international turkish hope school 2014 – 2015...

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INTERNATIONAL TURKISH HOPE SCHOOL2014 – 2015 ACADEMIC YEAR

CHITTAGONG SENIOR SECTIONBIOLOGY HANDOUT – OSMOSIS, DIFFUSION AND ACTIVE TRANSPORT

CLASS 9Name : ………………….... Date:........................

d) Movement of substances into and out of cellsStudents will be assessed on their ability to:2.12 understand definitions of diffusion, osmosis and active transport2.13 understand that movement of substances into and out of cells can be by diffusion, osmosisand active transport2.14 understand the importance in plants of turgid cells as a means of support2.15 understand the factors that affect the rate of movement of substances into and out ofcells, to include the effects of surface area to volume ratio, temperature and concentrationgradient2.16 describe experiments to investigate diffusion and osmosis using living and non-living systems.

Human BiologyStudents will be assessed on their ability to:a) Recall simple definitions of diffusion, osmosis and active transport.b) Understand that movement of substances into and out of cells can be by diffusion, osmosisand active transport.c) Understand the factors that affect the rate of movement of substances into and out of cellsto include the effects of surface area to volume ratio, temperature and concentration gradient.d) Describe how to carry out simple experiments on diffusion and osmosis using living andnon-living systems.

Cambridge Specification2.1 Diffusion 2.2 Osmosis 2.3 Active transportCandidates should be able to:(a) define diffusion as the movement of molecules from a region of their higher concentration toa region of their lower concentration, down a concentration gradient;(b) define osmosis as the passage of water molecules from a region of higher water potential to aregion of lower water potential, through a partially permeable membrane;(c) describe the importance of a water potential gradient in the uptake of water by plants andthe effects of osmosis on plant and animal tissues;(d) define active transport as the movement of ions into or out of a cell through the cellmembrane, from a region of their lower concentration to a region of their higher concentrationagainst a concentration gradient, using energy released during respiration;(e) discuss the importance of active transport as an energy-consuming process by whichsubstances aretransported against a concentration gradient, as in ion uptake by root hairs andglucose uptake by cells in the villi.


Examples of active transport include the uptake of glucose in the intestines in humansand the uptake of mineral ions into root hair cells of plants.

Concentration gradient: The difference between the water potential of two solutionswhich causes substances to move from higher to lower regions.

The movement of particles from a region ofHigher concentration to a region of Lowerconcentration, along the concentrationgradient, is known as DIFFUSION.

Eg: Dissolving of ink; Smell travelling acrossroom.

The movement of ions from a region ofLower concentration to a region of Higherconcentration, against the concentrationgradient, using ENERGY (ATP)

[from Mitochondria by Respiration] is knownas ACTIVE TRANSPORT

The movement of water molecules from a regionof higher water potential to a region of lowerwater potential, across a partially permeablemembrane, along the gradient, is known asOSMOSIS.

Eg: Absorption of water from soil by Root HairCells and Turgidity in Plant Cells.

Movement of water into cells.

http://en.wikipedia.org/wiki/Root_hair


Comparison between osmosis and diffusion

Similarities

1. They are both a passive process [do not require energy].

2. They occur down a concentration gradient [higher to lower].

Differences

Diffusion Osmosis

1. It is the movement of particles.

2. It does not require a semi permeablemembrane.

It is the movement of water molecules.

Requires a semi permeable membrane

Water Potential: The tendency of a solution to lose water from a higher waterpotential to a lower water potential region, i.e. Dilute solution to concentratedsolution, or hypertonic to hypotonic.Solution: A mixture of a Solute (Sugar) and a Solvent (Water)

Solutions are compared using the following terms.Hypotonic: A solution containing a higher water potential. [More water]Hypertonic: A solution containing a lower water potential. [Less water]Isotonic: Same solute and solvent.

Wilting: The condition of a plant in the presence of less water in cells which cause thecells to lose turgidity and ultimately lose their shape.

Turgidity: Plant cells have cell walls which prevent the cells from bursting when placedin a hypotonic solution. The water inside the cell exerts pressure on the cell wall andbecomes swollen. This is known as turgor pressure. The process is known as turgidity.

Partially permeable membrane: The membrane that allows only small molecules toenter and exit a cell. Large molecules are prevented to enter through the tiny pores,e.g. cell membrane.

Plasmolysis: The shrinkage of the cytoplasm of a plant cell.

Crenation: The shrinkage of the cytoplasm of an animal cell.


EFFECT OF OSMOSIS IN PLANT AND ANIMAL CELL.

a) Plant cell in hypotonic solution (dilute)-water moves into the cytoplasm which has a lower water potential, from the outside(solution), which has a higher water potential, through the partially permeablemembrane by osmosis. -The cell sap in the vacuole has a lower water potential. Therefore water moves intoit from the cytoplasm. The vacuole swells and pushes the cytoplasm and the cellmembrane.-The cell wall is strong and prevent the cell from bursting.-The cell wall is known as turgid.

b) Plant cell in hypertonic solution: (concentrated solution)-water moves out of the cytoplasm, which has a higher water potential, from theoutside solution, through the partially permeable membrane by osmosis.-the cell sap in the vacuole has a higher water potential. Therefore, water moves outof it into the cytoplasm. The vacuole and the cell membrane loses shape and shrinks insize. -the cell wall is strong and prevents the cell from collapsing.-the cell is said to be flaccid and plasmolysed.

c) Animal cell in hypertonic solution: (dilute)-water moves into the cell by osmosis from outside.-the cell swells in size and bursts, as there is no cell wall to prevent it from bursting.-the cell is said to be plasmolysed.

d) Animal cell in hypertonic solution (less water/concentrated):-water moves out of the cell by osmosis, from inside.-the cell loses shape and forms spikes, as there is no cell wall to keep it firm.-the cell is said to be crenated.

e) Plant and Animal cell in isotonic solution:-a solution that is isotonic with respect to both cells, there is no net movement ofwater in or out of the cell. Both cells remain unaffected.


