Photosynthesis

Abstract

All forms of life in this universe require energy for growth and maintenance. Plants and some forms of bacteria capture light energy directly from solar radiation and utilize it for synthesis of food materials besides producing basic raw materials from which other cellular biomolecules are produced. The term photosynthesis describes the process by which green plants synthesize organic compounds from inorganic raw materials using light. Photosynthesis is the source of all biological energy, viz., food, biological fuels, and biomass, and is also most important for availability of free oxygen. Whatever free oxygen is there in the atmosphere is the result of photosynthesis. Since heterotrophic organisms including animals cannot use sunlight as direct source of energy, they consume plants as the source of energy. Photosynthesis is the means for solar energy to enter into the global ecosystem, and it alone is the essential biological process by which solar energy is transformed into metabolic form of energy for all forms of life on earth. An understanding of the fundamental and applied aspects of the process comes from a wide range of studies including agriculture, forestry, plant biochemistry, plant molecular biology, tissue culture, and metabolic engineering.

Multiple-Choice Questions

• 1. Excited state of chlorophyll molecule responsible for the photochemical reaction of photosynthesis is:

  • (a) First singlet state

  • (b) Second singlet state

  • (c) Triplet state

  • (d) None of the above

• 2. Photochemical reaction requires:

  • (a) 10⁻³ seconds

  • (b) 10⁻¹² seconds

  • (c) 10⁻⁹ seconds

  • (d) 10⁻² seconds

• 3. Phenomenon of loss of energy of excited pigment molecule as light wavelength of longer wavelength than the wavelength of absorbed light is known as:

  • (a) Homogenous energy transfer

  • (b) Resonance

  • (c) Fluorescence

  • (d) Phosphorescence

• 4. Primary electron acceptor from excited P₆₈₀ in PSII is:

  • (a) Q_A

  • (b) Phylloquinone

  • (c) Tyr_z

  • (d) Pheophytin

• 5. Primary electron donor to P₆₈₀ ⁺ in PSII is:

  • (a) Tyr_z

  • (b) H₂O

  • (c) Oxygen-evolving complex

  • (d) Q_B

• 6. Quantum yield in photosynthesis is defined as:

  • (a) Number of quanta required for release of one O₂

  • (b) Number of O₂ molecules produced per quanta absorbed

  • (c) Number of chlorophyll molecules required to absorb one quanta

  • (d) Number of chlorophyll molecules responsible for release of one O₂

• 7. (Tick which is not right) Activation of Rubisco by light is due to:

  • (a) Decrease in pH of lumen

  • (b) Increase in pH of stroma

  • (c) Due to release of Rubisco from thylakoids into the stroma

  • (d) Due to Mg⁺² moving out of thylakoid lumen to stroma

• 8. Which of the following reactions in Calvin cycle is reversible?

  • (a) Conversion of sedoheptulose 1,7-bisphosphate to sedoheptulose 7-phosphate

  • (b) Synthesis of ribulose 1,5-bisphosphate from ribose 5-phosphate

  • (c) Synthesis of 3-phosphoglyceraldehyde from 3PGA

  • (d) Conversion of xylulose 5-phosphate to ribulose 5-phosphate

• 9. The three types of C4 plants differ from each other on the basis of:

  • (a) Chemical nature of C4 compound transported out of mesophyll cells

  • (b) Decarboxylation reaction of C4 compound in bundle sheath cells

  • (c) Chemical nature of C3 compound which is returned to mesophyll cells

  • (d) The enzyme which is responsible for initial carboxylation of CO₂ acceptor

• 10. Tick incorrect statement:

  • (a) Oxidation of glycolate to glyoxylate occurs in peroxisomes

  • (b) P-glycolate is dephosphorylated to glycolate in peroxisomes

  • (c) NH₃ is produced in mitochondria

  • (d) α-hydroxypyruvate is reduced to glycerate in glyoxysomes

Answers

1. a	2. b	3. c	4. d	5. a	6. b	7. c
8. d	9. b	10. b