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Reproduction in Flowering Plants Using Sexual Reproduction
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- Location of Reproduction: The reproductive parts of angiosperms are located in the flower.
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- Different parts of a flower are sepals, petals, stamens and pistils.
- Reproductive Parts: Stamens and pistils are the reproductive parts of a flower which contain the germ-cells, orchestrating sexual reproduction in plants.
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Involvement of Different Parts:
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- Sexual Reproduction in Flowers: The flower may be unisexual (corn, cucumber, papaya, watermelon) when it contains either stamens or pistil or bisexual (hibiscus, mustard, rose, petunia) when it contains both stamens and pistil.
- Male Part: Stamen is the male reproductive part and it produces pollen grains that are yellowish in color.
- Female Part: Pistil is present in the center of a flower and is the female reproductive part.
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- It is made of three parts: ovary, style and stigma.
- Ovary: The swollen bottom part is the ovary, the middle elongated part is the style and the terminal part which may be sticky is the stigma.
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- The ovary contains ovules and each ovule has an egg cell.
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Pollination
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- Meaning: The transfer of pollen from the stamen to the stigma is called pollination.
- Self-pollination: If this transfer of pollen occurs in the same flower, it is referred to as self-pollination.
- Cross-pollination: If the pollen is transferred from one flower to another, it is known as cross-pollination.
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- This transfer of pollen from one flower to another is achieved by agents like wind, water or animals.
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Fertilization
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- Meaning: The process of fusion of male and female gametes (to form a zygote) is called fertilization.
- Fusion of Gametes: The cell which results after fusion of the gametes is called a zygote.
- The zygote develops into an embryo.
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Germination
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- After the pollen lands on a suitable stigma, it has to reach the female germ-cells which are in the ovary.
- For this, a tube grows out of the pollen grain and travels through the style to reach the ovary.
- After fertilization, the zygote divides several times to form an embryo within the ovule.
- Seed: The ovule develops a tough coat and is gradually converted into a seed.
- Fruit: The ovary grows rapidly and ripens to form a fruit.
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- Meanwhile, the petals, sepals, stamens, style and stigma may shrivel and fall off.
- The seed contains the future plant or embryo which develops into a seedling under appropriate conditions.
- This process is known as germination.
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- Fruits and Seed Formation in Sexual Reproduction: After fertilization, the ovary grows into a fruit and other parts of the flower fall off.
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- The fruit is the ripened ovary.
- The seeds develop from the ovules.
- The seed contains an embryo enclosed in a protective seed coat.
- Some fruits are fleshy and juicy such as mango and orange.
- Some fruits are hard like almonds and walnuts.
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Seed Dispersal: The Vital Connection to Sexual Reproduction in Plants
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- Sexual Reproduction’s Impact: Seed dispersal is important because if seeds fall and grow in the same place, there would be severe competition for sunlight, water, minerals and space.
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- As a result the seeds would not grow into healthy plants.
- Sexual Reproduction’s Advantage: Plants benefit by seed dispersal. It prevents competition between the plant and its own seedlings for sunlight, water and minerals.
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- It also enables the plants to invade new habitats for wider distribution.
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Diverse Agencies of Dispersal in Plants
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- Seeds and fruits of plants are carried away by wind, water and animals.
- Winged seeds such as those of drumstick and maple, light seeds of grasses or hairy seeds of aak (Madar) and hairy fruit of sunflowers get blown off with the wind to far away places.
- Some seeds are dispersed by water.
- In the context of Sexual Reproduction, these fruits or seeds usually develop floating ability in the form of spongy or fibrous outer coat as in coconut.
- Some seeds are dispersed by animals, especially spiny seeds with hooks which get attached to the bodies of animals and are carried to distant places.
- Examples: Xanthium and Urena.
- Some seeds are dispersed when the fruits burst with sudden jerks. The seeds are scattered far from the parent plant.
- Example: castor and balsam.
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