Sunshine StateSTANDARDSSC.F.1.3.1: The studentunderstands that livingthings are composed of major systems that function in reproduction, growth,maintenance, and regulation.SC.F.1.3.5: The studentexplains how the lifefunctions of organismsare related to whatoccurs within the cell.

Plants are a diverse group of organisms.Plants are nearly everywhere. Walk through a forest, and you’re sur-rounded by trees, ferns, and moss. Drive along a country road, andyou pass fields planted with crops like cotton or wheat. Even a busycity has tree-lined sidewalks, grass-covered lawns, and weeds growingin vacant lots or poking through cracks in the pavement.

Earth is home to an amazing variety of plant life. Plants come inall shapes and sizes, from tiny flowers no bigger than the head of a pinto giant trees taller than a 12-story building. Plants are found in alltypes of environments, from the icy Arctic to the steamy tropics.

Chapter 11: Plants 375

VOCABULARYvascular system p. 377transpiration p. 378

BEFORE, you learned

• All organisms have certainbasic needs and characteristics

• The bodies of multicellularorganisms are organized

• Plants are producers

NOW, you will learn

• About plant diversity• About common characteristics

of plants• How the bodies of plants

are organized

KEY CONCEPT

Plants are adapted toliving on land.

EXPLORE Leaf Characteristics

What is a leaf?

PROCEDURE

Examine the leaf your teacher gives you carefully. Try to notice as many details as you can.

Make a drawing of both sides of your leaf in your notebook.Label as many parts as you can and write down your ideasdescribing each part’s function.

Compare your diagram and notes with those of your classmates.

WHAT DO YOU THINK?• What characteristics did most or

all of your leaves have?• How would you describe your leaf

to someone who could not see it?

3

2

1

MATERIALS• assorted leaves• hand lens

MIND MAPMake a mind map forthe first main idea:Plants are a diversegroup of organisms.

376 Unit 3: Diversity of Living Things

Plants share certain characteristics.Scientists estimate that at least 260,000 different species of plants liveon Earth today. The photographs on this page show three examples ofplants that are very different from one another.

Orchids are flowering plants that mostly grow in tropical rainforests. To get the sunlight they need, many orchids grow not in thesoil but on the trunks of trees. Horsetails are plants that produce tinygrains of a very hard substance called silica. Sometimes called scour-ing rushes, these plants were once used to scrub clean, or scour, dishesand pots. Bristlecone pine trees live on high mountain slopes in NorthAmerica, where there is little soil and often high winds. These treesgrow very slowly and can live for several thousand years.

You can see from these three examples that plant species showgreat diversity. Despite how different an orchid is from a horsetail anda bristlecone pine, all three plants share certain characteristics. Theseare the characteristics that define a plant as a plant:

• Plants are multicellular organisms.

• A plant cell has a nucleus and is surrounded by a cell wall.

• Plants are producers. They capture energy from the Sun.

• Plant life cycles are divided into two stages, or generations.

Check Your Reading What characteristics are shared by all plants?

Diversity of Plants

Horsetails have a distinctiveshape and texture.

Horsetails

reminder

The word species comesfrom a root word meaning“kind” or “type.” In science, species is a classification for a group oforganisms that are so similar that members of thegroup can breed and produce offspring that canalso reproduce.

Plant species live in a variety of environments and have a wide range of features.

Seed pods of the vanilla orchid are used to flavor food.

Orchids Bristlecone Pine

Bristlecone pines are some ofthe oldest trees on Earth.

re

Chapter 11: Plants 377

Plant parts have special functions.You could say that a plant lives in two worlds. The roots anchor a plant in the ground. Aboveground, reaching toward the Sun, are stemsand leaves. Together, stems and leaves make up a shoot system. Thesetwo systems work together to get a plant what it needs to survive.

