chapter24 section02 edit

7/30/2019 Chapter24 Section02 Edit

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Copyright Pearson Prentice Hall

Biology


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24-2 Seed Development

and Germination


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24-2 Seed Development and

Germination

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Seed and Fruit Development


As angiosperm seeds mature, the ovary

walls thicken to form a fruit that enclosesthe developing seeds.


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A fruit is a ripened ovary that contains angiosperm

seeds.

As seeds mature, the ovary walls thicken to form a

fruit that encloses the developing seeds.


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Germination

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Seed Dispersal

How are seeds dispersed?


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Germination


Seed Dispersal

Seed Dispersal

Seeds are dispersed by animals, wind, and

water.

Seeds dispersed by animals are typically

contained in fleshy, nutritious fruits.


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Seed Dispersal

Seeds of many plants are eaten by animals.

These seeds are covered with tough coatings that

protect them from digestive chemicals, allowing them

to pass through an animals digestive system

unharmed.

The seeds then sprout in the feces eliminated from

the animal.


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Seed Dispersal

Seeds dispersed by wind or water are

typically lightweight, allowing them tobe carried in the air or to float on the

surface of the water.


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Seed Dispersal

Some seeds are encased in winglike structures that

spin and twirl, helping them glide from their parent

plants.

A coconut is buoyant enough to float in seawater

within its protective coating for many weeks.

Tumbleweed plants break off at their roots and

scatter their seeds as they are blown by the wind.


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Seed Dormancy

Seed Dormancy

Many seeds will not grow when they first mature.

These seeds enter a period ofdormancy, during

which the embryo is alive but not growing.

The length of dormancy varies in different plant

species.


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Seed Dormancy

What factors influence the dormancy and

germination of seeds?


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Seed Dormancy

Environmental factors such as

temperature and moisture can cause a

seed to end dormancy and germinate.

Seed dormancy can be adaptive in several

ways:

allows for long-distance dispersal allows seeds to germinate under ideal

growth conditions


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Seed Germination

Seed Germination

Seed germination is the early growth stage of the

plant embryo.

When seeds germinate, they absorb water whichcauses food-storing tissues to swell and crack

open the seed coat.

The young root grows through the cracked seedcoat.

24 2 S d D l d S d G i i


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Seed Germination

In most monocots, the single cotyledon remains

underground.

The growing shoot emerges while protected by a

sheath.

24 2 S d D l t d S d G i ti


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Seed Germination

Corn (monocot)

Young

shoot

Germinating

seedPrimary

root

Foliage

leaves



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Seed Germination

In dicots, germination takes place in one of two ways.

In some species, the cotyledons emerge aboveground, protecting the stem and first foliage

leaves.

In other species, the cotyledons stayunderground and provide a food source for the

growing seedling.



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Seed Germination

Cotyledons

Bean (dicot)

Germinatingseed

Primary

root

Young

shoot Cotyledons

Seed coat

Foliage

leaves


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24-2
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24-2

A germinating corn seedling has

a. a single cotyledon, which remains belowground.

b. two cotyledons, which push above ground.

c. a single cotyledon, which pushes aboveground.

d. two cotyledons, which remain below

ground.


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24-2

Angiosperm fruits develop from

a. the ovary wall of the flower.

b. seed endosperm.

c. swollen sepals of the flower.

d. flower stamens.


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24-2

An example of a seed that is transported by

water is a

a. coconut.

b. tumbleweed.c. blackberry.

d. maple seed.


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24-2

The seeds of many plants that form fruits are

dispersed mainly by

a. animals.

b. water.c. wind.

d. the plant itself.


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24-2

An environmental condition that can cause the

activation of a dormant seed is

a. a sharp drop in temperature.

b. the heat from a forest fire.c. an extended drought.

d. falling from a great height.


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