4- cell transport mechanisms Flashcards
fluid mosaic model
a model that describes the structure of cell membranes. it suggests that membranes are a fluid, flexible lipid bilayer in which proteins are embedded and float freely
lipid bilayer
two layers of phospholipids arranged with their hydrophilic heads facing outwards and hydrophobic tails facing inwards, creating a barrier that is selectively permeable
proteins in cell surface membrane
- embedded in the lipid bilayer and several key functions:
- transport proteins: these assist in the movement of substances in and out of the cell
- receptor proteins: these are used by cells to communicate with their environment. they bind with specific molecules (like hormones), triggering a response within the cell
cholesterol
another lipid, embedded in the membrane, which gives the membrane stability and prevents it from becoming too fluid
glycoproteins and glycolipids
these are proteins and lipids with attached carbohydrate chains. they are involved in cell recognition and act as markers for cellular identification
fluidity of membrane
due to unsaturated fatty acids in the phospholipids and the presence of cholesterol, the membrane is fluid, allowing for movement of proteins within the lipid bilayer
passive transport mechanisms
- diffusion
- facilitated diffusion
- osmosis
diffusion
the movement of molecules down its concentration gradient
facilitated diffusion
a form of diffusion where carrier proteins and protein channels are used to help transport molecules across the cell membrane
osmosis
the movement of water molecules down its concentration gradient/ against the solute concentration gradient, across a selectively permeable membrane
in animals- water potential =
osmotic potential
water potential
potential energy of water in a system relative to pure water
direction of water potential in animals
water moves from high to low water potential
osmotic potential
potential of water to move from a hypotonic to hypertonic solution
osmotic potential direction in animals
water moves from high to low osmotic potential
value of osmotic potential meaning
0 for pure water, negative for solutes
in plants- water potential =
osmotic pressure + turgor pressure
osmotic pressure value meaning
numerically equivalent to the osmotic potential
turgor pressure
pressure exerted by cell contents against the cell wall in plant cells
turgor pressure value meaning
positive for turgid cells, 0 for flaccid cells. the cell is at turgor when it is balanced with osmotic pressure
plasmolysis in plants
- plasmolysis is the shrinkage of the protoplasm due to the loss of water
- incipient plasmolysis is where 50% of the cells are plasmolysed
endocytosis
molecules are enclosed in vesicles made from the cell membrane and taken in the cell
exocytosis
molecules are enclosed in vesicles, which fuse with the cell membrane, thus expelling the molecules from the cell
active transport
the movement of molecules against its concentration gradient, where ATP is used
what molecules are transported with diffusion?
small, non polar, lipid soluble molecules (CO2, O2)
what molecules are transported with facilitated diffusion?
charged, polar, water soluble molecules (Na+, glucose, amino acids)
what molecules are transported via osmosis?
water molecules
what molecules are transported via endo/exocytosis?
large molecules
the phosphorylation of ADP requires
energy
the hydrolysis of ATP provides
an accessible supply of energy for biological processes