A plant’s root system can be as extensive as the stems and leavesthat you see aboveground. Roots absorb water and nutrients from thesoil. These materials are transported to the leaves through the stems.The leaves use the materials, along with carbon dioxide from the air,to make sugars and carbohydrates. The stems then deliver these energy-rich compounds back to the rest of the plant.

C heck Your Reading What are two plant systems, and what are their functions?

Transporting Water and Other MaterialsStems serve as the pathway for transporting water, nutrients, andenergy-rich compounds from one part of a plant to another. Inmost plants, the materials move through a(VAS-kyuh-lur) that is made up of long, tubelike cells. These tissues are bundled together and run from the roots to the leaves.A vascular bundle from the stem of a buttercup plant is shown.

Transport is carried out by two types of tissue. Xylem (ZY-luhm)is a tissue that carries water and dissolved nutrients up from the roots.Phloem (FLOH-em) is a tissue that transports energy-rich materialsdown from the leaves. Xylem cells and phloem cells are long and hollow,like pipes. The xylem cells are a little larger than the phloem cells. Bothtissues include long fibers that help support the plant body, as well ascells that can store extra carbohydrates for energy.

vascular system

reminder

Plants, like animals, haveseveral levels of organiza-tion. The root system andshoot system are organ systems.

Vascular System

Sugar is produced in theleaves and transporteddownward to other parts of the plant.

Water and nutrientsenter through the roots andare transported upward tothe rest of the plant.

phloem

xylem

The vascular system transports materials throughout a plant’s body.

This vascular bundle hasbeen magnified 113�.

stems

leaves

roots

378 Unit 3: Diversity of Living Things

Making SugarsPlants produce sugars through the process of photosynthesis.Photosynthesis is a series of chemical reactions that capture lightenergy from the Sun and convert it into chemical energy stored insugar molecules. The starting materials needed are carbon dioxide,water, and light. The end products are sugars and oxygen. The chemi-cal reactions for photosynthesis can be summarized like this:

carbon dioxide � water � sunlight → sugars � oxygen

Photosynthesis takes place in chloroplasts, structures that containchlorophyll. Chlorophyll absorbs the sunlight that the chloroplasts needto produce the reaction. Most chloroplasts in a plant are located in leafcells. As you can see from the illustration on page 379, the structure ofthe leaf is specialized for capturing light energy and producing sugar.

Check Your Reading What is photosynthesis, and why is it important?

The upper surface of the leaf, which is turned toward the Sun, haslayers of cells filled with chloroplasts. Vascular tissue located towardthe center of the leaf brings in water and nutrients and carries awaysugars and other carbohydrates. Tiny openings at the bottom of theleaf, called stomata (STOH-muh-tuh), lead to a network of tiny spaceswhere gases are stored. The carbon dioxide gas needed for photosyn-thesis comes in through the stomata, and oxygen gas moves out. Thisprocess is called gas exchange.

Controlling Gas Exchange and Water LossFor photosynthesis to occur, a plant must maintain the balance ofcarbon dioxide and water in its body. Carbon dioxide gas from the airsurrounding a plant enters through the stomata in its leaves. Open stomata allow carbon dioxide and oxygen to move into and out of theleaf. These openings also allow water to evaporate. The movement ofwater vapor out of a plant and into the air is called (TRAN-spuh-RAY-shuhn). Both sunlight and wind cause water inleaves to evaporate and transpire.

For photosynthesis to occur, a plant needs to have enough carbondioxide come in without too much water evaporating and movingout. Plants have different ways of maintaining this balance. The sur-faces of leaves and stems are covered by a waxy protective layer, calleda cuticle. The cuticle keeps water from evaporating. Also, when the airis dry, the stomata can close. This can help to prevent water loss.

Check Your Reading What are two ways plants have to keep from losing too much water?

transpiration

Open Stomata

Closed Stomata

214�

reminder

Remember what youlearned about the impor-tance of photosynthesis incell functions in Chapter 6.

