Site of Photosynthesis- structure of the leaf
- 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.
outline for photosynthesis
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.
The making of ATP- Light dependant reaction
- 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
Photolysis of Water- Ligh dependant reaction
- 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.
Photolysis of Water 2- Light dependant reaction
Site of the light dependant reaction
- 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
The light independant reaction- Calvin Cycle
- 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
Site of the light independant reaction
- 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.
Factors affecting photosynthesis
- 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