[Biology F4 Chapter 3]

8/2/2019 [Biology F4 Chapter 3]

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Movement of substances acrossthe plasma membrane





(A)

(B)

(D)

(E)

(C)

(F)



Structure of the plasma membrane

• composed mainly of ▫ phospholipids and

▫ proteins

• The movement of substances

in and out of a cell occursthe plasma membrane

• The fluid-mosaic model

▫ proposed that

membrane proteins aredispersed throughout and inserted into the

phospholipid bilayer



• Phospholipid molecule▫ polar head - hydrophilic

property and

▫ a pair of non-polar tails-

• Phospholipid bilayer acts as

▫ a barrier

▫ isolates the two sides of the membranes

• Cholesterol molecules▫ stabilize the structure of

the plasma membrane



• Pore protein▫ protein molecule that

forms a channel or a pore

• Carrier protein

▫ protein molecule that acts as a carrier• glycoproteins

▫ membrane proteinsthat have

carbohydratesattached to them• The phospholipid

bilayer, proteins andother components

▫ not rigid or static



• Selective Permeable / Semi Permeable

• Carrier Protein



The permeability of the plasma

membrane• Selectively permeable/semi-permeable

▫ some substances can move across the membrane

• Factors that determine permeability

▫ the size and

▫ polarity

• pass through the phospholipids bilayer freely ▫ Lipid soluble molecules

▫ Non Polar Molecules



• hydrophobic tails - prevent polar molecules topass through 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

• Carrier proteins▫ Used by large water-soluble molecules such as

amino acids and glucose to pass through theplasma membrane





The movement of substances across the

plasma membrane : passive transport

• Simple diffusion▫ Net movement of

articles (molecules )

▫ from of higherconcentration to aregion of lowerconcentration.

• Expenditure of energy -not required• continue until -

dynamic equilibrium is

reached



• Example of processin living organismsis the diffusion of

oxygen from thealveolus into theadjacent blood

capillaries





Osmosis



Osmosis

• Net movement of water molecules

• from a region of higher concentration of water

water molecules

• through a partially permeable membrane.

• Eg.

▫ reabsorption of water molecules from thenephron into the blood capillaries



Facilitated diffusion

• The passivemovement of molecules or ions

gradient.• involves

▫ pore proteins(channel proteins) or

▫ carrier proteins



• The particularmolecules combinewith the specific active

site of the carrier protein.

• The carrier proteinchan es its sha e

• After assisting themovement of moleculesto the other side of theplasma membrane, it isfree to bind with othermolecules



• Example- thereabsorption of glucose and amino

acids from the villiinto the bloodcapillaries



• Active Transport

• Definition :

• Energy Involve

• Concentration Gradient :

• Name of energy :

• Source :



The movement of substances across the

plasma membrane : active transport

• The movement of substances (ions) acrossa cell membrane

• from a re ion of lower

concentration to aregion of higherconcentration,

• against a concentration

gradient.▫ requires expenditure of

energy from ATP



• particularmolecules/ionscombine with▫ specific active site of

the carrier protein.

• carrier protein changeits shape▫ when the phosphate

group from ATPmolecules binds to it toa ow t e mo ecu es/ions to pass throughto the other side of theplasma membrane.

• After assisting tomovement of molecules

to the other side of theplasma membrane,▫ it is free to bind with

other molecules



• Active transport▫ result in the

accumulation of orelimination of molecules

▫ Carrier proteins are oftencalled pumps as they actlike water pumps whichuse energy to move wateragainst the gravity

• Example-

▫ the absorption of mineralsalts into the hair roots





• Isotonic :

• Hypotonic :

• Hypertonic :



The movement of substances across

the plasma membrane• Movement of substances across the plasma

membrane is necessary :a To su l nutrients to the cell

b) To allow exchange of respiratory gasesc) To remove waste products• Substances may move through a membrane by

simple diffusion, facillitated diffusion, osmosisand active transport



Movement of substances across theplasma membrane in everyday life

• Isotonic solution – asolution that has the sameconcentration of solutes asanother solution

–

solution that has a lowertotal concentration of solutes than anothersolution

• Hypertonic solution – a

solution that has a highertotal concentration of solutes than anothersolution



Define

• Crenation

• Haemolysis

• Turgid



Animal and plant cells in an isotonicsolution

• Water moleculesmove into and out of a cell at the same

rate and the cellretains its normalshape (normal

concave disc shapered blood cell andplant cells)



Animal and plant cells in anhypertonic solution

• Water leaves a cell by osmosis causingthe cell to shrink loose water . The

cell shrivel and theplasma membranecrinkles up of red

blood cell known as

crenation and inplant known asplasmolysis



Animal and plant cells in anhypotonic solution

• Water enters a cell by osmosis causingthe cell to swell. The

bursting of red blood cell is knownas haemolysis and in

plant known asturgid





Generate ionic

Gradients essential

For muscular and

Nervous activities

Secrete useful

substances

To remove toxic

substances

Maintain a suitable pH

And ionic concentrationInside the cell

Obtain certain

Food supplies

across membrane



Task :

1. Activity 3.4 (Page 48 Biology Text Book)

2. Visualizing Main Idea (Page 54 Biology Text Book)

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[Biology F4 Chapter 3]

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