K.C.S.E Biology Q & A - MODEL 2010PP2QN04

K.C.S.E Biology Q & A - MODEL 2010PP2QN04

The diagram below shows how the iris and pupil of a human eye appear under different conditions..

(a) Name the structures labelled X and Y. 
 X
 Y
(b) (i) State the condition that leads to the change in appearance shown in the diagram labelled B. 
(ii) Describe the changes that lead to the appearance of the iris and pupil as shown in the diagram labelled B. 
(iii) What is the significance of the changes described in (b) (ii) above? 

ANSWERS

(a) X Pupil;
Y Circular muscles; 
(b) (i) Dull/dim light/low light intensity; 
(ii) Circular muscles (in iris) relax; while radial muscles contract; the pupil becomes bigger; allowing more light to enter the eye; 
(iii) Allows one to visualize objects/see under dim light;