Question

2. Describe the process of obtaining energy (light-dependent reactions) and the process of using that energy for carbon fixation (light-independent reactions) in photosynthesis. Make sure to mention where in the cell each of these reaction types are occurring and what the chemical inputs and outputs are for each of those processes.

Answer 1

2. Plants are able to collect solar energy because of the light absorbing pigment molecules in their leaves. During the first stage of photosynthesis light energy is converted into chemical energy, involving a series of chemical reactions. Photosystems (complexes where photosynthetic pigments organized along with proteins) play an important role in light reaction. There are two kinds of photosystems - photosystem I or PSI, whose special pair is called as P700 and photosystem II or PSII, whose special pair is called as P680.

• Light absorption in PSII
• ATP synthesis
• Light absorption in PSI
• NADPH formation

The net effect is to convert light energy into chemical energy in the form of ATP and NADPH.

Subpart :

• Cell needs a molecule called RuBP
• Cell needs an enzyme called RuBisco

With carbon dioxide, RuBP, RuBisco the plant cell can fix carbon. RuBisco takes the CO2 and adds it to RuBP, creating an intermediate molecule. The whole molecule is separated into 3-carbon molecule called 3PG, by forming 3PG molecule carbon fixation is done.

RuBP + CO2 = 2(3PG)