Photosynthesis in Higher Plants: Class 11 Biology Q&A
28 free answers on Photosynthesis in Higher Plants (Biology) for Class 11 students, across CBSE, ICSE and State boards. Includes questions such as “What do NADP and ADP stand for?”, “What is photolysis of water?”, “What is the source of oxygen in photosynthesis?”
Question & Answer
Questions
- BiologyClass 11All
What do NADP and ADP stand for?
NADP - Nicotinamide Adenine Dinucleotide Phosphate Function: Acts as an electron and hydrogen carrier in photosynthesis Forms: Exists as NADP⁺ (oxidized form) and NADPH (reduced form) Role: NADPH produced during light reactions serves as a reducing agent in the Calvin cycle, providing hydrogen and high-energy electrons for CO₂ reduction to form glucose Structure: C
- BiologyClass 11All
What is photolysis of water?
Photolysis of water is the light-dependent splitting of water molecules that occurs during photosynthesis. This critical process takes place in the thylakoid membranes of chloroplasts during the light reactions. When light energy is absorbed by chlorophyll and other photosynthetic pigments, it triggers the breakdown of water molecules (H₂O) into hydrogen ions (H⁺), electrons (e⁻), and oxygen gas (O₂). The chemical equation for this process is: 2H₂O &ra
- BiologyClass 11All
What is the source of oxygen in photosynthesis?
The source of oxygen released during photosynthesis is water (H₂O), not carbon dioxide as commonly misunderstood. This was scientifically proven through experiments using isotope labeling techniques. During the light-dependent reactions of photosynthesis, water molecules undergo photolysis (light-driven splitting) in the thylakoid membranes of chloroplasts. When water splits, it produces: Oxygen gas (O₂) – released into the atmosp
- BiologyClass 11All
What are the end products of dark reactions of photosynthesis?
The dark reactions of photosynthesis, also called the Calvin cycle or light-independent reactions, produce glucose (a simple sugar) as the primary end product, along with other important byproducts. Main end products: Glucose (C₆H₁₂O₆): The principal carbohydrate product that serves as an energy source and building block for more complex carbohydrates like starch and cellulose. <l
- BiologyClass 11All
What is the importance of electron emission from chlorophyll during photosynthesis?
Electron Emission from Chlorophyll: When chlorophyll molecules absorb light energy, electrons in the chlorophyll are excited to higher energy levels and are eventually ejected. This process is crucial for several reasons: Energy Conversion: Converts light energy into chemical energy by initiating the electron transport chain ATP Synthesis: The flow of electrons through the electron transport chain creates a pr
- BiologyClass 11All
What is the CO₂ acceptor during the dark reaction of C3 photosynthesis?
The CO₂ acceptor in the dark reaction (Calvin cycle) of C3 photosynthesis is Ribulose-1,5-bisphosphate (RuBP), a five-carbon sugar molecule. During carbon fixation, the enzyme RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes the attachment of CO₂ to RuBP, forming an unstable six-carbon intermediate that immediately splits into two molecules of 3-phosphoglycerate (3-PGA), a three-carbon compound. This is the first stable product of C3 photosynthesis, which i
- BiologyClass 11All
What is the product formed during the C3 cycle of the dark reaction?
The primary product formed during the C3 cycle (Calvin cycle) is glucose (C₆H₁₂O₆), a six-carbon sugar molecule. However, the immediate products and intermediates include: Immediate Products: 3-Phosphoglycerate (3-PGA): First stable three-carbon compound formed when CO₂ combines with RuBP Glyceraldehyde-3-phosphate (G3P or PGAL): A three-carbon sugar that is the actual product of the Calvin cy
- BiologyClass 11All
Where do light and dark reactions of photosynthesis occur?
Light Reaction (Light-dependent reaction) Location: Thylakoid membranes of chloroplasts (grana) Function: Converts light energy into chemical energy (ATP and NADPH) Requirements: Requires sunlight, chlorophyll, and water Products: ATP, NADPH, and oxygen (released as byproduct) Dark Reaction (Calvin Cycle/Light-independent reaction)<
- BiologyClass 11All
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
- BiologyClass 11All
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
- BiologyClass 11All
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)
- BiologyClass 11All
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
- BiologyClass 11All
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
- BiologyClass 11All
What are light harvesting complexes?
Light-Harvesting Complexes (LHC) are pigment-protein antenna complexes embedded in thylakoid membranes that: Structure: 200-300 chlorophyll molecules (mainly chlorophyll a and b) Carotenoid pigments (30-50 molecules) Integral membrane proteins (LHCI in PS I, LHCII in PS II) Function: Absorb phot
- BiologyClass 11All
Why do the leaves appear green in colour?
Leaves appear green because: Chlorophyll absorption spectrum: Chlorophyll a and b absorb strongly in: Blue region (430-450 nm) Red region (640-680 nm) Reflection of green light: Chlorophylls poorly absorb green wavelengths (500-600 nm), which are instead reflected and transmitted, making leaves appea
- BiologyClass 11All
What is RuBisCO? Where is it present in C3 and C4 plants? RuBisCO (Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase):
Properties: Most abundant enzyme on Earth (~50% of leaf soluble protein) Molecular weight: ~540 kDa Structure: 8 large subunits + 8 small subunits (L₈S₈) Dual activity: Carboxylase (CO₂ fixation) and oxygenase (photorespiration) Location in different plant types: P
- BiologyClass 11All
Differentiate between photorespiration and aerobic respiration.
Feature Photorespiration Aerobic Respiration Site Green photosynthetic cells only All living cells (green and non-green) Light requirement</str
- BiologyClass 11All
Complete the given below sequence of C4 pathway. CO₂ fixation → [C₄ acid] → Transport → Decarboxylation → [C₃ acid + CO₂]
Complete pathway: CO₂ fixation (mesophyll): PEP + CO₂ → Oxaloacetate (C₄ acid) Reduction (mesophyll): Oxaloacetate → Malate/Aspartate (C₄ acids) Transport (via plasmodesmata): C₄ acids move to bundle sheath cells Decarboxylation (bundle sheath): C₄ acid → Pyruvate (C₃ acid) + CO₂ Calvin cycle (bundle sheath): Released CO₂ f
- BiologyClass 11All
Describe briefly the contribution of Joseph Priestley. Joseph Priestley's experiments (1770):
Mouse + candle in sealed bell jar → both died due to "vitiated air" Mint plant + mouse in sealed bell jar → mouse survived Mint plant alone for several days → "restored" the air Conclusion: Plants release a substance (later identified as oxygen) that purifies air "fouled" by respiration and combustion. Significance: First evidence that plants and animals have complement
- BiologyClass 11All
Describe photosynthetic unit.
A photosynthetic unit (or quantasome) is the smallest functional unit capable of photosynthesis, consisting of: Components: 200-300 chlorophyll molecules (mostly chlorophyll a and b) 50-100 accessory pigment molecules (carotenoids, xanthophylls) 1 reaction center chlorophyll molecule (P700 in PS I, P680 in PS II) Pr