unit c cycling of matter in living systems. plasma membrane, semi permeable membrane protective...
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Transport across the Cell Membrane
Unit C Cycling of Matter in Living Systems
Cell Membrane (pg 271-273) Plasma membrane, semi permeable
membrane Protective layer between environment &
cell’s fragile contents (“biological barrier”) Maintains equilibrium (balance) inside cell Structure
Phospholipid bi-layer (head and tail) Contains embedded proteins for transport and
chemical reactions “Fluid Mosiac Model”
Transport across cell membrane ( pg 274-283)
Semi-permeable/Selectively permeable= only certain solutes are SELECTED to cross membrane
Cells use the following to help transport materials: Energy (ATP) Theory of Brownian motion Natural concentration gradient
End result always equilibrium
Background
Solute Substance that is dissolved in a solution
Eg. Glucose, salt, Potassium, Iron, oxygen, carbon dioxide
Background
Brownian Motion Particles are constantly moving in
random motion
Background
Concentration Gradient Difference of concentrations of
solutes/water between 2 areas Determines direction water or solutes
will move Brownian motion (random movement)
means particles (solutes/water) will naturally flow to an area where they are less concentrated
Two categories of Transport
Passive Transport Active Transport
Passive Transport
Natural movement of particles/water from an area of high concentration to area of low concentration (DOWN the concentration gradient)
Does NOT require energy 3 types of Passive Transport
1. Diffusion2. Osmosis3. Facilitated Diffusion
#1 Diffusion
Movement (high to low) of SOLUTES (fatty acids, glycerol, CO2, O2)
Rate of diffusion how long it takes for diffusion to occur Can be altered by adding energy (eg
stirring or heating) to speed up movement of particles
#2 Osmosis
Movement (high to low) of WATER If a solute is too big, has a charge or not
soluble then it won’t pass by diffusion so water moves instead
Can predict water movement based on the solute concentrations inside and outside of cell 3 conditions that are relative to each other:▪ Isotonic▪ Hypertonic▪ Hypotonic
Isotonic
When two solutions have same concentrations of solutes
Solutes/Water will move between solutions but no net change in amount of either will occur
Hypertonic vs Hypotonic
Two solutions differ in concentration of solutes/water The one with more solutes is hypertonic to
one with less The solution with less solute is hypotonic to
one with more solutes Water concentration of the hypertonic
solution is less than water concentration of hypotonic solution so net movement of water is from hypotonic to hypertonic solution
#3 Facilitated Diffusion
Movement (high to low) of larger SOLUTES (glucose) that need the help of PROTEIN FACILITATOR Channel Protein▪ Creates channels or pores for small water
particles to move Carrier Protein▪ Attach to larger molecules, changes shape
and physically moves molecules across membrane
ActiveTransport
Movement of particles from an area of low concentration to area of high concentration (AGAINST the concentration gradient)
Requires ATP (adenosine triphosphate) energy
Use carrier proteins as a “pump” 3 types of Active Transport
1. Endocytosis2. Exocytosis3. Protein Carriers
#1 Endocytosis
Bringing large particles INTO cell Engulfs large particle using a vesicle
sac to surround, contain then “pinch” off
E.g. Ameoba getting food
#2 Exocytosis
Getting large particles OUT of cell Vesicle surrounds particle and fuses
with cell membrane then ruptures and contents leave cell
#3 Protein Carriers
Movement (low to high) of larger SOLUTES (glucose) that need the help of PROTEIN Carrier Carrier Protein▪ Attach to larger molecules, changes shape
and physically moves molecules across membrane
REVIEW TRANSPORT
Passive Transport Does not require energy Movement DOWN/WITH concentration gradient Transports smaller, water soluble particles (CO2,
O2, H2O, glucose) Includes diffusion, osmosis, facilitated diffusion
Active Transport Requires energy Movement UP/AGAINST concentration gradient Transport of larger particles & ions (Al, Fe, Ca) Includes protein carriers, endocytosis, exocytosis
Why are cells so small?
Transport of materials in/out of cells critical
Ability to transport materials must be at maximum
Larger the cell the more: Volume it has Molecules will be needed to carry out life
functions Distance molecules has to travel from cell
to surface increases
Surface area to volume
As a cell size increases its surface to volume ratio decreases (SA/V)
Meaning that there is less cell membrane to do transport but more cell to get materials to
Think about it
Size of cell is limiting factor
The greater the surface to volume ratio the more efficient the cell is at transportation
Size is the limiting factor of cells Smaller cell with greater SA/V ratio
require less molecules to diffuse across the membrane with more membrane to do it
Example
Oxygen exchange Oxygen is obtained form the surrounding
environment such as water or blood (depends on the cell) and DIFFUSES across the cell membrane.
More membrane more diffusion (Surface area= increases by the 2).
A big cell needs more oxygen than a little cell (volume= increase by the 3)
Big cell has relatively small surface area compared to its volume i.e. the surface area: volume ratio is small.
Larger cells become limited by the rate of gas exchange.
Explain
Obtaining nutrient (glucose) Excretion of waste molecules ( urea,
ammonia, carbon dioxide).