Seeds and Fruits

Fertilization of the egg produces a diploid sporophyte zygote. Initially the zygote is attached to the parent plant and derives nutrition by direct transfer during differentiation of embryonic tissues. The zygote undergoes mitotic divisions to become an embryo sporophyte. The seed is a mature ovule, which encases an embryo sporophyte and food reserves inside a protective coat.

The seed is the mature ovule. During embryo development, the parent plant transfers nutrients to the tissues of the ovule, expanding the endosperm or cotyledons. Cotyledons (seed leaves) develop for the purpose of utilizing the endosperm during germination. The ovule eventually separates from the ovary wall and develops seed coats.

The protective seed coat is derived from integuments that enclosed the ovule. Nutritious endosperm is a food reserve. The embryo has one or two cotyledons. A monocot has one cotyledon. A dicot has two cotyledons.

A fruit is a mature ovary with seeds (ovules) inside. Fruits may be dry (e.g. grains and nuts) or fleshy (e.g. apples). Fruits may be classified as simple, aggregate, multiple, or accessory.

A simple fruit is derived from the ovary of one flower.

An aggregate fruit is derived from many ovaries of one flower. It is formed from the many carpels of a single flower and is made up of many simple fruits attached to a fleshy receptacle. Blackberries and raspberries are examples.

A multiple fruit is derived from the individual ovaries of many flowers that grew clumped together. Examples are pineapples and figs

In an accessory fruit, most tissues are not derived from an ovary. Examples are apples and strawberries.

Fruits function in seed protection and dispersal in specific environments by means of "wings," hooks, hairs, sticky surfaces, even animal digestive wastes.

A dicot embryo absorbs nutrients from endosperm and stores them in its two cotyledons. In a monocot embryo, digestive enzymes are stockpiled in the single cotyledon. Enzymes do not tap into the endosperm until the seed germinates.

This animation (Audio - Important) describes dicot seed development.

Seed Germination

Germination is the process by which an immature stage in the life cycle resumes growth after a period of arrested development. Germination depends on water (often spring rains), oxygen, temperature, light, daylength, and other environmental factors. Oxygen moves in and allows the embryo to switch to aerobic metabolism. Repeated cell divisions produce a seedling with a primary root.

This animation (Audio - Important) describes seed germination.

These two videos from the Indiana University Plants in Motion site illustrate germination of Arabadopsis and corn.

REVIEW: A seed leaf is a

REVIEW: Cotyledons develop as part of all flowering plant _____ .

REVIEW: Seeds are mature _____; fruits are mature _____ .

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