survival and response

Question 1

Exercise causes an increase in heart rate.

Describe the role of receptors and of the nervous system in this process. (4)

Answer 1

 1.      Chemoreceptors detect rise in CO2/ fall in pH

2.      Send impulses to medulla;

3.      More impulses to SAN;

4.      By sympathetic nervous system

Question 2

Describe how a heartbeat is initiated and coordinated. (5)

Answer 2

SAN sends wave of electrical impulses across atria causing atrial contraction

Non-conducting tissue prevents immediate contraction of ventricles

AVN delays impulse whilst blood leaves atria

AVN sends wave of electrical impulses down bundle of his

Causing ventricles to contract from base up

Question 3

The heart controls and coordinates the regular contraction of the atria and ventricles.

Describe how. (5)

Answer 3

1.      SAN → AVN → bundle of His / Purkyne fibres;

2.      Impulses (over atria);

3.      Atria contract;

4.      Non-conducting tissue (between atria and ventricles);

5.      Delay (at AVN) ensures atria empty / ventricles fill before ventricles contract;

6.      Ventricles contract from apex upwards;

Question 4

The cardiac cycle is controlled by the sinoatrial node (SAN) and the atrioventricular node (AVN).

Describe how. (5)

Answer 4

1.      SAN initiates heartbeat

2.      (SAN) sends wave of electrical impulses (across atria) causing atrial contraction;

3.      AVN delays (electrical activity / impulses);

4.      (Allowing) atria to empty before ventricles contract

5.      (AVN) sends wave of electrical impulses down Bundle of His

6.      (Causing) ventricles to contract (from base up)

Question 5

Explain how a rise in blood pressure results in a decrease in the rate of heartbeat. (6)

Answer 5

1. baroreceptors in aorta
2. send impulses to medulla
3. impulses via parasympathetic nerves
4. to SAN;
5. decreases impulses from SAN;
6. decreases impulses to AVN

Question 6

A woman takes moderate exercise. Explain what causes her heart rate to increase while she exercises. (6)

Answer 6

Rate of respiration increases

Carbon dioxide concentration increases

Chemoreceptors in aorta

Impulses to medulla

Increased frequency of impulses

Along sympathetic pathway to SAN