Question

Indole acetic acid is a:
(A) Chemical found in the retina of nocturnal animals
(B) Pesticide
(C) Good fertiliser
(D) Naturally occurring auxin

Answer 1

Hint: A living organism is composed of mainly six elements which include Carbon, Nitrogen, Hydrogen, Oxygen, Phosphorus, and Sulphur. They consist of about 98% of body weight. The atoms of these elements join together via chemical bonds and form molecules of chemical compounds like Sucrose, Glucose, Water, etc.

Complete answer:
Nocturnal animals' retina has a high number of rods containing rhodopsin which improves eyes sensitivity towards low light and hence helps them to have night vision. Pesticides are chemical compounds used to kill pests. Chemically they have various compositions, most common being DDT, Chlordane, Endosulfan, Endrin Aldehyde. A good fertilizer is composed of mainly three elements i.e Nitrogen, Phosphorus, and Potassium.
Chemically, Indole acetic acid consists of an indole ring on which at the ${C_3}$ position, the carboxyl group is attached through a methylene group. Indole acetic acid is synthesized through multiple pathways. Tryptophan acts as a precursor molecule for the synthesis of indole acetic acid in some plants.
Indole acetic acid is the naturally occurring plant hormone known as Auxin present in vascular plants. Auxin is a plant growth regulator that controls many physiological processes such as, cell division and cell enlargement. They cause the growth of the root that's why it's also called a rooting hormone. They have an inhibitory effect on stem growth as they inhibit the growth of axillary buds and this inhibition of growth of axillary buds is called Apical dominance.

So, the correct answer is an option (D).

Note:
Apart from Indole-3-acetic acid, naturally occurring auxins include 4-chloro-indoleacetic acid, indolebutyric acid, and phenylacetic acid. Indolebutyric acid along with acting as auxin also modulates free IAA levels. Indole acetic acid levels can be detected by using actinobacteria by Bano and Musarrat method which involve the use of Salkowski reagent.