PAG 11: Plant + Animal Responses

Question 1

What is the normal heart rate for a human? (1)

Answer 1

60-80 bpm.

Question 2

What is the equation for cardiac output? (1)

Answer 2

Cardiac output = stroke volume × heart rate

Question 3

How does exercise affect heart rate? (6)

Answer 3

1. Exercise requires muscle contraction, which needs ATP from respiration
2. CO₂ is released into the blood
3. CO₂ lowers blood pH
4. Chemoreceptors detect the change and send impulses to the medulla oblongata
5. The medulla sends impulses via the sympathetic nervous system to the SAN
6. Noradrenaline is released, increasing SAN activity, leading to increased heart rate

Question 4

What is the advantage of increasing heart rate during exercise? (1)

Answer 4

Increased blood flow to lungs to remove CO₂ and take in O₂ for delivery to respiring cells.

Question 5

Describe a method to investigate the effect of exercise on heart rate. (5)

Answer 5

1. Measure resting heart rate by counting beats for 15 seconds and multiplying by 4
2. Perform low-intensity exercise for 5 minutes (e.g., stepping on and off a step)
3. Measure heart rate immediately after exercise
4. Repeat with 9 more participants
5. Use a paired Student’s t-test to check if the increase is significant

Question 6

Write a suitable null hypothesis for this investigation. (1)

Answer 6

Exercise has no effect on heart rate.

Question 7

Explain why a paired Student’s t-test was appropriate. (1)

Answer 7

The investigation compared the means of two sets of data from the same individuals (two measurements were taken from the same individual)

Question 8

Suggest what variables should be controlled. (5)

Answer 8

Age of individuals
Gender of individuals

Diet/exercise history/other health issues

Intensity of exercise
Duration of exercise

Question 9

Explain why the number of heartbeats was measured for 15 seconds rather than one minute. (2)

Answer 9

High heart rate makes it difficult to count

So counting for a longer period would increase the chance of error.

Question 10

Why might a reduced heart rate be seen in someone who is very fit? (2)

Answer 10

Increased stroke volume

Increased thickness/strength of heart muscle.

Question 11

Some sprinters take one breath at the start of a race and don’t inhale again until the end of the race. Suggest how sprinters can expend so much energy without needing to carry out aerobic respiration. (2)

Answer 11

Cells are able to tolerate high levels of lactate

Cells have high phosphocreatine stores.

Question 12

What type of animals are Daphnia? (1)

Answer 12

Daphnia are small ectothermic animals.

Question 13

Why does a change in the surrounding medium affect Daphnia rapidly? (1)

Answer 13

Changes in the surrounding medium can result in a rapid physiological response.

Question 14

Why should an appropriate range of temperatures be used when investigating Daphnia? (2)

Answer 14

Freshwater ponds are the natural habitat of Daphnia

An appropriate range of temperatures should be used so as not to cause harm.

Question 15

Describe the method for investigating the effect of temperature on Daphnia heart rate. (10)

Answer 15

1. Support a cavity slide on modelling clay in a Petri dish
2. Use a pipette to transfer a small volume of water into the cavity and then transfer one Daphnia into the dimple on the cavity slide
3. Place the Petri dish on the microscope stage and view the Daphnia with the lowest powered objective lens
4. Use a pipette to add water at the desired temperature to the Petri dish (suitable range: 0°C - 40°C)
5. Allow 10 minutes for the Daphnia to acclimatise (use a thermometer to monitor temperature and adjust as needed)
6. Observe the Daphnia through the light microscope and count the number of heartbeats in 15 seconds using a stopwatch. Multiply by 4 to calculate heart rate in beats per minute
7. Repeat 10 times using the same temperature but a different Daphnia each time
8. Repeat the experiment using the other temperatures
9. Calculate a mean heart rate for each temperature
10. Compare the results by plotting a graph of mean heart rate (beats per minute) against temperature

Question 16

How is electrical activity detected in muscles? (3)

Answer 16

Attach two electrodes to each muscle and a third electrode on an inactive point

Connect electrodes to an amplifier and a computer

Switch off other electrical equipment to reduce noise.

Question 17

What does a straight line on an electromyogram indicate? (1)

Answer 17

The muscle is relaxed

Question 18

What happens when a muscle contracts during electromyography? (1)

Answer 18

Spikes appear in the graph as motor units are activated

Question 19

How does lifting a weight affect the electromyogram trace? (2)

Answer 19

The amplitude of the trace increases

More motor units are activated to contract the muscle

Question 20

Why does muscle fatigue increase the amplitude of the electromyogram trace? (1)

Answer 20

The brain activates more motor units to generate needed force.

Question 21

What is the aim of an investigation into phototropism? (1)

Answer 21

To investigate how shoots respond to light by growing towards it.

Question 22

Describe the method for investigating phototropism in wheat shoots. (5)

Answer 22

1. Take nine wheat shoots and plant them in individual pots in the same type of soil
2. Cover the tips of three shoots with foil caps (Shoot A), leave three without foil (Shoot B), and wrap the bases of three shoots with foil, leaving the tip exposed (Shoot C)
3. Place the shoots under a light source ensuring all roots are the same distance from the light
4. Leave the shoots to grow for two days
5. Record the amount and direction of growth after two days

Question 23

What variables were controlled in the phototropism experiment? (3)

Answer 23

Distance of shoots from the light source

Light intensity

Environmental factors like moisture, temperature, and nutrients.

Question 24

What is the purpose of investigating geotropism? (1)

Answer 24

To study how plant roots grow in response to gravity.

Question 25

Why are the Petri dishes wrapped in foil during the geotropism investigation? (1)

Answer 25

To prevent light from reaching the seeds and ensure only gravity affects growth.

Question 26

Describe the method for investigating geotropism in cress seedlings. (9)

Answer 26

1. Line three Petri dishes with moist cotton wool, ensuring the same volume of water and cotton wool in each dish 2. Space out 10 cress seeds on the surface and press them lightly into the wool 3. Put a lid on each dish and wrap them in foil to block light 4. Place the dishes in a warm environment with constant temperature 5. Set up the dishes at different angles: One dish at a 90-degree angle (upright), One dish at a 45-degree angle (tilted), One dish on a flat, horizontal surface 6. Leave the seeds for 4 days 7. Unwrap each dish and observe the direction of shoot and root growth 8. Record in a table 9. The roots should have grown towards gravity.

Question 27

Describe the method for investigating the role of auxins in apical dominance. (8)

Answer 27

1. Put 30 similar plants (same height, age, and weight) in pots containing the same soil 2. Count and record the number of side shoots growing from the main stem of each plant 3. For 10 plants, remove the tip of the shoot and apply a paste containing auxins to the top of the stem 4. For another 10 plants, remove the tip of the shoot and apply a paste without auxins to the top of the stem 5. Leave the final 10 plants as they are. These are untreated controls for comparison 6. Leave the plants to grow for 6 days, keeping control variables constant 7. After 6 days, count the number of side shoots growing from the main stem of each plant. Record in a table 8. The plants with the auxin paste should prevent extra side shoots from growing.

Question 28

What is the role of sodium hydroxide in a respirometer experiment? (1)

Answer 28

Sodium hydroxide absorbs the carbon dioxide released by the organisms so that the only change in volume is due to the absorption of oxygen.