Ch 24 Plant Reproduction and Response

1 Explain Why is it adaptive for some seeds to remaindormant before they germinate

Apply Concepts The seeds of a bishop pinegerminate only after exposure to the extreme heatof a forest fire. Evaluate the significance of thisstructural adaptation

2 Pose a Question A new angiosperm species isdiscovered. What questions would you ask beforepredicting how its seeds are dispersed- explain whyyou would ask each.

CH 24 PLANT REPRODUCTION AND RESPONSE

24.2 Fruits and Seeds

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Seed and Fruit Development

After fertilization, nutrients flow into the flowertissue and support the development of thegrowing embryo within the seed

Fruit

Mature angiosperm ovary, usually containing seeds

Fruit isn’t limited to “fruits” like apples but alsoincludes rice, corn, etc…

Ovary wall surrounding a fruit may be fleshy,(grapes and tomatoes) or tough and dry (shell thatsurrounds peanuts).

Dispersal by Animals

Many seeds especially those in sweet, fleshy fruitsare often eaten by animals

Seeds are covered with tough coatings, allowingthem to pass through an animal’s digestive systemunharmed

Seeds then sprout in the feces of the animal.

Dispersal by Animals

Fruits provide nutrition for the animal

Help the plant disperse its seeds

Often to areas where there is less competition withthe parent plants.

Dispersal by Animals

Dry fruits sometimes have burrs or hooks thatcatch in an animal’s fur.

Dispersal by Wind and Water

Typically contained in lightweight fruits that allowthem to be carried in the air or in buoyant fruitsthat allow them to float on the surface of thewater

Dandelion seed

Coconut.

Dormancy

Embryo is alive but not growing

Germination

Growth of plant embryo resumes.

How Seeds Germinate

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Seeds absorb water

Causes food-storing tissues to swell and crack open theseed coat

Young root emerges and begins to grow

Shoot then emerges.

The Role of Cotyledons

First leaves

Store nutrients and transfers them to growingembryo as the seed germinates.

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Monocots have one cotyledon

Stays underground to nourish young plant

Growing monocot shoot emerges from the soilprotected by a sheath.

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Dicot have two cotyledons

Lack protection of a sheath for plant tip

Upper end of the shoot bends to form a hook thatforces its way through the soil

Protects tip of plant, which straightens as itemerges into the sunlight.

Advantages of Dormancy

Allow for long-distance dispersal

Allow for seeds to germinate under ideal growthconditions

Some seeds need cold temperature before seedsgerminate.

The graph shows germination rates for Arisaemadracontium gathered at two locations.

1.Interpret Graphs What effect does chilling have ongermination of seeds from Ontario. How does iteffect seeds from Louisiana

2.Form a Hypothesis Describe how the different ratesof seed germination might be explained in terms ofadaptation to the local climate

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