Content ReviewFLORIDA

Inside a Leaf

The leaf is an organ that produces sugars.It is made up of different types of cellsand tissues.

How is the top of a leaf different from the bottom of a leaf?

Cells at the surface producea waxy cuticle that keepsthe leaf from losing water.

Carbon dioxide, oxygen,and water vapor moveinto and out of the leafthrough stomata.

Most chloroplasts arelocated in cells of theupper layer of the leaf.

Xylem transports water and nutrients up from the roots.

Chapter 11: Plants 379

Phloem transports energy-richcompounds made in the leafdown to other parts of the plant.

380 Unit 3: Diversity of Living Things

The stomata are an adaptation that allows aplant to adjust to daily changes in its environment.Plants can respond to hot, dry weather by keepingtheir stomata closed. Stomata can be open duringthe night, when evaporation is less likely to occur.Most plants have stomata.

Some species of plants have special adaptationsfor survival in a particular environment. For exam-ple, a cactus plant has adaptations that allow it tosurvive in a desert. The spines of a cactus are actu-ally modified leaves. A plant with regular leaveswould lose too much water through transpiration.In cacti, most photosynthesis occurs in the thickfleshy stem, where the cactus also stores water andcarbon dioxide gas.

Plants grow throughout their lifetimes.Plants grow as long as they live. This is true for plants that live foronly one season, such as sunflowers, and for plants that can live formany years, such as trees. Plants grow bigger when cells at the tips oftheir roots and stems divide and multiply more rapidly than otherplant cells do. A plant’s roots and stems can grow longer and thickerand can branch, or divide. However, only stems grow leaves. Leavesgrow from buds produced by growth tissue in a plant’s stems. The budof an oak tree is shown on page 381.

Plant stems are structures with more than one function. You haveread that a plant’s stem includes its vascular system, which allows theplant to transport materials between its leaves and roots. Long stifffibers in the tissues of the vascular system provide support and givethe plant shape. Plant stems can also store the sugars produced byphotosynthesis. Many plants, including broccoli, celery, and carrots,convert sugars into starch and then store this energy-rich material intheir stems or roots.

Check Your Reading What are three functions of plant stems?

Plants with Soft StemsThe soft stems and leaves of many wildflowers, garden flowers, andvegetables die when the environment they live in becomes too cold ortoo dry. This type of plant survives by using the carbohydrates storedin its roots. Then, when the environment provides it with enoughwarmth, water, and sunlight, the plant will grow new, soft, green stemsand leaves.

spines

stem

APPLY Plant stems branchas they grow. Do cactusplants have branches?

RESOURCE CENTERCLASSZONE.COM

Learn more about plantsystems.

Plants with Woody StemsSome plants, such as trees and shrubs, have tough, thick stems that donot die each year. These stems keep growing longer and thicker. As thestems grow, they develop a type of tough xylem tissue that is not foundin soft stems. This tough xylem tissue is called wood. The growing tis-sues in woody stems are located near the outer surface of the stem, rightunder the bark. This means that, for a tree like one of the oaks in thephotograph above, the center of the trunk is the oldest part of the plant.

KEY CONCEPTS1. What characteristics do all

plants have in common?

2. How does the structure of aleaf relate to its function?

3. What tissues move materialsthroughout a plant?

CRITICAL THINKING4. Summarize Describe how the

structure of a leaf allows aplant to control the materialsinvolved in photosynthesis.

5. Analyze Do you think thestems of soft-stemmed plantshave chloroplasts? How aboutwoody-stemmed plants?Explain your reasoning. Hint:Think about the color of each.

CHALLENGE6. Evaluate Scientists who study

the natural world say thatthere is unity in diversity. Howdoes this idea apply to plants?

Chapter 11: Plants 381

Plants, such as these oak trees, grow most when there is enough warmth,water, and sunlight.

Plant Growth

The tips of the shoots pro-duce buds, which becomenew leaves and stems.

Oak Bud