Choose all the answers that apply.
fertilization
is the union of an egg and sperm cell
results in a new cell with half the chromosomes of a gamete
combines the chromosomes from two gametes
can occur inside or outside the body
is necessary for sexual reproduction

it provides an alternative energy pathway for the reaction to proceed.

a catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction.

catalysts increase the rate of reaction without being used up. they do this by lowering the activation energy needed. with a catalyst, more collisions result in a reaction, so the rate of reaction increases. different reactions need different catalysts.

a catalyst works by providing an alternative reaction pathway to the reaction product. the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.

the planets have a circular orbit around the sun.