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Transport Systems in Living Things Diffusion, Osmosis and Active transport Diffusion is the spreading out of one substance through another due to the random motion of particles. Diffusion is the net movement of molecules or ions in response to a concentration gradient by moving from the region of higher concentration to a region of lower concentration. (Concentration - Number of molecules or ions per unit volume. Concentration gradient - Difference in concentration between adjoining regions of fluid.) The rate of diffusion depends on five factors: 1. Size. It takes more energy to move a large molecule than it does to move a small one. Thus, smaller molecules diffuse more quickly than larger ones. 2. Temperature. Molecules move faster at higher temperature, so they collide more often. Thus, the higher the temperature, the faster the diffusion. 3. Steepness of the concentration gradient. The rate of diffusion is higher with steeper gradients, because molecules collide more often in a region of greater concentration. 4. Charge can affect the rate and direction of diffusion between two regions. Each ion or charged molecule in a fluid contributes to the fluid’s overall electric charge. A difference in charge between two regions can affect the rate and direction of diffusion between them. For example, positively charged substances, such as sodium ions, diffuse toward a region with an overall negative charge. 5. Pressure. Diffusion may be affected by a difference in pressure between two adjoining regions. Pressure squeezes molecules together, and molecules that are more crowded collide and rebound more frequently. Thus, diffusion occurs faster at higher pressures. Figure 1A Figure 1A can help to visualize diffusion across a membrane. Figure 1A shows a solution of green dye separated from pure water by a membrane. Assume that this membrane has microscopic pores through which dye molecules can move. Thus, we say it is permeable to the dye. Although each molecule moves randomly, there will be a net movement from the side of the membrane where dye molecules are more concentrated to the side where they are less concentrated. Put another way, the dye diffuses down its concentration gradient. 1 Eventually, the solutions on both sides will have equal concentrations of dye. At this dynamic equilibrium, molecules still move back and forth, but there is no net change in concentration on either side of the membrane. Figure 1B Figure 1B illustrates the important point that two or more substances diffuse independently of each other; that is, each diffuses down its own concentration gradient. Diffusion in Cells Diffusion is an important means by which materials are exchanged between a cell and its environment. For example, cells constantly use oxygen in various chemical reactions. Consequently, the oxygen concentration in cells always remains low. The cells, then, contain a lower concentration of oxygen than does the environment outside the cells. This creates a concentration gradient, and the oxygen molecules diffuse from the outside of the cell to the inside. Diffusion can take place only as long as there are no barriers to the free movement of molecules. In the case of a cell, the plasma membrane surrounds the cell and serves as a partial barrier to the movement of molecules through it. If a molecule is able to pass through the membrane, the membrane is permeable to the molecules. Because the plasma membrane allows only certain molecules to pass through it, it is selectively permeable. A molecule’s ability to pass through the membrane depends on its size, electrical charge, and solubility in the plasma membrane. In certain cases, the membrane differentiates on the basis of molecular size; that is, the membrane allows small molecules, such as oxygen or water, to pass through but prevents the passage of larger molecules. The membrane may also regulate the passage of ions. If a particular portion of the membrane has a large number of positive ions on its surface, positively charged ions in the environment will be repelled and prevented from crossing the membrane. Because a cell does not have to do work when molecules diffuse across its membrane, such movement across a membrane is called passive transport. Much of the traffic across cell membranes occurs by diffusion. Diffusion in living things In living organisms, many organs have specialised features to improve the efficiency of diffusion of materials. These specialised features are mainly developed to increase the surface area so that they can carry out their functions more efficiently. Some examples of important diffusion of substances in living things: 2 - Gases exchange between the lungs and blood capillaries - Absorption of simple food substances in the small intestine - Gases exchange between the stomata and the atmosphere Osmosis is the diffusion of water across a membrane Osmosis is the movement of water molecules from the region of higher water concentration to a region of lower water concentration through a partially permeable membrane. Partially permeable membrane is a membrane that only allows certain substances to pass through but not the other. It restricts the movement of substances based on their size. Substances of larger size such as starch cannot pass through it. The partially permeable membrane can be divided into two groups: Natural: Cell membrane found in plant cells and animal cells Artificial: Visking tubing and cellophane bag A dilute solution has a higher water concentration than a concentrated solution. The concentration of water molecules is higher in a dilute solution. Therefore, water molecules move from the dilute solution into the concentrated solution. Figure 2.The selectively permeable membrane dividing this Ushaped tube permits water but not solutes to pass. Water diffuses from the left side (low solute concentration) toward the right side (high solute concentration). At equilibrium, water flow is equal in both directions, and the solute concentrations will be equal on both sides of the membrane. 3 Osmosis affects the size and the mass of the living cells. When water enters a potato strip, it causes the length of the strip to increase due to the expansion in the size of the cells inside it. The mass of the strip increases as well due to net gain of water molecules. Some examples of osmosis in living things: — Uptake of water molecules from the soil by the root hair cells — Absorption of water molecules in human large intestine Effect of osmosis on living cells The term tonicity refers to the ability of a surrounding solution to cause a cell to gain or lose water. The tonicity of a solution mainly depends on its concentration of solutes that cannot cross the plasma membrane relative to the concentration of solutes inside the cell. Figure 3 illustrates how the principles of osmosis and tonicity apply to cells. The effects of placing an animal cell in solutions of various tonicities are shown in the top row of the illustration; the effects of the same solutions on a plant cell are shown in the bottom row. When the overall solute concentrations of the two fluids differ, the fluid with the lower overall concentration of solutes is Figure 3 said to be hypotonic. The other one, with the higher overall solute concentration, is hypertonic. Fluids that are isotonic have the same overall solute concentration. When an animal cell is immersed in a solution that is isotonic to the cell, the cell’s volume remains constant. The solute concentration of a cell and its isotonic environment are essentially equal, and the cell gains water at the same rate that it loses it. In your body, red blood cells are transported in the isotonic plasma of the blood. What happens when an animal cell is placed in a hypotonic solution, a solution with a solute concentration lower than that of the cell. (Can you figure out in which direction osmosis will occur? Where are there more free water molecules available to move?) The cell gains water, swells, and may burst (lyse) like an over-filled balloon. 