Biology 101

Lizeth Leon

1.The light-dependent reactions starts within Photosystem II. When the excited electron reaches the special chlorophyll molecule at the reaction centre of Photosystem II it is passed on to the chain of electron carriers. This chain of electron carriers is found within the thylakoid membrane. As this excited electron passes from one carrier to the next it releases energy. This energy is used to pump protons (hydrogen ions) across the thylakoid membrane and into the space within the thylakoids. This forms a proton gradient. The protons can travel back across the membrane, down the concentration gradient, however to do so they must pass through ATP synthase. ATP synthase is located in the thylakoid membrane and it uses the energy released from the movement of protons down their concentration gradient to synthesis ATP from ADP and inorganic phosphate. The synthesis of ATP in this manner is called non-cyclic photophosphorylation uses the energy of excited electrons from photosystem II.
2.The light independent reactions of photosynthesis occur in the stroma of the chloroplast and involve the conversion of carbon dioxide and other compounds into glucose. The light-independent reactions can be split into three stages, these are carbon fixation, the reduction reactions and finally the regeneration of ribulose bisphosphate. Collectively these stages are known as the Calvin Cycle.During carbon fixation, carbon dioxide in the stroma (which enters the chloroplast by diffusion) reacts with a five-carbon sugar called ribulose bisphosphate (RuBP) to form a six-carbon compound. This reaction is catalyzed by an enzyme called ribulose bisphosphate carboxylase large amounts present within the stroma, otherwise known as rubisco. As soon as the six-carbon compound is formed, it splits to form two molecules of glycerinate 3-phosphate. Glycerinate 3-phosphate is then used in the reduction reactions.
3.Plants make their own food. They take water...