Plant cells and photosynthesis

What molecule is split by photosynthesis II during the light reactions, and what are its byproducts?

Water (H2O) is split, producing oxygen (O2), protons (H+), and electrons.

What is the role of photosystem II in the light reactions?

PSII absorbs light and uses the energy to excite electrons, transferring them through the ETC, split water molecules to release electrons and oxygen

What happens to the electrons after they leave photosystem II

They are passed to the cytochrome b6/f complex via the electron transport chain.

How does the cytochrome b6/f complex contribute to ATP production?

t pumps protons into the thylakoid lumen, creating a proton gradient used by ATP synthase to produce ATP.

What is the primary role of Photosystem I (PSI)?

PSI re-energizes electrons and transfers them to NADP+, forming NADPH.

How is NADPH produced during the light reactions?

electrons from PSI reduce NADP+ to NADPH.

What is the function of ATP synthase in the light reactions?

ATP synthase uses the proton gradient to convert ADP and inorganic phosphate into ATP.

What is the purpose of the proton gradient created during the light reactions?

The proton gradient drives ATP synthesis through ATP synthase.

What are the two main products of the light reactions that are used in the Calvin Cycle?

ATP and NADPH.

What gas is released as a byproduct of the light reactions in photosynthesis?

Oxygen (O2).

What makes plant cells unique to animal and fungal cells?

cell wall, chloroplasts, large central vacuole, plasmodesmata

What are chloroplasts origin?

Chloroplasts are thought to have originated through an endosymbiotic event where a primitive eukaryotic cell engulfed a photosynthetic cyanobacterium. This became a permanent symbiotic organelle.

What is the structural elements of chloroplasts?

• Thylakoid Membranes: These are stacked into structures called grana and house the machinery for the light-dependent reactions of photosynthesis.

• Stroma: The fluid-filled space surrounding the thylakoids, where the Calvin Cycle (light-independent reactions) takes place.

• Chlorophyll: The pigment that captures light energy is located in the thylakoid membranes.

• Double Membrane: Chloroplasts have an inner and outer membrane, supporting the endosymbiotic theory.

What are the main products of the light reaction of photosynthesis?

• ATP: Provides energy for the Calvin Cycle.

• NADPH: An electron carrier used to reduce carbon in the Calvin Cycle.

• Oxygen (O2): Produced as a byproduct from the splitting of water.

What are the main events associated with each of the 2 photosystems in the light reaction?

• Photosystem II (PSII): Absorbs light at 680 nm (P680), oxidizes water to oxygen, and passes electrons to the plastoquinone pool via a series of redox reactions.

• Photosystem I (PSI): Absorbs light at 700 nm (P700), and the electrons from PSII are used to reduce NADP+ to NADPH.

What is the difference between antenna pigments and reaction centre pigments?

• Antenna Pigments: These pigments (like chlorophyll and carotenoids) capture light energy and transfer it to the reaction center without directly participating in the redox reactions.

• Reaction Center Pigments: Chlorophyll molecules in the reaction center (P680 in PSII, P700 in PSI) participate directly in the transfer of excited electrons to electron acceptors, initiating the light reactions.

What is photophosphorylation and what is the relationship between this process and the importance of the thylakoid membrane?

• Photophosphorylation: This is the process of generating ATP from ADP and inorganic phosphate using the energy derived from light. It occurs in the thylakoid membrane.

• Importance of the Thylakoid Membrane: The thylakoid membrane provides a platform for the electron transport chain (ETC), where the energy from electrons is used to pump protons (H+) into the thylakoid lumen, creating a proton gradient. ATP synthase uses this proton gradient to generate ATP.

Distinguish between no cyclic and cyclic electron flow and photophosphorylation? What products are produced by each? Why is cyclic photophosphorylation essential to the Calvin cycle?

• Noncyclic Electron Flow: Electrons move from water (via PSII and PSI) to NADP+, producing ATP, NADPH, and O2. This process is linear and provides the ATP and NADPH needed for the Calvin Cycle.

• Cyclic Electron Flow: Electrons are cycled from PSI back to the cytochrome b6/f complex, generating only ATP but not NADPH or O2. This is necessary to balance the ATP/NADPH ratio since the Calvin Cycle consumes more ATP than NADPH.

Why is NADP+ reduced to NADPH?

Used in the Calvin cycle to synthesize sugar

Can you explain the role of each of the protein complexes involved in photosynthesis?

• Photosystem II (PSII): located at the start of the ETC, it Absorbs light, splits water into protons, electrons, and oxygen, excite electrons and sends electrons into the electron transport chain.

