Membrane Structure and Transport Worksheet with Answers

You may refer to the textbook or internet. Portions not completed in class are considered homework. You’re required to use your own paper (if needed) for Concept Checks and the recommended Chapter Review (examinable). Please bring this on quiz/ test days for teacher’s inspection and recording of Learning Skills. Past year questions (if any) may encompass more than one chapter or subtopics yet to be covered. Concept Checks (For suggested answers, see Appendix A of the textbook). Answer the questions from either the eleventh (11e) or twelfth (12e) of the book edition which you’re using: 11e/ 12e Inquiry Do membrane proteins move? (p. 198) Experiment Larry Frye and Michael Edidin, at Johns Hopkins University, labeled the plasma membrane proteins of a mouse cell and a human cell with two different markers and fused the cells. Using a microscope, they observed the markers on the hybrid cell. Conclusion The mixing of the mouse and human membrane pro- teins indicates that at least some membrane proteins move sideways within the plane of the plasma membrane. Data from L. D. Frye and M. Edidin, The rapid intermixing of cell surface antigens after formation of mouse-human heterokaryons, Journal of Cell Science 7:319 (1970). WHAt IF? Suppose the proteins did not mix in the hybrid cell, even many hours after fusion. Would you be able to conclude that proteins don’t move within the membrane? What other explanation could there be? Proteins within membranes of the same species could move. But perhaps lipids and proteins from another species aren’t able to mingle with those from the other species because of some incompatibilities. 1 ConCept CHeCK 8.1 11e/ 12e 1. VIsUAL sKILLs carbohydrates are attached to plasma membrane proteins in the ER (see Figure 8.9). on which side of the vesicle membrane are the carbohydrates dur- ing transport to the cell surface? They re on the inner side of the transport vesicle membrane. Choose ONE: Q2 11e 2. WHAt IF? how would the membrane lipid composi- tion of a native grass found in very warm soil around hot springs compare with that of a native grass found in cooler soil? explain. 12e 2. WHAT IF? Some membrane proteins diffuse faster in the plasma membrane when the cytoskeleton or the extracellular matrix is artificially removed than when cells are unperturbed. Explain why. The grass living in the cooler region would be expected to have more unsaturated fatty acids in their membranes because those fatty acids remain fluid at lower temperatures. The grasses living immediately adjacent to the hot springs would be expected to have more saturated fatty acids. Which would allow the fatty acids to “stack” more closely, making the membranes less fuid and therefore helping them to stay intact at higher temperatures. 11e/ 12e ConCept CHeCK 8.2 1. What property allows O2 and CO2 to cross a lipid bilayer without the aid of membrane proteins? O2 and CO2 arae both nonpolar molecules that can easily pass through the hydrophobic interior of a membrane. 2. VIsUAL sKILLs examine Figure 8.2. Why is a transport protein needed to move many water molecules rapidly across a membrane? Water is a polar molecule, so it cannot pass very rapidly through the hydrophobic region in the middle of a phospholipid bilayer. 3. MAKe ConneCtIons Aquaporins exclude passage of hydronium ions (H3O+), but some aquaporins allow pas- sage of glycerol, a three-carbon alcohol (see Figure 5.9), as well as H2O. + Since H3O is closer in size to water than glycerol is, yet cannot pass through, what might be the basis of this selectivity? The hydronium ion is charged while glycerol is not. Charge is probably more significnt than a size as a basis for exclusion by the aquaporin channel. 2 ConCept CHeCK 8.3 Choose ONE: Q1 11e 1. how do you think a cell performing cellular respiration rids itself of the resulting CO2? 12e 1. To manipulate yeast cells experimentally, their cell walls are sometimes digested. Which type of solution should be used to preserve the cells without cell walls? Explain. Co2 is a nonpolar molecule that can diffuse through the plasma membrane. As long as it diffuses away so that the concentration remains low outside the cell, it will continue to exit the cell in this way. 11e/ 12e 2. WHAt IF? if a Paramecium (video here) swims from a hypotonic to an isotonic environment, will its contractile vacuole become more active or less? Why? The activity of paramecium caudatum’s contractile vacuole will decrease. The vacuole pumps out excess water that accumulates in the cell; this accumulation occurs only in a hypotonic environment. 