Transport across cell membranes Flashcards
How do movement across cell membranes occur by?
- Simple and facilitated diffusion
- Osmosis
- Active transport
- Co-transport
What is simple diffusion?
The net movement of molecules down a concentration gradient from an area of high concentration to an area of low concentration.
What point does diffusion occur till?
Dynamic equilibrium, until the concentration in both substances are equal
Why is simple diffusion passive?
Because it does not require energy in the form of ATP
How do molecules move with no chemical energy.
Kinetic energy
What must the molecules be like in order for them to diffuse across the membrane using simple diffusion?
Lipid-soluble and small
What are the factors that affect the rate of simple diffusion and how?
- Concentration gradient.
The higher the concentration gradient, the increase in rate of simple diffusion - Diffusion distance.
The larger the diffusion distance, the more decrease there will be in rate of simple diffusion. It is only effective in transporting substances over a short distance - Surface area.
The larger the surface area the increase in rate of simple diffusion - Molecular size.
Smaller molecules will diffuse faster - Temperature
The higher the temperature, the more kinetic energy the particles will have which means there will be an increase in the rate of simple diffusion - Stirring
This applies to experiments which will increase the rate of simple diffusion
Why does the membrane have to be thin?
To provide the shortest pathway for the substances to diffuse across.
What is facilitated diffusion? Is it passive?
The process where ions and molecules are transported across the membrane using protein channels and carrier proteins since they cannot be transported by simple diffusion. It is passive since it does not require ATP.
What kind of molecules pass through facilitated diffusion?
Large molecules that cannot diffuse by simple diffusion.
What is osmosis?
The movement of water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane.
What is water potential and its units?
The pressure created by water molecules and is measured in kPa.
What is the water potential of pure water?
0
When solutes are dissolved in water, does the water potential become more negative or more positive?
Negative
What is an isotonic solution?
When the water potential is the same in the solution and the cell within the solution.
What is a hyper-tonic solution?
When the water potential of a solution is more negative than the cell.
What is a hypo-tonic solution?
When the water potential of a solution is more positive than the cell.
What happens if animal cells are placed in solutions that are:
- Isotonic
- Hypotonic
- Hypertonic
Isotonic:
No loss or gain of water.
Hypertonic:
More water leaves the cell causing it to shrivel
Hypotonic:
More water enters the cell causing it to burst
Why is the plasma membrane referred to as fluid-mosaic?
Mosaic - different components including phospholipids and glycoproteins
Fluid - movement of these components.
What are the molecules in the plasma membrane that make up the partially permeable membrane?
Phospholipids, proteins, glycoproteins and glycolipids, cholesterol.
How is the phospholipid bilayer arranged.
Two layers of phospholipids. Hydrophilic heads face outside hydrophobic tails face inside.
What is the difference between hydrophobic tails and hydrophilic heads?
Hydrophobic tails repel water
Hydrophilic heads attract water
What is the purpose of cholesterol and how is this useful?
- Restricts the lateral movement of other molecules in the membrane.
- This prevents the membrane from being too fluid which causes gaps in the membrane and causes water and dissolved ions to leak out of the cell causing the cell to burst.
Where are proteins found and what are the 2 types?
They are embedded across the cell membrane.
Peripheral - embedded completely across the membrane
Integral - embedded from one side of the bilayer to the other.
