Question

The ground substance of chloroplast is

(a) Stoma

(b) Stroma

(c) Granum

(d) Cristina

Answer 1

This is a kind of gel fluid phase that surrounds the thylakoids of grana. It contains protein, ribosomes, and DNA. This also refers to the site of carbon dioxide fixation and where the synthesis of sugar, starch, fatty acids, and some protein occurs.

Complete answer:

The matrix or stroma fills most of the volume of the chloroplast. The stoma is responsible for cellular stress and signaling between various organelles. The stroma also played an important role in light- dependent and light- independent reactions.

According to Schimper, plastids are classified into three types as follows:

Leucoplast

These colorless plastids are found in embryonic and germ cells. These are found in those regions of the plant which do not receive light. They store carbohydrates, lipids, and protein and accordingly are of the following types- amyloplast, elaioplast, and proteinoplast.

Chromoplast

These are the colored plastids containing carotenoids and other pigments. They impart color to a certain portion of plants such as petals. These are of two types- phenoplast and rhodoplast.

Chloroplast

These occur mostly in the green algae and plants and contain pigments like chlorophyll-a and chlorophyll-b and DNA and RNA.

So, the correct answer is, ‘stroma.’

Note:

- Envelope: The entire chloroplast is bound by an envelope which is made of a double unit membrane. Across the double- membrane envelope, the exchange of molecules between chloroplast and cytosol takes place.

- Thylakoids: These consist of flattened and closed vesicles arranged as a membrane network. Thylakoids are stacked like a neat pile of coins forming grana. This has approx 40 to 60 grana in the matrix of a chloroplast. This is a site for light reaction in the thylakoids membrane.