22-1

Chapter 22

Lecture Outline

22-2

What Is a plant?

Eukaryotic Multicellular Photosynthetic Contains chlorophyll a and b Has cellulose cell walls Live in a variety of terrestrial habitats

– And a few shallow aquatic habits

Exhibits alternation of generations

22-3

Plant Diversity

22-4

Alternation of Generations

A life cycle that involves two generations1. Sporophyte generation

Diploid Undergoes meiosis to generate haploid spores Spores germinate and divide by mitosis to give rise to

a haploid gametophyte generation.

2. Gametophyte generation Haploid generation Undergoes mitosis to produce haploid gametes Gametes unite to form a zygote. Zygote divides by mitosis to form the sporophyte

generation.

22-5

Alternation of Generations

22-6

The Evolution of Plants

Freshwater green algae are thought to be the ancestors of plants.– Green algae have the same types of chlorophyll.– There is great similarity in the DNA of green algae

and plants. The evolution of plants shows two trends.

– Toward greater specialization for living in a dry environment

– Toward a more prominent sporophyte generation

22-7

The Evolution of Plants

Primitive plants– Lack vascular tissue to carry water– Usually live in moist situations– Have dominant gametophyte generation

More advanced plants– Have specialized cells that transport water– Typically live in dryer situations– Have dominant sporophyte generation

22-8

The Evolution of Plants

22-9

Nonvascular Plants

Commonly known as the bryophytes

Include– Mosses, hornworts, liverworts

Common features– Lack vascular tissue– Do not have true roots or leaves– Gametophyte is dominant– Sperm swim to egg– Are small and confined to moist

habitats

22-10

Moss Life Cycle

22-11

Kinds of Nonvascular Plants

Mosses– Grow as a carpet of many individual

gametophyte plants– Each individual is less than 5 cm tall.

Liverworts and hornworts– Form flat sheets only a few cells thick– Cells of hornworts only contain one

large chloroplast.

22-12

The Significance of Vascular Tissue

Vascular tissue allows plants to transport water and nutrients throughout the plant

Vascular tissue is associated with development of – Leaves for photosynthesis – Stems for positioning leaves and transporting materials– Roots for absorbing water and minerals– An increase in plant size– The appearance of a waterproof coating on the plant

surfaces Two types of vascular tissue

– Xylem– Phloem

22-13

Xylem

A series of dead, hollow cells that form tubes

Transports water and minerals from the soil to the leaves

22-14

Xylem

22-15

Phloem

Carries organic molecules produced in the leaves to the rest of the plant

– Sugar– Amino acids

22-16

Phloem

22-17

The Development of Roots, Stems, and Leaves

The appearance of vascular tissue allowed for the development of specialized plant parts.

Roots are specialized for absorption.

Stems are specialized for transport.

Leaves are specialized for photosynthesis.

22-18

Roots

Underground parts of a plant that – Anchor in the soil– Absorb water and nutrients

Move the nutrients into the vascular system

Grow from the tips Important storage sites for food

22-19

Stems

Above-ground structures that

– Support the leaves– Transport raw material

from the roots to the leaves

– Transport manufactured material from the leaves to other parts of the plant

The Love TreeRAY: This was sent to us by Bob Powers from Shreveport, LA. Here it is.A teenage boy smitten with a teenage girl in his high school freshman class, made his feelings known. Overjoyed at finding them reciprocated, he took pen knife to a young hard wood in the vicinity and carved their initials within a heart, five feet up the tree's trunk. TOM: I see the puzzler already. RAY: By their senior year, however, the girl's ardor had cooled. She took her diploma, went away to the big city and married. The boy was crushed, inconsolable. Bidding his family farewell, he took his small savings that he got from selling lemonade, bought a bus ticket, went to the east coast and shipped out in a menial job on a broken down freighter. Twenty-five years later, captain of his own vessel, owner of a small freighter fleet and with a major interest in a few oil tankers, he indulged in a nostalgic whim and returned for the first time ever, to his old hometown. Imagine his joy, when he discovered his old sweetheart living there, now a widow.One thing led to another. The flame reignited, and one day they searched for their tree. It was not hard to find. It was near a rock, near a river, and they immediately found it. Now, here's the puzzler. If the tree had added 35% to its height in the first 15 years of his absence, 10% in the following in the five years and 2.5% in the ensuing eight years, how far up the trunk did they have to look to find the carving with their initials?  Think you know? Drop Ray a note!

22-20

Leaves

Specialized for photosynthesis– Have large surface area to collect sunlight– Relatively thin to allow light penetration– Have bundles of vascular tissue to support

leaf tissue and provide transport Water and minerals transported to the leaf Sugar produced by photosynthesis from the

leaf

– Are arranged to minimize shading of lower leaves

– Covered by a waxy coating to minimize water loss

22-21

The Structure of a Leaf

22-22

Leaves

Transpiration, stomates, and photosynthesis– Transpiration involves several processes

Water evaporates and exits leaves through stomates.

