Biology Lab C_FALL

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Sexual Reproductive Strategies

25-1

25.1 Plants have a sexual life cycle called

alternation of generations

 Alternation of generations

 Sporophyte

 Dominant in flowering plants

 Bears flowers – reproductive structures

 Diploid or 2n

 Produces haploid microspores and megaspores by meiosis

 Gametophyte

 Haploid or n

 Produces gametes

 Microscopre undergoes mitosis and becomes pollen grain,

male gametophyte

 Megaspore undergoes mitosis to become embryo sac,

female gametophyte

25-2

25.1 Plants have a sexual life cycle called

alternation of generations

 Upon fertilization, cycle returns to 2n sporophyte

 Once sperm fertilizes egg, zygote becomes embryo,

still within ovule

 Ovule develops into seed, which contains embryo

and stored food surrounded by seed coat

 Ovary becomes fruit, which aids in dispersing seeds

 When seed germinates, new sporophyte emerges

and, through mitosis and growth, becomes mature

organism

 Sexual life cycle of flowering plants is adapted to

land existence

25-3

25-4 Figure 25.1A

diploid (2n)

haploid (n)

seed

zygote

sporophyte

ovary ovule

FERTILIZATION

egg

Female gametophyte

(embryo sac)

Male gametophyte

(pollen grain)

anther

microspore

MEIOSIS

megaspore

sperm

25.1 Plants have a sexual life cycle called

alternation of generations

 Flowers are unique to angiosperms

 Produce spores, protect gametophyte, attract

pollinator, produce fruits

 Major factor in success of flowering plants

 Typical flower

 Four whorls of modified leaves attached to receptacle

at end of stalk (peduncle):

1. Sepals – protect bud

2. Petals – corolla

3. Stamens – anther and filament

4. Carpel – stigma, style and ovary

25-5

25-6

carpel stamen

anther filament

petal

sepal receptacle

stigma style ovary ovule

Figure 25.1B

25-7 Figure 25.1C

25-8 Figure 25.1D

HOW LIFE CHANGES

25A Evolution of Seed Plants

 Large part of adaptation to life on land is

protecting all stages of life cycle from drying out

 Gametophyte and embryo protected

 Bryophytes have dominant gametophyte

 Sperm must swim to egg

 Ferns have dominant sporophyte

 Gametophyte is independent

 Sperm must also swim to egg

 Seed plants

 Production of two types of spores and two types of

gametophytes

25-9

25-10

25-11 Figure 24A

(n)

Moss

rhizoids

(2n)

seed

Angiosperm

roots

seed

Gymnosperm

roots

spores

Fern

rhizoids

roots

spores

HOW LIFE CHANGES

25B Evolution of Insect Pollination

 Although we generally associate insect

pollination only with angiosperms, this practice

may have evolved first among gymnosperms

 Cycads and beetles may have developed

relationship before flowering plants evolved

 During the Cretaceous period, both flowers and

insects diversified greatly

 Adaptations between flowers and pollinators can

be highly specific

25-12

25-13 Figure 25B

25.2 Pollination and fertilization

bring gametes together during

sexual reproduction

 Sexual reproduction involves:

1. Production of pollen grains (male gametophytes) in

anthers of stamens

2. Production of embryo sac (female gametophyte) in

ovule located within ovary of carpel

 Pollination

 Pollen transferred from anther to stigma so egg within

female gametophyte is fertilized

 Self-pollination vs. cross-pollination

 Most angiosperms use animals to carry out pollination

25-14

Figure 25.2A 25-15

Stamen

anther

filament

Carpel

stigma

style

ovary

ovule

Sporophyte Mitosis

fruit

(mature ovary) seed

(mature ovule)

seedcoat

embryo

endosperm (3n)

Seed

diploid (2n) MEIOSIS MEIOSIS

microspore

mother cell

Ovule pollen sac

Anther

Carpel

stigma

style

ovary

megaspore

mothe rcell

25-16

haploid (n) Pollen grain Microspores

(all survive)

