Ans 9 a)DCholesterol E Protein/glycoprotein/intrinsic protein/protein channel/transport protein/carrier protein FPhospholipid (bilayer)/phospholipids head b)DStabilises the membrane; maintain fluidity; reduce permeability to polar (charged) particles Eallow communication across membrane; allow polar/charged, particles to pass through FAct as a barrier to polar/charged particles/ selectively permeable c)Communication between cells; cell recognition/identification d)Allow cells/ tissues/organs to work together Coordination between actions of different cells; to trigger response/reaction inside the cell Glycoprotein has a specific shape/tertiary structure Complementary to shape of ligand (signalling/communicating molecule) Ligand attaches/binds to receptor 1 Qs 10 Describe the roles of the different components of the plasma membrane Ans 10 Phospholipids, separates cell contents from exterior / acts as (physical) barrier ; (Phospholipid) allows diffusion (of suitable substance) / selective / stops some substances passing through / allows some substances through ; (carrier / transport / transmembrane) protein used for, active transport (e.g. ions against a concentration gradient, utilising energy) (channel / carrier / transport / transmembrane) protein used for facilitated diffusion (e.g. glucose) ; hydrophilic channel / water-lined pore ; protein changes shape ; aquaporins for transport of water ; transport proteins are specific ; glycoprotein / glycolipid, for cell recognition / for signalling / act as antigens ; (glycoproteins / glycolipids are) receptors for / attachment of, hormones / neurotransmitters / antibodies (glycoproteins / glycolipids allow) attachment of one cell to another ; cholesterol, determines fluidity / maintains mechanical stability (of membrane) (cholesterol) allows, bulk flow / endocytosis / exocytosis / pinocytosis / phagocytosis ; (as) membrane is self sealing ; (some proteins are) enzymes attached to membrane carbohydrate chains form hydrogen bonds with water to stabilise membrane 2 Qs 11 A student investigated the effect of temperature on the release of pigment from pieces of beetroot. She cut a fresh beetroot into four pieces and placed each piece into water at a different temperature. After 10 minutes she removed the beetroot and used a colorimeter to test how much pigment had entered the water. She placed the coloured water into the colorimeter and measured the percentage transmission of light through the water. Her results are shown in the Table The results show that below 50 C little pigment had entered the water. a)Explain why there was no transmission of light after the beetroot had been placed in water at 100 C. b)Suggest three ways in which the student could have improved her investigation 3 Ans 11 a)cell surface / plasma, membrane damaged pigment, released / leaks out pigment, absorbs / takes up, the light ACCEPT description of damage - e.g. proteins denatured / phospholipids separate / bilayer melts ACCEPT cell contents for pigment b)more samples at each temperature same / fixed, volume of water all samples same, size / surface area ref to further cutting to increase surface area pieces, rinsed / blotted, after cutting more (intermediate) temperatures same beetroot used / same part of beetroot used 4 Qs 12 The equation below represents Ficks. first law of diffusion. a)Use Ficks law to explain why some cells which are concerned with absorption by diffusion: (i)possess a brush border of microvilli. (ii)make a very thin membrane. b)In some membranes absorption involves active transport. Explain why cells in these membranes: (i)contain many mitochondria. (ii)possess large quantities of cholesterol and other lipids in their cell membranes. c)Explain how the following substances cross the plasma membrane. (i)carbon dioxide. (ii)glucose. 5 Ans 12 a) i) increases surface area/value of A; if A is increased then J is increased; thus more absorption per unit time ii)(if membrane is thin) Dx is small; thus J is large; thus more absorption per unit time (b) i)provide ATP; for active transport; to maintain/work against concentration gradient ii)ref. cholesterol will mix with water and allows passage of some water soluble substances; will accelerate diffusion/entry of non-polar substances; e.g. oxygen/carbon dioxide; c) i)diffusion; down concentration gradient; as hydrogen carbonate ions / as dissolved CO 2 ii)either: facilitated diffusion; glucose binds to carrier/protein; protein changes shape/carries glucose across; or: active transport; glucose binds to carrier/protein; energy or ATP required; protein changes shape; carries glucose across; ref. needs Na+ to be carried at the same time; Qs 13 The diagram shows part of the cell-surface membrane of a cell from the small intestine. Molecule Y acts as a cell-surface receptor for growth hormone. a)State the likely nature of molecule Y. b)State the approximate length of molecule Y. c)Explain why molecule Y is only able to recognise growth hormone. d)Suggest why pygmies are unable to achieve normal growth despite producing normal amounts of growth hormone. 