Animal Classification (Biology Summary Notes 2011)
General Features of animals:
- Multicellular: The body is made up of many cells arranged into tissues.
- Heterotrophic: They ingest other organisms to obtain energy. Herbivores eat plants (Autotrophs) while carnivores consume heterotrophs. Carnivores consume decomposing matter.
- Active movement: Animals are mobile, they are able to move rapidly and in complex ways (flight).
- No cell walls: Animals lack a rigid cell wall, but are held together by extracellular frames of structural protein collagen.
- Reproduction: Most animals carry out sexual reproduction. (Gametes are formed by meiosis).
- Diversity: 99% of animals are invertebrates, others are vertebrates. The size of animals varies from microscopic organisms to enormous animals.
- Embryonic development: The zygote*1 undergoes mitotic cell division called cleavage and becomes a solid ball of cells called morula, then it becomes hollow and this is now called a blastula. The hollow part of the blastula is filled with fluid called the Blastocoel.
Gastula = ---> Development of specialized cells that form layers.
--->The formation of layers to specialize cells.
---> Every layer would give rise to organs and systems.
Evolution of the animals' body plan:
TO BE CONTINUED ...
*1 Zygote = fertilization of the egg