Untitled Flashcards Set

What are the main stages of photosynthesis?

Light-dependent reactions (in the thylakoid membrane) and the Calvin Cycle (in the stroma).

Where does photosynthesis occur in plants?

In the chloroplasts of plant cells.

What is the role of chlorophyll in photosynthesis?

It absorbs light energy, primarily in the violet-blue and red parts of the spectrum.

What is photolysis in photosynthesis?

The splitting of water molecules by light energy in Photosystem II.

What happens to the electrons released by photolysis?

They are passed to the electron transport chain in the thylakoid membrane.

What is the primary product of Photosystem II?

ATP, synthesized via chemiosmosis.

What is the primary product of Photosystem I?

NADPH, a high-energy electron carrier.

What is the purpose of ATP and NADPH in photosynthesis?

They provide the energy and reducing power for the Calvin Cycle to synthesize sugars.

How is the proton gradient created in the thylakoid membrane?

By the movement of electrons through the electron transport chain, pumping protons into the thylakoid lumen.

What is chemiosmosis in photosynthesis?

The process of using a proton gradient to drive ATP synthesis via ATP synthase.

What enzyme is responsible for ATP synthesis in the light reactions?

ATP synthase.

What is the purpose of the Calvin Cycle?

To convert atmospheric CO₂ into organic sugars (G3P) using ATP and NADPH.

What is carbon fixation, and which enzyme is responsible for it?

It’s the process of incorporating CO₂ into organic molecules, catalyzed by the enzyme RuBisCO.

What is RuBisCO?

An enzyme that fixes CO₂ into RuBP during the first step of the Calvin Cycle.

What molecule is regenerated at the end of the Calvin Cycle?

Ribulose-1,5-bisphosphate (RuBP).

How many molecules of CO₂ are needed to produce one G3P in the Calvin Cycle?

Three molecules of CO₂.

What are the three phases of the Calvin Cycle?

1. Carbon fixation. 2. Reduction phase. 3. Regeneration of RuBP.

What are the products of the Calvin Cycle?

G3P (used to form glucose), ADP, and NADP⁺.

What role do accessory pigments play in photosynthesis?

They broaden the range of light wavelengths absorbed and protect chlorophyll from damage.

Why is the thylakoid membrane important?

It houses the photosystems, electron transport chain, and ATP synthase for the light-dependent reactions.

What is cyclic electron flow?

A pathway that produces ATP but not NADPH, recycling electrons back to Photosystem I.

Why is oxygen produced during photosynthesis?

As a byproduct of water splitting in Photosystem II.

What is the role of the stroma in photosynthesis?

It is the site of the Calvin Cycle where sugar synthesis occurs.

What happens when chlorophyll absorbs light?

An electron is excited to a higher energy state.

What is the source of energy that drives the Calvin Cycle?

ATP and NADPH produced in the light reactions.

What wavelength of light does Photosystem II absorb best?

680 nm (P680).

What wavelength of light does Photosystem I absorb best?

700 nm (P700).

What happens to G3P produced in the Calvin Cycle?

It can be used to form glucose and other organic compounds.

Why is photosynthesis considered a redox process?

Water is oxidized to oxygen, and carbon dioxide is reduced to form sugars.

How does CO₂ enter the chloroplasts?

Through stomata, small openings in the leaf.

What are carotenoids, and why are they important?

Accessory pigments that protect the chloroplast by dissipating excessive light energy as heat.

Why do plants appear green?

Chlorophyll reflects green light and absorbs other wavelengths.

What is the difference between the light-dependent reactions and the Calvin Cycle?

Light-dependent reactions produce energy, while the Calvin Cycle uses that energy to synthesize sugars.

What is photorespiration, and why is it inefficient?

A process where RuBisCO binds O₂ instead of CO₂, consuming energy without producing sugar.

How do C4 plants minimize photorespiration?

By spatially separating carbon fixation and the Calvin Cycle in different cell types.

How do CAM plants adapt to arid environments?

By fixing CO₂ at night and using it during the day.

What are the reactants of the light-dependent reactions?

Light, water, ADP, and NADP⁺.

What are the products of the light-dependent reactions?

ATP, NADPH, and oxygen.

Why is the splitting of water necessary in photosynthesis?

To provide electrons for the electron transport chain and protons for the proton gradient.

What is the Z-scheme in photosynthesis?

A model describing the flow of electrons from water to NADP⁺ through Photosystem II and I.

What happens to NADPH in the Calvin Cycle?

It donates high-energy electrons to reduce 3-PGA into G3P.

How many turns of the Calvin Cycle are required to produce one glucose molecule?

Six turns (producing two G3P molecules).

What happens to the ADP and NADP⁺ after the Calvin Cycle?

They are recycled back to the light-dependent reactions.

What is the role of plastoquinone (PQ) in the electron transport chain?

It transfers electrons from Photosystem II to the cytochrome complex.

What is the cytochrome complex?

A protein that transfers electrons and pumps protons into the thylakoid lumen.

What is plastocyanin (PC), and what does it do?

A mobile protein that transfers electrons from the cytochrome complex to Photosystem I.

What happens to the oxygen generated during photosynthesis?

It is released into the atmosphere as a byproduct.

How do ATP and NADPH interact in the Calvin Cycle?

ATP provides energy, and NADPH provides reducing power to convert 3-PGA to G3P.