AQA biology a-level paper 2 / Edexcel A Level Biology Question and answers Paper 2 June 2023 (Salters Nuffield) GRADED A + Describe and explain the steps in the light dependent reaction of photosynthesis - ANSWER-1. photoionis

AQA biology a-level paper 2 / Edexcel A Level Biology Question and answers Paper 2 June 2023 (Salters Nuffield) GRADED A + Describe and explain the steps in the light dependent reaction of photosynthesis - ANSWER-1. photoionisation: light reaches chlorophyll in PSII, which is absorbed by an electron, which becomes excited and moves to a higher energy level. 2. the electron passes to a carrier protein in the thylakoid membrane, and is passed down a series of carrier molecules called an electron transfer chain. 3. as the electron moves down, energy is lost from the electron and is released as ATP. 4. the loss of electron from PSII is 'refilled' by an electron produced by photolysis, which also produces hydrogen and oxygen. 5. the lost electron reaches PSI, which absorbs light energy and boosts another electron to a higher energy level (excitation). 6. this electron also goes down an electron transport chain. 7. this reaches the final electron acceptor which is a proton. they combine to form H and reduce NADP to NADPH. describe and explain the role of hormones in osmoregulation. - ANSWER-eceptors in hypothalamus detect fall in water potential as they begin to shrink, causing hypothalamus to produce ADH. 2. ADH goes to posterior pituitary gland, where it is secreted into capillaries. 3. ADH goes from blood to kidneys, where it binds to receptors on the cells of of distil convoluted tubule and collecting duct. 4. this activates phosphorylase enzyme. 5. this causes vesicles, which contain water channel proteins, to fuse with cell surface membrane. hence, making it more permeable to water. 6. also increases permeability of collecting duct to urea so it passes out and lowers water potential, so more water can pass out by osmosis. describe what is happening to a neurone at resting potential. - ANSWER-1. neurone is polarised 2. Na+ actively transported out of axon 3. K+ actively transported in to axon 4. 3 sodium move out for every 2 potassium in hence, the outward movement of Na+ is greater than the inward movement of K+. this creates an electrochemical gradient as the outside is more negative than inside. 5. K+ begins to diffuse back out while Na+ diffuses back in, although most Na+ gates are closed.