Photosynthesis Quiz

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Questions and Answers

What is the immediate outcome of photon emission in the context of photosynthesis?

Emission of longer wavelength light (correct)

Formation of carbohydrates

Absorption of energy

Production of oxygen

Where do the light-dependent reactions occur in the chloroplast?

Stroma

Cytoplasm

Granum

Thylakoid membranes (correct)

Which process involves the direct use of light energy to convert it into ATP and NADPH?

Light-dependent reactions (correct)

Dark reactions

Light-independent reactions

Calvin cycle

Which of the following pigments primarily absorb light energy during photosynthesis?

Chlorophylls Signup and view all the answers

What major event occurs during the light-dependent reactions after chlorophyll a absorbs a photon?

Excitation of electrons to a higher energy state Signup and view all the answers

What is released as a by-product during the light-dependent reactions?

Oxygen Signup and view all the answers

Which complex is the first to act when the light-dependent reactions begin?

Photosystem II Signup and view all the answers

In which part of the chloroplast do the light-independent reactions take place?

Stroma Signup and view all the answers

What is the final electron acceptor in the electron transport chain during photosynthesis?

NADP+ Signup and view all the answers

Which complex transfers electrons from Photosystem II to Photosystem I?

Cytochrome b6f Signup and view all the answers

What is generated by the oxidation of water in Photosystem II?

Oxygen and hydrogen ions Signup and view all the answers

What role does ATP synthase play in photosynthesis?

It creates ATP Signup and view all the answers

Which of the following statements about Photosystem I is true?

It contains the chlorophyll dimer P-700. Signup and view all the answers

What phenomenon occurs when electrons flow through the electron transport chain?

Photophosphorylation Signup and view all the answers

What is the function of ferredoxin in photosynthesis?

It transfers electrons to NADP+. Signup and view all the answers

Which process creates a proton gradient used by ATP synthase?

Oxidation of water at PSII Signup and view all the answers

What is the main function of photosynthesis in plants?

To utilize sunlight to produce energy Signup and view all the answers

In oxygenic photosynthesis, which molecule is reduced?

Carbon dioxide (CO2) Signup and view all the answers

Which type of photosynthesis is used by purple bacteria?

Anoxygenic Signup and view all the answers

What do chloroplasts store that is essential for photosynthesis?

Chlorophyll Signup and view all the answers

Which process results in the evolution of molecular oxygen?

Photosynthesis Signup and view all the answers

Which organelle contains thylakoids as structural units of photosynthesis?

Chloroplast Signup and view all the answers

What is a significance of photosynthesis in terms of atmospheric gases?

It consumes atmospheric carbon dioxide and produces oxygen. Signup and view all the answers

What do leucoplasts primarily store?

Fat and starch Signup and view all the answers

What enzyme is responsible for cleaving sedoheptulose-1,7-bisphosphate into sedoheptulose-7-phosphate?

Sedoheptulose-1,7-bisphosphatase Signup and view all the answers

How many molecules of G3P are converted to RuBP in the Calvin cycle?

Five G3P Signup and view all the answers

Which molecule is produced as a competitive product during photorespiration?

2-phosphoglycolate Signup and view all the answers

Which of the following represents the final phosphorylated product in the regeneration phase of the Calvin cycle?

Ribulose-1,5-bisphosphate Signup and view all the answers

What is the primary purpose of C4 carbon fixation in plants?

To circumvent photorespiration Signup and view all the answers

What is the consequence of photorespiration for plants?

Loss of fixed CO2 Signup and view all the answers

What carbohydrate molecule is the precursor for the formation of xylulose-5-phosphate during the process described?

Glyceraldehyde-3-phosphate Signup and view all the answers

What is the role of phosphopentose isomerase in the Calvin cycle?

Conversion of R5P to Ru5P Signup and view all the answers

What is the primary function of cyclic photophosphorylation?

Create ATP and regulate NADPH levels Signup and view all the answers

What compound is initially split during the carbon fixation process in the Calvin cycle?

Ribulose-1,5-bisphosphate (RuBP) Signup and view all the answers

Which enzyme catalyzes the reduction of 1,3-bisphosphoglycerate (1,3BPGA) during carbon reduction?

Glyceraldehyde 3-phosphate dehydrogenase Signup and view all the answers

In which phase of the Calvin cycle do the majority of the ATP and NADPH produced in the light reactions fuel chemical reactions?

Reduction phase Signup and view all the answers

What is the first product formed when RuBisCO catalyzes the reaction between RuBP and CO2?

Enediol-enzyme complex Signup and view all the answers

Which process converts triose phosphate into dihydroxyacetone phosphate (DHAP) during the regeneration phase?

Triose phosphate isomerase action Signup and view all the answers

What happens to the phosphate ion during the conversion of G3P and DHAP into fructose 6-phosphate?

