(a) Describe the principle of hydroelectric power generation. What environmental and geographical constraints limit the widespread development of hydropower? (b) Describe the hydrosphere and the major components of Earth's water. How does the water cycle maintain the distribution of freshwater? (c) Explain the causative agent, mode of transmission, and life cycle of the dengue virus. How does the Aedes mosquito contribute to the spread of the disease? (d) Discuss the role of Decision Support Systems (DSS) in organizational management and strategic planning.

(a) Principle of hydroelectric power

A hydroelectric plant converts the potential energy of water stored at a height into electricity. Water held behind a dam flows down through a pipe called the penstock, gaining kinetic energy. It strikes the blades of a turbine, which turns the shaft of a generator; the generator converts mechanical energy into electrical energy by electromagnetic induction. The output depends on the height of fall (head, H), the flow rate (Q) and the plant's efficiency (η): P = η ρ g Q H. Run-of-river plants use the natural flow with little storage, while pumped-storage plants pump water uphill when demand is low and release it at peak times. Tarbela and Mangla are Pakistan's largest storage-based hydropower stations.

Constraints: (i) suitable sites need both a large head and a reliable flow, mostly in mountainous regions far from load centres, which increases transmission costs; (ii) sedimentation reduces reservoir capacity — Tarbela has lost a large part of its original storage to silt; (iii) displacement of communities and loss of farmland; (iv) ecological damage to fish migration, downstream flows and deltas (the Indus delta suffers from reduced flow); (v) seismic and geological risks; (vi) dependence on rainfall and glacier melt, which climate change makes less predictable; (vii) very high capital cost and long construction time; and (viii) inter-provincial and international water disputes.

(b) The hydrosphere

The hydrosphere is all the water on, under and above Earth's surface: oceans, seas, ice caps, glaciers, groundwater, lakes, rivers, soil moisture and atmospheric water vapour. About 97 percent of Earth's water is saline ocean water; only about 2.5–3 percent is freshwater. Of this freshwater, roughly two-thirds is frozen in ice caps and glaciers, around 30 percent is groundwater, and less than 1 percent is in lakes, rivers, soil and the atmosphere.

The water cycle keeps freshwater distributed. Solar energy evaporates water from oceans and lakes and plants release it by transpiration. Water vapour rises, cools and condenses into clouds, which winds carry over land. Precipitation falls as rain or snow; part of it runs off into rivers and back to the sea, part infiltrates to recharge groundwater, and part is stored as snow and ice that melt in summer. Evaporation leaves salt behind, so the cycle acts as a natural desalination system that continuously renews freshwater on land.

(c) Dengue

Causative agent: the dengue virus (DENV), an RNA virus of the genus Flavivirus (family Flaviviridae), with four serotypes (DENV-1 to DENV-4). Infection with one serotype gives lifelong immunity to that serotype only; a later infection with a different serotype increases the risk of severe dengue.

Transmission: through the bite of an infected female Aedes mosquito, mainly Aedes aegypti and also Aedes albopictus. It does not spread directly from person to person in normal contact.

Life cycle: a mosquito bites an infected person during the viraemic phase and takes in the virus. The virus multiplies in the mosquito's gut and reaches its salivary glands in about 8–12 days (extrinsic incubation); the mosquito then remains infective for life. When it bites a healthy person, the virus enters the bloodstream, multiplies, and symptoms appear after about 4–10 days: high fever, severe headache, pain behind the eyes, joint and muscle pain, and rash. Severe dengue can cause plasma leakage, bleeding and shock.

Role of Aedes: it bites during the day, especially early morning and late afternoon; it breeds in clean, stagnant water in containers, tyres, flower pots and water tanks around homes; and it often bites several people during one blood meal, spreading infection quickly. This is why dengue outbreaks in Pakistan peak after the monsoon. Control relies on removing breeding sites, covering water containers, larvicides, protective clothing and repellents.

(d) Decision Support Systems

A DSS is an interactive computer-based system that helps managers make semi-structured and unstructured decisions. It has three main components: a database (internal and external data), a model base (statistical, financial, forecasting and optimisation models) and a user interface that allows "what-if" analysis.

Unlike routine management information systems, which produce standard reports, a DSS supports judgement. In management it helps with budgeting, scheduling, inventory control and pricing. In strategic planning it is used for scenario analysis, forecasting demand, evaluating investment options, choosing plant locations and assessing risk. Examples include airline route planning, bank credit-risk models and disaster-management dashboards. A DSS improves speed and consistency of decisions, but its value depends on accurate data and on managers who understand the assumptions behind its models.