Question 1
1
The image was obtained with a mobile phone camera pointing down the eyepiece tube of a light microscope. It shows onion (Allium cepa) epidermal cells after immersion in a hypertonic salt solution during an experiment on osmosis.
structured0 marks
Question 1(b)
1(b)
0 marks
Question 1(b)(ii)
1(b)(ii)
Explain the effect of the salt solution on these cells.
Mediumstructured2 marks
Answer
a. cells are plasmolyzed/flaccid OR plasma membrane has separated from the cell wall OR cytoplasm/cell/vacuole has shrunk/decreased in size/lost mass; b. cells have lost water (by osmosis);
Question 1
1
Solutions of ions, for example NaCl dissolved in water, can be used to investigate the concentration of solutes in plant tissues. After immersion in solutions of varying concentration, the percentage changes in mass of potato samples were measured. The graph shows the results.
0 marks
Question 1(a)
1(a)
0 marks
Question 1(a)(i)
1(a)(i)
Estimate the osmolarity of the plant tissue. moles \(\mathrm{dm}^{-3}\)
Mediumstructured1 marks
Answer
a. 0.28 «moles \(\mathrm{dm}^{-3} »\) b. 0.56 «osmoles \(\mathrm{dm}^{-3}\) » Allow answers in the range of 0.27 to 0.29 «moles \(\mathrm{dm}^{-3}\) ». Allow answers in the range of 0.55 to 0.57 «osmoles \(d m^{-3}\) ».
Question 1(a)(ii)
1(a)(ii)
Identify which part of the graph represents samples measured in a hypotonic solution.
Easystructured1 marks
Answer
ii a. «any» part of the line above 0 percent change in mass b. 0 to 0.28 molarity of NaCl solution Allow ECF for upper value of molarity. 1 max
Question 1(a)(iii)
1(a)(iii)
State one possible source of error when collecting data during this experiment.
Easystructured1 marks
Answer
iii a. too few samples weighed b. not dried before weighing c. samples from different sources d. not cut all same way so different surface area e. temperature of each sample not the same f. potatoes not left for the same time in the solutions g. error due to the limitation of the apparatus/equipment Differentiate between errors and mistakes eg: do not accept "balance read incorrectly". Do not accept mass/weight differences. 1 max
Question 1
1
The micrograph shows a human cheek cell magnified with a light microscope.
structured0 marks
Question 1(c)
1(c)
Describe what would happen to the cheek cell if it was placed in a hypertonic salt solution.
Easystructured1 marks
Answer
cells would shrink/crenate/lose water;
Question 1
1
An experiment was carried out to measure the osmolarity of cantaloupe (fruit of Cucumis melo) tissue by placing pieces in salt solutions of different concentrations. The results are shown in the graph. Removed for copyright reasons
structured0 marks
Question 1(a)
1(a)
0 marks
Question 1(a)(ii)
1(a)(ii)
Identify the concentration of salt solution with an osmolarity equal to that of the cantaloupe tissue.
Mediumstructured1 marks
Answer
7 (\% salt solution); Accept range from 6.2 to 7.2 inclusive.
Question 1(b)
1(b)
Using the graph, explain what happened when the pieces of tissue were placed in a hypertonic salt solution.
Mediumstructured1 marks
Answer
a. loses mass as water leaves/moves out (the tissue); b. loses mass by osmosis; c. loses mass as water moves from a higher concentration to a lower concentration of water OR loses mass as water moves from hypotonic to hypertonic solution OR loses mass as water moves from low solute to high solute concentration; Both loss of mass and reason required. 1 max
Question 1(c)
1(c)
Describe two factors that should be kept constant in this experiment in order to obtain an accurate measurement of the osmolarity of the cantaloupe tissue.
Mediumstructured2 marks
Answer
a. (each piece should be approximately) the same surface area/size/shape/mass; b. leave the pieces of tissues in the solutions for the same period of time; c. all done at the same temperature; d. same volume / type of salt used in solution; e. use the same method to dry pieces before weighing; f. same fruit/age of fruit/type of tissue; Mark the first two only 2 max
Question 1
1
An experiment was carried out to determine the change in mass due to osmosis. Potato cubes were soaked in different concentrations of sodium chloride for 12 hours. The table shows the mean data for the mass of potato before and after the 12-hour period.
structured0 marks
Question 1(a)
1(a)
Outline the conditions necessary for osmosis to occur.
Mediumstructured2 marks
Answer
a. partially/semi permeable/selective membrane (to water); b. solute molecules/ions cannot pass through membrane; c. different solute/water concentrations/concentration gradients/osmolarity; d. suitable temperature (for osmosis to occur); 2 max
Question 1(b)
1(b)
Explain how the data may be used to determine the solute concentration of the potato tissue.
Mediumstructured2 marks
Answer
a. calculate percentage difference in mass; b. plot (percentage change) mass against concentration; c. concentration of solutes in potato tissues corresponds to 0 / zero / no mass change OR where the line (of best fit) crosses the mass change at zero is the potato tissue concentration; Accept the correct calculation for percentage (final mass - initial, divided by initial and times 100). Accept annotated graph. 2 max
Question 1(c)
1(c)
Estimate the solute concentration of the potato tissue.
