- they require nutrition
- they respire
- they excrete their waste
- they respond to their surroundings
- they move
- they control their internal conditions
- they reproduce
- they grow and develop.
What you need to know is that to be a living organism you must do all of the above.
A good way to remember this is a pneumonic: Mrs C. Gren is one example, trying to think of the colour sea green may help.