(a) What is role of Carbohydrates and Vitamins in the body? Discuss briefly. (b) Discuss the functioning of Liver and Pancreas. (c) What are the standards of drinking water? How Heavy Metals in the water affect the living organisms? (d) What is radioactivity? Discuss the laws of radioactivity. Name two radioactive elements.

(a) Role of carbohydrates and vitamins

Carbohydrates

(i) they are the body's main energy source, with glucose used for cellular respiration, particularly by the brain; (ii) they store energy as glycogen in the liver and muscles; (iii) they spare protein from being used for energy; (iv) they form parts of larger molecules, such as ribose in RNA and glycoproteins; (v) dietary fibre aids digestion.

Vitamins: these organic nutrients are needed in small amounts and regulate many body processes. Many B vitamins act as coenzymes in metabolism. Vitamin A supports vision and immunity, vitamin C supports collagen formation and acts as an antioxidant, vitamin D helps absorb calcium, vitamin E is an antioxidant, and vitamin K is needed for blood clotting. Lack of a vitamin causes a deficiency disease, such as scurvy or rickets.

(b) Functioning of the liver and pancreas

Liver: the largest internal organ, it manages metabolism of carbohydrates, fats and proteins; stores glycogen and vitamins; produces bile for digesting fats; makes plasma proteins and clotting factors; detoxifies drugs and toxins; and converts ammonia to urea.

Pancreas: this organ has a double function. Its exocrine part releases pancreatic juice into the duodenum, with amylase, lipase and proteases such as trypsin to digest food, and bicarbonate to neutralise stomach acid. Its endocrine part, the islets of Langerhans, secretes the hormones insulin, which lowers blood sugar, and glucagon, which raises it.

The two work together: bile and pancreatic juice reach the intestine through a common route, and pancreatic hormones regulate the storage and release of glucose by the liver.

(c) Drinking water standards and heavy metals

Standards: national standards vary, but commonly cited WHO values for safe drinking water include:

E. coli: none detectable in 100 mL pH: 6.5 to 8.5 Turbidity: below 5 NTU, ideally below 1 Arsenic: 0.01 mg/L (Pakistan's limit is 0.05 mg/L) Lead: 0.01 mg/L Mercury: 0.006 mg/L Cadmium: 0.003 mg/L Fluoride: 1.5 mg/L Nitrate: 50 mg/L

Effects of heavy metals on living organisms: these metals do not break down, and they bioaccumulate in tissues and biomagnify along food chains. They damage cells by blocking enzymes and creating oxidative stress.

Lead: damages the brain and nerves, particularly in children. Arsenic: causes skin lesions and cancers, a problem in parts of Punjab and Sindh groundwater. Mercury: damages the nervous system, as seen in Minamata disease. Cadmium: damages kidneys and bones. Chromium: hexavalent chromium is carcinogenic. Aquatic life: metals harm gills, reproduction and growth in fish, and reduce biodiversity. Plants: they reduce growth and pass the metals into crops.

(d) Radioactivity

Radioactivity is the spontaneous emission of radiation (alpha, beta and gamma) by unstable atomic nuclei as they decay to more stable forms. It is unaffected by temperature or pressure.

Laws of radioactivity

Displacement law (Soddy and Fajans): in alpha decay, the mass number falls by 4 and the atomic number by 2. In beta (minus) decay, the mass number stays the same and the atomic number rises by 1. In gamma emission, neither changes. Law of radioactive decay: the rate of decay is proportional to the number of undecayed nuclei: dN/dt = −λN, giving N = N₀e^(−λt), where λ is the decay constant. Half-life: the time for half the nuclei to decay, given by T½ = 0.693/λ.

Two radioactive elements: uranium and radium.