What is the shortening of a muscle cell called?

1.contraction
2.expansion
3.piling
4.none of the above

The afrikaners are an example of a founder effect that occurs when a new colony is started by a few members of the original population and the random decrease in genetic variation is an example of

Long term exposure to waves can cause sunburns and skin cancer.

Give three examples of plant activities that are affected by circadian rhythms and natural fluctuations in the length of daylight?