Struggle for existence- organisms produce more offspring than can survive. Struggle for existence refers to competition between living things to survive.
Survival of the fittest is saying that if you want something then you have to be faster than everyone else say there was a deer and 2 lions the quicker lion will get the deer so you have to be fit to survive.
Natural selection is the process where organisms better adapted to there environment tend to survive and produce more offspring. Since the environment can't support unlimited population growth, not all individuals get to reproduce to there full potential.
Extinct: describes a species that has completely disappeared from Earth. Adaptation: is a structure, behaviour, or physiological process that helps an organism survive and reproduce in a particular environment. e.g.: Hibernation is an example of a physiological adaptation