• Cytochrome b6/f Complex: Transfers electrons from PSII to PSI while pumping protons from the storms into the thylakoid lumen, contributing to the proton gradient used by ATP synthase.

• Photosystem I (PSI): Absorbs light and re-energizes electrons, passing electrons to NADP+ to form NADPH.

• ATP Synthase: Uses the proton gradient created by the ETC to convert ADP into ATP.

What is the function of plasmodesmata in plant cells?

Plasmodesmata are channels that allow communication and transport between plant cells.

What are the two main types of pigments involved in photosynthesis?

Chlorophyll and carotenoids.

What role do thylakoid membranes play in photosynthesis?

Thylakoid membranes house the photosystems involved in converting light energy into chemical energy (ATP and NADPH).

Why is light important for photosynthesis?

Light provides the energy required to drive the process of photosynthesis.

What is phototropism?

Phototropism is the growth of plants toward light.

Which hormone is responsible for phototropism, and how does it work?

The hormone auxin causes cells on the shaded side of a plant to elongate, allowing the plant to bend toward the light.

How does light influence the distribution of auxin in plant cells?

Light causes auxin to accumulate on the shaded side of the plant, promoting cell elongation and bending towards the light.

What is the function of chloroplasts in plant cells?

They convert light energy into chemical energy during photosynthesis.

What role do stomata guard cells play in plants?

They enable gas exchange and are crucial for photosynthesis.

What are the two main stages of photosynthesis?

The Light Reaction and Carbon Fixation (Calvin Cycle).

Where does the light reaction occur in plant cells?

In the thylakoid membrane.

What is the role of chlorophyll a in photosynthesis?

It is the main pigment that absorbs light and drives the photosynthetic process.

What is the Calvin Cycle’s primary function?

It uses ATP and NADH to synthesize sugars.

What happens during photolysis in Photosystem II?

Water is split into electrons, protons, and oxygen.

What does the cytochrome b6/f complex do?

It acts as a mobile electron carrier in the Electron Transport Chain.

How does cyclic photophosphorylation differ from noncyclic?

Cyclic photophosphorylation only produces ATP and does not generate NADPH, while noncyclic generates both.

What are the three possible fates of excited electrons in pigments?

Released as heat or fluorescence, transferred via resonance energy transfer, or sent to the electron transport chain (ETC).

What does ATP stand for, and why is it important?

ATP stands for Adenosine Triphosphate, and it is the primary energy currency of the cell.

Why are plant cells considered eukaryotic and how does this impact their structure?

Plant cells are eukaryotic because they have a true nucleus and membrane-bound organelles, which allows them to compartmentalize different cellular functions.

Q: How do cellulose cell walls benefit plant cells compared to animal cells?

Cellulose cell walls provide structural support and rigidity to plant cells, helping them maintain shape and resist external pressures, unlike animal cells which lack such rigid support.

What is totipotency in plant cells and how does it contribute to plant regeneration?

Totipotency is the ability of a single plant cell to develop into an entire organism. Totipotency allows any plant cell to differentiate into a whole plant, making it possible for plants to regenerate from single cells and adapt to various environmental conditions.

What is the significance of chloroplasts in terms of energy conversion in plant cells?

Chloroplasts convert light energy into chemical energy through photosynthesis, producing sugars (glucose) that serve as energy sources for the plant.

Why is the light reaction crucial for the overall process of photosynthesis?

The light reaction is crucial because it captures light energy to produce ATP and NADH, which are then used in the Calvin Cycle to synthesize sugars.

How does the Calvin Cycle utilize the products of the light reaction?

The Calvin Cycle uses ATP and NADH produced in the light reaction to fix carbon dioxide and produce sugars.

What role does chlorophyll play in the absorption of light during photosynthesis?

Chlorophyll absorbs specific wavelengths of light and transfers the energy to the reaction center, initiating the photosynthetic process.

How does the electron transport chain contribute to the formation of ATP?

The electron transport chain creates a proton gradient across the thylakoid membrane, and the flow of protons back through ATP synthase drives the synthesis of ATP from ADP and Pi.

How does the extraction of electrons from water by Photosystem II affect the plant cell?

It replaces lost electrons from P680, releases oxygen as a byproduct, and contributes to the creation of a proton gradient essential for ATP synthesis.

In what way does Photosystem I differ from Photosystem II in the light reaction?

Photosystem I primarily produces NADPH, whereas Photosystem II primarily produces ATP. Both systems work together in noncyclic photophosphorylation.

Why might an organism rely on cyclic photophosphorylation instead of noncyclic photophosphorylation?

An organism might rely on cyclic photophosphorylation to generate additional ATP when NADPH is not needed or when Photosystem II is absent or nonfunctional.