Diffusion and transport Flashcards
Define Diffusion?
The net movement of molecules from an area of high concentration to an area of low concentration
What molecules can use simple diffusion to enter a cell?
- Non-polar
- Small
What prohibits a molecule from entering a cell using simple diffusion?
- Too big
- Polar
What factors affect diffusion?
- Heat
- Size of molecules
- Steepness of concentration gradient
Do the molecules move in a pattern?
Nah they random
When does diffusion stop?
When all molecules are evenly distributed in the solvent
What is facilitated diffusion?
When diffusion is assisted using a carrier protein or molecule imbedded in the membrane
Are protein channels specific?
Yes, they can only move one type of molecule each
Can facilitated diffusion move a molecule against its concentration gradient?
No
Does facilitated diffusion require energy?
No
What determines the direction of diffusion?
The concentration gradient
Define amphiphilic
When molecules have a polar and non-polar end,
- capable of interacting with both hydrophobic and hydrophilic environments
What is passive transport?
A method of transporting a material through a membrane that does not require energy
What is a solute?
A molecule capable of being dissolved in a liquid to form a solution
What is osmosis?
The movement of water molecules through a semi-permiable membrane along its concentration gradient, due to the presence of a solute that cannot pass through the membrane.
What is aquaporin?
The protein channel responsible for the diffusion of water across the plasma membrane at a very high rate
What does hypertonic mean?
- Water leaves the cell
The extracellular solution has a higher osmolarity than the fluid inside the cell
What does hypotonic mean?
- Water enters the cell
The extracellular solution has a lower osmolarity than the fluid inside the cell
What does isotonic mean?
- No net diffusion
The osmolarity inside the cell is equal to the extracellular solution
What is osmolarity?
The total amount of substance dissolved in a specific amount of solution/ dissolved solutes
What is a solute?
The dissolved molecules in a solvent solution
What is tonicity?
The amount of solute in a solution
What is osmotic pressure?
The pressure that must be applied to a solution to prevent the flow of water across a membrane by osmosis
What is the equation for osmotic pressure?
Π = cRT Π - Osmotic pressure c - Total solute concentration R - The gas constant T - Absolute temperature
How does osmosis differ in plant and animal cells?
- Animal cells: Can modify the shape of cells
- Plant cells: Can still change shape but the cell wall holds its general structure
- Cell walls can limit the volume of water that can be absorbed, animal cells will absorb water until it bursts if the concentration gradient is high enough
What is turgor pressure?
The internal pressure against the cell wall builds up preventing more water from entering
- Pushes the water back
Can water diffuse across a membrane faster, slower, or the same speed as simple diffusion?
Faster
Why can water diffuse faster across a membrane?
- Water can “hitchhike” with ions such as Na+ as they pass through ion channels
- Aquaporin are channels that allow large amounts of water to diffuse across the membrane
What are the 3 types of endocytosis?
- Phagocytosis
- Pinocytosis
- Receptor-mediated endocytosis
When does a cell use phagocytosis?
A variation of endocytosis, used If the material the cell absorbs is particulate/a macromolecule (Cellular eating)
- Bacteria
- Organic fragments
When does a cell use pinocytosis?
A variation of endocytosis, use If the material absorbed is a liquid (Cellular drinking)
- imports macromolecules from the extracellular fluid that the cell needs
When is receptor-mediated endocytosis used?
When the material absorbed is a specific molecule/particle that can bind to receptors on the plasma membrane
How does the process of receptor-mediated endocytosis differ from other types of endocytosis?
- There is a pit on the surface of the plasma membrane with receptor proteins protruding from it,
- This pit is coated in a protein called clathrin
- Target molecules attach to the protein receptors
- When a sufficient amount of the receptors are filled the pit caves in, seals, and forms a clathrin-coated vesicle inside the cell
What is endocytosis?
A type of active transport that moves substances, including fluids and particles, into the cell by engulfing
What is exocytosis?
A process of passing bulk material out of the cell,
- Vesicle packages inside the cell migrate to the plasma membrane, fuse with the membrane, and release their contents outside the cell
How does the Na/K pump work?
- 3 Sodium ions bind to a protein channel in the membrane,
- An ATP molecule provides energy to the protein channel so it can change shape
- One phosphate group from the ATP remains bound to the channel, this causes the change in shape
- The protein channel then drives the Na+ through the channel to the outside of the cell
- The new shape of the cell (open to the outside) has a high affinity for K+ ions now and 2 ions attach to the inside of the protein channel
- This binding causes a change in the shape of the protein channel and makes it face inwards, the phosphate group is consequently released
- The K+ is then released into the cell
Which direction does sodium travel in the Na/K pump?
Inside to outside
Which direction does potassium travel in the Na/K pump?
Outside to inside
What is active transport?
A method of moving substances against their concentration gradient that requires energy
What is an electrochemical gradient?
A gradient produced by the combined forces of an electrical gradient and a chemical gradient
What is a pump?
The active transport mechanism that works against electrochemical gradients
What is a transport protein?
A membrane protein that facilitates the passage of a substance across the membrane by binding to it
In what direction do carrier proteins move substances in active transport?
From low to high concentration,
- Only one direction, in or out
What is ATP hydrolysis?
The breakdown of ATP into ADP and a release of energy
What are the two types of active transport?
- Primary
- Secondary
What is primary active transport?
Involves direct hydrolysis of ATP for energy to move a substance against its concentration gradient,
- When a molecule moves across the membrane, an ATP molecule is used
What is secondary active transport?
Uses the energy from an ion concentration gradient or an electrical gradient,
- The gradients are established by primary active transport
What is an example of secondary active transport?
The Na+/K+ pump
What does endocytosis depend on?
- Integral and membrane protein receptors called Ligands
- When a vesicle forms around a substance involved in endocytosis, the receptors, ligands, and present substances near the site of endocytosis are included in the vesicle as the portion of the membrane splits off into the cell
