Biological membranes Flashcards
define the term simple diffusion
diffusion is the met movement of particles (atoms, molecules or ions)from a region of higher concentration to a region of lower concentration. it is a passive process and will continue until there is an equilibrium between the two areas. there is no membrane!
define the term facilitated diffusion.
the same as simple diffusion - a net movement of particles from an area of higher to an area of lower concentration - except this happens over a membrane or partially permeable membrane. it can involve the use of protein channels or carrier proteins.
define the term osmosis.
the net movement of water molecules across a partially permeable membrane from one solution to a more concentrated one with a lower water potential. it is a passive process.
define the term passive transport
no energy from the cell is used in the process of transport
define the term active transport.
the movement of molecules or ions across membranes, using ATP to drive protein pumps within the membrane. happens against the concentration gradient.
define the term endocytosis
a form of bulk transport into the cell
define the term exocytosis
a form of bulk transport out of the cell
define the term phagocytosis.
when solid materials are moved into or out of the cell by bulk transport
define the term pinocytosis.
when liquids are moved into or out of the cell by bulk transport.
what is the difference between a carrier protein and a channel protein?
channel proteins are non polar channels through the membrane. carrier proteins are shaped to allow one specific molecule through and can be opened and closed.
list the factors affecting rate of diffusion.
- temperature
- concentration gradient
- stirring/moveing
- surface area of membrane
- thickness of membrane
- size of the molecule/s
explain how substances can move across a membrane by simple diffusion.
small molecules such as gases can fit through the gaps in between lipid molecules so can diffuse down the concentration gradient. this is also true of lipid-soluble molecules that can diffuse without a protein. simple diffusion occurs when molecules are small, non polar and lipid soluble.
which types of molecules can travel using simple diffusion?
- small
- non-polar
- lipid-soluble.
Explain how substances can move across a membrane by facilitated diffusion.
Facilitated diffusion occurs when molecules cannot pass directly through the membrane bilayer so must use a protein. Channel proteins allow smaller ions to pass through using a hydrophilic channel. Carrier proteins allow much larger molecules such as glucose to pass through the membrane. These proteins are often specific to certain molecules or ions.
Describe the process of endocytosis.
When materials are bulk transported into the cell. In phagocytosis (solid materials) the cell surface membrane surrounds and engulfs a material forming a vehicle with the outer membrane
Describe the process of exocytosis.
When a vehicle within the cell merges with the cell surface membrane, expelling its contents outside the cell
Which transport mechanisms require ATP?
Active transport
Endocytosis
Exocytosis
Why is it easier for an oxygen molecule to diffuse across the membrane than it is for a water molecule?
Oxygen is not a charged/ polar molecule so it is not affected by the polar regions of the phospholipids in the membrane. Oxygen is also a smaller molecule than water.
Why is it easy for steroid hormones to cross the cell membrane?
Because they are lipid based molecules so will dissolve in the bilayer
Explain why ions are only able to cross the membrane via a protein channel.
Because they are charged. This means that they cannot dissolve in the bilayer and cannot get past the charged phosphate heads of the lipids. The protein channel is a non polar channel through the membrane that doesn’t repel them.
State the five roles of membranes within and on the surface of cells.
- separating cell contents from the outside environment
- separating cell components from the cytoplasm
- cell recognition and cell signalling
- holding the components of metabolic pathways in place
- regulating transport of materials in and out of cells
Define compartmentalisation and state why it’s useful.
When membranes form around organelles such as the mitochondria or chloroplasts.
It is useful to the cell as it stops potentially harmful substances from getting into the cytoplasm. It can also be useful to some organelles that use the membrane (photosynthesis occurs in the membrane of a chloroplast)
