Photosystem I and Photophosphorylation Quiz

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Questions and Answers

What is the main function of sieve tube members in Angiosperm cells?

To transport sugars from source to sink (correct)

To facilitate absorption of carbon dioxide

To produce oxygen during photosynthesis

To store excess water in the leaves

How do sugars primarily travel from the source to the sink in Angiosperm cells?

By passive transport using only sieve tube members

Via active transport using companion cells and sieve tube members (correct)

By absorption through the stomata on the leaf surface

Through diffusion across cell membranes

Where does the Dark Reaction of photosynthesis take place?

In the companion cells

On the thylakoid membrane

In the stroma (correct)

In the chloroplasts' outer membrane

What is the main function of chlorophyll a and b pigments in photosynthesis?

Absorb light energy for photosynthesis Signup and view all the answers

In which season do we primarily see yellow/orange/red colors in leaves due to beta keratin pigment?

Fall Signup and view all the answers

Why does the Sieve tube members actively transport sugars from source to sink?

Due to water entering sieve tube members by osmosis Signup and view all the answers

What is the function of the epidermis in a leaf?

To protect the leaf and control what moves in and out Signup and view all the answers

What happens when light energy hits pigment molecules in photosynthesis?

Electrons in pigment molecules get excited and absorbed Signup and view all the answers

Which molecules are the primary electron acceptors in the reaction center during photosynthesis?

Primary acceptors donate electrons to Fd molecules Signup and view all the answers

Why is having two photosystems with different maximum absorption wavelengths beneficial for photosynthesis?

To enhance the range of light wavelengths absorbed Signup and view all the answers

What is the role of NADPH in the light reactions of photosynthesis?

To accept high-energy electrons and become reduced Signup and view all the answers

What do sieve tube members do in the context of plant physiology?

Transport organic compounds from source to sink Signup and view all the answers

What is the main purpose of the process called chemiosmosis in photosynthesis?

To convert light energy into chemical energy Signup and view all the answers

In the Calvin cycle, what is the role of RUBISCO?

Grab CO2 and bind them to 6 RUBP molecules Signup and view all the answers

Why do C3 plants experience a decrease in photosynthesis rate when there is an abundance of oxygen?

RUBISCO prefers O2 over CO2 Signup and view all the answers

What is the main reason C4 plants have evolved separate pathways for carbon fixation?

To avoid binding of oxygen by RUBISCO Signup and view all the answers

Which pathway involves fixing CO2 at night and storing it for use during the day to minimize water loss?

CAM pathway Signup and view all the answers

In cellular respiration, where does glycolysis occur?

Cytoplasm Signup and view all the answers

Which process involves oxidative phosphorylation and substrate-level phosphorylation to produce ATP?

Krebs cycle Signup and view all the answers

What is the primary function of the Electron Transport Chain (ETC) in cellular respiration?

Produce ATP through redox reactions Signup and view all the answers

Which organelle has cristae that increase surface area for cell respiration to occur?

Mitochondrion Signup and view all the answers

What happens when electrons move down the Electron Transport Chain (ETC)?

Energy is used to create a concentration gradient of H+ ions Signup and view all the answers

Study Notes

Sieve Tube Members

Transport sugars from source (where they are produced) to sink (where they are used or stored) in Angiosperm cells.
The movement of sugars from source to sink is driven by active transport, meaning it requires energy.

Sugar Transport

Sugars primarily travel from source to sink through sieve tubes, which are long, hollow cells connected end-to-end within phloem.
The process, called translocation, involves the movement of sugars in solution within phloem.

Dark Reaction

Occurs in the stroma of chloroplasts.
The Calvin cycle uses energy from ATP and NADPH generated in the light-dependent reactions to fix carbon dioxide into sugar.

Chlorophyll Pigments

Chlorophyll a and b primarily absorb light energy in the blue and red wavelengths, with chlorophyll a being the primary pigment in photosynthesis.
The absorbed light energy is used to excite electrons in the pigment molecule, which then initiates the electron transport chain in photosynthesis.

