Sexual Reproduction in plants

Identify in diagrams and images and draw the following parts of an insect-pollinated flower:

• Sepals: Green, leaf-like structures that protect the flower bud before it opens.

• Petals: Often brightly colored and scented to attract insects for pollination.

• Stamens: The male reproductive organs, consisting of the filament and anther.

  • Filaments: Thin stalks that support the anthers.

  • Anthers: Located at the top of the filaments; they contain pollen grains (male gametes).

• Carpels (Pistils): The female reproductive organs, consisting of the stigma, style, and ovary.

  • Style: The stalk-like structure that connects the stigma to the ovary.

  • Stigma: The sticky, receptive surface where pollen grains land.

  • Ovary: The base of the carpel that contains the ovules (female gametes).

  • Ovules: Located inside the ovary, they contain the eggs that, once fertilized, will develop into seeds.

2. State the functions of the structures listed in 16.3.1:

• Sepals: Protect the flower bud before it opens.

• Petals: Attract pollinators by being colorful and fragrant.

• Stamens: Produce and release pollen (male gametes).

  • Filaments: Support the anthers, keeping them in a position to release pollen.

  • Anthers: Contain and release pollen during pollination.

• Carpels: The female reproductive organs involved in receiving pollen and producing seeds.

  • Style: Supports the stigma and provides a pathway for pollen tubes.

  • Stigma: Receives pollen during pollination.

  • Ovary: Houses the ovules and develops into fruit after fertilization.

  • Ovules: Contain eggs that, once fertilized by pollen, will develop into seeds.

3. Identify in diagrams and images and describe the anthers and stigmas of a wind-pollinated flower:

• Anthers (Wind-Pollinated Flower):

  • Description: In wind-pollinated flowers, the anthers are often exposed and loose to release large amounts of pollen into the air.

  • Structure: They are typically smaller and lighter compared to those of insect-pollinated flowers.

• Stigmas (Wind-Pollinated Flower):

  • Description: The stigma is feathery or brush-like, which helps it catch and trap pollen carried by the wind.

  • Structure: The stigma is often large and spread out to increase surface area for pollen capture.

4. Distinguish between the pollen grains of insect-pollinated and wind-pollinated flowers:

• Insect-Pollinated Flowers:

  • Pollen: The pollen grains are usually larger, sticky, and spiky to stick to the bodies of insects.

  • Quantity: They produce a moderate amount of pollen, enough to be transferred by insects but not so much as to waste.

• Wind-Pollinated Flowers:

  • Pollen: The pollen grains are generally smaller, lighter, and smooth to be carried easily by the wind.

  • Quantity: These flowers produce a large amount of pollen to increase the chance of some being carried to another flower.

5. Describe pollination as the transfer of pollen grains from an anther to a stigma:

• Pollination: It is the process of transferring pollen grains from the anther (male part) to the stigma (female part) of a flower.

  • Insect Pollination: Insects such as bees, butterflies, or moths carry pollen from one flower to another as they gather nectar.

  • Wind Pollination: Pollen is carried by the wind to the stigma of another flower.

9. Describe self-pollination as the transfer of pollen grains from the anther of a flower to the stigma of the same flower or a different flower on the same plant:

• Self-Pollination:

  • Definition: Self-pollination occurs when pollen from the anther of a flower lands on the stigma of the same flower or another flower on the same plant.

  • Example: Peas, tomatoes, and some types of beans can self-pollinate.

• Advantages of Self-Pollination:

  • Ensures reproduction even when pollinators are absent.

  • Can be efficient in isolated plants or populations.

10. Describe cross-pollination as the transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species:

• Cross-Pollination:

  • Definition: Cross-pollination occurs when pollen is transferred from the anther of a flower on one plant to the stigma of a flower on another plant of the same species.

  • Pollinators: This type of pollination relies on external agents such as insects, wind, or water.

• Advantages of Cross-Pollination:

  • Increases genetic diversity, which can make offspring more resistant to diseases and environmental changes.

11. Discuss the potential effects of self-pollination and cross-pollination on a population, in terms of variation, capacity to respond to changes in the environment, and reliance on pollinators:

Self-Pollination:

• Variation: Limited genetic variation because the offspring are genetically similar to the parent.

• Capacity to Respond to Changes in the Environment: Reduced ability to adapt to environmental changes due to low genetic diversity.

