Plant Diversity

What is a Plant? 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

Plants are so different from animals that sometimes there is a tendency to think of them as not being alive However, plants are alive, everywhere, and

highly successful

The Plant Life Cycle Plants have life cycles that are characterized

by alternation of generations In this life cycle, the haploid gametophyte phase

alternates with the diploid sporophyte phase A gametophyte is a haploid, or gamete-

producing, phase of an organism A sporophyte is a diploid, or spore-producing,

phase of an organism

Alternation of Generations Life Cycle in Plants

What Plants Need to Survive The lives of plants revolve around the

need for: Sunlight Water & minerals Gas exchange Movement of water & nutrients throughout the

plant body

Evolution of Plants The first plants evolved from an organism much like

the multicellular green algae living today However, the evolution of plants favored species that were

more resistant to the drying rays of the sun

FloweringplantsCone-bearing

plantsFerns and

their relativesMosses and

their relatives

Green algaeancestor

Flowers; SeedsEnclosed in Fruit

Seeds

Water-Conducting(Vascular) Tissue

Overview of the Plant Kingdom The great majority of plants alive today are

angiosperms (the flowering plants)

Cone-bearing plants760 species

Ferns andtheir relatives11,000 species

Mosses andtheir relatives15,600 species

Floweringplants235,000 species

Figure 29.1 Some highlights of plant evolution

4 Main Groups of Land Plants Bryophytes: non-vascular plants

mosses, hornworts, and liverworts Pteridophytes: seedless vascular plants

Club moss, horsetails, ferns Gymnosperms: vascular seeded cone-

bearers Ginkgos, cycads, gnetophytes, conifers

Angiosperms: vascular seeded flowering plants Monocots & dicots – any plant, tree, or shrub that

flowers or fruits

The Nonvascular Plants - Bryophytes Mosses and their relatives are generally

called Bryophytes (nonvascular plants) THEY HAVE NO ROOTS, STEMS, OR

LEAVES They have a life cycle that depends on water

for reproduction They lack vascular tissue and therefore must

grow low to the ground Groups of Bryophytes include:

1. Mosses2. Liverworts3. Hornworts

Mosses The most common

bryophytes are mosses They grow abundantly in

areas with water They can tolerate cold

climates well They do not have true

roots, stems, or leaves – instead, they have rhizoids (long, thin cells) that anchor them to the ground

Liverworts Liverworts are Bryophytes that produce gametes in

structures that look like little green umbrellas during sexual reproduction Liverworts can also reproduce asexually by means of gemmae

(small cup-like spheres that contain haploid cells)

SEXUALASEXUAL

Hornworts Hornworts are generally found only in soil

that is damp nearly year round Their gametophytes look like those of

liverworts

Life Cycle of Mosshttp://www.sumanasinc.com/webcontent/animations/content/moss.html

Evolution of Plants

Floweringplants

Cone-bearingplants

Ferns andtheir relatives

Mosses andtheir relatives

Green algaeancestor

Flowers; SeedsEnclosed in Fruit

Seeds

Water-Conducting(Vascular) Tissue

BRYOPHYTES

Three variations on gametophyte/sporophyte relationships

Evolution of Vascular Tissue

What happened to allow plants to grow taller than mosses? Fossil evidence shows that these plants contained vascular

tissue – tissue that is specialized to conduct water and nutrients through the body of a plant

Vascular Tissue The first vascular plants had a new type of

cell that was specialized to conduct water Tracheids are the cells found in xylem, a form

of tissue that carries water upward from the roots to every part of a plant

Phloem transports solutions of nutrients and carbohydrates produced by photosynthesis

Lignin is a substance produced by plants that makes cell walls rigid

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

Seedless Vascular Plants - Pteridophytes Seedless vascular plants include:

1. club mosses2. horsetails 3. ferns

These plants HAVE true roots, leaves, and stems

ROOTS – underground organs that absorb water & minerals

LEAVES – photosynthetic organs STEMS – supporting structures that

connect roots and leaves

Club Mosses These are small plants that live in moist

woodlands and near streambeds and marshes Lycopodium is the most common club moss

today – it looks like a mini pine tree

Horsetails The only living genus of horsetails is

Equisetum Its leaves are arranged in distinctive whorls at

joints along the stem

Ferns Ferns are members of the phylum Pterophyta

They have creeping or underground stems called rhizomes and large leaves called fronds

They are most abundant in wet habitats – water is required for reproduction!

frond

roots

rhizome

The Life Cycle of a Fern

Fern sperm use flagellato swim from the antheridia to eggs in the archegonia.