7 Ans 13 a)protein b) nm c) shape of receptor site is specific to growth hormone/only growth hormone fits d)receptor damaged / mutation affects protein; unable to recognise/bind with growth hormone Qs 14 The figure shows the fluid mosaic model of the plasma membrane. a)State the approximate width of the membrane. b)Identify, A B C. c) Explain why the membrane may be described as fluid. d)Distinguish each of the following pairs. 1. exocytosis and endocytosis. 2. phagocytosis and pinocytosis. 8 Ans 14 a)range nm b) A = glycocalyx B = intrinsic/integral/internal protein; C = phospholipid bilayer; (c)lipids/proteins can move laterally/change places d)exocytosis: when material is passed out from the cell using a vesicle endocytosis: is the uptake of material into the cell by forming a vesicle with the plasma membrane phagocytosis takes solid material into the cell pinocytosis takes fluid into the cell 9 Qs 15 The graph below shows the rate of movement of solute molecules across a plasma membrane by simple diffusion and facilitated diffusion. a)Which type of uptake is shown by line Y. Explain your answer. b)State two factors which may limit the rate of simple diffusion. c)Explain how the concentration of ions such as sodium and chloride are kept at high levels outside cells but low levels within. 10 Ans 15 a) facilitated rate of transport levels off; when number of solute molecules exceeds number of carriers / proteins b)any two of: concentration gradient/difference / size/shape of molecule /polarity of molecule / temperature c) active transport / use of ATP; sodium/chloride pumps move ions out cannot re-enter because cell membrane is impermeable to these ions Qs 16 A student investigated the effect of putting cylinders cut from a potato into sodium chloride solutions of different concentration. He cut cylinders from a potato and weighed each cylinder. He then placed each cylinder in a test tube. Each test tube contained a different concentration of sodium chloride solution. The tubes were left overnight. He then removed the cylinders from the solutions and reweighed them. a)Before reweighing, the student blotted dry the outside of each cylinder. Explain why. The student repeated the experiment several times at each concentration of sodium chloride solution. His results are shown in the graph. 12 Qs 16 (continued) The student made up all the sodium chloride solutions using a 1.0 mol dm -3 sodium chloride solution and distilled water. b)Complete the table to show how he made 20 cm 3 of a 0.2 mol dm -3 sodium chloride solution. c)The student calculated the percentage change in mass rather than the change in mass. Explain the advantage of this d)The student carried out several repeats at each concentration of sodium chloride solution. Explain why the repeats were important. e)Use the graph to find the concentration of sodium chloride solution that has the same water potential as the potato cylinders. 13 Ans 16 a)Water will affect the mass / only want to measure water taken up or lost; Amount of water on cylinders varies / ensures same amount of water on outside b)4 cm 3 (of 1.0 mol dm -3 sodium chloride solution), and, 16 cm 3 (of distilled water) c)Allows comparison / shows proportional change; Idea that cylinders have different starting masses / weights d)(Allows) anomalies to be identified / ignored / effect of anomalies to be reduced / effect of variation in data to be minimised; Makes the average / mean/ line of best fit more reliable / allows concordant results e)0.35 (mol dm -3 ) whwre line crosses x axis Qs 17 A scientist investigated the effect of cyanide on the uptake of sodium ions by animal tissue. He set up two beakers, J and K. He put equal volumes of a solution containing sodium ions and equal masses of an animal tissue in each beaker. He added cyanide to beaker J He did not add cyanide to beaker K He measured the concentration of sodium ions remaining in the solution in each beaker, for 80 minutes. The graph shows his results a)Calculate the rate of uptake of sodium ions by the tissue in beaker K for the first 30 minutes. Show your working. b)Adding cyanide affects the uptake of sodium ions by the tissue. Use the graph to describe how Cyanide is a substance which affects respiration. c)Use information in the question to explain the effect of cyanide on the uptake of sodium ions by the tissue. 15 Ans 17 a)0.2 (concentration / time = 6 / 30) b)(Uptake) decreases / slower, then no further uptake / uptake / stops (Decreases) to / no uptake after 20 / 22minutes c)Stops/ reduces / inhibits respiration No / less energy released / ATP produced; (ATP / energy needed) for active transport Qs 18 Amoeba is a single-celled aquatic organism. Substances in the water can enter the cell by a variety of mechanisms. An experiment was carried out to compare the uptake into Amoeba of substance A and substance B. Some of these organisms were placed in a solution containing equal concentrations of both substances and kept at 25 C. The concentration of substances A and B, in the cytoplasm of these organisms, was measured every 30 minutes over a period of 5 hours. The results of this experiment are shown in the graph a)Using the information in the graph, compare the uptake of substance A with the uptake of substance B during this period of 5 hours. b)Substance B enters the cells by diffusion. Describe and explain how the results of this experiment support this statement. c)Substance A enters the cells by active transport. Give two differences between active transport and diffusion. 