Photosynthesis Mechanisms Quiz

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the absorption peak wavelength of Photosystem II?

680 nm

Explain how C4 plants minimize photorespiration, focusing on the role of the Kranz anatomy and the specific enzymes involved.

C4 plants have a specialized Kranz anatomy with a bundle sheath surrounding the vascular tissue. PEP carboxylase in mesophyll cells initially fixes CO2 into a 4-carbon compound (malate). Malate is then transported to bundle sheath cells, where it is decarboxylated by malic enzyme, releasing CO2 and pyruvate. This concentrated CO2 in the bundle sheath ensures RuBisCo primarily fixes CO2 and not O2, minimizing photorespiration.

What is the main function of light harvesting complexes (LHC) in photosynthesis?

To absorb light energy.

What happens to an electron in chlorophyll when it absorbs a photon?

It is energized and moves to a higher energy orbital. Signup and view all the answers

Describe the difference in CO2 uptake and fixation between C4 and CAM plants, highlighting the timing of stomatal opening.

C4 plants fix CO2 during the day with stomata open. They use PEP carboxylase in mesophyll cells to initially fix CO2, then transport the 4-carbon compound to bundle sheath cells for decarboxylation and Calvin cycle activity. CAM plants, however, fix CO2 primarily during the night with stomata open. They store the fixed CO2 in organic acids within vacuoles and then release it during the day for the Calvin cycle with stomata closed. Signup and view all the answers

Explain the adaptive advantage of NAD-malic enzyme type in certain C4 plants, particularly in relation to the location of decarboxylation.

NAD-malic enzyme type in some C4 plants decarboxylates malate in mitochondria within the bundle sheath cells. Unlike the NADP-malic enzyme that releases CO2 in bundle sheath chloroplasts, this type allows for the production of ATP with the reduction of NAD+ in mitochondria, providing additional energy for the plant, particularly under stress conditions. Signup and view all the answers

During the transient excited state of chlorophyll, what form of energy is released?

Heat. Signup and view all the answers

What is the chemical reaction that describes the oxidation of water during photosynthesis?

2H2O → O2 + 4H+ Signup and view all the answers

Describe how CAM plants utilize their vacuoles and how this adaptation helps them survive in arid environments.

CAM plants store organic acids formed during nocturnal CO2 fixation in vacuoles. During the day, these acids are decarboxylated to release CO2, minimizing water loss by keeping stomata closed. This enables water conservation while still allowing photosynthesis, crucial for survival in dry environments. Signup and view all the answers

What is the role of the oxygen-evolving complex (OEC) in Photosystem II?

It facilitates the oxidation of water. Signup and view all the answers

Compare and contrast the limitations of C4 and CAM plants in relation to their respective environmental conditions and photosynthetic efficiency.

C4 plants are efficient in high light and temperature conditions but require more energy for initial CO2 fixation. CAM plants thrive in arid environments but have lower photosynthetic rates due to slower decarboxylation. While both reduce photorespiration, C4 plants have a higher capacity for overall photosynthesis when water is readily available, while CAM plants conserve water at the expense of reduced photosynthetic output. Signup and view all the answers

In photophosphorylation, what potential is created by hydrogen ions across the thylakoid membrane?

Transmembrane chemiosmotic potential. Signup and view all the answers

What are the two main components of a light harvesting complex?

Reaction center and antenna. Signup and view all the answers

Why is the excited state of an electron in chlorophyll considered unstable?

It does not persist for an extended period. Signup and view all the answers

Name one of the two types of photophosphorylation.

Cyclic photophosphorylation. Signup and view all the answers

What is the primary purpose of cyclic photophosphorylation in photosynthesis?

To generate ATP without producing NADPH or releasing oxygen. Signup and view all the answers

What are the three main products of the light reactions in photosynthesis?

NADPH, ATP, and oxygen. Signup and view all the answers

How does a rise in NADPH levels affect the electron flow during the light reactions?

It stimulates a shift from non-cyclic to cyclic electron flow to meet ATP demand. Signup and view all the answers

What role does RuBP play in the carbon fixation phase of the Calvin cycle?

