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KEY CONCEPT
Many plants reproduce
with flowers and fruit.
BEFORE, you learned
NOW, you will learn
• Seed plants do not have
• About flowers and fruit
• About the relationship
swimming sperm
• Gymnosperms reproduce with
pollen and seeds
VOCABULARY
angiosperm p. 107
flower p. 108
fruit p. 108
between animals and
flowering plants
• How humans need plants
EXPLORE Fruit
What do you find inside fruit?
PROCEDURE
1
Place the apple on a paper towel. Carefully cut
the apple in half. Find the seeds.
2 Place the pea pod on a paper towel. Carefully
MATERIALS
•
•
•
•
apple
paper towel
plastic knife
pea pod
split open the pea pod. Find the seeds.
3 Both the apple and the pea pod are examples
of fruits. In your notebook, draw a diagram of
the two fruits you examined. Label the
fruit and the seeds.
WHAT DO YOU THINK?
• How many seeds did you find?
• What part of an apple do you eat?
What part of a pea?
Angiosperms have flowers and fruit.
MIND MAP
Make a mind map
diagram for the main
idea: Angiosperms have
flowers and fruit.
Have you ever eaten peanuts, grapes, strawberries, or squash? Do you
like the way roses smell, or how spider plants look? All of these plants
are angiosperms, or flowering plants. An angiosperm (AN-jee-uhSPURM) is a seed plant that produces flowers and fruit. Most of the
species of plants living now are angiosperms. The grasses at your local
park are angiosperms. Most trees whose leaves change color in the fall
are angiosperms.
The sperm of a flowering plant are protected in a pollen grain and
do not need an outside source of water to reach the eggs. The eggs
develop into embryos that are enclosed within seeds. Both generations
of angiosperms and gymnosperms occur within a single plant.
Chapter 3: Plants 107
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The reproductive cycles of angiosperms and gymnosperms are
alike in many ways. Both angiosperms and gymnosperms have
separate male and female reproductive structures. In some species,
male and female parts grow on the same plant, but in others there are
separate male and female plants.
VOCABULARY
Remember to add word
triangles for flower and
fruit to your notebook.
An important difference between angiosperms and gymnosperms
is that in angiosperms, the sperm and egg cells are contained in a
flower. The flower is the reproductive structure of an angiosperm.
Egg cells develop in a part of the flower called an ovary. Once the eggs
are fertilized and the seed or seeds form, the ovary wall thickens and
the ovary becomes a fruit.
Check Your Reading
What reproductive structures do angiosperms have that
gymnosperms do not?
The diagram on page 109 shows the life cycle of one type of
angiosperm, a cherry tree. As you read the numbered paragraphs
below, follow the numbers on the labels in the diagram.
1
The reproductive structures of a cherry tree are its flowers. The
anther is the male part. The pistil is the female part. Meiosis in the
anther produces sperm cells enclosed within pollen grains. Meiosis
in the ovary of the pistil produces egg cells.
2
The pollen grains are released. When a pollen grain is caught on
the pistil of a flower, a pollen tube starts to grow. Within the ovary
one of the egg cells matures.
3
Fertilization occurs when the pollen tube reaches the ovary and a
sperm fertilizes the egg. The fertilized egg grows into an embryo
and develops a seed coat. The ovary develops into a fruit.
4
The fruit may fall to the ground or it may be eaten by animals.
If the seed inside lands in a place where it can germinate and
survive, it will grow into a new cherry tree.
Check Your Reading
What is the flower’s role in the sexual reproduction of an
angiosperm?
Many flowering plants also reproduce asexually. New shoots can
grow out from the parent plant. For example, strawberries and spider
plants can reproduce by sending out shoots called runners. New
plants grow from the runners, getting nutrients from the parent until
the roots of the new plant are established. Plants can spread quickly
this way. This form of asexual reproduction allows plants to reproduce
even when conditions are not right for the germination of seeds.
108 Unit 1: Diversity of Living Things
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Life Cycle of a Cherry Tree
seed
fruit
4
1
Meiosis
Meiosis takes place in flowers
on the cherry tree. This flower
has both male and female
reproductive structures.
Seeds and Fruit
The fertilized egg becomes an
embryo within a seed. The ovary
wall thickens and forms a fruit
around the seed.
anthers (male)
pollen
grain
3
flower
Fertilization
pollen
grains
Sperm move through
the pollen tube to
fertilize the egg.
pistil
(female)
pollen tube
egg
sperm
2
Pollination
Pollen grains carry sperm to the
tip of the pistil. A pollen tube
starts to grow toward the ovary,
which contains the egg cells.
egg cells
ovary
pistil
Compare this cherry tree life cycle with the pine tree life cycle on
page 101. How are they the same? How are they different?
