(a) Discuss importance of preservatives and antioxidants in food. (b) Comment, Green House Effect is a blessing. Also discuss Enhanced Green House Effect and its relation with global warming.

(a) Preservatives and antioxidants in food

Preservatives are substances that slow spoilage, chiefly by inhibiting bacteria, yeasts and moulds. Examples include sodium benzoate in soft drinks and sauces, potassium sorbate in cheese and bakery items, nitrites in cured meat, and sulphites in dried fruit. Salt, sugar and vinegar are traditional preservatives.

Importance of preservatives

(i) Food safety: they reduce the risk of food poisoning; nitrites, for example, inhibit the bacterium that causes botulism. (ii) Longer shelf life: food can be stored and transported for longer. (iii) Less waste: less food is lost in the supply chain. (iv) Wider availability: seasonal foods are available all year, including in remote areas. (v) Quality: colour, texture and flavour are maintained.

Antioxidants are compounds that slow oxidation, usually by neutralising free radicals or reacting with oxygen. Oxidation makes fats and oils rancid and causes browning. Common food antioxidants include vitamin C (ascorbic acid), vitamin E (tocopherols), BHA and BHT.

Importance of antioxidants

(i) they prevent rancidity, off-flavours and odours in oils, snacks and baked goods; (ii) they preserve colour, for example by limiting the browning of cut fruit; (iii) they protect nutrients such as fat-soluble vitamins and essential fatty acids; (iv) antioxidants naturally present in fruit and vegetables are part of a healthy diet, helping the body's defences against oxidative damage.

Caution: additives must stay within approved limits. Sulphites can provoke reactions in sensitive people, and nitrites can form harmful nitrosamines, particularly under high heat. Their use must therefore balance benefit against risk, and labelling must be accurate.

(b) The greenhouse effect is a blessing

The greenhouse effect is a natural process. Sunlight passes through the atmosphere and warms the Earth's surface, which then emits infrared radiation. Greenhouse gases such as water vapour, CO₂, methane and nitrous oxide absorb some of this radiation and re-emit it, part of it back towards the surface.

It is a blessing because without it the Earth's average temperature would be about -18°C instead of about +15°C, a difference of 33°C. Water would largely be frozen, and life as we know it could not exist. It also reduces the difference between day and night temperatures. The Moon has no such blanket and swings to extreme temperatures.

Enhanced greenhouse effect and global warming

The enhanced greenhouse effect is the additional warming caused by greenhouse gases that human activity adds to the atmosphere. The sources are burning coal, oil and gas; deforestation; livestock and rice cultivation, which release methane; fertiliser use, which releases nitrous oxide; and industrial gases. Atmospheric CO₂ has risen from about 280 parts per million before industrialisation to over 420 ppm today.

Relation with global warming: more greenhouse gases trap more outgoing heat, so the planet absorbs more energy than it loses, and temperature rises until a new balance is reached. Global warming is this long-term rise in average temperature, and the IPCC reports warming of about 1.1°C by 2011-2020 compared with 1850-1900. Feedbacks amplify it: warmer air holds more water vapour, and melting ice reflects less sunlight.

Consequences: melting glaciers, rising seas, stronger heatwaves, changing rainfall, more intense floods and droughts, ocean acidification and threats to food and water security. Pakistan, with its glacier-fed rivers, is particularly exposed.

In short, the natural effect keeps the planet habitable, and the danger lies only in its human-driven enhancement. The remedy lies in cutting emissions through clean energy and efficiency, protecting forests, and adapting to changes already under way.