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

Apply Concepts The seeds of a bishop pine germinate only after exposure to the extreme heat of a forest fire. Evaluate the significance of this structural adaptation

2 Pose a Question A new angiosperm species is discovered. What questions would you ask before predicting how its seeds are dispersed- explain why you would ask each.

CH 24 PLANT REPRODUCTION AND RESPONSE24.2 Fruits and Seeds

Seed and Fruit Development

After fertilization, nutrients flow into the flower tissue and support the development of the growing embryo within the seed

Fruit Mature angiosperm ovary, usually containing

seeds Fruit isn’t limited to “fruits” like apples but also

includes rice, corn, etc…

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

Dispersal by Animals

Many seeds especially those in sweet, fleshy fruits are often eaten by animals

Seeds are covered with tough coatings, allowing them to pass through an animal’s digestive system unharmed

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 with the parent plants.

Dispersal by Animals

Dry fruits sometimes have burrs or hooks that catch in an animal’s fur.

Dispersal by Wind and Water

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 Dandelion seed Coconut.

Dormancy Embryo is alive but not growing

Germination Growth of plant embryo resumes.

How Seeds Germinate

Seeds absorb water Causes food-storing tissues to swell and crack open the

seed coat Young root emerges and begins to grow Shoot then emerges.

The Role of Cotyledons

First leaves Store nutrients and transfers them to growing

embryo as the seed germinates.

Monocots have one cotyledon Stays underground to nourish young plant Growing monocot shoot emerges from the soil

protected by a sheath.

Dicot have two cotyledons Lack protection of a sheath for plant tip Upper end of the shoot bends to form a hook that

forces its way through the soil Protects tip of plant, which straightens as it

emerges into the sunlight.

Advantages of Dormancy

Allow for long-distance dispersal Allow for seeds to germinate under ideal growth

conditions Some seeds need cold temperature before seeds

germinate.

The graph shows germination rates for Arisaema dracontium gathered at two locations.

1. Interpret Graphs What effect does chilling have on germination of seeds from Ontario. How does it effect seeds from Louisiana

2. Form a Hypothesis Describe how the different rates of seed germination might be explained in terms of adaptation to the local climate