Cell Transport Flashcards
(33 cards)
Purpose of the glycocalyx
- hormone receptors, cell recognition , cell adhesion
How do small molecules move between the phospholipid bilayer
Small molecules like carbon dioxide and oxygen move between phospholipid molecules and diffuse across the membrane
How do lipid soluble substances move across the phospholipid bilayer
They dissolve in the phospholipid and diffuse across the membrane they move easily As the pplb is hydrophobic and move macros more easily than water soluble molecules
How do water soluble molecules move across the phospholipid bilayer
Glucose polar molecules and ions cannot readily difffuse through the phospholipids sp must pass through the intrinsic protein molecules which form water filled channels across the membrane.
As a result of this the cell surface membrane is selectively permeable to water and some solutes
What type of transport id simple diffusion
Passive transport
Factors affecting the rate of simple diffusion
- concentration gradient
- thickness of the exchange surface / distance
- surface area
- size of molecule
- lipid solubility and polarity
- temperature
- chemical composition of the membrane
- number of pores on the membrane
What is facilitated diffusion
The passive movement of molecules or ions down a concentration gradient across a membrane by the channel or carrier protein molecules in the membrane
How does the channel protein carry out facilitated diffusion
The channel protein is lined with polar groups
The channels are hydrophilic so ions which are water soluble can pass through by facilitated difffusion
The channels open and close according to the needs of the cell
How do carrier proteins carry out facilitated diffusion
- allow the diffusion of larger polar molecules like sugars and amino acids across the membrane
- the molecule attaches to its binding site on the carrier protein
- the carrier protein changes shape and releases the molecule on the other side of the membrane before changing back to its original shape as the molecule is released from the binding site
What is active transport
The movement of ions or molecules cross a membrane against a concentration gradient using energy from the hydrolysis of atp made by the cell in respiration
Describe the features of active transport
- moving ions and molecules against the concentration gradient using
- requires atp anything affecting respiration will affect active transport
- occurs through the carrier proteins which span the membrane before changing
- rate is limited by the number and availability of carrier proteins
Describe the process of active uptake of a single molecule or ion
The ion combines with a SPECIFIC carrier protein on the inside of the membrane
- atp transfers a phosphate group to the carrier protein on the inside of the membrane
Te carrier protein changes shape and carries the ion across the membrane to the inside of the cell
- the molecule or ion is released into the cytoplasm
- the phosphate ion is released back into the cytoplasm from the carrier protein and it recombines with ADP to form ATP
- the carrier protein returns to its original shape
What is cotransport
A transport mechanism in high facilitated diffusion brings molecules AND ions across the cell membrane into a cell
Describe the stages of co transport
- glucose molecule and 2 sodium ions outside the cell bind to a carrier protein in the cell membrane
- carrier protein changes shape and deposits the glucose and sodium ions into the cell that is FD
- the glucose mol and the sodium ions diffuse separately through the cytoplasm to. The opposite membrane
- the glucose passes into the blood by facilitated diffusion
- the ions are carried out of the epithelial cell by AT so the the sodium ion concentration of the cell remains low so more sodium ions move in from the intestinal lumen bringing in glucose on he same carrier molecule
What is osmosis
The net passive diffusion of water molecules across a selectively permeable membrane from a region of high water potential to a region o low water potential
What is water potential (ψ)
The tendency of water molecules to move -
measured in (kPa)
ψ of pure water is zero
What is solute potential (ψs)
The tendency of water molecules to move out of a solution
What is pressure potential (ψp)
A force which increase the tendency of water to move out of the
How is water potential calculated
ψcell = ψp +ψs
what is an external solution that is hypotonic to the cell
the water potential of the cell is lower than the water potential of the solution outside the cell so water flows into the cell
what is an external solution that is hypertonic to the cell
the water poential of the solution inside the cell is higher than the water potential of the solution outside the cell so water flows out of the cell
what is isotonic
the water potential of the solution in the cell and the water potential of the solution outside the cell are equal
what is plasmolysis
plantmcells in a hypertonic soluion lose water by osmosis
- the vacuole shrinks and the cytoplasm draws away from the cell wall
- when complete the cell is completely flaccid
what is incipient plasmolysis
cytolplasm begins to pull away from cell wall
ψp = 0 kpa
ψcell =ψs of the external solution
- occurs in an isotonic solution
