Which organelle is the powerhouse of the cell, the site of cellular respiration?

What is thought to have caused the mass extinction at the end of the cretaceous period?

Elephants in the savanna regions of africa dig holes in dried up river beds to reach water lying just below the surface. these holes provide drinking water for other animals as well. so, without the elephants, many animals might otherwise die from lack of water during the dry season. the location in which the elephants live is an example of a/n and the role they play in creating water holes is an example of a a) ecosystem; habitat b) community; niche c) habitat; niche d) niche; habitat

The cluster of developing cells from conception until birth is called an