Tuberculosis and hepatitis, the mechanism and construction of fibre optic cable, middle latitude cyclones and tornadoes, and ionic and covalent bonding

Understanding the topic

This question tests four distinct scientific skills: explaining diseases without confusing causes and symptoms, describing how a communication technology works, comparing two atmospheric systems, and distinguishing two forms of chemical bonding. Each part carries five marks, so the best answer is compact but structured. Define the terms first, explain the mechanism or distinction, and then add examples or applications.

(a) What is the Tuberculosis and Hepatitis? Explain briefly.

Tuberculosis

Tuberculosis, or TB, is an infectious disease caused mainly by the bacterium Mycobacterium tuberculosis. It usually affects the lungs, although it may also involve lymph nodes, bones, kidneys, the brain and other organs. Pulmonary TB spreads through airborne droplets released when a person with active disease coughs, sneezes or speaks.

TB infection and TB disease are not the same. A person with TB infection carries the bacteria but has no symptoms and does not transmit the disease. In active TB disease, the bacteria multiply and may cause a persistent cough, chest pain, fever, night sweats, fatigue, weight loss and sometimes blood in the sputum. Diagnosis commonly combines clinical assessment, chest imaging and laboratory testing of sputum.

TB is preventable and curable. The BCG vaccine gives children useful protection against severe forms such as TB meningitis, but it does not reliably prevent all pulmonary infection. Active drug-susceptible TB is treated with a prescribed combination of antibiotics for several months. Completing the full regimen is essential because irregular treatment encourages drug resistance.

Hepatitis

Hepatitis means inflammation of the liver. It may result from viruses, alcohol, certain medicines, toxins, autoimmune disease or metabolic disorders. The principal viral forms are hepatitis A, B, C, D and E. Hepatitis A and E usually spread through contaminated food or water and are commonly acute. Hepatitis B, C and D are primarily blood-borne; B and C may become chronic and cause cirrhosis or liver cancer.

Symptoms may include fatigue, nausea, abdominal discomfort, dark urine, pale stools and jaundice, although many infections initially produce no obvious symptoms. Prevention depends on the type. Safe vaccines are widely used against hepatitis A and B, and hepatitis B vaccination also prevents hepatitis D because D requires hepatitis B infection. There is no vaccine for hepatitis C. Safe water, screened blood, sterile needles and infection-control practices reduce transmission. Treatment ranges from supportive care for many acute cases to antiviral therapy for chronic hepatitis B or curative direct-acting antivirals for most hepatitis C infections.

(b) Explain the mechanism of Fiber Optic Cable for signal. Explain its construction.

An optical-fibre cable carries information as pulses of light rather than as electric current. Its central core is a very clear strand of glass or plastic. The core is surrounded by cladding whose refractive index is slightly lower. A protective buffer coating, strengthening material and outer jacket guard the delicate fibre against moisture, bending and mechanical damage.

At the transmitting end, a laser diode or light-emitting diode converts an encoded electrical signal into rapid light pulses. The pulses enter the core at a suitable angle. When they reach the core-cladding boundary, they undergo total internal reflection because they are travelling from the optically denser core towards the lower-index cladding and strike beyond the critical angle. Repeated reflections keep most of the light confined within the core as it travels along the cable.

At the receiving end, a photodiode detects the arriving pulses and converts them back into an electrical signal. The equipment then amplifies and decodes that signal into sound, data or video. Long links may use optical amplifiers or repeaters to compensate for attenuation. Fibre carries large amounts of data, suffers little electromagnetic interference and loses less signal over distance than ordinary copper cable.

(c) Explain the difference between Middle Latitude Cyclones and Tornadoes.

A middle-latitude cyclone, also called an extratropical cyclone, is a large low-pressure weather system that develops mainly between about 30° and 60° latitude. It forms where contrasting warm and cold air masses meet along fronts. A tornado is a much smaller, violently rotating column of air extending from a thunderstorm cloud to the ground.

• Formation: A middle-latitude cyclone draws energy from horizontal temperature contrasts and develops warm and cold fronts. A tornado usually develops within a severe thunderstorm when instability, moisture and vertical wind shear produce a rotating updraft.
• Scale: A cyclone may extend over hundreds or more than a thousand kilometres and influence several regions. A tornado is normally tens to hundreds of metres wide, although exceptional tornadoes can be wider.
• Duration: A cyclone commonly persists for several days. Most tornadoes last minutes, though some remain on the ground much longer.
• Weather: A cyclone brings widespread cloud, changing winds and prolonged rain or snow. A tornado produces a narrow path of extremely intense winds and concentrated damage.
• Observation: Cyclones are tracked through pressure maps, satellites and weather models. Tornado intensity is assessed with the Enhanced Fujita scale from observed damage. The Saffir-Simpson scale applies to hurricanes, not middle-latitude cyclones.

Both systems rotate around low pressure, counterclockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere at cyclone scale. Tornado rotation is strongly shaped by its parent storm and local wind shear.

(d) What is difference between the Ionic and Covalent bonding? Give examples.

Chemical bonds hold atoms together by involving their valence electrons. In ionic bonding, one atom transfers one or more electrons to another. The transfer creates positively charged cations and negatively charged anions, which remain together because opposite charges attract. Ionic bonding is common between a metal and a non-metal. Sodium chloride is formed when sodium transfers an electron to chlorine, producing Na+ and Cl- ions. Magnesium oxide, MgO, is another example.

In covalent bonding, atoms share one or more pairs of electrons. It is common between non-metals whose attraction for electrons is similar enough to favour sharing rather than complete transfer. Two hydrogen atoms share electrons with oxygen in water, H2O. Methane, CH4, oxygen, O2, and carbon dioxide, CO2, also contain covalent bonds.

The resulting properties differ. Ionic compounds usually form crystalline solids with relatively high melting points. They conduct electricity when molten or dissolved in water because their ions can move, but they generally do not conduct as solids. Covalent substances may be gases, liquids or solids and often have lower melting points, although giant covalent structures such as diamond are major exceptions. Most simple covalent substances do not conduct electricity because they lack mobile charged particles.