Photosynthesis Light-Dependent Reactions
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Questions and Answers

What role does a photon of light energy play in the light-dependent reactions of photosynthesis?

  • It binds to NADP+ to form NADPH.
  • It initiates the Calvin cycle.
  • It catalyzes the splitting of water molecules.
  • It excites an electron in a chlorophyll molecule. (correct)

What happens to chlorophyll during the light-dependent reactions?

  • It produces ribulose bisphosphate (RuBP).
  • It donates electrons to an electron transport chain. (correct)
  • It absorbs protons from the surrounding medium.
  • It converts sunlight into chemical energy directly.

Which molecule is primarily generated by the light-dependent reactions to store energy for later use?

  • 3-PGA
  • RuBP
  • ATP (correct)
  • Glucose

How is NADPH formed during the light-dependent reactions?

<p>By capturing a hydrogen ion and an excited electron. (D)</p> Signup and view all the answers

What is the primary purpose of splitting water molecules in the light-dependent reactions?

<p>To replace lost electrons from chlorophyll. (A)</p> Signup and view all the answers

Which enzyme is responsible for catalyzing the carbon fixation stage of the Calvin cycle?

<p>Ribulose bisphosphate carboxylase/oxygenase (rubisco) (B)</p> Signup and view all the answers

What is generated as a result of the electron transport chain in the light-dependent reactions?

<p>Oxygen and hydrogen ions (A)</p> Signup and view all the answers

What is the significance of the Calvin cycle in C3 plants?

<p>It fixes carbon dioxide into organic compounds. (C)</p> Signup and view all the answers

What is the primary role of NADPH in the reduction phase of the Calvin cycle?

<p>To donate electrons necessary for the conversion of 3-PGA to G3P (D)</p> Signup and view all the answers

In C4 plants, where does the Calvin cycle take place?

<p>In the chloroplasts of bundle-sheath cells (A)</p> Signup and view all the answers

What happens to the majority of G3P molecules produced in the Calvin cycle?

<p>They are used to regenerate RuBP (D)</p> Signup and view all the answers

Which enzyme is responsible for fixing CO2 in the mesophyll cells of C4 plants?

<p>PEP carboxylase (A)</p> Signup and view all the answers

How do CAM plants minimize photorespiration effectively?

<p>By storing organic acids at night for CO2 release during the day (B)</p> Signup and view all the answers

What is the initial product formed from the fixation of CO2 in C4 plants?

<p>Oxaloacetate (A)</p> Signup and view all the answers

Which process do CAM plants use to ensure that CO2 is available for photosynthesis during the day?

<p>They transport stored organic acids from vacuoles to release CO2 (C)</p> Signup and view all the answers

Which statement accurately describes the journey of malate in C4 plants?

<p>Malate releases CO2 in the bundle-sheath cells for fixation by rubisco (A)</p> Signup and view all the answers

Flashcards

Light-dependent reactions

The first stage of photosynthesis, requiring sunlight and occurring in the thylakoid membranes.

Photosystem

A group of pigment molecules and proteins that absorb light energy, initiating the light-dependent reactions.

Electron excitation

A chlorophyll electron absorbs light energy, becoming energized and breaking free from the chlorophyll molecule.

ATP

An energy-carrier molecule storing energy in a phosphate bond.

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NADPH

An energy-carrier molecule storing energy in a hydrogen bond.

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Carbon Fixation

The first step of the Calvin cycle where carbon dioxide combines with RuBP, creating a 3-carbon compound.

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RuBP

A five-carbon acceptor molecule in the Calvin cycle that combines with carbon dioxide.

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Calvin Cycle

The second stage of photosynthesis converting energy into sugar using ATP and NADPH.

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Reduction in Photosynthesis

The process where NADPH donates electrons to a 3-carbon intermediate, converting it into G3P, a three-carbon sugar.

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Regeneration of RuBP

The process where five out of six G3P molecules are used to regenerate RuBP, the starting molecule for the Calvin cycle.

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C4 Plants

Plants with a specialized adaptation to minimize photorespiration, where the light-dependent reactions and Calvin cycle are physically separated.

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Bundle-Sheath Cells

Specialized cells in C4 plants where the Calvin cycle occurs, surrounding the leaf veins.

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PEP Carboxylase

An enzyme in C4 plants that fixes CO2 to form oxaloacetate, avoiding the binding of oxygen to rubisco.

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CAM Plants

Plants adapted to arid regions, separating the light-dependent reactions and CO2 fixation in time, not space.

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Organic Acid Storage

CAM plants store fixed CO2 as an organic acid in vacuoles during the night, releasing it for the Calvin cycle during the day.

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Study Notes

Light-Dependent Phase of Photosynthesis

  • Light-dependent reactions require sunlight, occurring in thylakoid membranes within chloroplasts
  • Photosystems are groupings of pigments and proteins in thylakoid membranes
  • Pigment molecules absorb photons (packets of light energy)
  • Chlorophyll absorbs light, excites an electron
  • Excited electron escapes from chlorophyll
  • A water molecule splits to replace lost electron; releasing oxygen and hydrogen ions
  • Energy from sunlight stored in energy carriers ATP and NADPH
  • ATP and NADPH carry energy to the Calvin cycle
  • ATP loses a phosphate, NADPH loses hydrogen to become lower-energy ADP and NADP+

Generating an Energy Carrier (ATP)

  • Light energy stored by ATP and NADPH
  • Phosphate bond used for energy storage / release
  • ATP and NADPH lose atoms becoming ADP and NADP+ during energy release to Calvin Cycle

Generating Another Energy Carrier (NADPH)

  • Light re-energizes electron in photosystem I using another photon
  • Electron Energy formation of NADPH from NADP+ and hydrogen ions (H+)
  • Stored solar energy used in making sugar molecules

The Dark Reactions (Calvin Cycle in C3 Plants)

  • Divided into three stages: carbon fixation, reduction, and regeneration
  • Carbon fixation: CO2 combines with RuBP (five-carbon molecule); catalyzed by Rubisco
  • Reduction: ATP and NADPH used to convert 3-PGA into G3P (three-carbon sugar)
  • Regeneration: 5 G3P molecules recycled to regenerate RuBP (requires ATP)

The Dark Reactions in C4 Plants

  • Light-dependent and Calvin cycle physically separated (mesophyll and bundle sheath cells)
  • CO2 fixed into 4-carbon acid (oxaloacetate) in mesophyll cells, then transported to bundle sheath cells
  • Malate releases CO2, enters Calvin Cycle, generates sugar
  • No photorespiration

The Dark Reactions in CAM Plants

  • Light-dependent and Calvin cycle separated temporally (day/night)
  • CO2 absorbed at night, stored as organic acids (oxaloacetate or malate)
  • Stomata closed during day, organic acids break into CO2 and enter Calvin Cycle.

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Photosynthesis Notes PDF

Description

Explore the intricate process of light-dependent reactions in photosynthesis. This quiz covers key concepts such as the role of chlorophyll, the function of photosystems, and the production of energy carriers like ATP and NADPH. Test your understanding of how these elements contribute to energy storage in plants.

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