Photobiophysics – MCQs 50 Score: 0 Attempted: 0/50 Subscribe 1. Photobiophysics primarily studies: (A) Interaction of light with biological molecules (B) Sound waves in tissues (C) Electrical signaling in neurons (D) Pressure effects on macromolecules 2. The energy of a photon is given by: (A) E = mc² (B) E = hv (C) E = ½mv² (D) E = kT 3. Which molecule is the primary light absorber in photosynthesis? (A) Hemoglobin (B) Chlorophyll (C) Myoglobin (D) Cytochrome c 4. The absorption spectrum of chlorophyll shows peaks mainly in: (A) Red and blue regions (B) Green region (C) Infrared region (D) Ultraviolet region only 5. Fluorescence occurs when: (A) Excited electron returns to ground state emitting a photon (B) Electron is lost from the molecule (C) Proton transfer occurs (D) Molecule dissociates 6. The Jablonski diagram is used to explain: (A) Electronic transitions in molecules (B) Mechanical motion in proteins (C) Enzyme kinetics (D) Ion channel conductance 7. Singlet oxygen is: (A) A reactive oxygen species generated by light excitation (B) A stable oxygen molecule (C) An oxygen radical with paired spins (D) Oxygen in its ground triplet state 8. Förster resonance energy transfer (FRET) depends on: (A) Distance between donor and acceptor fluorophores (B) Molecular mass (C) Temperature only (D) Ionic strength 9. Fluorescent proteins like GFP are widely used for: (A) Visualizing cellular processes (B) Generating ATP (C) Catalyzing reactions (D) Ion transport 10. The primary photoreceptor in human vision is: (A) Rhodopsin (B) Hemoglobin (C) ATP synthase (D) Myosin 11. In rhodopsin, light absorption causes: (A) 11-cis-retinal to isomerize to all-trans-retinal (B) ATP hydrolysis (C) Protein unfolding (D) Covalent bond cleavage 12. Photobleaching refers to: (A) Irreversible loss of fluorescence due to light exposure (B) Increase in fluorescence lifetime (C) Energy transfer between chromophores (D) Quantum yield enhancement 13. The quantum yield of fluorescence is defined as: (A) Number of emitted photons / absorbed photons (B) Energy emitted / energy absorbed (C) Lifetime of excited state (D) Absorbance value at λmax 14. Which photosystem absorbs light at ~680 nm? (A) Photosystem I (B) Photosystem II (C) Cytochrome complex (D) ATP synthase 15. The photochemical reaction center in Photosystem II is known as: (A) P680 (B) P700 (C) P450 (D) P800 16. Photodynamic therapy (PDT) uses: (A) Light-activated photosensitizers to kill cancer cells (B) X-rays to break DNA (C) Magnetic fields to target tumors (D) Enzymes to block DNA repair 17. The main pigment in rod cells is: (A) Rhodopsin (B) Iodopsin (C) Hemocyanin (D) Chlorophyll 18. Carotenoids in photosynthesis mainly act as: (A) Light-harvesting pigments and photoprotective agents (B) Enzymes (C) Electron donors (D) ATP producers 19. Which law states that the energy of light is proportional to its frequency? (A) Planck’s law (B) Newton’s law (C) Beer–Lambert law (D) Coulomb’s law 20. Beer–Lambert law relates: (A) Absorbance to concentration and path length (B) Fluorescence to wavelength (C) Conductivity to ions (D) Magnetism to electric current 21. In photophysics, the “Stokes shift” refers to: (A) Difference between absorption and emission maxima (B) Difference in quantum yield (C) Shift in protein conformation (D) Delay in synaptic transmission 22. The photochemical event in photosynthesis is: (A) Excitation of chlorophyll by photons (B) ATP hydrolysis (C) Carbon fixation (D) NADPH oxidation 23. Fluorescence lifetime is