Question

What is the photosynthetic product in blue-green algae
A. Normal starch
B. Glycogen
C. Cyanophycean starch resembling glycogen
D. None of these

Answer 1

Hint: Cyanobacteria are the most ancient organisms having oxygenic photosynthesis and thus, played a significant role in the evolution of aerobic forms of life.

Complete Answer:
Cyanobacteria is autotrophic Eubacteria. Cyanobacteria make food with the help of oxygen present in water. The characteristics feature of cyanobacteria cell is the presence of a system of photosynthetic pigments present in the thylakoids are chlorophyll a and phycobilins i.e., phycocyanin(blue coloured), phycoerythrin(red coloured) and allophycocyanin(light blue coloured).

The cyanobacteria cell contains reserve food material in the following forms:
1. Cyanophycean granules(Protein).
2. Beta granules (Fat droplets).
3. Cyanophycean or myxophyceae starch or alpha granules (Similar to glycogen but negative to iodine test).
4. Volutin body (Reserve phosphate).
5. Polyhedral body (Rubisco rich).

So the correct answer is Option (C).

Additional Information:
- The cell structure in cyanobacteria is typically prokaryotic. The cell lacks a well-defined nucleus and the chromatin material is centrally located, resembling the bacterial chromosome.
- The cell wall is four-layered and is invariably covered by a mucilaginous sheath, composed largely of muropeptides. Protoplasm is a cyanobacteria cell that can be distinctly divided into two parts: the centroplasm and chromoplasm. The central colourless centroplasm contains the chromatin material. The peripheral protoplasm is coloured or pigmented because of the presence of thylakoids, called chromoplasm.
- The protoplast lacks membrane-bound organelles like endoplasmic reticulum, Golgi bodies, mitochondria, lysosome, plastics and contain 70S ribosomes.

Note: Cyanobacteria convert atmospheric nitrogen into ammonium compounds and excess of these compounds is excreted out, enriching the soil. The death and decay of these also increase the soil fertility, particularly the nitrogen content of the soil. Tolypothrix and Aulosira fix nitrogen non-symbiotically in rice fields.