4

Sporangia release spores.Most fern species produce a singletype of spore that gives rise to abisexual gametophyte.

1 The fern sporedevelops into a small,photosynthetic gametophyte.

2 Although this illustration shows an egg and sperm from the same gametophyte, a variety of mechanismspromote cross-fertilizationbetween gametophytes.

3

On the undersideof the sporophyte‘sreproductive leavesare spots called sori.Each sorus is acluster of sporangia.

6

A zygote develops into a newsporophyte, and the young plantgrows out from an archegoniumof its parent, the gametophyte.

5

MEIOSIS

Sporangium

Sporangium

Maturesporophyte

Newsporophyte Zygote

FERTILIZATION

Archegonium

Egg

Haploid (n)Diploid (2n)

Spore Younggametophyte

Fiddlehead

Antheridium

Sperm

Gametophyte

Key

Sorus

Figure 29.12

Fern Sori

Evolution of Plants

Floweringplants

Cone-bearingplants

Ferns andtheir relatives

Mosses andtheir relatives

Green algaeancestor

Flowers; SeedsEnclosed in Fruit

Seeds

Water-Conducting(Vascular) Tissue

Seedless Vascular Plants

BRYOPHYTES

Seed Plants Over millions of years, plants with the ability to

forms seeds became the most dominant group of photosynthetic organisms on land

Seed plants are divided into 2 groups:1. Gymnosperms – bear seed directly on cones

Conifers Cycads Ginkos Gnetophytes

2. Angiosperms – flowering plants that bear their seeds within a layer of tissue that protects the seed Grasses Flowering trees and shrubs All flowers

Reproduction Free From Water Adaptations that allow seed plants to

reproduce without water include flowers or cones

the transfer of sperm by pollination

the protection of embryos in seeds

Cones & Flowers The gametophytes of seed plants grow

and mature within sporophyte structures called cones or flowers Cones are the seed-bearing structures of

gymnosperms Flowers are the seed-bearing structures of

angiosperms

Pollen In seed plants, the entire

male gametophyte is contained in a tiny structure called a pollen grain The pollen grain is carried

to the female gametophyte by wind, insects, birds, small animals, or bats

The transfer of pollen from the male gametophyte to the female gametophyte is called pollination

Seeds A seed is an embryo of a plant that is

encased in a protective covering and surrounded by a food supply An embryo is the early developmental stage of

the sporophyte plant The seed coat surrounds and protects the

embryo and keeps the contents of the seed from drying out

After fertilization, the zygote contained within a seed grows into a tiny plant – the embryo

Seed coat

Embryo

Storedfood supply

Seed

Wing

A

B

Section 22-4The Structure of a Seed

Seed: embryo of plant that is wrapped in a protective covering and surrounded by a food supply.

Presence of a seed allows for reproduction free of water.

Gymnosperms – Cone Bearers Gymnosperms include:

Gnetophytes Cycads Ginkoes Conifers

Gnetophytes Welwitschia, an

inhabitant of the Namibian desert in southwestern Africa, is one of the most remarkable gnetophytes it has 2 huge

leathery leaves which can grow continuously and spread across the ground

Cycads Cycads are members of

the phylum Cycadophyta They are palm-like plants

that reproduce with large cones

They can be found in all tropical and subtropical zones around the world

Ginkgoes Today, the phylum Ginkgophyta contains

only one living species, Ginkgo biloba (the maiden-hair tree)

Cultivated and protected in China by monks

The male species of this tree is often planted in urban settings in the US, where their resistance to air pollution make them popular shade trees

The female tree smells like vomit

Conifers Conifers are by far the most common

gymnosperms The phylum Coniferophyta includes:

Pines Spruces Firs Cedars Sequoias Redwoods Yews

Conifers Conifers thrive in a wide variety

of habitats Mountains, sandy soil, cool, moist

areas Conifers have leaves that are

long and thin – which reduces the surface area from which water can be lost by evaporation

They also have a thick, waxy layer that covers their leaves – again to reduce water loss

Most conifers are “evergreens” – meaning they retain their leaves year round

Figure 30.6

Ovule

Megasporocyte (2n)

IntegumentLongitudinalsection ofovulate cone

Ovulatecone

Pollencone

Maturesporophyte(2n)

Longitudinalsection ofpollen cone

Microsporocytes(2n)

