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4.1 Structure of the cell-surface membrane AQA AS Biology B4 Transportation Acroos Membrane Kerboodle Answer.
1.Ans Functions of cell-surface membrane are :
- Plasma membrane forms boundary between the cell cytoplasm and the environment.
- It helps in establishing different conditions inside and outside of the cells.
- It also controls the movement of substances in and out of the cell.
2Ans Hydrophobic tails of the phospholipid molecule lies towards the inside of the cell-surface membrane. 2.A)Ans As it is clear that membrane is majorly made of phospholipids thus a molecule soluble in lipids can easily get in or out of the cell across the concentration gradient through phospholipid bilayer. (b) Ans Mineral ions are passed through the protein channels in order to get in or out of the cell. Q 4 Ans Two properties that a drug should possess if it is to enter a cell rapidly:
- Drug should be lipid soluble so that it can directly diffuses through the phospholipid bilayer.
- Drug should have specific receptore on the plasma membrane which will help the drug entry into the cell.
4.2 Diffusion AQA AS Biology B4 Transportation Acroos Membrane Kerboodle Answer.
Q 1 Ans Three factors which affect rate of diffusion are:
- Distance
- Concentration gradient
- Surface area of the cell.
Q 2Ans
- Simple diffusion – moves things from high to low, no energy required, doesn’t require a protein
- Facilitated diffusion – moves things from high to low, no energy required, requires a protein
Q 3 Ans The solute can move “downhill,” from regions of higher to lower concentration, relying on the specificity of the protein carrier to pass through the membrane. This process is called passive transport or facilitated diffusion, and does not require energy. For movement energy comes from the kinetic energy of the molecules. Q 4 Ans Glucose is not lipid soluble thus phospholipid membrane is not permeable to glucose. Besides this glucose is large in size and polar in nature. Q 5Ans By increasing the surface area of the cell and by increasing the number of carrier proteins on the cell rate of glucose transport can be increased. Q 6 (a) The surface area of the alveoli in doubled. Ans It will increase the rate of diffusion of oxygen by double. (b) Ans It will not create any effect on the rate of diffusion of oxygen. (c) Ans It will decrease the diffusion of oxygen. (d) Ans It will increase the rate of diffusion of oxygen.
4.3 Osmosis AQA AS Biology B4 Transportation Acroos Membrane Kerboodle Answer.
Q 1 Ans Plasma membrane around the cell and cell organelle are selectively permeable that means they allow water molecules and few other small molecules to pass through it not the larger molecules. Q 2 Ans Zero. Ans
Osmosis and plant cells 1 Ans Presence of cell wall in the plant cell restricts the entry of water molecule once the cell reached at this turgid stage. Thus prevent it from bursting while in case of animal cells cell wall is not present. Cell surface membrane cannot resist the force applied by the cytoplasm and thus resulted in bursting of cell. Q 2 Ans (a) Solution A= -400 kPa: when plant cell with water potential -600 kPa is placed in this solution it will get plasmolysed. Water will flow from higher water potential (-600 kPa; cell) to lower water potential (-400 kPa; solution A). (b) When the cell is placed in solution B (-600 kPa) it will remain as it is. Because, the cell and the solution have equal water potentials. No net movement of water will be there. (c) In this solution cell become turgid. (d) It this solution cell become turgid. Q 3 Ans The cell is likely to burst in pure water. Because in case of pure water equilibrium between water potentials will achieve later as compare to solution C.
4.4 Active transport AQA AS Biology B4 Transportation Acroos Membrane Kerboodle Answer.
Q 1 Ans Similarity: both involve the carrier proteins for the transport. Difference: In case of facilitated diffusion, diffusion of molecules occurs down the concentration gradient, i.e., from lower concentration to higher concentration. Whereas in case of active transport, transport occurs against the concentration gradient, i.e., from lower concentration higher concentration. Q 2 Ans Mitochondria are known as power house of the cell because they are the site for ATP synthesis. They provide energy required for different metabolic activities taking place in cells. For active transport energy is required in the form of ATP. Thus presence of many mitochondria is typical feature of cells carrying active transport. Q 3 Ans To ensure that all the nutrients are absorbed in blood, active transport occurs. Such as glucose and amino acids are also transported by active transport. Because diffusion results in equilibrium of concentration, so, in this way all the glucose and amino acids are not getting absorbed into the blood and some may pass out of the body. To prevent this loss glucose and amino acids are also being absorbed by active transport.
4.5 Co-transport and absorption of glucose in the ileum AQA AS Biology B4 Transportation Acroos Membrane Kerboodle Answer.
Q 1 Ans Three ways in which rate of movement across membrane can be increased, are:
- By changing the temperature.
- By increasing the density of the carrier proteins.
- Surface area of the cell.
Q 2 Ans The term co-transport is used to describe the transport of glucose into cells because either glucose or amino acids are drawn into the cells along with sodium ions which have been actively transported out by the sodium potassium pump. Q 3 Ans (a) Active transport; (b) passive transport; (c) active transport.
Oral rehydration therapy Q 1 Ans Glucose stimulates the uptake of sodium ions from the intestine and also it provides energy. Q 2. Ans Sodium is included in ORS mixture because of the following reasons:
- For replacing the sodium ions lost from the epithelial cells of the intestine
- For optimising the use of the alternative sodium-glucose carrier proteins.
