Question

The eyes of cats, cows, buffalo and some nocturnal animals shine at night. It is due to the presence of tapetum lucidum between the choroid and retina. This shining is due to the presence of a pigment made of:
A.Cytosine
B.Uracil
C.Guanine
D.Thiamine

Answer 1

Hint: Tapetum Lucidum is a refro receptor which contributes to the superior night vision. Eyeshine is a type of an ability in which the color varies with the angle at which it is seen and the minerals which make up the reflective tapetum-lucidum crystals.

Complete answer:
The Tapetum Lucidum is a layer of tissue in the eye of many vertebrates present behind the retina. It acts as a retro reflector and reflects the incident light back to its original path. Both the reflected and original light mix together which gives the photoreceptor another chance to absorb the light. Thus, produce a brighter image of the object and so, animals are able to see easily in the dark.

The main function of this reflective layer is to increase the light that is available to the photoreceptors in the eyes. They are special neurons in the retina that convert visible light by absorbing photons of light into the signals that can sometimes set the biological processes in the body.
Tapetum Lucidum has its own colour but the eyeshine shows luminous colours that seem to change when seen from different angles. So, its colour depends upon the minerals from which Tapetum Lucidum is made.
The Tapetum Lucidum is found with a, white colour compound guanine present on the epithelium surface which reflects light outward and thereby allows a second chance for its absorption by visual pigments at very low light intensities.

Hence, the correct answer is option (B)

Note: The Human Being lacks this third photoreceptor Tapetum Lucidum. It is only present in the nocturnal animals which enable them to see the lights even at low intensity. When a Tapetum Lucidum is present, in the animals it enhances the eyeball variation which improves night vision in the center of the animal's field of view.