11e/ 12e ConCept CHeCK 8.4 1. Sodium-potassium pumps help nerve cells establish a voltage across their plasma membranes. Do these pumps use ATP or produce ATP? explain. The pump uses ATP. To establish a voltage, ions have to be pumped against their gradients, which requires energy. 2. VIsUAL sKILLs compare the sodium-potassium pump in Figure 8.15 with the cotransporter in Figure 8.18. explain why the sodium-potassium pump would not be considered a cotransporter. Each ion is being transported against its electrochemical gradient. If either ion were transported down its electrochemical gradient, this process would be considered cotransport. 11e/ 12e ConCept CHeCK 8.5 1. As a cell grows, its plasma membrane expands. Does this involve endocytosis or exocytosis? Explain. Exocytosis: When a transport vesicle fuses with the plasma membrane, the vesicle membrane becomes part of the plasma membrane. 3 Past year questions December 2019 (C) 15. Explain what is meant by the term “fluid mosaic model” of the plasma membrane. (6 marks) The cell membrane as a tapestry of several types of molecules that are constantly moving. This movement helps the cell membrane maintain its role as a barrier between the inside and outside of the cell environment. 16. Discuss what makes up the cell membrane, and at least four different components embedded in it. (6 marks) The cell membrane is made up of embedded proteins, carbohydrates, glycolipids and glycoproteins. The plasma membrane protects intracellular components from the extracellular environment. The plasma membrane mediates cellular processes by regulating the materials that enter and exit the cell. 4 June 2019 1. The proteins found in the cell membranes of cells A and B were stained using different dyes. The membrane proteins of cell A were stained red and the membrane proteins of cell B were stained green. The cells were then fused (merged together) to form a hybrid cell. The figure below shows the distribution of proteins in the cells before and after fusion, incubated at 37 °C. (a) Using your knowledge of the properties of cell membranes, explain the observed results. (2marks) Two cells are under a fusion, merging together, to form a hybrid cell. The membranes are dyed so that they are visible before and after the fusion. (b) If the cells were incubated at 0 °C, predict the outcome of the experiment. (2 marks) Either incomplete fusion or an uneven ratio of fusion from cells A and B. (c) Give an explanation for your answer in (b). (1 mark) Due to low temperatures, lower than 37 degrees; the atoms contracted thus the reaction was slower taking longer to finish the reaction or making an uneven ratio of cell fusion. (d) Provide ONE reason as to why different dyes were used. (1 mark) So that the proteins are clearly visible before and after fusions. 5 Dec 2018 1. The figure below is that of a typical cell membrane of various organs you have studied. You may refer to the figure below to answer the questions which follow. a. Why doesn’t the cell surface membrane provide a barrier to the entry of hydrophobic molecules into the cell? (2 marks) (Hint: Relate your answers to the property of the major component of the plasma membrane) The plasma membrane is selectively permeable, hydrophobic molecules and small polar molecules can diffuse through the lipid layer. a. Suggest three reasons why exchange between the cell and its environment is essential. (3 marks) Cells need to move water, materials for energy, waste to maintain homeostasis. Gain nutrients Secrete hormones/enzymes 6 May/ June 2018 Q1. The following experiment aimed to determine when the water concentration in the potato cells equalled that of the surrounding solution. Comparable 2 mm thick discs of potato tuber were cut out and weighed. Replicate samples were taken and placed in distilled water and a series of sucrose solutions, ranging from 0.1 to 0.6 M, in covered dishes at a constant temperature of 20 C. After one hour, the samples were removed and dabbed with tissue paper rapidly between sheets of filter paper and re-weighed. The results are shown in the figure below. o (a) With reference to the graph above, fill up any THREEcells in the table below in order to explain the changes occurring in the potato discs in the sucrose solutions of various concentrations (M) below in terms of water potential, net water movement and direction