To get Merit or Excellence grades in Science, you need to expand on simple answers, but don't skip the basics.
try this process 'DEL': define, explain, link
define terms
explain your answer
make links to bigger Science ideas
some examples of bigger Science ideas to link to:
for Genetics: survival of a species, genetic variation within a population, evolution, natural selection, shuffling of genes (which results in greater variation)
for Acids and Bases: valence electron movements, ionic bonding, dissociation (bonds breaking), the octet rule, stability resulting from full valence shell