Pollengrains (n)(containing malegametophytes)

MEIOSIS

Micropyle

Germinatingpollen grain

Megasporangium

MEIOSIS

SporophyllMicrosporangium

Survivingmegaspore (n)

Germinatingpollen grain

ArchegoniumIntegumentEgg (n)

Femalegametophyte

Germinatingpollen grain (n)

Dischargedsperm nucleus (n)

Pollentube

Egg nucleus (n)FERTILIZATION

Seed coat(derived fromparentsporophyte) (2n)

Food reserves(gametophytetissue) (n)

Embryo(new sporophyte)(2n)

Seeds on surfaceof ovulate scale

Seedling

Key

Diploid (2n)Haploid (n)

The Life Cycle of a Pinehttp://bcs.whfreeman.com/thelifewire/content/chp30/30020.html

A pollen cone contains many microsporangia held in sporophylls. Each microsporangium contains microsporocytes (microspore mothercells). These undergo meiosis, giving rise tohaploid microspores that develop into pollen grains.

3

In mostconifer species,

each tree hasboth ovulate

and pollencones.

1

A pollen grainenters throughthe micropyleand germinates,forming a pollentube that slowlydigeststhrough themegasporangium.

4

While thepollen tubedevelops, themegasporocyte(megasporemother cell)undergoes meiosis,producing fourhaploid cells. Onesurvives as amegaspore.

5

The female gametophytedevelops within the megasporeand contains two or threearchegonia, each with an egg.

6

By the time the eggs are mature,two sperm cells have developed in thepollen tube, which extends to thefemale gametophyte. Fertilization occurswhen sperm and egg nuclei unite.

7

Fertilization usually occurs more

than a year after pollination. All eggs

may be fertilized, but usually only one

zygote develops into an embryo. The

ovule becomes a seed, consisting of an

embryo, food supply, and seed coat.

8

An ovulate cone scale has twoovules, each containing a mega-sporangium. Only one ovule is shown.

2

Evolution of Plants

Floweringplants

Cone-bearingplants

Ferns andtheir relatives

Mosses andtheir relatives

Green algaeancestor

Flowers; SeedsEnclosed in Fruit

Seeds

Water-Conducting(Vascular) Tissue

GymnospermsSeedless Vascular Plants

Bryophyta

Angiosperms – Flowering Plants Angiosperm means “enclosed seed” Angiosperms have unique reproductive organs

known as flowers Flowers attract pollinators, which makes spreading seeds

more efficient than the wind pollination of most gymnosperms

Flowers contain ovaries, which surround and protect the seeds After pollination, the ovary develops into a fruit, which

protects the seed and aids dispersal Fruit is a thick wall of tissue and another reason why

angiosperms are successful – the fruit attracts herbivores – which eat the fruit and then spread the seeds

Figure 30.10

Key

Mature flower onsporophyte plant(2n)

Ovule withmegasporangium (2n)

Female gametophyte(embryo sac)

Nucleus ofdevelopingendosperm

(3n)

Dischargedsperm nuclei (n)

Pollentube

Male gametophyte(in pollen grain)

Pollentube

Sperm

Survivingmegaspore(n)

Microspore (n) Generative cell

Tube cell

Stigma

OvaryMEIOSIS

MEIOSIS

Megasporangium(n)

Pollengrains

EggNucleus (n)

Zygote (2n)

Antipodal cellsPolar nucleiSynergidsEgg (n)

Embryo (2n)

Endosperm(foodSupply) (3n)

Seed coat (2n)

Seed

FERTILIZATION

Haploid (n)

Diploid (2n)

Anther

Sperm(n)

Pollentube

Style

Microsporangium

Microsporocytes (2n)

GerminatingSeed

Anthers contain microsporangia.Each microsporangium contains micro-sporocytes (microspore mother cells) thatdivide by meiosis, producing microspores.

1 Microspores formpollen grains (containingmale gametophytes). Thegenerative cell will divideto form two sperm. Thetube cell will produce thepollen tube.

2

In the megasporangiumof each ovule, themegasporocyte divides bymeiosis and produces fourmegaspores. The survivingmegaspore in each ovuleforms a female gametophyte(embryo sac).

3

After pollina-tion, eventuallytwo sperm nucleiare discharged ineach ovule.

4

Double fertilization occurs. One spermfertilizes the egg, forming a zygote. Theother sperm combines with the two polarnuclei to form the nucleus of the endosperm,which is triploid in this example.

