Describe the biological needs for cells to be surrounded by a membrane that is selectively permeable for different materials.

Plsss > .< compare and contrast the characteristics of flatworms rounds worms and earthworms

What are the student's observations and inferences before he starts his investigation?

Which of the following statements is true about the relationship between genetic variation and natural selection? a. genetic variation must be present in a population before natural selection can act on it. b. genetic variation arises in a population as a result of natural selection. c. natural selection can act on a population whether there is genetic variation within the population or not. d. after natural selection acts on a population, the amount of genetic variation in the population always increases.