Sunshine StateSTANDARDSSC.F.2.3.3: The studentknows that generallyorganisms in a popula-tion live long enoughto reproduce becausethey have survivalcharacteristics.SC.G.1.3.3: The studentunderstands that theclassification of livingthings is based on agiven set of criteriaand is a tool for under-standing biodiversityand interrelationships.

382 Unit 3: Diversity of Living Things

BEFORE, you learned

• All plants share certain characteristics

• The body of a plant has specialized parts

• Plants grow throughout theirlifetimes

NOW, you will learn

• About the first plants• About reproduction in nonvas-

cular plants, such as mosses• About reproduction in vascular

plants, such as ferns

KEY CONCEPT

Most mosses and ferns livein moist environments.

Plant species adapted to life on land.Evidence indicates that life first appeared on Earth about 3.8 billionyears ago. Tiny single-celled and multicellular organisms lived inwatery environments such as warm shallow seas, deep ocean vents,and ponds. Fossil evidence suggests that plant life did not appear onland until about 475 million years ago. The ancestors of the firstplants were among the first organisms to move onto land.

What did these plantlike organisms look like? Scientists think theylooked much like the green algae you can find growing in wateryditches or shallow ponds today. Both green algae and plants areautotrophs, or producers. Their cells contain chloroplasts that enablethem to convert the Sun’s light energy into the chemical energy storedin sugars.

EXPLORE Moss Plants

What do moss plants look like?

PROCEDURE

Use a hand lens to examine a moss plant. Look for different structures and parts you can identify.

Draw a diagram of the moss plant in your notebook. Label parts you identified and parts you would like to identify.

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?

3

2

1

MATERIALS• live moss plant• hand lens

RESOURCE CENTERCLASSZONE.COM

Explore plant evolution.

The First PlantsSuppose that hundreds of millions of years ago, the area now occupied by your school was a shallow pond full of tiny, floatingorganisms that could photosynthesize. The Sun overhead providedenergy. The pond water was full of dissolved nutrients. The organ-isms thrived and reproduced, and over time the pond becamecrowded. Some were pushed to the very edges of the water. Then,after a period of dry weather, the pond shrank. Some organisms atthe 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 organismsthat were stranded and were able to survive became ancestors to thefirst plants. Life on land is very different from life in water. The firstplants needed to be able to get both nutrients and water from theland. There is no surrounding water to provide support for the bodyor to keep body tissues from drying out. However, for organisms thatsurvived, life on land had many advantages. There is plenty of carbondioxide in the air and plenty of direct sunlight.

Check Your Reading Why is having plenty of sunlight and water an advantage for a plant? Your answer should mention photosynthesis.

Mosses and FernsAmong the first plants to live on Earth were the ancestors of themosses and ferns you see today. Both probably evolved from species ofalgae that lived in the sea and in freshwater. Mosses are simpler instructure than ferns. Mosses, and two closely related groups of plantsknown as liverworts and hornworts, are descended from the firstplants to spread onto the bare rock and soil of Earth. Ferns and theirrelatives appeared later.

Scientists think the firstplants shared a commonancestor with green algae,shown here magnifiedabout 80�.

This diorama shows whata forest on Earth mighthave looked like about350 million years ago.

Chapter 11: Plants 383

Mosses are nonvascular plants.Moss plants have adaptations for life on land. For example, each mosscell, like all plant cells, is surrounded by a thick wall that provides itwith support. Moss cells also have special storage areas for water andnutrients. Mosses do not grow very large, but they have simple struc-tures that function like roots, stems, and leaves. These adaptationshelp 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 actu-ally made up of many tiny, dark green plants. Mosses belong to agroup called nonvascular plants. Nonvascular plants do not have vascular tissue. Water and nutrients simply move through nonvascularplants’ bodies cell by cell. A plant can get enough water this way aslong 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 reproduc-tion. If conditions are right and there is enough water, the plant entersa spore-producing stage, the second part of the cycle.

384 Unit 3: Diversity of Living Things

How much sunlight reaches an organism living in water?PROCEDURE

Thread the string through the holes in the button so that the button hangsflat. Fill the empty bottle with clean water.

Look down through the top of the bottle. Lower the button into the wateruntil it either disappears from view or reaches the bottom. Have a classmatemeasure how far the button is from the surface of the water.

Add two spoonfuls of kelp granules to the water. Repeat step 2.

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 thisexperiment represent? What does that suggest aboutthe advantages of living on land?

