the pain. [3]

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A marathon on a hot morningWritten question · 9 marks

On a 34 °C morning, a 60 kg runner in an Adelaide marathon lost 2.4 L of water as sweat and drank 0.6 L during the race. Her core temperature rose from 37.0 °C to 38.6 °C and then levelled off. (1 L of water has a mass of 1 kg.)

(a) Calculate her net water loss during the race as a percentage of her body mass. [2]

(b) Describe how the stimulus-response model applies to the rise in her core temperature. [3]

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An artificial pancreasWritten question · 7 marks

Many people with type 1 diabetes in South Australia now wear a small sensor under the skin that measures glucose in the fluid around their cells every five minutes. In a closed-loop system (sometimes called an artificial pancreas), software uses each reading to set how much insulin a pump delivers through a fine tube under the skin, without the person entering each dose. The systems are expensive, and the sensor's readings lag a few minutes behind blood glucose.

(a) Explain how the closed-loop system copies the negative feedback normally provided by the pancreas. [3]

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(b) Evaluate the use of closed-loop systems to manage type 1 diabetes. [4]

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A Coorong plant and salinityWritten question · 5 marks

Students from an Adelaide school collected a salt-tolerant aquatic plant from the southern Coorong. They grew ten plants in tanks at each of seven salinities for four weeks and recorded how many survived and how much their shoots grew (table).

Survival and growth of a Coorong aquatic plant after four weeks at seven salinities
Salinity (g L⁻¹)	Plants alive (out of 10)	Mean shoot growth (mm)
20	10	32
40	10	45
60	10	38
80	9	21
100	6	9
120	2	1
140	0	0

(a) From the table, identify the optimum salinity for growth and the range of salinity in which the upper tolerance limit lies. [2]

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(b) Explain why none of the plants survived at 140 g L⁻¹. [3]

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Before a sprintWritten question · 6 marks

At a school athletics carnival in Murray Bridge, a student waits on the starting line of the 100 m sprint. Within a second of the starter's call her heart is pounding, and her heart rate stays high for several minutes after the race.

(a) Explain how the nervous and endocrine systems work together to prepare her body to sprint. [4]

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(b) State two differences between the way the nervous and endocrine systems carry messages. [2]

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