It is lost into solution Signup and view all the answers

Which component of the ATP synthase is located outside the membrane?

F1 portion Signup and view all the answers

What is the primary advantage of kranz anatomy in C4 plants?

To concentrate CO2 around RuBisCO and avoid photorespiration Signup and view all the answers

During the C4 pathway, which enzyme is responsible for converting pyruvate to phosphoenolpyruvate (PEP)?

Pyruvate orthophosphate dikinase Signup and view all the answers

What is the role of malate in the C4 pathway?

To be decarboxylated and release CO2 into the bundle-sheath cells Signup and view all the answers

How does the C4 pathway compare to the C3 pathway in terms of energy usage?

C4 pathway requires more energy because every CO2 molecule is fixed twice Signup and view all the answers

Which cells in C4 plants lack grana in their chloroplasts?

Bundle sheath cells Signup and view all the answers

What is the purpose of the low conductance boundary layer in kranz anatomy?

To maintain a high concentration of CO2 in the bundle sheath cells Signup and view all the answers

What happens to the CO2 fixed by PEP carboxylase in the C4 pathway?

It is converted to malate and transported to bundle-sheath cells Signup and view all the answers

Who elucidated the C4 carbon fixation pathway?

Marshall Davidson Hatch and C.R. Slack Signup and view all the answers

Study Notes

Photosynthesis Overview

Photosynthesis is the process used by plants, algae, and some bacteria to convert light energy into chemical energy.
This process harnesses energy from sunlight to produce carbohydrates.
Two types of photosynthesis exist: oxygenic and anoxygenic.

Oxygenic Photosynthesis

The most common type, found in plants, algae, and cyanobacteria.
Light energy transfers electrons from water (H₂O) to carbon dioxide (CO₂), producing carbohydrates.
In this process, CO₂ is reduced, and water is oxidized.
Ultimately, oxygen (O₂) is produced along with carbohydrates.

Anoxygenic Photosynthesis

Typically occurs in certain bacteria like purple bacteria and green sulfur bacteria.
Uses electron donors other than water.
Produces sulfur when hydrogen sulfide (H₂S) is used as an electron donor.

Significance of Photosynthesis

Converts solar energy into organic matter.
Consumes atmospheric carbon dioxide and produces oxygen.
Maintains atmospheric oxygen levels, crucial for respiration in other living organisms.
Provides the building blocks (carbohydrates, organic acids, proteins, etc.) for other biological molecules.
Provides energy for various metabolic activities and movements in living organisms.

Photosynthetic Requirements

Photosynthetic eukaryotic organisms contain plastids (organelles) in their cytoplasm.
Plastids are surrounded by a double membrane and can contain pigments or store nutrients.
Different types of plastids include chloroplasts (with chlorophyll), chromoplasts (with carotenoids), and leucoplasts (non-pigmented, storing starch and fat).

Chloroplast Structure

Chloroplasts are double-membrane-bound organelles performing photosynthesis.
The grana are the innermost portion, consisting of stacked disc-shaped thylakoid membranes.
Thylakoids contain light-harvesting complexes where electron transfer takes place.
The empty spaces between grana are the stroma.

Thylakoids

The thylakoid is the structural unit of photosynthesis.
The photosynthetic membrane is vesicular, with an outer stroma phase and an inner lumen.
The photosynthetic membrane contains most of the pigments and proteins needed for light reactions.

Pigments

Pigments bestow color to plants, algae, and bacteria and are crucial for trapping sunlight.
Different pigments absorb different light wavelengths.
Chlorophylls (a, b, and c) absorb blue and red light, carotenoids absorb bluish-green light, and phycobilins absorb light wavelengths not well absorbed by other pigments (found in cyanobacteria and red algae).

Absorption of Light Energy

Photosynthesis is primarily driven by visible light (400-700 nm).
Light is captured by pigment molecules (chlorophyll a and b, carotenoids) in light-harvesting protein complexes within the photosynthetic membrane.
Light-harvesting complexes surround the reaction centers that act as antennas.
A photon's energy is absorbed by an antenna molecule, causing a transition to an excited state.
Excited state decays within femtoseconds (10⁻¹⁵ s) to the first excited singlet state, and energy is transferred to other nearby molecules before ending at the reaction center.

Chlorophyll Fluorescence

Excitons (excited electrons) are converted back to photons and emitted as fluorescence (a longer wavelength).
Used as an indicator of photosynthetic energy conversion performance in plants, algae, and bacteria.
Fluorescence can also indicate plant stress or damage to the photosynthetic apparatus.

Chlorophyll Phosphorescence

A type of photoluminescence related to fluorescence.
A phosphorescent material takes time to re-emit the absorbed radiation.
Phosphorescence involves radiative electronic transitions from triplet to ground states in pigment molecules.

