Diffusion, Active Transport, Osmosis 2.1.5 (d,e) Flashcards
what are the two types of exchange of substances between cells?
passive
active
what is active exchange?
exchange which requires metabolic energy
what is diffusion?
the net movement of particles from a region of high concentration to low concnetration
what is simple diffusion?
diffusion in the absence of a barrier/membrane
which molecules can freely pass through the phospholipid bilayer?
non-polar molecules (like oxygen)
small molecules
which molecules cannot pass freely through the phospholipid bilayer?
charged molecules (ions)
polar molecules (water)
large molecules
why can’t charged molecules pass through the phospholipid bilayer?
they are charged and thus repelled by the hydrophobic fatty acid core
can water diffuse through the phospholipid bilayer?
yes but very slowly
as it is polar it is only partially charged
why are membranes partially permeable?
they allow certain molecules in and not others
what affects the rate of diffusion?
temperature
concentration gradient
surface area
thickness of membrane
how does an increased temperature affect the rate of diffusion?
a higher temperature means the particles have more kinetic energy to so move at higher speeds
how does an increased concentration gradient affect the rate of diffusion?
a steeper concentration gradient between two regions will increase the rate of diffusion
how does the thickness of the membrane affect the rate of diffusion?
the thinner the membrane the shorter the diffusion distance so the rate of diffusion increases
how does surface area affect the rate of diffusion?
a larger surface area the faster the rate of diffusion
what is facilitated diffusion?
diffusion across a membrane through the use of a channel and carrier proteins
what two proteins are used in facilitated diffusion?
carrier proteins
channel proteins
how are carrier proteins used in facilitated diffusion?
used to move large molecules (polar molecules and ion) down the concentration gradient
how does a carrier protein work passively?
large molecule binds to the carrier protein
protein changes shape
the molecule is released on the opposite side
how are channel proteins used in facilitated diffusion?
they have hydrophilic interiors which allow large polar molecules to pass through
what factors affect facilitated diffusion?
temperature
concentration gradient
surface area
membrane thickness
number of channel proteins present
how does the number of channel proteins present affect the rate of diffusion?
the more channel proteins the higher the rate of diffusion
what is active transport?
the movement of molecules/ions into a cell from a region of low concentration to high concnetration
is active transport active or passive?
active
require ATP
outline active transport
the molecule binds to receptors in the carrier protein
ATP binds to the carrier protein and is hydrolysed to from ADP + P
the P group binds to the carrier protein to cause it to change it’s shape
this new shape opens up on the other side of the cell, with the molecule being released to enter the cell
ADP + P recombine to form ATP and the carrier protein returns to it’s original shape
what is bulk transport?
the movement of large molecules too large to be transported by facilitated diffusion
what are examples of molecules too large to be transported by facilitated diffusion?
enzymes
hormones
bacteria
what are the two types of bulk transport?
endocytosis
exocytosis
what is endocytosis?
the bulk movement of material INTO cells
what are the two types of endocytosis?
phagocytosis
pinocytosis
what is phagocytosis?
bulk transport of solids INTO a cell
what is pinocytosis?
bulk transport of liquids INTO a cell
what is exocytosis?
the bulk movement of material OUT of cells
is bulk transport active or passive?
active
requires ATP for the movement of vesicles along the cytoskeleton
what is osmosis?
the movement of water from a region of high water potential to low water potential across a partially permeable membrane
what is water potential?
the pressure exerted by water molecules on a container/membrane
what is the water potential of pure water?
0 kPa
the more concentrated the solution
the more negative the water potential
what is an isotonic solution?
when the water potential outside the cell and inside the cell are equal
what is the net movement in an isotonic solution?
no net movement
water moves in both directions
what is a hypertonic solution?
when the water potential inside the cell is greater than outside the cell
what is the net movement in a hypertonic solution?
water moves out of the cell
what happens to an animal cell in a hypertonic solution?
the cell shrink and shrivel
what happens to a plant cell in a hypertonic solution?
the cell becomes plasmolysed as the plasma membrane and cytoplasm ew pulled away from the cell wall
what solution fills the gap between the cell membrane and cell wall in a plasmolysed cell?
the contents of the outside solution
what is a hypotonic solution?
when the water potential outside the cell is greater than inside
what is the net movement in a hypotonic solution?
water moves into the cell
what happens to an animal cell in a hypotonic solution?
the cell swells and will eventually burst (cytolysis)
what happens to a plant cell in a hypotonic solution?
the cell swells and becomes turgid
it does not burst
why does a plant cell not burst when in a hypotonic solution?
it has a cell wall which can withstand the turgor pressure generated by the influx of water
