Chapter 7 – Photosynthesis Vocabulary

A comprehensive set of vocabulary flashcards covering key terms, structures, enzymes, and pathways involved in photosynthesis as presented in the lecture notes.

Photosynthesis

Process that converts solar energy into the chemical energy of carbohydrate (generally glucose) and releases O₂ as a by-product.

Autotroph

An organism, such as a plant, alga, or cyanobacterium, that produces its own food via photosynthesis.

Heterotroph

An organism that must obtain pre-formed organic molecules; consumer in a food chain.

Mesophyll

Leaf tissue whose cells are specialized for photosynthesis.

Stoma (plural stomata)

Small leaf opening through which CO₂ enters and water vapor/ O₂ exit.

Chloroplast

Double-membraned organelle in plants and algae where photosynthesis occurs.

Stroma

Semifluid interior of a chloroplast containing enzymes for the Calvin cycle.

Thylakoid

Flattened sac inside chloroplast; its membrane contains photosynthetic pigments and electron carriers.

Granum (plural grana)

Stack of thylakoids that resembles a pile of coins.

Chlorophyll a

Primary photosynthetic pigment that absorbs violet, blue, and red light; reflects green.

Chlorophyll b

Accessory chlorophyll pigment that broadens the absorption spectrum; also reflects green.

Carotenoids

Accessory pigments (yellow-orange) that absorb violet-blue-green light and protect chlorophyll from damage.

Absorption Spectrum

Graph showing wavelengths of light absorbed by a pigment.

NADP⁺

Oxidized coenzyme that accepts electrons and H⁺ during the light reactions to become NADPH.

NADPH

Reduced coenzyme that carries high-energy electrons and H⁺ to the Calvin cycle.

ATP

Energy currency of the cell produced during light reactions and consumed during the Calvin cycle.

Light Reactions

First stage of photosynthesis in thylakoid membranes; convert solar energy to chemical energy (ATP, NADPH) and split water to release O₂.

Calvin Cycle

Second stage of photosynthesis in the stroma; uses ATP and NADPH to reduce CO₂ and synthesize carbohydrate.

Photosystem II (PS II)

Light-capturing unit that first absorbs solar energy, splits water, and passes energized electrons to an ETC.

Photosystem I (PS I)

Light-capturing unit that re-energizes electrons and ultimately reduces NADP⁺ to NADPH.

Electron Transport Chain (ETC)

Series of carriers in the thylakoid membrane that pass electrons, pump H⁺, and contribute to ATP formation.

Plastoquinone (Pq)

Mobile carrier that moves electrons from PS II to the cytochrome complex while pumping H⁺ into the thylakoid space.

Cytochrome Complex

ETC component that helps establish the H⁺ gradient between thylakoid space and stroma.

ATP Synthase

Enzyme channel that uses the H⁺ gradient to join ADP + Pᵢ, producing ATP (chemiosmosis).

Chemiosmosis

ATP production tied to the diffusion of H⁺ down an electrochemical gradient through ATP synthase.

Noncyclic Pathway

Main flow of electrons from water → PS II → ETC → PS I → NADP⁺; produces both ATP and NADPH.

Redox Reaction

Coupled chemical process in which one substance is oxidized (loses e⁻/H) and another is reduced (gains e⁻/H).

Oxidation

Loss of electrons (often with loss of hydrogen) from a molecule.

Reduction

Gain of electrons (often with addition of hydrogen) to a molecule.

RuBP (ribulose-1,5-bisphosphate)

Five-carbon molecule that initially reacts with CO₂ in the Calvin cycle.

RuBP Carboxylase/Oxygenase (Rubisco)

Slow but abundant enzyme that catalyzes CO₂ fixation to RuBP; can also bind O₂, causing photorespiration.

CO₂ Fixation

First Calvin-cycle step in which CO₂ is attached to RuBP to form two 3-carbon 3PG molecules.

3-Phosphoglycerate (3PG)

First stable 3-carbon product of CO₂ fixation in the Calvin cycle.

Glyceraldehyde-3-Phosphate (G3P)

Reduced 3-carbon sugar formed in Calvin cycle; precursor of glucose, sucrose, starch, cellulose, and lipids.

Photorespiration

Wasteful process in which Rubisco combines O₂ with RuBP, releasing CO₂ and reducing photosynthetic efficiency.

C₃ Plant

Plant (e.g., wheat, maple) whose first detectable CO₂-fixation product is the 3-carbon 3PG and that is susceptible to photorespiration.

C₄ Photosynthesis

Pathway in which CO₂ is initially fixed into a 4-carbon oxaloacetate in mesophyll cells and delivered to bundle-sheath cells; minimizes photorespiration.

PEP (Phosphoenolpyruvate)

Three-carbon compound that accepts CO₂ in C₄ and CAM plants.

PEP Carboxylase (PEPCase)

Enzyme that fixes CO₂ to PEP; has no affinity for O₂, avoiding photorespiration.

Bundle Sheath Cell

Leaf cell surrounding vascular tissue where the Calvin cycle operates in C₄ plants.

Oxaloacetate

Initial 4-carbon product of PEPCase reaction in C₄ and CAM metabolism.

Malate

Reduced form of oxaloacetate that transports CO₂ to bundle sheath cells (C₄) or stores CO₂ at night (CAM).

CAM Photosynthesis

Temporal separation strategy in succulents where CO₂ is fixed to C₄ acids at night and released to Calvin cycle by day; conserves water.

Visible Light

Portion of the electromagnetic spectrum (380–750 nm) used for photosynthesis.

Electromagnetic Spectrum

Range of all types of electromagnetic radiation, from gamma rays to radio waves.

Hydrogen-Ion (Proton) Gradient

Difference in H⁺ concentration across the thylakoid membrane that drives ATP synthesis.

NADP⁺ Reductase

Enzyme adjacent to PS I that catalyzes reduction of NADP⁺ to NADPH.

Fossil Fuel

Energy-rich substance like coal formed from ancient photosynthesizers millions of years ago.