Download I. Plants in Our Lives Objectives: • Summarize how plants are

HOLT BIOLOGY
UNIT 6-EXPLORING PLANTS
CHAPTER 23
INTRODUCTION TO PLANTS
I. Plants in Our Lives
Objectives:
• Summarize how plants are adapted to living on land.
• Distinguish nonvascular plants from vascular plants.
• Relate the success of plants on land to seeds and flowers.
• Describe the basic structure of a vascular plant sporophyte.
A. Establishment of Plants on Land
1. Plants are the dominant group of organisms on land, based on weight.
a. Plants probably evolved from multicellular aquatic green algae that could not survive on land.
b. Before plants could thrive on land, they had to be able to do three things:
i. absorb nutrients from their surroundings.
ii. prevent their bodies from drying out.
iii. reproduce without water to transmit sperm.
2. Absorbing Nutrients
a. Aquatic algae and plants take nutrients from the water around them.
b. On land, most plants take nutrients from the soil with their roots.
c. Botanists think that fungi may have helped early land plants to get nutrients from Earth’s rocky
surface.
d. Symbiotic relationships between fungi and the roots of plants are called mycorrhizae.
3. Preventing Water Loss
a. A watertight covering, which reduces water loss, made it possible for plants to live on land.
b. This covering, called a cuticle, is a waxy layer that covers the non-woody aboveground parts of
most plants.
c. Pores called stomata permit plants to exchange oxygen and carbon dioxide.
d. A pair of specialized cells called guard cells border each stoma.
e. Stomata open and close as the guard cells change shape.
4. Reproducing on Land
a. In most plants, sperm are enclosed in a structure that keeps them from drying out.
b. The structures that contain sperm make up pollen.
c. Pollen permits the sperm of most plants to be carried by wind or animals rather than by water.
B. Vascular Tissue, Seeds, and Flowers
1. Advantages of Conducting Tissue
a. Specialized cells that transport water and other materials within a plant are found in vascular
tissues.
b. The larger, more-complex plants have a vascular system, a system of well-developed vascular
tissues that distribute materials more efficiently.
c. Relatively small plants that have no vascular system are called nonvascular plants.
d. Plants that have a vascular system are called vascular plants.
2. Advantages of Seeds
a. A seed is a structure that contains the embryo of a plant.
b. An embryo is an early stage in the development of plants and animals.
c. Most plants living today are seed plants-vascular plants that produce seeds.
d. Seeds offer a plant several survival advantages:
i. The seed coat protects the embryo from drying out, injury, and disease.
ii. M most kinds of seeds store a supply of nutrients.
iii. Seeds disperse the offspring of seed plants.
iv. Seeds make it possible for plant embryos to survive through unfavorable periods such as
droughts.
3. Advantages of Flowers
a. The last important adaptation to appear as plants evolved was the flower, a reproductive structure
that produces pollen and seeds.
b. Most plants living today are flowering plants-seed plants that produce flowers.
c. Flowering plants that are pollinated by animals produce less pollen, and cross-pollination can
occur between individuals that live far apart.
C. Plant Life Cycles
1. Plants have life cycles in which haploid plants that make gametes (gametophytes) alternate with
diploid plants that make spores (sporophytes).
a. A life cycle in which a gametophyte alternates with a sporophyte is called alternation of
generations.
b. Unlike the green algae with alternation of generations, plants have gametophytes and
sporophytes that look very different.
2. The Vascular-Plant Sporophyte
a. The sporophytes of vascular plants have a vascular system with two types of vascular tissue.
b. Relatively soft-walled cells transport organic nutrients in a kind of tissue called phloem.
c. Hard-walled cells transport water and mineral nutrients in a kind of tissue called xylem.
3. The part of a plant’s body that grows mostly upward is called the shoot.
a. In most plants, the part of the body that grows downward is called the root.
b. Zones of actively dividing plant cells, called meristems, produce plant growth.
II. Kinds of Plants
Objectives:
• Describe the key features of the four major groups of plants.
• Classify plants into one of the 12 phyla of living plants.
A. Nonvascular Plants
1. Key Features of Nonvascular Plants
a. All nonvascular plants are small and relatively simple.
b. The gametophytes of nonvascular plants are larger and more noticeable than the sporophytes.
c. Hairlike projections called rhizoids anchor the gametophytes to the surfaces on which they grow.
2. Nonvascular plants must be covered by a film of water in order for fertilization to occur.
3. The mosses (phylum Bryophyta) are the most familiar nonvascular plants.
4. Like the mosses, liverworts (phylum Hepatophyta) grow in mats of many individuals.
a. Liverworts have no conducting cells, no cuticle, and no stomata.
b. The hornworts (phylum Anthocerophyta) are a small group of nonvascular plants that, like the
liverworts, completely lack conducting cells.
B. Seedless Vascular Plants
1. Vascular plants that do not produce seeds are called seedless vascular plants.
a. The earliest known seedless vascular plant, Cooksonia, had sporophytes that had branched,
leafless stems that were only a few centimeters long.
b. Rhynia, another early seedless vascular plant, had horizontal underground stems, or rhizomes.
2. Seedless vascular plants have a vascular system with both xylem and phloem.
a. The sporophytes of seedless vascular plants are larger than the gametophytes.
b. The spores of the seedless vascular plants have thickened walls that are resistant to drying.
3. The ferns (phylum Pterophyta) are the most common and most familiar seedless vascular plants.
a. Most fern sporophytes have a rhizome that is anchored by roots and leaves called fronds.
b. Unlike true mosses, the club mosses (phylum Lycophyta), have roots, stems, and leaves.
c. Some club mosses have clusters of nongreen spore-bearing leaves form a structure called a cone.
