ANWSER
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Question 1(a):
Answer:
i. Biosphere: The biosphere refers to the global ecological system integrating all living organisms and their interactions with the abiotic components (lithosphere, hydrosphere, and atmosphere). It encompasses all ecosystems on Earth.
ii. Lithosphere: The lithosphere is the rigid outer layer of the Earth, consisting of the crust and upper mantle. It includes rocks, minerals, and soil, and plays a key role in nutrient cycling.
iii. Geologic processes: These are natural mechanisms such as weathering, erosion, plate tectonics, and volcanic activity that shape the Earth’s surface and contribute to the cycling of elements like carbon and sulfur.
iv. Atmosphere: The atmosphere is the layer of gases surrounding Earth, composed mainly of nitrogen (78%) and oxygen (21%). It regulates climate and supports life by providing essential gases.
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Question 1(b):
Answer:
The Nitrogen Cycle describes the transformation of nitrogen in various forms (N₂, NH₃, NO₃⁻, etc.) through biotic and abiotic processes. Key steps include:
1. Nitrogen Fixation: Conversion of atmospheric N₂ to ammonia (NH₃) by bacteria (e.g., *Rhizobium*) or industrial processes.
2. Nitrification: Oxidation of NH₃ to nitrite (NO₂⁻) and nitrate (NO₃⁻) by soil bacteria (*Nitrosomonas*, *Nitrobacter*).
3. Assimilation: Uptake of NO₃⁻ or NH₄⁺ by plants to form organic nitrogen (e.g., amino acids).
4. Ammonification: Decomposition of organic nitrogen back to NH₃ by decomposers.
5. Denitrification: Reduction of NO₃⁻ to N₂ by bacteria (*Pseudomonas*), releasing nitrogen back into the atmosphere.
*(A detailed diagram would show these processes interconnected with arrows, highlighting atmospheric, terrestrial, and aquatic reservoirs.)*
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Question 1(c):
Answer:
i. Carbon: A fundamental element in organic molecules (e.g., glucose, DNA), cycled through photosynthesis, respiration, and combustion.
ii. Phosphorus: Essential for ATP and nucleic acids; cycled via weathering of rocks and decomposition, with no significant atmospheric phase.
iii. Sulfur: Found in amino acids (e.g., cysteine); cycled through volcanic activity, decomposition, and industrial emissions (SO₂).
iv. Nitrogen: A key component of proteins and nucleic acids; cycled via fixation, nitrification, and denitrification.
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Question 2(a):
Answer:
i. Ammonification: Decomposers convert organic nitrogen (e.g., dead plants) into ammonia (NH₃).
ii. Nitrification: Bacteria oxidize NH₃ to nitrite (NO₂⁻) and then nitrate (NO₃⁻), a plant-usable form.
iii. Denitrification: Anaerobic bacteria reduce NO₃⁻ to N₂ gas, returning nitrogen to the atmosphere.
iv. Nitrogen Fixation: Conversion of N₂ to NH₃ by symbiotic bacteria (e.g., in legume root nodules) or lightning.
v. Combustion: Burning fossil fuels releases nitrogen oxides (NOₓ), contributing to pollution and acid rain.
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Question 2(b):
Answer:
i. Carbon Cycle:
– Processes: Photosynthesis (CO₂ → organic compounds), respiration (organic compounds → CO₂), decomposition, and combustion.
– Reservoirs: Atmosphere (CO₂), oceans (dissolved CO₂), biomass, and fossil fuels.
*(Diagram would show arrows between these reservoirs.)*
ii. Oxygen Cycle:
– Processes: Photosynthesis (produces O₂), respiration (consumes O₂), and ozone (O₃) formation in the stratosphere.
– Linked to: Carbon cycle via photosynthesis/respiration.
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Question 3:
Answer:
Two key techniques:
1. Enzyme Assays: Measure activity of glycolytic/TCA enzymes (e.g., hexokinase, citrate synthase) under varying substrate concentrations or inhibitors to study regulation (e.g., ATP inhibition of PFK-1).
2. Radioisotope Tracers (e.g., ¹⁴C-glucose): Track labeled carbons through metabolic pathways to map flux and identify rate-limiting steps (e.g., pyruvate dehydrogenase regulation by NADH).
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Question 4:
Answer:
– Enzyme Inhibition: Example: Allosteric inhibition of phosphofructokinase-1 (PFK-1) by ATP in glycolysis, preventing excess ATP production.
– Tracer Studies: Using ¹³C-glucose, researchers traced carbon flow to reveal how insulin upregulates glycolysis and represses gluconeogenesis in hepatocytes.
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Question 5(a):
Answer:
The TCA cycle is amphibolic because it serves both catabolism (oxidizing acetyl-CoA to CO₂ for ATP) and anabolism (providing intermediates for biosynthesis, e.g., oxaloacetate for gluconeogenesis, α-ketoglutarate for amino acids).
Question 5(b):
Answer:
1. Energy: Catabolism releases energy; anabolism consumes energy.
2. Molecules: Catabolism breaks down complex molecules; anabolism builds them.
3. ATP: Catabolism generates ATP; anabolism uses ATP.
4. Examples: Glycolysis (catabolic); protein synthesis (anabolic).
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