4 The upper right shows the opposite case — an animal cell placed in a hypertonic solution (hyper, above), a solution with a higher solute concentration. The cell shrivels and can die from water loss. For an animal to survive in a hypotonic or hypertonic environment, it must have a way to prevent excessive uptake or excessive loss of water. The control of water balance is called osmoregulation. For example, a freshwater fish, which lives in a hypotonic environment, has kidneys and gills that work constantly to prevent an excessive buildup of water in the body. Figure 3, a plant cell immersed in an isotonic solution is flaccid (limp). In contrast, a plant cell is turgid (very firm), which is the healthy state for most plant cells, in a hypotonic environment. To become turgid, a plant cell needs a net inflow of water. Although the somewhat elastic cell wall expands a bit, the pressure it exerts prevents the cell from taking in too much water and bursting, as an animal cell would in a hypotonic environment. Plants that are not woody, such as most house-plants, depend on their turgid cells for mechanical support. In a hypertonic environment (bottom right), a plant cell is no better off than an animal cell. As a plant cell loses water, it shrivels, and its plasma membrane pulls away from the cell wall. This process, called plasmolysis, causes the plant to wilt and can be lethal to the cell and the plant. The walled cells of bacteria and fungi also plasmolyse in hypertonic environments. Thus, meats and other foods can be preserved with concentrated salt solutions because the cells of food-spoiling bacteria or fungi become plasmolysed and eventually die. Simple diffusion gets rid of an existing concentration gradient. Often, however, a cell needs to do the opposite: create and maintain a concentration gradient. A plant’s root cell, for example, may need to absorb nutrients from soil water that is much more dilute than the cell’s interior. In active transport, a cell uses a transport protein to move a substance against its concentration gradient—from where it is less concentrated to where it is more concentrated (Figure 4). Because a gradient represents a form of potential energy, the cell must expend energy to create it. Energy for active transport 5 often comes from ATP. Cells must contain high concentrations of K+ and low concentrations of Na+ to perform many functions. In animals, for example, sodium and potassium ion gradients are essential for nerve and muscle function. One active transport system in the membranes of most animal cells is a protein called the sodium– potassium pump (Figure 5 ), which uses ATP as an energy source to expel three sodium ions (Na+ ) for every two potassium ions (K+ ) it admits. Maintaining these ion gradients is costly: the million or more sodium–potassium pumps embedded in a cell’s membrane use some 25% of the cell’s ATP. Figure 5. The Sodium–Potassium Pump. This ―pump‖ is a protein embedded in the cell membrane. It uses energy released in ATP hydrolysis to move potassium ions (K+) into the cell and sodium ions (Na+) out of the cell. In each case, the ions move from where they are less concentrated to where they are more concentrated. MCQ 1. A root hair cell absorbs water through__________because the cell sap of the root hair cell has a__________water potential than the water in the soil. A. osmosis; higher B. osmosis; lower C. diffusion; higher D. diffusion; lower 2. Which of the following represents the reason why glucose molecules can pass through the Visking tubing? A. Glucose molecules are very heavy. B. Glucose molecules are very large. C. Glucose molecules are very small. D. Glucose molecules are very light. 6 3. Which of the following is an example of diffusion in a plant? A. Carbon dioxide from the air moving into a photosynthesizing leaf B. Nitrate ions moving into root hairs against a concentration gradient C. Sugars in the phloem moving from leaves to roots D. Water in the xylem moving from roots to leaves 4. Which of the following processes involves osmosis? A. Circulation of blood in the blood vessels B. Conduction of water up the xylem C. Absorption of water in the large intestines of humans D. Uptake of oxygen in the alveoli 5. Red blood cells were placed in water and in three salt solutions of different concentrations. Cells from each solution were examined under the microscope. Which diagram shows the appearance of a cell in pure water? (B) 6. The diagrams show a mixture of water and sugar solution at two different times By what process has the two liquids been mixed? A. Absorption B. Conduction C. Diffusion 7. The apparatus shown in the diagram was set up. After one hour, the water in the beaker turned red. What is the most likely reason for this colour change? A. Molecules of red ink move through the membrane by diffusion. B. Molecules of red ink move through the membrane by osmosis. C. Molecules of water move through the membrane by diffusion. D. Molecules of water move through the membrane by osmosis. 7 D. Osmosis 8. Which of the following are examples of osmosis? (1) The absorption of water by root hairs (2) The absorption of mineral salts by root hairs (3) The absorption of water by dry cotton wool (4) The absorption of water by the large intestines (5) The movement of water across the surface of the floor A. (1) and (2) only B. (3) and (5) only C. (1) and (4) only D. (1), (4) and (5) only 9. The diagram below shows an experimental set-up to investigate osmosis. Which of the following combinations of liquids would cause X to rise to the highest level in the glass tube after three hours? Liquid X Liquid Y A Concentrated sucrose solution Dilute sucrose solution B Concentrated sucrose solution Water C Dilute sucrose solution Concentrated sucrose solution D Water Concentrated sucrose solution For questions 10 and 11, refer to the following diagram of four plant cells. 10. Which of the cells shown above have low water potential? A. P and Q B. Q and S C. P and R D. R and S 11. If the cells remain in contact as shown, which of the following shows the direction of movement of water molecules? A. R to Q and Q to P B. Q to S and R to Q C. P to Q and R to S D. Q to P and S to R 8 For questions 12 and 13, refer to the following diagram which represents an experiment that is used to investigate movement of substances in potato tissue. 