4. The vertical stems of horsetails, which grow from a rhizome, are hollow and have joints.
5. The whisk ferns (phylum Psilotophyta) probably most closely resemble the earliest vascular plants.
C. Gymnosperms
1. Gymnosperms are seed plants whose seeds do not develop within a sealed container (a fruit).
a. The word gymnosperm comes from the Greek words gymnos, meaning “naked,” and sperma,
meaning “seed.”
2. All gymnosperms produce seeds.
3. All seed plants produce very tiny gametophytes of two types—male and female.
a. The sperm of gymnosperms do not swim through water to reach and fertilize eggs.
b. Instead, the sperm are carried to the structures that contain eggs by pollen, which can drift on the
wind.
4. Kinds of Gymnosperms
a. The conifers (phylum Coniferophyta) are the most familiar, and most successful, gymnosperms.
b. The cycads (phylum Cycadophyta) have short stems and palmlike leaves.
c. The only living species of ginkgo (phylum Ginkgophyta), or maidenhair tree, has fan-shaped
leaves that resemble the leaves of the maidenhair fern.
5. The gnetophytes (phylum Gnetophyta) are a diverse group of trees, shrubs, and vines that produce
pollen and seeds in cones that resemble flowers.
D. Angiosperms
1. Most seed plants are flowering plants, or angiosperms.
a. Angiosperms produce seeds that develop enclosed within a specialized structure called a fruit.
b. The word angiosperm comes from the Greek words angeion, meaning “case,” and sperma,
meaning “seed.”
2. Key Features of Angiosperms
a. The male and female gametophytes of angiosperms develop within flowers, which promote
pollination and fertilization more efficiently than do cones.
b. Although fruits provide some protection for developing seeds, their primary function is to
promote seed dispersal.
c. The seeds of angiosperms have a supply of stored food called endosperm at some time during
their development.
3. Kinds of Angiosperms
a. Botanists divide the angiosperms into two subgroups—monocots and dicots.
b. The monocots are flowering plants that produce seeds with one seed leaf (cotyledon).
c. The dicots are flowering plants that produce seeds with two seed leaves.
III. Adaptations of Plants
Objectives:
• Identify foods that come from plants and their dietary importance.
• Describe several ways that wood is used.
• Explain how plants are used to treat human ailments.
• Identify plants that are used to make paper and cloth.
A. Plants as Food
1. Fruits and Vegetables
a. The United States government identifies food that comes from a plant as an agricultural
commodity.
b. To a botanist, a fruit is the part of a plant that contains seeds, and a vegetative part is any nonreproductive part of a plant.
c. Fruits and vegetables provide dietary fiber and are important sources of essential vitamins and
minerals.
2. Root Crops
a. Potatoes are classified as a root crop because they grow underground.
b. But, potatoes are actually tubers, modified underground stems that store starch.
c. Yams, an essential food crop in many tropical parts of the world, are also tubers.
3. Legumes
a. Many members of the pea family, which are called legumes, produce protein-rich seeds in long
pods.
b. Peas, peanuts, and the many different types of beans are the seeds of legumes.
c. Like many legumes, alfalfa has nitrogen-fixing bacteria, which add nitrogen compounds to the
soil, in its roots.
B. Cereals
1. Cereals are grasses that are grown as food for humans and livestock.
a. Cereal grasses produce large numbers of a type of edible, dry fruit called a grain.
b. A grain contains a single seed with a large supply of endosperm.
2. Wheat
a. For more than one-third of the world’s population, wheat is the primary source of food.
b. The endosperm of wheat grains, which is high in carbohydrates, is commonly ground into white
flour and used to make breads and pasta.
c. One of the world’s best wheat-growing areas is the Great Plains region of the United States and
Canada—a temperate grassland biome.
3. Corn
a. Corn is the most widely cultivated crop in the United States.
b. Corn is also one of the world’s chief foods for farm animals.
c. About 70 percent of the corn crop harvested in the United States is consumed by livestock.
d. Other uses for corn include the production of corn syrup, margarine, corn oil, cornstarch, and
fuel-grade ethanol.
4. Rice
a. For more than half of the people in the world, rice is the main part of every meal.
b. Although it is low in protein, rice is an excellent source of energy-rich carbohydrates.
c. In the United States, rice is grown in central California, in the Southeast, and along the Gulf
Coast in fields.
C. Nonfood Uses of Plants
1. Wood
a. After food, wood is the single most valuable resource obtained from plants.
b. Nearly 75 percent of the lumber cut in the United States is used for building construction.
c. The rest is used to make products that contain wood, or it is ground and moistened to make wood
pulp.
d. Wood pulp is made into paper, rayon, and many other products.
2. Medicines
a. People have always used substances obtained from plants to treat a variety of ailments.
b. By studying the plants traditionally used to treat human ailments, researchers have developed
many “modern” medicines.
c. For example, willow tree (Salix) bark was a traditional cure for aches.
d. Salicin is the pain-relieving chemical found in willows.
e. Acetylsalicylic acid, a derivative of salicin, was first sold under the name “aspirin.”
3. Fibers
a. In plants, fibers help provide support for the plant body.
b. The strength and flexibility of plant fibers make them ideal materials for making paper, cloth,
and rope.
c. Most of the fibers used to make paper come from wood.
d. For centuries, people have made clothing with cloth made of cotton, the world’s most important
plant fiber.