Question

Angular collenchyma occurs in
A. Datura and Cucurbita
B. Helianthus
C. Althaea
D. None of the above

Answer 1

Hint: Cells of collenchyma are living, elongated with an uneven thickening. The main function of collenchyma is providing support mainly in regions of primary growth. In the case of angular collenchyma, the cells are thickened at corners and it provides great mechanical resistance to the plant.

Complete answer:
Collenchyma consists of elongated cells that provide mechanical support to the plant. In this type, primary walls are thickened unevenly. In angular collenchyma, angles or corners of the cell are thickened and intercellular spaces are absent. The thickenings are like pillars arranged longitudinally in the plant body, providing great mechanical resistance. It is present in Datura, Cucurbita, pumpkin and lemon. Four main types of collenchyma are present:
i. Tangential collenchyma: Tangential face of the cell wall is thickened and cells are arranged in rows. Example: Sunflower.
ii. Annular collenchyma: Cells have uniformly thickened cell walls. Example, Nerium.
iii. Lacunar collenchyma: Intercellular spaces are present in this type of collenchyma.
iv. Sclerified collenchyma: It provides mechanical support to plants.
The other two types of tissues present are parenchyma and sclerenchyma. Parenchyma are living tissues, whereas sclerenchyma are dead tissues. They also provide mechanical strength to plants.
Hence, the correct answer is option (A).

Note: Collenchyma are living. Some cells of collenchyma may contain chlorophyll and are involved in photosynthesis. In secondary growth, collenchyma regains meristematic activity, an example is of periderm that is produced by phellogen. Collenchyma cells have thick deposits of cellulose in their cell walls and appear polygonal in cross section.