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WEEK 4
BIOLOGY
TOPIC: REPRODUCTIVE SYSTEMS IN PLANTS
CONTENT:
- Structures and functions of the reproductive organs in plants.
- Arrangement of reproductive organs in different plants.
- Types of flowers (i) Hypogenous and (ii) Perigynous.
- Kinds of placentation.
SUB-TOPIC 1: Structures and functions of the reproductive organs of plants.
The flower is the major reproductive organ of the flowering plant. Flowers exist in different sizes, shapes, colours and patterns of arrangements.
A flower is a cluster of modified leaves carried on a reduced stem called flower stalk or pedicel. The flower is made up of four floral parts. These are;
(i) Sepals (calyx)
(ii) Petals (corolla)
(iii) Stamen (androecium)
(iv) Carpel (gynoecium)
The structures and their functions are as listed below:
- Sepals (Calyx): this consists of a circular outermost layer of leaf-like structures called sepals which are fixed to the receptacles. Sepals protect the flower during the bud stage. They are mostly greenish are also photosynthetic. Some sepals are brightly coloured and look like petals (petaloids). These serve to attract pollinators. Sepals: may be separated (polysepalous) as in Pride of Barbados. Others are fused or partly joined together to form a cup-like structure (gamosepalous) called Pappus (Tridax).
- Petals (Corolla): these are large brightly coloured modified leaf like structure called petals. They arise within the calyx. They are most conspicuous and prominent part of the flower which attract pollinators to the flower. Petals could be separated as in Hibiscus and Pride of Barbados (Polypetalous) or fused to form a tube are in Allamanda and Milk Bush (Gamopetalous). Petals are usually brightly coloured or scented thereby attracting pollinators. Petals also serve to protect the stamen and the carpals. In a few cases, petals appear greenish (Perianth).
Androecium: this consists of the whorls or group of the male reproductive organs of the flower called stamens. These lie inside the corolla. Each stamen is made up of a lobed or swollen head called Anther and a long slender stalk called the filament which bears the Anther. Each anther is composed of four pollen grains (the male gametes) flowers may be free or united. The filament may also be united while the anthers are free. The fused filaments from a stamina tube as in hibiscus. In sunflower, the anthers are fused while the filaments are attached like petals (epipetalous).
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