Mediumstructured1 marks
Answer
Any number from \(0.31 \mathrm{~mol} \mathrm{dm}^{-3}\) to \(0.39 \mathrm{~mol} \mathrm{dm}^{-3}\); Units required.
Question 1
1
5 marks
Question 1(b)
1(b)
A study was done on the osmolarity of semen and sperm movement (motility).
2 marks
Question 1(b)(ii)
1(b)(ii)
The same study showed that blood plasma has a lower osmolarity than semen. Explain how that would affect the movement of water between blood plasma and semen.
Mediumstructured1 marks
Answer
ii water would move from blood plasma to the semen as it follows the concentration gradient / from low osmolarity to higher; Must include reason/explanation.
Question 1(d)
1(d)
Explain a change that would take place in sperm placed in a hypotonic solution.
Mediumstructured1 marks
Answer
a. water will enter (by osmosis) causing sperm to swell/enlarge/burst; b. water will enter (by osmosis) causing sperm to become more mobile as osmolarity decreases; Do not accept turgidity. Must show movement of water.
Question 1
1
The micrograph shows part of a cardiac muscle cell.
0 marks
Question 1(b)
1(b)
Explain the changes that would occur in a cardiac muscle cell placed in a hypotonic solution.
Mediumstructured2 marks
Answer
a. cardiac muscle cell has a higher solute concentration/lower water potential than hypotonic solution OR (in osmosis) water moves from a solution with higher water potential to lower water potential OR (in osmosis) water moves from lower concentrated solution to higher concentrated solution; b. water entering (by osmosis) causes cell to be swollen/enlarged/burst; Do not accept "solution moves..." instead of water moves..."
Question 1
1
Data was collected on rabbit red blood cells that were exposed to sodium chloride (NaCl) and scorpion venom. Under some osmotic conditions red blood cells swell and burst, releasing hemoglobin (hemolysis). The graph shows the response of red blood cells to different concentrations of sodium chloride, with and without scorpion venom.
0 marks
Question 1(a)
1(a)
Outline the effect of the venom on the hemolysis of red blood cells.
Mediumstructured2 marks
Answer
a. in NaCl concentrations between 0.3 to 0.5 % venom increases the percentage of hemolysis/more cells lyse b. venom has no effect below 0.3 % and above 0.55 % NaCl OR Venom has no effect at very low or very high NaCl concentrations
Question 1(b)
1(b)
Describe how the variables would be controlled in an experiment to estimate the osmolarity of plant tissue.
Mediumpractical3 marks
Answer
a. weigh all pieces to ensure same amount of plant material/allow comparisons b. control surface area by having same shape/ size c. carry out experiment at same temperature e.g. using a water bath or constant room temperature d. all samples in solution for same length of time e. all samples from same plant (to minimize variability) f. use a range of solutions of the same solute g. constant method of removing excess fluid before weigh tissue samples Do not accept just a list of controlled variables.
Question 1
1
An experiment was carried out on osmosis in carrot (Daucus carota) root tissue and potato (Solanum tuberosum) tuber tissue. Similar sized pieces of tissue were cut and soaked in different sucrose solutions for 24 hours. The results are shown in the graph below.
0 marks
Question 1(a)
1(a)
Using the graph, estimate isotonic sucrose solutions for potato tissue and carrot tissue. Potato: Carrot:
Mediumstructured2 marks
Answer
a b potato: \(0.26 \mathrm{~mol} \mathrm{dm}^{-3}\) carrot: \(0.50 \mathrm{~mol} \mathrm{dm}^{-3} \) Allow a range of 0.22-0.32 Allow a range of 0.45-0.55 (Allow 1 max if no units or either unit is omitted)
Question 1(b)
1(b)
Suggest a reason for the difference in the isotonic points for the potato and the carrot tissues.
Mediumstructured1 marks
Answer
different dissolved solutes/sugars/sucrose/salts/molarities OR may have been grown in different soils giving their tissues different contents OR may have been stored under different conditions OR may be more dehydrated / different water content OR different types of tissue / different age Do not accept starch. 1 max
Question 1(c)
1(c)
From the evidence provided by the graph, evaluate the reliability of these data.
Mediumstructured2 marks
Answer
a the data show clear trends OR a trend line could be drawn through these data OR there are no outliers 2 max b the error bars/standard deviations shown OR the error bars/standard deviations vary with concentration C sample size is unknown
Question 1(d)
1(d)
Explain one reason for calculating the percentage change in mass.
Easystructured2 marks
Answer
a the change in mass indicates whether the tissue has gained/lost water 2 max b the pieces of tissue will not be the same mass «at the beginning of the experiment» C to compare the relative changes in mass
Question 2
2
The salt concentration inside the Paramecium is 1.8 %. The salt concentration in the surrounding medium suddenly drops to 0.2 %. What will be the likely response?
Mediummcq1 marks
Answer
B