Module 5.2 Membrane Transport Flashcards
True or False: Membranes are selectively permeable
True
What does selectively permeable mean?
Only some substances can cross the phospholipid bilayer of the membrane
What are some of the selective substances that can cross the phospholipid bilayer?
Selective substances include small neutral molecules such as O2 or CO2 and completely hydrophobic lipids like triglycerides or cholesterol.
Because water is polar, its diffusion through a membrane’s hydrophobic interior is
relatively slow
Water can diffuse quickly through a channel called
aquaporin
The protein channel aquaporin makes what possible
The very rapid diffusion of water into and out of certain cells, such as plant cells, kidney cells, and red blood cells
A single aquaporin allows the entry or exit of up to
3 billion water molecules per second
What is the role of aquaporin in cell membranes?
Facilitates rapid diffusion of water, allowing up to 3 billion water molecules per second
Aquaporins enable a tremendous increase in
water transport over simple diffusion.
Define concentration gradient.
The concentration of solute from one area to another. Just like a gradient in color.
How do molecules move in a concentration gradient?
From an area of higher concentration to lower concentration. They are taking the path of least resistance
Molecules go from an area of higher concentration to lower concentration because they want to take the path of
least resistance
Equilibrium occurs when there is
no longer a gradient and there is an even distribution of molecules
Molecules are said to be in equilibrium when
there is an even distribution of molecules and there is no longer a gradient
How do molecules move during equilibrium?
They are still moving because molecules always more, but there is no net movement in one direction
What is diffusion?
The process of molecules moving from higher to lower concentration until equilibrium is reached.
Diffusion does not require
energy
Diffusion is the result of
the random movement of molecules
Diffusion is one type of
passive transport
What is passive transport?
Diffusion across a membrane with no energy investment.
Concentration gradients often exist on
opposite sides of a membrane
What happens when oxygen is used quickly by a cell?
Creates an oxygen gradient that allows oxygen to diffuse very passively/easily across the membrane.
Osmosis is a type of
passive transport
What is osmosis?
The movement of free water not bound to a solute across a membrane by passive transport.
In osmosis the more solute in a solution the less
free water there is.
How are free water and solute related
inversely related
Because water and solute are inversely related water will move across the membrane in the
opposite direction as solute
In biological membranes, only water goes across membranes by
passive transport
Since water is polar, it cannot pass directly through the
phospholipid bilayer
Nearly all cells have a
channel protein
Nearly all cells have a channel protein in their membranes called
aquaporin
Which protein helps with the passive transport of water?
Aquaporin.
Aquaporin does what passively?
It passively transports water across the membrane using no energy
Aquaporin facilitates moving
3 billion water molecules per second across the membrane
Aquaporin still doesn’t cost any
energy
What does tonicity refer to?
The ability of a surrounding solution to cause a cell to gain or lose water.
Tonicity directly relates to the
solute concentration
Hypo- prefix means
less
A hypotonic solution has
less solute than the cell
Hyper- prefix means
more
Hypertonic solution has
more solute than the cell
Iso- prefix means
same
An isotonic solution has
the same solute as the cell
Blood cells are often used as a model for
what occurs in all cells
Cells in an isotonic solution
the solute and water concentration are the same in the solution and in the cells
Isotonic results in no
concentration gradient of water so there is no net movement of water across the membrane
What does is mean when we say there is no net movement of water across the membrane
The same amount of water flowing into the red blood cell is the same amount coming out
A hypertonic solution
has more solute in the solution
In a hypertonic solution, there is more
free water inside the cell than in the solution.
When there is more water inside the cell than in a solution,
water goes down the concentration gradient, travelling out of the cell into the solution
What happens to cells in a hypertonic solution?
They shrink and become shriveled due to water moving out of the cell.
What occurs in isotonic solutions?
The solute and water concentrations are the same, resulting in no net movement of water.
A hypotonic solution has
has less solute in the solution
In a hypotonic solution, there is more
free water inside the cell than in the solution.
When there is less water inside the cell than in a solution,
water goes down the concentration gradient, travelling into the cell from the solution.
What happens to cells in a hypotonic solution?
The become full of water and burst
The last type of diffusion/passive transport is called
facilitated diffusion
What is facilitated diffusion?
Diffusion of a solute across a membrane using a transport protein.
When is facilitated diffusion used
When a polar or charged molecule cannot pass through the phospholipid bilayer
All passive transport is
high to low concentration with 0 energy/ATP
What types of proteins are involved in facilitated diffusion?
- Channel proteins
- Carrier proteins.
Channel proteins are like
tunnels through the membrane
Carrier proteins are shape-
changers to bring molecules across the membrane
What is active transport?
The transportation of molecules against the concentration gradient from low to high
What is required for active transport?
- A carrier protein in the membrane
- Energy, usually as ATP.
A sodium potassium pump is a type of
active transport
An endocytosis is another type of
active transport
What is endocytosis?
Moving large molecules into the cell using vesicles.
In Endocytosis, cells can bring in
large amounts of water and solutes
An exocytosis is another type of
active transport
What is exocytosis?
Moving large molecules out of the cell using vesicles.
Exocytosis can be used to get rid of waste like
protein, polysaccharides or CO2
