Photosynthesis Photosynthesis Pigments and Absorption 2 — Questions and Answers
Question 1: Chlorophyll b most strongly absorbs light at which wavelengths?
- Blue (~453 nm) and orange-red (~642 nm) (Correct answer)
- Green (~550 nm) and yellow (~580 nm)
- Red (~700 nm) and far-red (~730 nm)
- Ultraviolet (~360 nm) and violet (~400 nm)
Correct answer: Blue (~453 nm) and orange-red (~642 nm)
Chlorophyll b absorbs maximally in the blue region near 453 nm and the orange-red region near 642 nm, complementing chlorophyll a's absorption range.
Question 2: Which laboratory technique is commonly used to separate different photosynthetic pigments from a leaf extract?
- Paper chromatography (Correct answer)
- Gel electrophoresis
- Centrifugation
- Western blotting
Correct answer: Paper chromatography
Paper chromatography separates photosynthetic pigments based on their solubility in a solvent and their affinity for the paper, producing distinct colored bands.
Question 3: Which part of the chlorophyll molecule is primarily responsible for absorbing light energy?
- The porphyrin ring (head) containing magnesium (Correct answer)
- The phytol tail
- The ester linkage
- The carbon backbone
Correct answer: The porphyrin ring (head) containing magnesium
The porphyrin ring of chlorophyll contains a central magnesium ion and a conjugated system of double bonds that absorbs photons of light.
Question 4: Phycocyanin is a photosynthetic pigment found primarily in which group of organisms?
- Cyanobacteria and red algae (Correct answer)
- Green plants only
- Brown algae
- Fungi
Correct answer: Cyanobacteria and red algae
Phycocyanin is a phycobiliprotein pigment characteristic of cyanobacteria and red algae, where it absorbs wavelengths that chlorophyll cannot.
Question 5: What is the role of antenna pigments (light-harvesting complexes) in the photosynthetic process?
- Absorb photons and funnel the excitation energy to the reaction center (Correct answer)
- Catalyze the reduction of CO2 to glucose
- Transport electrons through the thylakoid membrane
- Synthesize ATP using a proton gradient
Correct answer: Absorb photons and funnel the excitation energy to the reaction center
Antenna pigments form large complexes that capture photons from a broad range of wavelengths and transfer the excitation energy to the reaction center chlorophyll.
Question 6: According to the action spectrum of photosynthesis, which wavelengths of visible light are LEAST effective at driving the process?
- Green wavelengths (~500–560 nm) (Correct answer)
- Red wavelengths (~650–700 nm)
- Blue wavelengths (~430–450 nm)
- Violet wavelengths (~400–420 nm)
Correct answer: Green wavelengths (~500–560 nm)
Green wavelengths are the least effective because chlorophyll reflects rather than absorbs green light, resulting in minimal photosynthetic activity at those wavelengths.
Photosynthesis Photosynthesis Pigments and Absorption 2
Chlorophyll b most strongly absorbs light at which wavelengths?