Chapter 3: Plants 109
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Flowers
Flowers vary in size, shape, color, and fragrance. They all have some
similar structures, although they are not always as easy to see as in the
lily pictured below. Also, in some species, male and female reproductive structures are on different flowers. In others, there are distinct
male and female plants.
reading tip
•
As you read, match the
bulleted items in the text
with the colored labels on
the photograph below.
Sepals are leafy structures that enclose the flower before it opens.
When the flower blooms, the sepals fall open and form the base
of the flower.
•
Petals are leafy structures arranged in a circle around the pistil.
The petals open as the reproductive structures of the plant
mature. Petals are often the most colorful part of a flower. The
petals help to attract animal pollinators.
•
The stamen is the male reproductive structure of a flower. It
includes a stalk called a filament and the anther. The anther
produces sperm cells, which are contained in pollen grains.
•
The pistil is the female reproductive structure of the flower. The
ovary is located at the base of the pistil and contains the egg cells
that mature into eggs. At the top of the pistil is the stigma, where
pollen grains attach.
Check Your Reading
What are the stamen and pistil?
Parts of a Flower
stigma
stamen
pistil
anther
filament
The stamen is the
male reproductive
structure of
the flower.
ovary
The pistil
is the female
reproductive
structure of
the flower.
sepal
In some flowers, such as this lily,
the sepals look like the petals.
In many other flowers, sepals are
green and look more like leaves.
110 Unit 1: Diversity of Living Things
petal
The petals help
attract animal
pollinators.
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Flower Parts
What parts of a flower can you identify?
SKILL FOCUS
Observing
PROCEDURE
1
Examine the flower you are given. Try to notice as many details as you can.
Draw a diagram of the flower in your notebook and label its parts.
2 Carefully take your flower apart. Sort the parts. Draw and label one example
of each part in your notebook.
MATERIALS
• assorted flowers
• hand lens
TIME
15 minutes
WHAT DO YOU THINK?
• Which of the parts of a flower labeled in the diagram
on page 110 did you find in your flower?
• Based on your experience, what would you look for if
you were trying to decide whether a structure on an
unfamiliar plant was a flower?
Fruit
A fruit is a ripened plant ovary. Some ovaries contain more than one
seed, such as an apple. Some contain only one seed, like a cherry.
Apples and cherries are called fleshy fruits, because they have juicy
flesh. The corn you eat as corn on the cob is a fleshy fruit. There are
also dry fruits. Peanuts, walnuts, and sunflowers are dry fruits. The
shells of dry fruits help protect the seeds. Some dry fruits, like the
winged fruit of a maple tree or the feathery tip of a dandelion seed,
have structures that allow the seeds to be carried by the wind.
Animals spread both pollen and seeds.
Reproduction in many types of flowering plants includes interactions
between plants and animals. The plants are a source of food for the
animal. The animals provide a way to transport pollen and seeds. As
they eat, animals move pollen from flower to flower and seeds from
place to place.
Have you ever watched a honeybee collect nectar from a flower?
Nectar is a sweet sugary liquid located at the bottom of the flower. As
the bee crawls around in the flower, reaching down for the nectar, it
rubs against the anthers and picks up pollen grains. When the bee
travels to another flower, some of that pollen rubs off onto the pistil
of the second flower.
Check Your Reading
How do bees benefit from the flowers they pollinate?
pollen grains
Chapter 3: Plants 111
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An animal that pollinates a flower is called a pollinator. Bees and
other insects are among the most important pollinators. Bees depend
on nectar for food, and they collect pollen to feed their young. Bees
recognize the colors, odors, and shapes of flowers. Thousands of
species of plants are pollinated by bees, including sunflowers and
lavender.
reading tip
The word pollinate means
“to transfer pollen from an
anther to a stigma.” Note
the differences in spelling
between pollen and
pollinate, pollinator.
The relationship between angiosperms and their pollinators can be
highly specialized. Sometimes the nectar is located in a tube-shaped
flower. Only certain animals, for example hummingbirds with long, slender beaks, can pollinate those flowers. Some flowers bloom at night.
These flowers attract moths and bats as pollinators. Night-blooming
flowers are usually pale, which means they are visible at night. Also, they
may give off a strong scent to attract animal pollinators.