12. Which diagram shows the result after twenty-four hours? (B) 13. Which of the following processes are shown in the above experiment? A. Photosynthesis B. Osmosis C. Respiration D. Diffusion 14. An experiment was set up as shown in the diagram below. After some time has elapsed, the Visking tube containing liquid X collapsed while the tubing containing liquid Y was firm and hard. Which of the following could be a correct description of the liquids at the start of the experiment? Liquid X Liquid Y A concentrated sucrose water solution B dilute sucrose solution concentrated sucrose solution C water concentrated sucrose solution D water dilute sucrose solution Liquid Z dilute sucrose solution water dilute sucrose solution concentrated sucrose solution 15. A cube of fresh potato is weighed. It is then placed in a test tube containing a dilute solution of sucrose. After a day, its mass has increased. Which process has occurred and what has happened to the concentration of the solution in the test tube? process occurred concentration of solution A diffusion of sucrose molecules decreased B diffusion of sucrose molecules increased C osmosis of water molecules decreased D osmosis of water molecules increased 9 16. The diagram below shows an apparatus used to investigate osmosis. After a few hours, which changes in levels will occur and which substances will move across the membrane? Level M Level N Substance A. Fall Rise Starch B. Fall Rise Water C. Rise Fall Starch D. Rise Fall Water Questions 17 and 18 refer to the diagram below. It shows a typical plant cell after being placed in beaker of salt solution for 10 minutes. 17. What could be the concentration of the salt solution in the beaker? A. 5% salt solution B. 15% salt solution C. 20% salt solution D. 25% salt solution 18. Which process is involved to cause this observation of the cell? A. Osmosis B. Diffusion C. Expansion D. Active transport 19. The diagram below shows an experiment to investigate the movement of substances. Which of the following most likely will not happen to the respective regions 1, 2 and 3 at the end of the experiment? A. Region 1 increases in volume. B. There are same number of glucose molecules in these three regions. C. Regions 2 and 3 have equal volume. D. Blue-black observed in region 3 when two drops of iodine is added to it. 20. The diagram below shows the effect of solution Y on a red blood cell after half an hour. 10 Which statement is not correct from this observation? A. Solution Y contains a higher concentration of solute than in the red blood cell B. The cell membrane of this red blood cell eventually will break apart. C. The red blood cell is said to be dehydrated. D. The red blood decreases in its volume and becomes soft. Short Structured Questions 1(a) Define 'diffusion'. (b) Define 'osmosis’. (c) Compare and contrast diffusion and osmosis using the table below. diffusion osmosis particles involved movement of particles involvement of membrane (d) State two examples in living things where diffusion and osmosis occur. particles involved movement of particles involvement of membrane diffusion Small particles such as glucose and ions High to low concentration osmosis Only water molecules High to low water potential no Partially permeable membrane (d) Diffusion: absorption of glucose in the small intestines, entry of carbon dioxide through stomata Osmosis: absorption of water by root hair cells and the large intestines 11 2. Study the diagram carefully. (a) The apparatus is left standing for a few hours. What will happen to the level of sucrose solution in the capillary tube? Explain your answer. (b) With the help of the key provided, draw the movement of particles in the movement in the space provided. (c) The sucrose solution in the Visking tube was replaced with glucose solution. With the help of the key provided, draw the movement of particles in the experiment in the space provided. (d) What does this experiment show you about the size of the two sugar molecules and their ability to cross the partially permeable membrane of the Visking tube? (e) Other than size of molecules, state two other factors that affect the movement of substances across a partially permeable membrane. 12 (a) The sucrose solution level will increase. The water potential in water is higher compared to sucrose solution. Hence osmosis of water molecules into the sucrose solution, across the partially permeable Visking tube occurs. (d) Glucose molecules are smaller than sucrose molecules and hence can cross the partially permeable membrane. Sucrose molecules are too big to cross. (e) Size of membrane pore; temperature. 13 3. As shown in the diagram below, cell X was placed in a beaker of solution A for 20 minutes and showed no visible difference, cell X was then placed in solution B. After 20 minutes in solution B, it was noticed that cell X had become bloated. (a)(i) Identify cell X. (ii) Explain why there was no visible difference in cell X after being placed in solution A (b)(i) Explain the appearance of cell X after being placed in solution B. (ii) Describe how cell X is adapted for its function of water absorption (a)(i) Root hair cell (ii) No difference in water potential. No net movement of water molecules by osmosis (b)(i) Difference in water potential. There was net movement of water molecules from solution B into the cell by osmosis. (ii) Protrusion increases surface area to volume ratio for efficient absorption of water by osmosis. Concentrated cell sap keeps internal water potential low, so osmosis of water molecules into the cell is possible. 14 4 The picture below shows a plant cell that was placed in a concentrated sucrose solution. (a) State the condition of the plant cell. (b) Explain the appearance of the cell. (c) What does the part labelled Y contain? Explain the reason for your answer. (d) The same cell was then placed in pure water. The following diagram shows the appearance of the cell after the treatment in pure water. (i) State the condition of the plant cell above. (ii) Explain the appearance of the cell. (iii) Explain why the cell did not burst. (e) Describe and explain the effects of placing a red blood cell in (i) concentrated sucrose solution. (ii) pure water. (a) Plasmolysed (b) There was higher water potential in the cell sap compared to the sucrose solution. Water molecules move out of the cell sap by osmosis, causing the cell membrane to detach from the cell wall. (c) Sucrose solution. The cell membrane has detached. The cell wall is fully permeable, thus allowing sucrose molecules to enter. (d) (i) Turgid (ii) There was higher water potential in the pure water compared to the cell sap. Hence water molecules move into the cell sap by osmosis, causing the cell to become turgid. (iii) The cell wall exerts an opposing force to prevent the cell from bursting. (e) (i) There is higher water potential in the cytoplasm of the red blood cell compared to the sucrose solution. Water molecules move out of the cytoplasm by osmosis, causing the cell to form spikes or become crenate. (ii) There is higher water potential in the pure water compared to the cytoplasm of the red blood cell. Hence water molecules move into the cytoplasm of the red blood cell by osmosis, causing the cell to swell and eventually lyse. 15 5. The figure shows the experiment set up using Visking tubings. The solution in the beaker turns blue at