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Chapter 22

Plant Diversity

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22–1 Introduction to Plants

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Objectives• Explain what a plant is

• Describe what plants need to survive

• Describe how plants first evolved

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What Is a Plant?• Plants are members of the

kingdom Plantae• Plants are multicellular eukaryotes

that have cell walls made of cellulose. They develop from multicellular embryos and carry out photosynthesis using the green pigments chlorophyll a and b

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The Plant Life Cycle• Plants have life cycles that are

characterized by alternation of generations

• the two generations are the haploid (N) gametophyte, or gamete-producing plant, and the diploid (2N) sporophyte, or spore-producing plant.

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What Plants Need to Survive

1. Sunlight

2. Water and Minerals

3. Gas Exchange

4. Movement of water and nutrients

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Early Plants• The first plants evolved

from an organism much like the multicellular green algae living today.

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The First Plants • The first true plants were still

dependent on water to complete their life cycles, similar to today’s mosses in that they were simple in structure and grew close to the ground.

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• From these plant pioneers, several major groups of plants evolved.

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Mosses

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Ferns

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Cone Bearing Plant

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Flowering plant

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Overview of the Plant Kingdom

• Botanists divide the plant kingdom into four groups based on three important features:

1. Water conducting tissues

2. Seeds

3. Flowers

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22 – 2 Bryophytes a.k.a (Non-vascular plants)

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Objectives• Describe the adaptations of

Bryophytes

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bryophytes • Type of early plant with no

vascular tissue that draw water in their cells by osmosis.

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Moss

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Liverwort

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Hornwort

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• During at least one stage of their life cycle, bryophytes produce sperm that must swim through water to reach eggs of other individuals.

• Therefore, they must live in places where there is rainfall or dew for at least part of the year

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Sexual Reproductive/ Photosynthetic

Part

Asexual Reproductive Part

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22–3 Seedless Vascular Plants

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Objectives• Explain how vascular tissue is

important to ferns and their relatives

• Describe the three phyla of spore-bearing plants

• Identify the stages in the cycle of ferns

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• In just a few million years, plants grew to a whole new scale on the landscape.

Q: What caused this increase in size?

A: Vascular Tissue

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Vascular tissue • A type of tissue that is specialized

to conduct water and nutrients through the body of the plant

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Evolution of Vascular Tissue

• Both forms of vascular tissue—xylem and phloem—can move fluids throughout the plant body, even against the force of gravity.

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Xylem

• Carry water upwards from the roots to every part of the plant

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Phloem• Transports nutrients and

carbohydrates produced by photosynthesis from the leaves down to the roots

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• Vascular plants also evolved the ability to produce lignin, a substance that makes cell walls rigid.

• The presence of lignin allows vascular plants to grow upright and tall

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Ferns and Their Relatives

• Seedless vascular plants include club mosses, horsetails, and ferns.

• Like other vascular plants, ferns and their relatives have true roots, leaves, and stems.

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Roots• Absorb water

and minerals

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Leaves• Collect light for photosynthesis

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Veins • Made of xylem and phloem

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Stems • Used for

support, connect roots and leaves, carry water between them

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Club Mosses 

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Horsetails

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Ferns

Underground Stem

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22 – 4 Seed Plants

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Objectives• Describe the reproductive

adaptations of seed plants

• Describe the evolution of seed plants

• Identify the four groups of gymnosperms

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• Over millions of years, plants with a single trait—the ability to form seeds—became the most dominant group of photosynthetic organisms on land.

• Seed plants are divided into two groups:

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Gymnosperms

• Cone plants

• Bear their seeds directly on the surfaces of cones

Ex.) conifers, pines, spruces, cycads, ancient ginkgoes and gnetophytes

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Angiosperms• Flowering plants

• Bear their seeds within a layer of tissue that protects the seed

Ex.) grasses, flowering trees shrubs, wild flowers

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Reproduction Free From Water• Unlike mosses and ferns, however, seed

plants do not require water for fertilization of gametes.

Q: Why was this an advantage? A: They could live further away from water• Adaptations that allow seed plants to

reproduce without water include flowers or cones, the transfer of sperm by pollination, and the protection of embryos in seeds.

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Cones and Flowers

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Cones• Seed bearing structures of

gymnosperms

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Flowers

• Seed bearing structures of angiosperms

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Pollen

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Pollen grain • Contains the male gamete

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Pollination

• The transfer of pollen from the male gametophyte to the female gametophyte

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Seeds

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seed

• An embryo of a plant that is encased in a protective covering and surrounded by a food supply

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embryo• Early development stage of a

sporophyte plant

• The seed’s food supply provides nutrients to the embryo as it grows

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Seed Coat• Surrounds and protects the

embryo and keeps the contents of the seed from drying out

• Can be specialized for dispersal

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Evolution of Seed Plants• Over a period of millions of years,

continents became much drier, making it harder for seedless plants to survive and reproduce.

• For that reason, many moss and fern species became extinct. They were replaced by seed plants with adaptations that equipped them to deal with drier conditions.

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Gymnosperms—Cone Bearers

• The most ancient surviving seed plants are the gymnosperms.  

• Gymnosperms include:

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Gnetophytes

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Cycads

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Ginkgos

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Conifers

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22–5 Angiosperms - Flowering Plants

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Objectives• Identify the characteristics of

angiosperms

• Explain what monocots and dicots are

• Describe the three different life spans of angiosperms

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• Flowering plants originated on land and quickly came to dominate Earth’s plant life.

• The vast majority of living plant species reproduce with flowers.

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Flowers and Fruits• Angiosperms have unique

reproductive organs known as flowers.

Q: Why are flowers evolutionary adaptations?

A: they attract animals that pollinate them

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• Flowers contain ovaries, which surround and protect the seeds

• After pollination, the ovary develops into a fruit, which protects the seed and aids in its dispersal.

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Fruit • Ripened ovary, thick wall of tissue

that surrounds the seed

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Diversity of Angiosperms

• The angiosperms are an incredibly diverse group. Not surprisingly, there are many different ways of categorizing these plants.

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Monocots and Dicots• Monocots and dicots are named

for the number of seed leaves, or cotyledons, in the plant embryo. Monocots have one seed leaf, and dicots have two seed leafs

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Woody and Herbaceous Plants 

• Woody plants – Have woody stems

Ex.) trees, shrubs, vines

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Herbaceous Plants • Plant stems that are smooth and

nonwoody

Ex.) dandelions, petunias, and sunflowers

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Annuals, Biennials, and Perennials 

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Annuals

• Angiosperms that complete a life cycle within one growing season

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Biennials

• Angiosperms that complete their life cycle in two years

• In the first year, biennials germinate and grow roots, stems, leaves

• During their second year, biennials grow new stems and leaves and then produce flowers and seeds

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Perennials • Flowering plants that live for more

than two years