Photosynthesis

The chloroplast You need to be able to draw and label this for your exam.

Photosynthesis is a two step process: 1 Photosynthesis is a two step process: 1. The light dependent reactions convert the light energy into chemical energy (ATP) 2. The light independent reactions use the chemical energy to synthesise organic compounds (e.g. glucose) The organic molecules produced in photosynthesis can be used in cellular respiration to provide the energy needed by the organism

Light spectrum The visible light spectrum includes many colours, we are going to consider three regions of the spectrum: Red end of spectrum Green middle of spectrum Blue end of spectrum When struck by a particular wavelength of light substances: Absorb that wavelength Reflect that wavelength

Light Dependent Reactions Light stimulates chlorophyll to release electrons, which results in the production of ATP Light energy also splits water molecules (photolysis), producing oxygen and hydrogen The hydrogen is taken up by a hydrogen carrier (NADP+) to form NADPH The splitting of water also releases electrons, which replace those lost by the chlorophyll The ATP and hydrogen (NADPH) are taken to the site of the light independent reactions Photophosphorylation helps to make ATP Occurs on the Thylakoid membrane Can be cyclic or non-cyclic

Light independent reaction ATP and hydrogen (carried by NADPH) are products of the light dependent reactions They are used to fix carbon molecules together (add CO2 to basic carbon compounds) This allows for the production of more complex organic molecules (e.g. sugars) These organic molecules can then be stored to use in cellular respiration as required

Short Video clip to summarise

Light dependent reaction Thylakoid Two major groups of pigments involved – chlorophylls and the carotenoids Organization region: Chlorophyll α molecules (P680 and P700) Accessory pigments A protein matrix Reaction centre: Pair of chlorophyll molecules A matrix of protein A primary electron acceptor

Photosystems Photosystem I – Most efficient at 700nm Photosystem II – Most efficient at 680nm

Key Summary Questions What are the names of the two chlorophyll α molecules and what photosystems are they found in? What name do we give the ‘packet’ of energy from light? What are the final products of the light-dependent reaction? What is the name of the electron carrier involved in the final stages of Photosystem I? What is the name of the process that is involved in the production of ATP?

Key Summary Questions What are the names of the two chlorophyll α molecules and what photosystems are they found in? P680 – PS 2, P700 PS 1 What name do we give the ‘packet’ of energy from light? Photons What are the final products of the light-dependent reaction? NADPH (reduced) and ATP What is the name of the electron carrier involved in the final stages of Photosystem I? ferredoxin What is the name of the process that is involved in the production of ATP? chemiosmosis

The light independent reaction