the end of the experiment. When two drops of iodine are added into the beaker, no blue-black colour is observed. (a)(i) Suggest the final concentration of blue dye solution, greater than 10% lesser than 10% or remaining as 10%, in the Visking tubing A. [1] (ii) Explain how you derive your answer. [3] (b) From what evidence can you conclude that Visking tubing is a partially permeable membrane? Explain your answer. [2] (c)(i) What would happen to mass of the Visking tubing B, increase, decrease or remain the same, at the end of experiment? [1] (ii) Explain your answer. [2] (d) Would you expect the content of Visking tubing B to turn blue at the end of the experiment? Explain your answer. [2] (a)(i) Less than 10% (ii) Blue dye particle can pass through the Visking tubing. Therefore, they will move from a region of high concentration in the Visking tubing to a region of low concentration in the beaker until both sides have equal concentration. (b) It prevents starch to move across it but allows blue dye particles and water to move through. (c)(i) Increase (ii) The concentration of water molecules is higher in the beaker than in the tubing, so water molecules diffuse into the tubing from the beaker by osmosis. (d) Yes. Since blue dye can pass through the Visking tubing, it will enter Visking tubing B since there is a low concentration of blue dye particles. 16 Transport in Plants There are two separate systems to transport water, mineral salts and nutrients: 1. Xylem vessels 2. Phloem tissues Water and dissolved mineral salts are transported inside the xylem vessels in an upward direction. Food substances made in the leaves are transported in the plant by phloem tissues in all directions. Xylem and phloem tissues are grouped together to form vascular bundles. Uptake of water Roots have many root hairs to increase the surface area by developing an elongated structure, so water can be absorbed in a faster rate. 17 The solution inside the root hair cell is more concentrated than in the soil particles. As a result, the concentration of water molecules is lower in the cell than in the soil. Thus, water enters the root hair cells by osmosis. Once inside the root hair cell, the water dilutes the solution in the cytoplasm, it is now less concentrated compared to the root cell next to it. Water moves to that root cell by osmosis. The process of osmosis continues throughout the root cells until it reaches the xylem vessel. When water evaporates in leaves, it creates a pulling force that move the water up the stem to the leaves. Xylem Transport. Transpiration of water from leaves pulls water up a plant’s stem from the roots. The cohesiveness of water makes xylem transport possible. Uptake of mineral salts 18 Soil water contains high concentration of dissolved mineral salts compared to the solution in the root hair cells. Mineral salts enter root hair cells by diffusion. Sometimes soil water has a lower concentration of dissolved mineral salts compared to the cytoplasm and the vacuole of root hair cells. In this case, mineral salts enter the root hair cells by active transport. Active transport is a process when a substance moves from its region of low concentration to its region of high concentration. Energy is involved. A plant’s root cell, for example, may need to absorb nutrients from soil water that is much more dilute than the cell’s interior. In active transport, a cell uses a transport protein to move a substance against its concentration gradient—from where it is less concentrated to where it is more concentrated. Because a gradient represents a form of potential energy, the cell must expend energy to create it. Transport of food Food made in the leaves is needed by all the cells in the plant. Phloem tissue transports the food to all parts of the plants upwardly and downwardly. Multiple-Choices Questions 19 1. What is the process by which large amount of water is lost from the stomata in leaves? A. Diffusion B. Osmosis C. Respiration D. Transpiration 2. Anita bought a bunch of blue flowers from the market. In order to find out whether the colour was artificially introduced or not, she prepared a section of the stem and observed it under the microscope. Which of the following correctly shows the condition of the section of the colour if the flowers were artificially introduced? The dark area is the place where the colour is present. (B) 3. A piece of a plant with a transparent stem was placed in a beaker containing a blue dye and then examined 5 hours later. Which of the following explains the change in appearance? A Blue dye diffuses through the stem. B Blue dye moves up the stem by osmosis. C Blue dye moves up through the xylem due to transpiration. D Blue dye moves up through the phloem due to transpiration 4. Which of the following situations would cause a plant to wilt? Water loss Water uptake A High High C Low High Water loss Water uptake B High Low D Low low 20 5. Four similar plants are growing under different conditions of temperature and humidity. Which plant is likely to wilt first? Temperature Humidity A High High C Low High Temperature Humidity B High Low D Low low Extra info: Humidity is the amount of water vapor in the air. A hygrometer is an instrument used for measuring humidity or the moisture content in the environment. Humidity measurement instruments usually rely on measurements of some other quantity such as temperature, pressure, mass or a mechanical or electrical change in a substance as moisture is absorbed. By calibration and calculation, these measured quantities can lead to a measurement of humidity. A psychrometer measures relative humidity, using the cooling effect of evaporation. Psychrometer 21 6. The roots of a plant were placed in a coloured dye. The diagrams below show the transverse sections of its leaf, stem and root after one day. Which of the numbered tissues of the leaf, stem and root would be most heavily stained by the dye? A 1, 3, 5 B 1, 3, 6 C 1, 4, 5 7. The diagram below shows a section of a plant stem. Which tissue would show radioactivity when the plant is exposed to radioactive carbon dioxide during photosynthesis? (B) 8. The diagram shows an experiment. Which of the following affects the amount of water droplets formed in the bell jar? A The humidity of the air surrounding the bell jar B The size of the bell jar C The temperature of the air surrounding the bell jar D The velocity of the air movement outside the bell jar 9. The photomicrograph below shows part of a section of a young root. Which type of cells does not respire? (C) 22 D 2, 3, 6 10. What are the possible functions of water in plants? (1) As a requirement for respiration (2) As raw material for photosynthesis (3) As a medium for food transport A (1) and (2) only B (1) and (3) only C (2) and (3) only D (1), (2) and (3) 11. Which of the following instruments is often used to measure the rate of water uptake in plants? A Potometer B Photometer C Respirometer Potometer The diagram shown in question 12 is a potometer, too. 23 D Data logger 12. The diagram shows an experimental set-up to investigate the rate of transpiration. Under which of the following environmental conditions would the air bubbles in the capillary tube move at the fastest rate? A Cold, dry and windy B Cold, humid and windy C Warm, dry and windy D Warm, humid and without wind 13. Miss Daisy carried out marcotting on her balsam plant. What causes the swelling seen above the removed ring? A Accumulation of salts and water due to interruption of the phloem tissue B Accumulation of salts and water due to interruption of the xylem tissue C Accumulation of food materials due to interruption of the phloem tissue D Entry of bacteria from the atmosphere due to removal of the bark How a marcotted part look like. If you want to know more about marcotting, go to the following website. http://www.cropsreview.com/marcotting.html 24 14. The diagram below shows a tree whose bark at the base of the stem has been scraped away by wild forest dogs. Why did the tree die after several weeks? A. The xylem had been destroyed. B. Microorganisms attacked the tree. C. The root lacked the supply of organic foods. D. Water had been lost at the wound. 