4. Cell membranes and transport
A section of Biology, 9700
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The diagram shows a phospholipid molecule divided into three regions, X, Y and Z. R, in region X, represents a range of possible chemical groups. O R O O C O CH2 CH CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH CH CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 CH2 O O – P O C O CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3 X Z Y Regions X, Y and Z affect the properties of cell surface membranes in different ways. Which row shows the effect of each region on the properties of a cell surface membrane?
9700_m21_qp_12
MCQ
2021
Paper 1, Variant 2
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High concentrations of ethanol disrupt cell membrane structure by denaturing proteins and increasing the separation of adjacent phospholipid molecules. As a result, cell membranes can decrease in thickness by up to 30% and become more permeable. Yeast cells release ethanol as a waste product of metabolism. In response to increased ethanol concentration in their environment, yeast cells are able to increase the tolerance of their cell membranes to ethanol. Which statement correctly explains a response to ethanol that could account for the increase in tolerance of yeast cell membranes to ethanol?
9700_m22_qp_12
MCQ
2022
Paper 1, Variant 2
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is a diagram representing part of the phospholipid bilayer of a cell surface membrane. OH OH OH OH OH A cholesterol fatty acid tails phosphate heads Identify the part of a phospholipid molecule, labelled A in , that forms bonds with the phosphate heads and with the fatty acid tails. Cholesterol is an important lipid component of many cell surface membranes. shows the structure of a cholesterol molecule. OH non-polar part of cholesterol molecule polar hydroxyl group Using the information in , explain the orientation of cholesterol molecules in the phospholipid bilayer, as shown in . State one role of cholesterol in phospholipid bilayers. Explain why sodium ions cannot cross phospholipid bilayers by simple diffusion. Ions and some molecules move across cell surface membranes by facilitated diffusion and active transport. Compare facilitated diffusion and active transport by stating one way in which they are similar and two ways in which facilitated diffusion is different from active transport. similarity difference 1 difference 2 Prostaglandins are small lipids produced in many tissues of the body. One role of prostaglandins is to cause inflammation at the site of an injury or infection. Inflammation is the normal first response of the immune system to injury or infection. Cyclooxygenase (COis an enzyme that catalyses one of the steps in the reaction pathway for the formation of prostaglandins from phospholipids. The reaction pathway occurs in the smooth endoplasmic reticulum (SER) of cells. Part of the reaction pathway is shown in . phospholipid arachidonic acid prostaglandin COX Suggest an advantage for this reaction pathway occurring in the smooth endoplasmic reticulum of a cell rather than in the cytoplasm. Sometimes inflammation can have side-effects, such as pain. Aspirin is a drug that can be used to reduce these side-effects. Aspirin reduces the catalytic activity of the COX enzyme by modifying the R-group of one of the amino acids. Suggest how modifying the R-group of an amino acid in the COX enzyme can reduce the catalytic activity of the enzyme. Prostaglandins are examples of cell-signalling molecules. Outline the process of cell signalling that leads to a response by the cells involved in inflammation.
9700_m24_qp_22
THEORY
2024
Paper 2, Variant 2
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Questions Discovered
418