Question

Which of the following statements is true?
A. The collenchyma occurs in layers below the epidermis in monocotyledonous plants.
B. Sclerenchyma cells are usually dead and without protoplasts.
C. Xylem parenchyma cells are living and thin walled and their cell walls are made up of lignin.
D. The companion cells are specialized sclerenchymatous cells.
E. Phloem fibres are generally present in the primary phloem.

Answer 1

Plant cells are eukaryotic cells with true nucleus and membrane bound organelles that play various functions. The plant cells are rectangular in shape and comparatively larger than animal cells. They are enclosed with a rigid cell wall. The plant cells are of different types. They are collenchyma cells, sclerenchyma cells, parenchyma cells, xylem cells and phloem cells. These cells form as the building blocks of plants.

Complete explanation:
Option A: Collenchyma cells are simple permanent cells which are axially elongated with a non-uniform and thickened cell wall. They are generally located underneath the epidermis. They are absent in monocots and in the region of the root system.
Option A is incorrect.
Option B: Sclerenchyma cells are rigid woody cells arranged in a compact system. These cells provide mechanical strength and rigidity to the plants. Upon maturity the sclerenchyma cells become dead cells with no protoplast.
Option B is correct.
Option C: Xylem parenchyma cells are the only living cells of xylem. Their main function is to store starch and fat. They have a well-defined nucleus and protoplast. They have a very thin cell wall made up of cellulose. Lignin is not present.
Option C is incorrect.
Option D: Companion cells are linked with sieve elements of the phloem. They are found in flowering plants. They transport sugar and amino acids in and out of the sieve elements through active transport. They are not related to sclerenchyma.
Option D is incorrect.
Option E: Phloem fibres are found in secondary phloem. They commonly occur as bands. Phloem fibres are also called bast fibres. They provide mechanical strength to the plant stem.
Option E is incorrect.

Therefore, Sclerenchyma cells are usually dead and without protoplasts is the correct answer.

Note:
Plant Cells are known as the building block of plants. They perform photosynthesis which is one of the most significant functions of plant cells. Photosynthesis occurs in the chloroplasts of the plant cell. The plant cells also store and translocate food materials from one place to another. Some of the plant cells like phloem fibres and sclerenchyma provide rigidity and mechanical strength to plants.