13. Very Short Question Answer: Earth as a System: Energy, Matter, and Life

Q1: What is the geosphere?

Ans: The geosphere consists of solid rocks, soil, landforms such as the Deccan plateau and the Thar desert, and the Earth’s interior. It is one of the five major spheres that make up the Earth system.

Q2: What is the cryosphere? Give two examples.

Ans: The cryosphere is the solid form of water on the Earth, such as ice and snow. Examples include the Himalayan glaciers and polar ice caps.

Q3: What is the biosphere?

Ans: The biosphere includes all living organisms and their habitats, such as mangroves, forests, farms, ocean plankton and coral reefs. It is the sphere that supports all life on the Earth.

Q4: What is insolation?

Ans: The amount of the Sun’s radiation that reaches the Earth’s surface is called insolation. It is responsible for warming the Earth’s surface and its atmosphere.

Q5: What is the solar constant and what is its value?

Ans: The average amount of solar energy received per unit time per unit area perpendicular to the Sun’s rays at the top of the Earth’s atmosphere is called the solar constant. Its value is approximately $1.4{\text{kWm}}^{-2}$ (or about $1400{\text{J s}}^{-1}{\text{m}}^{-2}$).

Q6: Which three regions of the electromagnetic spectrum contain about 99 per cent of the Sun’s energy that reaches the Earth?

Ans: About 99 per cent of the Sun’s energy reaching the Earth falls within the ultraviolet (UV), visible and infrared (IR) ranges of the electromagnetic spectrum. These three regions shape the Earth’s climate and support life.

Q7: What is albedo?

Ans: The fraction of solar radiation reflected by a surface is called its albedo. The word comes from Latin, meaning whiteness. High albedo surfaces stay cool because they reflect more light, while low albedo surfaces heat up quickly.

Q8: What are the main gases that make up the Earth’s atmosphere and in what proportions?

Ans: The Earth’s atmosphere consists mainly of nitrogen (78%) and oxygen (21%), along with small amounts of argon, carbon dioxide, water vapour and other gases.

Q9: In which layer of the atmosphere do nearly all weather phenomena take place?

Ans: Nearly all weather phenomena take place in the troposphere, which has an average height of about 12 km. In this layer, temperature decreases with height at about $6.5{}^{\circ }\text{C/km}$.

Q10: Where is the ozone layer located and what is its function?

Ans: The ozone layer is located in the stratosphere, between 12 km and 50 km above the Earth’s surface. It absorbs harmful UV rays from the Sun, protecting life on the Earth.

Q11: Name any three greenhouse gases present in the Earth’s atmosphere.

Ans: Three greenhouse gases are carbon dioxide $({\text{CO}}_2)$, methane $({\text{CH}}_4)$ and water vapour. They trap outgoing infrared heat from the Earth’s surface, keeping the Earth warm enough to support life.

Q12: What is a valley breeze and when does it occur?

Ans: During the day, mountain slopes facing the Sun heat up faster than the valley floor. The warm air over the slopes rises, and cooler air from the valley moves up to replace it. This upward flow of air is called a valley breeze.

Q13: What is a mountain breeze and when does it occur?

Ans: After sunset, the mountain slopes cool faster than the valley floor. The cooler, denser air over the slopes flows down into the valley. This downward flow of air is called a mountain breeze.

Q14: What are gyres?

Ans: The Earth’s rotation deflects moving ocean water masses, forming large circular patterns called gyres. These rotate clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere.

Q15: What is a biogeochemical cycle?

Ans: The cyclic movement of matter and energy between the abiotic (non-living) and biotic (living) components of the Earth is called a biogeochemical cycle. It ensures that essential nutrients such as carbon, nitrogen and oxygen are recycled and remain available to support life.

Q16: Name any four processes involved in the water cycle.

Ans: Four processes involved in the water cycle are evaporation, transpiration, condensation and precipitation. Together, they continuously move water between water bodies, the atmosphere and the land surface.

Q17: What happens to carbon dioxide in the fast carbon cycle?

Ans: In the fast carbon cycle, which happens over days to years, plants convert atmospheric ${\text{CO}}_2$ into glucose through photosynthesis. ${\text{CO}}_2$ is released back into the atmosphere through respiration and decomposition.

Q18: What is nitrification?

Ans: The process by which nitrifying bacteria convert ammonia $({\text{NH}}_3)$ into nitrite $({\text{NO}}_2^{-})$ and then into nitrate $({\text{NO}}_3^{-})$ in the soil is called nitrification. Bacteria such as Nitrosomonas and Nitrobacter carry out this process.

Q19: Name two nitrogen-fixing bacteria and state where they are found.

Ans: Rhizobium is found in the root nodules of legumes and Azotobacter is found in the soil. Both convert atmospheric nitrogen $({\text{N}}_2)$ into ammonia $({\text{NH}}_3)$, which plants can absorb.

Q20: What is eutrophication?

Ans: The overuse of fertilisers in agriculture adds excessive nitrogen via nitrates to rivers and lakes, causing widespread growth of algae (algal blooms) that deplete oxygen and kill fish. This process is called eutrophication and it threatens water bodies and coastal fisheries.