Photosynthesis: Light Reactions & Calvin Cycle – Lecture Review

A set of 50 Q&A flashcards covering core principles, structures, and mechanisms of photosynthesis—especially the light-dependent reactions and Calvin cycle—based on the lecture transcript.

What type of reaction is cellular respiration: exergonic or endergonic?

Exergonic.

What type of reaction is photosynthesis?

Endergonic.

During photosynthesis, which molecule is reduced to form carbohydrate?

Carbon dioxide (CO₂).

Which molecule is oxidized to release O₂ in photosynthesis?

Water (H₂O).

Why do plants need to be watered, in terms of electron supply?

Water provides electrons by being split during the light-dependent reactions.

Name the two linked sets of reactions in photosynthesis.

Light-dependent reactions and the Calvin cycle (dark reactions).

Which reactions actually produce sugar: light reactions or Calvin cycle?

The Calvin cycle.

Which reactions split water and release molecular oxygen?

Light-dependent (light-capturing) reactions.

Where in the chloroplast do Calvin-cycle reactions occur?

In the stroma.

Where do the light-dependent reactions take place?

On the thylakoid membranes.

What are stacks of thylakoids called?

Grana (singular: granum).

What is the fluid-filled interior space of a thylakoid called?

The lumen.

What is the fluid outside the thylakoids but inside the inner chloroplast membrane?

The stroma.

Roughly how many chloroplasts can a single plant cell contain?

About 40–50.

Which pigment is primarily responsible for the green color of plants?

Chlorophyll.

Why do plants appear green to human eyes?

They reflect green light while absorbing red and blue wavelengths.

Which end of the visible spectrum carries more energy, blue/violet or red?

Blue/violet light carries more energy.

Which class of pigments acts as accessory pigments in plants?

Carotenoids.

What colors do carotenoids typically reflect?

Yellow, orange, and red.

What seasonal change makes carotenoid colors visible in leaves?

Breakdown of chlorophyll in fall.

What are the two main types of chlorophyll discussed?

Chlorophyll a (alpha) and chlorophyll b (beta).

Besides blue, which other region of the spectrum do chlorophylls absorb strongly?

Red light (~700 nm).

What happens to an electron in chlorophyll when a photon excites it?

It jumps to a higher energy level (excited state).

How many energy levels does a red photon raise a chlorophyll electron?

One energy level.

How many energy levels does a blue photon raise a chlorophyll electron?

Two energy levels.

What complex funnels excitation energy toward the reaction center?

The antenna (light-harvesting) complex.

What term describes energy movement between pigments without electron transfer?

Resonance energy transfer.

In a photosystem, where does the actual redox reaction occur?

In the reaction center.

After the reaction center of Photosystem II, what molecule is the first electron acceptor?

Pheophytin.

Which quinone shuttles electrons from Photosystem II to the cytochrome complex?

Plastoquinone (PQ).

What is an electron transport chain (ETC)?

A series of proteins and carriers that move electrons through a membrane.

Which two molecule types make up ETC chains in chloroplasts and mitochondria?

Cytochromes and quinones.

What gradient is created by pumping protons into the thylakoid lumen?

An electrochemical (proton) gradient.

Which enzyme uses the proton motive force to synthesize ATP?

ATP synthase.

What is ATP formation driven by light called?

Photophosphorylation.

Photophosphorylation in chloroplasts is analogous to what mitochondrial process?

Oxidative phosphorylation.

Which two high-energy molecules produced by light reactions fuel the Calvin cycle?

ATP and NADPH.

What are the oxidized and reduced forms of the photosynthetic electron carrier NADP?

NADP⁺ (oxidized) and NADPH (reduced).

Cutting off light or water stops photosynthesis by halting which "gears"?

The light-dependent reactions, which then halt the Calvin cycle.

What structural feature of ATP synthase allows protons to flow through it?

A channel/rotor specifically shaped for H⁺ ions.

What term describes the rotational force generated by flowing protons?

Proton motive force.

What overall role of vacuoles was mentioned at the lecture start?

They store materials and can later release O₂ to the atmosphere.

Why is ultraviolet (UV) radiation potentially more harmful than red light?

UV has a shorter wavelength and therefore higher energy.

Why is a lead apron used during X-ray procedures?

To shield body tissues from high-energy radiation that can cause cancer.

Where does visible light lie relative to ultraviolet and infrared on the spectrum?

Between UV and IR; a small fraction of the electromagnetic spectrum.

What happens to potential energy each time excitation energy is transferred between pigments?

Some potential energy is lost at each transfer step.

What descriptor is used for the entire pigment-protein group that captures light?

A photosystem.

What drives the endergonic reduction of CO₂ in the Calvin cycle?

Energy from ATP and electrons from NADPH produced by light reactions.

What term describes the series of protein-embedded cytochromes in thylakoid membranes?

The cytochrome complex.

In what form does light energy first enter the photosynthetic apparatus?

Photons.