Why are cacti green and why do they need needles

The needle-like leaves act as a self-defense mechanism that protects the plant from predators. The stem of the cactus plant is swollen and contain numerous collapsible water-storage cells that store water for a relatively long period. The stem is green and performs photosynthesis.

Explanation:

answer; /// i believe the correct answer is (reactants);

the offspring would all be white. if the parents are both white flowers then they have the genotype rr, which when crossed results in an all white punnet square.