ANWSER
Question 1
(a) Short notes on the following terms:
i. Biosphere:
The biosphere refers to the global ecological system integrating all living organisms (biota) and their interactions with the abiotic components (lithosphere, hydrosphere, and atmosphere) of Earth. It encompasses all ecosystems, from the deepest oceans to the highest mountains, where life exists.
ii. Lithosphere:
The lithosphere is the rigid outer layer of the Earth, comprising the crust and the uppermost part of the mantle. It is involved in geologic processes like plate tectonics and provides the physical substrate for terrestrial ecosystems.
iii. Geologic processes:
These are natural mechanisms that shape the Earth’s structure over time, including erosion, sedimentation, volcanic activity, and plate tectonics. They play a role in nutrient cycling (e.g., phosphorus release from rocks).
iv. Atmosphere:
The atmosphere is the layer of gases surrounding Earth, primarily composed of nitrogen (78%), oxygen (21%), and trace gases like CO₂. It regulates climate, protects life from solar radiation, and facilitates biogeochemical cycles (e.g., carbon and nitrogen cycles).
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(b) Description and Diagram of the Nitrogen Cycle:
Description:
The nitrogen cycle describes the transformation of nitrogen among its various chemical forms (e.g., N₂, NH₃, NO₃⁻) through biological and physical 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 synthesize 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 to the atmosphere.
Diagram: (Illustrate arrows connecting N₂ → NH₃ → NO₂⁻ → NO₃⁻ → Organic N → NH₃ → N₂, with labels for each process and organisms involved.)
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(c) Description of Terms:
i. Carbon:
A fundamental element in organic molecules (e.g., carbohydrates, lipids). It cycles through photosynthesis, respiration, decomposition, and combustion, linking biotic and abiotic systems.
ii. Phosphorus:
A key nutrient in DNA, ATP, and bones. Its cycle involves weathering of rocks, uptake by plants, and recycling via decomposition, but lacks a significant gaseous phase.
iii. Sulphur:
Essential in amino acids (e.g., cysteine). Cycles through volcanic emissions, bacterial action (e.g., *Desulfovibrio*), and industrial processes, often involving sulfate (SO₄²⁻).
iv. Nitrogen:
A critical component of proteins and nucleic acids. Its cycle includes fixation, nitrification, and denitrification, driven primarily by microbial activity.
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Question 2
(a) Processes in the Ecosystem:
i. Ammonification:
Decomposers (bacteria/fungi) convert organic nitrogen (e.g., dead plants, urine) into ammonium (NH₄⁺), releasing it into the soil for reuse.
ii. Nitrification:
Two-step oxidation of NH₄⁺ → NO₂⁻ → NO₃⁻ by aerobic bacteria (*Nitrosomonas* → *Nitrobacter*), making nitrogen available for plant uptake.
iii. Denitrification:
Anaerobic bacteria (*Pseudomonas*) reduce NO₃⁻ → N₂ or N₂O, returning nitrogen to the atmosphere and completing the cycle.
iv. Nitrogen Fixation:
Conversion of N₂ to NH₃ by symbiotic bacteria (e.g., *Rhizobium* in root nodules) or free-living microbes (*Azotobacter*).
v. Combustion:
Burning fossil fuels or biomass releases nitrogen oxides (NOₓ), contributing to pollution and acid rain while cycling nitrogen.
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(b) Cycles:
i. Carbon Cycle:
– Description: CO₂ is fixed by plants via photosynthesis, incorporated into organic matter, and released through respiration, decomposition, or combustion. Fossil fuels represent long-term carbon storage.
– Diagram: (Show CO₂ ↔ Organic matter ↔ Fossil fuels, with arrows for photosynthesis, respiration, and combustion.)
ii. Oxygen Cycle:
– Description: Oxygen is produced by photosynthesis and consumed in respiration and combustion. The atmosphere and oceans act as reservoirs.
– Diagram: (Illustrate O₂ release by plants → uptake by animals/combustion → CO₂ release → photosynthesis loop.)
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Question 3
Experimental Techniques for Glycolysis & TCA Cycle:
1. Enzyme Assays:
– Measure activity of key enzymes (e.g., hexokinase, citrate synthase) under varying substrate concentrations or inhibitors.
– Regulation Insight: Reveals allosteric control (e.g., ATP inhibition of phosphofructokinase in glycolysis).
2. Radioisotope Tracers (e.g., ¹⁴C-glucose):
– Track labeled carbons through metabolic intermediates via chromatography or scintillation counting.
– Regulation Insight: Identifies flux directions and rate-limiting steps (e.g., citrate’s role in TCA cycle feedback).
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Question 4
Enzyme Inhibition & Tracer Studies in Glucose Metabolism:
– Enzyme Inhibition:
– Example: Alloxan inhibits glucokinase, mimicking diabetes to study insulin’s role in glycolysis.
– Application: Demonstrates metabolic control points (e.g., PFK-1 inhibition by citrate).
– Tracer Studies:
– Example: ¹³C-glucose traces carbon fate in liver vs. muscle, revealing tissue-specific pathways like gluconeogenesis.
– Application: Quantifies pathway dominance under hypoxia (e.g., lactate fermentation).
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Question 5
(a) Amphibolic Nature of TCA Cycle:
The TCA cycle is amphibolic, serving both catabolism (oxidizing acetyl-CoA to CO₂ for ATP) and anabolism (providing intermediates for biosynthesis, e.g., α-ketoglutarate → glutamate, oxaloacetate → glucose).
(b) Anabolic vs. Catabolic Pathways:
1. Energy: Anabolism consumes ATP; catabolism generates ATP.
2. Molecules: Anabolism builds complex molecules (e.g., proteins); catabolism breaks them down (e.g., glycolysis).
3. Redox Cofactors: Anabolism uses NADPH; catabolism generates NADH/FADH₂.
4. Regulation: Opposing hormones (e.g., insulin promotes anabolism; glucagon stimulates catabolism).