Red blood Cells/ erythrocytes
Plant cellsExplain what hypotonic, hypertonic and isotonic solutions are
1. Hypotonic solution refers to a solution that contains less solute compared to the cytoplasm of the cell.
2. If the solution surrounding the cell is hypotonic, osmosis causes water to have a net flow into the cell,
3. Hypertonic solution refers to a solution, has a higher concentration of solutes than another solution, so that water is drawn out of the cells and into the solution by osmosis.
4. A hypertonic solution is the opposite of a hypotonic solution.
5. isotonic solution - is a solution where the solute concentration of the solution that the cell is in is the same as the solute concentration of the cell's cytoplasm.
Explain the effect of hypotonic, hypertonic and isotonic solutions on plant cell and animal cell.
Animal and plant cells in an isotonic solution
When a cell is placed in a solution where the solute concentration is the same on both sides of the cell membrane, they neither gain nor lose water by osmosis.
Such a solution is said to be isotonic.
Cell in an isotonic environment is in a state of equilibrium with its surroundings.
When the amount of impermeable solute is the same on the inside and outside of the cell, osmotic pressure becomes equal; the force of water trying to exit and enter the cell balances out.
When red blood cells are placed in a 0.9% salt solution, the cell will neither shrink nor swell. So 0.9% sodium chloride (salt) solution is isotonic to blood cells.
When onion cell is placed in an isotonic solution such as 5% sucrose solution, there is no change in its shape because there is no net movement of water by osmosis.
Plant cells in an isotonic environment are flaccid, and they will wither.
The equilibrium of water movement is unable to provide plant cells with internal pressure for structural support, and therefore plants prefer to live in a hypotonic environment.
In this situation, the concentration of solutes inside plant cells is higher than outside, and the plants use active transport to transport solutes in. This also ensures the concentration of water will be higher outside plant cells than inside.
Explain plasmolysis, deplasmolysis, heamolysis and crenation.
Animal and plant cells in a hypotonic solution
1. When an animal cell is set to a hypotonic environment the cell will eventually lyse (rupture) due to the osmotic pressure.
2. A red blood cell placed in a hypotonic solution (e.g., pure water/distilled water) water will enter by osmosis. The red blood cell would take in a lot of water and might lyse ("hemolysis")due to pressure inside. This is a possible because animal cells have no tolerance under hypotonic situations.
3. In a plant, the cell will not lyse but become turgid because of its strong cell wall that prevents it from bursting. These allow the buildup of turgor within the cell. When the turgor pressure equals the osmotic pressure, osmosis ceases.In fact, it is the osmotic pressure (or turgor pressure) that helps keep the plant from wilting and losing its shape.
4. Turgidity is important in young plants where its help in support.
Animal and plant cells in a hypertonic solution
1. In animal cells, being in a hypertonic environment results in crenation, where the shape of the cell becomes distorted and wrinkled as water leaves the cell by osmosis.
2. Examples of hypertonic solution is sea water, 5% sodium chloride solution, 30% sucrose solution
3. In plant cells, the cell membrane pulls away from the cell wall, but the cell remains joined to the adjacent cells at points called plasmodesmata. This condition is known as plasmolysis.
4. Plasmolysis is the seperation of plant cell cytoplasm from the cell wall as a result of water loss. The plant cell becomes flaccid (soft and weak)
5. If the plasmolysed cell is placed in a hypotonic solution, it will absorb water causing the cytoplasm to expand and comes into contact with the cell wall again. This is called deplasmolysis.
The effects and applications of osmosis in everyday life
1. Osmosis has a number of life-preserving functions: it assists plants in receiving water, it helps in the preservation of fruit and meat, and is even used in kidney dialysis.
2. In addition, osmosis can be reversed to remove salt and other impurities from water.
3. The excessive use of chemical fertilizers will cause the plant cells to lose water. Plant cells plasmolysed and later on the whole plant wilt.
4. Dissolved ions from chemical fertilisers such as phosphates, nitrates, calcium, and magnesium, in the soil around the roots and root hairs, will cause the increase in solute concentration, but decrease in water molecules concentration, hence, water diffuse from the cell sap into soil water by osmosis.
5. When water is drawn out of the plant cell, the cytoplasm shrink away from the cellulose cell wall and cause plasmolysis.
6.Plasmolyzed cells lose turgidity and support, causing the whole plant to wilt.
