In which layer of the plant tissue Guard cells are present ?
- A.Palisade mesophyll
- B.Spongy mesophyll
- C.Epidermis
- D.Xylem
Correct answer
Explanation
The correct answer is C, Epidermis. Guard cells are specialised epidermal cells that surround each stoma on the surface of a leaf.
Each stoma is a tiny pore bordered by two guard cells, which are bean-shaped in most plants and dumb-bell shaped in grasses. Unlike other epidermal cells, guard cells contain chloroplasts. When they take in water and become turgid, their thicker inner walls make them bow apart and the pore opens; when they lose water, the pore closes. In this way they control the exchange of gases for photosynthesis and respiration and the loss of water vapour in transpiration. Stomata are usually more numerous on the lower epidermis of a leaf.
Option A is wrong because the palisade mesophyll is the layer of tall, chloroplast-rich cells just below the upper epidermis where most photosynthesis happens. Option B is wrong because the spongy mesophyll is the loosely packed layer with air spaces below it. Option D is wrong because xylem is the vascular tissue that carries water and minerals.
Exam tip: guard cells = epidermis, have chloroplasts, open the stoma when turgid.
Practice Questions
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