Sexual reproduction in plants Revision Notes

Sepals protect the flower bud before it opens. Petals are often colorful and scented to attract insects for pollination.

• Sepals form the outermost layer.
• Petals attract pollinators with color and scent.

Stamens consist of filaments and anthers. The filament is a stalk that holds the anther, where pollen is produced.

• Filament supports the anther.
• Anther produces pollen grains.

The carpel includes the stigma, style, ovary, and ovules. The stigma receives pollen, the style is a tube connecting stigma to ovary, and the ovary contains ovules which develop into seeds after fertilization.

• Stigma catches pollen.
• Style connects stigma to ovary.
• Ovary contains ovules (female gametes).

The testes produce sperm cells and the hormone testosterone. The sperm duct carries sperm from the testes to the urethra. The urethra transports sperm out of the body during ejaculation.

• Testes produce sperm and testosterone.
• Sperm duct transports sperm to urethra.
• Urethra expels sperm from the body.

The ovaries produce eggs (ova) and hormones such as estrogen and progesterone. The oviducts (fallopian tubes) transport eggs from the ovaries to the uterus. The uterus is where a fertilized egg can implant and develop into a fetus.

• Ovaries produce eggs and hormones.
• Oviducts carry eggs to uterus.
• Uterus supports fetal development.

Each structure plays a vital role in producing gametes, transporting them, and supporting fertilization and development, ensuring successful human reproduction.

• Testes and ovaries produce gametes and hormones.
• Transport structures move gametes to fertilization site.
• Uterus provides environment for embryo growth.

In wind-pollinated flowers, anthers are large and hang outside the flower. This exposed position allows pollen grains to be released directly into the air, increasing the chance of dispersal by wind.

The large size of the anthers supports the production of abundant pollen grains, which is necessary because wind dispersal is less targeted than insect pollination.

• Anthers are large to produce many pollen grains.
• Anthers hang outside the flower for easy pollen release into the air.

The stigmas in wind-pollinated flowers are large and feathery. This feathery structure increases the surface area, making it easier to catch pollen grains carried by the wind.

Stigmas are also positioned outside the flower to maximize exposure to airborne pollen.

• Stigmas are large and feathery to trap pollen effectively.
• Positioned outside the flower to intercept wind-borne pollen.

These structural features of anthers and stigmas increase the efficiency of pollination by wind, compensating for the randomness of wind dispersal.

By producing large amounts of pollen and having stigmas adapted to catch airborne pollen, wind-pollinated flowers maximize their chances of successful fertilization.

• Large pollen production offsets random wind dispersal.
• Feathery stigmas improve pollen capture efficiency.

Insect-pollinated flowers produce larger and heavier pollen grains. This size helps the pollen stick to the bodies of insects during visits.

Wind-pollinated flowers produce smaller and lighter pollen grains, which can be carried easily by air currents over long distances.

• Insect-pollinated pollen grains are large and heavy.
• Wind-pollinated pollen grains are small and light.

Pollen grains of insect-pollinated flowers are sticky or have spiky surfaces to attach firmly to insects.

Wind-pollinated pollen grains are smooth to reduce air resistance and prevent clumping, aiding wind dispersal.

• Insect-pollinated pollen is sticky or spiky for attachment.
• Wind-pollinated pollen is smooth for easy wind transport.

Sticky or spiky pollen ensures effective transfer by insects, which visit flowers deliberately.

Light, smooth pollen is produced in large quantities to compensate for the randomness of wind dispersal, increasing chances of reaching a stigma.

• Sticky pollen clings to insect bodies.
• Light pollen travels further in the wind.
• Large quantities of wind pollen increase pollination success.

Pollination is the transfer of pollen grains from the anther, the male part of a flower, to the stigma, the female part.

This transfer can occur via agents such as wind, insects, or other animals that carry pollen between flowers.

• Pollen moves from anther to stigma.
• Pollination can be by wind, insects, or animals.

