Bio 20 Photosynthesis to chemiosmosis

Autotroph

A living organism that produces its own food; plants are autotrophs ("self-feeders").

Heterotroph

An organism that ingests food from external sources; most animals are heterotrophs.

Photosynthesis

The process where light energy is used to convert CO₂ and H₂O into glucose and O₂.

Metabolic Pathway

A series of chemical reactions within a cell; photosynthesis is one example.

By-product of Photosynthesis

Oxygen (O₂) is released during photosynthesis.

Metabolism

The sum of all chemical reactions in a cell.

Anabolic Reaction

A type of metabolism that builds larger molecules from smaller subunits.

Catabolic Reaction

A type of metabolism that breaks down large molecules into smaller parts.

Activation Energy

The minimum energy required to start a chemical reaction.

Catalyst

A substance that lowers activation energy and speeds up a reaction.

Enzyme

A biological catalyst made of protein that lowers activation energy inside cells.

Oxidation

Loss of electrons (LEO – Loses Electrons = Oxidation), resulting in loss of energy.

Reduction

Gain of electrons (GER – Gains Electrons = Reduction), resulting in gain of energy.

Redox Reaction

A chemical reaction where oxidation and reduction happen at the same time.

Chloroplast

The organelle in plant cells where photosynthesis occurs.

Stroma

Yellowish fluid inside the chloroplast that contains enzymes for photosynthesis.

Thylakoid

Flattened sac-like membrane inside chloroplasts where light-dependent reactions occur.

Grana

Stacks of thylakoids inside chloroplasts; singular is granum.

Oxygen in Photosynthesis

A by-product of photosynthesis produced during the light-dependent reactions.

Electromagnetic Spectrum

A range of light wavelengths; plants absorb visible light during photosynthesis.

Plant Pigments

Molecules that absorb specific wavelengths of light; includes chlorophylls and carotenoids.

Chlorophyll A

The main pigment in photosynthesis that directly absorbs light energy.

Chlorophyll B

An accessory pigment that absorbs light in a similar range as chlorophyll A.

Carotenoids

Accessory pigments that absorb additional light wavelengths and transfer energy to chlorophyll A.

Absorption Spectrum

The range and amount of light wavelengths absorbed by pigments.

Action Spectrum

Shows which wavelengths are most effective for photosynthesis.

Light-Dependent Reactions

Occur in the thylakoids during daylight; light energy produces ATP and NADPH.

Light-Independent Reactions

Also called the Calvin Cycle; occur in the stroma and use ATP/NADPH to make glucose.

Photosystem

A light-harvesting complex in the thylakoid membrane made of pigments and proteins.

Photosystem II

The first photosystem; absorbs light and splits water to release electrons, H⁺, and O₂.

Photolysis

The process where water is split by enzymes to produce electrons, H⁺, and oxygen.

Electron Transport Chain

A sequence of molecules that transfer electrons and pump H⁺ to create a gradient.

Photosystem I

The second photosystem; re-energizes electrons and helps form NADPH.

NADPH

A high-energy molecule formed by adding electrons to NADP⁺ during the light-dependent reactions.

ATP Synthase

An enzyme that uses H⁺ flow to bond ADP and phosphate into ATP.

Chemiosmosis

Process of making ATP using a proton gradient across the thylakoid membrane.