Beta Keratin

Beta keratin is a type of pigment responsible for the yellow/orange/red colors seen in leaves during the autumn season (fall).
As chlorophyll breaks down, these pigments become more visible.

Epidermis

Epidermis is the outermost layer of cells on a leaf, providing protection and regulating gas exchange.
It is often covered in a waxy cuticle to prevent water loss.

Light Energy

Light energy excites electrons within chlorophyll molecules, boosting them to a higher energy level.
This excited electron can then be transferred to a nearby molecule within the reaction center, initiating the electron transport chain.

Electron Acceptors

Primary electron acceptors in the reaction center of photosynthesis are chlorophyll molecules specifically:
- P680: This is the reaction center of photosystem II and absorbs light maximally at 680 nm.
- P700: The reaction center of photosystem I, which absorbs light maximally at 700 nm.

Photosystems

Having two photosystems with different maximum absorption wavelengths allows plants to capture a broader spectrum of light.
This increases photosynthetic efficiency by utilizing more of the available light energy to produce ATP and NADPH.

NADPH

NADPH (Nicotinamide adenine dinucleotide phosphate) is a reducing agent. It carries energized electrons from the light-dependent reactions to the Calvin cycle.
It is essential for reducing carbon dioxide to carbohydrates in the Calvin cycle.

Sieve Tube Members Function

Translocate sugars from the source (leaves) to the sink (roots, fruits, or storage organs) in plants.
Sieve tube members are living cells, but lack a nucleus, ribosomes, and many other organelles, maximizing their ability to efficiently transport sugar.

Chemiosmosis

Chemiosmosis is the process by which ATP is produced by the movement of protons across a membrane within the chloroplasts.
This proton gradient is established by the light-dependent reactions of photosynthesis and is the driving force for ATP synthesis.

RUBISCO

RUBISCO (ribulose bisphosphate carboxylase/oxygenase) is an enzyme that catalyzes the initial step in carbon fixation in the Calvin cycle.
It binds to both carbon dioxide and oxygen, which can lead to photorespiration, a process that reduces photosynthetic efficiency.

C3 Plants

C3 plants experience a decrease in photosynthesis rate when there is an abundance of oxygen.
This is because RUBISCO, the enzyme responsible for carbon fixation, can also bind to oxygen, leading to photorespiration.

C4 Plants

C4 plants have evolved separate pathways for carbon fixation to minimize photorespiration, which occurs in high-oxygen environments.
They use a different enzyme, PEP carboxylase, which has a higher affinity for carbon dioxide and doesn't bind to oxygen.

CAM Plants

CAM (Crassulacean acid metabolism) pathways fix carbon dioxide at night and store it for use during the day.
This strategy is particularly beneficial in arid environments where water loss is a concern.

Glycolysis

Glycolysis occurs in the cytoplasm of the cell.
It is the first stage of cellular respiration, breaking down glucose into pyruvate.

Oxidative Phosphorylation and Substrate-Level Phosphorylation

These are the processes by which ATP is generated in cellular respiration.
Oxidative phosphorylation is the major ATP production pathway, occurring in the electron transport chain.
Substrate-level phosphorylation produces a smaller amount of ATP during glycolysis and the Krebs cycle.

Electron Transport Chain

The electron transport chain (ETC) is a series of protein complexes embedded in the inner mitochondrial membrane.
It uses the energy from electrons flowing down a gradient to pump protons across the membrane, generating a proton motive force that drives ATP synthesis.

Mitochondria

Mitochondria have cristae, folded inner membranes that significantly increase the surface area available for cellular respiration.
This allows for more efficient ATP production.

Electron Movement in ETC

As electrons move down the electron transport chain, they lose energy which is used to pump protons across the inner mitochondrial membrane.
This creates a proton gradient, which then fuels the production of ATP by ATP synthase.

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Description

Test your knowledge on Photosystem I, photophosphorylation, and chemiosmosis in the process of ATP production during photosynthesis. Understand how electron transport chain generates a concentration gradient of H+ ions to produce ATP.