In people with sickle-cell disease, red blood cells break down, clump, and clog blood vessels. blood vessels and broken cells accumulate in the spleen. among other symptoms, this leads to physical weakness, heart failure, pain, and brain damage. such a suite of symptoms can be explained by

Name the glands associated with human digestive system

What is it called when part of a cell membrane closes around a molecule to allow the molecule to enter the cell? a. passive transport b. diffusion c. endocytosis d. exocytosisc. endocytosis

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.