3

2

1

Capturing the Sun’s EnergyCapturing the Sun’s EnergySKILL FOCUSMeasuring

MATERIALS• white button• string• empty clear

plastic bottle• water• ruler• kelp granules• tablespoon

TIME20 minutes

Chapter 11: Plants 385

Mosses reproduce with spores.Mosses, ferns, and fungi all reproduce with spores. Spores are animportant adaptation that allowed the ancestors of these organisms toreproduce on land. A spore is a single reproductive cell that is pro-tected by a hard, watertight covering. The covering prevents the cellfrom drying out. Spores are small and can be transported through theair. This means offspring from spores can grow in places that are dis-tant from the parent organisms.

The green moss plants you are familiar with have grown fromspores. They represent the first generation. Within a clump of mossare both male and female reproductive structures. When conditionsare right, these structures produce sperm and eggs. Fertilization canoccur only if water is present because the tiny moss sperm move byswimming. A layer of water left by rain is one way sperm can move tothe 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 fromthe female moss plant. Inside the capsule, the process of meiosis pro-duces thousands of tiny spores. When the spores are released, asshown in the photograph, the cycle can begin again.

capsule

stalk spores

IDENTIFY Point out thetwo generations of themoss plant shown here.

Moss Releasing Spores

reminder

Sexual reproduction involvestwo processes: fertilizationand meiosis.

moss plant

Nonvascular

386 Unit 3: Diversity of Living Things

Mosses, like other plants, can also reproduce asexually. A small piece ofa moss plant can separate and can grow into a new plant, or new plantscan branch off from old ones. Asexual reproduction allows plants tospread more easily than sexual reproduction. However, the genetic materialof the new plants is the same as that of the parent. Sexual reproductionincreases 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 horsetailsand club mosses, were the first plants on Earth with vascular systems.The tubelike tissue of a vascular system moves water through a plant’sbody quickly and effectively. Because of this transport system, vascularplants can grow much larger than nonvascular plants. Vascular tissuealso provides support for the weight of a larger plant.

The presence of vascular tissue has an effect on the developmentof 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 sup-port. The stems can branch out and more leaves can grow. This resultsin more sugars and other materials needed for energy and growth.

COMPARE AND CONTRAST How do the penny and the person helpto show that the tree ferns are much larger than the liverworts?

Liverworts are tiny nonvascular plants. The liverworts shown here are life-size.

Vascular

Ferns are vascular plants. Notice how tall atree fern can grow.

Ferns reproduce with spores.You may have seen ferns growing in the woods orin a garden. The leaves of ferns, called fronds, areoften included in a flower bouquet. The next timeyou have a chance to look at a fern frond, take alook at the back. You will probably see many smallclusters similar to those shown to the right. Theclusters are full of spores.

Ferns, like mosses, have a two-part life cycle. In ferns, sporesgrow into tiny structures that lie very close to the ground. Youwould have to look closely to find these structures on theground, for they are usually smaller than the size of yourthumbnail. Within these structures are the sperm- and egg-producing parts of the fern plant. This is the first generation ofthe plant. Like mosses, the sperm of a fern plant need water toswim to the egg. So fertilization occurs only when plenty ofmoisture is present.

The second part of a fern life cycle is the plant with fronds thatgrows from the fertilized egg. As the fronds grow, the small egg-bearing part of the plant dies away. The fronds produce clusters, andcells within those clusters undergo meiosis and produce spores. Themore the fern grows, the more clusters and spores it produces. Thespores, when they are released, spread through the air. If conditionsare right where the spores land, they grow into new fern plants and anew cycle begins. This is sexual reproduction. Ferns, like mosses, alsoreproduce asexually. New ferns branch off old ones, or pieces separatefrom the plant and grow.

Check Your Reading Explain one way that sexual reproduction in ferns is similar to reproduction in mosses. Explain one way it is different.

KEY CONCEPTS1. For the ancestors of the first

plants, what were some advan-tages to living on land?

2. What are three adaptationsthat make mosses able to liveon land?

3. What are two characteristicsyou can observe that distin-guish vascular plants fromnonvascular plants?

CRITICAL THINKING4. Synthesize Vascular plants

such as ferns can grow biggerand taller than nonvascularplants such as mosses. Doesthis mean they can also cap-ture more sunlight? Explainyour answer.

5. Compare Make a chart thatshows how the life cycles ofmosses and ferns are different,and how they are similar.

CHALLENGE6. Evaluate Consider the

conditions that are needed formosses and ferns to reproducesexually. Sexual reproductionincreases genetic diversitywithin a group of plants, whileasexual reproduction does not.Explain why asexual reproduc-tion is still important for bothmoss and fern plants.

Chapter 11: Plants 387

spores

As fern fronds grow, theyproduce clusters of sporeson the back of the fronds.

spore cluster