A-level Biology OCR [New Spec] - Photosynthesis: The Light Dependent Stage | A-level Biology | OCR, AQA, Edexcel

Photosynthesis: The Light Dependent Stage in a Snap! Unlock the full A-level Biology course at http://bit.ly/2VYdiTw created by Adam Tildesley, Biology expert at SnapRevise and graduate of Cambridge University. The key points covered of this video include: 1. Overview of the Light Dependent Stage 2. Photolysis of Water Overview of the Light Dependent Stage The light dependent stage is the first stage of photosynthesis and occurs in the thylakoids of the grana in chloroplasts. The light dependent stage can be divided into three steps: The photolysis of water, The production of ATP in the presence of light - this process is called photophosphorylation, The formation of reduced NADP. Photolysis of Water The photolysis of water is the first step in the light dependent stage of photosynthesis. In photolysis, water molecules are split into protons, electrons and oxygen in the presence of light. Photolysis is catalysed by an enzyme which is present in photosystem II (PSII). The oxygen produced during photolysis is used for respiration by the plant. If the rate of photosynthesis is greater than the rate of respiration, any excess oxygen will diffuse out the plant leaves via the stomata. The protons and electrons from photolysis will be important in the next step of the light dependent reaction which is photophosphorylation. Summary The light dependent stage of photosynthesis takes place in the thylakoid membranes of the grana in the chloroplasts The light dependent stage consists of three main steps which are photolysis, photophosphorylation and the reduction of NADP The photolysis of water is the first step of the light dependent stage In photolysis water is broken down in the presence of light to form oxygen, electrons and protos The oxygen formed is used for respiration or diffuses out of the stomata if in excess The electrons and protons are used later in the light dependent stage during photophosphorylation