15. The graph below shows the changes in the transpiration rate of a plant during a dry, hot, sunny day Which of the following could be the reason for the sudden drop in the transpiration rate at 1400 hour? A The sky became cloudy temporarily. B The temperature rose. C There was more carbon dioxide in the air. D The stomata closed. Question 16 and 17 refer to diagram in the right which shows cross-section of the stem of a green plant. 16. Which part is responsible for transporting water and mineral salts? (B) 17. Which part most likely contains the substance which gives a positive result with Benedict's test? (A) Benedict's solution is used to test for the presence of sugar eg glucose. 25 A negative test (left) and a positive test (right) The presence of glucose is indicated by the formation of orange-red precipitate as shown on the right diagram. To test for sucrose, a few drops of dilute hydrochloric acid + a few drops of Benedict's solution is used. If sucrose is present, orange-red precipitate is observed. 26 Structured Questions 1. The diagram below shows sections of a young plant. X and Y represent tissues which carry substances within the plant (a)(i) Name the sections A and B of the plant. (ii) Name the substances carried by X and Y. (iii) Describe the structure of X and explain how it is adapted to carry out its functions. (b) Describe briefly a simple method to show that substances move through tissue X. (c) Suggest one way in which the movement of substances in plants differs from that in animals. (d) Explain why tissue X is located towards the centre of the plant. (a)(i) A : stem; B: root (ii) X: water and mineral salts Y: manufactured food / sucrose and amino acids (iii) X is hollow for continuous flow of water; reinforced with lignin to prevent collapse and for mechanical support of the plant. (b) Place the stem in coloured water for a few hours. Cut a cross section and observe which vessels the dye travelled through. (c) Movement of substances in animals occurs at high pressure due to presence of muscular pump (heart). There is no muscular pump in plants, so transport is at lower pressure. / Animals' transport does not rely on external environmental factors. Plants, transport is affected by external environmental factors such as temperature and air movement. (d) This is to ensure that the plants do not collapse and is kept upright by being supported in the centre. 2. Melanie placed three stalks of celery under the conditions indicated in the diagram below, with their stalks dipping into a coloured dye. 27 (a) State what she would see, after 24 hours, inside the plastic bag that is wrapped around P. (b) Give an explanation for your answer in (a) (c) In which of the plants, P, Q or R, would the dye move furthest up the stalk? Explain your answer. (a) Water droplets (b) Transpiration occurred. Water vapour evaporated from the stomata and condensed on the plastic bag. (c) R. For plant P, the movement of the dye solution is limited by the humidity or amount of water vapor in the air within the plastic bag. For Q, there is no leaf to cause transpiration to occur. For R, transpiration can occur continuously, resulting in the furthest movement of the dye solution. 28 3. Mr Wong set up an experiment to investigate water loss by two young shoots. The two shoots were kept under conditions which varied but were always the same for both shoots. The volume of water remaining in each tube was observed each day, for three days. The results he obtained are shown in the table below. Water level (cm) Time (day) Tube A Tube B 0 10.0 10.0 1 8.8 9.1 2 7.4 8.5 3 5.8 7.5 (a) Name the process which caused the loss of water from the shoots (b) Which tube, A or B lost more water? (c) On which day was the most water lost by the shoots? (d) Suggest an explanation for more water being lost on this day than on the other two (a) Transpiration (b) A (c) Day 3 (d) Higher temperature / low humidity / windy on Day 3 compared to Day 1 and 2. 29 4. Gilbert carried out an experiment to study the impact of girdling on plants. Diagram 1 shows the girdling of a woody shoot by removal of a ring of bark, leaving the xylem intact. The girdled region is smeared with Vaseline. Diagram 2 shows the appearance of this shoot four weeks after the girdling treatment. (a)(i) Which vascular tissue is removed in the girdling treatment of the woody shoot? (ii) What is the purpose of covering the girdled region with Vaseline? (b) Describe and explain the resulting appearance of the woody shoot above the girdled region. (c) What will be the fate of this tree? Explain your answer. (d) If the girdling action removed all the vascular tissues, what would be the resulting appearance of the leaves present at region X one week after the girdling treatment? Explain your answer. (a) (i) Phloem tissue (ii) To prevent evaporation of water from the xylem tissue (core of stem) (b) The base of the upper section of shoot above the girdled region becomes swollen. Phloem tissue is removed, food manufactured in the leaves cannot be transported across the girdled region to the lower regions of the shoot, hence it accumulates at the base of the upper section, which becomes swollen. (c) The tree will die after a while. The manufactured food cannot be transported down to the lower parts of the tree, especially the roots. Absorption of water and dissolved mineral salts will be affected if cells around the roots die from lack of nutrients. (d) The leaves will wilt. 30 Xylem tissue is removed, water absorbed by the roots cannot be transported up to the leaves. The water lost by leaves cannot be replaced, resulting in wilting. Photosynthesis cannot occur. The leaves and eventually the tree die. 5. A plant was placed in a beaker containing red dye solution as shown in Diagram A. One hour later, thin slice was cut from the stem and the result was shown in Diagram B. (a)(i) Name the tissue X which has been stained with red dye solution. (ii) Explain why that tissue X was stained with red dye solution. (b) Through what process do red dye particles enter the root hairs of the plant? (c) What could most likely the objective of this investigation be? (a) (i) Xylem (ii) Xylem is responsible for transporting water. Water contains red dye, so it is transported together with the red dye by the xylem. (b) Diffusion (c) To show that xylem tissues are responsible for transporting water in the plant transport system. 