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The Life Cycle of Plants



Vegetative Propagation

Problem : How does a pollen grain function in fertilization?

Pollen grains, or the male gametophytes of flowering plants, carry the sperm cells to the female reproductive organs. They are transported either by the wind (as in conifers) or by insects (as in most flowering plants).

Problem : What are the three main components of a seed, and from what are they derived?

The three components of the seed are the embryo, the food source (derived from gametophyte tissue in gymnosperms and from endosperm in angiosperms), and the seed coat (derived from the integument of the ovule).

Problem : What is the female reproductive organ of a flowering plant, and where must pollen land in order to fertilize the eggs it contains?

Pistils are the female reproductive organs of angiosperms, and pollen grains must land on their stigmas, or tips, in order to reach the egg cells.

Problem : Are ovaries characteristic of angiosperms or gymnosperms? What are their functions?

Ovaries, found in angiosperms, enclose the ovules and develop into fruits after fertilization. Ovaries protect the embryos from drying out and help in their dispersal.

Problem : How is cross-pollination encouraged in most angiosperms?

Cross-pollination is encouraged through differential development of the male and female gametophytes on a flower, or through the positioning of these gametophytes so that self-pollination is difficult.

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