Photosynthesis Light Reactions Lecture Review

Vocabulary flashcards covering the chloroplast structure, light-dependent reactions, cyclic and linear electron transport, chemiosmosis, and laboratory procedures from the photosynthesis lecture.

Chlorophyll a and b

The two primary photosynthetic pigments embedded in thylakoid membranes that capture light energy mainly in the blue-purple and red wavelengths while reflecting green light.

Thylakoid Membranes

Stacked internal chloroplast membranes linked into grana where light is captured, water is split, and the light-dependent reactions produce $ATP$ and $NADPH$.

Stroma

The fluid space surrounding thylakoid membranes in the chloroplast where carbon fixation occurs and carbon dioxide is converted into glucose.

Light-Dependent Reactions

The initial phase of photosynthesis occurring in the thylakoid membrane where light excites electrons, water is split into hydrogen ions and oxygen gas, and $ADP$ and $NADP^+$ are converted into $ATP$ and $NADPH$.

Carbon Fixation

The light-independent phase in the stroma that uses the energy from $ATP$ and $NADPH$ to combine six carbons and water into glucose without releasing oxygen.

NADPH

The reduced, high-energy electron carrier formed when $NADP^+$ accepts electrons and hydrogen ions from split water; it carries more energy than $ATP$.

Photosystem I (PSI)

A linked pigment-protein complex discovered first in bacteria that has an absorption maximum at $700\,\text{nm}$ ($P700$) and can participate in both cyclic and linear electron transport.

Photosystem II (PSII)

A pigment-protein complex discovered in plants with an absorption maximum at $680\,\text{nm}$ ($P680$) that initiates linear electron flow by capturing light and splitting water with a dehydrogenase enzyme.

Cyclic Electron Transport

A low-energy pathway restricted to photosystem I where electrons cycle through ferredoxin, the cytochrome $b_6f$ complex, and plastocyanin back to $P700$, generating a proton gradient for $ATP$ synthesis without yielding $NADPH$ or oxygen.

Linear Electron Transport

The noncyclic pathway in plants running from photosystem II ($P680$) through an electron transport chain to photosystem I ($P700$) and ending at $NADP^+$ to form $NADPH$.

Cytochrome b6f Complex

A membrane protein complex in the electron transport chain that pumps protons from the stroma into the thylakoid space to generate a proton gradient.

Plastocyanin

An electron carrier that transports electrons from the cytochrome $b_6f$ complex to photosystem I.

Chemiosmosis

The movement of protons down their electrochemical gradient from the thylakoid space into the stroma through $ATP$ synthase via facilitated diffusion, causing the enzyme to rotate and synthesize $ATP$.

Photophosphorylation

The production of $ATP$ from $ADP$ and inorganic phosphate ($P_i$) powered by the light-driven proton gradient created across the thylakoid membrane.

Paper Chromatography

A laboratory technique used to separate and observe the individual pigment components extracted from plant leaves.

Photosynthesis and Respiration Lab Measurements

The tracking of gaseous exchange rates under light and dark conditions; photosynthesis is measured by an increase in oxygen and decrease in carbon dioxide, while respiration is measured by a decrease in oxygen and increase in carbon dioxide.