General Biology (chapter 8) Overview

Photoautotrophs

Organisms that produce their own food using light energy (e.g., plants, algae, cyanobacteria).

Photosynthesis

Process converting CO₂ + H₂O → glucose + O₂ using sunlight.

Chloroplast

Organelle in plant cells where photosynthesis occurs.

Thylakoid

Membrane-bound discs in chloroplasts where light reactions occur.

Stroma

Fluid-filled space in chloroplasts where the Calvin cycle occurs.

Stomata

Leaf pores for gas exchange (CO₂ in, O₂ out).

Chlorophyll

Pigment absorbing blue/red light; reflects green.

Carotenoids

Accessory pigments absorbing blue/green light; protect chlorophyll.

Photosystem II (PS II)

Protein-pigment complex that splits water and initiates the electron transport chain.

Photosystem I (PS I)

Protein-pigment complex that re-energizes electrons to make NADPH.

Electron Transport Chain (ETC)

Proteins in the thylakoid membrane that transfer electrons and pump H⁺ ions.

ATP Synthase

Enzyme that produces ATP as H⁺ ions flow through it.

NADPH

Electron carrier molecule used in the Calvin cycle.

Photolysis

Splitting of water into O₂, H⁺, and electrons using light.

Calvin Cycle

Light-independent reactions that fix CO₂ into glucose.

RuBisCO

Enzyme that fixes CO₂ to RuBP in C₃ plants.

RuBP

Ribulose bisphosphate; a 5-carbon molecule that binds CO₂.

3PG (3-Phosphoglycerate)

First stable molecule formed after CO₂ fixation.

G3P (Glyceraldehyde-3-Phosphate)

3-carbon sugar used to make glucose, starch, and lipids.

Photorespiration

Wasteful process where O₂ binds RuBisCO instead of CO₂.

C₃ Plants

Plants using only the Calvin cycle (e.g., rice, wheat).

C₄ Plants

Plants that spatially separate CO₂ fixation (mesophyll) and the Calvin cycle (bundle sheath).

CAM Plants

Plants that fix CO₂ at night and run the Calvin cycle during the day (e.g., cacti).

PEP Carboxylase

Enzyme in C₄/CAM plants with high CO₂ affinity.

Malate

Molecule that stores CO₂ in C₄/CAM plants.

Bundle Sheath Cells

Cells in C₄ plants where the Calvin cycle occurs.

Mesophyll Cells

Leaf cells where CO₂ fixation occurs in C₃/C₄ plants.

Glucose Phosphate

Molecule derived from G3P; precursor to sucrose and starch.

Sucrose

Disaccharide used for energy transport in plants.

Starch

Polysaccharide used for long-term energy storage.

Cellulose

Polysaccharide in plant cell walls.

ATP

Energy currency molecule produced in light reactions.

NADP+

Electron carrier molecule reduced to NADPH.

Electromagnetic Spectrum

Range of light wavelengths; plants use visible light (400-700 nm).

Visible Light

Wavelengths (400-700 nm) used in photosynthesis.

Redox Reaction

Reaction involving electron transfer (CO₂ is reduced, H₂O is oxidized).

Light Reactions

Phase converting sunlight to ATP and NADPH.

Cyclic Electron Flow

Pathway producing ATP only (no NADPH or O₂).

Noncyclic Electron Flow

Pathway producing ATP, NADPH, and O₂.

Photophosphorylation

ATP synthesis using light energy.

Light-Dependent Reactions

Phase converting sunlight into ATP and NADPH; occurs in thylakoids.

Calvin Cycle (C₃ Pathway)

Light-independent reactions in stroma; converts CO₂ → glucose.

Immediate Product of Photosynthesis: Glucose

G3P is converted into glucose, which serves as an energy source for the plant.