Angiosperm Reproduction

Chapter 38

• Phylum Bryophyta

– Moss

– Non vascular

Gametophyte is dominant generation (1n)

Vascular plants

• Phylum Pterophyta:

Ferns

Sperm flagellated

(swim)

Water required for fertilization

• Phylum Anthophyta

– Angiosperms

– Most advanced vascular plants

– Flowering

• Phylum Coniferophyta

Gymnosperms

Angiosperm plant reproduction

• Adult plant is a sporophyte

– Diploid

– Flowering

• Gametophyte

– Haploid

Flowers Organs

1. Sepal

2. Petal

Reproductive organs

3. Stamens - Filament

- Anther w/ pollen sacs (microsporangia)

4. Carpals (pistil) - Ovary

- Style + Stigma (sticky to receive pollen)

Stamen Anther

Filament

Stigma

Carpel

Style

Ovary

Receptacle

Sepal

Petal

(a) Structure of an idealized flower

Great diversity in flower types

• Flower types

– Complete flowers – have the 4 floral organs (both male and female)

elderberry

– Incomplete flowers

• May lack petals, sepals, repro organs

Knotweed lacks petals Squash flower

Male gametophyte = pollen grain (microscopic)

Completes its development in anther

Pollen sac (microsporangia)

contain microsporocyte cells (2n)

which divide into 4 microspores (1n)

Each microspore contains:

1 generative cell produces 2 sperm cells

1 tube cell will produce pollen tube

Pollen is unique

(a) Development of a male gametophyte (in pollen grain)

Microsporangium (pollen sac)

Microsporocyte (2n)

4 microspores (n)

Each of 4 microspores (n)

Male gametophyte

Generative cell (n) forms 2 sperm

MEIOSIS

Ragweed pollen grain

Nucleus of tube cell (n)

MITOSIS

20 µm

75 µm

animation

Female Gametophyte = embryo sac

Location: Ovary

Megasporocytes(2n)

Produce 4 megaspores cells (1n) in ovules

1 megaspore survives

female gametophyte

Ovule

(b) Development of a female gametophyte (embryo sac)

Megasporangium (2n)

Megasporocyte (2n)

Integuments (2n)

Micropyle

MEIOSIS

Surviving megaspore (n)

3 antipodal cells (n)

2 polar nuclei (n)

1 egg (n)

2 synergids (n)

Fem

ale

gam

eto

ph

yte

(e

mb

ryo sa

c)

Ovule

Embryo sac

Integuments (2n)

MITOSIS

100 µ

m

Female gametophyte contains:

• 1 Ovum

• 2 Polar nuclei

Pollination

Abiotic Pollination by Wind

Hazel staminate flowers (stamens only)

Hazel carpellate flower (carpels only)

Wind 20% of angiosperms

Inconspicuous flowers

Ex. grasses

No advantage to

colorful flowers

Pollination by Bees

Common dandelion under normal light

Common dandelion under ultraviolet light

Insects 65% of angiosperms

Nectar

Flowers bright colors

Bees most important

Pollination by Moths and Butterflies

Moth on yucca flower

Anther

Stigma

Hummingbird drinking nectar of poro flower

Pollination by Birds

Birds

Long-nosed bat feeding on cactus flower at night

Pollination by Bats

Fertilization 1. Pollen grain lands on stigma

– Absorbs water

– Tube cell produces pollen tube

2 sperm released to female gametophyte

Ovule

Polar nuclei

Egg

Synergid

2 sperm

Double fertilization 2 sperm released to female gametophyte

- Attracted to egg by chemicals

- 1 sperm fertilizes egg to form zygote (2n)

- Other sperm unites with polar nuclei to form 3n endosperm

Endosperm nucleus (3n) (2 polar nuclei plus sperm)

Zygote (2n) (egg plus sperm)

Lily plant

Anther

Pollen tube

Germinated pollen grain (n) (male gametophyte)

Ovary

Ovule

Embryo sac (n) (female gametophyte)

Egg (n)

Sperm (n)

Zygote

(2n)

Seed

Seed

Embryo (2n) (sporophyte)

Simple fruit

Germinating seed

Mature sporophyte

plant (2n)

(b) Simplified angiosperm life cycle

Key

Haploid (n)

Diploid (2n)

FERTILIZATION

True or false?

