Explain why xylem moves water in only one direction

It can and does pass fluids in either direction. Functionally, flow in xylem is only in one direction primarily because roots are at one end of the tree and evaporation/transpiration is at the other. Water also gets unloaded throughout the tree by osmosis.

Explanation:

both anaerobic and aerobic respiration use glucose (or other carbohydrates), proteins and lipids to produce atp and nadh. cell uses those energy molecules, obtained from food and   breaks them down during the chemical reactions of respiration. in anaerobic respiration, nadh is regenerated to nad+ by enzymes lactate dehydrogenase (lactate is produced, e.g. in muscle cells) or by alcohol dehydrogenase where ethanol is produced (alcohol fermentation), while in aerobic respiration, electrons from nadh are deposited in the mitochondria to regenerate nad+ (electron transport chain. anaerobic respiration produces 2 atp per molecule of glucose compared to aerobic respiration where about 38 atp molecules are produced.

the sphincter muscles at the end of the digestive tract is the anus.