ANWSER
Question 1 (2021/2022):
(a) Short notes on the following terms:
(i) Biogeochemical cycle: The biogeochemical cycle refers to the movement of elements like carbon, nitrogen, and phosphorus through the Earth’s systems (atmosphere, hydrosphere, lithosphere, and biosphere). These cycles are essential for sustaining life and maintaining ecological balance.
(ii) Atmosphere: The atmosphere is the layer of gases surrounding Earth, primarily composed of nitrogen (78%) and oxygen (21%). It plays a critical role in regulating climate and supporting life.
(iii) Biosphere: The biosphere includes all living organisms and their interactions with the other Earth systems (atmosphere, hydrosphere, and lithosphere). It encompasses ecosystems from the deepest oceans to the highest mountains.
(iv) Hydrosphere: The hydrosphere consists of all water on Earth, including oceans, rivers, lakes, groundwater, and glaciers. It is vital for life and participates in cycles like the water and carbon cycles.
(v) Lithosphere: The lithosphere is the rigid outer layer of Earth, including the crust and upper mantle. It is involved in processes like rock formation and nutrient cycling.
(b) Draw and write short notes on the following cycles:
(i) Carbon-Oxygen cycle: This cycle describes the exchange of carbon and oxygen between living organisms and the environment. Photosynthesis converts CO₂ and water into glucose and oxygen, while respiration reverses this process.
(ii) Nitrogen cycle: The nitrogen cycle involves the conversion of nitrogen between its various forms (N₂, NH₃, NO₃⁻). Key processes include nitrogen fixation, nitrification, denitrification, and ammonification.
(iii) Carbon cycle: The carbon cycle tracks the movement of carbon through the atmosphere, oceans, soil, and living organisms. It includes processes like photosynthesis, respiration, decomposition, and combustion.
(iv) Oxygen cycle: The oxygen cycle involves the production of oxygen through photosynthesis and its consumption via respiration and combustion. It is closely linked to the carbon cycle.
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Question 2 (2021/2022):
(a) Differentiation between nitrogen fixation processes:
(i) Atmospheric fixation: Occurs naturally when lightning converts atmospheric nitrogen (N₂) into nitrogen oxides (NOₓ), which dissolve in rainwater to form nitrates.
(ii) Industrial nitrogen fixation: Human-made process (Haber-Bosch) that converts N₂ and H₂ into ammonia (NH₃) for fertilizers and industrial use.
(iii) Biological nitrogen fixation: Carried out by nitrogen-fixing bacteria (e.g., Rhizobium) that convert N₂ into ammonia (NH₃), which plants can use.
(b) Roles in biogeochemical cycles:
(i) Water: Acts as a solvent and medium for chemical reactions; essential for life and nutrient transport.
(ii) Carbon: Building block of organic molecules; central to energy transfer (e.g., glucose).
(iii) Nitrogen: Essential for proteins, nucleic acids, and chlorophyll.
(iv) Phosphorus: Key component of DNA, RNA, and ATP; involved in energy transfer.
(v) Sulfur: Found in amino acids (e.g., cysteine) and coenzymes; important for protein structure.
(c) Processes that use up atmospheric oxygen:
– Respiration (aerobic organisms)
– Combustion (burning of fuels)
– Rusting (oxidation of metals)
– Decomposition (organic matter breakdown)
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Question 3 (2021/2022):
(a) Definitions:
(i) Metabolism: The sum of all biochemical reactions in an organism, including catabolism (breakdown) and anabolism (synthesis).
(ii) Metabolic pathways: Series of linked chemical reactions that convert substrates into products (e.g., glycolysis).
(iii) Metabolic map: A diagram showing interconnected metabolic pathways and their relationships.
(iv) Metabolic cycle: A circular pathway where intermediates are regenerated (e.g., Krebs cycle).
(b) Common metabolic fuels:
– Glucose: Primary energy source for cells.
– Fatty acids: Stored as triglycerides; used for long-term energy.
– Amino acids: Can be converted to glucose or ketone bodies during starvation.
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Question 4 (2021/2022):
(a) Oxidation-reduction reactions:
These reactions involve the transfer of electrons (e⁻) between molecules. Oxidation is loss of e⁻, while reduction is gain of e⁻. Example: In cellular respiration, glucose is oxidized to CO₂, and O₂ is reduced to H₂O. NAD⁺ and FAD act as electron carriers.
