17) Energy for biological responses

    Cards (46)

    • energy requiring processes:
      • anabolism
      • active transport
      • nerve transmission
      • endocytosis
      • exocytosis
      • transcription
    • ATP
      • adenine
      • phosphate
      • ribose
    • ATP+ H20 = ADP + P + energy
    • ATP
      • not a good long term energy source, due to its relative instability of the phosphate bonds, so fats and carbohydrates are better for storage
      • ATP is a source of immediate energy
    • ATP
      • small, moves easily in and out of organelles
      • soluble, energy requiring processes takes place in aqueous solutions
      • phosphate bonds have intermediate energy, the quantities of energy released are large enough to support cellular reactions but not so large that energy is wasted
      • easily regenerated
    • The hydrolysis of one mole of ATP generates 30.5 kj/mol
    • photosynthesis:
      6CO2 + 6H20 = C6H1202 + 6o2
    • Light dependent reaction
      • energy from the sunlight is absorbed and ATP is formed
      • hydrogen from water is used to replace the co-enzyme NADP to reduced NADPH
    • Light independent reaction (calvin cycle)
      • hydrogen from reduced NADP and carbon dioxide are used to build organic molecules such as glucose
      • ATP from light dependent stage supplies energy
    • autotrophs make their own food using carbon dioxide via photosynthesis
    • heterotrophs assimilate energy by consuming plants and animals
    • chloroplasts
      • double membrane - has pigments of chlorophyll for light absorption
      • stroma - site of many chemical reactions, as it contains enzymes and the correct pH level for light independent reaction
      • thylakoid - Has ATP synthase for photophosphorylation, which absorbs light
      • granum - flat membrane stacks increase SA:V ratio for a faster rate of absorption
      • lamella - connects thylakoids and provides structure and supports to the chloroplast
    • respiration:
      6o2 + C6H12o6 = 6CO2 + 6H20 + energy
    • Photosynthesis stages:
      • Capturing of light energy - pigments of chlorophyll.
      • Light dependent reaction - light energy converted into chemical energy.
      • Light independent reaction - sugars and other organic molecules are produced.
    • Photosynthetic pigments:
      chlorophyll a - main pigment that absorbs red and blue light and reflects green light
      chlorophyll b - an accessory pigment mostly found with chlorophyll a in light-harvesting complex
      Xanthophylls and carotenoids - absorb different wavelengths than chlorophyll, broadening the spectrum of light that can drive photosynthesis.
    • Light dependent stage:
      • takes place in thylakoid membrane
      • light energy absorbed by photosystems
      • water split by photolysis
      • excited electrons are passed along the electron transport chain
      • some ATP is produced by photophosphorylation
      • NADP is reduced
    • LDS:
      1. light is absorbed & electrons get excited
      • light shines on photosystem 2
      • the absorbed energy leads to excitation of 2 electrons which then are accepted by the electron transport chain
    • LDS:
      2. water is split into protons, electrons and oxygen
      • photosystem 2 contains an enzyme that split water in the presence of light - photolysis
      • the 2 electrons are used to replace the 2 excited electrons which have left chlorophyll in photosystem 2
    • Photolysis - splitting of water by light
    • photolysis equation:
      2H20 = O2 + (4H+) +(4e-)
    • LDS:
      3. high energy electrons are moved along the electron transport chain
      • at each stage a small amount of energy is released
      • electron carriers are molecules which all contain iron
      • energy is used to pump protons (H+) across the thylakoid membrane from stroma into thylakoid space forming a proton pump
    • LDS:
      4. Proton gradient is used to drive the production of ATP by ATP synthase
      • this is chemiosmosis
      • Production of ATP from ADP and phosphate using light is called photophosphorylation
    • photophosphorylation - ATP formed using light energy
    • two types of photophosphorylation:
      • cyclic
      • non-cyclic
    • cyclic photophosphorylation:
      • uses only photosystem 1
      • excited electrons pass to an electron acceptor and back to the chlorophyll molecule
      • electron pass along electron transport carriers
      • electrons leaving return to photo stage 1
      • energy released is used to synthesise ATP
      • no NADP is formed/used
    • non-cyclic photophosphorylation:
      • involves photosystem 1 and 2
      • light strikes photosystem 2, excites electrons which pass along electron transport chain and energy released is used to synthesise ATP - chemiosmosis
      • electrons lost from ps2 are replaced from water by being broken down by photolysis
      • light strikes photosystem 1 and a pair of electrons are lost which travel along ETC and ATP is produced - chemiosmosis
      • electrons get accepted along with hydrogen ion, by NADP forming reduced NADP
    • Light independent reaction
      • builds sugars from carbon dioxide and regenerates ribulose bisphosphate (RuBP)
      • takes place in the stroma of the chloroplast
      • uses ATP and reduced NADP from the light independent stage
    • Light independent reaction
      1. fixation
      2. reduction
      3. regeneration
    • Light independent reaction
      1. fixation
      • the RUBISCO enzyme catalyses the combination of ribulose bisphosphate (RuBP) and carbon dioxide
      • RuBP is a 5-carbon compounds which forms a transient (breaks down easily) molecule
      • The 6-carbon immediately splits into two molecules of glycerate-3-phosphate (GP)
    • Light independent reaction - fixation stages as a flow chart
      RuBP (5c) + Co2 (1c) (catalysed by RUBISCO) = 6c = 3c (GP) + 3C (GP)
    • Light independent reaction:
      2. reduction
      • glycerate-3-phosphate (GP) is then changed into triose phosphate (TP) by the addition of phosphate (from ATP) and hydrogen (from reduced NAPD) from the light dependent reaction
    • Light independent reaction:
      3. regeneration
      • 5 out of every 6 molecules of triose phosphate (TP) are recyled by phosphorylation, using ATP from the light dependent reaction and the rest are used to make glucose, lipids and amino acids
    • Light independent reaction
      • some glycerate-3-phosphate (GP) is used to make amino acids and fatty acids
      • glucose can be isomerised to form fructose
      • glucose and fructose can combine to form sucrose
      • pairs of triose phosphate (TP) can form sugars
    • photosynthesis requires:
      photosynthetic pigment - absorb light energy
      co2 - provides carbon to make glucose
      water - provides electrons and hydrogen irons
      light energy - energy to split water into ATP and reduced NADP
      enzymes - internal
    • limiting factor - factor in lowest supply and therefore limiting the rate of reaction
    • Light intensity:
      • limits the light dependent reaction
      • less light = less excitation of chlorophyll and electrons
      • less electrons pass down the electron transport chain
    • Light intensity:
      • limits the light dependent reaction and glucose-3-phosphate (GP) accumulates
      • ATP and reduced NADP are not produced, therefore GP cannot be reduced to triose phosphate (TP)
    • Light intensity:
      low light intensity - limits LDS, so not much ATP and NADPH are produced. Slows LIR and photosynthesis slows.
      moderate light intensity - produced more ATP and NADPH in LDS, which regenerates RuBP in LIS quicker. More GP converted into TP.
      high light intensity - more light than needed, so temperature becomes limiting factor and rate plateaus
    • carbon dioxide concentration:
      • co2 concentration limits light independent reaction
      • less co2 means there is less available to combine with RuBP
    • carbon dioxide concentration:
      • less co2, means less RuBP converted to GP
      • RuBP accumulates and GP will decrease
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