PLANT REPRODUCTION AND PLANT STRUCTURE

Plant Reproduction and Plant Structure



Plant Reproduction and Plant Structure

Question 1

A

Although their reproductive organs differ as do the environments in which they live and reproduce the basic principles of sexual reproduction are the same in a moss, a flower, a bee and a human. In this investigation, you will learn how the structures of a flower serve the reproductive function.

Carefully strip away the sepals and petals with the probe or blade to examine the reproductive structures. Around a central stalk like body are 5 to 10 delicate stalks, each ending in a small sac. These are the male reproductive organs, or stamens. Thousands of pollen grains are produced in the anther. The number of stamens varies according to the type of flower. Shake some of the pollen into a drop of water on a clean slide, add a cover slip and examine with a microscope. The central stalk surrounded by the stamens is the female reproductive organ, known as a carpel or pistil. It is composed of an enlarged basal (bottom) part, the ovary, above which is an elongated part, the style, ending in a stigma. Use a probe or blade to cut into the ovary lengthwise.

B

The outermost whorl of floral parts may be green or brown and leaf-like. These sepals protected the flower bud when it was young. In some flowers the sepals look like an outer whorl of petals. Petals are usually large and colored and lie inside the sepals. Both sepals and petals are attached to the enlarged end of a branch. These parts of the flower are not directly involved in sexual reproduction. SEPALS make up the lower (or outermost) whorl of floral leaves. They are frequently, but not always, green and rather leaf-like in appearance, although they usually are smaller than the foliage leaves of the plant. Collectively, all sepals of a flower constitute the CALYX. The major function appears to be protection of the flower parts during early development. The angiosperms2, flowering plants, are the largest and most diverse group of vascular plants (we will study the other category of plants, the non-vascular plants, later in the course). Angiosperms constitute most of the visible vegetation on earth and most of the plants that you are familiar with are angiosperms. Organisms in the phylum Anthophyta (angiosperms), the largest phylum of photosynthetic organisms, range in size from the 300-foot Eucalyptus tree of Australia3 to the aquatic duckweed4 (family Lamnacieae) of only a few millimeters (imagine how small the flowers are of a plant that is only one millimeter). Primary distinguishing characteristics of angiosperms include the presence of flowers, fruits (seed(s) enclosed in a vessel or carpel, the basic unit of the pistil), and double fertilization5 (one to produce the endosperm and the other to form the zygote).

C

Flowering plants display striking variation between species in the number of ovules produced by flowers. Curiously, in wind-pollinated plants, most species produce only a single ovule in each ...