PHOTOSYNTHESIS
PHOTOSYNTHESIS = the process by which plants make glucose with the use of carbon dioxide,
water. In order for photosynthesis to take place, light must be present at some point.
This glucose is what is needed by animals to perform respiration to obtain energy. Plants use the
carbon dioxide released by animals. Hence plants and animals need one another.
Photosynthesis takes place in the chloroplast of the plant cell. As discussed, plants have mitochondria
to perform respiration and chloroplast to perform photosynthesis. In a way, they are self sufficient.
However, often the plants do not obtain the necessary amount of carbon dioxide they need to do
photosynthesis from their own respiration. So, they rely on us.
Photosynthesis Reaction:
6CO2 + 6H2O + light  C6H12O6 + 6O2
Structure of the chloroplast:
There are 2 types of reactions that make up photosynthesis: Light and Dark
***Light Reactions (aka...Light Dependent)
- the “photo” part of the name photosynthesis
- light is necessary at this stage...only occurs during the day (or with light present)
- occurs in the grana (or thylakoids...the pancake disks) of the chloroplast
- stage where the reactant water is used
- Photolysis = break down of water in the presence of light
- so sunlight breaks the 6H2O that is taken in by the plant into 12 Hydrogens and 6 Oxygen atoms
- Oxygen is a waste product. Oxygen is also diatomic. Therefore the 6 oxygen atoms leave the plant
as 3 O2 molecules (diatomic). You see in the reaction that 6 oxygen molecules are
released.....here are the first 3 to go.
- The 12 Hydrogens are kept to be used in the dark reactions.
- SO.....WE HAVE USED WATER AND SUNLIGHT AS REACTANTS TO THUS FAR PRODUCE 3
DIATOMIC OXYGEN MOLECULES (THAT ARE WASTE AND RELEASED). WE STILL HAVE
TO MAKE GLUCOSE AND RELEASE 3 MORE DIATOMIC OXYGEN MOLECULES
***Dark Reactions (aka....Light Independent or Calvin Cycle)
- the “synthesis” part of the name photosynthesis
- can occur during the day or night (light or dark)
- synthesis means to make.....glucose will be made
- takes place in the stroma of the chloroplast....the fluid part
- stage where the reactant carbon dioxide is used
- 6CO2 molecules enter......(which is 6 carbons and 12 oxygens) and this combines with the 12
Hydrogens left from the light reactions......
- Glucose is made with the 6 carbons, 12 hydrogens, and only 6 of the oxygens will be needed. The
other 6 oxygens will leave.
- Oxygen is a waste product. Oxygen is also diatomic. Therefore the 6 oxygen atoms leave the plant
as 3 O2 molecules (diatomic). You see in the reaction that 6 oxygen molecules are
released.....here are the last 3 to go.
- SO....WE HAVE USED CARBON DIOXIDE AS A REACTANT IN THE DARK REACTION TO
PRODUCE GLUCOSE AND ANOTHER 3 DIATOMIC OXYGEN MOLECULES TO BE
RELEASED AS WASTE