SolveItClass 9 · NCERT

NCERT Solutions · Class 9 Science Reproduction: How Life Continues

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Pause and Ponder 11.2–11.3 (part 4 of 19)

  1. Exercise 11.2

    Look at the pictures (Fig. 11.16\displaystyle 11.16) of calotropis (madar) seeds and dandelion seeds given below. Can you guess what kind of seed dispersal these seeds are adapted for?NCERT_Question_Class9_Science_Ch11_PP_Q11-2

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    Both are adapted for seed dispersal by wind.
    Madar (calotropis) seeds carry a tuft of long silky hairs, and dandelion seeds carry a parachute of fine hairs at the top.
    These hairs make the seed very light for its surface area, so even a light breeze lifts it and floats it far from the parent plant.
    The chapter lists wind, water and animals as the agents of seed dispersal; a small, dry, plumed seed with no fleshy pulp and no hooks points to wind, not to water or animals.
    Being carried away matters: the new seedling then germinates where it is not competing with its parent for water, light and nutrients.

  2. Exercise 11.3

    A farmer plants two varieties of maize side by side, but notices that seeds form only when pollen from one variety reaches the stigma of the other. What type of pollination is this? Bridging Science and Society Sexual reproduction in plants has an applied importance in plant breeding. There are several methods of plant breeding, such as selective breeding, artificial hybridisation, genetically engineered crops, and more. In selective breeding, farmers select plants of desirable characters for reproduction. Process of artificial hybridisation involves removal of the stamens from the flowers, covering it with a bagging to prevent self-pollination, and manual transfer of the pollens with desired characters. Genetic engineering is also applied by inserting the genetic material of desired characters into the DNA of the selected varieties. This leads to the development of new varieties, such as high yielding varieties, disease resistant varieties, and so on. This has revolutionised crop production in agriculture.

    Not cross-checked

    NCERT prints no numerical answer for this exercise, so this working has not been cross-checked against the book.

    This is cross-pollination.
    NCERT_Solution_Class9_Science_Ch11_PP_Q11-3
    The pollen is going from the anther of a flower on one plant to the stigma of a flower on another plant of the same type — the chapter's exact definition of cross-pollination.
    Had the pollen reached the stigma of the same flower, or another flower on the same plant, it would have been self-pollination.
    The farmer's observation — seeds forming only when one variety's pollen reaches the other variety's stigma — shows these two maize varieties depend on pollen from a different plant to set seed.