Photosystem I and Photophosphorylation Quiz

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.

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.