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KEY CONCEPT
Most mosses and ferns live
in moist environments.
Sunshine State
STANDARDS
SC.F.2.3.3: The student
knows that generally
organisms in a population live long enough
to reproduce because
they have survival
characteristics.
SC.G.1.3.3: The student
understands that the
classification of living
things is based on a
given set of criteria
and is a tool for understanding biodiversity
and interrelationships.
BEFORE, you learned
NOW, you will learn
• All plants share certain
characteristics
• The body of a plant has
specialized parts
• Plants grow throughout their
lifetimes
• About the first plants
• About reproduction in nonvascular plants, such as mosses
• About reproduction in vascular
plants, such as ferns
EXPLORE Moss Plants
What do moss plants look like?
PROCEDURE
1
Use a hand lens to examine a moss plant.
Look for different structures and parts
you can identify.
MATERIALS
• live moss plant
• hand lens
2 Draw a diagram of the moss plant in your
notebook. Label parts you identified
and parts you would like to identify.
3 Write a brief description of each
part’s function.
WHAT DO YOU THINK?
• How would you describe a moss plant to someone who had never seen one?
• How does a moss plant compare with the other plants you are familiar with?
Plant species adapted to life on land.
Evidence indicates that life first appeared on Earth about 3.8 billion
years ago. Tiny single-celled and multicellular organisms lived in
watery environments such as warm shallow seas, deep ocean vents,
and ponds. Fossil evidence suggests that plant life did not appear on
land until about 475 million years ago. The ancestors of the first
plants were among the first organisms to move onto land.
RESOURCE CENTER
CLASSZONE.COM
Explore plant evolution.
What did these plantlike organisms look like? Scientists think they
looked much like the green algae you can find growing in watery
ditches or shallow ponds today. Both green algae and plants are
autotrophs, or producers. Their cells contain chloroplasts that enable
them to convert the Sun’s light energy into the chemical energy stored
in sugars.
382 Unit 3: Diversity of Living Things
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The First Plants
Suppose that hundreds of millions of years ago, the area now
occupied by your school was a shallow pond full of tiny, floating
organisms that could photosynthesize. The Sun overhead provided
energy. The pond water was full of dissolved nutrients. The organisms thrived and reproduced, and over time the pond became
crowded. Some were pushed to the very edges of the water. Then,
after a period of dry weather, the pond shrank. Some organisms at
the edge were no longer in the water. The ones that were able to
survive were now living on land.
Scientists think that something like this took place in millions
of watery environments over millions of years. Those few organisms
that were stranded and were able to survive became ancestors to the
first plants. Life on land is very different from life in water. The first
plants needed to be able to get both nutrients and water from the
land. There is no surrounding water to provide support for the body
or to keep body tissues from drying out. However, for organisms that
survived, life on land had many advantages. There is plenty of carbon
dioxide in the air and plenty of direct sunlight.
Check Your Reading
Scientists think the first
plants shared a common
ancestor with green algae,
shown here magnified
about 80 .
Why is having plenty of sunlight and water an advantage for
a plant? Your answer should mention photosynthesis.
Mosses and Ferns
Among the first plants to live on Earth were the ancestors of the
mosses and ferns you see today. Both probably evolved from species of
algae that lived in the sea and in freshwater. Mosses are simpler in
structure than ferns. Mosses, and two closely related groups of plants
known as liverworts and hornworts, are descended from the first
plants to spread onto the bare rock and soil of Earth. Ferns and their
relatives appeared later.
This diorama shows what
a forest on Earth might
have looked like about
350 million years ago.
Chapter 11: Plants 383
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Capturing the Sun’s Energy
How much sunlight reaches an organism
living in water?
Measuring
MATERIALS
PROCEDURE
1
SKILL FOCUS
Thread the string through the holes in the button so that the button hangs
flat. Fill the empty bottle with clean water.
2 Look down through the top of the bottle. Lower the button into the water
until it either disappears from view or reaches the bottom. Have a classmate
measure how far the button is from the surface of the water.
3 Add two spoonfuls of kelp granules to the water. Repeat step 2.
• white button
• string
• empty clear
plastic bottle
• water
• ruler
• kelp granules
• tablespoon
TIME
20 minutes
WHAT DO YOU THINK?
• How did the distance measured the second time compare
with your first measurement?
• Why might a photosynthetic organism living on land get
more sunlight than one living in water?
CHALLENGE What do the kelp granules in this
experiment represent? What does that suggest about
the advantages of living on land?
Mosses are nonvascular plants.
Moss plants have adaptations for life on land. For example, each moss
cell, like all plant cells, is surrounded by a thick wall that provides it
with support. Moss cells also have special storage areas for water and
nutrients. Mosses do not grow very large, but they have simple structures that function like roots, stems, and leaves. These adaptations
help moss plants survive on land, while algae survive only in water.
If you look closely at a clump of moss, you will see that it is actually made up of many tiny, dark green plants. Mosses belong to a
group called nonvascular plants. Nonvascular plants do not have
vascular tissue. Water and nutrients simply move through nonvascular
plants’ bodies cell by cell. A plant can get enough water this way as
long as its body is no more than a few cells thick.
Check Your Reading
What limits the size of moss plants?
Water also plays a part in the reproductive cycle of a moss plant.
