C.1.3 Photosynthesis

Based on the 3rd edition biology textbook written by C.J. Clegg, Andrew Davis, Christopher Talbot

photosynthesis

the production of glucose from carbon dioxide and water, in the presence of chlorophyll and enzymes, using light energy, producing oxygen as a waste product

chlorophyll

the main photosynthetic pigments of green plants, occurring in the grana membranes (thylakoid membranes) of the chloroplasts; also found in cyanobacteria and in the chloroplasts of algae

pigment

coloured compounds produced by metabolism

accessory pigments

light-absorbing compounds that trap light energy and channel it to chlorophyll a, the primary pigment, which initiates the reactions of photosynthesis

photolysis

the splitting of water molecules using light energy

chromatography

the technique used to separate components of a mixture involves letting soluble substances spread across filter paper (or through a powder)

chromatogram

the pattern formed on an adsorbent medium showing the result of separating the components of a mixture by chromatography

R(f) value

a constant distance that a particular substance moves up a chromatogram relative to its solvent front; the R(f) value of the compound is equal to the distance travelled by the compound divided by the distance travelled by the solvent front (both distances measured from the origin)

absorption spectrum

a graph showing the relative absorbance of different wavelengths of light by a pigment

action spectrum

range of wavelengths of light within which a process like photosynthesis takes place

light-dependent reactions

part of photosynthesis occurs in. the grana of chloroplasts and requires light, water is split, and ATP and NADPH are generated

photophosphorylation

the formation of ATP using light energy (in the light-dependent step of photosynthesis)

light-independent reactions

part of photosynthesis occurring in the stroma of chloroplasts; it uses the products of the light-dependent step to reduce (or fix) carbon dioxide to glucose

photosystems

molecular arrays of chlorophyll, accessory pigments and proteins (light-harvesting complexes) with a special chlorophyll as the reaction centre from which an excited electron is emitted

light-harvesting complex (LHC)

an array of protein and chlorophyll molecules embedded in the thylakoid membrane of plants =, algae, and cyanobacteria, which transfer light energy to one chlorophyll a molecule at the reaction centre of a photosystem

photosystem 1

a chlorophyll-protein complex that uses light energy to release excited electrons, replacing each lost electron with one in the ground state (electrons are received from photosystem 2); it is activated by the light wavelength 700nm

photosystem 2

a membrane super-complex of proteins and several hundred chlorophyll molecules, plus accessory pigments, that carries out the initial reaction of photosynthesis; light from the Sun excites electrons, which pass down an electron transport chain: these electrons are replaced by splitting water to release protons and electrons; it is activated by the light wavelength 680nm

ground-state electrons

the energy level normally occupied by an electron; the state of lowest energy for an electron

high-energy (excited) electrons

chlorophyll in photosystems 1 and 2 absorbs light energy (photons), which increases the energy level of electrons

non-cyclic photophosphorylation

process used to produce NADPH in addition yo ATP; requires presence of water

cyclic photophosphorylation

process that produces a steady supply of ATP in the presence of sunlight

Calvin cycle

a cycle of reactions in the stroma of the chloroplast, also known as the light-independent reactions, in which carbon dioxide is converted to carbohydrate

rubisco (RuBisCo)

ribulose-1,5-bisphosphate carboxylase is an enzyme involved in the first major step of carbon fixation; it is the central enzyme of photosynthesis

fixation

carbon dioxide combines with ribulose biphosphate, forming an unstable 6-carbon sugar that splits immediately to form two molecules of glycerate 3-phosphate

reduction

glycerate 3-phosphate combines with H from NADPH using energy from ATP (both taken from light-dependent stage) and forms water and triose phosphate

regeneration

triose phosphate is used directly to convert to RuBP, the acceptor molecule, using ATP energy to reorganize back to the correct shape

product synthesis

triose phosphate is used directly in respiration or converted to glucose using ATP energy to organize carbons taken from carbon dioxide