(a) What are antioxidants and why are they used in foods? Write a short note on natural and synthetic antioxidants. (b) How the carbohydrates, proteins, and fats are digested in humans? (c) How does the Navstar GPS system work for different applications? (d) (i) Differentiate between network and internet. (ii) What is the difference among application, program and software?

(a) Antioxidants

Antioxidants are substances that slow or prevent oxidation, usually by neutralising free radicals or reacting with oxygen.

Why they are used in foods: to prevent fats and oils from turning rancid; to keep the flavour, odour and colour of food; to limit browning of cut fruit; to protect nutrients; and to extend shelf life.

Natural antioxidants occur in plants and other natural sources. These include vitamin C (ascorbic acid) in citrus fruit, vitamin E (tocopherols) in vegetable oils and nuts, carotenoids in carrots and tomatoes, and polyphenols in tea and spices. They are generally well accepted by consumers, but may be costlier, less stable, and may affect flavour.

Synthetic antioxidants are made industrially, such as BHA (butylated hydroxyanisole), BHT (butylated hydroxytoluene), TBHQ and propyl gallate. They are cheap, stable and effective at low concentrations. Their use is limited by food regulations, owing to safety concerns about high doses.

(b) Digestion in humans

Carbohydrates: digestion starts in the mouth, where salivary amylase acts on starch, and it stops in the acidic stomach. In the small intestine, pancreatic amylase breaks starch into maltose and short chains. Maltase, sucrase and lactase on the intestinal lining then produce the simple sugars glucose, fructose and galactose, which are absorbed into the blood.

Proteins: digestion starts in the stomach, where hydrochloric acid denatures proteins and activates pepsin, which cuts them into polypeptides. In the small intestine, pancreatic trypsin and chymotrypsin, and then peptidases, break these into amino acids and small peptides, which are absorbed into the blood.

Fats: a small amount is digested by lingual and gastric lipases, but most is digested in the small intestine. Bile salts from the liver emulsify the fat into small droplets, and pancreatic lipase breaks it into fatty acids and monoglycerides. These form tiny micelles, enter the intestinal cells and are reassembled into chylomicrons, which pass into the lymph.

(c) Navstar GPS

Navstar GPS is the United States' Global Positioning System. It has at least 24 satellites at about 20,200 km altitude, ground control stations, and user receivers.

How it works: each satellite carries atomic clocks and broadcasts its position and the time. A receiver finds its distance from a satellite by multiplying the signal's travel time by the speed of light. Using distances from at least four satellites, it calculates latitude, longitude, altitude and the correction for its own clock error, a method known as trilateration. Accuracy can be improved with differential correction.

Different applications: vehicle, ship and aircraft navigation; mapping and land surveying; precision agriculture; disaster relief; tracking of logistics and fleets; military guidance; and timing for banks, telecommunication networks and power grids. All of these rely upon the same signals, and differ in how the receiver processes and uses them.

(d)(i) Network and internet

A network is a group of two or more connected computers or devices that share data and resources, such as an office LAN. The internet is a worldwide network of networks, in which millions of networks are connected using the common TCP/IP protocols.

Scope: a network can be small and local, while the internet is global. Control: a network is usually owned and managed by one organisation, while no single body owns the internet. Access: a private network can be restricted to authorised users, while the internet is publicly accessible. Example: a school's computer lab forms a network, while websites and email operate over the internet.

(d)(ii) Application, program and software

Program: a set of instructions written to perform a specific task on a computer, e.g. a small calculator routine. Software: a broad term for all programs, along with their data and documentation, that run on a computer. It includes system software such as Windows, and application software. Application: a type of software built for end users to carry out particular tasks, such as a word processor, browser or mobile app.

In short, software is the broadest category. Every application is a kind of software, and software is made up of one or more programs.