Question

Describe the light reactions of photosynthesis and, for both a C3 and a C4 plant, trace the path of a carbon dioxide molecule from the point at which it enters a plant to its incorporation into a glucose molecule. Include leaf anatomy and biochemical pathways in your discussion of each type of plant

Answer 1

Solution: Light reaction also known as thylakoid reactions occurs in the thylakoid regions of specialized organelle chloroplast. The thyalkoid membranes of chloroplast can be divided into grana lamellae (the stacked regions) and stoma lamellae (the unstacked regions). On these regions of thylakoid have different proteins arranged for harvesting light and for the transport of electrons to the terminal electron acceptor NADP+. The light absorbed by the pigments are funneled into reaction center chlorophyll, P680 for photosysytem 2 (PSII) and p700 for photosystem 1(PSI). These photosystem absorb lights from different wae lengths. Photosystem 2 prefers light from red region of the spectrum whereas photosystem 1 prefers light from far red region. The water spliting complex near PSII splits water releasing H+ into the lumen of thylakoid and electrons into the elecreon transport proteins. Different electron transport proteins in Z scheme transport these electrons to reduce NADP+ into NADPH by ferredoxin NADP+ reductase. The NADPH generated would be used in carbon reactions. During the electron transport, a proton gradient is also generated. This gradient is utilized for the synthesis of ATP molecule later by ATP synthase protein.