Question

Diatoms belong to
A) Dinoflagellates
B) Bacillariophyta
C) Pyrrophyta
D) Euglenoids

Answer 1

Diatoms are unicellular, photosynthetic, algae and are present as solitary cells or in colonies, which can take up the shape of ribbons, fans, stars, or, zigzags. The size of individual cells ranges from 2 to 200 micrometers. If sufficient nutrients and sunlight are available, the diatoms can double approximately every 24 hours by asexual multiple fission.

Complete answer:
They are present in every aquatic environment including fresh and marine waters, soils, basically, almost anywhere moist. A characteristic feature of the diatom anatomy is that they are surrounded by a cell wall made up of silica (hydrated silicon dioxide), known as frustule. These frustules have structural coloration due to their photonic nanostructure, and they are described as "jewels of the sea" and "living opals".
Movement occurs passively due to water currents and wind-induced water turbulence. However, the male gametes of centric diatoms have flagella, which helps them for active movement for seeking female gametes.
Both benthic and planktonic forms exist. Diatoms are classified as belonging to the Division Chrysophyta of Class Bacillariophyceae. Hence, the correct option is B, ‘Bacillariophyta’.
Diatomaceous earth, or diatomite, is a group of diatom shells found in the earth's crust. They are soft, silica-containing sedimentary rocks that can easily crumble into a fine powder and usually have a particle size of 10 to 200 μm. Diatomaceous earth is used for a lot of purposes like water filtration, as a mild abrasive, and as a dynamite stabilizer.
Decomposition and decay of diatoms lead to organic and inorganic (in the form of silicates) sediment. The inorganic component can be used as a method for examining past marine environmental conditions by corings of ocean floors or bay muds since the inorganic matter is embedded in the deposition of clays and silts and forms a permanent geological record of such marine strata.
Diatoms, and their shells (frustules) as diatomite or diatomaceous earth, are important industrial resources used for fine polishing and liquid filtration. The complex structure of their microscopic shells has been proposed as a material for nanotechnology.

Hence, the correct option is B, ‘Bacillariophyta’.

Note: Diatoms are present in large numbers and can be well preserved enough to form sediments made almost entirely of diatom frustules (diatomites). These deposits are of economic benefit, they are used in filters, paints, toothpaste, and many other applications.