Transport Across Membranes Flashcards
What is diffusion
The net movement of particles from a region of high concentration to a region of low concentration down the concentration gradient
What is equilibrium
When the concentrations of particles are the same on both sides it is called equilibrium
At equilibrium what occurs
There is no net movement of particles, so diffusion has stopped.
What is a feature of diffusion
It is a passive process that doesn’t require metabolic energy to take place
What is metabolic energy
Energy that is produced by respiration
What is the first factor affecting diffusion (conc g)
Concentration gradient - the greater the concentration gradient the greater the rate of diffusion
What is the second factor affecting rate of diffusion (+ or -)
Charge of the particles - because the cell membrane contains a hydrophobic core charged particles such as ions will not be able to diffuse through the membrane easily. Whereas uncharged molecules diffuse rapidly across membranes.
What is the third factor affecting rate of diffusion (big small)
Size of particles-
Smaller particles will diffuse faster than larger particles.
What is the 4th factor affecting rate of diffusion (temp)
Temperature- in warmer conditions particles have more kinetic energy so diffuse faster than in colder conditions.
What is the 5th factor affecting rate of diffusion (SA)
SA- diffusion takes place quicker if the membrane has a larger surface area.
Factors that affect the rate of diffusion 6 (cm)
Distance - the greater the distance the slower the rate of diffusion
Factors that affect the rate of diffusion 7 (protein)
Presence of protein channels or carrier proteins in the membrane for facilitated diffusion
Why do not all substances diffuse across the cell membrane at the same rate
As the centre of the cell membrane is hydrophobic (due to the fatty acid tails). Hydrophobic substances such as steroid hormones diffuse rapidly whereas hydrophilic substances such as ions and polar molecules can’t diffuse across the membrane.
What is the exception to this
Water can diffuse across the membrane because it is a very small molecule
Why does facilitated diffusion occur
many hydrophilic substances are required for processes in the cell. So cells transport them by facilitated diffusion.
What happens in facilitated diffusion
Hydrophilic substances move across the cell membrane via protein molecules.
The protein molecules allow the hydrophilic substances to pass through without interacting with the hydrophobic centre of the phospholipid bilayer.
What are the two types of proteins involved in facilitated diffusion examples of
Carrier proteins and channel proteins
What do carrier proteins do
They have a binding site for a specific chemical.
When the chemical binds the carrier protein undergoes a change in the tertiary structure.
This change brings the chemical across the membrane and the chemical is then released.
What are protein channels
A protein with a central pore.
The channel or pore is lined with hydrophilic amino acids and contains water.
As a result hydrophilic substances can pass through the channel from one side of the membrane to the other.
What is a feature of proteins involved channels (selectivity )
protein channels are selective for the chemical that can pass through
What is a feature of protein channels (opening)
Some protein channels are always open whereas others only open in response to a certain trigger.
E.g chemicals binding to the protein channel
E.g A change in voltage across the membrane
What is active transport
Where carrier proteins in the membrane transport a chemical from a region of low concentration to high concentration against the concentration gradient.
What does active transport require
Energy which is provided by ATP
What does the molecule or ion that is transported do
It attaches to the receptor site on the carrier protein. At the side of the membrane with a low concentration of the chemical.
What is the second stage of active transport
the molecule of ATP binds to the carrier protein and then undergoes hydrolysis producing phosphorus and ADP
What is the third stage of active transport
The phosphate attaches to the carrier protein causing it to change shape. The carrier protein then transports the molecule or ion to the other side of the membrane where it is released.
What does the phosphate then do
it leaves the carrier protein returning to its previous shape.
What does the ADP and Pi do it reforms to ATP during respiration.
As a result of active transport requiring ATP what do cells that carry out lots of it have
They have lots of mitochondria in the cell
What is a feature of the carrier proteins
They are selective and will only carry one type of molecule or ion
What type of particles (size) do cell require to pass across cell membranes
They require larger particles or molecules to pass across the cell membrane including large protein molecules that are exported from cells. E.g enzymes and antibodies
They arose need large particles to pass into cells e.g antigens and bacteria
What is a property of these large particles
they are too large to cross the cell membrane by facilitated diffusion or active transport.
How are these large particles transferred in cells
By endocytosis and exocytosis
What is a property of endocytosis and exocytosis
They both transfer a large quantity of material, so the processes are called bulk transport.
What occurs in endocytosis and what molecules are transported
Particles or molecules are transported into the cell and large molecules such as proteins and cells like bacteria are transported.
