This was one of the most unpopular questions. A few candidates were able to correctly
define elimination, excretion and secretion. Majority of the candidates could not
efficiently describe the digestion of boiled fish in the gut of humans. The few
candidates that attempted the diagram of villus did not draw it properly.
The expected answers are:
(a) Definition of terms
- Elimination: Removal of undigested food; from the body of living organisms.
Excretion: Removal of waste products of metabolism; from the cells/tissues
of an organism; may be toxic if retained in the body.
- Secretion: Production and release of substances; useful to the body; by
specialised glands of living organisms.
(b) Digestion of Boiled Fish in the Gut of Humans
Boiled fish is a source of protein; chewed and swallowed into the stomach; digestion
of protein starts from the stomach; stomach secretes gastric juice; containing pepsin,
rennin and hydrochloric acid; pepsin in acidic medium acts on the boiled fish and convert
it to peptides; peptides move into the duodenum / small intestine; into which pancreatic
juice is secreted; undigested protein is acted upon by trypsin in alkaline medium; into
peptides/peptones; erepsin finally acts on peptides/peptones in alkaline medium; and
converts it into amino acids.
(c) Diagram of Villus
Title (TL) - Longitudinal section of villus
Size (Sz)(8 – 10cm long)
Quality (Q)
Clarity of lines (CL)
Neatness of Labels (NL)
Details (D)
Epithelium layer shown (EL)
Conical shape of villus (One cell thick) (CV)
Labels (L)
Epithelium layer, blood capillary, lacteal, lymphatic vessels, goblet cells,
venule, arteriole, Crypt of Lieberkuhn, cells of Paneth, Muscularis mucosa.