• Reliance on Pollinators: Self-pollinating plants don’t rely as much on pollinators because they can fertilize themselves, making them more independent of external conditions.

Cross-Pollination:

• Variation: Increases genetic variation because offspring inherit a mix of genes from two different plants.

• Capacity to Respond to Changes in the Environment: Enhanced ability to adapt to changes in the environment due to the genetic diversity within the population.

• Reliance on Pollinators: Cross-pollinating plants depend heavily on pollinators (e.g., insects, birds), which makes them vulnerable to a decline in pollinator populations.

• 6. State that fertilisation occurs when a pollen nucleus fuses with a nucleus in an ovule:

  • Fertilisation:

    • Definition: Fertilisation occurs when the nucleus of a pollen grain (from the male gamete) fuses with the nucleus of an ovule (female gamete) within the ovary of the flower.

    • Outcome: The result of fertilisation is the formation of a zygote, which will develop into a seed.

    • Pollen Tube: The pollen grain grows a pollen tube that carries the male gamete to the ovule for fertilisation.

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  7. Describe the structural adaptations of insect-pollinated and wind-pollinated flowers:

  Insect-Pollinated Flowers:

  • Brightly-Colored Petals: Often brightly colored to attract insects like bees, butterflies, and moths.

  • Scented Flowers: Flowers may produce sweet fragrances to attract pollinators.

  • Sticky Pollen: Pollen grains are sticky to adhere to the bodies of insects as they visit flowers.

  • Nectar: Nectar is produced as a reward for the pollinators, encouraging them to visit the flowers.

  • Large, Showy Petals: Petals are often large and showy to ensure that insects can easily find the flower.

  • Anthers and Stigmas:

    • Anthers are usually inside the flower, positioned so that insects brush against them.

    • Stigmas are sticky to catch pollen from the insects as they move from one flower to another.

  Wind-Pollinated Flowers:

  • Small, Green Petals: These flowers lack large, showy petals since they do not rely on visual attraction.

  • No Scent or Nectar: Wind-pollinated flowers typically do not produce fragrance or nectar since they do not need to attract pollinators.

  • Light, Small Pollen Grains: The pollen grains are smaller, lighter, and more numerous, allowing them to be carried by the wind.

  • Exposed Anthers: Anthers are often exposed outside the flower to release large amounts of pollen into the air.

  • Feathery Stigmas: The stigma is often large, feathery, or brush-like to catch the small pollen grains carried by the wind.

  • Flowers Are Often Located in Large Groups: Wind-pollinated plants often grow in dense groups to increase the chances of cross-pollination via the wind.

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  8. Investigate and describe the environmental conditions that affect germination of seeds, limited to the requirement for: water, oxygen, and a suitable temperature:

  • Water:

    • Requirement: Water is essential for seed germination because it activates enzymes that break down stored food in the seed, providing energy for the growing seedling.

    • Effect of Water: Inadequate water will prevent the seed from swelling and softening the seed coat, hindering germination. Excessive water can cause the seed to rot.

  • Oxygen:

    • Requirement: Oxygen is needed for cellular respiration, which provides the energy required for seed growth.

    • Effect of Oxygen: Without oxygen, seeds will not be able to carry out respiration and thus cannot germinate.

  • Suitable Temperature:

    • Requirement: Seeds need a specific temperature range for enzymes to work effectively during germination.

    • Effect of Temperature: If the temperature is too low, enzymatic activity slows down, and the seed cannot germinate. If the temperature is too high, it can damage the seed, preventing germination.

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  12. Describe the growth of the pollen tube and its entry into the ovule followed by fertilisation (details of production of endosperm and development are not required):

  • Pollen Tube Growth:

    • After pollination, the pollen grain germinates on the stigma of the flower.

    • A pollen tube begins to grow from the pollen grain through the style, the narrow stalk connecting the stigma to the ovary.

  • Entry into the Ovule:

    • The pollen tube carries the male gamete (sperm cell) down through the style and into the ovary, where it reaches the ovule.

    • The pollen tube penetrates the micropyle (an opening in the ovule) and delivers the male gamete into the ovule.

  • Fertilisation:

    • The male gamete fuses with the female gamete (egg cell) inside the ovule to form a zygote.

    • This fertilisation results in the formation of the seed, which will develop into a new plant.

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