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Photosynthesis and Light Reactions Quiz

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19 Questions

What is the primary purpose of the light reactions in photosynthesis?

To convert light energy into chemical energy in the form of NADPH

Which cellular component in eukaryotes is responsible for hosting the light reactions of photosynthesis?

Chloroplasts

What is the role of Photosystem II in the light reactions of photosynthesis?

It donates high energy electrons to the electron transport chain

What is the purpose of the proton gradient generated across the thylakoid membrane during the light reactions?

To power the synthesis of ATP through ATP synthase

What is the role of the electron transport chain in the light reactions of photosynthesis?

To transport electrons from Photosystem II to Photosystem I

What is the final electron acceptor in the light reactions of photosynthesis?

NADP+

What is the role of the enzyme NADP+ reductase in the light reactions of photosynthesis?

To reduce NADP+ to NADPH

What is the role of the electron carrier Plastoquinone (PQ) in the light reactions of photosynthesis?

To transport electrons from Photosystem II to the cytochrome complex

What is the purpose of Photosystem I in the light reactions of photosynthesis?

To absorb light energy and excite electrons to a higher energy level

Which of the following is NOT a product of the light reactions in photosynthesis?

Glucose

What is the primary role of the enzyme Rubisco in the Calvin cycle?

To catalyze the covalent bonding of CO2 to ribulose-1,5-bisphosphate (RuBP)

Which of the following statements about the light reactions is incorrect?

The light reactions produce glucose as an energy-rich molecule

In which phase of the Calvin cycle does carbon fixation occur?

Carbon fixation phase

What is the primary function of the chloroplast stroma during photosynthesis?

To provide a location for the Calvin cycle

Which of the following is NOT a role of the photosystem II (PSII) complex in the light reactions?

Reducing NADP+ to NADPH

What is the primary role of the electron transport chain in the light reactions?

To produce ATP through chemiosmosis

Which of the following is NOT a function of the Calvin cycle?

Producing ATP and NADPH

Which of the following statements about the products of photosynthesis is correct?

G3P can be used to synthesize other organic molecules like fatty acids and amino acids

Which of the following processes is NOT a part of the light reactions in photosynthesis?

Carbon fixation by Rubisco

Study Notes

Photosynthesis

  • Photosynthesis transforms light energy into chemical energy and is part of the carbon cycle, synthesizing new carbon backbones from CO2.

Location of Photosynthesis

  • In eukaryotes (plants and algae), photosynthesis occurs in the chloroplasts, using components in the stroma, thylakoid membranes, and the thylakoid lumen.

Light Reactions

  • The light reactions use two photosystems to capture light and generate high energy electrons.
  • Photosystem II donates high energy electrons to an electron transport chain (ETC) starting with the high energy electron carrier PQ.
  • PQ reduces cytochrome complex, which uses energy from electrons to pump hydrogen ions across the membrane into the thylakoid lumen, generating a H+ gradient across the thylakoid membrane.
  • Low energy electrons reduce PC, the last step in the ETC.
  • Photosystem I accepts low energy electrons from PC and re-excites them back to high energy levels before reducing feridoxin (FD).
  • Feridoxin delivers high energy electrons to the enzyme NADP+ reductase, reducing the final electron acceptor NADP+ and making the high energy electron carrier, NADPH.
  • The flow of H+ from high concentration in the lumen to low concentration in the stroma powers the enzyme complex ATP synthase, resulting in the formation of ATP in the stroma (=photophosphorylation).
  • Electrons leave the light reactions in NADPH, and new electrons are obtained by the splitting of water through photolysis by PSII.

Photolysis

  • Photolysis is the splitting of water, which resupplies PSII with low energy electrons.

Calvin Cycle

  • The Calvin Cycle fixes inorganic carbon from CO2 in the form of organic carbon chains, storing energy in chemical bonds.
  • CO2 is covalently bonded to the 5C molecule RuBP by the enzyme Rubisco, generating two 3C organic molecules in the carbon fixation phase.
  • The product of the reduction phase is glyceraldehyde-3-phosphate (G3P).
  • One G3P is exported while five go to the regeneration phase and are made back into three molecules of RuBP.

Products of Photosynthesis

  • The G3P from photosynthesis is used to make other organic molecules, including fatty acids, amino acids, and nucleic acids.

Test your knowledge on photosynthesis and the light reactions in eukaryotes. Explore concepts such as the transformation of light energy into chemical energy, the carbon cycle, chloroplast components, and photosystems.

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