Name_______________________________________________
Unit 3 Lesson 2 Notes
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The series of stages that a living thing goes through as it develops is called a life cycle. It is important
to understand plant life cycles, because most of our food comes from plants.
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Most plants grow from seeds.
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First, a seed is placed in soil, so it can sprout. Next, the plant grows until it reaches maturity. A
mature plant may grow flowers or cones. Then, these structures make more seeds.
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A radish goes through three stages during its life cycle.
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A radish seed contains an embryo of a plant. When a seed sprouts during a process called
germination, an embryo begins to grow.
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As a plant continues to grow, it gets larger.
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When a plant grows to its full size, it reaches maturity. Mature plants can make seeds that
can grow into new plants.
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Flowers and cones are reproductive structures that make seeds. They produce sex cells.
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Sex cells are used during sexual reproduction.
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Male sex cells are called sperm, and female sex cells are called eggs.
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Fertilization is the process of a sperm and an egg cell joining together.
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A fertilized egg grows into a new plant inside a seed.
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In plants with cones, sperm are made in male cones, and eggs are made in female cones.
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Most cone-bearing plants are trees, such as pines, spruces, and cycads.
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Most plants produce seeds in flowers.
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Petals are the outer parts of a flower.
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The male organ is the stamen. It consists of a thin stalk topped by a saclike anther, which produces
pollen. These grains of pollen contain the sperm.
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The female organ is the pistil. Its rounded base contains eggs.
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Many flowers have both anthers and a pistil.
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Plants reproduce through pollination.
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Pollination is the process of pollen moving from a male plant part to a female plant part.
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Plants can be pollinated by wind, flowing water, or pollinators, such as bees, birds, and butterflies.
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Animals play a big role in moving plant seeds.
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Many animals eat fruit, which helps spread the seeds contained in the fruit.
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Other animals, such as squirrels, will find and bury seeds.
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Seeds, such as burs, can also travel on an animal’s body.
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Wind and flowing water also move seeds.
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A spore is a cell that can form into a new plant when the conditions are right.
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Some plants, such as mosses and ferns, grow from spores instead of seeds.
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Plants that grow from spores have two distinct forms in their life cycles. Spores are released when
the structures that hold them break open. Wind carries the spore to a new spot. If the spot
is good, the spore will grow into a plant.
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A fern, or frond, is one form of the plant. Spore clusters will grow on the underside of the fronds.
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If a spore lands in a place with good light and water, it begins to grow into a tiny, flat,
heart-shaped structure.
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The heart-shaped structure is the other form of the plant. It produces eggs and sperm.
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If a sperm cell fertilizes an egg cell, a curled frond will begin to develop and push out of the ground.
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The new plant reaches maturity when it can reproduce.