Chapter 22 Lecture Outline See PowerPoint Image Slides

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Chapter 22

Lecture OutlineSee PowerPoint Image Slidesfor all figures and tables pre-inserted intoPowerPoint without notes.

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What is a plant?

Eukaryotic Multicellular Contains chlorophyll a and b Carries on photosynthesis Has cellulose cell walls Lives in a variety of terrestrial habitats

– And a few shallow aquatic habits Exhibits alternation of generations


Plant Diversity


Alternation of Generations A life cycle that involves two generations

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

the gametophyte generation.– Gametophyte generation

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

generation.


Alternation of Generations


The Evolution of Plants

Photosynthetic algae are thought to be the ancestors of plants.– Green algae have the same types of chlorophyll.– There is extensive DNA homology between plants

and green algae. The evolution of plants shows two trends.

– Toward greater specialization for living in a dry environment

– Toward a more prominent sporophyte generation


The Evolution of Plants

Primitive plants– Lack vascular tissue to carry water– Have flagellated sperm; no seeds– Have to live in moist habitats– Have dominant gametophyte generation

More advanced plants– Have specialized cells that transport water– Have seeds that do not require water for distribution– Have dominant sporophyte generation


The Taxonomy of Plants


Nonvascular Plants Include

– Mosses, hornworts, liverworts Known as the bryophytes Common features

– Lack vascular tissue Use diffusion and osmosis to obtain water and nutrients

– Do not have true roots or leaves– Gametophyte is dominant– Sperm swim to egg

Must have water to reproduce sexually– Are small and confined to moist habitats


Moss Life Cycle

http://www.youtube.com/watch?v=jcWYAnmm-QE





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

– Each cell contains one large chloroplast.

Non-vascular plants

http://www.youtube.com/watch?v=kBPLKUTtXBM





The Significance of Vascular Tissue Vascular tissue is an adaptation to living in dry

environments.– Allows plants to transport water and nutrients throughout

the plant– Associated with the development of

Leaves for photosynthesis Roots for absorbing water and minerals

– Vascular tissue allowed for an increase in plant size– Accompanied by the appearance of a waterproof coating on

the plant surfaces Two types of vascular tissue

– Xylem– Phloem


Xylem

A series of dead, hollow cells that form tubes– Vessel elements

Form long tubes with cells end-to-end– Tracheids

Tapered cells with holes Overlap to form a sieve-like tube

The walls of these cells are strengthened by cellulose and lignin.

Transports water and minerals from the soil to the leaves


Xylem


Phloem

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

– Sugar– Amino acids

Consists of two types of cells– Sieve-tube elements

Lack a nucleus and organelles, but have cytoplasm Have holes in the end walls for the transport of material

– Companion cells Actively transport sugars and amino acids out of the leaf cells

and into the sieve-tube elements


Phloem

Video Xylem and phloem

http://www.youtube.com/watch?v=J1PqUB7Tu3Y





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.


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

– Explore new areas of soil for water and nutrients– Root tips have root hairs that increase their absorptive

surface. Can be important storage sites

– Many plants store carbohydrates in their roots during growing season to be used during the winter.

– Carrots, turnips, radishes, maple trees, rhubarb, grasses


Kinds of Roots


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 Vary greatly in diameter and length

– Tree trunks are large and support branches.– Dandelion stems are short.– Some stems are underground.


Stems

The structure of cell walls allows the stem to support the leaves.– Cell walls are made of cellulose interwoven into a

box. When cells are full of water, the cell walls will not

stretch. This makes the cells turgid, stiff and able to support

weight.– Woody plants have especially thick cell walls.

These have lignin in them. Allows woody plants to grow tall and withstand wind


Stems

Stems contain a lot of vascular tissue.

Stems also– Store food

Sugar cane Yams Potatoes

– Photosynthesize– Have waterproof layers

Can be waxy or woody


Leaves

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

Water and minerals needed for photosynthesis into the leaf

The sugar that is made out of the leaf– Thick cell walls for support– Are arranged to minimize shading of lower leaves


The Structure of a Leaf


Leaves

Specialized for photosynthesis– Covered by a waxy coating to minimize water loss

Water evaporates from leaves through transpiration.– Pulls water and nutrients up from the roots– Transpiration must be regulated so plant doesn’t

lose too much water.– Water and oxygen exit, and carbon dioxide enters,

through stomata.


Stomates


Seedless Vascular Plants

Include– Whisk ferns– 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


Fern Life Cycle


Kinds of Seedless Vascular Plants

Ferns– Most common seedless

vascular plant Whisk ferns

– Lack roots and leaves– Anchored by an

underground stem Modifications of the

stem serve the functions of roots and leaves.


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– Usually evergreen– Low-growing, branching plants– Some are called ground pines.


