Multiple Choice Questions
1. Which of the following tissues has dead cells?
(a) Parenchyma (b) Sclerenchyma (c) Collenchyma
(d) Epithelial tissue
Answers
Answer:
(b) Sclerencyma
Explanation:
- Sclerencyma tissue cell are dead.
- They do not have cytoplasm and the nucleus.
- It mainly provide mechanical support to plant and seed coat of plants such as nuts.
- It provide stiffness to the organ.
- They do not contain chlorophyll in any condition as they are dead cells.
- The cell are usually long, narrow, pointed at both ends and uniformly thickened by the deposition of lignin.
Answer: Sclerenchyma
Explanation:
Sclerenchyma cells have thickened lignified walls, which make them strong and waterproof. They are commonly classified into support types and conducting forms.
Support sclerenchyma is comprised of sclereids and fibers. This tissue reduces wilting, but it is energetically costly for the plant to create. Sclerenchyma matures with the surrounding tissues and provides more permanent support than collenchyma, maintaining the established morphology of the plant. Fibers have tapered ends, can be many centimeters long, and comprise the bundle caps and sheaths characteristic of vascular bundles, especially in monocotyledonous plants. The bundle sheath may form bundle sheath extensions by spreading to the epidermis, especially in grass leaves.
Sclereids are roughly isodiametric, and clumps of these “stone cells” (brachysclereids) give the Bartlett pear (Pyrus communis) its distinctive grittiness. Testas (seed coats) of many plants, especially legumes, are made of two layers of sclereids while sclereids comprise the thick dense layer forming the shell (endocarp) of the coconut. Star-shaped or branched astrosclereids make water lily leaves (Nymphaea sp.) tough but pliable, allowing them to withstand the tearing forces of waves and currents.
The conducting types of sclerenchyma are the tracheids and vessel elements of the xylem, the tracheary elements of plants.