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TOPIC: DEVELOPMENT OF NEW SEEDS
CONTENT:
- Progress of development of zygote in the flowering plant
- Germination of seeds
SUB-TOPIC I: PROGRESS OF DEVELOPMENT OF ZYGOTE IN THE FLOWERING PLANT
Meaning of seed
Seeds are plant parts containing embryo and this embryo give rise to new individual.
Pollination is the first step in the process of sexual reproduction in flowering plants. It is followed by fertilization and development of zygote. These steps change the flower into a fruit enclosing seeds, the potential next plant
Pollination: this is the process whereby mature pollen grains are transferred from the anthers to the mature stigmas or pollination is the transfer of pollen grains from the anther to the mature stigma of a flower.
There are two types of pollination, they are:
- Cross pollination
- Self-pollination
Bumblebee Pollinating
When a bee such as this bumblebee visits a flower, tiny grains called pollen stick to the bee. The bee then carries the pollen to another flower. This process, known as pollination, is necessary for many plants to make seeds and fruit.
Cross Pollination
Cross pollination occurs when the pollen grains from one flower are transferred to the mature stigma of another plant of the same species.
Features Of Cross Pollination
- Male and female reproductive parts occur in different flowers i.e. the flowers are unisexual
- If the plant is dioecious, then the male and the female flower occur on different plants of the same species.
- In monoecious plants, where male and female flowers occur on the same plants, self pollination is prevented by:
(a) The stamens ripening before the stigmas (flower is described as being protandrous e.g. sunflower, sativa)
(b) The stigmas ripening before the stamen (protogynous e.g. grasses)
- Self sterility which may occur in some flowers. This means that the pollen will not fertilize the ovary of the same flower or another flower of the same plant because the pollen cannot grow or grows slowly on the stigma. The flower eventually dies before fertilization occurs. Examples of this are the flowers of many leguminous plants and Ixora
- Some upright cross pollinated flowers have their stamen arranged below the stigmas. This will prevent pollination and may ensure that the visiting insect touches the stigmas before the stamens.
Self Pollination
Self pollination occurs when the pollen grains from a flower are transferred to the mature stigma of the same plant of the same species.
Features of Self-Pollinated Flowers
- In composite plants e.g. sunflower, the flowers first have a chance of cross pollination hence they are protandrous. If cross pollination fails, the self pollination occurs by the stigmas growing and curling backward to pick up pollen grains remaining in their styles.
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