transport across cell membranes Flashcards
give 3 functions of the cell surface membrane
- separates cell contents from outside environment
- allows different conditions inside and outside the cell
- selectively permeable (regulates transport of materials in and out)
- cell signalling and recognition
what substances can pass across the cell surface membrane by simple diffusion/osmosis?
- alcohol
- gases
- non-polar steroids
- water
how do ions and large polar molecules pass across the cell surface membrane?
via embedded proteins
what are the two types of proteins that are inserted into the phospholipid bilayer?
- intrinsic
- extrinsic
what is an intrinsic protein?
a protein that completely spans across the whole phospholipid bilayer (one side to the other)
what is an extrinsic protein?
a protein that only occurs in the surface of the phospholipid bilayer and never extends across it
where are the carbohydrates found on the cell surface membrane?
on the outside of the membrane, either attached to a lipid (glycolipid) or protein (glycoprotein)
what is the function of glycoproteins in the cell surface membrane?
- act as recognition sites
- help cells attach to each other
- allows cells to recognise each other
what is the functions of glycolipids in the cell surface membrane?
- act as recognition sites
- help cells attach to each other
- helps maintain stability in the membrane
what is the function of cholesterol in the cell surface membrane?
- reduce lateral movement of molecules (phospholipids ect)
- makes the membrane less fluid at higher temperatures
- prevents leakage of water and dissolved ions
why is the cell surface membrane is known as fluid?
the phospholipid molecules can move relative to one another
why is the cell surface membrane known to be mosaic?
because it contains a mixture of proteins and phospholipids that are different sizes
why do substances need to cross plasma membrane?
- nutrients and oxygen need to enter
- waste and hormones need to exit
what is diffusion?
the net movement of molecules or ions from a region pf high concentration to low concentration until equilibrium is reached
what kind of process is diffusion?
a passive process that relies on the kinetic energy of the particles
how is the rate of diffusion affected by the concentration gradient?
the steeper the concentration gradient is, the faster the rate of diffusion
how is the rate of diffusion affected by surface area?
the larger the surface area, the faster the rate of diffusion as there is more area for the molecules to go through
how is the rate of diffusion affected by the length of the diffusion pathway?
the smaller the diffusion pathway, the faster the rate of diffusion
what is ficks law?
the relationship between the factors that affect the rate of diffusion?
what is the formula for ficks law?
rate of diffusion =
SA x conc grad
———————–
len of pathway
what type of molecules can go through the gaps created by the phospholipid molecules in the plasma membrane?
- small
- non polar
- lipid soluble
is water a polar or non-polar molecule?
polar
can water go through the plasma membrane?
yes, despite being polar, water can go through the gaps because it is so small
what is the definition of facilitated diffusion?
the transport of chemical substances across a membrane from an area of high concentration to a low concentration with help from a transport membrane
