Photosynthesis

A comprehensive set of vocabulary flashcards covering the stages, structures, chemical reactions, pigments, and limiting factors of photosynthesis based on the lecture notes.

Photosynthesis

The process by which plants, some bacteria, and some protistans use sunlight energy to produce glucose from carbon dioxide and water, forming oxygen as a byproduct.

Chlorophyll a

The primary photosynthetic pigment present in all photosynthetic organisms that absorbs light energy from violet-blue and reddish orange-red wavelengths, and absorbs little from intermediate wavelengths.

Accessory pigments

Pigments that absorb light energy that chlorophyll a does not absorb, including chlorophyll b (also c, d, and e in algae and protistans), xanthophylls, and carotenoids such as beta-carotene.

Chlorophyll molecule structure

Consists of a lipid-soluble hydrocarbon tail ($C_{20}H_{39}-$) linked by an ester bond to a flat hydrophilic head containing a magnesium ion at its centre.

Xylem vessels

Specialized plant cells through which water absorbed by the roots is transported up to the leaves.

Cuticle

The protective waxy layer covering the leaf that guards against drying out and through which carbon dioxide cannot pass.

Stomata

Specialized structures on leaves, each flanked by two guard cells (singular: stoma), that allow carbon dioxide to enter and oxygen and water vapor to exit the leaf.

Thylakoid

The structural unit of photosynthesis consisting of flattened sacs or vesicles containing photosynthetic chemicals, present in both photosynthetic prokaryotes and eukaryotes.

Grana

Pancake-like stacks of thylakoids (singular: granum) within a chloroplast where the light-dependent reactions take place.

Stroma

The fluid-filled areas between grana in the chloroplast where the light-independent reactions of photosynthesis take place.

Photoexcitation

The process where electrons in a chlorophyll molecule gain energy from absorbed light and move to higher energy levels.

Photoionisation

The process in which chlorophyll absorbs sufficient light energy to ionise the molecule, freeing an electron and leaving behind a positively charged chlorophyll ion.

Photosystem

A functional complex consisting of a core of a chlorophyll molecule associated with an electron acceptor and an electron donor.

Photolysis

The splitting of water molecules by light energy into oxygen, hydrogen ions, and electrons ($2H_2O \rightarrow 4H^+ + O_2 + 4e^-$), which provides electrons to replace those lost by photoionised chlorophyll.

Photosystem II (PSII)

The photosystem (also called P680) that functions first in non-cyclic photophosphorylation, named second because of the order of its discovery, which absorbs light most efficiently at $680\,nm$.

Photosystem I (PSI)

The photosystem (also called P700) that absorbs light most efficiently at $700\,nm$ and participates in both cyclic and non-cyclic photophosphorylation.

Z scheme

The electron transfer process occurring across PSII and PSI, named for the Z shape formed by the accompanying energy changes when drawn out.

Phosphorylation

A condensation reaction that involves the addition of a phosphate group to an organic compound, such as forming ATP from ADP and phosphate with the elimination of water.

Chemiosmosis

The mechanism of ATP synthesis wherein energy from electron transport pumps $H^+$ ions from the stroma into the thylakoid compartment, creating an electrochemical gradient whose diffusion drives ATP production.

Non-cyclic phosphorylation

A light-dependent pathway involving both PSII and PSI that transfers electrons from water to $NADP^+$, producing ATP, NADPH, and oxygen.

Cyclic phosphorylation

A light-dependent pathway involving only Photosystem I where excited electrons are transferred to the electron transport chain between PSII and PSI and recycled back to PSI, generating extra ATP without producing NADPH.

Carbon fixation

The incorporation of inorganic carbon dioxide into organic compounds during the light-independent reactions of photosynthesis.

Ribulose 1,5-biphosphate (RuBP)

A five-carbon sugar that combines with carbon dioxide during the initial step of the light-independent reactions to form an unstable six-carbon intermediate.

Glycerate 3-phosphate (GP)

A three-carbon compound (also known as phosphoglycerate or PGA) formed when the unstable six-carbon sugar breaks down in the Calvin cycle; it is the first stable product of the cycle.

Glyceraldehyde 3-phosphate (GALP)

A three-carbon atom molecule (also called PGAL or phosphoglyceraldehyde) produced by phosphorylating GP using ATP and reducing it with NADPH; it is used to produce glucose or regenerate RuBP.

Limiting factors

Environmental factors—specifically light intensity, carbon dioxide concentration, and temperature—that determine and restrict the overall rate of photosynthesis.