The anther produces pollen grains containing male gametes.

The stigma receives pollen grains and provides a surface for pollen to land and germinate.

• Anther produces pollen.
• Stigma receives pollen for fertilisation.

Pollination is necessary for fertilisation to occur, which leads to seed and fruit development.

Without pollination, the male gametes cannot reach the female gametes inside the ovule.

• Pollination enables fertilisation.
• Fertilisation leads to seed formation.

Fertilisation is the fusion of the male nucleus from the pollen grain with the female nucleus inside the ovule.

After pollination, the pollen grain grows a pollen tube down the style to deliver the pollen nucleus to the ovule.

• Pollen nucleus fuses with ovule nucleus.
• Fusion occurs inside the ovule.

The pollen nucleus carries the male genetic material (male gamete).

The ovule contains the female nucleus (egg cell) that fuses with the pollen nucleus.

• Male nucleus = pollen nucleus.
• Female nucleus = ovule nucleus.

The fusion forms a fertilised egg cell (zygote) that will develop into a seed.

Fertilisation is essential for sexual reproduction and seed formation in plants.

• Fusion creates a zygote.
• Zygote develops into seed.

These flowers often have bright colors and strong scents to attract insects.

They produce nectar as a food reward for pollinators.

Their pollen grains are sticky or spiky to attach to insect bodies.

The stigma is sticky to catch pollen brought by insects.

• Brightly colored petals and scent attract insects.
• Nectar rewards pollinators.
• Sticky or spiky pollen adheres to insects.
• Sticky stigma traps insect-borne pollen.

Wind-pollinated flowers are usually small, dull-colored, and lack scent since they do not need to attract insects.

They produce large amounts of light, smooth pollen to be carried by wind.

Their stigmas are large and feathery to catch airborne pollen effectively.

• Small, dull petals with no scent.
• Produce large quantities of light, smooth pollen.
• Large, feathery stigmas to catch wind-borne pollen.

Insect-pollinated flowers invest in attracting and rewarding insects to ensure targeted pollen transfer.

Wind-pollinated flowers rely on producing abundant pollen and specialized stigmas to maximize chances of pollination by wind, which is less precise.

• Insect-pollinated flowers attract and reward pollinators.
• Wind-pollinated flowers maximize pollen dispersal and capture.

Water is essential for seeds to germinate because it activates enzymes and softens the seed coat. This allows the embryo inside to begin growing by starting metabolic processes.

• Water uptake triggers enzyme activation.
• Softens seed coat to allow growth.

Oxygen is required for aerobic respiration in the seed, which releases energy needed for cell division and elongation during germination.

• Oxygen enables aerobic respiration.
• Energy from respiration powers growth.

Temperature affects enzyme activity controlling germination. Seeds have an optimal temperature range where enzymes work best. Too low temperatures slow enzyme activity; too high temperatures can denature enzymes and stop germination.

• Optimal temperature range varies by species.
• Low temperature slows germination.
• High temperature can damage enzymes and prevent germination.

Self-pollination occurs when pollen grains produced by the anther are transferred directly to the stigma of the same flower or to the stigma of another flower on the same plant. This transfer does not involve pollen from a different plant.

The anther, part of the male reproductive organ (stamen), produces pollen grains containing male gametes. The stigma, part of the female reproductive organ (pistil), receives these pollen grains to enable fertilization.

• Pollen moves from anther to stigma within the same flower or between flowers on the same plant.
• No involvement of pollen from other plants.
• Fertilization occurs when male gametes from pollen unite with female gametes in the ovule.

Self-pollination ensures that a plant can reproduce even when pollinators or other plants are scarce, making it advantageous in stable or isolated environments.

Because the pollen comes from the same plant, offspring tend to be genetically similar, which can be beneficial for maintaining successful traits but limits genetic diversity.

• Enables reproduction without relying on external pollen sources.
• Common in some flowering plants to guarantee fertilization.
• Results in less genetic variation compared to cross-pollination.