31 Transport System in Humans The human transport system is called the circulatory system. The circulatory system can be divided into three major parts: Heart Blood vessels Blood The circulatory system is responsible for transporting substances throughout the entire body. 1. Bringing nutrients, water, oxygen and other substances to the body cells 2. Removing waste substances such as carbon dioxide from the body cells Double Circulatory system in humans Pulmonary Circulation : Blood is pumped out of the right side of the heart and travels to the lungs. In the lungs blood picks up oxygen and becomes oxygenated at the same time carbon dioxide is removed. The oxygenated blood then travels back to the left side of the heart. 32 Systemic Circulation : The oxygenated blood is pumped by the left side of the heart to the rest of the body. It delivers oxygen to the body’s cells and becomes deoxygenated. It also picks up Carbon dioxide and other waste products. This deoxygenated blood then makes it way back to the right side of the heart where the cycle is repeated. Heart The human heart is a four-chambered muscular pump which pumps blood around the circulatory system. The pumping action is as follows: When the heart muscles contract (systole phase), blood is forced out. When the heart muscles relax (diastole phase), blood is pulled in. 33 Left ventricle has a thicker muscular wall because it needs to pump blood at a higher pressure as the blood needs to travel a greater distance to all parts of the body from the heart. Right ventricle has a thinner muscular wall because it pumps blood at a lower pressure as the blood only needs to travel to the lungs which is a shorter distance from the heart. There are valves in the heart to make sure that blood flows in one direction only. Blood vessels 34 Arteries Veins Capillaries Function carry blood away from carry blood towards the allow exchange of the heart heart substances between blood and the body cells Structure Thick, elastic and Thin, less elastic and One-cell thick to allow muscular wall less muscular wall substances can diffuse to and from the cells Valves Absent Present Absent Blood Very fast as blood is Slow as under low Slow as under low flow under high pressure pressure pressure In spurts Smooth flow Size of Small Large Very narrow lumen 35 Let’s follow the flow of blood through the human circulatory system. Starting in the right ventricle in the figure above, we trace the pulmonary circuit first. The right ventricle pumps oxygen-poor blood to the lungs via the pulmonary arteries. As blood flows through capillaries in the lungs, it takes up oxygen and unloads carbon dioxide. Oxygen-rich blood flows back through the pulmonary veins to the left atrium. Next, the oxygen-rich blood flows from the left atrium into the left ventricle. The figure shows, the left ventricle pumps oxygen-rich blood into the aorta. The aorta is our largest blood vessel, with a diameter of about 2.5 cm. The first branches 36 from the aorta are the coronary arteries (not shown), which supply blood to the heart muscle itself. Next there are large branches leading to the head, chest, and arms, and the abdominal regions and legs. For simplicity, the figure does not show the individual organs, but within each organ, arteries lead to arterioles that branch into capillaries. The capillaries rejoin as venules, which lead to veins. Oxygen-poor blood from the upper part of the body is channeled into a large vein called the superior vena cava, and from the lower part of the body it flows through the inferior vena cava. The two venae cavae empty into the right atrium. As the blood flows from the right atrium into the right ventricle, we complete our journey, only to start the pulmonary circuit again at the right ventricle. Remember that the path of any single red blood cell is always heart to lung capillaries to heart to body tissue capillaries and back to heart. In one systemic circuit, a blood cell may travel to the brain; in the next (after a pulmonary circuit), it may travel to the legs. A red blood cell never travels from the brain to the legs without first returning to the heart and being pumped to the lungs to be recharged with oxygen. Blood A healthy adult has about five litres of blood in their vessels. Blood is known as the fluid of life. It is a fluid tissue which consists of the following components: Red blood cells White blood cells Platelets Plasma Blood acts as a transport medium in the human body. 1. It transports the following substances to the body cells: Oxygen (for respiration) Hormones (important chemical substances for various chemical activities) Nutrients (such as glucose, amino acids, fatty acid, glycerol and vitamins) 2. It transports the following substances from the body cells: Carbon dioxide (waste from the respiration) 37 Waste products from other processes (such as excess water and urea) 38 Component Red blood cells (Erythrocytes) Description and function Transport oxygen from the lungs to all cells in the body. Oxygen combines with a red pigment knows haemoglobins in the cell to be transported. Transport oxygen from lungs to aerobically respiring cells and facilitate movement of carbon dioxide to the lungs. Red blood cells lose their nucleus and other organelles as they develop. Mature red blood cells are flexible disks with a depression at their center. Their flexibility allows them to slip easily through narrow blood vessels, and their flattened shape facilitates gas exchange. Haemoglobin fills the interior of the mature red blood cell. Most oxygen that enters the blood travels to the tissues while bound to the haemoglobin. A mature red blood cell has enough stored sugars, RNAs, and other molecules to live about 120 days. White blood cells They form part of the immune system. Destroy foreign substances, initiate inflammation, fight infection. Five types of white blood cells. The cells differ in their size, nuclear shape, and staining traits, as well as function. These cells participate in many immune responses. Some secrete signaling molecules that provoke inflammation, whereas others destroy microbes or produce antibodies. 1.Neutrophils, the most abundant white cells, are phagocytes that engulf bacteria and debris. 2. Eosinophils attack larger parasites, such as worms. 3. Basophils secrete chemicals that have a role in inflammation. 