Question

Cork cells are made impervious to water and gases by the presence of

• A. cellulose
• B. lipids
• C. suberin
• D. lignin

Answer 1

The correct option is C

suberin

The correct option is C

The explanation for the correct option:

1. As the stem continues to increase in girth its outer cortical and epidermis layers get broken
2. To replace the broken layer and provide new protective cell layers meristematic tissue called cork cambium or phellogen develops
3. Phellogen cuts off cells on both sides.
4. The outer cells differentiate into the cork, inner cells differentiate into the secondary cortex or phelloderm
5. Cork is the outer protective layer of bark of a tree. They are dead and compactly packed cells with no intercellular space.
6. So they are made up of suberin a waxy layer to protect them from mechanical injury and also prevent the loss of water by evaporation

The explanation for incorrect options:

Option A

1. Cellulose is present in the plant cell walls, it gives strength to the cell.
2. Cellulose is a polysaccharide formed of a linear chain of D-glucose units.

Option B

1. Lipid especially phospholipid is composed of the cell membrane.
2. They are not polar in nature and repel water.
3. So cell membrane is bilayer so that nonpolar long chain fatty acid is away from the aqueous environment

Option D

1. Lignin is found in the middle lamella and in the secondary cell wall of xylem vessels and the fibers that strengthen plants.
2. They are present mainly in wood and bark and provide rigidity.
3. It also helps in water transport, mechanical support, and resistance to various stresses.

Final answer: Cork cells are made impervious to water and gases by the presence of suberin.