1. Explain why it is advantageous for organisms to respond to changes in their environment.
Answer
Increases their chance of survival.
2. Woodlice can be found under leaves where it is cool and dark. When the temperature becomes less favourable, woodlice increase their rate of movement, and this movement is random. What type of behaviour is this ?
Answer
Kinesis, because it is random movement. Rate of movement faster when environment less favourable.
3. How do rods and cones respond to light ?
Answer
They contain pigments, which absorb light and are broken down, resulting in a generator potential.
4. A student had a stroke volume of 72 cm3 and a cardiac output of 5.4 dm3. Calculate the student's heart rate.
Answer
HR = CO ÷ SV = 5.4 ÷ 0.072 = 75
5. Paroxysmal supraventricular tachycardia (PSVT) is where a person experiences periods of rapid heart rate. A doctor may treat this in a patient in an emergency situation by massaging the person's neck, applying slight pressure to the baroreceptors in the carotid artery. Suggest how this might reduce the patient's heart rate.
Answer
Pressure receptors (baroreceptors) detect increased pressure and send more impulses to the cardiac centre in the medulla. The medulla oblongata then causes the heart rate to decrease by sending more impulses to the SAN via the parasympathetic nerve.
6. Stimulating a Pacinian corpuscle leads to the establishment of a generator potential. Explain how.
Answer
Stimulating a Pacinian corpuscle leads to a generator potential because pressure distorts the membrane and opens stretch‑mediated Na+ channels. Sodium ions then enter the axon, depolarising the membrane.
7. The figure below shows the size of the generator potential produced by a Pacinian corpuscle in response to different intensities of a stimulus. Describe the pattern.
Answer
As the stimulus increases in intensity, the size of the generator potential increases rapidly. When the stimulus is about 50% intensity, the generator potential increases at a slower rate.
8. Use your knowledge of the structure of a Pacinian corpuscle to explain how this response occurs.
Answer
The greater the pressure, the more the stretch‑mediated channels open. More sodium ions enter the corpuscle, causing greater depolarisation of the membrane.
9. Explain the advantage of a Pacinian corpuscle showing this pattern of response.
Answer
Allows the body to respond to different intensities of stimulus. Low intensity stimuli may be sub-threshold.
10. Explain why when you enter a dimly lit space, you have difficulty seeing at first. However, after a few minutes you can see much better.
Answer
Cones cannot respond to dim light, so rods are needed. In light, rhodopsin is bleached and takes time to reform. Once rhodopsin has reformed, rods can operate.