Explain the basic steps in the first half of photosynthesis. Describe the movement of electrons and the importance of hydrogen ions in developing a proton gradient that allows for ATP production.

This simply refers to photolysis of water.

Explanation

Generally,two steps are involved in photosynthesis.

The light  dependent stage or light reaction,(which is the first part of photosynthesis,

The light independent stage (which is the second part.)

The light independent reactions involved the trapping of sunlight by the photo systems, in the leaves,and the splitting of the water molecules by sunlight.

          H20 + Sunlight → 1/2H+ +2 e- +1/2 O2.

The  movement of electron can be cyclic or non cyclic photophosphorylation, In Cyclic, photo system 1 absorbs  the electrons and pass these to the primary pigments in the leaves. This excited the electron  in chlorophyll molecule to higher energy levels , The electron emitted from the leaves is by a process called by photoactivation The emitted electron do not return to the photosystems,rather they are pick up by the primary electron acceptors  and returned to the chlorophyll molecules by electron carriers,NADP.

During this process Energy is released for ATPase synthase of  ATP for phosphorylation of ADP with phosphate,

In Non-cyclic photophorylation,photosystem I and II  absorbs the electrons as Z-scheme  movement of electrons.,Photoactivation  of chlorophyll takes place as in the Cyclic.The primary electron acceptors  takes the  excited electrons  to move along the chain of electron carriers.This makes the photosystems positively charged.

Hence to regain stability the primary pigment of photo system 1 takes electrons from photosystem II.To replace its lost electrons, P II takes electrons from the photolysis of water.ATP is generated  as the carriers molecules transport electrons from the energy produced.

The hydrogen ions is used for the production of electrochemical gradients,which supplies the energy used by the ATPase synthase for the ATPs production.The process is called chemiosmosis. It  involved the  transports of H atoms by NADPH into the stroma,and the splitting of these into protons and electrons,The electrons  form ETC,which forms the PMF.The latter  pumped protons  into the thylakoid membrane,and as this returns it  generate the electrochemical gradient.

The ATP is used in the Calvin Cycle for CHO,proteins productions,

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