Sexual and asexual reproduction (AQA GCSE Biology): Revision Notes
Sexual and asexual reproduction
Living things can make new individuals in two main ways. They can reproduce sexually or asexually. Each method has different features and benefits.
What are the two types of reproduction?
Sexual reproduction needs two parents. The parents make special sex cells called gametes. These gametes join together to create offspring that are different from their parents.
Asexual reproduction needs only one parent. The parent makes copies of itself called clones. These offspring are identical to their parent.
The key difference is in the number of parents required and whether the offspring are identical to or different from their parents.
Key differences between sexual and asexual reproduction
Understanding the main differences helps explain why organisms might use one method over another:
| Feature | Sexual reproduction | Asexual reproduction |
|---|---|---|
| Number of parents | Two | One |
| Meiosis happens? | Yes | No |
| Gametes join together? | Yes | No |
| Mitosis happens? | Yes | Yes |
| Genetic mixing | Yes - genes mix | No - no mixing |
| Offspring | Different from parents | Identical to parent |
Important facts about gametes
Gametes are sex cells made by meiosis during sexual reproduction. There are two types:
- Male gametes are sperm cells in animals and pollen cells in plants
- Female gametes are egg cells in both animals and plants
How mitosis helps both types of reproduction
Mitosis makes clones - cells that are genetically identical. In asexual reproduction, mitosis creates the identical offspring. In sexual reproduction, mitosis helps organisms grow by making more cells.
Sexual reproduction
Advantages of sexual reproduction
Sexual reproduction has several benefits:
- Creates variation - offspring are different from parents and each other
- Helps survival - variation means some individuals may survive environmental changes better
- Allows natural selection - the best-adapted individuals survive and reproduce
- Useful for humans - we can use selective breeding to improve crops and animals
The main advantage of sexual reproduction is genetic variation. This variation is essential for species survival when environments change, as some individuals are more likely to have characteristics that help them survive.
Disadvantages of sexual reproduction
Sexual reproduction also has drawbacks:
- Takes time and energy - individuals must find a mate
- Slower process - producing gametes and finding mates takes time
Asexual reproduction
Advantages of asexual reproduction
Asexual reproduction has these benefits:
- No mate needed - saves time and energy
- Faster reproduction - many offspring can be made quickly when conditions are good
Asexual reproduction is particularly advantageous when environmental conditions are stable and favourable, allowing rapid population growth without the need to find a mate.
Disadvantages of asexual reproduction
The main problems with asexual reproduction:
- No variation - all offspring are identical to the parent
- Poor adaptation - if the environment changes, all individuals may struggle to survive or may die
Examples in nature
Worked Example: Fungi and Plasmodium
Many fungi can reproduce both ways:
- Asexually by making spores in mushrooms and toadstools
- Sexually to create variation in the population
The Plasmodium parasite (causes malaria) reproduces asexually in humans but sexually in mosquitoes.
Worked Example: Plant Reproduction Strategies
Many plants have clever reproduction strategies:
- Strawberry plants spread using runners - this is asexual reproduction
- Daffodils can form underground bulbs that split - also asexual reproduction
- Plants usually have features that help their seeds spread away from the parent plant to reduce competition for resources
Sexual reproduction in plants creates variation, which helps the population survive environmental changes.
Key Points to Remember:
- Sexual reproduction uses two parents, creates variation, and helps species adapt to changes
- Asexual reproduction uses one parent, creates identical clones, and is faster when conditions are good
- Meiosis makes gametes for sexual reproduction
- Mitosis makes identical cells for growth and asexual reproduction
- Both methods have advantages and disadvantages depending on the environment