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What is the Life Cycle of a
Plant?
Plants begin their
life as a seed. With water, right temperature and right location,
the seed germinates. It becomes a seedling. Roots push down into
the ground to get water and minerals. The stem reaches for the sun,
and leaves begin to unfold. A bud appears. The plants then produce
flowers. The flowers are then pollinated in many ways – by bees,
moths, butterflies, insects, moths, bats, butterflies and even by
the wind. The pollinated flower turns into fruit. The new seeds are
inside the fruit. The ripe fruit drops to the ground and the cycle
begins again.
This page
introduces you to the basic steps in the lifecycle of flowering
plants.
Germination:
sprouting of the seed. Timing is
critical. Germinating too early, too late, or in the wrong place
spells death. Plants use various germination cues. These include the
ratio of daylight to darkness, temperature, moisture (timing and
quantity), fire, abrasion, and even animal digestive enzymes. For
example, passing through the digestive system of an animal usually
indicates that the seed has been dispersed (moved away) from its
parent (so won't compete), that the seed might be deposited under a
nurse tree if the animal is a bird that defecated while perched, and
that there is some fertilizer.
Growth:
development from seedling to
mature plant.
Reproduction:
production of offspring.
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Egg/Sperm Production:
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eggs are produced in the
ovary, along with two polar nuclei per egg
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sperm is produced and
packaged in the
anther (2 sperm cells per pollen grain)
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Pollination:
transfer of pollen from
anther to
stigma (by wind, water or animal).
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Double Fertilization:
when pollen is
accepted by the stigma, a pollen tube grows down the style and
into the ovary. Both sperm cells from the pollen grain travel
down the pollen tube to the ovary. One sperm cell fertilizes the
egg to form the zygote which develops into the embryo and
eventually the new plant. The other sperm cell fuses with the
two polar nuclei to form the endosperm which provides food for
the embryo. (Next time you eat a peanut, look for the small
embryo, which has the leaves; the rest is endosperm
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Seed
Production:
the embryo and endosperm
are surrounded by a seed coat to form the seed.
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Seed
Dispersal:
movement of seeds away from
parent. Seed dispersal is critical to avoid competition with the
parent plant and to occupy new, maybe better, sites. Plants use
various, ingenious methods to disperse their seeds (e.g., hooked
seeds to stick on a passing animal, edible ovary to be eaten and
dispersed by an animal, etc.).
Death:
if plants die after
less than a year, then they are called
annuals (or
ephemerals). If plants
die after two years, then they are called biennials, and if they
live for more than two years, then they are called
perennials.
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