Mutation are two types somatic and germ cell mutation...as there is mutation in germ cell it will alter the normal behavior and produce variation !
random fertilization also causes variation as different setup of genes meets with another different...so chances of variation increases !
and third crossing over is in meiosis when chiasmata forms....so in this two homologous chromosome attach to each other and on separation ... some part exchange so leads to variation !
Enzymes reduce the activation energy allowing chemical reactions to occur in living things.
it is not because trees do not grow fast enough
