1. Biosynthetic pathways in living organisms are usually different from degradation pathways for flexibility and to overcome Le Châtelier's principle. 2. Carbohydrate biosynthesis includes conversion of CO2 to glucose in plants, synthesis of glucose from non-carbohydrate sources via gluconeogenesis in animals, and conversion of glucose to other carbohydrates. 3. Fatty acid biosynthesis occurs in the cytosol using acetyl-CoA as a starting material, while degradation occurs in mitochondria. Membrane lipids are synthesized from fatty acid derivatives and glycerol phosphate. Cholesterol is derived from acetyl-CoA and mevalonate is a key intermediate in its synthesis.