General Q&A for Class 12 · Page 236
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
What is the difference between respiration in plants and respiration in animals?
Respiration in Plants Respiration in Animals Slow rate of gas exchange Fast rate due to specialized organs Each plant part performs individual respiration Centralized
- GeneralClass 12All
Which protein acts as a mobile carrier in mitochondrial ETC?
Cytochrome c is a small, water-soluble protein attached to the outer surface of the inner mitochondrial membrane. It acts as a mobile electron carrier between Complex III (cytochrome bc₁ complex) and Complex IV (cytochrome c oxidase).
- GeneralClass 12All
Expand the following:
(A) NAD Nicotinamide Adenine Dinucleotide – a coenzyme involved in redox reactions, acting as an electron carrier. (B) EMP Embden–Meyerhof–Parnas pathway – the classical glycolytic pathway discovered by Gustav Embden, Otto Meyerhof, and Jakub Karol Parnas.
- GeneralClass 12All
What is the process in which FADH₂ gives rise to ATP molecules?
FADH₂ is oxidized during the Electron Transport System (ETS) in the inner mitochondrial membrane. Each FADH₂ molecule generates approximately 2 ATP molecules through oxidative phosphorylation.
- GeneralClass 12All
How many carbon atoms are present in the following molecules?
Molecule Carbon Atoms (A) Pyruvate 3 carbons (B) Acetyl CoA 2 carbons (C) Oxaloacetic acid</stro
- GeneralClass 12All
Name the sugars that normally enter glycolysis.
Glucose and fructose are the primary monosaccharides that enter the glycolytic pathway. Other hexoses like galactose are first converted to glucose-6-phosphate before entering glycolysis.
- GeneralClass 12All
Write the overall equation of aerobic respiration.
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 36–38 ATP This equation represents the complete oxidation of one glucose molecule, yielding carbon dioxide, water, and energy stored in ATP molecules.
- GeneralClass 12All
Who worked out the detailed steps of the citric acid cycle?
Sir Hans Adolf Krebs elucidated the citric acid cycle in 1937, working on flight muscles of pigeons. He was awarded the Nobel Prize in Physiology or Medicine in 1953.
- GeneralClass 12All
What is the substrate of the TCA cycle?
Acetyl Coenzyme A (Acetyl CoA) is the primary substrate that enters the tricarboxylic acid (TCA) cycle, also known as the Krebs cycle or citric acid cycle.
- GeneralClass 12All
Name the energy currency of cells.
Adenosine triphosphate (ATP) is the universal energy currency of cells. It stores energy in high-energy phosphate bonds and releases it upon hydrolysis to ADP and inorganic phosphate (Pi).
- GeneralClass 12All
In which phase of respiration does the oxidation of NADH take place?
The oxidation of NADH occurs during the Electron Transport System (ETS), which takes place on the inner mitochondrial membrane. NADH is oxidized by NADH dehydrogenase (Complex I), releasing electrons that pass through a series of carrier proteins.
- GeneralClass 12All
Explain the significance of the three phases of Calvin cycle.
The Calvin cycle has three critical phases: Phase 1: Carboxylation (CO₂ Fixation) Reaction: RuBP (C₅) + CO₂ → 2 × 3-Phosphoglycerate (3-PGA, C₃) Enzyme: RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) Significance: Only pathway for net carbon fixation in photosynthesis Rate-limiting step of
- GeneralClass 12All
How does PS II supply electrons continuously in noncyclic ETS?
Continuous electron supply mechanism: Problem: PS II loses electrons when P680 is photooxidized (P680 → P680⁺) Solution: Water photolysis (splitting) Reaction: 2H₂O → 4H⁺ + O₂ + 4e⁻ Mechanism: Oxygen-Evolving Complex (OEC): Contains 4 manganese ions (Mn), 1 calcium ion (Ca)</stron
- GeneralClass 12All
Briefly describe the Z-scheme and why is it called so?
The Z-Scheme describes non-cyclic electron flow: Why "Z-shaped"? When electron carriers are arranged on a redox potential scale (vertical axis) and sequence of transfer (horizontal axis), the path resembles the letter "Z". Electron flow sequence: PS II (P680) → excited electrons to high energy level Downhill</stron
- GeneralClass 12All
List the processes which occur during the photochemical phase of photosynthesis.
The Light Reaction (Photochemical Phase) includes: Light absorption: Pigments in LHC capture photons Energy transferred to reaction centers (P680, P700) Water splitting (photolysis): 2H₂O → 4H⁺ + O₂ + 4e⁻ Occurs at oxygen-evolving complex (OEC) in PS II Requires manganese
- GeneralClass 12All
Briefly describe the contribution of Jan Ingenhousz, which led to gradual development in our understanding of photosynthesis.
Jan Ingenhousz's experiments (1779): Key observations: Light requirement: Placed aquatic plants in sunlight → small bubbles formed around green parts Darkness test: Same plants in dark → no bubble formation Gas identification: Bubbles were oxygen (supported combustion) Green tissue specifi
- GeneralClass 12All
What is the advantage of having more than one pigment molecule in the photosynthetic unit?
Multiple pigments provide several critical advantages: Expanded absorption spectrum: Chlorophyll a: 430 nm, 662 nm Chlorophyll b: 453 nm, 642 nm Carotenoids: 450-550 nm Combined effect: Capture 400-700 nm (PAR = Photosynthetically Active Radiation) Increased photosynthetic efficiency
- GeneralClass 12All
How many ATP and NADPH molecules will be required to make one molecule of glucose through the Calvin pathway?
For synthesis of 1 glucose molecule (C₆H₁₂O₆): Requirement:6 turns of Calvin cycle (fixing 6 CO₂ molecules) Energy consumption per turn: 3 ATP molecules (2 for reduction, 1 for regeneration) 2 NADPH molecules (for reduction phase) Total for 1 glucose: 18 ATP molecules (6 × 3)
- GeneralClass 12All
Give comparison between the cyclic and non-cyclic photophosphorylation.
Feature Cyclic Photophosphorylation Non-cyclic Photophosphorylation Photosystems involved PS I only (P700) Both PS I and PS II (P700 + P680) El
- GeneralClass 12All
What is Blackman's law of limiting factors?
Blackman's Law of Limiting Factors (1905): Statement: "If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value. It is this factor which directly affects the process if its quantity is changed." Application to photosynthesis: Example at dawn: - Low light intensity → Light is limiting factor - Inc