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.

Answer 1

Hint: The plant ground tissue can be divided into three types. The parenchyma, collenchyma, and sclerenchyma. The three tissues have markedly different features.

Complete answer:
The sclerenchyma tissues are dead cells that become dead after attaining maturity. They lose their protoplasm content on attaining maturity. They are lined with a chemical substance called lignin. The hardened walls are called secondary walls. The function of these tissues is to provide mechanical strength and support to the plants.
-The layer of collenchyma cells is a characteristic of the stem and leaf stalk of dicot plants and is absent in monocot plants. Thus the collenchyma layer is absent below the epidermis in monocot plants. Thus it is not an appropriate option.
-The cell walls of xylem parenchyma are thin since they are thin and are composed of cellulose and pectin. And they are living cells. Thus it is not an appropriate answer.
-The companion cells are composed of specialized parenchymatous cells and not sclerenchyma cells, thus it is not an appropriate option.
Therefore from the given set of options, the correct statement is B, that is sclerenchyma cells are usually dead and without protoplasm.

Note: The collenchyma tissue consists of elongated cells that are thick-walled and they provide support to the plant body. The thickness of the walls is due to the deposition of cellulose and pectin. Unlike the sclerenchyma cells, collenchyma is living in nature. They are found predominantly in actively growing areas such as leaves and stems. They have active protoplasms.