Diffusion Flashcards
What are the 3 different ways ions and molecules pass through the cell membrane?
Diffusion
Carrier mediated transport
Vesicular transport
What is passive transport?
transport that occurs without the input of energy from the cell
Give examples of a passive process
Facilitated diffusion, osmosis and diffusion
What are active processes?
Transport that uses energy from the cell is needed to for the transportation to occur
Give examples of an active process
Vesicular transport
Active transport
What is diffusion?
The passive movement of molecules or particles from a region of high concentration to a region of low concentration, to reach equilibrium over the available space
Can substances soluble in lipids (eg. Alcohol, steroids and fatty acids) diffuse through a membrane?
Yes they can through the lipid part of the membrane. Oxygen and CO2 can also diffuse through.
How do water soluble substances/molecules enter or leave the cell, through diffusion?
They can go through a membrane channel if they are small enough to fit.
Eg. Water, sodium, calcium, chloride ions etc…
Glucose is too large
What is osmosis?
Passive movement of water through a selectively semi-permeable membrane, from a region of high water concentration (low solute) to an region of low water concentration (high solute), to reach equilibrium.
What is carrier mediated transport?
Molecules being transported through a carrier, like enzymes they are specific so they only bind to a specific molecule and they get saturated, increasing the concentration doesn’t make it faster
What are two types of carrier mediated transport?
Facilitated diffusion
Active transport
Describe what occurs in facilitated diffusion through a carrier protein
For example:
Glucose attaches to a binding site on the carrier, the carrier changes shape, and the molecule is released on the other side of the membranes.
Describe the process of active transport in a carrier mediated transporter?
Requires ATP to act as a ‘credit card’ to transport molecules against the concentration gradient. The molecule ‘pays’ the protein by giving it ‘ATP money’ on which then it is allowed passage out of the cell.
Describe the process of facilitated diffusion through a channel protein
They form narrow passageways through which small ions can diffuse through rapidly from a high ion concentration to a lower ion concentration.
Only specific ions of a specific shape and size can pass through, a particular channel.
What is vesicular transport?
Movement of substances across the cell membrane in vesicles
What is endocytosis in vesicular transport?
Taking liquids or solids into the cell
What is pinocytosis?
Cell drinking
Vesicles contains liquid particles
What is phagocytosis?
Cell eating
Vesicles contains solid particles
How does endocytosis occur?
The cell membrane folds around a droplet of liquid or solid particle until the droplet is completely enclosed. The vesicles formed then pinches off and is suspended in the cells cytoplasm.
What is exocytosis?
Contents inside the vesicle, in the cell are passed OUT of the cell
How does exocytosis occur?
Vesicles in the cell migrate to the cell membrane and fuses with it where it will then ‘expel’ its contents into the extracellular fluid
Explain diffusion into the cell
Before diffusion, high concentration of water molecules are outside the cell than inside where a low concentration is.
After diffusion, concentration of water molecules is the same outside and inside the cell
What does osmosis do to the cell?
Concentration of the solution that surrounds a cell will affect the state of the cell
What are the three possible concentrations of solution during osmosis?
Isotonic
Hypertonic
Hypotonic
What is an isotonic solution?
A solution in the extracellular fluid has the same concentration than to the intracellular fluid.
What happens to the cell when it is in an isotonic solution?
There is no change to the cell size.
The amount of water transported into the cell equal to the amount of water transported out the cell
What is a hypertonic solution?
A solution of high concentration of water in the intracellular fluid then the extracellular
Intracellular contains dilute solution of salt compared to a concentration solution of salt outside
Eg. Cell placed in salt water
What occurs to an animal cell when placed into a hypertonic solution?
Water moves out of the cell as the cell has more concentration of water than the extracellular, as of this the cell shrinks or crenate.
What happens to a plant cell when placed in a hypertonic solution?
Water will leave the cell, as the cell contains a higher concentration of water than the extracellular fluid because of this the cytoplasm shrinks and plasmoyse, and the cell becomes flaccid.
What is a hypotonic solution?
A solution of low concentration of water in the intracellular than the extracellular.
Water moves from the more diluted solution of salt in the extracellular into the more concentrated solution of salt in the intracellular
Eg. Cell placed in distilled water
What happens to an animal cell when placed in a hypotonic solution?
Water enters the cell, as the cell has less concentration of water than the extracellular, the cell swells and may burst or lyse.
What happens to a plant cell when placed in a hypotonic solution?
Water enters the cell, as there is less concentration in the cell than the extracellular, the cell swells a bit and becomes turgid due to the cell wall preventing the cell from bursting.
What are the 6 factors affecting the rate of diffusion?
Concentration gradient Size of particles Membrane thickness Surface area Distance Temperature
How does concentration gradient affect the rate of diffusion?
The greater the difference in concentration of a substance in 2 areas, the faster the rate of diffusion
How does the size of particles affect the rate of diffusion?
Small particles tend to diffuse faster than larger particles.
How does membrane thickness affect the rate of diffusion?
Diffusion takes place more quickly through a thin membrane because there is only a short diffusion pathway.
How does surface area affect the rate of diffusion?
Diffusion is quicker if the membrane has a large surface area.
How does distance affect the rate of diffusion?
The shorter the distance between two regions, the faster the rate.
How does temperature affect the rate of diffusion?
An increase in temperature increases the rate of diffusion because the particles will have greater kinetic energy.
How does Volume and Surface Area ratio of a membrane affect the rate diffusion?
As organisms get bigger, Surface area:Volume ratio of a cell gets smaller.
So as organisms get bigger, the more difficult it is form them to exchange materials with the surroundings (diffusion)
Why are cells small?
They are small as,
A cell increasing in size reaches a point where the inward movement of essential substances and outward movement of wastes across the surface are by diffusion is not as fast and doesn’t come to the service of increasing volume of the cell.
