You are reading a scientific paper regarding the relationships of the anatomical and behavioral characteristics of chimpanzees and their implications for early hominid evolution. You note that the authors refer to human ancestors as hominids. This implies that the researchers are relying on:

what are the choices?

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

a chair, a bed, and a toothbrush

explanation:

i was told this before by a teacher, so yeah

many other transport proteins, often called pumps, move materials against a concentration gradient. active transport drives molecules across a membrane from a region of lower concentration to a region of higher concentration. this process, shown in figure 5.1, uses transport proteins powered by chemi- cal energy.