What is the first and second stage of endocytosis
The cell membrane folds inwards forming a cavity around the particles (this process is called invagination)
The particles that are transported are now in the cavity
What are the 3rd and 4th stages of endocytosis
The membrane then completely encircles the particles forming a vesicle
The vesicle then moves into the cell
What does what happens to the vesicle depend on
The substance inside the vesicle
e.g bacteria are digested by lysosomes
And other materials are delivered to different parts of the cell
What is phagocytosis
When solid materials are taken into cells by endocytosis it is called phagocytosis
What is pinocytosis
When fluid is transferred into the cell it is called pinocytosis
What does exocytosis do
it moves material out of the cell such as secreted proteins like hormones and enzymes
What is the first stage of exocytosis
The proteins are found in the Golgi apparatus where they are modified before secretion.
What is the second stage of exocytosis
Vesicles containing the protein bud off the Golgi apparatus and move towards the plasma membrane where they fuse with it and then its contents are secreted.
What do both exocytosis and endocytosis require
Energy, for example to move vesicle to and from the plasma membrane. This energy is provided by ATP.
What is osmosis
Osmosis is the movement of water molecules from a region of high water potential to low water potential through a partially or selectively permeable membrane.
What is a property of osmosis
It is a passive process that doesn’t require metabolic energy
What is water potential
There are water molecules on either side of the membrane that collide with it exerting a pressure on the membrane. this pressure is called water potential.
What is the symbol from water potential
DRAW IT
What is the units for water potential and why
As it is a measure of pressure it has the units kPA
What happens when both sides of the membrane have the same water potential
Water potential equilibrium is reached and osmosis stops. However, water molecules will still be moving across the membrane but the same number will be moving in each direction so there is no net movement of water particles.
What does pure/distilled water have
It has the highest possible water potential
As it has the highest possible concentration of water molecules
What is the water potential of water
0kPA
What will the water potential of a solution be and comparison between concentrated and dilute solution
Less than 0
And a more concentrated solution will have a lower water potential than a less concentrated solution.
What does the cytoplasm of animal cells contain and what is the result
The cytoplasm of all animals cells contains solutes dissolved in water (including glucose and mineral ions. As a result the cytoplasm has a negative water potential.
What happens if the water potential is the same both inside and outside the animal cell
Osmosis is not taking place and the solution is isotonic.
What occurs if an animal cells contains solutes is placed in a hypotonic solution
The water potential outside will be greater than inside, so water molecules will move inside the cell by osmosis. Causing the pressure inside the cell to increase. The cell will become lysis.
What occurs if an animal cells contains solutes is placed in a hypotonic solution
The water potential outside will be greater than inside, so water molecules will move inside the cell by osmosis. Causing the pressure inside the cell to increase. The cell will become lysis.
What is this pressure called
Hydrostatic pressure
What happens if the hydrostatic pressure continues to increase
The plasma membrane is not strong enough to withstand a significant increase in hydrostatic pressure inside the cell, so enough water molecules enter the cell the plasma membrane can rupture and the cell burst this is known as cytolysis
If cytolysis occurs in red blood cells what is it called
Haemolysis
What happens if an animal cells contains is placed in a hypertonic solution
The water potential inside the cell will be greater than outside the cell and water molecules will move out the cell by osmosis and the cell will undergo a reduction in its volume causing the plasma membrane to pucker. This is known as crenation.
What is tightly controlled in animal cells
The liquid around cells is tightly controlled so it is the same water potential as the cytoplasm
What are the differences between plant and animal cells to do with osmosis
Plant cells are surrounded by a cellulose cell wall and contain a large permanent vacuole filled with sugars and mineral ions.
What does the protoplast consist of
The plasma membrane the cytoplasm and the organelles found in the cytoplasm
What can plants not easily control
The environment around their cells.
What happens when plant cells are placed in a hypotonic solution
The water potential outside the cell will be greater than inside the cell and water will enter the cell by osmosis. As a result the turgor pressure inside the cell increases causing the protoplast to push against the cell wall, and because the cellulose cell wall is very strong it doesn’t burst and stays firm.
What is the plant cells called after absorbing the water molecules and what is the pressure called
The plant cell is called turgid and the pressure is called turgor pressure.
What can the turgor pressure prevent at a certain point
It can prevent any more water molecules entering the cell by osmosis.
What happens when a plant cells contains is placed in a hypertonic solution
The water potential inside the cell is greater than the water potential outside the cell and water molecules move out of the cell by osmosis. The protoplast pulls away from the cell wall. This is called plasmolysis and the plant cell is plasmolysed.
What is in the space between the cell membrane and cell wall
The space between the cell membrane and cell wall is now filled by the solution during plasmolysis.
