Chapter 16: Reproduction (Part 1)

01 Asexual reproduction

Definition

A process resulting in the production of genetically identical offspring (clones) from one parent.

Examples

Predominantly occurs in plants, but also in some animals like starfish.

Advantages

• Only one parent is needed, which is useful in desolate environments.
• Allows for rapid population of an area to dominate a habitat.
• Requires less energy and is faster than sexual reproduction.

Disadvantages

• Lack of genetic diversity makes the whole population vulnerable to the same disease.
• Organisms cannot easily adapt to environmental changes.
• Can lead to overpopulation and overcrowding.

02 Sexual reproduction

Definition

A process involving the fusion of the nuclei of two gametes to form a zygote, producing offspring that are genetically different from each other.

Gametes

The nuclei of gametes (sperm and egg cells) are haploid (containing half a set of chromosomes), while the nucleus of a zygote is diploid (containing a full set).

Advantages

• High genetic diversity allows for adaptation to environmental changes.
• Evolution can occur through natural selection as beneficial traits are passed on.

Disadvantages

• Requires two parents, which may be difficult for endangered species.
• Produces fewer offspring and is less energy-efficient than asexual reproduction.

03 Sexual reproduction in plants

Plants use flowers for sexual reproduction. Pollen is the male gamete, and ovules contain the female gametes.

Flower structure

• Sepals: Protect unopened flowers.
• Petals: Often brightly coloured/scented to attract insects.
• Stamen (male): Consists of the anther (produces pollen) and filament (supports the anther).
• Carpel (female): Consists of the stigma (collects pollen), style (location for pollen tube growth), and ovary (contains ovules).

Pollination

The transfer of pollen grains from an anther to a stigma.

• Insect-pollinated: Large, scented petals; sticky stigmas; produces nectar; fewer, larger, and spiked pollen grains.
• Wind-pollinated: Small, dull petals; feathery stigmas and anthers hanging outside the flower; produces large quantities of small, light, smooth pollen.

Self vs. cross pollination

• Self-pollination: Transfer of pollen to a stigma on the same plant. It uses less energy but results in less genetic diversity.
• Cross-pollination: Transfer of pollen to a stigma on a different plant of the same species. It promotes variation and resilience to disease.

Fertilisation

A pollen tube grows down the style into the ovule, where the pollen nucleus fuses with the ovule nucleus to form a zygote.

Germination

Requires water (for swelling/growth), oxygen (for respiration), and a suitable temperature (for enzyme activity).