What are free radicals? Explain their formation and the role of antioxidants in the prevention of degenerative disorders.

1. 1 · Open in two lines. A free radical is an atom or molecule with an unpaired electron. It is unstable and grabs electrons from lipids, proteins and DNA.
2. 2 · Draw the defence chain. [Diagram: O2 → superoxide → (SOD) → H2O2 → (catalase / glutathione peroxidase) → H2O; side arrow H2O2 + Fe2+ → •OH]
3. 3 · List the ROS and their sources.
   • ROS: superoxide, H2O2, hydroxyl radical, singlet oxygen, nitric oxide.
   • Inside the body: ETC leak, phagocytes, xanthine oxidase, cytochrome P450, free iron (Fenton).
   • Outside: smoke, pollution, UV and X-rays, alcohol, reused frying oil.
4. 4 · Explain the damage. Lipid peroxidation of membrane PUFA (initiation, propagation, termination), protein damage and DNA mutation.
5. 5 · Describe the antioxidants.
   • Enzymes: SOD, catalase, glutathione peroxidase.
   • Dietary: vitamins C and E, β-carotene, polyphenols; minerals selenium, zinc, copper, manganese.
6. 6 · Significance. Antioxidants help protect against atherosclerosis (oxidised LDL), cancer, cataract, diabetic complications, Alzheimer's disease and ageing.
7. 7 · Nutrition link. Amla, guava, green leafy vegetables, carrot, groundnut, nuts and turmeric; whole foods rather than high-dose pills.
8. 8 · Close in one line. Health depends on balancing free radical production with antioxidant defence; an imbalance is called oxidative stress.

Scoring tip: Name Indian food sources for each dietary antioxidant. It is the Home Science angle examiners look for.