of water movement. (Think of water potential as ‘water concentration’, though this term is inaccurate) (3 marks) 7 0.1 M net water movement 0.35 M 0.6 M Net water movement into potato cells. The direction of water movement water potential This is because water potential is *__________ in the cell sap than the sucrose solution Q1. (b) After 24 hours, potato cells from one of the sucrose concentrations were observed under microscope as shown as in the figure below. Suggest ONE sucrose concentration from the graph above that caused the cells to appear as they do below. (1 mark) 8 2017 1. One of the most important functions of cell membranes is to control the movement of substances in and out of the cell. a) With the aid of a diagram, explain how the structure of the cell membrane is able to accomplish this task. (5 marks) - Simple diffusion Facilitated diffusion Primary active transport (ATP) b) Using the diagram, explain briefly how the following molecules are able to get into or out of the cell: O2, H2O, Na+, glucose, large proteins. (5 marks) - O2/H2O ⇒ passive diffusion Na+ ⇒ Diffusion through an aqueous channel Glucose ⇒ Facilitated diffusion with a carrier protein Large proteins ⇒ Active transport against concentration gradient with the input of ATP (energy) Assessment As Learning Assessment As Learning: Assessed by: _________________________________ channel carrier Made of protein protein shape fixed changes Binding to transport substance? no yes 9 Membrane transport comparison worksheet (combined as of 04 Feb 2021) (Teacher’s reference: Membrane transport exercises SC Jan 2015) You may refer to the textbook or internet. Portions not completed in class is considered homework. You’re required to use your own paper (if needed) for Concept Checks and the recommended Chapter Review (examinable). Please bring this on quiz/ test days for teacher’s inspection and recording of Learning Skills. Past year questions (if any) may encompass more than one chapter or subtopics yet to be covered. Assessment As Learning: Assessed by: _________________________________ Q. What are the differences between passive and active transport? Compare among osmosis, diffusion, various carrier-mediated & bulk active transport. Passive Active Simple diffusion Osmosis Facilitated diffusion Active transport (carrier-mediated ) Phagocytosis (non-carrier-medi ated active transport 1) Pinocytosis (non-carrier-medi ated active transport) Exocytosis Part of membrane where process takes place Lipid bilayer Lipid bilayer, Transmembrane transport proteins in membrane Transmembrane transport proteins in membrane Entire membrane Entire membrane Entire membrane Energy requirement No energy needed None Yes Energy needed Energy needed Energy needed Transmembrane transport protein in the membrane None Primary: source direct Secondary: source direct 1 Solomon , Berg and Martin (2005) (7th Ed). P. 110. 10 Simple diffusion Osmosis Facilitated diffusion Active transport (carrier-mediated ) Phagocytosis (non-carrier-medi ated active transport 2) Pinocytosis (non-carrier-medi ated active transport) Exocytosis Direction of molecule movt. relative to conc. Gradient Concn gradient must exist, move down concn gradient Water potential must exist, move down water potential gradient Concn gradient must exist, move down concn gradient (High low) Concn gradient need not exist, can move with or Not necessary Not necessary Not necessary Transport protein None aquaporins (channel protein) channel and carrier proteins carrier protein None None None Types of molecules that diffuse through CO2 hydrocarbons, Water Polar molecules, charged particles/ ions, Polar molecules, charged particles/ ions, Only specific molecules can be transported by specific transport proteins Only specific molecules can be transported by specific transport proteins NA. Taking in large solid particles or even cells NA. Uptake of materials in 3 liquid form / Taking in droplets of dissolved materials 4 Both direction depends on concn gradient One direction only per solute, either in or out One direction only – from outside to inside One direction only from inside to outside Direction of movement of transported substance (in/out of cell) 2 3 4 Small lipid soluble molecules Both direction depends on concn gradient Both direction depends on water potential gradient against concn gradient One direction only from insid to outside Solomon , Berg and Martin (2005) (7th Ed). P. 110. NJC. SBM Instructor’s Manual, Chp 5. Answer to p. 112. 11