bab 3 plasma membrane

8/7/2019 bab 3 plasma membrane

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Each phospholipid molecule has a polar head

(hydrophilic) and a pair of non-polar tails

(hydrophobic ). Phospolipids in mambrane plasma

arrange themselves into bilayer.

The phospholipid bilayer acts as a barrier whichisolates the two sides of the membrane.

Cholesterol molecules help to stabilise and

strengthen the plasma membrane, making it

flexible , yet less permeable to water soluble

substances such as ions.


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There are various types of protein which are either

partially or fully embedded in the membrane.

Pore protein forms a channel whereas carrier protein

acts as a carrier.

Some membrane proteins that have carbohydrates

attached to them are called gycoproteins.

The phospholipid bilayer, proteins and othercomponents are not rigid or static but form a

dynamic and flexible structure.


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Function of the Plasma Membrane

Protects the cell.

Separates the intracellular components from theextracellular environment.

Controls what enters and exits the cell


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N

ecessities for the Movement of Su

bstancesacross the Plasma Membrane

To transport nutrients into the cell.

For gases exchange

To excrete metabolic waste.

To maintain the pH value and ionicconcentration of the cell.


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Permeability of the Phospholipids Bilayer

The permeability of the phospholipids bilayer

is determined by:

the size

and polarityof the substances pass through it.


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Although the hydrophobic tails of

phospholipids prevent polar molecules to passthrough it, but because of the small molecular

size of water , it can slide between the

phospholipids bilayer move through the pores.

Pore proteins allow small water-soluble

molecules and ions to pass through the plasma

membrane.

Large water-soluble molecules such as amino

acids and glucose use the carrier proteins to

pass through the plasma membrane.


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What is passive transport?

Passive transport is the movement of substances

across the cell membrane without the use of energy

by the cell.

During passive transport, substances move down

their concentration gradient, hence no energy is

required.

Passive transports can happen through three

different channels, namely

lipid bilayer

pore protein

carrier protein


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What is diffusion?

Diffusion is the movement of particles from a highdensity region to a low density region. No energy is

needed and no membrane involves in diffusion.

The Dynamic Equilibrium

Diffusion will continue until the concentration in all

region is the same. When this happen, we say it hasreached the dynamic equilibrium.


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Factors Affecting the Rate of Diffusion (How fast

diffusion happens)


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Particles that Move Through the Plasma

Membrane Through Diffusion

Substances soluble in fat: fatty acid, glycerol,

some vitamins (A,D,E,K)

Neutral particles: water, oxygen, carbondioxide,

Example of Diffusion

Between alveoli and blood capillaries in the

lung during gases exchange.


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What is Osmosis?

Osmosis is the diffusion of a water through a semi-

permeable membrane, from a solution oflow solute

concentration to a solution with high solute

concentration.

It is a physical process in which a solvent moves,

without input of energy, across a semi-permeable

membrane separating two solutions of different

concentrations.

Important Points:

It is the diffusion of water (normally) through a semi-

permeable membrane.

It is from a dilute solution to a more concentratedsolution.


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What is Facilitated Diffusion?

Facilitated diffusion is the passive transport of substances acrossthe plasma membrane with the help of transport proteins such

as the channel protein and the carrier protein.

Substances Pass through the Plasma Membrane through

Facilitated Diffusion

Particles undergo facilitated diffusion are the particles that cannot

diffuse through the phospholipid bilayer such as large particles

such as glucose, amino acids, proteins and nucleic acids

Some ions such as the sodium ions and chloride ions


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2 Types of Transport Protein

Facilitated diffusion occurs through 2 types of transport protein, namely

1.Channel Protein (Pore protein)

2.Carrier Protein

Mechanism ofFacilitated Diffusion


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What is Active Transport?

Active transport is the movement of substances acrossthe plasma membrane of cells against the

concentration gradient (From lower concentration to

higher concentration).

Since it is against the concentration gradient, energy is

needed in the process.

Video below shows how particles are transported

through the carrier protein in active transport. Take

notes that the process only happens when the carrier

protein receives energy from an ATP.


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Basic Requirements in Active Transport

Presence of the carrier protein

Presence ofATP (Adenosine Triphosphate)

Function of the ATP

ATP is the source of energy in active transport. It suppliesenergy to the carrier protein to carry out the process. It

is converted into ADP (Adenosine Diphosphate) after the

reaction.

Examples of Active Transport

Intake of mineral ions by the root hairs of a plant.


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What is Hypotonic Solution?

Hypotonic solution is the solution that has higher waterpotential than the other solution.

Water Concentration and Solute Concentration of a Cellin a Hypotonic Solution

Water concentration: Water concentration inside the cell

is lower than outside the cell.

Solute Concentration: Solute concentration inside the

cell is higher than outside the cell.


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Effect of Hypotonic Solution on Animal Cell

1. If an animal cell such as red blood cell is placed into a hypotonic

solution, water molecules is transported into the red blood

cells by osmosis (as shown in the diagram above).

2. The red blood cells will inflate and finally burst because the thin

membrane cannot withstand the high pressure inside the cell.

3. The red blood cells are said to undergo haemolysis.


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Effect of Hypotonic Solution on Plant Cell1.When a plant cell is placed in a hypotonic solution, water molecules is transported

into the cell by osmosis.

2.The water is then stored in vacuole causing it to expand and exerts pressure on

the cell wall. This pressure is called turgor pressure.

3.The turgor pressure caused the plant cell to become firm orturgid.

4.The rigid cell wall prevents cell from bursting.


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What is Isotonic Solution?

In isotonic solutions, both solutions have equal waterpotential.

Water Concentration and Solute Concentration of a

Cell in a Isotonic Solution

Water concentration and solute concentration are

equal in both solutions.


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1. If an animal cell such as red blood cell is placed into a isotonic solution, amount

of water molecules is transported into the red blood cells by osmosis is equal

to the amount of water molecules transported out from the cell (as shown in thediagram above).

2. Therefore the amount of water in the cell remain unchanged.

3. The red blood cells maintain their shape.

Effect of Isotonic Solution on Animal Cell


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Effect of Isotonic Solution on Plant Cell

1. When a plant cell is placed in an isotonic solution, solute

concentration in the external solution is equal to the solute

concentration i the cell sap.

2.Therefore the rate of diffusion of water into the cell is equal

to the rate of diffusion of water out from the cell.

3. As a result, the shape of the cell remain unchanged.


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What is Hypertonic Solution?

Hypertonic solution is the solution that has lowerwater potential than the other solution.

Water Concentration and Solute Concentration

of a Cell in a Hypertonic Solution

Water concentration: Water concentration inside

the cell is higher than outside the cell.

Solute Concentration: Solute concentration inside the

cell is lower than outside the cell.


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Effect of Hypertonic Solution on Animal Cell

1.If an animal cell such as red blood cell is placed into a hypertonic

solution, water molecules is transported out from the red blood

cells by osmosis (as shown in the diagram above).

2. The red blood cells will shrink due to the lost of water from the cell

and probably die.

3. The red blood cells are said to undergo crenation .


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Effect of Hypertonic Solution on Plant Cell

1. When a plant cell is placed in a hypotonic solution, water molecules is

transported out from the cell by osmosis.

2. The vacuole and cytoplasm are then shrink due to lost of water.

3. The plasma membrane is pulled away from the cell wall.

4.The process is called plasmolysed.

bab 3 plasma membrane

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