9. Photosynthesis

Light Reactions of Photosynthesis

Predict how the following conditions would affect the production of O2, ATP, and NADPH and state whether noncyclic or cyclic electron flow would occur in each: (1) Only blue photons hit a chloroplast

Reduce NADP+; oxidize H2O.

During the light reactions, photosystem I functions to_________, and photosystem II functions to __________.a) Reduce CO2; oxidize NADPH.b) Synthesize ATP; Produce O2.c) Produce O2; oxidize NADPH.d) Reduce NADP+; oxidize H2O.

Where do the electrons that are excited in photosystem II come from?a) CO2.b) O2. &nbsp;&nbsp;c) Glucose. &nbsp;&nbsp;d) Photosystem I. &nbsp;&nbsp;e) Water.

 Chlorophyll molecules in the antenna complex 

 No. Electrons do not move between pigments in the antenna complex. 

 No. This is not a source of electrons, but rather a product of photosystem activity. 

 No. This carries electrons but is not the source of electrons for PSII. 

 No. Light provides photons, not electrons. 

Think about an event associated with photosystem II that is not associated with photosystem I.

Where do the electrons entering photosystem II come from?

Conceptual overview of light dependent reactions

Light Reactions of Photosynthesis Example 1

Which of the following does not occur during the light reactions of photosynthesis?
a. Water is released;
b. Electrons from chlorophyll are moved to a higher-energy state by light;
c. ATP is produced;
d. NADPH is produced to carry electrons to the light-independent reactions;
e. Oxygen is produced when water is split.

When placed at the perimeter of a maze with food in the center, the plasmodial slime mold Physarum polycephalum explores the maze, retracts branches from dead-end corridors, and then grows exclusively along the shortest path possible to the food. How does Physarum do this? One theory is that it leaves behind slime deposits—an externalized “memory” that “reminds” it not to retry dead ends.

Develop simple experiments to test whether Physarum prefers (1) brightly lit or dark environments; (2) dry or moist conditions; (3) oats or sugar as a food source.

Animation: The Light Reactions

Which of the following sequences correctly represents the flow of electrons during photosynthesis?
a. NADPH→O2→CO2
b. H2O→NADPH→Calvin cycle
c. H2O→photosystem I→photosystem II 
d. NADPH→electron transport chain→O2

The text claims that the evolutionary history of protists can be understood as a series of morphological innovations that established seven distinct lineages, each of which subsequently diversified based on innovative ways of feeding, moving, and reproducing. Explain how the Alveolata support this claim.

Which of the following is a false statement about photosynthesis?
a. During the light-independent reactions, electrons and ATP from the light reactions combine with atmospheric carbon dioxide to produce sugars;
b. The light-independent reactions take place in the chloroplast stroma;
c. Oxygen produced during the light-independent reactions is released into the atmosphere;
d. Chlorophyll absorbs blue and red light and reflects green light;
e. The end product of photosynthesis is a carbohydrate such as glucose.

No. Stomatal opening does not produce O2.

No. The Calvin cycle does not produce O2.

 cyclic electron flow during the light reactions 

 No. Cyclic electron flow just recycles electrons that are already in the electron transport chain of the light reactions. 

 No. The electrons that feed into PSI have ultimately come from PSII, not from hydrolysis of water. 

 linear electron flow during the light reactions 

Think about photosystem II.

Molecular oxygen is produced during __________.

photosystem I, ETC, photosystem II, NADP+ reduction, chemiosmosis.

photosystem I, photosystem II, ETC, NADP+ reduction, chemiosmosis.

photosystem II, ETC, photosystem I, NADP+ reduction, chemiosmosis.

photosystem II, photosystem I, ETC, NADP+ reduction, chemiosmosis.

What is the correct order of steps of the light reactions of Photosynthesis?a) photosystem I, ETC, photosystem II, NADP+ reduction, chemiosmosis.b) photosystem I, photosystem II, ETC, NADP+ reduction, chemiosmosis.c) photosystem II, ETC, photosystem I, NADP+ reduction, chemiosmosis.d) photosystem II, photosystem I, ETC, NADP+ reduction, chemiosmosis.

