Q1: What is the approximate value of the solar constant at the top of the Earth's atmosphere? (a) 1.0 kW/m² (b) 1.4 kW/m² (c) 2.0 kW/m² (d) 0.8 kW/m²
Solution:
Ans: (b) Explanation: The solar constant represents the average solar energy received per unit area perpendicular to the Sun's rays at the top of the atmosphere, approximately 1.4 kW/m².
Q2: Which layer of the atmosphere contains the ozone layer that absorbs harmful UV radiation? (a) Troposphere (b) Mesosphere (c) Stratosphere (d) Thermosphere
Solution:
Ans: (c) Explanation: The stratosphere extends from 12-50 km altitude and contains the ozone layer, which absorbs UV rays and warms the atmosphere, causing temperature to increase with height.
Q3: What percentage of the atmosphere consists of nitrogen and oxygen combined? (a) 95% (b) 99% (c) 78% (d) 21%
Solution:
Ans: (b) Explanation: The atmosphere mainly consists of nitrogen (78%) and oxygen (21%), which together make up 99% of the atmospheric composition, along with small amounts of other gases.
Q4: Which bacteria convert atmospheric nitrogen into ammonia in the root nodules of legumes? (a) Nitrobacter (b) Pseudomonas (c) Nitrosomonas (d) Rhizobium
Solution:
Ans: (d) Explanation: Rhizobium is a nitrogen-fixing bacterium found in the root nodules of legumes that converts atmospheric nitrogen (N₂) into ammonia (NH₃) through nitrogen fixation.
Q5: What causes valley breezes to flow upward along mountain slopes during daytime? (a) Cooling of mountain slopes (b) Rising warm air over heated slopes (c) High pressure over valleys (d) Sinking cold air
Solution:
Ans: (b) Explanation: During the day, mountain slopes heat up faster than valley floors. Warm air over the slopes rises, creating low pressure, and cooler air from the valley moves upward.
Fill in the Blanks
Q1: The biosphere comprises all living organisms and their environments, including mangroves, forests, farms, ocean plankton, and _____.
Solution:
Ans: coral reefs
Q2: The fraction of solar radiation reflected by a surface is called its _____.
Solution:
Ans: albedo
Q3: The process by which nitrifying bacteria convert ammonia into nitrite and nitrate is called _____.
Solution:
Ans: nitrification
Q4: Large circular patterns of ocean currents that rotate clockwise in the Northern Hemisphere are called _____.
Solution:
Ans: gyres
Q5: The process where excess nitrogen in water bodies causes widespread algae growth that depletes oxygen is called _____.
Solution:
Ans: eutrophication
True or False
Q1: The Sun's electromagnetic radiation travels at the speed of light, which is 3 × 10⁸ m/s.
Solution:
Ans: True Explanation: The Sun's radiation travels as electromagnetic waves at light speed, which is 3 × 10⁸ m/s, carrying energy from the Sun to Earth.
Q2: Temperature increases with height in the troposphere at a rate of approximately 6.5°C per kilometre.
Solution:
Ans: False Explanation: Temperature decreases with height in the troposphere at approximately 6.5°C per kilometre, as the troposphere is heated from the Earth's surface below.
Q3: Snow and ice have high albedo values ranging from 0.80 to 0.90, reflecting most solar radiation.
Solution:
Ans: True Explanation: Snow and ice have high albedo (0.80-0.90), meaning they reflect much of the solar radiation, which helps keep polar regions cold.
Q4: The Haber-Bosch process converts atmospheric nitrogen into ammonia and uses about 1-2% of global energy.
Solution:
Ans: True Explanation: The Haber-Bosch process artificially fixes nitrogen to make ammonia for fertilisers and is energy intensive, using approximately 1-2% of global energy.
Q5: Ocean acidification occurs when excess atmospheric carbon dioxide decreases ocean absorption, making seawater less acidic.
Solution:
Ans: False Explanation: Ocean acidification occurs when excess atmospheric CO₂ increases ocean absorption, making seawater more acidic, which threatens marine organisms like plankton and coral reefs.
Match the Following
Column A
Column B
1. Geosphere
A. Process converting nitrates back to nitrogen gas
2. Cryosphere
B. Air surrounding Earth that we breathe
3. Atmosphere
C. Contains liquid water including oceans and rivers
4. Denitrification
D. Solid rocks, soil, landforms and Earth's interior
5. Hydrosphere
E. Represents solid water forms like ice and snow
Solution:
Ans:
1 - D: The geosphere includes solid rocks, soil, landforms like the Deccan plateau and Thar desert, as well as the Earth's interior.