RuBP acts as the CO2 acceptor, allowing carbon fixation to occur. Signup and view all the answers

What conversion occurs during the reduction phase of the Calvin cycle?

3-phosphoglycerate is converted to glyceraldehyde 3-phosphate (G3P) using ATP and NADPH. Signup and view all the answers

How many molecules of G3P are produced for every six molecules of 3-phosphoglycerate processed?

One molecule of G3P is produced from six molecules of 3-phosphoglycerate. Signup and view all the answers

What is the consequence of the Calvin cycle consuming more ATP than NADPH?

It leads to a temporary shift from non-cyclic to cyclic electron flow to balance ATP supply. Signup and view all the answers

Describe the outcome of the initial carbon fixation in the Calvin cycle.

It forms an unstable six-carbon compound that immediately splits into two molecules of 3-phosphoglycerate. Signup and view all the answers

What happens to five molecules of G3P formed in the Calvin cycle?

They are rearranged to regenerate three molecules of RuBP. Signup and view all the answers

What is the significance of ATP in the Calvin cycle?

ATP provides the necessary energy for the phosphorylation of 3-phosphoglycerate. Signup and view all the answers

What is the total number of ATP molecules needed for the net synthesis of one G3P in the Calvin cycle?

9 molecules of ATP. Signup and view all the answers

What are the consequences for C3 plants when their stomata close?

They experience reduced CO2 levels, leading to increased photorespiration. Signup and view all the answers

How does photorespiration affect the overall photosynthetic output of C3 plants?

It lowers photosynthetic output by releasing CO2, using ATP, and producing no sugar. Signup and view all the answers

What is the initial product formed in C4 plants during the Calvin cycle?

A four-carbon compound. Signup and view all the answers

Name a key adaptation mechanism that some plants utilize to minimize photorespiration.

The Hatch-Slack pathway (C4 pathway). Signup and view all the answers

What type of plant structures are tightly packed around leaf veins in C4 plants?

Bundle sheath cells. Signup and view all the answers

To produce one molecule of sugar (glucose), how many molecules of CO2 are required in the Calvin cycle?

6 molecules of CO2. Signup and view all the answers

Which two types of cells are involved in the photosynthetic process of C4 plants?

Bundle sheath cells and mesophyll cells. Signup and view all the answers

What specific process does Rubisco perform when CO2 levels are low in C3 plants?

Rubisco uses O2 as a substrate instead of CO2. Signup and view all the answers

Identify a plant variant that is commonly classified as a C3 plant.

Wheat. Signup and view all the answers

What is the primary function of chlorophyll in photosynthesis?

Chlorophyll captures light energy for the light reactions of photosynthesis. Signup and view all the answers

Describe the difference between C3, C4, and CAM cycles.

C3 cycle occurs in the presence of sunlight and uses RuBisCO for carbon fixation, C4 cycle minimizes photorespiration and is adapted to hot environments, while CAM cycle allows plants to fix CO2 at night. Signup and view all the answers

What are the two key stages of photosynthesis and where do they occur?

The two key stages are the light-dependent reactions in the thylakoids and the light-independent reactions (Calvin cycle) in the stroma. Signup and view all the answers

Explain the role of Emerson’s addition in photosynthesis.

Emerson's addition illustrates how the presence of two different wavelengths of light can enhance photosynthetic efficiency. Signup and view all the answers

What is photorespiration and how does it affect photosynthesis?

Photorespiration is a process that occurs when oxygen levels are high, leading to the consumption of energy and carbon, reducing the overall photosynthetic efficiency. Signup and view all the answers

Identify the absorption peaks for Chlorophyll a and b.

Chlorophyll a has absorption peaks at 430 nm (blue) and 662 nm (red), while chlorophyll b peaks at 450 nm (blue) and 640 nm (red). Signup and view all the answers

What are the two cooperating photosystems in the light reactions of photosynthesis?