In the first part of the cycle, the moss grows and maintains itself,
producing the male and female structures needed for sexual reproduction. If conditions are right and there is enough water, the plant enters
a spore-producing stage, the second part of the cycle.
384 Unit 3: Diversity of Living Things
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Mosses reproduce with spores.
Mosses, ferns, and fungi all reproduce with spores. Spores are an
important adaptation that allowed the ancestors of these organisms to
reproduce on land. A spore is a single reproductive cell that is protected by a hard, watertight covering. The covering prevents the cell
from drying out. Spores are small and can be transported through the
air. This means offspring from spores can grow in places that are distant from the parent organisms.
reminder
Sexual reproduction involves
two processes: fertilization
and meiosis.
The green moss plants you are familiar with have grown from
spores. They represent the first generation. Within a clump of moss
are both male and female reproductive structures. When conditions
are right, these structures produce sperm and eggs. Fertilization can
occur only if water is present because the tiny moss sperm move by
swimming. A layer of water left by rain is one way sperm can move to
the eggs on another part of the plant.
The fertilized egg grows into a stalk with a capsule on the end—
the second generation of the plant. The stalk and capsule grow from
the female moss plant. Inside the capsule, the process of meiosis produces thousands of tiny spores. When the spores are released, as
shown in the photograph, the cycle can begin again.
Moss Releasing Spores
IDENTIFY Point out the
two generations of the
moss plant shown here.
capsule
stalk
spores
moss plant
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Mosses, like other plants, can also reproduce asexually. A small piece of
a moss plant can separate and can grow into a new plant, or new plants
can branch off from old ones. Asexual reproduction allows plants to
spread more easily than sexual reproduction. However, the genetic material
of the new plants is the same as that of the parent. Sexual reproduction
increases genetic diversity and the possibility of new adaptations.
Check Your Reading
Compare and contrast sexual and asexual reproduction.
Your answer should mention genetic material.
Ferns are vascular plants.
Ferns, and two closely related groups of plants known as horsetails
and club mosses, were the first plants on Earth with vascular systems.
The tubelike tissue of a vascular system moves water through a plant’s
body quickly and effectively. Because of this transport system, vascular
plants can grow much larger than nonvascular plants. Vascular tissue
also provides support for the weight of a larger plant.
The presence of vascular tissue has an effect on the development
of roots, stems, and leaves. The root system can branch out more,
anchoring a larger plant as well as providing water and nutrients.
Vascular tissue moves materials more efficiently and gives extra support. The stems can branch out and more leaves can grow. This results
in more sugars and other materials needed for energy and growth.
Nonvascular
Vascular
Liverworts are tiny nonvascular plants.
The liverworts shown here are life-size.
Ferns are vascular plants. Notice how tall a
tree fern can grow.
COMPARE AND CONTRAST How do the penny and the person help
to show that the tree ferns are much larger than the liverworts?
386 Unit 3: Diversity of Living Things
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Ferns reproduce with spores.
You may have seen ferns growing in the woods or
in a garden. The leaves of ferns, called fronds, are
often included in a flower bouquet. The next time
you have a chance to look at a fern frond, take a
look at the back. You will probably see many small
clusters similar to those shown to the right. The
clusters are full of spores.
spores
Ferns, like mosses, have a two-part life cycle. In ferns, spores
grow into tiny structures that lie very close to the ground. You
would have to look closely to find these structures on the
ground, for they are usually smaller than the size of your
thumbnail. Within these structures are the sperm- and eggproducing parts of the fern plant. This is the first generation of
the plant. Like mosses, the sperm of a fern plant need water to
swim to the egg. So fertilization occurs only when plenty of
moisture is present.
spore cluster
The second part of a fern life cycle is the plant with fronds that
grows from the fertilized egg. As the fronds grow, the small eggbearing part of the plant dies away. The fronds produce clusters, and
cells within those clusters undergo meiosis and produce spores. The
more the fern grows, the more clusters and spores it produces. The
spores, when they are released, spread through the air. If conditions
are right where the spores land, they grow into new fern plants and a
new cycle begins. This is sexual reproduction. Ferns, like mosses, also
reproduce asexually. New ferns branch off old ones, or pieces separate
from the plant and grow.
Check Your Reading
As fern fronds grow, they
produce clusters of spores
on the back of the fronds.
Explain one way that sexual reproduction in ferns is similar to
reproduction in mosses. Explain one way it is different.
KEY CONCEPTS
CRITICAL THINKING
1. For the ancestors of the first
plants, what were some advantages to living on land?
4. Synthesize Vascular plants
such as ferns can grow bigger
and taller than nonvascular
plants such as mosses. Does
this mean they can also capture more sunlight? Explain
your answer.
2. What are three adaptations
that make mosses able to live
on land?
3. What are two characteristics
you can observe that distinguish vascular plants from
nonvascular plants?
5. Compare Make a chart that
shows how the life cycles of
mosses and ferns are different,
and how they are similar.
CHALLENGE
6. Evaluate Consider the
conditions that are needed for
mosses and ferns to reproduce
sexually. Sexual reproduction
increases genetic diversity
within a group of plants, while
asexual reproduction does not.
Explain why asexual reproduction is still important for both
moss and fern plants.
Chapter 11: Plants 387