2.4 Plasma membranes Flashcards
What are membranes made of?
Phospholipid bilayer
What is the name of the model that forms the basis of our understanding of membranes today?
Fluid-mosaic model
What are the 2 types of membrane proteins?
intrinsic and extrinsic
What are intrinsic proteins and name 2 examples?
- transmembrane proteins that are embedded through both layers of a membrane
- channel proteins
- carrier proteins
What type of membrane protein are glycoproteins?
intrinsic proteins
What do glycoproteins play a role in?
cell adhesion and as receptors for chemical signals
What do glycolipids play a role in?
cell markers or antigens
What are extrinsic proteins and name an example?
- Extrinsic proteins are present on one side of the bilayer
- cholesterol
What are the factors affecting membrane structure and permeability?
- temperature
- solvents
What is diffusion?
The net/overall movement of particles from a region of higher concentration to a region of lower concentration
Does diffusion occur between different concentrations of different substances?
no it only occurs between different concentrations of the same substance
What are the 2 factors that affect the rate of diffusion?
- temperature
- concentration gradient
What affects the rate at which molecules/ions diffuse across a membrane?
- surface area
- thickness of membrane
What is facilitated diffusion?
the movement of molecules down a concentration gradient via protein channels or carrier proteins
What is active transport?
the movement of molecules/ions into or out of a cell from a region of lower concentration to a region of higher concentration
What is bulk transport?
a form of active transport that involves large molecules
What is endocytosis?
the bulk transport of material into cells
What are the 2 types of endocytosis?
- phagocytosis (solids)
- pinocytosis (liquids)
What is exocytosis?
The bulk transport of material out of cells
What is osmosis?
the diffusion of water across a partially permeable membrane
Define water potential
the pressure exerted by water molecules as they cooled with a membrane/contained (measured in units of pressure)
Do all solutions have positive or negative water potentials?
negative
What is hydrostatic pressure?
the diffusion of water into a solution leads to an increase in volume of this solution and if in a closed system, this results in an increase in pressure
What is cytolysis?
when an animal cell is placed in a solution with a higher water potential than that of the cytoplasm so the cell-surface membrane breaks and the cell bursts
What is crenation?
when an animal cell is placed in a solution with a lower water potential than that of the cytoplasm so water is lost via osmosis down the water potential gradient which causes a reduction in the volume of the cell and the cell surface membrane ‘puckers’
What happens when the water potential of an external solution is higher than inside a plant cell?
The cell swells and becomes turgid
What happens when the water potential of an external solution is lower than inside a plant cell?
Plasmolysis