4. Monocytes are white cells that circulate in the blood for a few days, then move into the tissues, where they develop into phagocytic cells known as macrophages. Macrophages interact with lymphocytes to bring about immune responses. There are two types 39 Platelets Plasma of lymphocytes, B cells and T cells. B cells mature in bone, whereas T cells mature in the thymus. Both protect the body against specific threats Stop bleeding by clotting the blood flow when blood vessels are cut. Platelets are small, colorless cell fragments that initiate blood clotting. When a vessel is injured, it constricts (narrows), reducing blood loss. Platelets adhere to the injured site and release substances that attract more platelets. Plasma proteins convert blood to a gel and form a clot. During clot formation, fibrinogen, a soluble plasma protein, is converted to insoluble threads of fibrin. Fibrinforms a mesh that traps cells and platelets Dissolves and transports materials around the body, for example digested food, carbon dioxide and waste substances. The fluid portion of the blood, known as the plasma, constitutes about 50 to 60 percent of the blood volume. Plasma is mostly water with hundreds of different plasma proteins dissolved in it. Some plasma proteins transport lipids and fat-soluble vitamins; others have a role in blood clotting or immunity. Dissolved sugars, amino acids, vitamins, and some gases travel through the bloodstream in plasma. Blood clotting In a healthy circulatory system, platelets travel freely within the vessels. Sometimes, however, a wound nicks a blood vessel, or the blood vessel’s inner lining may become obstructed. Platelets then ―catch‖ on the obstacle and shatter, releasing biochemicals that combine with plasma proteins called clotting factors. The resulting complex series of reactions ends with the formation of a blood clot ‒ a plug of solidified blood. 40 (a) A cut blood vessel immediately constricts. Platelets aggregate at the injured site. Proteins called clotting factors participate in a cascade of reactions, producing a meshwork of protein threads. (b) Red blood cells trapped by protein threads in a clot. Blood that clots too slowly can lead to severe blood loss. Hemophilias, for example, are inherited bleeding disorders caused by absent or abnormal clotting factors. Deficiencies of vitamins C or K can also slow clotting and wound healing. Blood that clots too readily is also extremely dangerous. In atheroscle-rosis, platelets may snag on rough spots in blood vessel linings. The resulting clot may stay in place or travel in the bloodstream to another location; either way, the obstruction may cut off circulation and sometimes even cause death. 41 MCQ 1. Which of the following shows the thickness of the walls of blood vessels in ascending order? A. Capillaries, veins, arteries B. Arteries, veins, capillaries C. Veins, arteries, capillaries D. Arteries, capillaries, veins 2. What is the function of blood plasma? A Formation of clots B Transport of oxygen C Production of antibodies D Transport of dissolved nutrients and waste products 3. The diagrams show the crosssections of three different types of blood vessels P, Q and R. Which shows the correct type of blood vessels? P A Artery B Artery C Vein D Capillary Q Vein Capillary Capillary Artery 4. Which of the following statements about arteries is/are correct? (i) All arteries do not contain any valves. (ii) All arteries transport blood away from the heart. (iii) All arteries transport blood under high pressure. (iv) All arteries transport oxygenated blood. A. (ii) only B. (iii) only C. (i) and (ii) only D. (ii) and (iii) only (D) 42 R Capillary Vein Artery Vein 5. Which of the following shows the correct routes for blood to travel from the leg to the brain in the human body? A. Leg lungs heart lungs brain B. Leg heart lungs heart brain C. Leg arm lungs liver brain D. Leg liver heart lungs brain 6. The diagram shows a human blood sample in a blood vessel. Where is carbon dioxide found? (B) 7. The bar chart shows the concentration of carbon dioxide in blood samples taken from four different places in the human circulatory system. Which blood sample was taken from the pulmonary vein? (B) 8. The following graph shows how the concentration of oxygen changes when the blood flows in the blood vessels. What could most likely take place in region X which causes the concentration of oxygen to increase abruptly? 43 A. Red blood cells in the blood pick up oxygen from the alveoli when it reaches region X. B. The body cells in region X return the excess oxygen to the blood. C. The body cells in region X carry out chemical reactions which produce large quantity of oxygen. D. Haemoglobins in the red blood cells lose the ability to carry oxygen abruptly in region X. 9. Which of the following exerts the highest pressure during the beating of the mammalian heart? A. Left atrium B. Left ventricle C. Right atrium D. Right ventricle 10. Cholesterol plague is formed by the accumulation of cholesterol on the wall of arteries. Which of the following is the reason why a heart attack may occur if the coronary artery is blocked by cholesterol plague? A. The rate of heartbeat increases. B. Less blood is pumped out from the heart. C. The heart muscle breaks down. D. Less blood is supplied to the heart muscle. 11. The table shows the characteristics of the blood in one blood vessel in the body. Oxygen concentration Carbon dioxide concentration Pressure Low High High Which blood vessel contains blood with these characteristics? A. Aorta B. Pulmonary artery C. Pulmonary vein D. Vena cava 12. Which of the following components of the blood can destroy bacteria that have entered the body? (1) Antibodies (2) Phagocytes (3) Blood platelets A. (1) & (2) only B. (1) & (3) only C. (2) & (3) only D. (1), (2) & (3) 44 13. The photomicrograph below shows the transverse section of two blood vessels connecting the heart and the lungs. Which heart chamber is connected to vessel Q? A. Left atrium B. Left ventricle C. Right atrium D. Right ventricle 14. The diagram below shows a human heart and its attached vessels. Which of the following correctly describes the conditions of the blood in the different vessels? P Q R A Oxygenated, Deoxygenated, Deoxygenated, high pressure low pressure high pressure B Oxygenated, Deoxygenated, Deoxygenated, high pressure high pressure low pressure C Deoxygenated, Deoxygenated, Oxygenated, low pressure low pressure high pressure D Deoxygenated, Deoxygenated, Oxygenated, high pressure low pressure high pressure 45 S Oxygenated, high pressure Deoxygenated, low pressure Oxygenated, high pressure Oxygenated, high pressure 15. Which statement explains why white blood cells are produced in larger quantities when there is a wound on the skin? A. To stop the bleeding of blood by clotting B. To transport more oxygen to the cells nearby for respiration C. To prevent any unwanted foreign entities from entering the blood D. To facilitate platelets to form clot 46 Structured Questions 1. The figure below represents some blood cells. (a) In the figure above, label the cells X, Y and Z. (b) Describe the structure of X and what it contains. (c) State the function of cell Y. (d) State the function of cell Z (e) Explain why the number of cells Y and Z increase in numbers when a person has an influenza infection. (f) What is the fluid that surrounds the cells above? (a) X: red blood cell; Y: phagocyte; Z: lymphocyte (b) It has a biconcave disc shape to increase surface area to volume ratio for efficient transportation of oxygen. It contains haemoglobin to transport oxygen. It has no nucleus so that more space is available to transport oxygen. (c) To engulf foreign bodies (d) To produce antibodies (e) To destroy the influenza virus by producing antibodies and/or engulfing the virus (f) Plasma 47 2.