What are the 3 common factors that determine whether a molecule can pass through a plasma membrane? (3)
- molecular size
- polar molecule
- ionic charge
State examples of nonpolar molecules that can pass through the plasma membrane.(4)
- fatty acid
- glycerol
- fat soluble vitamins (A,D,E,K)
- steroid compounds
Give examples of small molecule & ion that can pass trough the plasma membrane. (3)
- polar molecules (water)
- nonpolar molecules (O2, CO2)
- ion ( K+, Na+, Ca2+, Mg2+)
Give examples of large molecules that can move across the plasma membrane. (2)
- glucose
- amino acid
What is passive transport and how many types are there (3)?
- movement of substances across the plasma membrane that does not involve the use of energy
- simple diffusion
- osmosis
- facilitated diffusion
What is simple diffusion? (4)
- movement of molecules/ions from an area o high concentration to an area of low concentration
- molecules move down the concentration gradient until dynamic equilibrium is achieved
- may occur with/without the presence of a plasma membrane
- example of substances: lipid soluble molecules (fatty acid, glycerol), O2 & CO2 diffuse through the phospholipid bilayer
What is osmosis? (3)
- net movement of water molecules from an area of high water potential to an area of low water potential randomly through a selectively permeable membrane
- the selectively permeable membrane is permeable to water but impermeable to some solutes like sucrose molecules
- occurs in cells through phospholipid bilayer
What is facilitated diffusion (4)?
- lipid-insoluble molecules (ions, amino acid, glucose) are unable to pass through the phospholipid bilayer
- move across the membrane with the aid of transport proteins (carrier/channel proteins)
- does not require energy because the transport proteins move down the concentration gradient
- continues until dynamic equilibrium is achieved (concentration of molecules is the same at both sides of the membrane)
How does facilitated diffusion occur through channel proteins? (2)
- form channels/canals to allow small solutes & ions to diffuse across the plasma membrane
- channels have specific internal characteristics that only allow specific ions to pass through it
How does facilitated diffusion occur through carrier proteins? (2)
- have specific sites & can only bind to certain molecules
- example: glucose can only bind to the specific site of a glucose carrier protein
How does facilitated diffusion of glucose molecules occur through carrier proteins? (4)
1) Extracellular glucose concentrations are higher than in cytoplasm.
2) Glucose binds with the specific site of the carrier proteins.
3) Carrier proteins change shape to allow glucose molecules to pass through the carrier proteins and enter the cell.
4) Carrier proteins return to their original shape & are ready to transport other molecules.
What are the characteristics of active transport (5)?
- occurs against a concentration gradient
- requires energy in the from ATP molecules
- requires specific carrier protein( aka pump) with specific sites
- carrier proteins have receptors to bind with ATP molecules & changes shape when a phosphate group attaches to it.
- results in the accumulation/excretion of molecules/ions
Explain the sodium-potassium [Na+ out of cell, K+ into cell] pump of animal cells. (6)
1) Extracellular fluid has high Na+ concentration, cytoplasm has low Na+ concentration. 3 sodium ions bind to the carrier protein.
2) ATP molecules decompose into ADP & P. The phosphate group is bound to the carrier protein.
3) Phosphate bond provides energy & changes shape of carrier protein, then sodium ion is transported through the carrier protein out of the cell.
4) Extracellular fluid had low K+ concentration, cytoplasm has high K+ concentration. 2 potassium ions from outside the cell bind with a carrier protein. The phosphate group leaves the carrier protein.
5) The loss of phosphate group restores the original shape of the carrier protein.
6) Potassium ion is transported through the carrier protein into the cell.
Explain the proton pump in the stomach cavity. (4)
1) Proton pumps can be found on the epithelial cells lining in the stomach cavity,
2) Causes the acidity of the stomach contents.
3) Energy from ATP enables the hydrogen ion to be transported by the carrier proteins.
4) Causes an accumulation of hydrogen ion & acid production in the stomach cavity.
State the similarities between passive transport & active transport. (2)
- move substances across a membrane
- occurs through a selectively permeable membrane
State the differences between passive transport (3) and active transport (3).
Passive transport
- energy is not required
- occurs following the concentration gradient
- occurs until a dynamic equilibrium is achieved
Active transport
- requires energy
- occurs against the concentration gradient
- accumulation and disposal of molecules/ions