Effect of OSMOSIS on an Animal Cell (RBC)

Effect of OSMOSIS on a Plant Cell


Factors favoring diffusion· Distance (the shorter the better), e.g. thin walls of alveoli and capillaries.· Concentration gradient (the bigger the better). This can be maintained by

removing the substance as it passes across the diffusion surface. (Think aboutoxygenated blood being carried away from the surface of alveoli).

· Size of the molecules (the smaller the better).· Surface area for diffusion (the larger the better).· Temperature (molecules have more kinetic energy at higher temperature).


EXPERIMENTS related to OSMOSIS and DIFFUSION

1.

Selectively permeable membrane - only allows small sized molecules (water, glucose & aminoacid) but not the large sized molecules (protein & starch) to pass through. e.g. cell membraneof all living cells, the internal wall of the gut & visking (dialysis) tubing.

Dialysis - A physical process by which small sized molecules (water, glucose & maltose) areseparated from large-sized molecules (starch & protein) by using a selectively permeablemembrane.

Food tests:Test for Starch-Iodine testAdd few drops of Iodine solution to the food sample.If the colour changes to blue/black, starch is present.If the colour remains brown/yellow, starch is absent.

Test for Glucose (reducing sugar)-Benedict's test.Add equal amount of benedict's solution to the food sample.Crush the food sample and add water in the food sample, if the food sample is solid.Heat the solution in water bath.If red precipitate is seen, glucose is present.If the colour remains blue, glucose is absent.


2. Experiment to show the selective permeability of visking (dialysis) tubing tostarch and glucose

Procedure1. Set up the apparatus as shown above.2. Wash the filled visking tubing under water before immersion in the distilled water (to

remove any starch and glucose on the outer surface).3. Test for the presence of starch and glucose (reducing sugar) in the distilled water

after 1 hour.ResultOnly glucose (simple sugar) is present in the distilled water outside the visking tubing.

InterpretationGlucose molecules are small enough to pass through the tiny pores on the selectivelypermeable membrane of the visking tubing by diffusion.Starch molecules are too large so they cannot pass through the membrane.

4. Experiment to show the action of saliva on starchy food

Procedure1. Fill one visking tubing with starch solution.2. Fill the other visking tubing with starch and saliva solution.3. Tie the other ends of both visking tubings with threads and support them with glass

rods.4. Wash the two visking tubings under water and then put them separately into a beaker

of distilled water as shown.5. After 30 minutes, take samples of distilled water from the two beakers to test for

starch and reducing sugar.


Result

Solution in dialysis tubingDistilled water outside the dialysis tubingBenedict's Test Iodine Test

StarchStarch + saliva

-+

--

1. No reducing sugar and starch are found in the distilled water surrounding the viskingtubing containing only starch solution.

2. Only reducing sugar is found in the distilled water surrounding the visking tubingcontaining both starch and saliva solution.

InterpretationSaliva contains a digestive enzyme, amylase, which can digest starch into smaller molecule -maltose. In the absence of saliva, the starch molecules are too large to pass through thevisking tubing. In the presence of saliva, the large starch molecules are broken down intosmaller maltose molecules which can then pass through the visking tubing.

ConclusionThe visking tubing represents the internal wall of the small intestine and the distilled waterrepresents the blood. In the presence of digestive enzyme (e.g. amylase) can the large foodmolecules (e.g. starch) be broken down into smaller molecules (e.g. maltose) and passedthrough the membrane or absorbed.

5. A potato was set up as shown in the figure below (left-hand side). Theinvestigation was left for several hours. The results are shown on the right-hand side of the figure.


1. Describe what happened toa. the water in the diskb. the salt solution in the hollow in the potato. [2 mark]

2. Name the process that is responsible for the changes that have occurred. [1 mark]3. Explain why these changes have occurred. [3 mark]4. Where does this process occur in a plant? [1 mark]5. What is the importance to the plant of this process? [1 mark]

Answers1. a. The volume of water in the dish decreased.

b. The volume of salt solution in the potato increased.2. Osmosis3. (3 points from)

- there was a higher concentration of water in the dish than in the potato- so water moved into the potato.- from a high concentration of water to a lower concentration of water- by osmosis.

4. Root hairs, or in the roots.5. Osmosis enables the plant to absorb water to maintain cell turgidity (or to replace water

lost by transpiration).


Surface area to volume ratio

Side = 1cm

Area = 1x1

Volume = 1x1x1

SA ‗ 6x1x1

Vo 1x1x1

Side = 10cm

Area = 10x10

Volume = 10x10x10

SA ‗ 6x10x10 ‗ 6 ‗ 0.6

Vo 10x10x10 10

Side = 100cm

Area = 100x100

Volume = 100x100x100

SA ‗ 6x100x100 ‗ _6_ ‗ 0.06

Vo 100x100x100 100

We can see that, as the cubes become bigger, their surface area increases. But theirsurface area to volume ratio decreased. Therefore, it would take more time forsubstances to diffuse into the longer cube.For examplev An ant has a small areav An Elephant has a large surface areav An ant has a small volumev An Elephant has a large volumev But the surface area to volume ratio of an ant is greater than that of an

Elephant.

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