(b) Amphibolic pathways:
Pathways that function in both catabolism and anabolism (e.g., Krebs cycle). It breaks down acetyl-CoA for energy (catabolism) and provides intermediates for biosynthesis (anabolism).
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Question 5 (2021/2022):
Four experimental methods for studying metabolism:
1. Radioisotope tracing: Tracking labeled atoms (e.g., ¹⁴C) through metabolic pathways.
2. Spectrophotometry: Measuring enzyme activity by absorbance changes (e.g., NADH/NAD⁺).
3. Chromatography: Separating and identifying metabolites (e.g., HPLC for amino acids).
4. Genetic knockout models: Disabling genes to study metabolic disruptions (e.g., yeast mutants).
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Question 1 (2022/2023):
(a) Short notes:
(i) Biogeochemical cycles: Movement of elements through Earth’s systems (e.g., carbon, nitrogen).
(ii) Geologic processes: Long-term cycles like rock weathering and sediment formation.
(iii) Industrial nitrogen fixation: Haber-Bosch process to produce ammonia for fertilizers.
(iv) Biological nitrogen fixation: Bacteria convert N₂ to NH₃ (e.g., Rhizobium in root nodules).
(b) Carbon cycle:
– Key processes: Photosynthesis (CO₂ → glucose), respiration (glucose → CO₂), decomposition, and combustion.
– Diagram: Show CO₂ exchange between atmosphere, plants, animals, and fossil fuels.
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Question 2 (2022/2023):
(a) Oxygen cycle:
– Diagram: Include photosynthesis (O₂ production) and respiration/combustion (O₂ consumption).
– Uses of oxygen: Aerobic respiration, combustion, ozone layer formation, medical therapy.
(b) Short notes on elements:
(i) Carbon: Basis of organic molecules; cycles via photosynthesis/respiration.
(ii) Phosphorus: DNA/ATP component; cycles via weathering and sedimentation.
(iii) Sulfur: Found in proteins; cycles via volcanic activity and bacterial action.
(iv) Nitrogen: Essential for amino acids; fixed by bacteria/lightning.
(v) Oxygen: Supports respiration and combustion.
(c) Lipid-related medical conditions:
1. Atherosclerosis (plaque buildup in arteries).
2. Obesity (excess fat storage).
3. Fatty liver disease (lipid accumulation in liver).
4. Hypercholesterolemia (high blood cholesterol).
5. Lipodystrophy (abnormal fat distribution).
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Question 3 (2022/2023):
(a) Nitrogen cycle steps:
1. Nitrogen fixation (N₂ → NH₃).
2. Nitrification (NH₃ → NO₂⁻ → NO₃⁻).
3. Assimilation (plants take up NO₃⁻/NH₄⁺).
4. Ammonification (organic N → NH₃).
5. Denitrification (NO₃⁻ → N₂).
(b) Definitions:
(i) Autotrophs: Produce own food (e.g., plants via photosynthesis).
(ii) Heterotrophs: Consume other organisms for energy (e.g., animals).
(iii) Detritivores: Feed on dead organic matter (e.g., earthworms).
(iv) Lithosphere: Earth’s rigid outer layer (crust and upper mantle).
(v) Biosphere: Global sum of all ecosystems.
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Question 4 (2022/2023):
(a) Definitions:
(i) Metabolism: All biochemical reactions in an organism.
(ii) Metabolic pathway: Linked reactions (e.g., glycolysis).
(iii) Metabolic map: Network diagram of pathways.
(iv) Metabolic cycle: Circular pathway (e.g., Krebs cycle).
(b) Anabolic vs. catabolic pathways:
– Anabolic: Build complex molecules (e.g., gluconeogenesis); requires energy.
– Catabolic: Break down molecules (e.g., glycolysis); releases energy.
(c) Common metabolic fuels: Glucose, fatty acids, amino acids.
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Question 5 (2022/2023):
(a) Intermediary metabolism in C. elegans:
Study of intermediate compounds in pathways (e.g., glycolysis, TCA cycle). C. elegans is used due to its simple genetics and conserved metabolic pathways.
(b) Major metabolic strategies:
1. Glycolysis (glucose breakdown).
2. Beta-oxidation (fatty acid breakdown).
3. Gluconeogenesis (glucose synthesis).