Transcript Lesson Overview

Lesson Overview
24.2 Fruits and Seeds
Lesson Overview
Fruits and Seeds
THINK ABOUT IT
What are fruits, and what purpose do they serve for the plants that
produce them?
You, and all the animals that enjoy eating fruits, are being used. Plants
may be smarter than you think.
Lesson Overview
Fruits and Seeds
Seed and Fruit Development
How do fruits form?
Lesson Overview
Fruits and Seeds
Seed and Fruit Development
How do fruits form?
As angiosperm seeds mature, ovary walls thicken to form a fruit that
encloses the developing seeds.
Lesson Overview
Fruits and Seeds
Seed and Fruit Development
Once fertilization of an angiosperm is complete, nutrients flow into the
flower tissue and support the development of the growing embryo
within the seed.
1. A fruit is a matured angiosperm ovary, usually containing
seeds.
Fruits vary in their structure.
Lesson Overview
Fruits and Seeds
Seed and Fruit Development
The term fruit applies to the sweet things we usually think of as fruits,
such as apples and strawberries. However, foods such as peas, corn,
rice, and tomatoes, which we commonly call vegetables, are also fruits.
Lesson Overview
Fruits and Seeds
Seed and Fruit Development
The ovary wall surrounding a fruit may be fleshy, as it is in grapes and
tomatoes, or tough and dry, like the shell that surrounds peanuts. (The
peanuts themselves are the seeds.)
Lesson Overview
Fruits and Seeds
Seed Dispersal
How are seeds dispersed?
Lesson Overview
Fruits and Seeds
Seed Dispersal
How are seeds dispersed?
Seeds contained in fleshy, nutritious fruits are usually dispersed by
animals.
Seeds dispersed by wind or water are typically contained in lightweight
fruits that allow them to be carried in the air or in buoyant fruits that allow
them to float on the surface of the water.
Lesson Overview
Fruits and Seeds
Dispersal by Animals
2. The seeds of many plants, especially those encased in sweet,
fleshy fruits, are often eaten by animals.
3. The seeds are covered with tough coatings, allowing them to
pass through an animal’s digestive system unharmed.
Lesson Overview
Fruits and Seeds
Dispersal by Animals
The seeds then sprout in the feces eliminated from the animal.
These 4. fruits provide nutrition for the animal and also help the
plant disperse its seeds—often to areas where there is less
competition with the parent plants.
Lesson Overview
Fruits and Seeds
Dispersal by Animals
Animals also disperse many dry fruits, but not necessarily by
eating them.
5. Dry fruits sometimes have burrs or hooks that catch in an
animal’s fur, enabling them to be carried many miles from
the parent plant.
Lesson Overview
Fruits and Seeds
Dispersal by Wind and Water
6. Seeds dispersed by wind or water are typically contained in
lightweight fruits that allow them to be carried in the air or in buoyant
fruits that allow them to float on the surface of the water.
A dandelion seed, for example, is attached to a dry fruit that has a
parachute-like structure, allowing the seed to glide considerable
distances away from the parent plant.
Lesson Overview
Fruits and Seeds
Dispersal by Wind and Water
Some seeds, like a coconut, are dispersed by water.
Coconut fruits are buoyant enough to float in seawater for many weeks,
enabling the seeds to reach and colonize even remote islands.
Lesson Overview
Fruits and Seeds
Seed Dormancy and Germination
What factors influence the dormancy and germination of seeds?
Lesson Overview
Fruits and Seeds
Seed Dormancy and Germination
What factors influence the dormancy and germination of seeds?
Environmental factors such as temperature and moisture can cause a
seed to end dormancy and germinate.
Lesson Overview
Fruits and Seeds
Seed Dormancy and Germination
7. Many seeds will not grow when they first mature. Instead, these
seeds enter a period of dormancy, during which the embryo is
alive but not growing.
8. Germination is the resumption of growth of the plant embryo.
Lesson Overview
Fruits and Seeds
Seed Dormancy and Germination
9. Environmental factors such as temperature and moisture can
cause a seed to end dormancy and germinate. The effect of
temperature on the germination of Arisaema seeds is shown in the
graph.
Lesson Overview
Fruits and Seeds
How Seeds Germinate
10. Before germinating, seeds absorb water, which causes foodstoring tissues to swell and crack open the seed coat.
Through the cracked seed coat, 11. the young root emerges and
begins to grow.
12. The shoot—the part of the plant that will emerge above
ground—emerges next, as seen in the germinating corn seed.
Lesson Overview
Fruits and Seeds
The Role of Cotyledons
13. Cotyledons are a flowering plant’s first leaves. They store
nutrients and then transfer them to the growing embryo as the
seed germinates.
Lesson Overview
Fruits and Seeds
The Role of Cotyledons
14. Monocots have a single cotyledon, which usually remains
underground while it passes nutrients to the young plant.
15. The growing monocot shoot emerges from the soil protected
by a sheath.
Lesson Overview
Fruits and Seeds
The Role of Cotyledons
16. In dicots have two cotyledons, there is no sheath to protect
the tip of the young plant.
17. Instead, the upper end of the shoot bends to form a hook that
forces its way through the soil.
This protects the delicate tip of the plant, which straightens as it
emerges into the sunlight.
Lesson Overview
Fruits and Seeds
Advantages of Dormancy
18. Seed dormancy can allow for long-distance dispersal, and for
seeds to germinate under ideal growth conditions.
For some species, a period of cold temperatures during which the seeds
are dormant is required before growth can begin.
The period of cold that is required is long enough that seeds will not
germinate until the dangerous winter season has passed.
Lesson Overview
Fruits and Seeds
Advantages of Dormancy
Sometimes, only extreme environmental conditions can end seed
dormancy.
Some pine trees, for example, produce seeds in cones that remain
sealed until the high temperatures generated by forest fires cause the
cones to open.
The high temperature both activates and releases the seeds, allowing
the plants to reclaim the forest quickly after a fire.