osmosis application Flashcards
Following digestion and absorption of food, the undigested remains are processed to form faeces in the parts of the intestine below the ileum.
The faeces of people with constipation are dry and hard. Constipation can be treated by drinking lactulose. Lactulose is soluble, but is not digested or absorbed in the human intestine.
Use your knowledge of water potential to suggest why lactulose can be used to help people suffering from constipation.
what should you use in this question
The idea that lactulose is soluble can gain water
faces is dry or hard without water
water potential gradient tells you that osmosis is involved
Lactulose) lowers the water potential of faeces / intestine / contents of the intestine;
Accept Ψ for water potential
- Water retained / enters (due to osmosis) and softens the faeces;
Accept descriptions of soft faeces, eg faeces is less dry / less hard
A high concentration of sodium in the blood can affect blood volume and cause hypertension.
Use your knowledge of water potential to suggest how high sodium concentrations in the medicines taken could affect blood volume.
(Sodium ions) lower the water potential (of blood);
Accept make the blood water potential more negative
Accept decrease the blood water potential
- Water would move into the blood by osmosis (from cells/tissue fluid);
- Increasing the blood volume;
When preparing the cells for observation the scientist placed them in a solution that had a slightly higher (less negative) water potential than the cytoplasm. This did not cause the cells to burst but moved the chromosomes further apart in order to reduce the overlapping of the chromosomes when observed with an optical microscope.
Suggest how this procedure moved the chromosomes apart
Water moves into the cells/cytoplasm by osmosis;
Reject water moving into chromosomes/nucleus.
- Cell/cytoplasm gets bigger;
The student produced the sucrose solutions with different concentrations from a concentrated sucrose solution.
Name the method she would have used to produce these sucrose solutions.
Name of method
Dilution series
Putting bee honey on a cut kills bacteria. Honey contains a high concentration of sugar.
Use your knowledge of water potential to suggest how putting honey on a cut kills bacteria
Water potential in (bacterial) cells higher (than in honey) / water potential in honey lower (than in bacterial cells);
Q candidates must express themselves clearly
- Must be comparative e.g. high WP in cell and low WP in honey
- Water leaves bacteria / cells by osmosis;
- (Loss of water) stops (metabolic) reactions.
Use your knowledge of water potential to suggest how watering plants with sodium chloride solution affects the fresh mass of the tomatoes.
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Water potential inside tomato plant becomes higher / less negative;
Water drawn out of tomato plants / more difficult for tomato plants to take up water;
By osmosis;
Six cylinders of a standard size were cut from a single large potato. One cylinder was placed in distilled water and the others were placed in sucrose solutions of different concentrations. The length of each cylinder was measured every 5 minutes for the next 50 minutes.
The graph shows the changes in length at each sucrose concentration.
(a) Explain why
(i) the potato cylinder in distilled water increased in length;
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potato more negative water potential / hypertonic;
(accept more concentrated)
water enters by osmosis causing cells to extend / become turgid;
the potato cylinder in the 1.0 mol dm–3 sucrose solution showed no further
decrease in length after 40 minutes
little / no water remaining in potato / fully plasmolysed /
all water has moved out;
cell wall prevents further shrinkage / sucrose solution moves in;
or, water potentials are equal / equilibrium / isotonic;
no net movement of water / no further osmosis;
After 45 minutes the potato cylinder in the 0.8 mol dm–3 solution was removed and blue dye added to this solution. Some of this blue-stained solution was drawn into a syringe. A drop was then released, slowly, halfway down a test tube of fresh 0.8 mol dm–3 sucrose solution as shown in the diagram. The blue drop quickly moved to the surface of the liquid in the test tube.
(i) The density of a solution depends on its concentration. The more concentrated the solution the greater its density. Explain why the blue drop had a lower density and therefore moved up.
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(2)
(ii) A sucrose solution of concentration 0.3 mol dm–3 has a water potential which is equivalent to that of the potato cells. Describe and explain what would happen to the blue drop from this solution.
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water moved into the solution from the potato;
solution diluted / becomes less concentrated;
2
(ii) no net movement of water (in or out);
drops move up / less dense;
or, no net movement of water (in or out);
drop would not move / densities the same;
