1. What is photosynthesis and why is it considered a means of autotrophic nutrition?
Answer: Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy stored in glucose. It is considered a means of autotrophic nutrition because these organisms produce their own food using light energy, carbon dioxide, and water.
2. Where does photosynthesis take place in plants?
Answer: Photosynthesis takes place in the chloroplasts of plant cells, primarily in the mesophyll cells of leaves.
3. What are the pigments involved in photosynthesis?
Answer: The main pigments involved in photosynthesis are chlorophyll a, chlorophyll b, and carotenoids. Chlorophyll a is the primary pigment, while chlorophyll b and carotenoids are accessory pigments that help capture light energy.
4. What are the photochemical and biosynthetic phases of photosynthesis?
Answer: The photochemical phase (light reactions) involves the absorption of light by chlorophyll and the conversion of light energy into chemical energy (ATP and NADPH). The biosynthetic phase (Calvin cycle or dark reactions) uses the ATP and NADPH to convert carbon dioxide into glucose.
5. Explain cyclic and non-cyclic photophosphorylation.
Answer: In cyclic photophosphorylation, electrons are recycled back to the photosystem I, generating ATP but no NADPH or oxygen. In non-cyclic photophosphorylation, electrons move from water through photosystems II and I to NADP+, forming NADPH and ATP, and releasing oxygen as a byproduct.
6. What is the chemiosmotic hypothesis?
Answer: The chemiosmotic hypothesis explains how ATP is produced during the light reactions of photosynthesis. It proposes that the energy from electron transport is used to pump protons across the thylakoid membrane, creating a proton gradient that drives ATP synthesis as protons flow back through ATP synthase.
7. What is photorespiration and how does it differ between C3 and C4 plants?
Answer: Photorespiration is a process where the enzyme RuBisCO oxygenates RuBP, leading to a loss of energy and carbon in C3 plants. C4 plants minimize photorespiration by spatially separating the initial CO2 fixation and the Calvin cycle, effectively concentrating CO2 around RuBisCO.
8. What factors affect the rate of photosynthesis?
Answer: Factors affecting the rate of photosynthesis include light intensity, carbon dioxide concentration, temperature, water availability, and the presence of chlorophyll.
9. Describe the process of glycolysis.
Answer: Glycolysis is the anaerobic process of breaking down one glucose molecule into two molecules of pyruvate, producing a net gain of 2 ATP and 2 NADH molecules.
10. What is fermentation and how does it differ from aerobic respiration?
Answer: Fermentation is an anaerobic process that allows the regeneration of NAD+ by converting pyruvate into ethanol or lactic acid, enabling glycolysis to continue. Unlike aerobic respiration, fermentation does not involve the TCA cycle or electron transport chain and produces much less ATP.
11. Outline the steps of the TCA cycle.
Answer: The TCA cycle (Krebs cycle) involves the oxidation of acetyl-CoA to CO2 and H2O, producing 3 NADH, 1 FADH2, and 1 ATP (or GTP) per acetyl-CoA molecule. The cycle includes steps such as citrate formation, isomerization, oxidative decarboxylations, and regeneration of oxaloacetate.
12. What is the electron transport system (ETS) in aerobic respiration?
Answer: The ETS is a series of protein complexes located in the inner mitochondrial membrane that transfer electrons from NADH and FADH2 to oxygen, creating a proton gradient that drives ATP synthesis through oxidative phosphorylation.
13. How many ATP molecules are generated from one glucose molecule through aerobic respiration?
Answer: Aerobic respiration of one glucose molecule typically yields a total of about 36-38 ATP molecules, including 2 from glycolysis, 2 from the TCA cycle, and approximately 32-34 from the electron transport chain and oxidative phosphorylation.
14. What are amphibolic pathways?
Answer: Amphibolic pathways are biochemical pathways that have both anabolic (building up) and catabolic (breaking down) functions. The TCA cycle is an example, as it is involved in both the degradation of molecules for energy and the synthesis of compounds for cell growth.
15. What is the respiratory quotient (RQ) and its significance?
Answer: The respiratory quotient (RQ) is the ratio of CO2 produced to O2 consumed during respiration. It indicates the type of substrate being metabolized; an RQ of 1.0 suggests carbohydrate metabolism, while values less than 1 indicate fats and proteins.
16. Describe the phases of plant growth.
Answer: The phases of plant growth include the lag phase (slow growth), the exponential phase (rapid growth), and the stationary phase (growth rate decreases as resources become limited). Growth rate can be measured in terms of increase in cell number, size, or biomass.
17. What conditions are necessary for seed germination?
Answer: Conditions necessary for seed germination include water, oxygen, suitable temperature, and, in some cases, light. These conditions activate metabolic pathways that enable the seed to grow and develop into a new plant.
18. Define differentiation, dedifferentiation, and redifferentiation in plant cells.
Answer: Differentiation is the process by which cells become specialized in structure and function. Dedifferentiation is the process by which specialized cells revert to a more primitive, unspecialized form. Redifferentiation is when dedifferentiated cells become specialized again.
19. List and briefly describe the main plant growth regulators.
Answer: The main plant growth regulators are:
- Auxins: Promote cell elongation, root initiation, and fruit development.
- Gibberellins: Stimulate stem elongation, seed germination, and flowering.
- Cytokinins: Promote cell division and delay leaf senescence.
- Ethylene: Involved in fruit ripening and response to stress.
- Abscisic Acid (ABA): Induces seed dormancy and helps plants respond to stress conditions like drought.
20. What is the sequence of developmental processes in a plant cell?
Answer: The sequence of developmental processes in a plant cell includes cell division, cell enlargement, cell differentiation, and finally, cell maturation. This sequence ensures the proper growth and development of plant tissues and organs.