Photosynthesis in Plants
Photosynthesis is a process where green plants transform light energy into chemical energy.
It is used to make food and habitats for animals. It releases oxygen and energy.
Light dependent reactions
It takes place in the chloroplast, and it uses light energy to make two energy storage
molecules needed for the next stage for photosynthesis. Photosystems consist of several
chlorophyll molecules and accessory pigments like Xanthophyll and Carotene Photosystem 1
transports electrons from one face of the photosynthetic membrane to the other.
Photosystem 2 makes oxygen to catalyse the photo-oxidation of water by using light energy.
In the light-dependent reaction, photolysis breaks down the hydrogen and oxygen of water
molecules that reside in plants. Sunlight will shine on the photosystem and excited electrons
from photosystem 2 are picked up by the first chain of electrons carriers. The electrons are
passed through carriers and the energy from the electrons is used to pump hydrogen ions
the first chain of electrons carriers picks up excited electrons from photosystem 2 the first
chain of electrons carriers picks up excited electrons from photosystem 2 into the lumen.
The energy released is coupled to reactions catalysing the formation of ATP. Hydrogen ions
concentrated in the lumen, leave through ATP synthase and produces ATP. Electrons from
P680 fall back to ‘ground state` and fill vacancies in the reaction centre of P700. Meanwhile,
the ‘hole` in the reaction centre P680 are filled by electrons released as water is spilt into
hydrogen ions and oxygen. Oxygen atoms combine to from O2. The hydrogen ions released
in photolysis are used to reduce NADP. Excited electrons from P700 are taken up by another
electron acceptor and passed two electrons at a time to NADP with the hydrogen ions from
photolysis.
, Light Independent Reactions (Calvin Cycle)
It takes place in the stroma of the chloroplast, and it does not need light and produces
organic molecules from carbon dioxide. An enzyme, Rubisco is used in this process. RuBP is
carbonylated fixing the CO2 and produces two 3C compounds called 3-phosphoglycerate.
G3P is phosphorylated and reduce to another 3C compound glyceraldehyde 3-phosphate.
ATP and five out of six molecules of triose phosphate are used during phosphorylation to
regenerate three molecules of RuBP. This reaction helps build a molecule of glucose.
Factors affecting the rate of photosynthesis
Light intensity
As light intensity increases, the rate of photosynthesis increases until another factor
becomes limiting. Then the rate of photosynthesis will have little to no change.
Method
1. I collected a stem of Elodea and remove several leaves from the bottom, then I cut a
portion of the stem at an angle. I lightly crush the cut end of the stem
2. I poured 30ml of sodium carbonate solution in the boiling tube.
3. I submerged the stem in the tube and place in a beaker of water.
4. I used my ruler to position the lamp 5cm from the tube and wait 1 minute
5. After that I counted the bubbles rising from the cut end of the stem for 3 minutes
and repeat it for two more rounds.
6. I moved the lamp to 10cm from the lamp and repeated steps 4-6
Number of bubbles in 3 minutes
Distance from Run 1 Run 2 Run 3 Average
light source
(cm)
Photosynthesis is a process where green plants transform light energy into chemical energy.
It is used to make food and habitats for animals. It releases oxygen and energy.
Light dependent reactions
It takes place in the chloroplast, and it uses light energy to make two energy storage
molecules needed for the next stage for photosynthesis. Photosystems consist of several
chlorophyll molecules and accessory pigments like Xanthophyll and Carotene Photosystem 1
transports electrons from one face of the photosynthetic membrane to the other.
Photosystem 2 makes oxygen to catalyse the photo-oxidation of water by using light energy.
In the light-dependent reaction, photolysis breaks down the hydrogen and oxygen of water
molecules that reside in plants. Sunlight will shine on the photosystem and excited electrons
from photosystem 2 are picked up by the first chain of electrons carriers. The electrons are
passed through carriers and the energy from the electrons is used to pump hydrogen ions
the first chain of electrons carriers picks up excited electrons from photosystem 2 the first
chain of electrons carriers picks up excited electrons from photosystem 2 into the lumen.
The energy released is coupled to reactions catalysing the formation of ATP. Hydrogen ions
concentrated in the lumen, leave through ATP synthase and produces ATP. Electrons from
P680 fall back to ‘ground state` and fill vacancies in the reaction centre of P700. Meanwhile,
the ‘hole` in the reaction centre P680 are filled by electrons released as water is spilt into
hydrogen ions and oxygen. Oxygen atoms combine to from O2. The hydrogen ions released
in photolysis are used to reduce NADP. Excited electrons from P700 are taken up by another
electron acceptor and passed two electrons at a time to NADP with the hydrogen ions from
photolysis.
, Light Independent Reactions (Calvin Cycle)
It takes place in the stroma of the chloroplast, and it does not need light and produces
organic molecules from carbon dioxide. An enzyme, Rubisco is used in this process. RuBP is
carbonylated fixing the CO2 and produces two 3C compounds called 3-phosphoglycerate.
G3P is phosphorylated and reduce to another 3C compound glyceraldehyde 3-phosphate.
ATP and five out of six molecules of triose phosphate are used during phosphorylation to
regenerate three molecules of RuBP. This reaction helps build a molecule of glucose.
Factors affecting the rate of photosynthesis
Light intensity
As light intensity increases, the rate of photosynthesis increases until another factor
becomes limiting. Then the rate of photosynthesis will have little to no change.
Method
1. I collected a stem of Elodea and remove several leaves from the bottom, then I cut a
portion of the stem at an angle. I lightly crush the cut end of the stem
2. I poured 30ml of sodium carbonate solution in the boiling tube.
3. I submerged the stem in the tube and place in a beaker of water.
4. I used my ruler to position the lamp 5cm from the tube and wait 1 minute
5. After that I counted the bubbles rising from the cut end of the stem for 3 minutes
and repeat it for two more rounds.
6. I moved the lamp to 10cm from the lamp and repeated steps 4-6
Number of bubbles in 3 minutes
Distance from Run 1 Run 2 Run 3 Average
light source
(cm)
