Many types of sea stars eat mussels and other shellfish. suppose an oil spill causes thousands of mussels in an area to die. how will this most likely affect the area's sea star population?

This could lead to the decrease in the areas sea star population. If there is not enough food, the animals may not be able to survive. 

Amutation is basically the change in the gene, caused by alteration of single based units in the dna, or the genes or chromosomes were rearranged in the dna

By water evaporation from the leaves is created a negative pressure at the top of the tree that promotes the ascension  of the water through channels that are called xylem. there are also two molecule forces that are involved: the intra-water molecules cohesion (water molecules stick to each other) and the adhesion when the water molecules stick to the channels they are running in. this is what enables water to go from the roots to the top of a tall tree.