Light Reactions of Photosynthesis

These flashcards cover key vocabulary and concepts related to light reactions in photosynthesis, enhancing understanding and retention for the upcoming exam.

Light reactions

The process that converts solar energy into chemical energy in the form of ATP and NADPH.

Chloroplasts

Organelles where photosynthesis occurs, acting as chemical factories powered by the sun.

Thylakoids

Membrane-bound compartments inside chloroplasts that contain chlorophyll and are crucial for light reactions.

Electromagnetic energy

Energy in the form of electromagnetic radiation, traveling in rhythmic waves.

Wavelength

The distance between the crests of electromagnetic waves; ranges from less than a nanometer to more than a kilometer.

Electromagnetic spectrum

The entire range of electromagnetic radiation, including visible light.

Visible light

The narrow band of wavelengths within the electromagnetic spectrum detectable by the human eye.

Photons

Discrete particles of light that carry a fixed quantity of energy.

Action spectrum

A graph depicting the effectiveness of different wavelengths in driving photosynthesis.

Absorption spectrum

A graph showing how well a pigment absorbs various wavelengths of light.

Pigments

Substances that absorb visible light, reflecting the color we see (e.g., chlorophyll).

Chlorophyll

The primary pigment in plants that absorbs violet-blue and red light for photosynthesis.

Carotenoids

Accessory pigments that absorb blue-green light and protect chlorophyll from excessive light.

Spectrophotometer

An instrument that measures how much light is absorbed by a solution at different wavelengths.

Excited state

The state of a pigment molecule when it absorbs energy and an electron is elevated to a higher energy shell.

Ground state

The normal state of a pigment molecule with its electrons in their lowest energy shells.

Reaction-center complex

The part of a photosystem where light energy is converted to chemical energy.

Primary electron acceptor

The molecule that accepts electrons from the excited chlorophyll in a photosystem.

Linear electron flow

The process by which electrons move through photosystems I and II during the light reactions.

Chemiosmosis

The process that generates ATP using a proton gradient across a membrane.

NADPH

An electron carrier molecule that stores energy in the form of high-energy electrons.

Proton gradient

A difference in proton concentration across a membrane used to generate ATP.

ATP synthase

An enzyme that synthesizes ATP as protons flow through it back into the stroma from the thylakoid space.

Stroma

The fluid-filled space surrounding the thylakoids in chloroplasts where the Calvin cycle occurs.

Electron transport chain

A series of proteins that transfer electrons, releasing energy that pumps protons across a membrane.

PS II (Photosystem II)

The first photosystem in the light reactions, absorbs light primarily in the red spectrum.

PS I (Photosystem I)

The second photosystem in the light reactions, primarily absorbs far-red light.

Photoprotection

The mechanism by which pigments like carotenoids protect chlorophyll from damage by excess light.

Action spectrum vs Absorption spectrum

An action spectrum shows effectiveness for photosynthesis, while an absorption spectrum shows wavelengths absorbed.

Fluorescence

The emission of light by excited pigments when they return to their ground state.

Energy transformation

The conversion of light energy into chemical energy in photosynthesis.

Electrons from water

The source of electrons in the light reactions, split to help generate ATP and NADPH.

Calvin cycle

The process that uses ATP and NADPH to synthesize sugars from carbon dioxide.

Carotenoids' role

Accessory pigments that broaden the spectrum of light absorbed and provide photoprotection.

Chlorophyll a and b

Types of chlorophyll that absorb light at different wavelengths.

Light-harvesting complex

Groups of pigment molecules that capture light and transfer energy to the reaction center.

Absorption of photons

When a pigment molecule absorbs light, raising an electron to a higher energy level.

Oxidation and reduction

The transfer of electrons during light reactions, where water is oxidized and NADP+ is reduced.

Z-scheme

A diagram illustrating the flow of electrons during the light reactions.

Thylakoid membrane

The site of light reactions where photosystems are embedded and ATP is generated.

Water as electron donor

Water molecules serve as the initial source of electrons in photosynthesis.

Theodor W. Engelmann

The botanist who demonstrated the action spectrum of photosynthesis.

Chemical factories of chloroplasts

The function of chloroplasts as they convert light energy into chemical energy.

Light intensity and plant response

How variations in light affect the rate of photosynthesis.

Proton motive force

The potential energy generated by the proton gradient used for ATP synthesis.

Chlorophyll's color absorption

Chlorophyll reflects green light while absorbing violet-blue and red light.

Light energy harvesting

The process by which light energy is captured and converted via photosystems.

Photosynthetic efficiency

The effectiveness of plants in converting light energy to chemical energy.

Light reactions summary

Light reactions convert solar energy to ATP and NADPH while releasing O2 as a by-product.

Chemical reduction

The process of gaining electrons, which occurs during NADP+ reduction.