BIOLOGY - Ch#3
Movement in and out of cells
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Notes
Section 1: Diffusion
Diffusion is the net movement of particles from an area of higher concentration to an area of
lower concentration(i.e. Down the concentration gradient) as a result of their random
movement.
● The movement of particles is completely random.
○ Because they are gases and spread.
○ Due to their kinetic energy.
○ It continues until they reach an equilibrium.
● Diffusion takes place in both gases and solutions. (can happen in both gases and liquids)
● Diffusion can also take place ‘through’ some materials.
○ Such as cell membrane. We call these ‘partially permeable’ membranes.
○ Generally, only very small molecules that are dissolved in the fluid, either inside
or outside the cell can diffuse through
■ This could include things like glucose, water, oxygen, or amino acids.
■ Larger molecules on the other hand, such as starch and proteins, can’t fit
through the membrane.
● Example:
○ A blood vessel is surrounded by multiple cells.
○ In order to function, cells require a lot of energy which they get from cellular
respiration.
○ This process requires a lot of oxygen and glucose which are found in high
concentrations in the blood vessels, but low concentrations in the cells that need
them.
○ Because of this, there’s a concentration gradient which allows glucose and
oxygen to diffuse into the cell, where they can be used in cellular respiration.
, ○ One of the waste products of this process is carbon-dioxide, and its
concentration builds up in the cytoplasm so that a gradient of concentration of
CO2 develops.
○ Because of its high concentration in the cells, it is able to diffuse out of the cell
into the bloodstream down its concentration gradient.
■ When we talk about the diffusion of particles down the concentration
gradient, it means that the particles move from an area where they are
more concentrated to an area where they are less concentrated.
○ Diffusion is ‘one’ way that some substances can pass in and out of cells.
Remember that the cell surface membrane is partially permeable - it allows
certain substances to enter or leave the cell. If there is a concentration gradient
of a substance across the cell-membrane, and the membrane is freely permeable
to that substance, the substance will enter or leave by diffusion.
○ Another example is photosynthesis.
■ Plants take in CO2 by diffusion. CO2 moves from higher to lower
concentration; from the surroundings to inside the plant ‘through’
stomata.
■ As a result, O2 is produced and moves outside the plant by diffusion.
● Diffusion is a passive process.
○ This means it doesn’t require energy from the cell.
○ It’s just the random movement of particles that results in diffusion.
Factors Affecting Diffusion:
● Concentration Gradient: The difference in concentration between 2 places.
●
● In both cases, there are more particles on the left side than the right side. So the
particles will diffuse from left to right.
○ However, the particles in the top box will diffuse across to the right more quickly
because there’s a bigger difference in the concentrations on either side.
■ Higher difference in the number of particles means more particles are
available to move from high concentration to low concentration areas.
Movement in and out of cells
___
Notes
Section 1: Diffusion
Diffusion is the net movement of particles from an area of higher concentration to an area of
lower concentration(i.e. Down the concentration gradient) as a result of their random
movement.
● The movement of particles is completely random.
○ Because they are gases and spread.
○ Due to their kinetic energy.
○ It continues until they reach an equilibrium.
● Diffusion takes place in both gases and solutions. (can happen in both gases and liquids)
● Diffusion can also take place ‘through’ some materials.
○ Such as cell membrane. We call these ‘partially permeable’ membranes.
○ Generally, only very small molecules that are dissolved in the fluid, either inside
or outside the cell can diffuse through
■ This could include things like glucose, water, oxygen, or amino acids.
■ Larger molecules on the other hand, such as starch and proteins, can’t fit
through the membrane.
● Example:
○ A blood vessel is surrounded by multiple cells.
○ In order to function, cells require a lot of energy which they get from cellular
respiration.
○ This process requires a lot of oxygen and glucose which are found in high
concentrations in the blood vessels, but low concentrations in the cells that need
them.
○ Because of this, there’s a concentration gradient which allows glucose and
oxygen to diffuse into the cell, where they can be used in cellular respiration.
, ○ One of the waste products of this process is carbon-dioxide, and its
concentration builds up in the cytoplasm so that a gradient of concentration of
CO2 develops.
○ Because of its high concentration in the cells, it is able to diffuse out of the cell
into the bloodstream down its concentration gradient.
■ When we talk about the diffusion of particles down the concentration
gradient, it means that the particles move from an area where they are
more concentrated to an area where they are less concentrated.
○ Diffusion is ‘one’ way that some substances can pass in and out of cells.
Remember that the cell surface membrane is partially permeable - it allows
certain substances to enter or leave the cell. If there is a concentration gradient
of a substance across the cell-membrane, and the membrane is freely permeable
to that substance, the substance will enter or leave by diffusion.
○ Another example is photosynthesis.
■ Plants take in CO2 by diffusion. CO2 moves from higher to lower
concentration; from the surroundings to inside the plant ‘through’
stomata.
■ As a result, O2 is produced and moves outside the plant by diffusion.
● Diffusion is a passive process.
○ This means it doesn’t require energy from the cell.
○ It’s just the random movement of particles that results in diffusion.
Factors Affecting Diffusion:
● Concentration Gradient: The difference in concentration between 2 places.
●
● In both cases, there are more particles on the left side than the right side. So the
particles will diffuse from left to right.
○ However, the particles in the top box will diffuse across to the right more quickly
because there’s a bigger difference in the concentrations on either side.
■ Higher difference in the number of particles means more particles are
available to move from high concentration to low concentration areas.
