PAG11: INVESTIGATION INTO THE MEASUREMENT OF PLANT OR ANIMAL RESPONSES

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

60-80 bpm.

What is the equation for cardiac output? (1)

Cardiac output = stroke volume × heart rate

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

60-80 bpm.

What is the equation for cardiac output? (1)

Cardiac output = stroke volume × heart rate

How does exercise affect heart rate? (6)

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.

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

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

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

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

Exercise has no effect on heart rate.

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

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

Suggest what variables should be controlled. (5)

- Age of individuals.

- Gender of individuals.

- Diet/exercise history/other health issues.

- Intensity of exercise.

- Duration of exercise.

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

- High heart rate makes it difficult to count

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

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

- Increased stroke volume.

- Increased thickness/strength of heart muscle.

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)

- Cells are able to tolerate high levels of lactate.

- Cells have high phosphocreatine stores.

What type of animals are Daphnia? (1)

Daphnia are small ectothermic animals.

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

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

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

- Freshwater ponds are the natural habitat of Daphnia

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

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

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.

How is electrical activity detected in muscles? (3)

- 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.

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

The muscle is relaxed

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

Spikes appear in the graph as motor units are activated

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

- The amplitude of the trace increases.

- More motor units are activated to contract the muscle

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

The brain activates more motor units to generate needed force.

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

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

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

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.

Record the amount and direction of growth after two days

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

- Distance of shoots from the light source.

- Light intensity.

- Environmental factors like moisture, temperature, and nutrients.

What is the purpose of investigating geotropism? (1)

To study how plant roots grow in response to gravity.

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

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

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

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.

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

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 to see the effect of the hormone on the plant.

6. Leave the plants to grow for 6 days, keeping control variables constant (e.g., same light intensity, water, temperature).

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.

Describe the method for investigating the role of gibberellins in stem elongation. (6)

1. Plant 40 plants that are of similar age, height, and mass in pots containing the same type of soil.

2. Leave 20 plants to grow, watering them all in the same way and keeping all other conditions the same (negative controls).

3. Leave the other 20 plants to grow in the same conditions, except water them with a dilute solution of gibberellin (100 mg dm⁻³).

4. Let all the plants grow for 28 days.

5. Every 7 days, measure the length of the stem of each plant.

6. Calculate the mean stem length for the plants watered normally and the plants watered with gibberellin. Plot a graph of stem length against time for both groups.

Describe the method for investigating the rate of respiration using a respirometer. (11)

1. Place a coloured liquid with detergent into the manometer tube as the manometer fluid.

2. Connect the apparatus with the taps open.

3. Measure the mass of the small organisms to be used.

4. Place the living organisms in the apparatus and leave the taps open.

5. Place the whole apparatus in a water bath until it is the same temperature as the water (about 10 minutes).

6. Record the starting level of the syringe near the top of the scale.

7. Mark the starting levels of the manometer fluid in the manometer with a marker pen.

8. Close the taps and leave the apparatus in the water bath for a set time period (e.g. 10 mins).

9. Measure the new level of the manometer fluid and calculate the change in level.

10. Push down the syringe barrel to reset the manometer fluid. The change in volume in the syringe (measured by the level change in the syringe plunger) is equal to the volume of oxygen absorbed by the organisms.

11. Calculate the oxygen absorbed per minute per gram of the organism.

Why should the total volume of the glass beads be the same as the total volume of the organisms? (1)

To ensure that any observed changes in volume are due to respiration and not differences in volume.

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

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

Why is the apparatus placed in a water bath before starting the experiment? (2)

- To ensure that the apparatus and organisms are at the same temperature as the water

- Preventing temperature fluctuations that could affect gas volume.