Photosynthesis

What is photosynthesis?

The process by which cells convert light energy into chemical energy, synthesizing organic molecules like glucose.

What are the two stages of photosynthesis?

Stage 1: Light-dependent reactions; Stage 2: Light-independent reactions (Calvin Cycle).

Where do the light-dependent reactions occur?

Thylakoid membranes of the chloroplast.

What is the purpose of light-dependent reactions?

Convert light energy into ATP and NADPH, split water molecules to release O₂ and protons, and build a proton gradient.

What role does chlorophyll a play in the light reactions?

It is the principal photoreceptor that absorbs light energy, exciting electrons.

What is produced when water is split during Photosystem II?

Electrons, protons, and oxygen.

What is the reaction center of Photosystem II?

P680.

What is the function of electron transport in the light reactions?

To transfer excited electrons through a chain, creating a proton gradient.

What is cytochrome b₆f complex?

A part of the electron transport chain where electrons travel and protons are pumped.

What is the reaction center of Photosystem I?

P700.

How is NADP⁺ reduced to NADPH?

Electrons are passed from Photosystem I to ferredoxin and then to ferredoxin-NADP⁺ reductase.

What enzyme generates ATP during the light reactions?

ATP synthase.

What is cyclic photophosphorylation?

A process where PSI cycles electrons back to cytochrome bf to produce ATP without NADPH or O₂.

What are accessory pigments?

Pigments like chlorophyll b and carotenoids that help capture light and protect from excess light energy.

What role do herbicides Diuron and atrazine play in photosynthesis?

They block Photosystem II.

What do chloroplasts contain that is crucial for their function?

DNA and rely on nuclear-encoded proteins.

When did photosynthesis evolve?

Approximately 2 billion years ago.

Where do the light-independent reactions occur?

In the stroma of the chloroplast.

What is the purpose of the Calvin Cycle?

To use ATP and NADPH from the light reactions to convert CO₂ into glucose.

What is RuBisCO's role in the Calvin Cycle?

It attaches CO₂ to ribulose-1,5-bisphosphate (RuBP) during carbon fixation.

What does G3P stand for and why is it important?

Glyceraldehyde-3-phosphate; it is the precursor to glucose and other carbohydrates.

What are the three stages of the Calvin Cycle?

1. Carbon Fixation, 2. Reduction, 3. Regeneration.

What are the structural components of chloroplasts?

Double membrane organelle, stroma, and thylakoid membranes.

What is the summary of electron flow in linear photosynthesis?

H₂O → PSII → Cyt b₆f → PSI → Ferredoxin → NADP⁺ → NADPH.

What does the linear electron flow generate?

O₂, a proton gradient, and NADPH.

How do photosynthesis and cellular respiration compare?

Photosynthesis converts light energy into chemical energy, while cellular respiration converts chemical energy into ATP.

What is photophosphorylation?

The process of generating ATP using the proton gradient created during the light reactions.

What occurs during the reduction phase of the Calvin Cycle?

ATP and NADPH reduce 3-PGA to G3P.

What is non-photochemical quenching (NPQ)?

A protective role that dissipates excess light energy as heat.

Identify one purpose of the Calvin Cycle in photosynthesis.

To convert atmospheric CO₂ into organic molecules like glucose.

What happens to some G3P molecules in the regeneration phase of the Calvin Cycle?

They are used to regenerate RuBP.

What byproduct is released as a result of photolysis during the light reactions?

Oxygen.

What happens to protons during the light-dependent reactions?

They are pumped into the thylakoid lumen, creating a proton gradient.

How does the structure of thylakoid membranes facilitate photosynthesis?

They contain photosystems, ATP synthase, and electron transport chains, essential for the light reactions.