Zusammenfassung der Ressource
Movement in
and out of cells
- Diffusion
- Explanation
- Diffusion is passive transport, which refers
to the natural, inbuilt motion of particles.
- All particles are constantly in motion
due to kinetic energy they possess.
- The motion is random
- Particles are constantly
bouncing off one another
and other objects
- If all particles are at one side, they will bounce and move to
the other side. There will be no movement in the reverse
direction initially, so there will be a net overall movement from
an area of high concentration to an area of lower concentration
- Definition
- The net movement of molecules or ions from a region where they are
more highly concentrated to one where their concentration is lower
- Rate of diffusion
- Concentration gradient
- Greater the difference
in concentration of
molecules or ions on
either side of an
exchange surface, the
faster the rate of
diffusion
- The path from an area of higher concentration
to an area of lower concentration
- Particles diffuse down the concentration gradient
- Area over which
diffusion takes place
- The larger the area of an
exchange surface, the
faster the rate of diffusion
- Thickness of exchange surface
- The thinner the
exchange surface, the
faster the rate of diffusion
- Surface area x difference in concentration/length of diffusion path
- Facilitated Diffusion
- Explanation
- Like diffusion, it
occurs down a
concentration
gradient, but it
occurs at
specificpoints on
the plasma
membrane where
there are special
protein molecules.
- These proteins form
water-filled channels
(protein channels)
across the membrane.
- The channels are selective, each openin only in the presence of a specific ion.
- These channels allow water soluable ions to pass through. Such molecules would usually
diffuse only very slowly through the phospholipid bilayer of the plasma membrane.
- An alternative form of facilitated diffusion involves carrier proteins that span the plasma membrane. When
a molecule, eg. glucose, that is specific to the protein present, it binds with the protein. This causes it to
change shape in such a way that the molecule is released to the inside of the membrane. No external
energy is required for this. The molecules move from a region where they are highly concentrated to one
of lower concentration, using only kinetic energy
- Osmosis
- Definition
- The
passage
of water
from a
region
where it
has a
higher
water
potential
to a
region
where it
has a
lower
water
potential
- Solutes and water potential
- Water potential
- The pressure
created by water
molecules. Pure
water is said to
have a water
potential of 0
- The addition of a solute to pure water will lower its WP
- WP of a solute must always be <0
- The more solute added, the lower its WP
- Water will move by osmosis from a region of higher (less negative) WP to one of lower (more negative) WP
- Active Transport
- Definition
- The movement of
molecules or ions into or
out of a cell from a
region of lower
concentration to an area
od higher concentration
- Explanation
- ATP is needed
- Used in 1 of 2 ways
- To directly move molecules
- Using a concentration gradient that has
already been set up by direct active transport.
Also known as co-transport
- Against the concentration gradient
- Carrier protein molecules are involved
- Process is selective, specific substances are transported
- Process
- Carrier proteins span cell surface membrance and accept molecules or ions to be transported
- Molecules or ions bind to receptors on the channels of the carrier protein
- Inside the cell, ATP binds to the protein, causing it to split into ADP and a phosphate molecule, casuing
the protein molecule to change shape and open to the opposite side of the membrane
- The molecules or ions are then released to the other side of the membrane
- The phosphate molecule is released from the protein and recombines with the ADP to form ATP during respiration
- The protein reverts to its original shape