"Answer DThe outermost layer of old epidermal cells are sloughed off and replaced every 15 to 30 days. The sebaceous glands secrete sebum which maintains the skin pH between 3 and 5. Bacteria which metabolize sebum live as opportunistic pathogens on the skin and cause skin infections."
Algae and nitrogen-fixing bacteria are photosynthetic organisms.
Passive membrane processes are those that do not require energy and move substances down a concentration gradient; namely, these are diffusion, facilitated diffusion and osmosis.
