Question

Auxospores and hormocysts are formed respectively by
A) Several diatoms and a few Cyanobacteria
B) Several Cyanobacteria and a few diatoms
C) Some Cyanobacteria and many diatoms
D) All Cyanobacteria and all diatoms

Answer 1

Hint:Diatoms are unicellular, eukaryotic microalgae found in moist soil and water bodies. One very distinct feature of diatoms is that its cell wall is made up of hydrated silicon dioxide. Cyanobacteria also are known as blue-green algae are organisms that may be unicellular, filamentous, or be a part of colonies. Just like diatoms, they are found in water bodies and moist soil able to perform photosynthesis.

Complete answer:
● Diatoms reproduce both sexually and asexually.
● During the asexual/ vegetative life cycle, the organism undergoes mitosis.
● The parent cell divides and the two daughter cells formed have one half (theca) of the parental cell wall.
● A new cell wall (theca) is generated for both the daughter cells. Once this is done both the daughter cells separate.
● Asexual reproduction over a period of time greatly reduces the cell size of diatoms.
● At a particular cell size, diatom can no longer reproduce asexually and it undergoes meiotic cell division to produce male and female gametes.
● This initiates sexual reproduction and a zygote is formed.
● The zygote enlarges to form the auxospore. This auxospore restores the diatom’s initial size.
● Cyanobacteria reproduce asexually via fragmentation, the formation of hormogonia, akinetes, and endospores.
● Hormocysts are structures found in certain cyanobacteria that help in reproduction.
Therefore, option A) is correct. Auxospores are formed in diatoms and hormocysts are formed in cyanobacteria.

Note:- Both cyanobacteria and diatoms play a part in nutrient cycling. Both organisms are major sources of oxygen on earth. Cyanobacteria also called blue-green algae, are actually prokaryotes. This is because they lack a membrane-bound nucleus. Companies involved in the production of water filters and construction, etc., have various uses of diatomaceous earth (fossilized diatoms).