Question

Assertion: Diatom frustules pile up at the bottom of water bodies and form big heaps of diatomite or diatomaceous earth.
Reason: Diatom frustules are resistant to natural degradation.
(a) Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.
(b) Both Assertion and Reason are correct but Reason is not a correct explanation for Assertion
(c) Assertion is correct but Reason is incorrect.
(d) Both Assertion and Reason are incorrect.

Answer 1

Diatoms are photosynthetic protists that are golden brown. Their cellulosic cell wall is impregnated with silica to form a transparent siliceous shell known as pustules. These silica shells of dead diatoms are naturally indestructible and thus get accumulated at the sea bed. Such huge rock-like deposits of hard shells of diatoms constitute diatomaceous earth.

Complete answer:
The diatoms are protists whose cell walls are made up of silica. These silica walls are naturally indestructible.
The diatomite obtained from the dead diatoms is used as filters in brewing industries, sugarcane refineries, in polishes of metals, toothpaste, for making insulating bricks, in the insulation of refrigerators, houses and for making the latter soundproof, in the manufacturing of dynamite, water glass or sodium silicate and strong acids. This is added to paint to increase its night visibility.

Additional Information:
-Diatoms are microscopic organisms possessing various colors. They are unicellular but may form colonies or pseudo filaments.
- These lack flagella except in the reproductive stage. They may be free-floating (phytoplanktonic), remaining afloat on the surface of water due to the presence of lightweight lipids.
-Depending upon the symmetry diatoms are of two types
pennate type (having bilateral symmetry).
centric type (having radial symmetry).
-The cell wall is characteristic, made up of two halves; one half covering the other (epitheca over hypotheca) resembling a soapbox.
-They have chlorophyll a and c which converts the solar energy into chemical energy through photosynthesis.
-They help in carbon fixation i.e.; they use carbon dioxide to form sugar by converting it into the organic carbon. Thus, they release oxygen as a bi-product.
- Since they are phytoplankton, they are responsible for the maintenance of the marine food web.

So, the correct answer is, “Both Assertion and Reason are correct and Reason is the correct explanation for Assertion.”

Note: - Protist algae is the other name for the photosynthetic protist as they do photosynthesis and possess chlorophyll pigment. It constitutes a major part of the phytoplankton.
- Diatoms and desmids together are known as Chrysophytes.
- A whitish powder is obtained from mined diatomaceous earth which is known as diatomite or kieselguhr or diatomaceous earth. The diatomite obtained is rough and gritty.