Cellulases are enzymes capable of breaking down cellulose, releasing molecules of glucose. to which category of organic macromolecules does cellulose belong?

Cellulose belongs to carbohydrates.  

Cellulose is classified as a carbohydrate, a polysaccharide, as they are formed of the glucose monomers chain. It is the prime component in the walls of the cells of plants, assisting the plants to remain upright and stiff. Humans cannot digest cellulose due to the absence of cellulase, however, it is essential in the diet as fiber.  

However, the animals like sheep, cows, and horses can digest cellulose that is why they can acquire nutrients and energy they require from the grass.  

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.