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8.2 - Photosynthesis

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8.2 - Photosynthesis 8.2.1 - Draw and label a diagram showing the structure of a chloroplast as seen in electron micrographs * cell wall * double membrane * starch grain * grana * thylakoid * internal membrane - location of the light dependent reaction * stroma - surrounds the thylakoids - location of the light independent reaction, including the Calvin cycle. Often contain large starch grains and oil droplets, products of photosynthesis 8.2.2 - State that photosynthesis consists of light-dependent and light-independent reactions Light Dependent Reaction * sun's energy is trapped by chlorophyll * light energy is used to split water - photolysis * hydrogen is retained by the hydrogen acceptor, NADP+ * ATP is generated from ADP and phosphate, using light energy * called photophosphorylation * oxygen is given off as a waste product * occurs in the grana, in the thylakoid membranes Light Independent Reaction * chemical energy is used - ATP and the reduced hydrogen acceptor NADPH + H+ * sugars are built up using CO2 * occurs in the stroma * can occur during dark periods if products of the light dependent reactions are available 8.2.3 - Explain the light-dependent reactions In the light dependent reactions, light energy from the sun is converted into chemical energy. ...read more.


The NADPH stays in the stroma to be used in the light independent reactions. Photosystem 1 is reduced by the electrons from PS2. Photosystem 2 is then reduced so that it can absorb more light. When water is split through photolysis, electrons are given to the photosystem. This is the source of H+ ions and the waste O2. Since there is a high concentration of H+ ions in the thylakoid lumen, they can diffuse back into the stroma through the pore in ATP synthase. This process drives the phosphorylation of ADP to ATP. During these redox reactions in the light dependent reactions, the energy levels of the electrons change. This is summarised below. 8.2.4 - Explain photophosphorylation in terms of chemiosmosis A high concentration of H+ ions accumulates in the thylakoid space due to proton pumping. This results in a proton gradient, causing protons to be pumped across the membrane through the ATPase molecules. This drives the motor mechanism of the structure, reducing ADP into ATP. This is like the process used in respiration. The excited electrons the move to fill the vacancies in the reaction centre of PS2, then in PS1. ...read more.


The rate of photosynthesis is highest and blue and red, and lowest at yellow and green because of the optimum wavelength for chlorophyll. 8.2.8 - Explain the concept of limiting factors in photosynthesis, with reference to light intensity, temperature and concentration of carbon dioxide At any given time, only one of these factors will be the one limiting the rate of photosynthesis. Light Intensity Light is essential for photosynthesis, however it reaches a compensation point when the amount of oxygen being produced is the same as that being consumed in respiration. As a result, the relationship reaches a plateau at high intensities. Light energy aids in the production of H+ ions from water and ATP. On the other hand, when there is no light, the plant can only respire. Too much light can damage the chlorophyll. Temperature As the surrounding temperature increases, the rate of photosynthesis increases, with each plant reaching an optimum temperature where the rate falls off steeply. The enzymes in the reactions a temperature-sensitive. Carbon Dioxide Concentration As the concentration of CO2 increases, the rate of photosynthesis increases, before it plateaus. Each plant has a different optimum concentration. When the CO2 is the limiting factor, the NADPH simply accumulates in the stroma, stopping the photosystems from operating. ATP is formed through cyclic photophosphorylation. ?? ?? ?? ?? http://ibscrewed4biology.blogspot.com/ ...read more.

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