Photosynthesis

• Large surface area- collects as much light as possible.
• Arrangement of leaves that minimises overlapping.
• Thin, most light is absorbed in the first few milimetres also keeps diffusion distance low.
• A transparent cuticle and epidermis allows light through.
• Lots of stomata for gasous exchange.
• stomata open and close depandant on light intensity.
• network of xylems bring water to leaf cells and phloems bring sugars.

1) Capturing of light energy- by chloroplast pigment eg chlorophyll

2) The light independant reaction-convert light energy into chemical energy. Photolysis occurs (splitting of water molecule by light to produce 2e, 2H+, O)

3) Light independant reaction- protons from light dependant reaction are used to reduce C02 into sugars and other oganic molecules.

• light hits the chlorophyll molecule and boosts the energy of a pair of electrons in the chlorophyll.
• Rasising them to a higher energy level and the electrons are said to be Exited.
• This causes the electrons to leave the chlorophyll.
• These electrons are taken up by electron carriers. (the chlorophyll has lost electrons so is oxidised the electron carriers have gained electrons so is reduced)
• electrons are passed along the chain in a series of oxidation reduction reactions.
• Each electron carrier has less energy than the one previous the exess energy is used to form ATP from ADP+Pi

• The loss of electron in the chlorophyll when the light hits it leaves it short of electrons and the elctrons are replaced
• This replacement comes from water molecules which are split using light.

• The hydrogen ions (protons) are taken up by electron carrier NADP and becomes reduced to NADPH, it then goes and enters the light independant reaction
• This NADPH has futer chemical potential.
• oxygen combines and diffuses out of the leaf.

• The light dependant reaction takes place in the thylakiods of the chloroplast.
• The thylakiod membranes provide a large surface area for electron carriers and enzymes to carry out the light dependant reation.
• Proteins in the grana hold the chlorophyll in a very precise manner that allows maximum absorbtion of light.
• Chloroplast contain DNA and ribsomes to synthesis protein needed for photosynthesis quickly

• CO2 diffuses into the leaf through the stomata and dissolves in water to allow it to enter the stroma of the chloroplast
• CO2 comibes with Ribulose-Bisphosphate (5 carbon) (RuBP) to give 2 molecules of Glycerate-3-phosphate (G3P) (3 carbon)
• ATP and NADPH are used to reduce G3P into Triose Phosphate (TP)
• NADP is reformed and enters the site of the light dependat stage 
• Some TP is used to make Gluecose
• But most is used to reform Ribulose-Bisphosphate

• The stroma contains all the enzymes needed for the light independant reaction to occur.
• Contains DNA and ribosomes for the production of any proteins that are needed for the light independant reaction.  

• Darkness- no photosynthesis would occur if there is no light
• Increased light intensity- rate of photosynthesis will increase upto a point where it has no futher effect on rate of photosynthesis.
• At this point other factors such as Carbon Dioxide is the limiting factor so that will increase photosynthsis rate.
• At this point CO2 will have no futher effect and so a different factor will limit photosynthesis eg Tempreture