The advantage of animal pollination is that the pollen goes to where
it is needed most. The pollen collected by a bee has a much better chance
of being brought to another flower. By comparison, pollen grains that
are spread by the wind are blown in all directions. Each grain has only a
small chance of landing on another flower. Wind-pollinated plants produce a lot more pollen than plants that are pollinated by animals.
Check Your Reading
SIMULATION
CLASSZONE.COM
Compare the different
ways seeds are dispersed.
What is the advantage of animal pollination over
wind pollination?
The fruits produced by angiosperms help to spread the seeds they
contain. Some seeds, like dandelion and maple seeds, are carried by
the wind. Many seeds are scattered by fruit-eating animals. The seeds
go through the animal’s digestive system and are eventually deposited
on the ground with the animal’s waste. Wide scattering of seeds
ensures that some seeds will land in an area with enough resources
and room to grow.
Animals eat fleshy fruit and distribute
the seeds with their waste.
112 Unit 1: Diversity of Living Things
The burrs in this horse’s
mane are dry fruit that
contain seeds.
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Animals also help to scatter some types of dry fruits—not by eating
them, but by catching them on their fur. Have you ever tried to pet a
dog that has run through a grassy field? You might have noticed burrs
stuck in the animal’s fur. The seeds of many grasses and wildflowers
produce dry fruits that are covered with spines or have pointed barbs.
Seeds protected by these types of dry fruits stick to fur. The seeds travel
along with the animal until the animal rubs them off.
Humans depend on plants for their survival.
Without plants, humans and all other animals would not be able to
live on Earth. After plants adapted to life on land, it became possible
for animals to live on land as well. Land animals rely on plants for
food and oxygen. Many animals live in or near plants. Plants also supply materials humans use every day.
Food and Oxygen
All organisms must have energy to live. For animals,
that energy comes from food. Plants, especially
angiosperms, are the ultimate source of food for all
land animals. Plants capture energy from the Sun
to make sugars and other carbohydrates. Those
same energy-rich materials are then consumed by
animals as food. Even animals that eat other animals depend on plants for survival, because plants may
provide food for the animals they eat.
Photosynthesis, the process that plants use to produce
sugars and carbohydrates, also produces oxygen. The
oxygen in the air you breathe is the product of the photosynthetic activity of plants and algae. Animals, including
humans, need oxygen to release the energy stored in food.
Energy Resources and Soil
Plants are an important source of many natural resources.
Natural gas and coal are energy resources that formed deep
underground from the remains of plants and other organisms. Natural gas and coal are important fuels for many
purposes, including the generation of electricity.
Plants capture light energy from
the Sun and store it in sugars and
other carbohydrates.
Even the soil under your feet is a natural resource associated with
plants. Plant roots can break down rock into smaller and smaller particles to form soil. When plants die, their bodies decay and add
richness to the soil.
Chapter 3: Plants 113
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From Plants to Products
1
Cotton Plant
U.S. farmers harvest
over 17 million
bales of cotton
each year.
2
Cotton Bale
A typical bale of cotton contains
over 200 kg of cotton fibers.
3
Cotton Mill
4
Cotton mills clean the fiber,
remove the seeds, and separate
the fibers into strands.
Final
Product
A bale of cotton has
enough fiber for over
200 pairs of jeans.
Other Products
Plant materials are part of many products people use every day. Plants
provide the wood used to build houses and the wood pulp used to
make paper for books like the one you are reading. The cotton in blue
jeans comes from plants. So do many dyes that are used to add color
to fabrics. Aspirin and many other medicines made by drug companies today are based on chemicals originally found in plants.
KEY CONCEPTS
CRITICAL THINKING
1. How do flowers relate to fruit?
4. Predict If you observed three
plants in a forest—a moss, a
fern, and a flowering plant—
which would have the most
insects nearby? Why?
2. How are animals involved in
the life cycles of some flowering plants?
3. List three ways that humans
depend upon plants.
114 Unit 1: Diversity of Living Things
5. Connect Draw an apple like
the one shown on page 107.
Label three parts of the fruit
and explain from which part of
an apple flower each part grew.
CHALLENGE
6. Synthesize There are more
species of flowering plants on
Earth than species of mosses,
ferns, or cone-bearing plants
such as pine trees. How do
you think the different ways
spores, pollen, and seeds are
spread affect the genetic diversity of different types of
plants? Explain your reasoning.