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ECF Saint Too Canaan College Biology public exam exercise Movement of substances across cell membrane Name: ___________________ Class: ______ ( ) Date: _____________________ CE 2000_I_Q.3(c) 1. To study the effect of sucrose solution on plant cells, a student used the lower epidermis of a Rhoeo discolor leaf, the cells of which contain a red pigment. He mounted a piece of the lower epidermis in a sucrose solution. He then observed the epidermis under the microscope immediately and after 10 minutes. The photomicrographs below show the conditions of the same epidermal cells under the low power of the microscope : (a) Describe and explain the change in the appearance of cell A 10 minutes after mounting. (4 marks) (b) Suggest a reason why cell B did not show the same change as cell A. (1 mark) (c) The student wanted to examine cell A under the high power of the microscope. (i) State one action that he might need to take before turning to the high power objective. (1 mark) (ii) State two actions that he might need to take after turning to the high power objective. (2 marks) Bio_public exam exercise_movement of substances across cell membrane P.1 CE 2003_I_Q.1(b) 2. A student carried out a study on the effect of two different sodium chloride solutions on red blood cells. He added a drop of citrated mammalian blood to 2 cm3 of each solution in separate test tubes, A and B. After five minutes, the mixtures in both tubes appeared light red in colour. He then examined a drop of each mixture under the microscope. After repeated examinations, he found that intact red blood cells were present in tube B only and they were in two different forms as shown below: The results are recorded in the table below: Concentration of Tube solution (%) A 0.3 Average number of different forms of intact red blood cells Wrinkled Smooth 0 0 1.5 15 5 B Note: All observations were done under the same magnification. (a) (i) In tube B, some red blood cells became wrinkled. How would you explain this? (ii) Both forms of red blood cells were observed in tube B. Give a reason for this. (4 marks) (b) (c) How could the student be sure that the red blood cells in tube B had reached equilibrium with the surrounding solution at the time when he made the observation? (2 marks) Account for the absence of intact red blood cells in the mixture in tube A and the light-red appearance of the mixture. (4 marks) Bio_public exam exercise_movement of substances across cell membrane P.2 CE 2005_I_Q.8(b)(iv) 3. A student flooded the soil with water. As a result, the air content of the soil became very low. Explain why this condition may lead to poor plant growth. (3 marks) CE 2007_I_Q.2 4. One day, when Keith and Jane walked past a fresh fruit juice shop, Keith noticed that some pears were cut into pieces and stored in a tank of water before use. (a) Keith thought that the shopkeeper stored the cut pears in water in order to extract more juice. Explain the biological principle behind Keith’s idea. (3 marks) (b) Jane disagreed with Keith because she found that the shopkeeper also stored whole pears in water tanks. Explain why this observation provides Jane with evidence to oppose Keith’s idea. (2 marks) (c) Suggest one possible hygienic (衞生) problem of storing the cut pears in water tanks. (1 mark) Bio_public exam exercise_movement of substances across cell membrane P.3 AL 2003_II_Q.1(a) 5. The following diagram is a model illustrating the structure of a plasma membrane. (a) Name this model. Give two features that justify such a name. (3 marks) (b) Explain how the nature and arrangement of molecules at W are related to the permeability of the membrane. (4 marks) AL 2003_II_Q.3(a) 6. Crops that are drought resistant are economically desirable because they can survive well in environments that have a limited water supply, whereas crops that are drought sensitive cannot. Drought-resistant crops can produce a metabolite that can adjust the osmotic potential of the cell sap in the root. In drought conditions, explain how the root cells of the following plants respond osmotically. (a) drought-sensitive plants (2 marks) (b) drought-resistant plants (2 marks) Bio_public exam exercise_movement of substances across cell membrane P.4 AL 2005_II_Q.3(a)(i)(ii)(iv) 7. It has been proposed that both the mitochondrion and the chloroplast might have been prokaryotic organisms such as an aerobic bacterium and a photosynthetic