Bioenergetics focuses on how energy is able to transform in living organisms. In plants the sun provides the cells with energy through the process of photosynthesis.
The pigment that absorbs light energy for photosynthesis is called the chlorophyll. This green pigment is found inside the chloroplasts of cells of plants and other photosynthetic organisms and is basically what makes plants green in colour!
When the chlorophyll is hit by light energy it loses electrons. Two electrons are released which are taken up by electron carriers which move down the electron transfer chain to make ATP. The transfer chain is located in the thylakoids.
After electrons have passed through the transfer chain they join hydrogen bonds. This process is slightly complex, but in simple terms the hydrogen atoms that are formed then join to a coenzyme called NADP to form reduced NADP.
Luckily, not all is lost as the chlorophyll is able to obtain electrons which have been lost through water. This is because light splits water and releases electrons as well as hydrogen ions and oxygen.
The oxygen that is released from the splitting of water then leaves the plant. Remember that plants release a lot of oxygen which allows us to breathe it in so we can use it for respiration – so it’s pretty important.
It’s always taught that light is needed for photosynthesis – this is obviously true – but there are elements in the process that do not need light, these are known as light-independent reactions.
Photosynthesis uses both light-dependent and light-independent reactions to produce energy. The light-independent reaction in photosynthesis involves the reduction of carbon dioxide using reduced NADP and ATP which was produced in the light-dependent reaction (which was explained above).
The light-independent reactions need NADPH and ATP, but does not need light.
These reactions make up the Calvin cycle, and they take place in the stroma of the chloroplast.
Carbon dioxide diffuses from the air, through the stomata, into the cell and then into the cytoplasm and then the chloroplast. It is then reduced in the light-independent reaction.
Within the stroma, carbon dioxide combines with RuBP (ribulose bisphosphate). This produces two molecules of glycerate three-phosphate. Glycerate three-phosphate, or GP for short, is a three carbon molecule. RuBP is a five carbon molecule. With the addition of one carbon from carbon dioxide, two, three carbon molecules can be made.
It’s also worth knowing how electrons are added and taken away. Simply reduction and oxidation!
Reduction involves the addition of electrons in a reaction that loses oxygen and in oxidation electrons are lost when oxygen is gained.