Question

Explain the major parts and functions of a chloroplast.

Answer 1

Chloroplasts are the green plastids which act as photosynthetic apparatus. In higher plants, they are mostly oval, spherical or discoid.

The major parts of chloroplast are:

1. Envelop:

• Each chloroplast is bounded by two smooth selectively permeable cytoplasmic membranes with an inter-membrane space which is filled with fluid.
• These  membranes are composed of lipo-protein sub-units.

2. Stroma:

• It is the colourless hydrophilic ground substance (matrix) which fills the internal space of chloroplast.
• It contains various enzymes required for the synthesis of glucose during dark phase of photosynthesis.
• Matrix contains 70S ribosomes, 2-6 copies circular DNA, water and enzymes.
• The most abundant enzyme is Rubisco (Ribulose Diphosphate Carboxylase)

3. Grana:

• It is embedded in the ground substance-Stroma
• It consists of many granums connected with each other by intergranal lamellae
• Each granum is made up of stack of thylakoids.
• Thylakoids are membrane-bound flattened, disc-shaped vesicles.
• Each thylakoid consists of alternate layers of lipids and proteins embedded with quantasomes.
• The chlorophyll pigments are organized into numerous photosynthetic units called quantasomes.
• Each quantasome contains about 230 to 300 units of chlorophyll molecules.
• They are capable of trapping light energy and converting it into ATP during the light reaction of photosynthesis.

Functions:

1. Chloroplasts are the site of photosynthetic reactions
2. Evolution of oxygen
3. Synthesis of ATP during phosphorylation
4. Synthesis of glucose
5. Photosensitivity in algae
6. Formation of chromoplast