Question

Which of the following is a characteristic of Nostoc?
A. Non- cellulosic cell wall
B. Uniflaggellate zoospore
C. Chlorophyll B
D. Sexual reproduction

Answer 1

Hint: The organism Nostoc belongs to the genus of cyanobacteria or blue-green algae. They are prokaryotic organisms, which are free-living as well as photosynthetic. They obtain energy through photosynthesis.

Complete answer: One of the most distinguishing characters of cyanobacteria (Nostoc) is the presence of mureins in their cell wall, thus having a non- cellulosic cell wall. Murein is peptidoglycan which is composed of proteins, lipids and carotenoids. Apart from this, they have internal membranes, which possess sac-like structure known as thylakoids, it is the site where photosynthesis takes place.

Considering the other options:
Uniflagellate zoospore is an asexual spore consisting of a single flagellum, which is a reproductive unit. But the method of reproduction in cyanobacteria is through fragmentation, which is also a form of asexual reproduction, involving the direct breaking down of the parent body to produce offspring. The photosynthetic pigments present in an organism are chlorophyll A, phycocyanin and phycoerythrin. Chlorophyll B is absent in such organisms and is mainly seen in further higher evolutionary plants. Sexual reproduction is the process of gamete production and is absent in a primitive organism like Nostoc, the method of reproduction is through fragmentation, which is an asexual method.

Hence, the correct answer is Option A.

Note: Cyanobacteria are organisms that are able to fix atmospheric nitrogen, thus, they have a symbiotic relationship with leguminous plants for their existence who can’t absorb the atmospheric nitrogen. They fix atmospheric nitrogen by anaerobic methods with the help of specialized cells known as heterocysts. The most common examples are Anabaena and Azolla.