CP 7

Question 1

Describe how you would dissect a locust to ensure that the gas exchange system is clearly visible.
(3)

Answer 1

 {fix / pin} the locust (1)
 cut body open (1)
 submerge under water
tissue must be stained when observing under a microscope

Question 2

BIOLOGICAL EXPLANATION

Answer 2

Locusts have spiracles, trachea and tracheoles for diffusion of oxygen into cells and diffusion of co2 out of cells.

Large locusts that respire a lot have air sacs ({supply / store of / reservoir of} oxygen) and mechanically ventilate by moving their abdomen

Question 3

A student investigated the effect of different gases on the breathing rate of a locust. The student blew exhaled air over a locust in a syringe and recorded its breathing rate. The locust was immediately given pure oxygen and the breathing rate was recorded.
.

The student concluded that carbon dioxide increased the breathing rate of the locust.

Comment on how the limitations of this method affect the validity of this conclusion.
(5)

Answer 3

 need a control with atmospheric air (1)
 exhaled air contains {other gases / oxygen / moisture}
 exhaled air is warmer which could affect breathing rate
 locust should be allowed to recover because {still affected by exhaled air / needs to return to normal} (1)
 only one carbon dioxide concentration tested (1)
 the experiment should be repeated to see if results are {consistent / not anomalous} (1)

Question 4

Explain the role of the following features of the locust gas exchange system.
(a) Spirals of thickened chitin in tracheae

Answer 4

The chitin spirals support the tracheae. They hold the tracheae open if they are squashed
as the insect moves

Question 5

Describe the approaches that were taken to ensure the ethically responsible use of animals in this practical activity

Answer 5

reducing the number of animals used
by working in groups or observing a teacher demonstration

any steps taken to reduce suffering
of animals or prevent them experiencing stress (e.g. humane killing)

This may be based around the three ‘R’s: Replacement, Reduction, and Refinement. Students may also describe steps they took to derive maximum benefit from the use of animals

Question 6

Describe the approaches that were taken to ensure the ethically responsible use of animals in this practical activity

Answer 6

reducing the number of animals used
by working in groups or observing a teacher demonstration

any steps taken to reduce suffering
of animals or prevent them experiencing stress (e.g. humane killing)

This may be based around the three ‘R’s: Replacement, Reduction, and Refinement. Students may also describe steps they took to derive maximum benefit from the use of animals

Question 7

b) Ventilation movements of the abdomen

Answer 7

Ventilation movements actively pump air into the tracheal system and increase the supply
of oxygen to very active tissues.

Expansion of the abdomen increases the volume and
therefore decreases the pressure inside the body so that pressure in the tracheae becomes lower than atmospheric pressure, drawing air in through open spiracles.

Compression of the abdomen decreases the volume and increases the pressure inside the body so that air moves out of the tracheae through open spiracles.

Question 8

Air sacs

Answer 8

Air sacs act as air reservoirs or bellows. They increase the volume of air moved through the respiratory system.

They have flexible walls so that changes in pressure caused by ventilating movements of the abdomen (or the thorax when in flight) inflate and deflate them.

Question 9

EVALUATION POINTS

Answer 9

● Care needs to be taken when removing the exoskeleton to prevent damage to the internal organs
● if dissecting microscope not available then the spiracles and sphincters will not be visible.