MEIOSIS

Megaspores

(one survives)

degenerating

megaspores

Ovule

Embryosac

(mature female gametophyte)

egg

DOUBLE FERTILIZATION

(mature male

gametophyte)

sperm

pollen

tube sperm and

polar nuclei

fuse

sperm and

egg fuse

generative cell

POLLINATION

Figure 25.2A (continued)

Figure 25.2B 25-17

 Coevolution

 As one species changes, other changes too, so both

species become suited to one another

25-18

nectar guides

As a bee sees it As we see it (both): © Heather Angel/Natural Visions

Figure 25.2B

25.2 Pollination and fertilization

bring gametes together during

sexual reproduction

 Double fertilization is unique in angiosperms

 Results in not only zygote, but also food source for

developing zygote

 Endosperm – nutritive tissue developing embryonic

sporophyte uses as energy source

 Mature seed contains:

1. Embryo

2. Stored food – endosperm

 Cotyledons – seed leaves take up endosperm in eudicots

3. Seed coat – develops from ovule wall

25-19

Figure 25.2D 25-20

Embryo

Seed coat

immature

leaves

hypocotyl

Cotyledon

(stored food)

radicle

(right): © Dwight Kuhn

Seed Development and Growth

25-21

25.3 A sporophyte embryo and its

cotyledons develop as a seed matures

Figure 25.3 25-22

1 Zygote stage

zygote

endosperm

cell

25-23

endosperm

proembryo

basal cell

of suspensor

Proembryo stage

Arabidopsis

thaliana

(proembryo): Courtesy Dr. Chun-Ming Liu

Figure 25.3 (continued)

25-24

3 Globular stage

A. thaliana

endosperm

(globular): Courtesy Dr. Chun-Ming Liu

Figure 25.3 (continued)

25-25

A. thaliana

Heart

stage

cotyledons

appearing

(heart): Courtesy Dr. Chun-Ming Liu

Figure 25.3 (continued)

25-26

Capsella

Torpedo

stage

endosperm

bending

cotyledons

(torpedo): © Biology Media/Photo Researchers, Inc.;

Figure 25.3 (continued)

25-27

Cap sella

Cotyledons

(stored food)

Mature embryo stage

radicle

(root apex)

hypocotyl

(root axis)

Seed

coat

Embryo:

epicotyl

(shoot apex)

(mature embryo): © Jack Bostrack/Visuals Unlimited

Figure 25.3 (continued)

25.4 The ovary becomes a fruit, which

assists in sporophyte dispersal

 Fruit derived from an ovary and sometimes other

flower parts

 Protects and helps disperse next 2n sporophyte

generation

 As fruit develops, ovary wall thickens to become

pericarp

 Layers that encircle seed:

1. Exocarp

2. Mesocarp

3. Endocarp

25-28

25.4 The ovary becomes a fruit, which

assists in sporophyte dispersal

 Fleshy versus dry fruits

 Dry fruits – dry at maturity

 Dehsicent – splits open to release seeds

 Indehiscent – does not split open

 Not just a seed

 Fleshy fruit

 Flesh from various sources pericarp, mesocarp

 Stone fruit or drupe has hard endocarp

25-29

Figure 25.4 25-30

pea flower pea pod

stigma

ovary wall

ovule

pericarp

(fruit wall)

Pea pods are a dry, dehiscent fruit.

seed

25-31

2 Maple tree fruits are dry, in dehiscent.

wing

seed covered by pericarp

Figure 25.4 (continued)

25.4 The ovary becomes a fruit, which

assists in sporophyte dispersal

 Simple versus aggregate and multiple fruits

 Simple fruits are derived from simple ovary of single

carpel, or from compound ovary of several fused

carpels

 Accessory fruits form from other flower parts in

addition to ovary

 Aggregate fruits and multiple fruits are examples of

compound fruits derived from several individual

ovaries

 Strawberry – aggregate fruit, each ovary becomes one-

seeded fruit

 Pineapple – multiple fruit derived from many individual

flowers, each with own carpel 25-32

25-33

one fruit

flesh is from

receptacle

Strawberries are a fleshy fruit.

