SEXUAL REPRODUCTION IN PLANTS
The flowering plants such as sunflower, marigold, wheat, maize, rice, mustard reproduce by sexual reproduction method. These plants contain male reproductive organs (stamen) and female reproductive organs (carpel) for the production of male gametes pollens and female gametes ovum respectively. The male gametes fuse with the female gametes to form a single cell called zygote which develops into the embryo of the seed.
Thus the sexual reproduction in plants involves the fusion of male gametes with the female gametes to form a zygote which develops into the embryo of the seed.
The reproductive organs (stamen and carpel) of flowering plants are present in its flower. In other words we can say that it is the flower of a plant which produces both the male and female gametes of flowering plants.
Parts of a flower
A flower is the most important organ of a plant with remarkable complexity and beauty. These are usually scented and brightly coloured to attract the insects. Flowers help the plants in sexual reproduction. Following are the main parts of a flower:
Receptacle is the base of a flower which connects the flower with the branch of that plant. The upper end of receptacle is usually swollen and it called thalamus.
Sepals are a whorl of green coloured leaf like parts which is present on the outermost circle of a flower. The group of sepals is called ‘calyx’. The function of sepals is to protect the flower during its initial stages of growth when it is in the form of bud.
Petals are the colourful parts of a flower which are present inside the sepals. The group of petals is called ‘corolla’. The petals can be of different colours. These are usually scented and their main function is to attract insects for the process of pollination and to protect the reproductive organs which are present at the centre of the flower.
Stamen is the male reproductive organ of a plant. It consists of two parts:
1. Filament and
Filament is a long thread like structure topped by a single enlarged, cylindrical or ovoid anther. A cross section of an anther shows that it consists of two lobes and each lobe further contains two pollen sacs. The pollen sacs are filled with a large number of small rounded structures called pollen grains. It is the pollen which contains male gametes of a plant in the form of two male nuclei.
5. Carpel or Pistil
Carpel is the female reproductive organ of a plant. It consists of three parts:
2. Style and
The lowermost swollen part of the carpel is called ovary. The function of ovary is to make ovules and to store them. Ovules contain the female gamete of a plant. The female gamete of a plant present in the ovule is called ovum. Ovules are present in large number inside the ovary. The upper end of the carpel is called stigma. It may be pointed, flattened or lobed in shape. The function of stigma is to receive the pollen grains from the anthers through the process of pollination. The middle elongated part of the carpel is called style. The function of style is to connect stigma with ovary and provide passage to the pollen tube.