1define system, give one example of system and mention its 3 comonents 2-give one example of negative feedback
3-give one example of positive feedback
4-explain 4 spheres in earth

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.

what about it?

is this a ?

critical-thinking skills and knowledge of environmental regulations-b.