Membrane Permeability Plasma membranes are semi-permeable – this means that some substances can pass through and others cannot. What is it that determines.

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Membrane Permeability Plasma membranes are semi-permeable – this means that some substances can pass through and others cannot. What is it that determines what substances pass through? The substance has to be very soluble in the oily phospholipid bilayer. Steroid hormones, oxygen and carbon dioxide are examples of such molecules. steroid hormone oxygen carbon dioxide Glucose Protein Lipid SOLUBLE INSOLUBLE

Permeability Three factors affect the permeability of a cell membrane:  heat  ethanol  pH Try and explain how these factors affect the membrane, by referring to the fluid mosaic model. A temperature exceeding the optimum and pH levels beyond the normal range can denature the membrane’s proteins. Ethanol dissolves the lipid components of the membrane. This all makes the membrane far more permeable acting as if it is full of holes. Help

Absorbance % Experiment 5°C 0.04 Click the arrows to adjust the temperature

Experiment 22.5°C Absorption % 0.075

Experiment 40°C Absorption % 0.12

Experiment 52°C Absorption % 0.25

Experiment 60°C Absorption % 0.64

Experiment 68°C Absorption % 0.70

Practical assessment Aim/prediction 2 Experimental design – drawing of apparatus, variables, range, control, risks. 9 Results – table, graph13 Analysis – trend, reliability, accuracy, conclusion, explain.15 Further work 5

Results Results Table – draw a graph of the data Temperature (°c)Absorption/ % (Room Temperature)

Results Results Table Graph Temperature (°c) Absorption/ % (Room Temperature)

Conclusion The increase in temperature causes the proteins in the membrane to denature and so its permeability increases, causing substances (purple dye in this case) to escape.

Conclusion As the temperature increases, the pigment/particles move quicker and diffusion happens at a faster rate. At around 60˚C the proteins in the membrane denature and the pigment can escape through the holes now present in the membrane. At 70˚C the lipids can melt and cover the gaps, temporarily preventing the dye from escaping.