5

The zygotedevelops into an

embryo that ispackaged alongwith food into aseed. (The fruit

tissues surround-ing the seed are

not shown).

6

When a seedgerminates, the

embryo developsinto a mature

sporophyte.

7

The Angiosperm Life Cyclehttp://www.sumanasinc.com/webcontent/animations/content/angiosperm.html

Diversity of Angiosperms Angiosperms are an incredibly diverse

group that includes: Monocots and dicots Woody and herbaceous plants Annuals, biennials, and perennials

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

Characteristics of Monocots & Dicots

Woody & Herbaceous Plants Flowering plants can be subdivided into

various groups according to the characteristics of their stems: Woody plants are made primarily of cells with

thick walls that support the plant body Trees Shrubs Vines

Herbaceous plants do not produce wood as they grow, but rather they have stems that are smooth

Dandelions Zinnias Petunias

Annuals, Biennials, Perennials There are 3 categories of plant life spans:

Annual – flowering plants that complete a life cycle within one growing season

Marigolds, pansies, zinnias, cucumbers

Biennial – flowering plants that complete their life cycle in 2 years

Primrose, parsley, celery

Perennial – flowering plants that live for more than 2 years

Peonies, asparagus, grasses

Evolution of Plants

Floweringplants

Cone-bearingplants

Ferns andtheir relatives

Mosses andtheir relatives

Green algaeancestor

Flowers; SeedsEnclosed in Fruit

Seeds

Water-Conducting(Vascular) Tissue

Vascular w/ Seeds

AngiospermsVascular w/ Seeds

GymnospermsVascular Seedless

PterophytaNon-Vascular

Bryophytes

Roots, Stems, and Leaves

Structure of Seed Plants

The three principal organs of seed plants are:

1. Roots Absorb water and dissolved nutrients Anchor plants to the ground Hold plants upright

2. Stems Supports body of plant Transports nutrients

3. Leaves Photosynthetic organs

Tissue Systems Plants consist of four tissue systems:

Meristematic tissue Dermal tissue Vascular tissue Ground tissue

Meristematic Tissue Is found only in the tips of shoots and

roots called apical meristem

Is the only plant tissue that produces new cells by mitosis

Is responsible for the growth that takes place throughout the life of the plant

Dermal Tissue

The outer covering of a plant consists of dermal tissue that consists of a single layer of epidermal cells The exposed outer surfaces of these cells are often

covered with a thick, waxy layer called a cuticle that protects against water loss & injury

The surfaces of some leaves also have trichomes – tiny projections which help protect the leaf and also give it a fuzzy appearance

On the underside of the leaves, dermal tissue contains guard cells, which regulate water loss and gas exchange

Vascular Tissue

Plant vascular tissue includes xylem and phloem Xylem – water

conducting tissue that consists of tracheids and vessel elements

Phloem – food-conducting tissue that consists of sieve tube elements and companion cells

Ground Tissue The cells that lie between dermal and

vascular tissues make up the ground tissues in plants In most plants, ground tissue consists of

parenchyma (packed with chloroplasts) and may contain collenchyma or sclerenchyma (both of which function in plant support)

Types of Roots

The two main types of roots are:1. Taproots – found mainly in dicots

This type of root grows long and thick

2. Fibrous roots – found mainly in monocots

This type of root branches to such extent that no single roots grows larger than the rest

Root Structure

Root Structure

Root Growth Roots grow in length as their apical meristem produces new

cells near the root tip. These fragile new cells are protected by a tough root cap

Roots Functions

Roots anchor a plant in the ground and absorb water and dissolved nutrients from the soil Most water & minerals enter a plant through

the tiny hairs on roots Essential plant nutrients include:

Nitrogen Phosphorus Potassium Magnesium Calcium

Stem Function

Stems have three important functions in plants: Production of leaves, branches, and flowers Holding leaves up to sunlight Transport substances between roots and

leaves

Stem Structure

In most plants, stems contain distinct nodes, where leaves are attached, and internodes, regions between the nodes Small buds are found

where leaves attach to the nodes

Buds contain undeveloped tissue that can produce new stems and leaves

Monocot & Dicot Stems In monocots, vascular bundles are scattered

throughout the stem In dicots and most gymnosperms, vascular bundles

are arranged in a cylinder

Formation of Bark On most trees, bark includes all of the tissues

outside the vascular cambium

Leaf Structure The structure of a leaf is optimized for absorbing light

and carrying out photosynthesis Blades are flattened sections that collect sunlight The petiole is a thin stalk that attaches the blade to the stem

