Biology (5090)
Carbohydrates: Main energy source. Found in rice, roti, potatoes. Broken into glucose. Proteins: Growth and repair. Found in meat, daal, eggs. Made of amino acids. Fats (Lipids): Energy store and insulation. Found in ghee, butter, oil. Broken into fatty acids + glycerol. Vitamins: Small amounts needed. Vitamin C (fruit) prevents scurvy. Vitamin D (sunlight) for bones. Minerals: Iron (for haemoglobin), Calcium (for bones and teeth). Fibre: Keeps digestive system healthy, prevents constipation. Water: Solvent for reactions, transport medium.
Work best at optimum temperature (~37°C for human enzymes) Work best at specific pH Lock and key model: Each enzyme has a specific shape that fits one substrate
Amylase: Starch → Maltose (in mouth and small intestine) Protease/Pepsin: Proteins → Amino acids (in stomach, pH 2) Lipase: Fats → Fatty acids + Glycerol (in small intestine) Bile: Not an enzyme! Emulsifies fats (breaks into smaller droplets). Made in liver, stored in gall bladder.
Topic 2 of 4Cambridge O Levels
Nutrition & Enzymes
Food groups, digestion, and how enzymes work
Your body needs food for energy, growth, and repair. Nutrition is the process of taking in and using food.
Food Groups:
Enzymes:
Biological catalysts that speed up reactions without being used up.
Digestive Enzymes:
Key Points to Remember
- 1Carbs = energy, Proteins = growth/repair, Fats = energy store
- 2Enzymes: biological catalysts with specific shapes (lock & key)
- 3Amylase → starch, Protease → protein, Lipase → fats
- 4Enzymes denatured above optimum temperature
Pakistan Example
Digesting Biryani
A plate of biryani is a chemistry lab! The rice (carbs) starts being digested in your mouth — amylase in saliva breaks starch into maltose. The chicken (protein) is attacked by pepsin in your stomach at pH 2 (very acidic). The ghee and oil (fats) get emulsified by bile in your small intestine, then lipase breaks them into fatty acids. A balanced Pakistani meal of daal (protein), chawal (carbs), and sabzi (vitamins + fibre) actually covers all food groups perfectly!