bacterium respectively. They had been engulfed by a larger eukaryotic cell and then evolved to establish a relationship of mutualism (互利共生) with the eukaryotic cell. (a) Use labeled diagrams to illustrate the process of a bacterium being engulfed by a eukaryotic cell and subsequently becoming a part of the cell. (4 marks) (b) Based on the process in (i), state the origin of each layer of the double envelope of the mitochondrion and the chloroplast. (2 marks) (c) If the relationship between the eukaryotic cell and the engulfed bacterium is a predator-prey one, describe how the eukaryotic cell would digest the engulfed bacterium and benefit from it. (4 marks) Bio_public exam exercise_movement of substances across cell membrane P.5 DSE 2014_IB_Q.7 8. (a) The following is a schematic diagram of a cell membrane. In the spaces provided, label membrane components X and Y. (2 marks) (b) The vacuoles of beetroot cells contain a red pigment which will be released from the cells if the cell membrane and vacuole membrane are damaged. In an investigation, Gary placed identical cylinders of beetroot tissues into four test tubes. Each tube contained the same volume of alcohol at different concentrations. The following photograph shows the appearance of the solutions bathing the beetroot cylinders after 30 minutes: (i) From the result of the above investigation, deduce which test tube contained the highest concentration of the alcohol. (4 marks) (ii) After three hours, Gary found that the colour intensity of the solutions of all the test tubes became the same. Suggest an explanation for this. (2 marks) Bio_public exam exercise_movement of substances across cell membrane P.6 DSE PP_2012_B_Q.2 9. Digested food is absorbed into the epithelial cells of the villi. With reference to the structure of the cell membrane as illustrated by the fluid mosaic model of cell membrane, explain of the following: (a) Fatty acids (non-polar molecules) can diffuse across the cell membrane into the epithelial cell. (2 marks) (b) Amino acids (polar molecules) can be taken up from the intestinal lumen into the epithelial cell but cannot diffuse across the epithelial cell membrane back to the lumen. (3 marks) DSE 2015_IB_Q.5 10. The table below lists some historical developments about the discovery of the structure of cell membrane: (a) What is the major component noted by Overton and Langmuir? (1 mark) Bio_public exam exercise_movement of substances across cell membrane P.7 10. (b) Gorter and Grendal proposed that the major component identified in (a) existed as a bilayer (Bilayer Model). With reference to the observation of Langmuir, suggest how this major component is oriented and arranged in the cell membrane. Explain your answer. (3 marks) (c) (i) The Bilayer Model proposed by Gorter and Grendal did not mention another major component of the cell membrane. What is this component? (1 mark) (ii) With reference to the Fluid Mosaic Model, briefly describe the orientation of this component in the cell membrane. (2 marks) (d) Models are often used by scientists to explain their findings. Complete the following table to elaborate on the aspects of the nature of science involved in the use of scientific models. (2 marks) Bio_public exam exercise_movement of substances across cell membrane P.8 ECF Saint Too Canaan College Biology public exam exercise – Movement of substances across cell membrane answer 1. (a) The water potential of the cell sap of cell A is greater than that of the sucrose solution. Water moves out of the cell by osmosis. The vacuole shrinks in size pulling the cytoplasm / cell membrane away from the cell wall. 1 1 1 1 (b) The water potential of the cell sap of cell B may be the same / lower than that of the surrounding solution. 1 (i) Adjust the position of the slide until cell A is at the centre of the field of vision. 1 (ii) Adjust the diaphragm / condenser to increase the illumination of the slide. Turn the adjustment knob until the cell is in focus 1 1 (c) (8) 2. (a) (i) (ii) (b) (c) The water potential of the red blood cells was higher than that of the surrounding solution. Water moved out of the cells. As a result the cells shrank and became wrinkled. 1 1 1 Because the water potential of some red blood cells was higher than, while that of others was equal to / lower than the water potential of the surrounding solution. 1 Observe the red blood cells again after some time. The proportion of the two forms should remain the same if they had reached equilibrium in the previous observation. 