transport across cell membranes 3.2.3 Flashcards
function of the cell membrane
controls which substances pass into + out of cell
3 functions of internal membranes
compartmentalisation
site for biochemical reactions
controls which substances pass into and out of organelles
5 main molecular components of a membrane
phospholipids
proteins
glycoproteins
glycolipids
cholesterol
3 functions of phospholipids
allow lipid soluble substances to enter and leave cell
prevent water soluble substances entering or leaving cell
makes membrane flexible and self sealing
2 functions of extrinsic proteins
provide mechanical support/adhesion
act as receptors for molecules
2 functions of intrinsic proteins
form protein channels
form carrier proteins
3 functions of cholesterol
reduces lateral movement of molecules
makes the membrane less fluid
prevents leakage from cell
3 functions of glycolipids
act as recognition site
helps maintain membrane stability
helps attach cells together to form tissues
2 functions of glycoproteins
act as recognition sites
help cells attach to each other to form tissues
define diffusion
the net movement of molecules or ions from a region of high concentration to an area of low concentration, until at equilibrium.
3 factors affecting rate of diffusion
surface area
difference in concentration
thickness of membrane
define osmosis
the passage of water molecules from a solution of high water potential to a solution of low water potential through a selectively permeable membrane.
define hypotonic
less concentrated
define hypertonic
more concentrated
define isotonic
at equilibrium
define water potential
the pressure created by water molecules trying to diffuse out of a solution down a gradient from a higher water potential to a lower water potential.
what has high water potential
a dilute solution as it has many free water molecules so water is more likely to move
what is the water potential to f pure water
0
what is a protoplast
the entire cell is excluding the cell wall
what is incipient plasmolysis
the point where plasmolysis takes place and half the cells are plasmolysed, half are not
what happens when an animal cell is in a solution of high water potential
cell bursts open
what happens when animal cell is in a solution of low water potential
cell shrinks and shrivels
what happens when a plant cell is in a solution of high water potential
protoplast is pushed tight against cell wall
what happens when a plant cell is in a solution with low water potential
protoplast shrinks away from cell wall
(plasmolysed)
what particles does a channel protein transport
small charged substances (usually ions)
what do channel proteins form
water filled pores lined with polar groups (so hydrophilic)
how do cells use channel proteins to control entry and exit
most channels are gated
what do carrier proteins transport
larger molecules such as glucose and amino acids are taken across
how does a carrier protein work
is able to bind with a specific shaped molecule
the carrier changes shape to release the molecules the other side of the membrane
define active transport
the movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins.
4 ways that active transport differs from passive transport
requires energy in the form of ATP
goes against the concentration gradient
only uses carrier proteins
process is very selective
what is co transport
where 2 substances are simultaneously transported across a membrane by 1 protein
define symport
2 molecules moved together from one area to another
define anti port
1 substance going in one direction, 1 in another
example of anti port
sodium potassium pump
2 adaptations of the ileum absorption
- large surface area for co transport proteins to fit on the membrane
- lots of mitochondria to produce ATP to provide energy for absorption
what is cotransported in the ileum
glucose molecules with sodium ions
what happens during co transport in the ileum
Na+ diffuses down the concentration gradient into the epithelial cell. This pulls glucose molecules into the epithelial cell against the concentration gradient.
To maintain a low Na+ concentration inside cells Na+ pumped into blood using sodium potassium pumps.
Glucose moves into blood down the concentration gradient by facilitated diffusion.
what does the sodium potassium pump require
ATP
does the sodium potassium pump go with or against concentration gradient
both potassium and sodium go against their concentration gradient
what direction does potassium go in the pump
into the cell from the blood
which direction does sodium go in the pump
goes from the cell into the blood
