Question

Describe the ultrastructure of a chloroplast. Add a note on the significance of photosynthesis?

Answer 1

The ultrastructure of the chloroplast contains the following parts:

a) Peristomium: A chloroplast is bounded by a double layered membrane known as peristomium made up of lipoproteins.

b) Stroma: Peristomium encloses a colourless matrix called stroma. Stroma contains DNA, RNA, ribosome and the enzymes which carry out dark reactions. DNA is circular. As there is a presence of DNA, chloroplast is a self-replicating and semi-autonomous cell organelles.

c) Grana: These are green coloured structures (40 - 60) embedded in the stroma, each consists of many disc-shaped lamellae or thylakoids stacked as coins. Each thylakoid is a sac-like structure with an internal space. Wall of thylakoid is called grana lamellae while space inside is called grana compartment. On the inner surface of grana lamellae, quantasome is present which behaves like the photosynthetic units. Quantasome contains two pigment systems PS I and PS II. Granum is well equipped for photochemical reaction.

d)Stroma Lamellae: These are membrane-like structures which interconnect grana. The lumen inside the stroma lamellae is called fret channel which helps in rapid transportation.

Significance of photosynthesis:

a) Converts trapped light energy into chemical energy.

b) Food synthesized is used as a source of energy by plants and heterotrophs. All living organisms directly or indirectly depend upon photosynthesis for energy.

c) Photosynthesis releases $O_2$ which purifies the air besides maintaining the balance of $O_2$ and $C{O}_2$ in the atmosphere.$O_2$ is used for making Ozone.

d) Photosynthesis produces biomass which is useful to animals for feeding, nesting etc.

e) Fossil fuels, coal, petroleum, natural gas are the products of photosynthesis.

f) Economically important plant products such as cotton, alkaloids, resins, gums, tannin, rubber are the products of photosynthesis.