Living organisms have certain life processes in common. There are seven things that they need to do to count as being alive. The phrase MRS GREN is one way to remember them:
- Movement - all living things move, even plants
- Respiration - getting energy from food
- Sensitivity - detecting changes in the surroundings
- Growth - all living things grow
- Reproduction - making more living things of the same type
- Excretion - getting rid of waste
- Nutrition - taking in and using food
- There are two types of nutrition
- Heterotrophic nutrition: animals eat other living beings.
- Autotrophic nutrition: plants do not eat other living beings. They obtain their food from water, air and soil.
It can be easy to tell if something is living or not. A teddy bear might look like a bear, but it cannot do any of the seven things it needs to be able to do to count as being alive.
A car can move, it gets energy from petrol (like nutrition and respiration), it might have a car alarm (sensitivity), and it gets rid of waste gases through its exhaust pipe (excretion). But it cannot grow or make baby cars. So a car is not alive.
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