Question

Algal blooms impart a distinct colour to water due to
A. Their pigments
B. Excretion of coloured substances
C. Formation of coloured chemicals in water facilitated by physiological degradation of algae
D. Absorption of light by algal cell wall

Answer 1

Rapid increase in the population of the algae in freshwater or marine water systems is called algal bloom. When a large population of algae covers the surface of any water body it causes discoloration in the water which is caused by their pigments.

Complete answer:
Algae are of many types of aquatic photosynthetic organisms, both macroscopic, multicellular organisms like seaweed and microscopic, unicellular organisms like cyanobacteria. An example of algal bloom is a kelp forest. Algal blooms are produced due to nutrients like nitrogen or phosphorus from fertilizer runoff which enters into water bodies.
Algal bloom affects the whole ecosystem and results in benign feeding of higher trophic levels, to more harmful effects like blocking the sunlight from reaching to other organisms which result in depletion of oxygen levels in the water bodies and also secrete toxins in the water. The process of production of algae on water bodies along with the oxygen depletion is called eutrophication. Algal bloom sometimes results in the dying of fishes and other organisms in the water bodies. Phytoplanktons also contain accessory pigments that allow them to use different wavelengths of sunlight for their growth and development.

Hence, the correct option is A. Their pigments.

Note: All photosynthetic phytoplankton have chlorophyll as their primary pigment therefore, researchers measure chlorophyll concentration to determine the phytoplankton population in a certain region.