Figure 25.4 (continued)

25-34

4 Raspberries are an aggregate fruit.

fruits from

ovaries of

one flower

one fruit

Figure 25.4 (continued)

25-35

one fruit

Pineapple is a multiple fruit.

fruits from

ovaries of

many flowers

Figure 25.4 (continued)

25.5 With seed germination, the life cycle

is complete

 Germination – seed forms into seedling

 Requires sufficient water, warmth, and oxygen to

sustain growth

 Seed dormancy is time during which no growth

occurs, even though conditions may be favorable

 In temperate zone, seeds often are exposed to period of cold

before dormancy is broken

25-36

Figure 25.5A 25-37

Embryo:

epicotyl-

plumule

hypocotyl

radicle

Seed coat

Cotyledon

(stored food)

Cotyledon

(two)

25-38

seed

coat

first true leaves

(primary leaves) epicotyl

with red

cotyledons

hypocotyl cotyledons

(two)

hypocotyl secondary

root

primary

root

primary

root

Figure 25.5A (continued)

25-39 Figure 25.5B

Asexual Reproductive Strategies

25-40

25.6 Plants have various ways of

reproducing asexually

25-41

 Asexual reproduction

 Production of an offspring identical to single parent

 Plants can grow from axillary buds of

aboveground or underground stems

 Stolon – aboveground horizontal stem

 Rhizome – underground horizontal stem

 Tuber – enlarged portion of rhizome

 Corm – bulbous underground stem

 Not a bulb – structure composed of modified leaves

Figure 25.6 25-42

Asexually produced offspring

stolon

25-43

Rhizome

rhizome

adventitious roots

tuber

axillary

bud

Tuber Corm

papery

leaves

rhizome

branch

adventitious roots

corm

axillary

bud

Figure 25.6 (continued)

25.7 Cloning of plants in tissue culture

assists agriculture

 Tissue culture

 Growth of tissue in artificial liquid or solid culture

medium

 Many plant cells are totipotent – each plant cell has

genetic capability of becoming entire plant

 Methods:

1. Somatic embryogenesis – uses hormones to cause plant

tissues to generate small masses of cells

2. Meristem tissue culture – many new shoot tips from single

shoot tip

3. Anther tissue culture – produces haploid plantlets or

chromosomal doubling is chemically induced

25-44

Figure 25.7A 25-45

(both): Courtesy Prof. Dr. Hans-Ulrich Koop, from Plant Cell Reports, 17:601-604

b. Cell wall regeneration a. Protoplasts, naked cells

25-46

c. Aggregates of cells d. Callus, undifferentiated mass

(both): Courtesy Prof. Dr. Hans-Ulrich Koop, from Plant Cell Reports, 17:601-604

Figure 25.7A (continued)

25-47

(both): Courtesy Prof. Dr. Hans-Ulrich Koop, from Plant Cell Reports, 17:601-604

e. Somatic embryo f. Plantlet

Figure 25.7A (continued)

25-48 Figure 25.7B

25.7 Cloning of plants in tissue culture

assists agriculture

 Cell suspension culture

 Allows scientists to extract chemicals (i.e., secondary

metabolites) from plant cells in high concentrations

and without having to over-collect wild-type plants

growing in natural environments

 Cells produce same chemicals as entire plant

produces.

 Cell suspension cultures of Cinchona ledgeriana produce

quinine, used to treat malaria

25-49

Connecting the Concepts:

Chapter 25

 Life, as we know it, would not be possible

without vascular plants

 Earliest humans were mostly herbivores and relied on

foods they could gather

 Later on, human civilizations could not have begun

without development of agriculture

 Although we now live in an industrialized society,

we still depend on plants and have put them to

many more uses

 Food, shelter, beauty, industrial substances,

pharmaceutical drugs 25-50