7. Osmosis helps us in preserving food. So that it last longer. By using a concentrated salt or sugar solution, all the water molecules within the food cells are drawn out by osmosis.
8. The food without water will hinder the bacteria and fungus from growing.
9. Animals living in an aquatic environment which are not isotonic to their body tissue may face problem due to the process of osmosis.
10. For example, unicellular organism such Paramecium sp. Living in fresh water, Paramecium has a higher concentration of materials inside the cell than are present in the outside environment. Thus, water is constantly flowing into the cell through the process of osmosis. Paramecium has two contractile vacuoles that eliminate water entering the cell by through osmosis and help maintain osmotic equilibrium.
11. Paramecium must constantly be expelling water to prevent the cell from becoming bloated with water and potentially bursting.
12.The plasma membrane, being semi permeable to certain substances will act as a gate keeper, regulating what goes in and out of the cell.
13. If there is any defect in the plasma membrane, many essential processes in the cells cannot be carried out. Thus the proper functioning of the plasma membrane is important to our health.
14. In order to maintain the proper function of the plasma membrane and the cell as a whole, it is important for us to take care of our food and water intake.
Questions for you to try out:
1. Cucumber slices are immersed in 0.1% sucrose solution. After 3 hours, the slices are found to be turgid and hard.Which of the following statements explains this phenomenon?
A The cucumber cell wall prevents it from shrinking
B The cell sap is hypotonic towards the sucrose solution
C The high concentration of the cell sap in the vacuole causes water to diffuse in
D The cucumber cell wall allows the sucrose molecules to diffuse into the cell
2. A plant cell immersed in distilled water. Which of the following is true about the movement of water molecules in the early stage?
A The rate of water molecules exiting the cell is higher than entering the cell
B The rate of water molecules entering the cell is higher than exiting the cell
C No water molecules are entering or exiting the cell
D The rate of water molecules entering and exiting the cell is the same
3. Siti is going to prepare some mango pickle. First, she cuts and washed the mangoes. Then she adds vinegar and sugar to the mangoes. After one month, the mango pickle remains in good edible condition because
I The pH of the solution is low
II The bacteria that cause food spoilage loses water to the surroundings
III The dehydrated condition of the fruit inhibits the grouth of bacteria
IV The high concentration of vinegar in the pickles is not conducive to the growth of bacteria
A I, II and III only
B I, III and IV only
C II, III and IV only
D I, II, III and IV
4. A plasmolysed cell can revert to its normal condition by being
A Immersed in pure water
B Immersed in a concentrated salt solution
C Immersed in 10% sugar solution
D Taken out quickly from the solution
5. Which of the following processes is affected by the presence of a metabolic poison?
A Absorption of water by root hairs
B Uptake of iodine by algae living in the sea
C Absorption of digested food in the small intestine
D The movement of amino acids across the plasma membrane
6. Preservation of the food by eliminating water from the food involves
A osmosis
B simple diffusion
C active transport
D facilitated diffusion
ESSAY QUESTION:
1(a) A student made the following observation.
The effects of distilled water on red blood cells differ from those on onion cells when
both are placed in equal volumes of
distilled water.
Explain the student’s observation. [5 marks]
(b) Some housewives believe soaking vegetables in salt solution
before cooking can help eliminate the harmful effects of
insecticides that are sprayed on the vegetables.
(i) Explain why vegetables become soft if they are soaked too long
in salt solution.
(ii) Suggest how the housewives can restore the vegetables which
Have become floppy to their normal condition.
[5 marks]
Suggested Answer:
1(a)- Distilled water is hypotonic to the cytoplasm of red blood cells and the cell sap
of the onion cells.(1m)
- Osmosis occurs, resulting in a net flow of water from the surrounding into the
cell.(1m)
- The red blood cells will swell and eventually burst (1m)
- The vacuoles in the onion cells expand, and the plant cells become turgid (1m)
- However, the cell wall prevents the onion cells from bursting because it is tough
and rigid (1m)
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5m
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(b)(i) -Vegetables which are soaked too long in a salt solution will become soft because
the salt solution is more hypertonic than the cytoplasm of the vegetable cells
(1m)
-Water flow out of the cells, causing the cytoplasm and the vacuoles to shrink
(1m).
-The plasma membranes pull away from the cell walls (1m)
-In this condition, the cells are said to be plasmolysed (1m)
(ii) To make the vegetables crisp again, housewives can soak the vegetables in
water (1m)
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5m
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