FLOWERING PLANT REPRODUCTION

A detailed lesson....

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The petals of the flower advertise its presence among the green leaves. This attracts insects and animals that visit the flower for nectar or other parts. As these animals forage for food, they may carry pollen from flower to flower (like bees).

Within the corolla are the stamens. Each one consists of a single elongated stalk, the filament, and at the end, the anther. The pollen grains, formed inside the anther, are the immature male gametophytes. When ripe, the pollen grains are released, often in large numbers, through slits or pores in the anther.

The center most parts of the flower are the carpels containing the female gametophytes. A single flower may have one or more carpels, which may be separate or fused together. The carpels consist of a stigma with a sticky surface to hold pollen grains, a stalk, the style for the pollen tubes to grow through and a swollen base called the ovary. Inside the ovary are one or more ovules each enclosing a female gametophyte or embryo sac. After the egg is fertilized it develops into a seed and the ovary into a fruit. The diagram below is of a pear flower.

The pollen tube of the pollen grain (male gametophyte) grows through the style and enters an ovule, which contains a seven celled embryo sac (female gametophyte). One of the sperm nuclei unties with the egg, forming the zygote. The other sperm nucleus fuses with the two polar nuclei that are in the single large cell. A triploid (3n) cell is formed and the endosperm will develop. The carpel in this drawing shows two ovules.

LIFECYCLE OF AN ANGIOSPERM

FRUIT OF THE ANGIOSPERM - PEAR

Vocabulary:

anther

The pollen bearing portion of a stamen in flowering plants.

carpels

A leaf like floral structure enclosing the ovule or ovules of angiosperms.

corolla

Petals, collectively; usually the colored flower parts.

egg

A female gamete.

embryo sac

The female gametophyte of a flowering plant, inside the ovule.

endosperm

In plants a triploid tissue containing stored food, develops from the union of a sperm nucleus and two nuclei of the central cell of the female gametophyte. Found only in angiosperms.

filament

A chain of cells, but in flowers it is the stalk of a stamen.

fruit

In angiosperms a matured, ripened ovary or group of ovaries and associated sturucure. Contains the seeds.

gametophyte

The haploid (n) gamete producing gernerat (plants have alternating haploid and diploid generations).

nucleus

In our discussion, the membrane bound structure characteristic of eukaroyotic cells that contains the genetic information in the form of DNA organized into chromosomes.

ovary

In flowering plants the enlarged basal portion of a carpel or fused carpel containing the ovule or ovules. Ovary matures to become the fruit.

ovules

In seed plants a structure composed of a protective outer coat, a tissue specialised for food storage, and a female gametophyte with an egg cell. Becomes a seed after it is fertilized.

pollen

In seed plants, spore consisting of an immature male gametophyte and a protective outer covering.

seed

A complex structor formed by the marutation of the ovule of seed plants following fertilization; upon germination a seed develops into a plant. Seed is made up of a seed coat, embryo and a food reserve.

stamens

The male structure of a flower which produces pollen.

stigma

In plants, the region of a carpel serving as a receptive surface for pollen.

style

In angiosperms, the stalk of a carpel which the pollen tube grows through.

zygote

The diploid (2n) cell resulting from the union of male and female gametes (fertilization).

Characteristics of Flowering Plants from TAMU
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UCMP Glossary of Natural History Terms - Volume #8: Botanical Terms
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Picture from: "Invitation to Biology" 5th Edition, The Biology of Plants, Worth Publishers, Helena Curtis, N. Sue Barnes, 1994

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