measured in: (A) Nanoseconds (B) Seconds (C) Minutes (D) Hours 24. The protein that regenerates 11-cis-retinal in the visual cycle is: (A) Retinal isomerase (B) Rhodopsin (C) Transducin (D) Opsin 25. In photosystem I, the reaction center absorbs light at: (A) 680 nm (B) 700 nm (C) 750 nm (D) 600 nm 26. The photoreceptor responsible for color vision is: (A) Cone cells (B) Rod cells (C) Bipolar cells (D) Ganglion cells 27. Which reactive oxygen species is often generated by photosensitizers in PDT? (A) Singlet oxygen (B) Hydroxyl ion (C) Superoxide ion only (D) Hydrogen gas 28. Two-photon excitation microscopy uses: (A) Simultaneous absorption of two low-energy photons (B) One high-energy photon (C) Light scattering (D) Bioluminescence 29. Bioluminescence in fireflies is due to: (A) Luciferin-luciferase reaction (B) ATP hydrolysis (C) Chlorophyll excitation (D) Proton gradient 30. Retinal is a derivative of: (A) Vitamin A (B) Vitamin B (C) Vitamin C (D) Vitamin D 31. The unit of light intensity is: (A) Candela (B) Tesla (C) Joule (D) Weber 32. In fluorescence recovery after photobleaching (FRAP), recovery reflects: (A) Molecular diffusion (B) Protein degradation (C) ATP hydrolysis (D) Electron transport 33. Opsins are: (A) Light-sensitive proteins bound to retinal (B) ATP synthase subunits (C) Photosystem pigments (D) Antioxidants 34. The photic zone in aquatic environments refers to: (A) Region where photosynthesis occurs (B) Deep ocean region (C) Sediment-water interface (D) Anaerobic zone 35. Which light has the highest photon energy? (A) UV (B) Infrared (C) Visible red (D) Microwave 36. Fluorophores are molecules that: (A) Emit light after excitation (B) Absorb sound waves (C) Conduct electricity (D) Bind to DNA only 37. The antenna complex in photosynthesis functions to: (A) Capture and transfer light energy to reaction centers (B) Fix carbon (C) Split water (D) Produce ATP directly 38. Rhodopsin activates which G-protein in vision? (A) Transducin (B) Gs (C) Gi (D) Gq 39. Time-resolved fluorescence spectroscopy measures: (A) Fluorescence lifetime and dynamics (B) Absorbance only (C) Ion concentration (D) ATP synthesis 40. Photophosphorylation in chloroplasts produces: (A) ATP (B) GTP (C) NADH (D) FADH₂ 41. Which pigment absorbs strongly in the green region and reflects red/blue? (A) Chlorophyll (B) Hemoglobin (C) Melanin (D) Rhodopsin 42. Melanin in human skin primarily protects against: (A) UV radiation damage (B) Mechanical stress (C) Pathogens (D) Salt imbalance 43. Which spectroscopy is widely used in photobiophysics? (A) UV-Vis spectroscopy (B) Mass spectrometry (C) NMR spectroscopy only (D) X-ray diffraction only 44. In photosynthesis, water is split during: (A) Light-dependent reactions (B) Calvin cycle (C) Carbon fixation (D) Dark reactions 45. The pigment responsible for red fluorescence in corals is: (A) DsRed (B) Rhodopsin (C) Chlorophyll (D) Melanin 46. In optogenetics, light is used to: (A) Control neurons using light-sensitive ion channels (B) Visualize tissues (C) Heat cells (D) Generate ATP directly 47. Photosynthetic efficiency is highest under: (A) Red and blue light (B) Green light (C) Infrared light (D) Yellow light 48. Which photoreceptor regulates circadian rhythms in mammals? (A) Melanopsin (B) Rhodopsin (C) Chlorophyll (D) Hemoglobin 49. Time-correlated single photon counting (TCSPC) is used to measure: (A) Fluorescence lifetimes (B) ATP levels (C) Protein folding rates (D) Ion currents 50. 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