1 1 The water potential of the red blood cells was lower than that of the surrounding solution. 1 Water entered the cells. The red blood cells expanded and burst releasing the haemglobin to the solution, thus making it red. 1 1 1 (10) Bio_public exam exercise_movement of substances across cell membrane P.9 3. When the soil became poorly aerated, plant roots would not have oxygen for respiration. Thus they cannot absorb mineral salts from the soil 1 1 by active transport resulting in poor plant growth. 1 (3) 4. (a) The water outside has a higher water potential than the cells of pears water moves into the cells increasing the volume of the cell content / water content of the cell. As a result, more fruit juice can be extracted. 1 1 1 (b) The skin of the fruit acts as barrier to water. Little / no water movement will occur. 1 1 (c) The water / pear may be contaminated with pathogens / lead to food poisoning. 1 (6) 5. (a) fluid mosaic model fluidity : lateral movement of protein / phospholipid molecules mosaic : protein molecules interspersed among phospholipid molecules 1 1 1 (b) Structural-functional relationships: W consists of 2 layers of phospholipid molecules / phospholipid bilayer. This allows lipid soluble substances to go through as they dissolve in it. Hydrophobic tails of the phospholipid molecules point inwards. They form an inner hydrophobic zone; make the membrane impermeable to charged molecules. 1 1 1 1 (7) 6. (a) root cells have a higher water potential than soil water water leaves the root cells by osmosis 1 1 (b) synthesis of the metabolite lowers the water potential / lowers the solute potential of root cells to below that of soil water cells will not lose water to the environment and survive / cells can still absorb water 1 1 (4) Bio_public exam exercise_movement of substances across cell membrane P.10 7. (a) Concept for mark award: Diagram showing : - invagination of plasma membrane of the eukaryotic cell to enclose the bacterium - closure of the invagination to form vacuole enclosing the bacterium inside the eukaryotic cell Labels to indicate: bacterium, eukaryotic cell, vacuole / phagosome, plasma membrane e.g. plasma membrane vacuole / phagosome bacterium eukaryotic cell 1 1 2 bacterium in vacuole bacterium eukaryotic cell (b) inner membrane comes from the bacterium outer membrane comes from the cell membrane of the eukaryote 1 1 (c) lysosome of eukaryotic cell fuses with vesicle containing the bacterium digestive / hydrolytic enzymes inside the lysosome digest the bacterium useful materials of digestion are absorbed into the cytoplasm as raw materials for growth / 1 1 1 respiration of the eukaryotic cell 1 (10) 8. (a) X: * protein (1) Y: * phospholipid (1) (b) (i) (2) tube D should have the highest concentration of alcohol (1) the amount of pigment released to the bathing solution would be the highest, as indicated by the highest colour intensity (1) this is because the phospholipids of the membrane dissolve in alcohol (1) (4) the cell membrane and vacuole membrane of the beetroot tissue bathing in the test tube with highest concentration of alcohol would be most damaged (1) Bio_public exam exercise_movement of substances across cell membrane P.11 8. (b) (ii) when the cell membrane and vacuole membrane are damaged, the pigment leaks out of the vacuole by diffusion (1) as time passes, it allows the diffusion of the red pigment in all 4 tubes to reach an equilibrium state at which the same concentration of red (2) pigment are found in the bathing solutions / the bathing solution becames saturated with the same amount of red pigment in all 4 tubes, i.e. same colour intensities (1) (8) 9. (a) The cell membrane is composed of a phospholipids bilayer. Being non-polar, the fatty acids can dissolve in the phospholipids layer and diffuse 1 1 through the cell membrane. (b) Being polar, the amino acids are repelled by the phospholipids bilayer / cannot dissolve in the phospholipids bilayer (1) and thus cannot diffuse across the cell membrane. 3 Some proteins spanning across the phospholipids bilayer (1) provide (hydrophilic) channels for the passage of the amino acids / act as carries for transporting the amino acids across the membrane. Transport of amino acids by these protein channels / carries is unidirectional. (1) (max. 3 marks) (5) Bio_public exam exercise_movement of substances across cell membrane P.12