Photosynthesis and the Calvin Cycle Concepts

This set of flashcards covers key concepts related to photosynthesis, the Calvin cycle, and the associated processes that occur in plant cells.

What is the primary function of photosynthesis?

To create carbohydrates.

What are the two main photosystems involved in photosynthesis?

Photosystem I (PSI) and Photosystem II (PSII).

What is produced when electrons are transferred to NADP+?

NADPH is produced.

What wavelength of light do plants typically absorb in photosynthesis?

Plants absorb light primarily at 680 nm.

What is the role of the cytochrome complex in photosynthesis?

It helps in pumping protons and transferring electrons.

What is a byproduct of splitting water during photosynthesis?

Oxygen is a byproduct.

What does the Calvin Cycle primarily utilize to synthesize carbohydrates?

It utilizes high-energy electrons generated during the light reactions.

How do plants utilize carbohydrates produced in photosynthesis?

Plants build structures using carbohydrates.

What energy form is required less for producing carbohydrates?

Carbohydrates require less energy to produce.

What happens to electrons during the light reactions of photosynthesis?

Electrons are excited by light and transferred through an electron transport chain.

What is the overall chemical equation for photosynthesis?

6CO2 + 6H2O + \text{Light Energy} \rightarrow C6H{12}O6 + 6O2

Where do the light-dependent reactions of photosynthesis occur?

In the thylakoid membranes of chloroplasts.

Where do the light-independent reactions (Calvin Cycle) of photosynthesis occur?

In the stroma of chloroplasts.

What are the two main stages of photosynthesis?

Light-dependent reactions and Light-independent reactions (Calvin Cycle).

What pigment is primarily responsible for absorbing light energy in plants?

Chlorophyll.

What colors of light does chlorophyll primarily absorb?

Red and blue-violet light.

Why do plants appear green?

Because chlorophyll reflects green light.

What is the primary product of the light-dependent reactions?

ATP and NADPH.

What is the primary goal of the Calvin cycle?

To synthesize glucose (or other carbohydrates) from carbon dioxide.

What organelle is the site of photosynthesis in eukaryotic cells?

Chloroplasts.

What are the flattened sacs within the chloroplast where light reactions take place?

Thylakoids.

What is a stack of thylakoids called?

A granum (plural: grana).

What is the fluid-filled space surrounding the grana within a chloroplast?

The stroma.

What is the main role of accessory pigments in photosynthesis?

To absorb light energy at different wavelengths and pass it to chlorophyll a.

What is the reaction center of Photosystem II (PSII)?

P680 (a specialized chlorophyll a molecule that absorbs light best at 680 nm).

What is the reaction center of Photosystem I (PSI)?

P700 (a specialized chlorophyll a molecule that absorbs light best at 700 nm).

What is the primary role of Photosystem II (PSII)?

To split water molecules and generate electrons for the electron transport chain.

What is the primary role of Photosystem I (PSI)?

To re-energize electrons and pass them to NADP+ reductase to form NADPH.

Which photosystem functions first in the linear electron flow?

Photosystem II (PSII).

What is the process of splitting water by light energy in PSII called?

Photolysis.

What are the products of water photolysis in PSII?

Electrons, protons (H^+), and molecular oxygen (O_2).

Where do the electrons from PSII go after being excited by light?

They are transferred to the primary electron acceptor and then to the electron transport chain.

What is the ultimate electron donor in linear electron flow?

H_2O (water).

What is the ultimate electron acceptor in linear electron flow?

NADP^+. Prior to reduction, NADP+ is the final acceptor.

What happens to the energy level of electrons as they move through the electron transport chain between PSII and PSI?

Their energy level decreases as the energy is used to pump protons.

What is the main protein complex that connects PSII and PSI?

The cytochrome b6f complex.

What does the cytochrome b6f complex do in the electron transport chain?

It pumps protons (H^+) from the stroma into the thylakoid lumen, contributing to the proton gradient.

What molecule carries electrons from the cytochrome b6f complex to Photosystem I?

Plastocyanin (Pc).

What molecule carries electrons from Photosystem II to the cytochrome b6f complex?

Plastoquinone (PQ).

What enzyme uses the proton gradient to synthesize ATP?

ATP Synthase.

What is the process of ATP synthesis powered by the flow of protons called?

Chemiosmosis.

Where does ATP synthase get the energy to create ATP from ADP and Pi?

From the electrochemical gradient of protons across the thylakoid membrane.

What is the term for the flow of electrons from water, through PSII, ETC, PSI, to NADP+?

Linear (non-cyclic) electron flow.

What is cyclic electron flow?

An alternative pathway that uses only Photosystem I to produce ATP, but not NADPH or oxygen.

Why might a plant use cyclic electron flow?

To generate extra ATP when the Calvin Cycle requires more ATP than NADPH.

What enzyme is responsible for reducing NADP+ to NADPH?

NADP+ reductase.

What are the three main phases of the Calvin Cycle?

Carbon fixation, Reduction, and Regeneration of RuBP.

What molecule is carbon dioxide fixed to in the Calvin Cycle?

Ribulose-1,5-bisphosphate (RuBP).

What enzyme catalyzes the carbon fixation step in the Calvin Cycle?

RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase).

What is the unstable 6-carbon intermediate formed by RuBisCO combining CO_2 and RuBP?

It immediately splits into two molecules of 3-phosphoglycerate (3-PGA).

How many molecules of 3-PGA are produced from one CO_2 molecule in the Calvin Cycle?

Two molecules.

What is the energy source used for the reduction phase of the Calvin Cycle?

ATP and NADPH from the light-dependent reactions.

What is 3-PGA reduced to in the Calvin Cycle?

Glyceraldehyde-3-phosphate (G3P).

What is the most common sugar produced directly from the Calvin Cycle?

Glyceraldehyde-3-phosphate (G3P).

How many turns of the Calvin Cycle are required to produce one molecule of G3P for export out of the cycle?

Three turns.

How many molecules of CO_2 are fixed to produce one net G3P molecule?

Three molecules of CO_2.

How many molecules of G3P are produced in three turns of the Calvin Cycle?

Six molecules of G3P.

How many G3P molecules are used to regenerate RuBP in the Calvin Cycle?

Five molecules of G3P.

What is the net gain of G3P molecules from three turns of the Calvin Cycle?

One molecule of G3P.

What is the primary fate of G3P produced in the Calvin Cycle?

It can be used to synthesize glucose, sucrose, starch, or cellulose.