1. Plants are the only photosynthetic organisms on Earth

2. Plants are heterotrophic organisms

3. Plants reproduce by binary fission

4. Angiosperms use double fertilization in sexual reproduction

5. Fern plants do not produce pollen

6. All stems are above ground

7. Apical buds are also lateral buds

8. Xylem is a vascular tissue of plants

9. Dermal tissue may be covered by a cuticle

10. Adult sporophytes may contain embryonic , meristematic, tissue

11. The male gametophyte is a pollen grain

12. Soil bacteria fix atmospheric nitrogen

13. A complete flower has both anther and carpal

14. Microsporocyte cells are located in the plant ovary

15. Angiosperms contain the embryo in a seed

16. Haploid refers to a cell with 2 sets of chromosomes

17. Fertilization is the same process as pollination

Seed Development (Chapter 38)

• Each ovule develops into a seed

• Ovary becomes the fruit enclosing the seeds

• Seed coat - hard protection around embryo

• Seed is dehydrated

Tomato seeds with seed coat Apple seeds with seed coat

In the seed:

• Endosperm - Forms from 1 sperm + 2 polar nuclei

• (3n, triploid)

• Contains nutrients

3n

2n

Seeds with endosperm

Coconut has liquid and solid endosperm

Plant development Mitosis cell division

Zygote embryo seedling plant

The mature seed

• Dehydrated

• Dormant

– Metabolism/growth ceases

• Hard, protective seed coat

• Cotyledon

– Becomes first leaves (monocot and eudicot)

• Radicle

– Embryonic root

radish

Seed develops from ovule

Epicotyl

Hypocotyl

Cotyledons

Radicle

Seed coat

(a) Common garden bean, a eudicot with thick cotyledons

seed coat, embryo, cotyledons, endosperm • Bean germination

(a) Common garden bean

Seed coat Radicle

Hypocotyl

Cotyledon

Cotyledon

Hypocotyl

Epicotyl

Foliage leaves

Cotyledon Hypocotyl

Radicle, cotyledon, seed coat

Dicot

(b) Maize

Radicle

Foliage leaves

Coleoptile Coleoptile

monocot

• Germination

– when conditions for growth are favorable

– Examples:

• Desert plant seeds germinate after substantial rainfall

• Some seeds require exposure to winter/cold

• Some must pass through animal digestive tract to soften seed coat

• Some require fire

Buttercup seed requires exposure to cold

Fruit forms from ovary

• Fruit protects seeds

• Aids in seed dispersal

• Dry fruits

– Nuts, legumes

Columbine

Milkweed

Sweet pea

Beans

Peanut

Runner Bean

buckwheat

sunflower

Wheat

Rice

Corn

Barley

Rye

Oats

Walnut

Hazelnut

Chestnut

Acorn

Fleshy fruits

Blackberry

Raspberry

Boysenberry

Loganberry

Cloudberry

Wineberry

Strawberry

Mulberry

Pineapple

Fig

Pomegranate

Date

Cornelian cherry

Goumi

Jujube

Jackfruit

Loquat

Kumquat

Persimmon

Kiwi

Guava

Longan

Lychee

Akee

Breadfruit

Camu Camu

Carambola

Chempedak

Custard apple

Durian

Guarana

Mamoncillo

Mango

Papaya

Pineapple

Rose apple

Tamarind

Pears

Apples

Quince

Chokeberry

Haw

Juneberry

Medlar

Rowan

Sorb apple

Cherry

Peach

Plum

Apricot

Olive

Lychee

Pin cherry

Coconut

Cucumber

Watermelon

Squash

Pumpkin

Honeydew melon

Sunberry

Lemon

Grapefruit

Limes

Citron

Mandarin

Clementine

Ugli fruit

Orange

Grapes

Tomatoes

Bananas

Avocados

Raspberry

Eggplants

Currants

Persimmons

• Seed dispersal mechanisms include:

1. Water

Ex. coconut is buoyant

Coconut

Dispersal by Water

2. Wind dispersal

Whirling Nut (Gyrocarpus)

sycamore

“parachute”

3. animal dispersal

Burdock seeds Tomato seeds

Ovary

Stigma

Pea flower Ovule

Seed

Stamen

Pea fruit

(a) Simple fruit

Fruits classified by developmental features:

Simple Fruit

Develops from one ovary

Tomato Fruit: The solitary Ovary has produced one Fruit.

• Aggregate fruit

– One flower, many ovaries (carpals fuse)

– Ex. strawberry

• Multiple fruit