Transport Across Membranes Flashcards
Name the 5 ways in which substances are moved across membranes
- Simple diffusion
- Facilitated diffusion
- Osmosis
- Active transport
- Co-transport
Define simple diffusion
NET movement of molecules from an area of highER concentration to an area of lowER concentration
What is diffusion described as?
A passive, random process
Why is diffusion described as a passive, random process
- no external energy source is required (environmentally provided)
- particles move independently from eachother
What is meant by the phrase “no net diffusion”
There is no overall change - the same number of particles are diffusing in each direction
Do polar molecules diffuse slowly or quickly across lipid bilayers?
Slowly
Why do polar molecules diffuse slowly across lipid bilayers?
Diffusion is inhibited by the NON-POLAR fatty acid tails, which repel the polar molecules
Which factors affect the rate of diffusion and how?
- Temperature - An increase in temperature increases the kinetic energy of molecules, so rate diffusion increases
- Concentration gradient - The greater the concentration gradient, the greater the rate of diffusion
- Area of exchange surface - Higher area = rate of diffusion increases
- Length of diffusion pathway - A shorter length = rate of diffusion increases
What is the difference between simple and facilitated diffusion?
Facilitated diffusion relies on the proteins present in plasma membranes
Why is facilitated diffusion used?
Because large and/or polar molecules cannot diffuse across a lipid bilayer fast enough
Which two types of membrane protein are involved in facilitated diffusion
- Channel proteins
- Carrier proteins
What is a channel protein?
- Span the membrane
- Specific (allowing certain molecules/ions to pass through)
- Allows a specific molecule/ion to passively diffuse through
What is a carrier protein?
- Bind with specific molecules (complementary binding site)
- Change shape and release the molecule on the other side (the carrier changes shape)
- Red blood cells move glucose into them in this way
- Passive
What is osmosis?
Diffusion of a water molecule across a partially permeable membrane from an area of higher water potential to an area of lower water potential
What is water potential (Ψ) ?
- Pressure created by water molecules.
- Measured in kilopascals (KPa)
- Under standard conditions of temperature and pressure (250C and 100KPa) pure water has a water potential of 0KPa.
What is a solute?
The thing that is dissolved
What is a solvent?
What it is dissolved in
What is a solution?
A solute that has been dissolved in a solvent
How does adding solute affect water potential?
It lowers the water potential, meaning that water potential is negative.
Which solution has the highest solute concentration out of -25KPa and -35KPa?
-35KPa
Which terms are used to describe osmosis in animal/plant cells?
- Hypotonic
- Isotonic
- Hypertonic
Define Hypotonic
- Less solute
- High water potential outside the cell
- Net osmosis into the cell
Define Isotonic (animal/plant cells)
- Same water potential on either side of the cell
- No net osmosis
Define Hypertonic
- More solute
- Low water potential outside cells
- Net osmosis out of cells
What term describes hypotonic in animal cells?
- Hemolysis
- Hemoglobin is released from cells
What term describes hypertonic in animal cells?
Crenation
What term describes hypotonic in plant cells?
- Turgid
- The water inside the cell pushes the cell out but wont burst it due to the cell wall
What term describes hypertonic in plant cells?
- Plasmolysed
- Cell membrane pulled away from the cell wall
- Due to water loss from the cytoplasm and vacuole
Which formula is used to calculate the molarity/volume of a solution?
M1V1 = M2V2
What does M1 mean?
The molarity of the stock solution
What does M2 mean?
The molarity that you want
What does V1 mean?
The volume of the stock solution
What does V2 mean?
The volume you want
How can this formula be rearranged to find the volume of stock solution?
V1 = M2V2/M1
Define active transport
The movement of molecules across a plasma membrane against a concentration gradient.
Describe the steps in active transport
- Molecules travel through carrier proteins
- Molecule binds to a carrier protein and ATP attaches to the membrane protein on the inside of the cell
- (the ATP changes the shape of the protein in 1 direction)
- The binding of a phosphate molecule to a the protein causes the protein to change shape
- This means that molecules can be accessed on the inside of the cell but the membrane is closed on the outside
How might more than one molecule be moved at the same time?
- During transmission of nerve impulses
- The sodium-potassium pump moves sodium ions out of neurons, while moving potassium ions in
Define co-transport
Co-transport utilises energy in the form of an electrochemical gradient, rather than requiring the direct binding of ATP to the transport protein.
What is another term for co-transport?
Secondary active transport
What is an example of co-transport?
The movement of sodium ions and glucose across the lining of the small intestine (ileum)
Describe an example of co-transport
- Sodium ions are actively transported out of the epithelial cell into the blood by a sodium potassium pump i.e. active transport.
- Sodium ions are now at a lower concentration in the epithelial cell than in the lumen of the small intestine.
- Sodium ions now diffuse down their concentration gradient through a co-transport protein present in the plasma membrane of the epithelial cell. – Glucose is moved against its concentration gradient at the same time.
How many sodiums/potassiums does the sodium potassium pump?
3 sodium ions, 2 potassium ions
What factors affect rate of movement across a membrane?
- Concentration gradient (Higher concentration gradient = faster rate)
- Temperature (Higher temp = faster rate)
- Surface area (Higher SA = Faster rate)
- Length of diffusion pathway (Shorter length = faster diffusion)
- Number of proteins (More = faster rate)
