External Fertilisation

Edexcel AS-level BiologyMeiosis and Sexual ReproductionLesson 24 of 28

In external fertilisation, males and females release their gametes into the surrounding water and the gametes fuse outside the body. Most bony fish, amphibians such as frogs, and many marine invertebrates such as sea urchins and corals reproduce this way.

Because the gametes are released into open water, many problems must be overcome:
• gametes are diluted, washed away or eaten, so very large numbers of gametes are released.
• males and females release gametes at the same time and place. This is called synchronised spawning and is triggered by environmental cues such as water temperature, day length or the lunar cycle, or by courtship behaviour (for example a male frog clasping a female while she lays eggs).

More in Meiosis and Sexual Reproduction

• Formation of Pollen
• Formation of Plant Egg Cells
• Pollination
• Internal Fertilisation
• Fertilisation in Humans
• Fertilisation in Plants
• Embryo Development in Mammals
• Differentiation

All 28 lessons in Meiosis and Sexual Reproduction · All Edexcel AS-level Biology topics