- For maintaining the co-transport of glucose and sodium.
Q3 Ans Boiled water is used to make oral rehydration solution. Domestic water supplies are expected to be contaminated with microorganisms in varying degrees. Such situations would have a bearing on the purity and safety of the water to be used for the preparation of oral rehydration solutions, and the risk involved in administering contaminated solutions. So it is recommended to use boiled water for making ORS. Q 4 Ans Potassium ions play important role in recovery of patients because of the following reason:
- It replaces the potassium ion lost during diarrhoea.
- It also stimulates appetite of the patient.
Q 5 Ans It improves the taste so children can easily have the drug. Q 6 Ans Excess glucose resulted in low water potential of the ileum lumen which resulted in withdrawal of more water from epithelial cells. This made the rehydration worse. Thus energy drink containing high glucose cannot be used as rehydration solution for patients suffering with diarrhoea. Q 7 Ans Amylase and maltase enzyme in the ileum resulted in break down the starch into its monomers. Scientist did so many experiments with different concentration of starch and finally they came up with the best concentration of starch. At this optimum concentration of starch, glucose is released at optimum rate and did not create any adverse effects on the water potential. Q 8 Ans Viscosity of the rice flour solution can be decreased by partially digesting the starch with amylase enzyme. The smaller and more soluble starch will produce a drink that is less viscous solution. Q 9 Ans Drugs must ultimately be tested on humans to ensure that these are no side effects of that drug and for safety issues also. There are different levels of testing in humans. Q 10 Ans Placebo will act as control and given to make sure that the effect is due to the drug only and not because of any other molecule or reasons. Q 11 Ans This reduces expectation bias by the subjects and experimenter bias by the researcher.
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Q 1 (a) Ans Water will affect the mass and only the water taken up or lost requires measurement. Thus blotting ensures that water is the same on the outside of all cyclinders taken for measurement. In this way the student minimizes the experimental errors. (b) Ans
| Volume of 1.0 mol dm-3 sodium chloride solution | Volume of distilled water |
| 4 cm3 | 16 cm3 |
Volume of stock solution: 20cm³x0.2moldm⁻³=4 4/1.0moldm⁻³=4cm³. Need 20cm³ therefore add 16cm³ distilled water. (c) Ans The initial cylinder masses won’t be identical. Therefore, by calculating the percentage change in mass rather than the change in mass, allows direct comparison between the different sucrose solutions. (d) Ans Student repeated the experiment for several time for the following reasons:
- In order to identify and remove anomalies.
- Allowing for variation within the data to be minimised.
- In order to calculate a mean value by adding the values and dividing by the number there arewhich makes the line of best fit more reliableand allows for concordant results.
(e) Ans Where it crosses the x-axis that will be the concentration of sodium chloride solution that has the same water potential as the potato cylinders. Q 2 Ans There are different ways by which substances can cross the cell surface membrane:
- Facilitated transport: where molecules or ions move through a channel/carrier protein in the membrane, down a concentration gradient, which doesn’t require energy.
- Active transport: where molecules are moved via protein pumps, which requires energy in the form of ATP, and which may move up a concentration gradient.
- Osmosis: water may move across membranes via osmosis, from high to low water potential, via water channels (known as aquaporins).
- Alternatively, substances contained within vesicles may exit the cell via fusion of the vesicular membrane with the plasma membrane, leading to the release of its contents to the extracellular space.
- Extracellular material may also enter the cell via phagocytosis, which involves the cell membrane surrounding and engulfing the substance, to form an intracellular vesicle or vacuole.
Q 3 (a) Ans
| Facilitated diffusion | Active Transport |
| Energy requirement | Required energy is derived from the kinetic energy of the moving molecules; no external source of energy is required for the movement. | Energy for the movement is derived from the external chemical energy source: ATP |
| Direction of the movement | Movement is down the concentration gradient, from high concentration to low concentration | Movement is against the concentration gradient. |
(b) (i) Ans Scientists want to see the effect of drug only. So they have used the control group to confirm that the effect is due to the drug and not due to anything else in the tablet. (ii) Ans Control was given the tablet which did not have the drug. (c) Ans It decreases the volume of acid secreted per hour/cm
3. It shows effects till 4 hours of the treatment after that the volume of acid secreted per hour/cm
3 starts to increase. (d) Ans At 8 hours volume of acid secreted per hour/cm
3 for group Q is 190 and for group P it is 90. So by applying the formula: Percentage decrease or change= (acid secretion by group Q –acid secreted by group P/acid secreted by Q) * 100 =(190-90/190)*100 = 100*100/ 190 = 52.63% Q 4 (a) Ans They first calculated the surface area of cell-surface membrane and then the mass of lipid. They multiply both and did this to all the lipids found in cell-surface membrane. Then they added them together and calculated the percentage of a lipid by applying the formula= (1 type of lipid/total of all lipids) X 100. (b) Ans Red Blood Cells forms the major part of blood. They are free and they don’t have structural support from other cells. Thus high percentage of cholesterol maintains their shape where as ileum has low percentage of cholesterol as compared to RBC thus it is more flexible and membrane fluidity will be high which ensures better absorption of nutrients. (c) Ans
E. Coli has cell wall around itself. Cell wall is composed of murein and it is strong and rigid thus maintains its shape. This the reason that
E. Coli despite not having the cholesterol in their membrane cell maintains a constant shape. Banner 3
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