Applicable for A-Level, IB, DSE, AP-Level Exams
Photosynthesis is the process of converting carbon dioxide and water into glucose and oxygen. Glucose is required for oxygen within the plant to release energy in the form of ATP. It occurs in 2 main stages, the light dependent reaction which occurs in the thylakoid membrane and the light-independent reaction (Calvin Cycle) which occurs in stroma of the chlroplast.
Light dependent reaction is the first step of photosynthesis.
Light causes photoionisation and excites electrons causing chlorophyll to be oxidised. Electrons are picked up by electron carriers and pass down the electron transport chain. As electrons lose energy they are being used to transport protons across the membrane from the stroma to the thylakoid. As protons diffuse back to the stroma through ATP synthase, ATP is produced from ADP and Pi. In Photosystem 1, electrons are excited once again and are picked up by NADP to form NADPH.
Light independent reaction is the second step of photosynthesis and occurs in the stroma.
As CO2 combines with RuBP to form GP catalysed by enzyme rubisco, carbon fixation occurs. Then, reduction occurs: GP is being reduced to TP by NADPH and ATP. Some TP is being used to produce glucose and the majority are used to regenerate RuBP.