osmosis&diffusion 3n

8/14/2019 osmosis&diffusion 3N

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Name:_____________________( ) Class:__________ Date:__________

Diffusion and Osmosis Chapter 2

At the end of the chapter, students should be able to:

1. Define diffusion and describe its role in nutrient uptake and gaseous exchange inplants and humans.

2. Define osmosis and describe the effects of osmosis on plant and animal tissues.

The plasma membrane is partially permeable only allows certain substances topass through

Substances cross the plasma membrane, leaving or entering cell by diffusion,osmosis and active transport.

Diffusion and osmosis 1


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Surface Area to Volume Ratio

Why are most cells microscopic?

Why are all large organisms made up of many cells but not just one cell?

Total surface area(height x width xnumber of sides xnumber of boxes)

6 250 750

Total volume(height x width xlength x number ofboxes)

1 125 125

Surface-area-to-volume ratio (area

volume)

6 1.2 6

In the diagram, cells are represented as boxes

As the size of cell increases to 5 units of length per side in (b), the ratio ofsurface area to volume ratio decreases compared to the smaller cell (a)

In a large cell (b), rates of movement of materials across cell membranes areneeded to meet the needs of cell may not be enough because most of the

cytoplasm is far away from the cell membrane

By dividing large cell to many small cells in (c), a high surface area to volumeratio can be restored. This can serve each cells need for getting nutrients andremove waste products

That is why larger organisms do not generally have larger cells than smallerorganisms, but more cells.



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Diffusion

Molecules of oxygen are moving about all the time. Molecules of a liquid, or asubstance like sugar dissolved in water also move around.

The movement cause molecules to spread themselves out evenly to fill all the

available space

Diffusion movement of molecules from a region of _______________concentration to a region of _________________ concentration, down aconcentration gradient.

Concentration gradient difference between high concentration and lowconcentration

Diffusion ________________________________.

Diffusion also occurs in liquids.

o When you add a drop of red ink to a beaker of water, the ink spread slowly

throughout the water without stirring.

o Water in beaker becomes evenly red



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Rate of diffusion depends on:

o Concentration gradient

The greater the difference in concentrations between two regions of a

substance, the faster the rate of diffusion __________________diffusion gradient, faster diffusion

o Distance over which diffusion takes place

Shorter distance between the 2 regions of concentration,__________________ rate of diffusion

o Area over which diffusion takes place

Larger surface area, ___________________ rate of diffusion.

Diffusion surfaces have structures for increasing surface area wherethey exchange material. Eg. Microvilli on cells lining the intestine.

o Size and nature of diffusion molecules

Small molecules dissolve ____________________

Molecules that dissolve in fats diffuse _____________________through cell membranes than molecules that dissolve in water.



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Importance of diffusion

Diffusion an important way which substances move in and out of cells. In booth plantand animal cells, gases are exchanged through diffusion

Examples:

o Presence of millions of alveoli in the lungs provides very large surface area

for gaseous exchange

o In plants, carbon dioxide diffuses in through the stomata during

photosynthesis and oxygen diffuses out

o In a one-celled organism called Amoeba, _________________ diffuses in

and __________________ diffuses out of it.

Osmosis

The figure shows a concentrated sugar solution, separated from a dilute sugarsolution by a partially permeable membrane.

o This membrane only allows _________________ molecules but not the larger

sugar molecules to pass through



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Water then diffuses from _____________ solution (more water molecules) into more____________________ solution (less water molecules) through partially permeablemembrane.

Process osmosis

o Definition: movement of ____________________________ from region of their_______________ concentration to a region of their _______________concentration, through a partially permeable membrane.

Water potential

Water potential of solution whether the solution lose water molecules or gainwater molecules from another solution

Pure water has highest water potential

Another way of defining osmosis movement of water molecules from a region of__________________water potential to a region of _________________ waterpotential, through a partially permeable membrane.

Importance of osmosis in the uptake of water by plants

Plants absorb water from soil through root hairs.

The __________________ is usually less concentrated than ______________ invacuole of root hair cell

Water moves into root hair cell by _____________, from higher water potential tolower water potential through partially permeable membrane (plasma membrane ofroot hair cell.

Water passes from one cell to another by _______________ until it reaches thexylem vessels.

Effect of Osmosis on Plant Cells

The effects of osmosis on plant cells can be observed by placing them in

a) Water

b) Concentrated sugar or salt solution (more concentrated than the cell sap inthe vacuole)



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In solution ofhigh water potential orpure distilled water

1. water _______________ cell by

osmosis

2. vacuole _______________ in size

3. cell contents are pushed against thecellulose cell wall

4. the cell wall prevents over expansionof the cell by exerting an opposingpressure preventing the entry of morewater

5. the cell becomes ______________

6. the plant cell does not _____________because the cell wall is tough

In solution with low water potential

1. water _____________ cell byosmosis

2. vacuole ______________ in size

3. cytoplasm shrinks away thecellulose cell wall and it stopspushing outwards on the cell wall

4. the cell becomes ______________

5. as more water is lost, the cytoplasmshrinks further into the centre of thecell but the cell wall is too stiff toshrink much

6. the cell membrane surrounding thecytoplasm tears away from the cellwall. The cell is ________________

7. Plasmolysis occurs when a plant cellis placed in a concentrated solution.



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Effect of Osmosis on Animal Cells

The effect of osmosis on animal cells can be shown by putting red blood cells in

a) Water

b) Strong salt solution (more concentrated than the cytoplasm)

In water

Water ___________________ cell by osmosis

Cells become larger and burst

In strong salt solution

Water _________________ cell by osmosis

Cells shrink

Active Transport

Requires energy (from respiration)

Enables cell to transport substances from a region of __________________concentration to a region of ___________________ concentration.

Example of active transport

o Root hair cells take in mineral salts from soil although the soil may not have a

lot of mineral salts


Strong salt solution water

osmosis&diffusion 3n

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