Reproductive System In Plants

CONTENT

• Structures and Functions of the Reproductive Organs in Plants
• Arrangement of  Reproductive Organs in Plants
• Types of Flowers     
• Kinds of Placentations

STRUCTURES AND FUNCTIONS OF THE REPRODUCTIVE ORGANS IN PLANTS

The flower is the reproductive structure of a flowering plant. It has both male and female sex organs hence it can carry out sexual reproduction. After fertilization has taken place in flowers, seeds are produced.

A flower has two major parts:

• The floral part (whorls)
• The flower stalk (pedicel).     

The floral part of the flower is formed by

• calyx (sepals)
• corolla (petals)
• androecium (stamens)

gynoecium (carpels)

PARTS OF A TYPICAL FLOWER

THE CALYX

The calyx consists of sepals which are usually small and green. They protect the flower present in the bud.  Sepals are usually up to 3-5 in numbers and they may be separated (polysepalous) or joined to form a cup (gamosepalous). Epicalyx may be present e.g in hibiscus flower.

THE COROLLA

The corolla consists of petals inside the sepals. Petals are the attractive part of the flower and could be up to 4-10 and may be separated (polypetalous) or joined to form a tube (gamopetalous). They are generally coloured and scented to attract pollinators (e.g insects)

THE ANDROECIUM

The androecium is the male reproductive organs of a flower. It is a group of stamens which consist of two parts –the filament and anthers. Stamens could be up to 3 or more (free or joined together).The anther is a 2-4 lobed structure producing the pollen grains (fine yellowish particles) which in turn produce the male gamete in flowers. At maturity, the anther lobes open to release the pollen grains.

THE GYNOECIUM

The gynoecium is the female reproductive organ of a flower. It is the inner most floral part of the flower. Gynoecium consists of carpels which may be one or many. Carpels may be separate (monocarpous)e.g flamboyant or may be fused (polycarpous) e.g. hibiscus. A Pistil or carpel consists of three parts, they areovary, style and stigma.

The ovary contains ovule which produces the female gamete.  After fertilization, the ovary develops into fruit while the ovule develops into seed.

TYPES OF OVARY

1. Superior Ovary- when it is above other floral parts and such flower is called hypogynous flower e.g. hibiscus
2. Inferior Ovary- when it is below other floral parts such flower is referred to as epigynous flower e.g. sunflower.
3. Half inferior Ovary- when the ovary is at the same level with other floral parts, such is called perigynous ovary e.g. rose flower.

EVALUATION

1. Describe the male reproductive parts of a flowering plant.
2. Explain the different types of ovary.

TYPES OF FLOWER

Generally, flowers defer in the following

• number of floral parts
• colour of petals
• size and shape
• symmetry

• Flowers can be radially symmetrical/regular (actinomorphic) or irregular (zygomorphic).
• A complete or perfect flower, when all the four floral parts are present,   or imperfect or incomplete flower if one or more of the floral parts are absent.
• Position of the ovary (hypogynous, epigynous or perigynous flowers).
• If flowers occur singly (solitary flower) or in group (inflorescence).
• If flowers are born in axils of leaves (axillary) or at the end of the stem or branches (terminal flowers).

EVALUATION

1. Classify flowers based on a) number of floral parts b) position of the ovary
2. List the factors to consider when classifying flowers.

SEXES IN PLANTS

Most flowers are bisexual i.e. they have both stamens and carpels while a few are unisexual (either male or female). Therefore, a plant can be monoecious (when both male and female flower occur on the same plant e. g. maize or dioecious (when male and female flower are found on different plant e. g. pawpaw.

PLACENTATION

This is defined as the arrangement of the ovules within the ovary of a flower. The ovules are attached to the ovary by fleshy structures called placenta through short stalks called funicles.

TYPES OF PLACENTATION;

1. Marginal placentation:  Ovule are arranged at the margin of the ovaries e.g. beans, flamboyant flowers
2. Parietal placentation:  Ovules are arranged to the side of the ovary or within a single chamber or cavity e.g. pawpaw.
3. Free central placentation: Ovules are born on a knob projecting from the base of the ovary e. g. water lily.
4. Axile placentation: Carpels meet at the centre to form the placenta for attachment of ovules e.g. tomatoes
5. Basal placentation: Ovules are attached to the base of ovule e. g. sunflower.

GENERAL EVALUATION

1. With a well labeled diagram   describe the structural make up of a flower.
2. With an example each state and explain the types of ovary.
3. List the four floral parts of a flower and their functions.
4. Classify flower based on sexes.
5. What is placentation?
6. Describe five types of placentation and give one example in each case.      

READNG ASSIGNMENT

College Biology, chapter 16, pages 305-324 

WEEKEND ASSIGNMENT

SECTION A

1. The reproduction structural part of the flower include the following except A. corolla B. androecium C. gynoecium D. stigma
2.  A flower having both male and female flowers on the same plant is referred to as  A. monoecious flower  B. dioecious flower C. hypogynous flower D. axillary flower.
3. An example of flower possessing half inferior ovary is A. hibiscus B. sun flower C. rose flower D. flamboyant
4. The arrangement of ovules in the ovaries is referred to as A. pollination B. placentation C. fertilization D. solitary
5. An example of axile placentation is found in   A. sunflower B. lily C. pawpaw D. tomato

SECTION B

1. With the aid of diagrams, distinguish between a monocarpous ovary and a syncarpous ovary.
2. Describe five types of placentation and give one example in each case.