blade

petiole

blade divided into many leaflets

single blade on petiole

Leaf Functions Plants must take in all the materials needed

for photosynthesis Specialized cells on the underside of the leaf

regulate this process Leaves absorb light and carry out most of the

photosynthesis in plants

6CO2 + 6H2O → C6H12O6 + 6 O2

Carbon dioxide + water → sugar + oxygen

Photosynthesis Photosynthesis is the process whereby an organism

use light energy to convert carbon dioxide and water into oxygen and high energy sugars

Leaf Function & Photosynthesis

The bulk of most leaves are composed of mesophyll tissue Mesophyll cells are packed with chloroplasts

and carry out nearly all photosynthetic activity of the plant

The stomata are the pore-like openings that allow CO2 and O2 to diffuse in and out of the leaf

Each stomata consists of 2 guard cells, which control the opening and closing of stomata by responding to water pressure

Leaf Function & Photosynthesis

Transpiration

Water is lost from leaves in a process called transpiration

Gas Exchange Plants keep their stomata open just enough to allow

photosynthesis to take place, but not so much that they lose an excess amount of water Guard cells control the stomata and thus regulate the

movement of gases into and out of the leaf tissues In general, stomata are open during the daytime when

photosynthesis is active and then close at night when open stomata would only lead to water loss

Water Transport

The combination of root pressure, capillary action, and transpiration provides enough force to move water through the xylem tissue of plants

Nutrient Transport

When nutrients are pumped into or removed from the phloem system, the change in concentration causes a movement of fluid in the same direction As a result, phloem is able

to move nutrients in either direction to meet the nutritional needs of the plant

source cells: cells that produce sugars by photosynthesis

sink cells: cells that use or store sugars

Reproduction of Seed Plants

Alternation of Generations

All plants have a life cycle in which a diploid sporophyte generation alternates with a haploid gametophyte generation Gametophyte plants produce male and female

gametes (sperm and eggs) When the gametes join, they form a zygote that

begins the next sporophyte generation The sporophyte is what we recognize as the

plant and the gametophyte is hidden deep within tissues of the sporophyte plant (inside cones or flowers)

Alternation of Generations An important trend in plant evolution is the

reduction of the gametophyte and the increasing size of the sporophyte

Life Cycle of Gymnosperms

Reproduction in gymnosperms takes place in cones, which are produced by a mature sporophyte plant Pollen cones are the male cones which produce

the male gametophyte pollen (sperm) Seed cones are the female cones which produce

female gametophytes (eggs) The gymnosperm life cycle takes 2 years to

complete It begins in the spring when the male cones

release pollen carried by wind to fertilize the female eggs

Pollen Cones and Seed Cones

seed cone (female)

pollen cone (male)

Life Cycle of Gymnosperms

Angiosperm Anatomy

Structure of Flowers

Flowers are reproductive organs that are composed of four kinds of specialized leaves:

1. Sepals2. Petals3. Stamens4. Carples

Sepals and Petals

The outermost circle of floral parts contains the sepals, which in many plants are green and closely resemble ordinary leaves Sepals enclose the bud

before it opens and protect the flower while it is developing

Petals, often brightly colored, are used to attract insects and other pollinators

Stamens and Carpels

Within the ring of petals are the structures that produce male and female gametophytes The male parts consist of an anther and a filament

that together make up the stamen The filament is a stalk that supports the anther,

which produces pollen grains The innermost floral parts are carpels, each of

which forms an ovary (containing eggs)

Stamens & Carpels

Life Cycle of Angiosperms

Reproduction in angiosperms takes place within the flower Following

pollination and fertilization, the seeds develop inside protective structures

Life Cycle of Angiosperms

Pollination

Most gymnosperms and some angiosperms are wind pollinated, whereas most angiosperms are pollinated by animals

Seed and Fruit Development As angiosperms seeds mature, the ovary

walls thicken to form a fruit that encloses the developing seed A fruit is a ripened ovary that contains

angiosperm seeds

Seed Dispersal

Seeds dispersed by animals are typically contained in fleshy, nutritious fruits

Seeds dispersed by wind or water are typically lightweight, allowing them to be carried in the air or to float on the surface of the water

