Metabolism All chemical reactions in a cell → arranged into metabolic pathways Intermediates in these pathways are called metabolites Catabolic reactions (e.g. respiration) release energy Anabolic reactions (e.g. photosynthesis) use up energy Leaf Structure Phototropism → growth towards light Large leaf surface area → captures more light Thin leaves → few cell layer → more light captured by chlorophyll Leaf mosaic increases leaf exposure to light Internal Structure Cuctile → reduces H2O loss by evaporation Palisade mesophyll → chloroplast can move around cell for max light absorption Spongy mesophyll → allows diffusion of gases through leaves Phloem sieve tube → removes products of photosynthesis Chloroplast Thylakoid membrane: light-dependent → large surface area Associated with chlorophyll, accessory pigments, ETC, enzymes Grana: stacks of thylakoid membranes Enclose hydrogen reservoir used in chemiosmosis Lamella: tubular extensions forming a network between grana Stroma: RuBP carboxylase catalyses light independent reaction Starch granule → insoluble storage carbohydrate product of photosynthesis Light Dependent Reaction In Thylakoid Membrane / Granum IMG 5-14-6 Chemiosmosis/Photophosphorylation produces ATP //H+ from photolysis remain in thylakoid space ETC releases energy Used to pump H+ from stroma into thylakoid space By active transport and electrochemical gradient H+ conc in thylakoid space > stroma H+ ions pass back from space between two mitochondrial membranes Through pores which are associated with the enzyme ATP synthetase Energy from the ETC will be used to produce ATP Diffuse down conc gradient across thylakoid membrane Produces ATP by photophosphorylation Light Independent Reaction In Stroma (Calvin Cycle) IMG 5-14-6 Summary The light dependent reaction takes place in the chloroplast and is important to produce ATP and NADPH + H+. Both molecules and carbon dioxide (CO2) are needed in the light independent reaction (Calvin Cycle) to produce a hexose sugar, such as glucose, from RuBP. Glucose is used to in the mitochondrion to produce the energy molecule ATP. NAD+ is also needed for respiration, but is not produced by photosynthesis. PARP (Poly-ADP-Ribose-Polymerase) and PARG (Poly-ADP-Ribose-Glycohydrolase) are important if the plant is exposed to excessive stress factors (such as extreme temperatures). Note: knowledge about PARP and PARG is not required for your exam. IMG Picture 5-1 from Bayer research. Genetic engineering improves crop yields, Braving the drought [view article] Energy Transfer Ecological pyramids Pyramids of numbers Total number of organisms in a food chain at each trophic level Highest number at the bottom (usually producers, then consumers) Pyramid will be inverted if lots of small animals are feeding off one large plant Pyramids of biomass Total biomass of organisms in a food chain at each trophic level Always pyramid shaped Organisms multiplying rapidly may have biomass less than primary consumers Dry mass is measured / H2O stores no energy and varies in different organisms Pyramid of energy Amount of energy transferred to each level of a food chain in an ecosystem Always pyramid-shaped / no energy loss Transfer of energy between trophic levels Food chains and food webs Energy is used to produce new cells / remains fixed in that organism Energy is passed on to the next trophic level through feeding Producers are photoautotrophs (plants) Transduce light energy into chemical P.E. by forming new tissues and storing organic compounds (starch, glucose, lipids, proteins) Consumers are herbivores, carnivores and omnivores Decomposers are detritivores and saprophytes Break down dead complex organic molecules into simple inorganic molecules Food chains are feeding relationships and linked with each other to form complex food webs Some organisms feed on different trophic levels / leaves and insects Some organisms feed on different foods when they are larvae (leaves) and when they are adult (nectar produced by different flowers) Energy transfer and efficiency 2% of light energy is converted to chemical P.E. by photosynthesis Rest is lost reflection from leaves / heat loss / not all wavelengths are utilised / light strikes non-photosynthetic structures 10% of that are passed on along trophic levels Rest is lost in respiration / as heat/faeces/urine Chemical P.E. / generates heat / stores energy by forming organic matter (new cells) Mammals are homeothermic / must maintain constant body temp Warm environment / less energy maintains body temp / more organic matter stored / more transferred to consumer Small organisms / large surface area:volume ratio / lose high amounts of energy Carnivores fix organic matter more efficiently than herbivores Herbivores feed on plants Thus, take up cellulose and lignin / difficult to digest Thus, more food passes through gut and is lost as faeces Trout fix organic matter most efficiently, they are Poikilotherms → must NOT maintain constant body temp More energy is used to fix organic matter Carnivores are harvested while they are still young and grow rapidly Trout transfer most energy to consumer (human) in terms of food [EXAM] Number of food chains is limited Due to energy losses (at each trophic level) In respiration/egestion/excretion/movement/as heat (Too) little energy is left to sustain higher trophic levels/to be passed on