deck_3744218 Flashcards
define: photosynthesis
Photosynthesis is a process used by plants and other organisms to convert light energy, into chemical energy that can be later released to fuel the organisms’ activities.-This is the ultimate source of all our food and most of our energy resources
what % of prescription drugs are derived from chemicals first identified in plants?
1) Over 50% 2) vinblastine and vincristine treatment of leukemia and Hodgkin’s lymphoma.
who discovered photosynthesis?
1) Joseph Priestly - 1771Mint leaves could restore bad air to good2) Jan Ingenhousz - 1796Carbon dioxide split by plants to make oxygen
where does the oxygen produced as a by-product of photosynthesis originate from?
1) water and not from carbon dioxide 2) Ruben & Kamen Used H2O ( containing oxygen isotope) to trace the path of the oxygen With water as the electron donor the complete reaction for the formation of triose sugars is:3CO2 + 6H2O Light C3H6O3 + 3H2O + 3O23) The oxygen is actually a waste product and mostly leaves the leaf through the stomata, although some oxygen remains in the plant to be used for aerobic respiration
how many stages are there in photosynthesis?
1) two stage process2) Effects of light intensity and temperatureShowed that part of the overall reaction varied with temperature (up to 30C) & not light intensity
how is light gathered by the plant?
Pigments in the leaves:1) Chlorophyll a2) Chlorophyll b3) Carotenoids
where is light gathered in a plant?
thylakoids in the chloroplasts
Chlorophyll molecules reach an excited state when they have absorbed light energy. The energy has 3 possible fates, list these fates.
1) Conversion to heat plus lower energy photon2) Energy transfer to another chlorophyll molecule (resonance energy transfer)3) High energy electron transferred to a neighbouring molecule (oxidation of chlorophyll)
name the pigments found in the photosystems.
1) Chlorophyll a – primary photosynthetic pigment2) Chlorophyll b – accessory pigment transfers energy to Chlorophyll a3) Carotenoids – primary function is to prevent oxidative damage of chlorophyll during photosynthesis
what is the purpose of the light and dark reactions?
1) light reaction - The main function of these reactions is to provide a source of ATP and reduced NADP, which are used to reduce CO2 in the light independent reactions.2) Carbon-fixation reactions (dark reactions/ light independent)
describe the structure of a chloroplast
1) Chloroplasts vary, but most are disc-shaped and approximately 2-10μm long. Each has a double membrane (called anenvelope), consisting of the inner membrane and outer membrane2)Chloroplasts contain stacks of flattened membrane compartments. Each stack is called a granum and eachcompartment is a thylakoid.3) Small, thin membranal extensions connect differentgrana, called intergranal lamellae4) The fluid surrounding the grana is called stroma5) Starch grains can also be found in the stroma matrix, as well as DNA and ribosomes, which can be used to make proteins6) The two stages of photosynthesis are the light-dependent reactions (the first or ‘light’ stage) and the light-independent reactions (the second or ‘dark’ stage). The first stage takes place in the grana, and the second stage in the stroma fluid of the chloroplast.
outline what happens during the light dependent stage of photosynthesis
1) Takes place in the thylakoid membranes. 2) Two photosystems are used in this stage: photosystem II and photosystem I, as well as the many ATP synthase enzymes embedded in the membranes to manufacture ATP. Two photosystems containing complexes of 250-400 pigment molecules forming: Antenna complex ( accessory pigments) and Reaction centre ( chlorophyll a)2) there is photolysis of water. 4 photons split 2 molecules of water into four electrons, four protons and one pair of oxygen atoms. This occurs at photosystem II (p680)3) electrons are accepted by the PSII, and the light energy excites the electrons causing them to move between the pigments, until they are accepted by an electron carrier which passes the electrons carrier-to-carrier, eventually they are passed to photosystem I (PSI)4) The movement of electrons between electron carriers (cytochromes) releases energy, which is used to actively pump protons across the membrane against the gradient5) As protons flow through, ATP synthase is activated and adds one phosphate group to a molecule of ADP to produce ATP- photophosphorylation6) when light energises Chlorophyll a in photosystem 1 (P700) the electrons are accepted by more carriers (ferredoxin) and eventually taken to an enzyme called NADP reductase which reduces a NADP to NADPH 7) cyclic photophosphorylation only uses photosystem I. When PSI absorbs light of wavelength over 680nm , chlorophyll a ends up emitting an excited electron which is passed around a chain of carriers before being returned to PSI again. The energy released by the movement of the electrons here is used to generate ATP. NADPH or O2 are not generated
outline what happens during the light independent stage ( calvin cycle) of photosynthesis.
1) does not need light and occurs in the stroma of the chloroplast.2) A molecule of ribulose bisphosphate (RuBP), a five-carbon compound, has carbon dioxide added to it by the enzyme RuBisCO ( 5 + 1 carbon = 6 carbon)3) 6 carbon molecule is hydrolysed to make 2 molecules of 3-phosphoglyceric Acid (PGA) RuBiSCO catalyses this reaction.4) 3-phosphoglycerate (PGA) is reduced to glyceraldehyde 3-phosphate (PGAL) this is a two step process which uses ATP and NADPH4) 5 out of 6 Glyceraldehyde 3-phosphate (G3P) molecules are used to regenerate 3 molecules of RuBP.
outline how much ATP and NADPH is used in the Calvin cycle
1) 3 molecules of CO2 fixed give a net yield of one molecule of glyceraldehyde 3-phosphate at a net cost of 9 molecules of ATP and 6 molecules of NADPH
list some C3 and C4 crops
These terms refer to the different pathways that plants use to capture carbon dioxide during photosynthesis. All species have the more primitive C3 pathway, but the additional C4 pathway evolved in species in the wet and dry tropics.C3:Sugar beet, Cereals, Pea & Bean family, Many fruitC4:Sugar Cane, Maize, Pineapple ,Miscanthus- atmospheric CO2 mainly carbon 12 but 1% carbon 13 - plants take up less 13 than 12: C3 -22 to -44 ppth, C4 -9 to -19 ppth .- Belgians (c3) diet about -25ppth - US (c4) diet about -11ppth