The two cooperating photosystems are Photosystem I (PSI) with a reaction center P700, and Photosystem II (PSII) with a reaction center P680. Signup and view all the answers

What is the significance of the chlorophyll a to chlorophyll b ratio in plants?

The ratio of chlorophyll a to chlorophyll b is approximately three to one, indicating a balance in light absorption for efficient photosynthesis. Signup and view all the answers

Study Notes

Photosynthesis Overview

Photosynthesis is a crucial biochemical process
It's the primary source of carbon in plants
Involves the conversion of CO2 from the atmosphere into organic compounds

Photosynthesis Processes

Light-dependent reactions:
- Involve chlorophyll and other pigments capturing light energy
- Drive the production of ATP and NADPH
- Occur in thylakoid membranes
- Emerson effect highlights the synergistic interaction of different pigments.
- Photosynthetic phosphorylation involves energy transformation during light reactions
Light-independent reactions (Calvin cycle):
- Utilize ATP and NADPH from light-dependent reactions
- Fix CO2 to produce sugars (carbohydrates)
- Occur in the stroma of chloroplasts
- Involves the cyclical steps of CO2 fixation, reduction/phosphorylation, and RuBP regeneration

Light Reaction Details

Two photosystems (PS I and PS II) cooperate
Photosystem I (PSI) has a reaction center (P700), absorbing best at 700 nm
Photosystem II (PSII) has a reaction centre (P680), absorbing best at 680nm
Electrons are transferred through a chain of electron carriers
Water is oxidized, releasing oxygen
A proton gradient created across the thylakoid membrane promotes ATP synthesis

Light Harvesting Complexes (LHC)

Function is to absorb light energy
Consists of reaction center (P680 or P700) and antenna molecules
Antenna molecules absorb photons and transfer energy to the reaction center

Photosystems

Two photosystems are involved
Photosystem II (PSII): Generates ATP using light energy
Photosystem I (PSI): Generates NADPH using light energy
Both photosystems are critical to the light-dependent reactions

Chlorophyll

Light energy is absorbed by chlorophyll molecules
Chlorophyll a and chlorophyll b are key pigments in photosynthesis

Water Photolysis

Water is split, releasing oxygen as a byproduct, along with hydrogen ions

Calvin Cycle Phases

Carbon fixation: RuBisCO enzyme catalyzes the joining of CO2 with RuBP (ribulose-1,5-bisphosphate), forming an unstable 6-carbon compound
Reduction: ATP and NADPH are used to convert the 3-PGA (3-phosphoglyceric acid) to G3P (glyceraldehyde-3-phosphate)
Regeneration: Some G3P molecules are used to regenerate RuBP for the next cycle, while others are used for glucose synthesis

Cyclic Photophosphorylation

Involves electron flow only through Photosystem I
Focus is on ATP production, not NADPH
Maintains ATP supply if necessary for the Calvin Cycle

Non-cyclic Photophosphorylation

Electron flow is not cyclic
Produces both ATP and NADPH
Essential for the Calvin Cycle

C3, C4, and CAM plants

C3 plants: Employ the Calvin cycle for CO2 fixation. More susceptible to photorespiration under hot, dry conditions
C4 plants: Employ a two-step method of CO2 fixation in mesophyll cells to reduce water use and maximize CO2 uptake. Bundle sheath cells are where the Calvin Cycle runs. Less susceptible to photorespiration
CAM (Crassulacean Acid Metabolism) Plants: Open stomata at night to fix CO2 as organic acids. These are stored and released during the day for photosynthesis, thus minimizing water loss.

Photorespiration

A process that occurs when CO2 levels are low in plants
Leads to decrease in photosynthetic outputs
Favors when stomata close

Additional Compounds produced

NADPH
ATP
Oxygen

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Test your knowledge on the intricacies of photosynthesis, focusing on Photosystem II, light harvesting complexes, and the differences between C4 and CAM plants. Explore key concepts like the role of enzymes, electron behavior in chlorophyll, and the adaptations of plants in arid environments. This quiz will deepen your understanding of plant biology and biochemical pathways.