Reproduction - Sexual Reproduction In Flowering Plants - Introduction

Definition of Sexual Reproduction
Importance of Sexual Reproduction in Plants
Alternation of Generations
Life Cycle of a Flowering Plant
The Female Reproductive Organ - Carpel
- Parts of a Carpel
- Functions of a Carpel
The Male Reproductive Organ - Stamen
- Parts of a Stamen
- Functions of a Stamen
Pollination
- Definition of Pollination
- Types of Pollination (Self-Pollination, Cross-Pollination)
Fertilization
- Definition of Fertilization
Seed Formation
- Process of Seed Formation
- Structure of a Seed

Definition of Pollination: The transfer of pollen grains from the anther to the stigma of a flower.
Types of Pollination:
- Self-Pollination: Pollen grains from the anther of a flower are transferred to the stigma of the same flower or another flower on the same plant.
- Cross-Pollination: Pollen grains from the anther of a flower are transferred to the stigma of a different flower on a different plant of the same species.

Wind Pollination: In some plants, pollen grains are light and produced in large quantities, and they are carried by wind to the stigma of the flower.
Insect Pollination: Many flowers produce nectar and have bright colors and attractive scents to attract insects, which inadvertently carry the pollen from one flower to another.

Definition of Fertilization: The fusion of the male and female gametes to form a zygote.
Process of Fertilization:
1. Pollen grain lands on the stigma.
2. A pollen tube grows from the pollen grain and enters the ovary through the style.
3. The nuclei in the pollen tube divide to form two male gametes.
4. One male gamete fuses with the egg cell to form a zygote.
5. The other male gamete fuses with the two polar nuclei to form the endosperm.

Process of Seed Formation:
1. After fertilization, the zygote develops into an embryo inside the ovule.
2. The ovule develops into a seed, consisting of the embryo, endosperm, and seed coat.
3. The ovary develops into a fruit that protects and disperses the seed.

Definition of Germination: The process by which a seed transforms into a seedling and starts to grow into a new plant.
Conditions required for Germination:
- Water: To activate enzymes and provide moisture.
- Oxygen: For respiration.
- Suitable Temperature: To ensure metabolic activities.
- Light: Some seeds require light to germinate, while others need darkness.

Epigeal Germination: The cotyledons emerge above the ground, e.g., in beans and peas.
Hypogeal Germination: The cotyledons remain below the ground, e.g., in maize and wheat.

Examples of Pollinators:
- Insects: Bees, butterflies, moths, beetles.
- Birds: Hummingbirds, sunbirds.
- Bats: Fruit bats.
- Wind: Wind-pollinated plants.

Genetic Variation: Sexual reproduction leads to genetic diversity, which helps in adaptation and evolution.
Dispersal of Offspring: Seeds and fruits aid dispersal, allowing plants to colonize new areas.
Repair and Regeneration: Sexual reproduction enables plants to repair damaged tissues and regenerate lost parts.

Floral Morphological Adaptations:
- Attractive Colors and Scents: To attract pollinators.
- Nectar: Serves as a reward for pollinators.
- Shape and Structure: Variations in shapes and structures of flowers to facilitate specific pollinators.

Hermaphroditism: In some plants, both male and female reproductive structures are present in the same flower (e.g., lilies).
Monoecious Plants: These plants have separate male and female flowers on the same plant (e.g., corn).
Dioecious Plants: These plants have male and female flowers on separate plants (e.g., papaya).

Unique feature in flowering plants.
Involves the fusion of one male gamete with the egg cell and another male gamete with the polar nuclei.
Results in the formation of the zygote and the endosperm, respectively.

A mechanism to prevent self-fertilization in plants.
Recognition proteins present on the stigma reject the pollen from the same plant.
This promotes outcrossing and genetic diversity.

Advantages of Seed Dispersal:
- Reduces competition between parent and offspring.
- Increases the chance of colonization in new areas.
- Prevents overcrowding and enhances genetic diversity.

Wind Dispersal: Lightweight seeds with structures like wings or hairs are carried by the wind (e.g., dandelion seeds).
Water Dispersal: Seeds are transported by water bodies, such as rivers and oceans (e.g., coconut seeds).
Animal Dispersal: Seeds may stick to fur or feathers of animals, or be ingested and excreted (e.g., burdock seeds).

Seed Dormancy: A period of inactivity in the life of a seed.
Advantages of Seed Dormancy:
- Helps seeds survive unfavorable conditions.
- Allows for proper timing of germination.

Types of Asexual Reproduction:
- Vegetative Propagation: New plants arise from vegetative parts like stems or leaves (e.g., runners in strawberry plants).
- Apomixis: Seeds are formed without the involvement of meiosis or fertilization.

Advantages of Asexual Reproduction:
- Rapid multiplication of desirable traits.
- No need for pollinators or external agents.
- Allows propagation of hybrid plants.
Disadvantages of Asexual Reproduction:
- Limited genetic variation.
- Vulnerability to diseases and pests.
- Lack of adaptability in changing environments.