The variety of organisms that exist on Earth today can be directly attributed to A.
steady climate over millions of years
B.
extinction
C.
speciation that occurs when empty niches are filled
D.
Both A and B

Atypical human cell is approximately 12.00 μm in diameter and enclosed by a membrane that is 5.000 nm thick. (a) what is the volume of the cell including the membrane? (b) what is the volume of the cell membrane? (c) what percent of the total volume does its membrane occupy? to simplify the calculations, model the cell as a sphere. enter your answers using four significant figures.

What are the proteins in connectivity tissues of your foot examples of?

What does the number 18.9984 represent in the image?