The key parts involved in self-pollination are the anther, which produces pollen, and the stigma, which receives pollen.

The pollen tube grows from the pollen grain on the stigma to deliver male gametes to the ovule for fertilization.

• Anther: produces pollen grains.
• Stigma: receives pollen grains.
• Pollen tube: transports male gametes to ovule.

Cross-pollination occurs when pollen grains produced by the anther of one flower are transferred to the stigma of a flower on a different plant, but within the same species.

This transfer is often facilitated by agents such as insects, wind, or animals that carry pollen between plants.

The pollen grain germinates on the stigma, leading to fertilization when male gametes fuse with female gametes in the ovule.

• Pollen moves from anther of one flower to stigma of another flower on a different plant.
• Both plants must be of the same species for successful fertilization.
• Pollination agents include insects, wind, and animals.

Cross-pollination increases genetic variation within a plant population because offspring inherit genes from two different parents.

Greater genetic variation improves the population's ability to adapt to environmental changes and survive challenges.

However, cross-pollination depends on the presence of pollinators or suitable agents to transfer pollen.

• Increases genetic diversity among offspring.
• Enhances adaptability and survival of the species.
• Relies on pollinators or environmental factors for pollen transfer.

The anther produces pollen grains that are transferred to the stigma of another flower on a different plant.

The stigma receives pollen grains and supports pollen germination and pollen tube growth for fertilization.

• Anther: produces pollen grains.
• Stigma: receives pollen grains from another plant.
• Pollen tube: grows to deliver male gametes to the ovule.

Self-pollination produces offspring genetically similar to the parent, resulting in reduced genetic variation within the population.

Lower genetic variation limits the population's ability to adapt to environmental changes or new challenges.

However, self-pollination does not require pollinators, allowing plants to reproduce even when pollinators are scarce or absent.

• Decreases genetic variation in the population.
• Limits adaptability to changing environments.
• Reduces dependence on pollinators for reproduction.

Cross-pollination mixes genetic material from different plants, increasing genetic variation within the population.

Higher genetic variation enhances the population's ability to adapt to environmental changes and survive.

Cross-pollination depends on pollinators such as insects, wind, or animals, making plants reliant on these agents for successful reproduction.

• Increases genetic variation in the population.
• Improves adaptability to environmental changes.
• Requires pollinators or agents for pollen transfer.

Plants may use self-pollination to ensure reproduction when pollinators or mates are unavailable, but this limits genetic diversity.

Cross-pollination promotes diversity and adaptability but depends on external factors like pollinator presence.

Understanding these impacts helps explain plant survival strategies in different environments.

• Self-pollination ensures reproduction but limits variation.
• Cross-pollination promotes variation but depends on pollinators.
• Both strategies have advantages and disadvantages depending on environmental conditions.

When a pollen grain lands on a compatible stigma, it absorbs moisture and begins to germinate.

A pollen tube starts to grow from the pollen grain, extending down through the style towards the ovary.

The pollen tube acts as a passageway for male gametes to travel to the ovule.

• Pollen grain lands on stigma and absorbs moisture.
• Germinates by producing a pollen tube.
• Pollen tube grows directionally down the style.

The pollen tube grows through the style tissue, guided chemically towards the ovule.

It enters the ovule through a small opening called the micropyle.

This targeted growth ensures delivery of male gametes to the female gamete inside the ovule.

• Pollen tube grows through style tissue.
• Tube enters ovule via micropyle.
• Growth is directed by chemical signals.

Male gametes travel down the pollen tube to reach the female gamete (egg cell) inside the ovule.

Fertilization occurs when a male gamete fuses with the female gamete, forming a zygote.

This initiates seed development, although details of endosperm formation are beyond this scope.

• Male gametes move through pollen tube to ovule.
• Fusion of male and female gametes occurs inside ovule.
• Zygote formation starts seed development.