Biology A2: RESPONSE

In humans, when the stomach starts to become full of food, receptors in the wall of the stomach are stimulated. This leads to negative feedback on the desire to eat. Suggest why this negative feedback is important. /3

1. (Negative feedback) stops desire / wish to eat / appetite; 2. (This) limits amount eaten / stops eating; 3. Prevents / reduces risk of obesity / too much energy intake

In this investigation, the higher the concentration of sucrose in a rat's mouth, the higher the frequency of nerve impulses from each taste receptor to the brain. If rats are given very high concentrations of sucrose solution to drink, the refractory period makes it impossible for information about the differences in concentration to reach the brain. Explain why. /2

1. (Refractory period) leads to discrete / separate nerve impulses / time when another nerve impulse can't happen; OR (Refractory period) limits number of impulses per second / frequency of nerve impulses; 2. When maximum frequency reached / exceeded, no further increase in information / all (higher) concentrations of sucrose seem the same

Diabetes can damage the nervous system. The response of the rats with diabetes to changes in blood pressure is less pronounced than the response of healthy rats. Use your knowledge of the control of heart rate by the nervous system to suggest an explanation for these results. /4

1. Damage to autonomic (nervous) system in diabetic rats; 2. (Could be) pressure receptors/baroreceptors (in aorta/carotid artery) don't work as well; 3. Damage to medulla OR Change in (number of) impulses to/from medulla; 4. (When pressure drops damage to) sympathetic system, so doesn't speed up heart rate (enough); 5. (When pressure rises damage to) parasympathetic system, so doesn't slow down heart rate (enough);

How can you tell the response is nervous, not hormonal? /2

rapid response short duration