17 Ans 18 a) 1. rate is same for up to 30 minutes 2. faster (uptake) for A than B 3. (uptake of) A is linear throughout whereas (uptake of) B is not 4. uptake of substance B levels off at {2 to 2.2} hours whereas uptake of A does not 5. credit correct manipulation of comparative figures b) 1. correct ref to diffusion (of substance B) occurring due to concentration difference 2. idea of rate of uptake decreases 3. as the concentration gradient decreases 4. (net) uptake stops 5. when concentration inside cell equals that outside the cell c) 1. active transport is {against concentration gradient } 2. active transport requires ATP 3. ref to involvement of (membrane) proteins in active transport Qs 19 When blood is collected from a donor, technicians sometimes separate the red blood cells from the plasma and other blood cells. They store these red blood cells at 4 o C. They mix the red blood cells with an isotonic solution before giving them to a patient. a)Suggest one reason why red blood cells are stored at 4 o C The red blood cells are mixed with an isotonic solution before they are used. b)Explain why it is important that this solution is isotonic with the red blood cells A large volume of isotonic solution containing red blood cells is often given to injured people who have lost a lot of blood. c)Suggest how this treatment might help to save their lives. 19 Ans 19 a)Reduces enzyme / metabolic activity that might damage / break down cells OR it slows respiration / metabolism; conserving energy reserves / so cells can live long b)water potential is the same as the cells so water doesnt enter or leave cells by osmosis so cells dont burst / shrinks c)Isotonic solution: increases blood volume; so keeps circulation to (vital) organs/tissues prevents osmotic damage red cells Red cells: carry oxygen so improve supply for / maintain respiration 20 A* 21 1The diagram below shows a small polypeptide integrated into a membrane Which line in the table below correctly classifies amino acids in this polypeptide? 2The diagram shows some of the main structures which form the cell membrane. Which two structures, when hydrolysed, would release amino acids? A2 and 3 B1 and 4 C2 and 5 D4 and 5 22 3The diagram below shows the arrangement of molecules in part of a cell membrane What types of molecule are represented by X and Y? 4The diagram below refers to the plasma membrane of an animal cell Identify the two processes X and Y.. 23 5The experiment below was set up to demonstrate osmosis. Visking tubing is selectively permeable. The following results were obtained. Initial mass of visking tubing + contents = 100g Mass of visking tubing + contents after experiment = 82g The results shown above could be obtained when AR is a 5% salt solution and S is a 10% salt solution BR is a 10% salt solution and S is a 5% salt solution CR is a 10% salt solution and S is water DR is a 5% salt solution and S is water. 24 6The diagram below shows cotransport (symport) of sodium ions (Na+) and glucose into a cell lining the gut. Which line in the table below represents the relative concentrations of glucose and Na+ on the two sides of the plasma membrane when cotransport occurs? 7Cortisol is a steroid hormone it is lipid soluble. Which letter in the diagram below shows the first stage in cell signalling for this hormone? 8Carrier molecules involved in the process of active transport are made of A protein Bcarbohydrate Clipid Dphospholipid. 25 9The diagram below represents part of the plasma membrane of a red blood cell The membrane is shown magnified 2 million times. What is the width of the membrane? (1 nanometre= 1 10 6 mm) A 06 nanometres B 6 nanometres C 24 nanometres D 60 nanometres 10The following diagram illustrates the fluid mosaic model of a cell membrane Which line in the table below describes correctly the uptake of substances P and Q and the nature of substances R and S? 26 12Vitamins and minerals need to cross the plasma membrane. Vitamins A, D, E and K are fat soluble; vitamin C is water soluble Which of the following combinations utilises facilitated diffusion to cross the plasma membrane A vitamin A and calcium atoms Bvitamin C and calcium ions Cvitamin C and calcium atoms Dvitamin A and calcium ions 11Which of the following statements is/are true? 1 Electron transport chains are located in the thylakoid membranes 2 Phospholipid bilayers are impermeable to protons 3 ATP synthase maintains chemiosmotic gradients A1, 2 and 3 BOnly 1 and 2 COnly 2 and 3 DOnly 1 13Which of the following is responsible for cell-cell recognition? A Glycoprotein BPhospholipid C Hormones D Peptidoglycan 27 14The diagram below shows the distribution of protein molecules in a cell membrane. Which line in the table below correctly identifies a peripheral and an integral membrane protein? 15The diagram below represents a cross-section of a membrane magnified 2 million times. What is the actual width of the membrane? 1 nm = 1 10 6 mm A16 nm B32 nm C80 nm D160 nm 28 QsAnswer 11B 12B 13A 14B 15C QsAnswer 1A 2C 3B 4A 5A 6B 7B 8A 9B 10D 29 Multiple Choice Questions Blank Answer Grid QsAnswer QsAnswer 30