(a) (i) "The length of the small intestine in various animals depends on the food they eat." Justify the statement.

(ii) Discuss the role of the pancreas and bile juice in the digestion of food in human beings.

(iii) How is the small intestine designed to absorb digested food?

OR

(b) (i) State the role of rings of cartilage present in the throat.

(ii) Discuss the role of the ribs and diaphragm when air is taken in during the breathing cycle.

(iii) Why do we get muscle cramps during heavy exercise? Explain.

(a)(i) Herbivores need a longer small intestine because plant cellulose is hard to digest and needs more time and surface area for breakdown; carnivores like tigers have a shorter small intestine because meat is comparatively easy to digest.

(a)(ii) The pancreas secretes pancreatic juice containing trypsin (digests proteins) and lipase (breaks down emulsified fats); bile juice from the liver makes the acidic food from the stomach alkaline for pancreatic enzymes to act, and emulsifies fats into smaller globules to increase the efficiency of enzyme action.

(a)(iii) The small intestine is very long and its inner lining has numerous finger-like villi, richly supplied with blood vessels, that greatly increase the surface area for the absorption of digested food into the blood.

OR

(b)(i) Rings of cartilage in the throat ensure that the air passage does not collapse, keeping it open for the smooth passage of air.

(b)(ii) During inhalation, the ribs are lifted and the diaphragm flattens, enlarging the chest cavity; this sucks air into the lungs and fills the expanded alveoli. During exhalation, the ribs and diaphragm return to their original positions, shrinking the chest cavity and pushing air out.

(b)(iii) During heavy exercise, the oxygen supply to muscle cells becomes insufficient for aerobic respiration, so cells switch to anaerobic breakdown of pyruvate into lactic acid; this build-up of lactic acid in the muscles causes cramps.