- Organisms can be characterised in the way they absorb oxygen.
- Fish – have gill to gain oxygen from water.
- Young amphibians – also have gills
- Adult amphibians – normally have lungs but can absorb oxygen through their moist skin.
- Mammals, birds and reptiles – have lungs
- Organisms can be characterised based on how they reproduce.
- External fertilisation – adult female releases her eggs in water and are fertilised by sperm released by an adult male.
- Internal fertilisation – takes place inside the female’s body.
- Oviparous – lays eggs (many vertebrate do this)
- Viviparous – give birth to live young (mammals)
- Organisms can be characterised on the way they regulate body temperature.
- Homeotherms – keep their body temperature constant and often warmer than their surroundings from reactions all over body.
- Poikilotherms – their body temperature varies based on their surroundings.
- Within a group species have different characteristics to the rest of the group; a few amphibians have gills even as adults and sharks have internal fertilisation and give birth to live young, even though they are fish. As a result, we have to look at many characteristics to see where to put an organism.
- A species can be defined as a group of organisms that can interbreed to reproduce offspring that are fertile. However this definition isn’t always clear cut because two closely related species can interbreed but produce hybrids which are infertile most of the time. This means they are unlikely to have offspring of their own and pass on their mix of characteristics.
- Another problem is that not all organisms need to interbreed to produce offspring. For example, many plants and fungi can produce new individuals from parts of adult organisms. Bacteria and many protoctists reproduce by splitting in half.
- If organisms never interbreed we cannot test whether or not two individuals are the same species.
That's the end of the topic!
Drafted by Joey (Biology)