Seed-producing Vascular Plants

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.– Aid in dispersal

Gymnosperms and angiosperms produce seeds. Accompanied by the development of pollen

– Encased sperm (male gametophyte generation)– Allows plants to reproduce without water


Gymnosperms

Means “naked seed” Woody, perennial

plants Produce seeds that are

not enclosed (naked)– Produce seeds in cones


The Pine Life Cycle


Kinds of Gymnosperms

Cycads– Wood 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


Kinds of Gymnosperms

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

leaves Do shed needles throughout the year

– Used in the production of lumber


Several Gymnosperms


Angiosperms

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

– A modification of the ovary wall


Flower Structure

Composed of highly modified leaves– Petals are usually colorful.– Sepals surround petals– Petals and sepals are arranged in whorls.

Specialized for sexual reproduction Female parts in the center

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


Flower Structure

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

Anther produces sperm.

Perfect flowers have both pistils and stamens.

Imperfect flowers have either pistils or stamens.


Flower Structure


The Life Cycle of a Flowering Plant


Pollination Strategies

Wind– Plants with inconspicuous flowers are usually

wind-pollinated.– Produce large numbers of flowers and pollen– Many species are wind-pollinated.

Grasses and sedges Aspens, birches and oaks

– Responsible for hay fever Some people have allergic reactions to pollen.


Strategies for Pollination

Animals– Plants with showy flowers are usually animal-

pollinated. These flowers usually produce nectar. Also smell good to attract animals

– Flowers attract insects, birds and small mammals.– The animals feed on the nectar and pick up the

pollen. Then move to another plant for more nectar, transferring

the pollen


Wind- and Insect-pollinated Flowers


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.


Types of Fruits


Angiosperm Diversity

Classified as either monocots or dicots– Refers to the number of cotyledons found in the

seeds of the species Monocots have one cotyledon (peanut). Dicots have two cotyledons (lima bean).

– Cotyledons (seed leaves) store food for the growing embryo.

They emerge as the first leaves.


Embryos in Dicots and Monocots


Monocots vs. Dicots


Angiosperm Diversity

Monocots– Yuccas and palms are woody.– The rest are herbaceous.

Wheat, rice, corn, sweet potatoes, onions, bananas

Dicots– Mints, carrots, cabbages, mustards, tomatoes and

potatoes are herbaceous dicots.– Aspen and sagebrush are woody dicots.

These are deciduous.


Deciduous Trees Lose their leaves once

a year– Occurs in the fall before

they go dormant The bark of the tree is

the phloem.– Produce a new layer of

xylem and phloem each year

– Therefore, the trunk increases in diameter each year.


Growth of Woody Plants

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

Growth occurs at the tips of the roots and stems.


Growth of Woody Plants

Grow in diameter by adding new xylem and phloem to the outside of the stem– Vascular cambium is made of xylem in the middle

and phloem around the perimeter (bark) Between the xylem and phloem is the cambium.

– The cambium is responsible for lateral growth. Cambium cells go thought mitosis, making two cells. One cell remains cambium; the other cell forms vascular

tissue.– As the xylem accumulates, it becomes wood.


A Cross Section of Woody Stem


Plant Responses to their Environment

Plants are constantly changing in response to changes in their environment.– They produce flowers at certain times of year.– Grow toward the light– Can mount an attack against a competitor


Tropisms

Growth toward or away from a stimulus Phototropism

– Growing toward light– Involves a hormone called auxin

The tip of the stem produces auxin– Transported into the stem on the shaded side– Stimulates cells on that side to divide and elongate– Causes the stem to bend toward the light


Phototropism


Tropisms

Thigmotropism– Climbing vines can wrap around an object using

tendrils.– Tendrils wave about and when they touch an

object, they wrap around it.– Once attached, the tendrils harden.– Sweet peas, grape vines and ivy exhibit

thigmotropism.


Thigmotropism


Seasonal Responses Plants can measure the length of the day.

– In response to day length, plants make hormones that trigger development of fruit or flowers.

– In deciduous trees, shortening days triggers leaves to fall off.

Plants can sense changes in temperature.– In dormant plants, warming of the soil triggers above

ground growth. Plants can sense the amount of water.

– During dry seasons, certain plants will lose their leaves and go dormant.

– When it begins to rain, these plants begin to grow and flower.


Response to Injury

Plants are attacked by pathogens and herbivores.

Plants can fight infection and repair damage by forming scar tissue.

Plants defend themselves against predation.– By producing toxins that interfere with herbivores’

metabolism– Once leaves are eaten, the new leaves produce

even more toxin.


Coevolution of Plants and Animals Plants evolved before animals.

– Insects and amphibians followed terrestrial plants. 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.

Chapter 22 Lecture Outline See PowerPoint Image Slides

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