chapter07 section03

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Copyright Pearson Prentice Hall

7-3 Cell Boundaries7-3 Cell Boundaries


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7-3 Cell Boundaries

All cells are surrounded by a thin, flexible barrierknown as the cell membrane.

Many cells also produce a strong supporting layeraround the membrane known as a cell wall.


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Cell Membrane

The cell membrane regulates what enters

and leaves the cell and also providesprotection and support.


Cell Membrane


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Cell Membrane

Cell Membrane

Outside ofcell

Cellmembrane

Inside of cell

(cytoplasm)Proteinchannel

Proteins

Lipid bilayer

Carbohydrate

chains


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Cell Walls

What is the main function of the cell wall?


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Cell Walls


Cell Wall

Cell walls are found in plants, algae, fungi, andmany prokaryotes.


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Diffusion Through Cell Boundaries

Measuring Concentration

A solution is a mixture of two or more substances.

The substances dissolved in the solution are calledsolutes.

The concentration of a solution is the mass ofsolute in a given volume of solution, ormass/volume.


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Diffusion

Particles in a solution tend to move from an areawhere they are more concentrated to an areawhere they are less concentrated.

Equilibrium
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Osmosis

Osmosis

Osmosis is the diffusion of water through aselectively permeable membrane.
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Osmosis

How Osmosis Works

Movement ofwater

Dilute sugarsolution(Water more

concentrated)

Concentratedsugar solution(Water lessconcentrated)

Sugarmolecules

Selectivelypermeablemembrane
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Osmosis

Water tends to diffuse from a highly concentratedregion to a less concentrated region.

If you compare two solutions, three terms can beused to describe the concentrations:

hypertonic (above strength).

hypotonic (below strength).

isotonic(same strength)


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Osmosis

Osmotic Pressure

Osmosis exerts a pressure known as osmoticpressure on the hypertonic side of a selectivelypermeable membrane.

3 C ll B d i


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Osmosis


7 3 C ll B d i F ili d Diff i


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Facilitated Diffusion

Facilitated Diffusion

Proteinchannel

Glucosemolecules

7 3 C ll B d i A ti T t


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Active Transport

Active Transport

Sometimes cells move materials in the oppositedirection from which the materials would normally

movethat is against a concentration difference.This process is known as active transport.

Active transport requires energy.

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Active Transport

Molecule to be carried

ActiveTransport

Molecular Transport

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Active Transport

Endocytosis and Exocytosis

Endocytosis is the process of taking material intothe cell.

Two examples of endocytosis are:

phagocytosis

pinocytosis

During exocytosis, materials are forced out of thecell.


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7-3
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7-3

Unlike a cell wall, a cell membrane

a. is composed of a lipid bilayer.

b. provides rigid support for the surrounding

cell.c. allows most small molecules and ions to

pass through easily.

d. is found only in plants, fungi, algae, andmany prokaryotes.


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7-3

The concentration of a solution is defined as the

a. volume of solute in a given mass of solution.

b. mass of solute in a given volume of solution.

c. mass of solution in a given volume of solute.

d. volume of solution in a given mass of solute.


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7-3

If a substance is more highly concentratedoutside the cell than inside the cell and thesubstance can move through the cell membrane,the substance will

a. move by diffusion from inside the cell tooutside.

b. remain in high concentration outside the cell.

c. move by diffusion from outside to inside thecell.

d. cause water to enter the cell by osmosis.


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7-3

The movement of materials in a cell against aconcentration difference is called

a. facilitated diffusion.

b. active transport.c. osmosis.

d. diffusion.


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7-3

The process by which molecules diffuse acrossa membrane through protein channels is called

a. active transport.

b. endocytosis.c. facilitated diffusion.

d. osmosis.


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