Photosynthesis: Light Reactions, Photosystems, and Electron Transport

What is the primary function of Photosystem II in the light-dependent reactions?

Photosystem II absorbs 680nm light (P680) to excite and transfer an electron to the primary electron acceptor, splitting water to replace the electron.

What is Plastoquinone (PQ) and its role in photosynthesis?

Plastoquinone (PQ) moves an electron to the Cytochrome Complex and helps transport hydrogen atoms across the membrane.

How does the Cytochrome Complex function in the light-dependent reactions?

The Cytochrome Complex accepts electrons from PQ and transfers them to Plastocyanin, which then passes the electrons to Photosystem I.

What happens to the electron after it is excited in Photosystem I?

The excited electron is accepted by an electron acceptor, which passes it to Ferredoxin, and then to NADP+ Reductase to form NADPH.

What is the significance of water in the light-dependent reactions?

Water is split into oxygen and hydrogen ions to provide electrons for Photosystem II.

What is the role of chemiosmosis in photosynthesis?

Chemiosmosis establishes a proton gradient that allows protons to flow through ATP Synthase, driving ATP synthesis.

What is the difference between linear and cyclic electron transport?

Linear electron transport moves electrons through both photosystems to form NADPH, while cyclic electron transport uses Photosystem I to pump protons and generate additional ATP.

What is the overall formula for photosynthesis?

CO2 + H2O → C6H12O6 + O2.

What are the main components of a chloroplast involved in photosynthesis?

Chloroplasts contain three membranes, chlorophyll, stroma, and thylakoids, where light absorption and ATP synthesis occur.

What is the absorption spectrum of chlorophyll a?

Chlorophyll a absorbs blue and red light.

What is the role of the Antenna Complex in photosynthesis?

The Antenna Complex captures and transfers light energy to chlorophyll a, which then transfers electrons to the Primary Electron Acceptor.

What pigments are involved in photosynthesis and their functions?

Chlorophylls (a and b) absorb light energy, while carotenoids transfer energy to chlorophyll molecules.

What is the purpose of the Calvin Cycle in photosynthesis?

The Calvin Cycle uses ATP and NADPH to convert CO2 into sugars and does not require light.

What is the role of ferredoxin in the light-dependent reactions?

Ferredoxin transfers electrons from Photosystem I to NADP+ Reductase, aiding in the formation of NADPH.

How does light energy affect electrons in photosynthesis?

Light energy excites electrons, raising them to a higher energy level, which can then be transferred to energy carrier molecules.

What is the significance of the proton gradient in photosynthesis?

The proton gradient created across the thylakoid membrane is essential for ATP synthesis during chemiosmosis.

What happens to the concentration of protons in the thylakoid lumen during photosynthesis?

Proton concentration increases as water is split and as protons are pumped across the membrane by PQ.

What is the function of NADP+ in the light-dependent reactions?

NADP+ acts as an electron acceptor, forming NADPH when it receives electrons from Ferredoxin.

What is the role of chlorophyll b in photosynthesis?

Chlorophyll b transfers energy to chlorophyll a, enhancing the light absorption capacity of the plant.

What is the significance of cyclic electron transport in plants?

Cyclic electron transport generates additional ATP needed for the Calvin Cycle, especially under conditions of water scarcity.

What is the primary electron acceptor in Photosystem II?

The primary electron acceptor in Photosystem II is a molecule that accepts the excited electron after it is energized by light.

What are the products of water splitting in the light-dependent reactions?

Water splitting produces oxygen gas (O2), hydrogen ions (H+), and free electrons.

What is the role of ATP Synthase in photosynthesis?

ATP Synthase synthesizes ATP as protons flow from the thylakoid lumen into the stroma.

What is the difference between light-dependent and light-independent reactions?

Light-dependent reactions require light to produce ATP and NADPH, while light-independent reactions (Calvin Cycle) use these products to synthesize sugars.