Daily Practice Problems

📝 SolutionGlycolysis is the breakdown of glucose into pyruvate, and this process always occurs in the cytoplasm of the cell, regardless of whether respiration is aerobic or anaerobic. Mitochondria come into play only in the next steps (Krebs cycle and electron transport chain) during aerobic respiration. Students often confuse this with mitochondria because respiration is generally associated with mitochondria — remember, glycolysis is the one common step (it always takes place in the cytoplasm) shared by all organisms before the pathway splits into aerobic or anaerobic routes.

📝 SolutionGuard cells become turgid (swollen) when water flows into them, which causes the stomatal pore to open. This typically happens during the day when photosynthesis is occurring, because the plant needs to take in CO2 for photosynthesis and the opening of stomata allows this gas exchange. At night, since photosynthesis stops, most plants close their stomata to conserve water. Option (a) and (d) are incorrect because closed stomata (not open) are associated with water loss prevention and reduced gas exchange. Option (c) is a distractor — wilting is linked to guard cells losing turgidity and stomata closing, which is the opposite of what's described.

📝 SolutionHumans are warm-blooded (endothermic) and need a continuous, efficient supply of oxygen to maintain body temperature and meet high energy demands. Double circulation ensures oxygenated blood from the lungs and deoxygenated blood from the body do not mix, so tissues receive blood with maximum oxygen-carrying efficiency. Fish have single circulation because their energy requirement is comparatively lower (cold-blooded/ectothermic), so mixing is not as big a concern. Option (a) is wrong because double circulation doesn't reduce heartbeats — in fact the heart pumps blood twice per cycle (hence 'double'). Option (c) is factually incorrect — blood always passes through the lungs in pulmonary circulation. Option (d) ignores the primary oxygen-transport role, which is the actual reason taught in NCERT.

📝 SolutionThe dialysis fluid is deliberately made similar in composition to blood plasma (containing glucose, salts, etc. in normal concentrations) but without nitrogenous wastes like urea. This creates a concentration gradient only for the wastes — since urea is absent in the dialysis fluid, it diffuses out of the blood into the fluid, while glucose and salts (already present in matching concentration) do not diffuse out unnecessarily. If pure water were used, it would cause excessive and uncontrolled diffusion of not just wastes but also useful solutes (and could damage cells due to osmotic imbalance), which is why option (a) and (b) need careful distinguishing — the key reason is selective removal of waste only, not cell protection alone. This question tests application of diffusion/concentration gradient concept from excretion, a favourite board question.

📝 SolutionThis is a classic HOTS/assertion-reason twist. The Reason (R) is TRUE: xylem is indeed made of dead, hollow, lignified cells that form continuous tubes, and transpiration pull does drive the largely upward, passive movement of water and minerals — this part is correctly described in NCERT. However, the Assertion (A) is FALSE because it makes an overgeneralized claim: while xylem transport (water/minerals) is indeed mostly unidirectional (roots to leaves), phloem transport (translocation of food, mainly sucrose) is NOT unidirectional — it is bidirectional, moving food from source to sink, which could be upward (from roots to growing shoots) or downward (from leaves to roots/storage organs) depending on plant needs, using ATP energy (active transport), not passive movement. Many students pick option (a) because R sounds correct and assume A must also be correct — but board exams specifically test this xylem-unidirectional vs phloem-bidirectional distinction. Always verify each statement (A and R) independently before deciding if R explains A.