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Q1. Which of the following is the best defining criteria to consider a thing as alive?
Cellular organization and metabolismWhile growth, reproduction, and movement are common in many living organisms, they are not universal (e.g., mules are sterile, plants show slow movement, crystals can grow). Cellular organization (being made of cells) and metabolism (sum of all chemical reactions) are the fundamental, universal properties that define life. Non-living things do not have cellular machinery or controlled metabolic reactions.
Q2. A newly discovered organism shows no visible movement but grows in size over time. To confirm if it is truly alive, what should be tested?
Occurrence of respiration at the cellular levelCellular respiration (breaking down glucose to release energy) is a definitive sign of life because all living cells must perform it to survive. Reproduction may not occur at all times, some living cells lack a nucleus (prokaryotes), and response to touch is not universal. Cellular respiration is a direct indicator of ongoing metabolic activity.
Q3. Which life process is defined as the sum total of all chemical reactions occurring inside a living organism?
MetabolismMetabolism includes both catabolism (breaking down substances to release energy) and anabolism (building complex molecules). Nutrition provides raw materials, excretion removes waste, and growth is an outcome, but metabolism is the comprehensive term for all chemical transformations inside an organism.
Q4. Which of the following is NOT a life process in humans?
TranspirationTranspiration is the loss of water vapor from plant surfaces, primarily through stomata. Humans do not perform transpiration; they lose water through sweating, urination, and exhalation, but those processes are not called transpiration. Respiration, excretion, and nutrition are essential life processes in humans.
Q5. The process by which living organisms obtain and utilize food for growth, maintenance, and energy is called:
NutritionNutrition is the broad process encompassing the intake, breakdown, absorption, and utilization of food. Digestion is only the breakdown step, assimilation is the incorporation into body tissues, and absorption is the uptake of nutrients. Nutrition covers all stages from acquisition to utilization.
Q6. Organisms that can synthesize their own food using simple inorganic substances are called:
AutotrophsAutotrophs (auto = self, troph = feeder) produce their own organic food from inorganic sources like carbon dioxide and water, using light (photoautotrophs) or chemical energy (chemoautotrophs). Heterotrophs depend on others, saprotrophs feed on dead matter, and parasites feed on living hosts.
Q7. Which of the following is an example of autotrophic nutrition?
A green alga performing photosynthesisGreen algae contain chlorophyll and perform photosynthesis to make their own food from carbon dioxide and water. Lions are heterotrophs, mushrooms are saprotrophs, and tapeworms are parasites—all depend on other organisms for food.
Q8. The process of obtaining food by autotrophs is primarily driven by which energy source?
Solar energyMost autotrophs (photoautotrophs) use sunlight as their primary energy source through photosynthesis. Some chemoautotrophs use chemical energy, but they are not the majority. Solar energy drives the vast majority of autotrophic nutrition on Earth.
Q9. In autotrophic nutrition, the raw materials required for photosynthesis are:
Carbon dioxide and waterThe photosynthesis equation (6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂) shows that carbon dioxide and water are the raw materials. Chlorophyll and sunlight are requirements (catalysts/energy sources), not raw materials. Nitrogen and minerals are needed for other plant functions but not directly for photosynthesis.
Q10. What actually happens during photosynthesis at the initial step?
Light energy is absorbed by chlorophyll and converted into chemical energyThe first step of photosynthesis is the absorption of light photons by chlorophyll pigments in the chloroplasts. This light energy is converted into chemical energy in the form of ATP and NADPH during the light reaction. Glucose breakdown is respiration, not photosynthesis.
Q11. During the light reaction of photosynthesis, water molecules are split to release:
Oxygen, protons, and electronsPhotolysis of water (2H₂O → 4H⁺ + 4e⁻ + O₂) releases oxygen gas, protons (H⁺), and electrons. The electrons are passed to chlorophyll to replace those lost during excitation, protons contribute to the proton gradient for ATP synthesis, and oxygen is released as a byproduct.
Q12. What actually happens during the dark reaction (Calvin cycle) of photosynthesis?
Carbon dioxide is reduced to form glucoseIn the Calvin cycle, carbon dioxide is fixed into organic molecules and then reduced (using ATP and NADPH from light reactions) to form glucose. Light absorption and water splitting occur in light reactions. ATP is consumed, not produced, in the dark reaction.
Q13. The first stable product of carbon fixation in C3 plants (like wheat and rice) is:
3-phosphoglyceric acid (3-carbon compound)In C3 plants, CO₂ combines with RuBP (5C) using the enzyme RuBisCO, producing an unstable 6C intermediate that immediately splits into two molecules of 3-phosphoglyceric acid (3PGA), a 3-carbon compound. Oxaloacetic acid is the first stable product in C4 plants.
Q14. During photosynthesis, what happens to the oxygen produced from the splitting of water?
It is released into the atmosphere as a byproductThe oxygen generated from photolysis is not used further in photosynthesis; it diffuses out of the leaf through stomata as a waste product. This oxygen is essential for aerobic respiration in most other organisms.
Q15. Which part of the plant cell is the actual site where photosynthesis occurs?
ChloroplastChloroplasts contain chlorophyll and the necessary enzymes for both light and dark reactions. The nucleus stores DNA, mitochondria are for cellular respiration, and vacuoles store water and waste. Photosynthesis occurs exclusively in chloroplasts.
Q16. What happens to the glucose produced during photosynthesis?
It is converted into various organic compounds like starch, cellulose, and oils for storage and growthGlucose is a simple sugar that is quickly converted into more stable storage forms: starch (storage in leaves/roots), cellulose (cell wall structure), and oils (seeds). Free glucose is not stored in vacuoles; it would disrupt osmotic balance.
