Photosyntnesis aqa a2 biol4

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  • Photosynthesis
    • Light independent reaction(stroma)
      • CO2 combines  with RuBP this is cataylsed by the enzyme rubsico to form two molecules of TP which are easily broken down to  form TP, the reduction of GP to TP requires the energy and proton from ATP and NADPH which are products of the  light dependent reaction. two TP molecules can form glucose( organic substances which are taken up by the plant via the stomata) which can be used elsewhere in the plant also RuBP  regenerated
    • Light-dependent reaction (thylakiod/grana)
      • light energy  is absorbed by the chlorophyll and excites the electrons to a higher energy level,also the photolysis of water molecules to make oxygen and protons and electrons occurs.  the high energy electrons are passed along electrons carriers chain due to redox reactions, the electrons gain energy as they go. the energy of the electrons is used to pump protons into the membrane creating a proton gradient. the final electron acceptor is  the coenzyme NADP, reducing it to NADPH. once proton gradient is created the protons pass  back via ATP synthase to form ATP from ADP and phosphate
    • limiting factors
      • CO2
        • in the dark  no photosynthesis is occurring so CO2 concentrationis high, as photosynthesis is unable to occur the rate of respiration is higher than the rate of photosynthesis so plants respire in the dark. the concentrationof CO2 decreases as height increases as  there is more photosynthesising tissue such as leaves  higher up above the ground
        • the day  photosynthesis is occurring, however in the night respiration is occurring, at ground level more respiration is occurring as animals are present , among the leaves more photosynthesis is occurring so CO2 is taken up by plants thus reducing in concentrationnet carbon uptake  occurs during the day
      • light intensity
        • an increase in light intensity will increase the rate of photosynthesis
        • if  it becomes more cloudier light intensity reduces thus photosynthesis reduces thus growth rate reduces, as light intensity is a limiting factor
        • only certain plants are able to photosynthesis in low light intensities such as shady areas provided by leaves above plant
        • species x is able to photosynthesis effectively in the lowest light intensity, the graph also shows that at higher light intensities the rate of photosynthesis of  species x is the highest thus species x  grows the quickest at high light intensities thus able to outcompete species z.and y
      • temperature
        • an increase will Increase the rate of photosynthesis, however above 35° the rubsico enzyme will be denatured
      • inhibitors
        • DCMU inhibits the  electron tranfer chain so little or no ATP and NADPH is produced so the rate of the light independent reaction reduces so less CO2 is taken up as the light independent reaction requires ATP and NADPH
    • tube A contains stroma and grana  tube B  contains stroma, ATP and NADPH (ATP, NADPH are products of the light dependent reaction which occurs in the stroma which is also present in tube A tube  C contains stroma. if tube A was placed in the dark the light dependent reaction will not occur so tube A will have similar results to tube C. the uptake of CO2 is less on tube C than in tube B    as ATP and NADPH are produced in the light dependent reaction, and can be used to form RuBP less GP is converted into less TP less is converted into RuBP


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