Cell Biology Workshop

Glossary

ATP - adenosine triphosphate.


Bundle Sheath - in C4 plants, a layer of photosynthetic cells between the mesophyll and a vascular bundle of a leaf.


C3 plant - a plant that used the Calvin Cycle for the initial steps that incorporate CO2 into organic material, forming a three carbon (C3) compound as the first stable intermediate Cc.f. C4 plant, CAM plant)


C4 plant - a plant that prefaces the Calvin Cycle with reactions that incorporate CO2 into four carbon (C4) compounds, the end product of which supplies CO2 for the Calvin Cycle. ( c.f. C3 plant, CAM plant).


Calvin cycle - a cycle of reactions resulting in the fixation of carbon dioxide into C3-carbohydrate in photosynthesis in plants.


CAM plant - a plant that used crassulacean acid metabolism, an adaptation for photosynthesis in arid conditions. CO2 entering open stomata during the night is converted into organic acids, which release CO2 for the Calvin Cycle during the day, when stomata are closed. (c.f. C3 plant, C4 plant).


Cellular respiration - oxidation of fuel molecules, that is, removal of electrons, coupled to synthesis of ATP.


Chloroplast - an organelle (plastid) containing membrane-bound light-absorbing pigments; functions in photosynthesis.


Citric acid cycle - also known as the Krebs cycle; cyclic series of reactions involving oxidation of fuel molecules; occurs in mitochondria in eukaryotes.


Covalent bond - bond formed between atoms due to sharing of electrons in their outermost orbitals.


Electron transport chain - the arrangement of cofactors such as NAD, FMN.


Fermentation - anaerobic production of alcohol, lactic acid or similar molecules from carbohydrates by the glycolytic pathway.


Glycolysis - anaerobic catabolism of glucose to pyruvic acid, producing two molecules of ATP.


Grana - stacks of thylakoids that form part of the internal membrane system of chloroplasts.


Hydrogen bond - relatively weak bond formed between hydrogen and another polar atom such as oxygen.


Ionic bond - bond formed when ions of opposite charge are attracted to each other.


Mesophyll - the internal parenchyma of a leaf, usually photosynthetic.


Mitochondrion - DNA containing organelle of eukaryotic cells; surrounded by a highly permeable double membrane; contain circular DNA molecules, RNA and small ribosomes; site of cellular respiration.


Osmosis - the movement of water from a region of low osmotic concentration (high water concentration, high water potential) to one of high osmotic concentration (low water concentration, low water potential), as a result of the random thermal motion of water molecules through a selectively permeable membrane.


Osmotic potential - a property of any solution, resulting from its solute content; it may be zero or have a negative value. A negative osmotic potential tends to cause water to move into the solution; it may be offset by a positive pressure potential in the solution or by a more negative water potential in a neighbouring solution. (Contrast with pressure potential).


Oxidation - reactions involving the breakdown of molecules by removal of electrons, especially those in which oxygen combines with, or hydrogen is removed from a compound.


PEP (phosphoenolpyruvate) - is a three carbon molecules. In C4 plants (q.v.) CO2 is added to PEP to form the four-carbon product oxaloacetate. The reaction is catalyzed by PEP carboxylase.


Photorespiration - a type of respiration in plants that occurs only in the light and is different from normal respiration, by various pathways, eg. using glycollate produced from a carbohydrate from photosynthesis, as a substrate.


Photosynthesis - the process by which solar energy is harvested and used to convert CO2 and water into carbohydrates; involves: absorption of energy from sunlight by means of pigments, reactivation of pigments, and carbon fixation to produce sucrose in 'dark reactions'.


Pressure potential - the actual physical (hydrostatic) pressure within a cell. (Contrast with osmotic potential, water potential).


Redox - mutual reduction and oxidation.


Reduction - reactions involving the breakdown of molecules by addition of electrons, especially those in which oxygen is lost and hydrogen accepted.


Ru BPC (ribulose bisphosphate) - a five carbon sugar which attaches to CO2 at the beginning of the Calvin Cycle. The reaction is catalyzed by Rubisco (q.v.).


Rubisco (Ribulose carboxylase) - the enzyme that catalizes the first step (the addition of CO2 to RuBP (q.v.), ribulose bisphosphate, of the Calvin Cycle.


Stroma (of chloroplast) - matrix enclosed within inner membrane.


Thylakoid - flattened disc-like sac that forms part of the internal membrane system of chloroplasts; site of location of photosynthetic pigments.


Water potential - in osmosis, the tendency for a system (a cell or solution) to take up water from pure water, through a differentially permeable membrane. Water flows toward the system with a more negative water potential. (Contrast with osmotic potential, pressure potential).