Light-Dependent Reactions (Light Reactions)

Light-dependent reactions require direct light energy and use captured light energy from chlorophyll a to make energy carrier molecules (ATP and NADPH).
Water is split, releasing oxygen (a byproduct) during these reactions.
This occurs on the thylakoid membranes. Major protein complexes involved: PSII, cytochrome b6f complex, PSI, and ATP synthase.

Photosystem II (PSII)

The first protein complex in the light-dependent reactions of oxygenic photosynthesis.
Catalyzes the capture of light photons to energize electrons.
Electrons are transferred through various coenzymes and cofactors to reduce plastoquinone to plastoquinol.
Water is oxidised to replenish lost electrons, releasing oxygen.

Cytochrome b6f complex

Transfers electrons from Photosystem II to Photosystem I (PSI).
It pumps protons into the thylakoid lumen, creating an electrochemical gradient.

Photosystem I (PSI)

The second photosystem.
The electron gets energy from another photon.
The final electron acceptor is NADP+.
This creates NADPH.

ATP Synthase

Creates the energy storage molecule, ATP, using the proton gradient formed by the electron transport chain.
It comprises two parts: FO embedded within the thylakoid membrane and F1 outside.

Non-cyclic and Cyclic Photophosphorylation

Non-cyclic: the primary electron flow from PSII to cytochrome b6f then to PSI to create ATP and NADPH.
Cyclic: ATP is produced, but no NADPH. The electron flow goes from PSII to cytochrome b6f to PSI, then back to the cytochrome b6f complex.

Calvin Cycle (Light-Independent Reactions or Dark Reactions)

Plants and algae use the Calvin cycle to convert carbon dioxide into sugars.
It occurs in the stroma of the chloroplasts.
It involves four main steps: carbon fixation, reduction, carbohydrate formation, and regeneration.
The cycle uses ATP and NADPH (created during light reactions) to fuel the reactions.

Carbon Fixation

The enzyme RuBisCO catalyzes the carboxylation of ribulose-1,5-bisphosphate (RuBP, a 5-carbon compound) by carbon dioxide (CO₂) in a two-step reaction.
Carbon dioxide is captured, producing a 6-carbon intermediate that then splits into two 3-carbon molecules (3-PGA).

Carbon Reduction

Enzyme phosphoglycerate kinase phosphorylates 3-PGA using ATP, producing 1,3-bisphosphoglycerate (1,3-BPG) and ADP
Enzyme glyceraldehyde-3-phosphate dehydrogenase catalyzes the reduction of 1,3-BPG by NADPH. This produces glyceraldehyde-3-phosphate (G3P) and oxidised NADP+.

Regeneration Phase

Molecules involved (fructose-1,6-bisphosphate and dihydroxyacetone phosphate) in converting five G3P molecules to three 5-carbon molecules of RuBP, also using ATP.

Photorespiration

RuBisCO sometimes reacts with oxygen (O₂) instead of carbon dioxide (CO₂), a process called photorespiration.
It's more active at higher temperatures and involves a loss of carbon dioxide.
The byproducts are converted into other compounds.

C4 Carbon Fixation

Evolved to minimize photorespiration in plants in hot, dry climates.
CO₂ is concentrated around RuBisCO, creating higher CO₂ substrate levels to reduce the competition for O₂ and CO₂ by RuBisCO.
Involves carbon fixation in mesophyll cells followed by transport to bundle-sheath cells, concentrating CO₂ around RuBisCO.
Multiple enzyme systems in the mesophyll and bundle sheath cells. Variations include malate or aspartate as the 4-carbon intermediates transported from mesophyll to bundle sheath.

C4 Leaf Anatomy

Kranz anatomy: leaf structure with concentric rings of cells surrounding the vascular bundles, consisting of mesophyll and bundle sheath cells.
Bundle sheath cells are rich in chloroplasts, often lacking grana, and have high concentration of CO₂, low O₂ levels.

C4 Pathway

The series of reactions of C4 pathway which involves creation of 4-carbon organic acids in mesophyll cells
These molecules then are transported to other cells for decarboxylation and carbon dioxide release to further enter Calvin Cycle. This pathway is used by tropical and warm climate plants.

CAM (Crassulacean Acid Metabolism)

Plants use this pathway to minimize water loss in hot, dry environments.
Carbon dioxide is fixed at night when stomata are open, during this time it is converted into organic acids (such as malate) and stored in vacuoles. During the day the stomata are closed, organic acids release carbon dioxide for further use in Calvin Cycle.

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Description

Test your knowledge on the processes and components of photosynthesis. This quiz covers key concepts such as photon emission, light-dependent reactions, and the role of pigments in energy absorption. Perfect for students studying biology or plant sciences.