Photosynthesis Summary

Photosynthesis

The main photosynthetic tissue of the leaf is the palisade mesophyll tissue.

These cells contain numerous organelles called chloroplasts, which are the site of photosynthetic reactions. These organelles are surrounded by a double membrane and they contain many internal membranes (thylakoid / grana) which provide a large surface area to hold numerous molecules of the photosynthetic pigment chlorophyll. They also contain their own DNA and ribosomes which allow them to synthesise their own proteins and enzymes needed for photosynthesis. Ther may be storage grains of the polysaccharide, starch present in the fluid part of the chloroplast (the stroma).

Light Dependent Reaction:

During the Light Dependant Reaction (LDR), light energy (of particular wave lengths: colours red and blue) is absorbed by chlorophyll molecules leading to photoionisation of the chlorophyll. This is where the light energy is transferred to electrons, raising them to a higher energy level so they are released from chlorophyll and transferred to the electron transport chain - a series of carrier molecules on the thylakoid membranes.

The Electron Transport Chain (ETC) transfers the electrons, in a series of oxidation - reduction reactions along the carrier molecules: each successive carrier is at a lower energy level and so the electrons lose energy as they are transferred between the carriers. At the end of the electron transport chain, the electrons are accepted by the co-enzyme NADP to form NADPH.

The energy lost by the electrons in the electron transport chain is used to actively transport hydrogen (H+ ions) from the stroma into the thylakoid lumen, building up a higher concentration than in the stroma. This creates an electro-chemical gradient across the thylakoid membranes. The protons then…