Biology › Section Q · Immunity and reproduction › Topic Q.7
Early development and organ formation
Every animal body starts as a single cell. In a fixed order (fertilisation, cleavage, a hollow ball of cells, three germ layers, then organs), that cell builds a body with a head and a tail, a back and a belly, and a left side and a right side.
In this topic
- Fertilisation begins development
- Cleavage: many cells, no growth
- The blastula and the mammalian blastocyst
- Gastrulation: three germ layers
- What each germ layer becomes
- Worked example: tracing tissues to germ layers
- Differentiation and organogenesis
- Building the nervous system
- Somites and the body axes
- Worked example: the organiser experiment
- Common mistakes to avoid
- Key takeaways
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