ATP Synthesis

• In photosynthesis, light provides the energy needed to build organic molecules such as glucose. 
• This energy can be used to form chemical bonds within ATP, it is the breaking of these bonds which releases energy used to form bonds as glucose is made.
• Glcuose and other organic molecules are broken down in respiration, the energy realeased from this is used in the syntehsis of ATP
• The ATP is then used in the cells to break bonds in metabnollic reactions. 

Energy (sun) ➡ ATP ➡ Large organic molecules (glucose) ➡ ATP ➡ processes requiring energy

• Photosynthesis 
• Respiration

• The ATP that is made in photosynthesis and respiration is usually synthesised by chemiosmosis. 
• Chemiosmosis- involved the diffusion of protons fron a region of high concentration to a region of low concentration through a partially permeable membrane.
• As the protons flow down the cocnentration gradient, energy is released which is used to attach a phosphate (Pi) to ADP
• ADP + Pi ➡ ATP

There are two ways in which electrons can be excited: 

• Those present in pigment molecules can be excited by absorbing light from the sun. Chlorophyl is an example of one such pigment. 
• High energy electrons are released when chemiocal bonds are broken in respiratory substrate molecules (glucose)
• The excited electrons pass into an electron transportchain and are then use to generate a proton gradient. 

• Consists of a series of electron carriers, each one has a progressively energy levels.
• As the high energy electrons move from carrier to carrier energy is released.
• The release of energy pumps protons across a membrane in turn creating a concentration gradient across the membrane, this is a proton gradient. 
• The proton gradient is maintained due to the impermeability of the membrane to hydorgen ions. 
• The only way that protons can move back through the membrane down their concentration gradient is through hydrophilic membrane channels that are linked to the enzyme ATP synthase. 
• The flow of proons through these channels provides the energy required to synthesis ATP. 
• In photosynthesis, ATP is used to synthesise glucose, the ATP produced in respiration provides the energy required by metabollic processes. 
• Oxidative phosphorylation and photophosphorylation are also vital to chemiosmosis.