Photosynthesis: Light Reactions, Calvin Cycle, and Pigments

What are the two main stages of photosynthesis?

The light reactions and the Calvin cycle.

Where do the light reactions of photosynthesis occur?

In the thylakoid membrane of the chloroplast.

What is produced as a byproduct of the light reactions?

Oxygen.

What is the main function of the Calvin cycle?

To fix carbon dioxide into sugar using ATP and NADPH.

What is chlorophyll a?

The main pigment involved directly in the light reactions.

What role do accessory pigments like chlorophyll b and carotenoids play?

They absorb light and pass energy to chlorophyll a.

What happens to leaves in the fall regarding chlorophyll and carotenoids?

Chlorophyll breaks down faster than carotenoids, revealing yellow and orange colors.

What is the role of Rubisco in the Calvin cycle?

It catalyzes the fixation of carbon dioxide onto RuBP.

What is the first step of the Calvin cycle?

Carbon fixation, where carbon dioxide is attached to RuBP.

What is produced from the carbon fixation reaction?

Two molecules of 3-phosphoglycerate (3-PGA).

What is chemiosmosis?

The process of generating ATP as protons flow down their gradient through ATP synthase.

How does the electron transport chain function in photosynthesis?

It passes excited electrons, releasing energy used to pump protons across a membrane.

What is the role of ATP synthase?

It produces ATP from ADP and phosphate using the flow of protons.

What is the difference between oxidation and reduction in photosynthesis?

Oxidation is the loss of electrons (water is oxidized at Photosystem II), while reduction is the gain of electrons (NADP+ is reduced to NADPH).

What is the stroma?

The fluid-filled space inside the chloroplast where the Calvin cycle occurs.

What is the thylakoid?

The internal membrane system of the chloroplast where the light reactions occur.

What is the significance of the proton gradient in photosynthesis?

It stores potential energy used to drive ATP production.

What distinguishes photosynthesis in purple nonsulfur bacteria from that in plants?

These bacteria use only one photosystem and do not produce oxygen.

What is NADP+ and its role in photosynthesis?

An electron carrier that is reduced to NADPH during the light reactions and used in the Calvin cycle.

What happens if a plant lacks all pigments?

It cannot absorb light, preventing the light reactions from occurring, thus halting ATP and NADPH production.

What is the function of carotenoids in plants?

They absorb light in wavelengths chlorophyll misses and protect the plant from excess light damage.

What is the role of Photosystem II in photosynthesis?

It excites electrons and replaces lost electrons by splitting water molecules.

What happens to electrons after they leave Photosystem I?

They pass through a second short electron transport chain and are used to reduce NADP+ to NADPH.

What is the relationship between light reactions and the Calvin cycle?

The Calvin cycle uses ATP and NADPH produced by the light reactions to fix carbon dioxide.

What is 3-phosphoglycerate (3-PGA)?

A three-carbon compound produced immediately after carbon fixation in the Calvin cycle.

What is the significance of the reaction center in a photosystem?

It is where light energy is converted into a flow of excited electrons.

What happens if a chemical blocks the flow of electrons between Photosystem II and Photosystem I?

Protons stop being pumped into the thylakoid space, decreasing the proton gradient and ATP production.

What is the role of phycoerythrin and phycocyanin?

They are accessory pigments found in red algae and cyanobacteria that assist in light absorption.

What is the function of the electron transport chain (ETC) in photosynthesis?

To pass electrons along, releasing energy used to pump protons across a membrane.