Seed Dormancy

Many seeds enter a period of dormancy when they first mature during which the embryo is alive but not growing Environmental factors such as temperature and

moisture can cause a seed to end dormancy Seed dormancy can allow seeds to germinate

under ideal growth conditions (most seeds germinate in spring)

Seed Germination Seed germination is the early growth stage of the

plant embryo

Plant Responses & Adaptations

Patterns of Plant Growth All plants follow a highly regulated pattern

of growth that continues throughout the life of the plant This pattern of growth leads to distinct shapes The secrets of plant growth are found in

meristems – regions of tissue that can produce cells that later develop into specialized tissue

Meristems are found only at the tips of growing stems and roots

Plant Hormones A hormone is a substance

that is produced in one part of an organism and affects another part of the same individual

Plant hormones are chemical substances that control a plant’s patterns of growth and development, and the plant’s responses to environmental conditions

The portion of an organism affected by a particular hormone is known as its target cell

Hormones are produced in apical meristems, young leaves, roots, and in growing flowers or fruits

Tropisms The responses of plants to environmental

stimuli are called tropisms Gravitropism – response to gravity Phototropism – response to sunlight Thigmotropism – response to touch

Phototropism Phototropism is the tendency of a plant to

grow toward a source of light

Auxins and Phototropism Auxins are produced in the apical

meristem and are transported downward into the rest of the plant They stimulate cell elongation and regulate cell

growth – this is what causes a plant to grow in a direction toward sunlight

They are also responsible for gravitropism – the tendency of a plant to grow in a direction in response to the force of gravity

Auxins & PhototropismA higher concentration of auxins accumulate in shaded parts of the stem, causing the plant to bend toward the sunlight

Auxins and Branching Apical dominance is a phenomenon in

which the closer a bud is to the tip of a stem, the more its growth is inhibited As a stem grows in length, it produces lateral

buds – an area on the side of a stem that gives rise to side branches

If you want your plants to be fuller instead of taller, you can clip off the top of the plant – thus removing the auxins and change the overall shape of the plant

Section 25-1

Apical meristem

Lateral buds

Apical meristem removed

Auxins produced in the apical meristeminhibit the growth of lateral buds.

Without the inhibiting effect of auxinsfrom the apicial meristem, lateral budsproduce many branches.

Auxins and Apical Dominance

Cytokinins Cytokinins are plant hormones that are

produced in growing roots and in developing fruits and seeds In plants, cytokinins stimulate cell division

and the growth of lateral buds, and cause dormant seeds to sprout

Thy often produce effects opposite to auxins

Gibberellins Plants can produce more than 60 similar compounds known

as gibberellins – growth promoting substances Gibberellins produce dramatic increases in size,

particularly in stems and fruit They are responsible for the rapid early growth of many

plants

Ethylene In response to auxins, fruit tissues release

small amounts of the hormone ethylene Ethylene then stimulates fruits to ripen Commercial fruits are often picked before they

ripen and then given a controlled dose of ethylene just before delivery to the store to produce a ripe color quickly

Photoperiodism Photoperiodism in plants is responsible

for the timing of seasonal activities such as flowering and growth

Short-day plants – a plant that flowers when daylight is short

Long-day plants – a plant that flowers when days are long

Effect of Photoperiod on Flowering

Winter Dormancy Dormancy is the period during which an

organism’s growth and activity decrease or stop As cold weather approaches, deciduous plants

turn off photosynthetic pathways, transport materials from leaves to roots, and seal leaves off from the rest of the plant

During winter, the continued presence of leaves would only be costly in terms of water loss

Adaptations of Aquatic Plants To take in sufficient oxygen, many aquatic plants

have tissues with large air-filled spaces through which oxygen can diffuse The reproductive adaptations of aquatic plants include

seeds that can float in water and delay germination until after periods of flooding

Adaptations of Desert Plants Xerophytes, or

desert plants, have evolved adaptations including extensive roots, reduced leaves, and thick stems that can store water The seeds of most desert

plants can remain dormant for years and germinate only when sufficient moisture is available

Nutritional Specialists Plants that have specialized features for

obtaining nutrients include: Carnivorous plants – digest insects

Venus’ flytrap Parasitic plants – grow into tissues of their

host plants Mistletoe

Epiphytes – grow directly on the bodies of other plants but are non-parasitic

Spanish moss

Chemical Defenses Many plants defend

themselves against insect attack by manufacturing compounds that have powerful effects on animals Foxglove is

poisonous when eaten

Nicotine is a natural insecticide