Q17. Which of the following statements correctly describes what happens during photolysis of water?
Water molecules are broken down using light energy to provide electrons to chlorophyllDuring photolysis, light energy splits water into electrons, protons, and oxygen. The electrons replace those lost by chlorophyll’s reaction center (P680) when it gets excited by light, allowing the electron transport chain to continue.
Q18. Why are plants called autotrophs while animals are called heterotrophs?
Plants can synthesize their own food, animals cannotAutotrophs (plants) produce organic compounds from inorganic sources using light or chemical energy. Heterotrophs (animals) cannot synthesize their own food and must consume other organisms. Both plants and animals respire and excrete; movement is not the defining criterion.
Q19. What happens to the energy from sunlight after it is absorbed by chlorophyll?
It is converted into electrical energy, then into chemical energy (ATP and NADPH)Absorbed light energy excites electrons in chlorophyll (electrical/chemical potential energy). These electrons pass through an electron transport chain, driving the production of ATP and NADPH (chemical energy). This energy is later used in the Calvin cycle to make glucose.
Q20. During photosynthesis, what happens to carbon dioxide after it enters the leaf through stomata?
It diffuses into the chloroplast stroma and is fixed into an organic moleculeCO₂ enters the leaf via stomata, diffuses through mesophyll cells, and enters the chloroplast stroma. In the Calvin cycle (dark reaction), CO₂ is fixed (attached) to RuBP by RuBisCO, eventually leading to glucose formation. It does not combine directly with glucose nor get stored in vacuoles.
Q21. Which of the following is NOT required for autotrophic nutrition in green plants?
Oxygen gasOxygen is a byproduct of photosynthesis, not a requirement. For autotrophic nutrition, plants need chlorophyll (to capture light), carbon dioxide (carbon source), water (electron and proton source), sunlight (energy), and minerals (for enzymes). Oxygen is not consumed during photosynthesis.
Q22. What happens to the ATP and NADPH produced in the light reaction?
They are used in the dark reaction to reduce carbon dioxide into glucoseATP provides energy, and NADPH provides reducing power (electrons/hydrogen) to convert fixed CO₂ into glucose during the Calvin cycle. These molecules are not stored; they are consumed and recycled back to ADP and NADP⁺ for reuse in light reactions.
Q23. During the process of photosynthesis, what happens to the stomata?
They open to allow carbon dioxide to enter and oxygen to exitStomata are pores that open to facilitate gas exchange: CO₂ enters for photosynthesis, and O₂ (produced during light reaction) exits. They close to prevent water loss in dry conditions but must be open for active photosynthesis. Stomata do not absorb light or produce chlorophyll.
Q24. What actually happens if a green plant is kept in complete darkness for several days?
It will stop producing glucose because the light reaction cannot occur, and the plant may eventually dieLight reactions require light to produce ATP and NADPH. In darkness, these do not form, so the Calvin cycle stops due to lack of energy and reducing power. The plant will consume stored starch and sugars for respiration and will eventually die when reserves are exhausted.
Q25. Which of the following correctly sequences what happens during photosynthesis from start to finish?
Light absorption → water splitting → ATP/NADPH formation → carbon dioxide fixation → glucose formationPhotosynthesis starts with light absorption by chlorophyll. This drives water splitting (photolysis), producing electrons that flow through the transport chain to form ATP and NADPH. These products then drive CO₂ fixation and reduction in the Calvin cycle, ending with glucose formation.
Q26. During autotrophic nutrition in plants, what happens to the mineral nutrients like nitrogen, magnesium, and phosphorus?
They are used to make other biomolecules like proteins, chlorophyll, and ATPMinerals are essential for plant structure and function. Nitrogen is incorporated into amino acids (proteins) and nucleic acids; magnesium is the central atom in chlorophyll; phosphorus is part of ATP, NADPH, and nucleic acids. They do not directly form glucose but are vital for overall metabolism.
Q27. What happens to the rate of photosynthesis if the carbon dioxide concentration around a plant is increased significantly?
It will increase up to a certain point, then level offCO₂ is a substrate for the Calvin cycle. Increasing CO₂ concentration initially increases the rate of photosynthesis until another factor (light, temperature, or enzyme capacity) becomes limiting. After that, the rate plateaus despite further CO₂ increase.
Q28. A student places a test tube containing pond water with green algae in bright sunlight. Bubbles start rising from the algae. What is happening?
The algae are photosynthesizing and releasing oxygen bubblesGreen algae perform photosynthesis in sunlight, splitting water and releasing oxygen gas as a byproduct. The visible bubbles are oxygen. Respiration releases CO₂, but CO₂ is highly soluble in water and would not form visible bubbles as readily as oxygen.
Q29. If a leaf is tested with iodine solution after being kept in sunlight, it turns blue-black. What does this indicate about what happened in the leaf?
Photosynthesis occurred and starch was produced and storedIodine solution turns blue-black in the presence of starch. Since the leaf was in sunlight, photosynthesis produced glucose, which was converted to starch for storage. A control leaf kept in darkness would not turn blue-black because no starch would be produced.
Q30. What actually happens to the electrons that are removed from water during photolysis?
They are passed through an electron transport chain to ultimately reduce NADP+ to NADPHElectrons from photolysis replace those lost by photosystem II, then travel through an electron transport chain (losing energy to pump protons for ATP synthesis). Finally, they reach photosystem I and are re-energized by light, then used to reduce NADP⁺ to NADPH, which carries reducing power to the Calvin cycle.