Question

Which one of the following is a characteristic feature of Chrysophytes?
A. They are parasitic forms, which cause diseases in animals
B. They have a protein rich layer, called pellicle
C. They have indestructible wall layers deposited with silica.
D. They are commonly called dinoflagellates.
E. They are saprophytic Protists.

Answer 1

Chrysophytes are golden brown photosynthetic protists, also referred to as protist algae/ Diatoms/ Desmids. They constitute a major portion of the phytoplankton sans support much of marine life.

Complete answer:
They are both aquatic and terrestrial. Some are marine.
- These are microscopic organisms possessing varying colors.
- They are basically unicellular but may form pseudo filament and colonies, lacking 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.
- The cell wall is cellulosic and is impregnated with silica. It results in a transparent siliceous shell, called a frustule. Depending upon the symmetry, diatoms may be pennate type, having bilateral symmetry (e.g., Navicula) and centric types, having radial symmetry (e.g., Melosira).
- The cell wall is made up of two halves; one half overlapping the other (epitheca over hypotheca) resembling a soapbox like configuration.
- Peripheral layer of the cytoplasm (primordial utricle) is enclosed by a cell wall, surrounding a large central vacuole.
- Mode of nutrition is holophytic (photoautotrophic), photosynthetic pigments are chlorophyll a, chlorophyll c, b-carotene, and special carotenoids containing fucoxanthin; xanthophylls like diatoxanthin, diadinoxanthin.

Therefore, the answer is (C) They have an indestructible wall layer deposited with silica.

Note:
They are responsible for almost 50% of the total organic matter synthesized in the biosphere.
- They mainly undergo the asexual mode of reproduction by binary fission.
- They reproduce sexually as well. It varies from isogamy to oogamy. It involves gametic meiosis as diatoms are generally diploid (diplontic life cycle).