Assalamualaikum.
CHAPTER 3 MOVEMENT OF SUBSTANCES ACROSS THE PLASMA MEMBRANE
-Movement of substance in and out of the cells is regulated by plasma membrane
The structure of the Plasma Membrane
-Composed mainly of phospholipids and protein
-Fluid-mosaic model of the membrane structure was introduced by S.Singer & G.Nicolson in
1972
=Membrane protein are dispersed throughout and inserted into the phospholipid bilayer.
a)Phospholipid bilayer
-polar head (hydrophilic property-attached to water)
-non-polar tail (hydrophobic property-repelled by water)
-Act as barrier that separate two sides of membrane
b)Glycoprotein
-to support in cell recognition functions
c)Cholesterol
-stabilise and strengthen the plasma membrane
d)Pore protein
-form channel that allows small water soluble molecules & ions pass through the plasma
membrane freely
Eg: K⁺ , Na⁺ , Ca²⁺
e)Carrier protein
-can change shape before transporting molecules
-have sites that can bind to specific molecules Eg: Glucose
The permeability of the plasma membrane
-semi-permeable / selectively permeable
-Whether a molecule can pass through the plasma membrane depends on its – size
- polarity
-molecules/ions that can pass through....
| Phospholipid bilayer | Pore protein | Carrier protein |
| -Fatty acid -Glycerol -O₂ -CO₂ -water | - K⁺ - Na⁺ - Ca²⁺ -water | -Glucose -Amino acids |
Movement of substances across the plasma membrane
A)Passive Transport B)Active Transport
-No energy input required -Need energy input
a)Simple diffusion
b)Osmosis
c)Facilitated diffusion
A)Passive Transport
a)Simple Diffusion
=Net movement of molecules or ions from a region of higher concentration to a region of
lower concentration , thus going down a concentration gradient until an equilibrium is
achieved
-does not need energy
-happen with or without semi-permeable membrane
-can be observed in liquids or gases
-molecules that move across the plasma membrane by simple diffusion
-Vitamin ADEK (lipid soluble)
-Water (small)
-O₂ , CO₂ (dissolved gases)
b)Facilitated Diffusion
=movement of water-soluble molecules or ions across the plasma membrane with the aid
of carrier and pore proteins
-carrier proteins : have binding sites that can combine with specific molecules
 | Glucose molecule move towards the binding sites of specific carrier proteins |
| Glucose molecule binds to the specific site on the carrier protein | |
| Carrier protein changes its shape to transport the glucose molecule across the plasma membrane | |
| Carrier protein back to its original shape and free to assist the passage of other similar molecules |
Facilitated diffusion of glucose molecules with the aid of carrier protein
-pore proteins : transporter with specific shapes and charges
: always open
: allows only specific ions to pass through
 | K⁺ move across the plasma membrane through pore protein |
Facilitated diffusion of K⁺ ion through a pore protein
c)Osmosis
=Net movement of water molecules from a region of low solute concentration to a region
of high solute concentration through a semi-permeable membrane. OR
=Net movement of water molecules from a region of high water concentration to a region
of low water concentration through a semi-permeable membrane
-also known as diffusion of water
-does not need energy
-only happen with presence of semi-permeable membrane
B)Active Transport
=Movement of molecules or ions from a region of lower concentration to a region of higher
concentration thus against the concentration gradient across the plasma membrane.
-require
a)carrier protein
-have active sites that – binds to a particular molecule
- binds with ATP molecule
-also called Pumps because its function just like water pumps
b)cellular energy in a form of ATP
-ATP generated during respiration in mitochondria
| . Concentration of Na⁺ ions higher on the outside of the cell . Na⁺ approach the carrier protein and bind with the specific site. . Another site bind with ATP molecule |
| . Carrier protein binds with Na⁺ . ATP molecule split into ADP & P The splitting releases energy to the carrier protein . P then attach itself to the carrier protein |
| . Energy change the shape of carrier protein causing it to release the Na⁺ outside the cell |
Mechanism of Active transport for Na⁺ ion
The process of passive and active transport in living organisms
| Simple Diffusion | Facilitated Diffusion | Osmosis | Active Transport |
| Gaseous exchange between alveoli and blood capillaries | Absorbtion of certain nutrients through the villi of the small intestine | Transport of water in the cortex of plant stems | Accumulation and elimination of substances by sea water organisms |
| Gaseous exchange through stomata | | Movement of water between plant cell | Uptake of mineral salts and ions by root hair |
| Gaseous exchange in unicellular organism | | Osmoregulation in aquatic organism | |
| | | Water uptake by plant root | |
3.2MOVEMENT OF SUBSTANCES ACROSS THE PLASMA MEMBRANE IN EVERYDAY LIFE
Animal Cell and Plant Cell in hypotonic , hypertonic and isotonic solution
Animal cell
Plant cell
| Cell | Hypotonic (Solution with a lower solute concentration) | Hypertonic (Solution with a higher solute concentration) | Isotonic (Solution which the concentrations of solutes are equal) |
| Red Blood Cell | -water diffuse into the cell through osmosis (Net movement of water into the cell) -the cell swell -plasma membrane is too thin and can’t withstand the osmotic pressure developes within the cell -cell burst -bursting of RBC known as Haemolysis | -water diffuse out of the cell through osmosis (Net movement of water from the cell) -the cell shrink or shrivel =>internal pressure decreased -plasma membrane crinkles up -RBC have undergone Crenation | -Water diffuse in and out of the cell at equal rates (No net movement of water) -Cell retain its normal shape |
Plant cell | -water diffuse into the cell through osmosis (Net movement of water into the cell) -the cell vacuole expand and swell -plasma membrane pushes against the cell wall -cell becomes turgid -turgor pressure created -cell does not burst because of its rigid cell wall *Herbaceous plant depends on turgor pressure to support its stem | -water diffuse out of the cell through osmosis (Net movement of water from the cell) -the vacuole and cytoplasm shrink -Shrinking of cytoplasm due to osmosis called Plasmolysis -Cell wall does not shrink because it is strong -plasma membrane pulls away from the cell wall -The cell becomes Flaccid *Flaccidity causes plant leaves to become limp and stem to droop *Plasmolysed cell can become turgid again by immersing into hypotonic solution .Process called Deplasmolysis | -Water diffuse in and out of the cell at equal rates (No net movement of water) -Cell retain its normal shape |
The effect and applications of osmosis in everyday life
a)In Plants
i)Too much fertiliser cause soil water become hypertonic
=>water diffuse from the cell into the soil by osmosis
=>cell are plasmolysed
=>plant will wilt
=>plant died if not watered immediately
b)Food preservation
i)Using natural preservatives eg: sugar / salt on food
=>solution outside the food more hypertonic compared to the contents of the food
=>water diffuse from the food by osmosis
=>cells in the food become dehydrated
=>bacteria & fungi also lose water and die
=>Food can last longer
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