(a) State the meaning of the followings: (i) an artery (ii) a vein (b) Capillaries have very thin walls surrounded by the body cells. What is the advantage of having thin walls? (c) Name two other substances, besides oxygen, which can pass through the wall of capillaries. (a) (ii) (b) (c) (i) An artery is the blood vessel which carries blood away from the heart. A vein is the blood vessel which carries blood towards the heart. So that diffusion of substances is easier between the blood and the body cells Carbon dioxide, glucose 48 3. The diagram below shows a vertical section of human heart (a) Using the letters provided in the diagram, state all the part(s) which (i) carry/carries oxygenated blood under low pressure. (ii) return(s) blood to the heart (iii) deliver(s) blood to the lungs (b) Explain why the muscular wall G is thicker than that of F (c) (i) Name structure E. (ii) Explain the role of structure E. (d) Explain the effects on a person if X and Y are faulty. (e) Complete the following table to indicate the characteristics of blood flow in regions A, B, C and D. Characteristics of blood Region Higher pressure deoxygenated blood Lower pressure oxygenated blood Higher pressure oxygenated blood Lower pressure deoxygenated blood (f)(i) To which organ Z does the blood flow to after leaving the heart? (ii) What would take place when blood reaches organ Z? (a) (i) R (ii) P and R (iii) Q (b) G has to withstand greater pressure as it has to transport blood furthest compared to F which only transports blood to the nearby lungs. (c) (i) Septum (ii) It prevents mixing of oxygenated and deoxygenated blood. It ensures that blood reaching all organs are fully oxygenated so that organs function at maximum efficiency. 49 (d) There will be backflow of blood. Heart muscles will enlarge to compensate for greater pressure needed to force the blood out. Heart disease will develop (heart enlargement) (e) Characteristics of blood Region Higher pressure deoxygenated blood B Lower pressure oxygenated blood D Higher pressure oxygenated blood C Lower pressure deoxygenated blood A (f)(i) Lungs (ii) Carbon dioxide diffuses out from the bloodstream into the lungs. Oxygen diffuses into the bloodstream from the lungs. 50 4. The photomicrograph below shows the cross-sections of two blood vessels lying side by side. The compositions of the blood in these two blood vessels are compared as shown in the table below Composition of blood Vessel X Vessel Y Oxygen Lower Higher Carbon dioxide Higher Lower (a) With reference to the photomicrograph only, decide which vessel, X or Y, is an artery. Give a reason for your answer. (b) Explain how the structure of vessel X is related to its function (c) With reference to the information given in the table, suggest an organ which X and Y are associated with. Name X and Y. (a) X; it has narrow lumen or thick muscular walls. (b) It has narrow lumen to maintain high pressure blood flow and thick muscular walls to withstand high pressure. (c) Lungs: X is pulmonary artery as it is the only artery which has low oxygen content; Y is pulmonary vein as it is the only vein with high oxygen content. 51 5. The diagram below shows a heart in which the coronary arteries are partially blocked. It is treated by a coronary bypass operation. This involves grafting sections of vein from the patient’s leg to the heart. (a) Name the blood vessel leading into chamber X (b) Name the organ which receives blood from vessel Y. (c) The circulation of blood around the body is reduced as a result of the partial blockage of the coronary arteries. Explain why this happens. (d) Suggest two reasons why a coronary bypass operation is preferable to a heart transplant operation. (e) Suggest an advantage and a disadvantage of using veins instead of arteries in the grafting surgery. (a) Pulmonary vein (b) Lungs (c) The heart muscles receive less oxygen and nutrients due to blockage. There is not enough energy to pump blood at high pressure, resulting in poor circulation of blood at low pressure. (d) Less risky; difficult to find matching donor; tissue rejection may occur for heart transplant (any two) (e) Advantage: Lumen of veins are wide. This reduces the chances of a relapse as the lumen is wide enough to reduce the risk of another blockage. Disadvantage: The wide lumen that reduces pressure means heart muscles receive blood at lower pressure. The person cannot physically exert himself. 52 During Coronary Artery Bypass Grafting, a healthy artery or vein from the body is connected, or grafted, to the blocked coronary artery. The grafted artery or vein bypasses (that is, goes around) the blocked portion of the coronary artery. This creates a new path for oxygen-rich blood to flow to the heart muscle. 53 6.(a)(i) What is the function of the heart in the human circulatory system? (ii) State two features of the heart which enables it to perform its function. (b)(i) List all the components found in blood. (ii) Which component is responsible for transporting hormones and food substances around the body? (c) (i) By taking the left atrium as the starting point, place the sequence of the blood flow correctly using the following items given below. Pulmonary vein Renal artery Right ventricle Pulmonary artery Lungs Right atrium Renal vein Left ventricle (ii) Name the organ in the body in which the blood would arrive at the end of this sequence. (d) State one chemical substance which passes in a higher amount (i) from capillaries to muscle cells before an exercise (ii) from muscle cells to capillaries after an exercise (a) (i) To pump blood so that it can flow in the vessels (ii) It contains valves to prevent the back flow of blood and it has muscular wall to exert pressure on blood. (b) (i) Plasma, white blood cells, red blood cells and platelets (ii) Plasma (c)(i) Left atrium Left ventricle Renal artery Renal vein Right atrium Right ventricle Pulmonary artery Lungs Pulmonary vein (ii) Heart (d) (i) Oxygen (ii) Carbon dioxide 54 7. The diagram below shows the blood flow containing blood cells in a capillary. (a)(i) Name the blood cell X. (ii) What is the main function of X? (b) White blood cells are made up of lymphocytes and phagocytes. What is their function? (c) Name two other components in the blood which are not identified in the diagram. (d) The capillary wall is one-cell thick. What is the advantage of having a one-cell thick wall? (a) (i) Red blood cells (ii) To transport oxygen (b) To kill bacteria (c) Plasma and platelets (d) It allows easier diffusion of substances so that the exchange of substances between the blood and the body cells is more efficient. 55 8. Fill in the blanks in the following table. The first one is done for you. Blood vessel Structure Function Arteries Thick muscular wall Narrow lumen Transport blood away from the heart Transport oxygenated blood only (except in the case of the pulmonary artery) Arterioles Tiny branches of arteries that lead to capillaries Transport blood from arteries to capillaries arteries to capillaries Arterioles are the main regulators of blood flow and pressure Capillaries Capillaries are tiny (extremely narrow) blood vessels Walls are only one cell thick Exchange of oxygen, carbon dioxide , water, salts, etc between the blood and the surrounding body tissues. Venules Minute branches of veins that drain blood from capillaries and into veins Drain blood from capillaries into veins, for return to the heart Veins Thin muscular wall Wide lumen Presence of valves Transport blood towards the heart Transport deoxygenated blood only (except in the case of the pulmonary vein) 56