 No. Consider how many membranes there are in the chloroplast and where the electron transport chain works. 

 No. This does not separate the locations where electrons are moved. 

 No. These are openings on the surface of a leaf that allow gas exchange. 

 No. These are structures found in the mitochondria. 

Think of chemiosmosis.

During photosynthesis in a eukaryotic cell, an electrochemical gradient is formed across the __________.

Cellular Respiration - Link Reaction and Krebs - Post 16 Biology (A Level, Pre-U, IB, AP Bio)

The appearance of cuticle and stomata correlated with what event in the evolution of green plants?
a. the first upright growth forms
b. the first woody tissues
c. growth on land
d. the evolution of the first water-conducting tissues

The Light Reactions of Photosynthesis

Steps of the Light Reactions

 No. The production of ATP occurs during the light reactions before any sugar has been synthesized. 

 No. The splitting of water provides electrons for photosystem II, but it does not produce energy for ATP synthesis. 

 No. Fluorescence occurs when the chlorophyll molecule does not pass its excited electron to a photosystem. The electron falls back to its ground state, releasing its energy as light. 

movement of H+ through a membrane

Consider that this process has features in common with processes that occur in mitochondria.

The energy used to produce ATP in the light reactions of photosynthesis comes from __________.

No. NAD+ is reduced to NADH in cellular respiration. NADP+ is reduced to NADPH in photosynthesis.

 No. Oxygen is not a by-product of cellular respiration. 

 No. Both are surrounded by two membranes. 

Relate chloroplast structure and function to mitochondrial structure and function.

Both mitochondria and chloroplasts __________.

Photosynthesis: Crash Course Biology #8

Photosynthesis: The Light Reactions and The Calvin Cycle

How to Memorize the Light Reactions of Photosynthesis

Photosynthesis - Light Dependent Reactions and the Calvin Cycle

In mechanism, photophosphorylation is most similar to
a. substrate-level phosphorylation in glycolysis.
b. oxidative phosphorylation in cellular respiration.
c. carbon fixation.
d. reduction of NADP+.

What important role does lignin play in vascular plants?

a. It is the major component of the cuticle, which prevents plants from drying out.
b. It forms the outer layer of pollen grains.
c. It forms the tough, rigid cell walls of water-conducting cells.
d. It nourishes the embryo in seed plants.

Production of NADPH used in cellular respiration.

Conversion of chemical energy to light energy.		

Describe the primary function of the light reactions of photosynthesis.a) Production of NADPH used in cellular respiration.b) Use of ATP to make glucose.c) Conversion of chemical energy to light energy.d) Production of ATP and NADPH.

 No. There is no specific fluorescence center. 

 No. This is not a description of an electron transport chain. 

No. This is the enzyme that reduces NADP+ to NADPH using electrons from PSI.

 No. This is the protein structure that synthesizes ATP using chemiosmosis. 

This is a system that reacts to light. .

What structure is formed by the reaction center, light-harvesting complexes, and primary electron acceptors that cluster in the thylakoid membrane?

 No. This is a molecule involved in the Calvin cycle.  

 No. Protons are pumped into the lumen of the thylakoid using the energy released due to electron movement through the electron transport chain. 

Review the details of photosystems I and II. .

Which of the following is cycled in the cyclic variation of the light reactions?

Which process is most directly driven by light energy?
a. creation of a pH gradient by pumping protons across the thylakoid membrane
b. reduction of NADP+ molecules
c. transfer of energy from pigment molecule to pigment molecule
d. ATP synthesis

BioFlix: The Light Reactions

 No. The formation of ATP results from chemiosmosis, not a reduction involving the transfer of electrons. 

 No. Electrons do not end up in oxygen, and sugar is not a product of the light reactions. 

 No. The high-energy electrons are removed from chlorophyll, not added to it. 

 No. Water is split during the light reactions, and sugar is not a product of the light reactions. 

Consider that the output of the light reactions is the input of the Calvin cycle.

The light reactions of photosynthesis generate high-energy electrons, which end up in __________ through linear electron flow. The light reactions also produce __________ and __________.

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