2 - E: The cryosphere represents solid water forms such as ice and snow, including Himalayan glaciers, snow in Ladakh, and polar ice caps.
3 - B: The atmosphere is the air around the Earth that we breathe, often cleaner in mountainous areas and forests.
4 - A: Denitrification is the process where denitrifying bacteria like Pseudomonas convert nitrates back into nitrogen gas, completing the nitrogen cycle.
5 - C: The hydrosphere contains liquid water, including oceans, rivers like the Ganga-Brahmaputra river system, lakes, and groundwater.
Short Answer Questions
Q1: Explain how the Earth's round shape affects the distribution of solar radiation across different latitudes.
Solution:
Ans: The Earth's round shape causes the Sun's rays to hit different latitudes at varying angles. At the equator, sunlight is concentrated over a smaller area, keeping it warm throughout the year. At the poles, sunlight spreads over a larger area, resulting in much colder conditions. This uneven heating creates temperature differences between the equator and the poles, driving global winds and ocean currents.
Q2: Describe the two critical roles of the atmosphere in regulating Earth's temperature.
Solution:
Ans: The atmosphere plays two critical roles: First, it partly absorbs incoming solar radiation-the ozone layer blocks harmful UV rays, and clouds and gases absorb some sunlight. Second, it traps outgoing heat through greenhouse gases like CO₂, CH₄, and water vapor, which absorb infrared radiation emitted by Earth's surface, preventing it from escaping into space. This keeps Earth warm enough for life.
Q3: How do ocean currents help regulate the Earth's climate?
Solution:
Ans: Ocean currents regulate Earth's climate by moving heat from the equator to the poles, reducing temperature differences across the planet. For example, the North Atlantic Drift carries warm water from southern North America to northwestern Europe, keeping many ports ice-free in winter. Ocean currents also transport nutrients, supporting vast ecosystems. They are driven by planetary winds, temperature differences, salinity variations, Earth's rotation, and land masses.
Q4: Explain the fast and slow cycles of the carbon cycle.
Solution:
Ans:
Fast Cycle (days to years): Plants convert atmospheric CO₂ into glucose through photosynthesis. CO₂ is released back through respiration and decomposition when organisms die.
Slow Cycle (millions of years): Dead plants and animals get buried and converted to fossil fuels like coal and oil. When these fuels are burnt for energy, carbon is released back as CO₂ very quickly, disrupting the natural balance.
Q5: What are the main steps involved in the nitrogen cycle?
Solution:
Ans:
Nitrogen Fixation: Bacteria like Rhizobium convert N₂ into ammonia.
Nitrification: Bacteria convert ammonia into nitrite and then nitrate.
Ammonification: Decomposers return nitrogen to soil from dead organisms.
Denitrification: Bacteria convert nitrates back to nitrogen gas, completing the cycle.
Long Answer Questions
Q1: Analyse how human activities have disrupted the carbon cycle and evaluate the potential consequences for Earth's climate and ecosystems.
Solution:
Ans: Human activities like burning fossil fuels and deforestation have increased atmospheric CO₂ by about 35% since 1960, from 315 ppm to 420 ppm. This unprecedented rise intensifies the greenhouse effect, leading to global warming, melting of glaciers and Arctic sea ice, rising sea levels, and more extreme weather conditions. Excess CO₂ also increases ocean absorption, making seawater more acidic (ocean acidification), which threatens marine organisms like plankton and coral reefs. In India, this disruption may cause more intense monsoons and threaten agriculture.
Q2: Compare the formation of valley breezes during daytime with mountain breezes after sunset, explaining the pressure differences involved.
Solution:
Ans: Valley breezes form during the day when mountain slopes heat up faster than valley floors. Warm air over the slopes rises, creating low pressure, and cooler air from the valley moves upward to replace it. Mountain breezes occur after sunset when mountain slopes cool faster than valley floors. The cooler, denser air over the slopes flows downward into the valley. These daily wind changes are common in hilly areas like Shimla and Dehradun, affecting local weather, agriculture, and daily life by regulating temperatures and moisture conditions.
Q3: Justify why the overuse of nitrogen fertilisers in agriculture poses a serious environmental threat and suggest sustainable alternatives.
Solution:
Ans: The overuse of nitrogen fertilisers adds excessive nitrogen via nitrates to rivers and lakes, causing widespread algae growth (algal blooms) that deplete oxygen and kill fish. This process, called eutrophication, threatens water bodies and coastal fisheries. It also degrades soil quality over time. Sustainable alternatives include practising crop rotation with legumes that naturally fix nitrogen, using organic manure, applying fertilisers based on soil testing, and promoting integrated nutrient management. India has promoted sustainable farming practices to restore ecosystem balance and protect water resources.
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