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Anatomy of Flowering Plants — BIOLOGY STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceBIOLOGYAnatomy of Flowering Plants3 Marks
Question
Give reason for each of the following:
  1. The vascular bundles of an isobilateral leaf are near similar in size, except that in the midrib.
  2. Heart wood is dark brown in colour.
  3. Cells of phellem/cork are impervious to water.
  4. Quantity of secondary xylem produced is more than the quantity of secondary phloem during secondary growth.
  5. Phellogen is a secondary meristem.
✓

Answer

  1. An isobilateral leaf shows parallel venation, where the veins except the main/mid vein are of same thickness; as the size of vascular bundles depends on the thickness of the veins, they are near similar in size.
  2. Heart wood is dark brown in colour due to accumulation of organic compounds like tannin, resin, oils, gums, and aromatic substances.
  3. Cells of phellem are suberised; hence, are impervious to water.
  4. The cambium is more active on its inner surface than the outer surface; hence, more secondary xylem than secondary phloem is produced.
  5. Phellogen differentiates from the outer layers of cortex during secondary growth; hence, it is a secondary meristem.

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