– Role of stomates Stomates must be open to allow water and oxygen to exit, and

carbon dioxide to enter leaves and allow for photosynthesis. Stomates can close to regulate water loss in drought or during

dry part of the day

22-23

Stomates

22-24

Seedless Vascular Plants

Include– Horsetails– Club mosses– Ferns

Have vascular tissue– Are not limited to aquatic environments

Do not have seeds– Have flagellated sperm– Must have moist conditions to reproduce

22-25

Fern Life Cycle

22-26

Kinds of Seedless Vascular Plants

Ferns– Most common

seedless vascular plant

22-27

Kinds of Vascular Seedless Plants

Horsetails– Low-growing plants with jointed stems– Most photosynthesis occurs in the stems.– Have silicon dioxide in their cell walls

Called (and used as) scouring brushes by pioneers

Club mosses

22-28

Seed-Producing Vascular Plants

Gymnosperms and angiosperms produce seeds.

A seed is a specialized structure that contains

– An embryo – Stored food– A protective outer coating (seed coat) that

prevents drying Seeds allow plants to live in dry habitats.

– Germinate and grow when conditions are right

– Aid in dispersal

22-29

Gymnosperms

Gymnosperm means “naked seed”.

Produce seeds that are not enclosed (naked)

– Produce seeds in cones

Woody, perennial plants

22-30

The Pine Life Cycle

22-31

Kinds of Gymnosperms

Cycads– Woody plants with a ring of

fern-like leaves at the top– Live in tropical regions

Ginkgo– Ginkgo biloba is the only living

species.– A tree with fan-shaped leaves

Used in many herbal medicines

22-32

Kinds of Gymnosperms

Conifers– Trees and shrubs that bear cones– Have needle-shaped leaves– Called evergreens because they do not lose their

leaves all at one time Do shed needles throughout the year

– Used in the production of lumber

22-33

Several Gymnosperms

22-34

Angiosperms

Produce flowers Have vascular tissue, seeds, and pollen Have seeds enclosed in a fruit

– A modification of the ovary wall

22-35

Flower Structure

Composed of highly modified leaves– Petals and sepals surround pistils and

stamens.– Petals and sometimes sepals are large

and showy in insect-pollinated plants.– Flowers of insect-pollinated plants typically

produce nectar and odors to attract insects.

– Much variation in structure of flowers

22-36

Flower Structure (continued)

Specialized for sexual reproduction– Female parts in the center

Pistil (stigma, style, and ovary)– Ovary produces eggs

– Male parts surround the pistil. Stamens (filament and anther)

– Anther produces pollen which contains sperm nucleus.

– Perfect flowers have both pistils and stamens.– Imperfect flowers have either pistils or stamens.

22-37

Flower Structure

22-38

The Life Cycle of a Flowering Plant

22-39

Pollination Strategies

Wind pollination– Plants with inconspicuous flowers are usually

wind-pollinated.– Produce many flowers and much pollen

Grasses and sedges Many trees such as aspens, birches, and oaks

– Responsible for hay fever Some people have allergic reactions to certain kinds

of pollen.

22-40

Strategies for Pollination

Animal pollination– Plants with showy flowers are usually animal-pollinated.– Flowers attract insects, birds, and small mammals.

These flowers usually produce nectar. Also produce odors that attract animals

– The animals feed on the nectar and pick up the pollen. Then move to another plant for more nectar, transferring

the pollen

22-41

Wind- and Insect-Pollinated Flowers

22-42

Fruit

A modification of the ovary that contains seeds Involved in dispersal of seeds Many fruits are nutritive to animals.

– The animals eat the fruit and ingest the seeds.– The seeds pass through the digestive tract unharmed

and get “planted” in the animals’ feces.

Other fruits burst open and release light seeds that are dispersed by wind.

Other fruits have sticky surfaces that cling to animals that pass by.

22-43

Types of Fruits

22-44

Angiosperm Diversity

Classified as either monocots or dicots– Cotyledons (seed leaves) store food for the

growing embryo. They emerge as the first leaves.

– Monocot and dicot refers to the number of cotyledons found in the seeds of the species.

Monocots have one cotyledon (grasses, lilies, etc). Dicots have two cotyledons (beans, apples, etc).

22-45

Embryos in Dicots and Monocots

22-46

Monocots vs. Dicots

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

22-47

Growth of Woody Plants

All gymnosperms and many dicots are woody plants.

Woody plants are perennials that have the ability to grow continuously for many years.– They get taller and grow in diameter each year.

Growth in length occurs at the tips of the roots and stems.

Growth in diameter occurs by adding new xylem and phloem to the outside of the stem.

22-48

Phototropism

22-49

Coevolution of Plants and Animals

The first terrestrial organisms were plants. Insects and amphibians were the terrestrial

animals. Symbiotic relationships evolved between plants and

animals.– Many flowering plants are pollinated by insects and birds.

These flowers are brightly colored, have nectar, and have odor.

– Grasses and grazers have coevolved. Grass has silicon that wears down grazers’ teeth. Grazers have very long teeth that take a long time to wear down.

– Many angiosperms produce nutritive fruit. Animals eat the fruit and distribute the seeds.