Active transport is the movement of molecules against the concentration gradient from an area of high concentration to an area of low concentration, which requires energy in the form of ATP. Hope this helps! ^.^
When we're doing scientific research, we should definitely be avoiding any sources which aren't scientific by nature. This means we should avoid sources which haven't been peer reviewed by fellow authors of a similar field. With this, we avoid using literature of questionable quality.
It allows the scientist to determine the age of the rock it is in
Answer:
Mechanical barriers — which include the skin , mucous membranes , and fluids such as tears and urine — physically block pathogens from entering the body. Chemical barriers — such as enzymes in sweat , saliva , and semen — kill pathogens on body surfaces.
