Photosynthesis Lecture Notes Review

These vocabulary flashcards cover the energy transfer processes, pigment roles, stages of photosynthesis (Light-dependent and Calvin cycle), limiting factors, and specialized adaptations in C4 plants.

Calvin cycle

The light independent stage of photosynthesis where energy transferred as ATP and reduced NADP is used to produce complex organic molecules.

Thylakoid

The internal membrane of a chloroplast that acts as the reaction site for light-dependent reactions, containing the electron transport chain and ATP synthase.

Stroma

The colorless, hydrophilic matrix surrounding the grana that contains enzymes, DNA, 70S ribosomes, and is the site of the Calvin cycle.

Absorption spectrum

A graph showing the absorbance of different wavelengths of light by a specific pigment, such as chlorophyll $a$ or $b$.

Action spectrum

A graph showing the rate of photosynthesis at different wavelengths of light, typically showing the best rates with violet-blue and red-orange light.

Chlorophyll a

A primary green pigment that acts as a reaction center and provides best absorption with blue-violet and red-orange light.

Carotenoids

Accessory pigments, such as orange carotene or yellow xanthophyll, that absorb blue-violet light and pass energy to primary pigments.

Rf value

A value used in chromatography to identify pigments, calculated as: $\text{Rf} = \frac{\text{distance travelled by solute}}{\text{distance travelled by solvent}}$

Photosystem I (PSI)

A light-harvesting cluster in the thylakoid membrane that absorbs light of wavelength $700\,nm$; it is the only photosystem involved in cyclic photophosphorylation.

Photosystem II (PSII)

A light-harvesting cluster present in plants that absorbs light of wavelength $680\,nm$ and includes a water-splitting enzyme for photolysis.

Photoactivation

The process in the light-dependent stage where an electron in a chlorophyll molecule is excited to a higher energy level and emitted.

Photolysis of water

The enzyme-catalyzed breakdown of water in PSII shown by the equation: $H_2O \rightarrow 2H^+ + 2e^- + \frac{1}{2} O_2$

Cyclic photophosphorylation

A process involving only PSI where excited electrons are returned to the chlorophyll via electron carriers to generate ATP but no reduced NADP.

Non-cyclic photophosphorylation

The 'Z scheme' of electron flow involving both PSI and PSII that results in the synthesis of both ATP and reduced NADP while evolving oxygen.

RuBP (ribulose bisphosphate)

A 5-carbon compound that combines with $CO_2$ at the start of the Calvin cycle, catalyzed by the enzyme rubisco.

GP (glycerate-3-phosphate)

A 3-carbon compound (also known as PGA) formed when the unstable 6-carbon intermediate in the Calvin cycle splits.

TP (triose phosphate)

A 3-carbon sugar formed by the reduction of GP using reduced NADP and ATP; it is used to make glucose or regenerate RuBP.

Limiting factor

The specific factor, such as light intensity, temperature, or $CO_2$ concentration, that has the greatest effect in reducing the rate of photosynthesis.

Hill reaction

An experiment investigating light-dependent reactions by using isolated chloroplasts and a redox indicator like DCPIP to monitor electron transfer.

DCPIP

A redox indicator that is blue when oxidised and becomes colourless when reduced by accepting electrons from the electron transport chain.

C4 plants

Plants like maize or sorghum adapted for high rates of carbon fixation by forming a 4-carbon compound (oxaloacetate) as the first stable product.

Photorespiration

An inefficient process where rubisco catalyses the reaction between RuBP and oxygen instead of $CO_2$, occurring mostly at high temperatures.

PEP carboxylase

An enzyme in the mesophyll cells of C4 plants that fixes $CO_2$ into oxaloacetate and has no tendency to bind to oxygen.

Bundle-sheath cells

Specialized cells in C4 plants where the Calvin cycle occurs, physically separated from air to prevent photorespiration.

Lamella

Chloroplast structures that connect and separate thylakoid stacks (grana).