A student cuts two roots. Root A shows 4 strands of xylem…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A student cuts two roots. Root A shows strands of xylem. Root B shows strands. Between neighbouring strands of xylem there is a patch of phloem. (a) Name the arrangement of root A and of root B. (b) How many patches of vascular tissue, xylem and phloem together, does each section show? (c) Which of the two roots is a monocot root, and which part of it is large?
Need a reminder? The key ideaShow
Dicot root: epidermis with root hairs, cortex, endodermis with Casparian strips of suberin, pericycle (lateral roots), radial bundles with two to four xylem strands (tetrarch), conjunctive tissue, small pith. Monocot root: same plan, more than six xylem strands (polyarch), large pith, no secondary growth. Dicot stem: epidermis with cuticle and trichomes, collenchymatous hypodermis, parenchymatous cortex, starch sheath endodermis, sclerenchymatous pericycle patches, medullary rays, a ring of conjoint open endarch bundles, a large pith. Monocot stem: sclerenchymatous hypodermis, ground tissue with no pith, scattered conjoint closed bundles with sheaths, smaller bundles near the edge, water-containing cavities.
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 names. Root A has four strands: it is tetrarch. Root B has more than six: it is polyarch.
Step 2. The patches. Root A has patches. Root B has patches.
Step 3. The class. A root with many strands, more than six, is a monocot root. It has a large pith.
Answer: (a) A is tetrarch and B is polyarch; (b) patches and patches; (c) root B is the monocot root, and its pith is large.
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