Explain the difference in the function of plant and animal cell organelles, including cell membranecell wall, nucleus, cytoplasm mitochondrion, chloroplast and vacuole.

What was the land like over 500 million years ago? what was under the sea?

Which blood cell spend most of their time in the lymphatic system?

The concept of keystone species is controversial among ecologists because most organisms are highly interdependent. if each of the trophic levels is dependant on all others how can we say one is most important