Tomas looks at the lower surface of a bean leaf under a microscope…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Tomas looks at the lower surface of a bean leaf under a microscope. He counts stomata on every square millimetre. He thinks about a patch of square millimetres. (a) How many stomata are on the patch? (b) How many guard cells? (c) Why do the guard cells have chloroplasts and an unevenly thick wall?
Need a reminder? The key ideaShow
Epidermal tissue system: epidermis with cuticle (cutin, absent in roots), stomata (bean-shaped guard cells in dicots, dumb-bell in grasses; thick inner wall, thin outer wall; subsidiary cells; the stomatal apparatus), root hairs (unicellular) and trichomes (multicellular, on stems). Ground tissue system: all but epidermis and vascular bundles; cortex, pericycle, medullary rays, pith; mesophyll in leaves. Vascular tissue system: xylem and phloem; open bundles (cambium, dicot stem) and closed (monocot stem); conjoint (stems, leaves) and radial (roots); collateral and bicollateral; endarch xylem in stems, exarch in roots.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. The stomata. stomata.
Step 2. The guard cells. Each stoma has two guard cells, so guard cells.
Step 3. The cells. The inner wall of each guard cell, next to the pore, is thick, and the outer wall is thin. When the cells take in water, the thin wall stretches more, the cell bends, and the pore opens. The chloroplasts let the guard cells make sugars that help them draw water in.
Answer: (a) stomata; (b) guard cells; (c) the unequal walls make the cell bend when it fills with water, and the chloroplasts help it to build up the sugars that draw the water in.
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