4.Transport Across Cel Membranes Flashcards
What is a plasma membrane
Membrane surrounding cells and their organelles
What is cell surface membrane for
Plasma membrane Forms boundary between environment and cytoplasm-controls movement in and out of cell
What do phospholipids do
Form bilayer
Hydrophilic phosphate heads attracted to and associate with water whereas hydrophobic tails repelled by water and form lipid soluble membrane
What’s the function of lipid soluble membrane
Only allows lipid soluble substance to pass through
Water soluble substance prevented from passing through
Makes me,brand flexible and self selecting
What are the types proteins used in the plasma membranes
Interspersed throughout
Embedded within the phospholipids
Intrinsic-carrier proteins and channel proteins, span across whole bilayer
Extrinsic-only in surface of bilayer, for mechanical support, form glycolipids, act as receptors
How do carrier and channel proteins work
Carrier-ions bind to protein then it changes shape releasing ion or molecule to other side
Channel-Water filled so only water soluble ions diffuse across membrane
What’s the function of membrane proteins
Structural support
Act as channels for transporting water soluble molecules
Active transport
Cell surface receptors for identifying cells
Help cells adhere
Receptors eg hormones
Facts about cholesterol in membranes
Embedded with phospholipid bilayer
Very hydrophobic
Pulls fatty acids tails together limiting their movement
Function of cholesterol in membranes
Reduces lateral movement
Adds strength
Makes membrane less fluid at high temp
Prevents leakage of water
What is a glycolipid
Carb covalently bonded to lipid
Carb extended from bilayer into watery environment
What’s the function of a glycolipid
Act as recognition sites
Helps cells attach to one another and form tissues
Cell surface receptors
What’s the function of glycoproteins
Act as cell surface receptors specifically for hormones and neurotransmitters
Recognition sites
Help cells attach to one another eg lymphocytes recognising self material
Why can’t most molecules freely diffuse across cell surface membrane?
Too large
Not lipid soluble
Get repelled if same charge as channel
If electrically charged have trouble passing through non polar hydrophobic bilayer
Why is the cell surface membrane related to fluid Mosaic model
Fluid-individual phospholipid molecules can move relative to one another, giving membrane a flexible structure that’s constantly moving and changing shape
Mosaic-the proteins that are embedded into the phospholipids bilayer vary in shape, size and pattern in the same way the tiles of a mosaic are
What is diffusion
The met movement of molecules or ions from a region where they are highly concentrated to a region where they are less concentrated until evenly distributed
What is simple diffusion
Passive transport
Movement is due to the kinetic energy that the particles possess
Move randomly
What’s facilitated diffusion
Passive process that requires a channel or carrier protein
What is osmosis
Passage of water from region of high water potential to a region of low water potential through s semi permeable membrane
Facts about water potential
Measured in kilopascals Standard conditions water has w.p of 0 Addition of solutes to pure water lowers its w.p Always -ve value The more solute the more -ve Water moves from less -ve to more -ve
What is a hypertonic solution
Has a lower w.p than the tissue
What’s a hypotonic solution
Higher w.p
What happens when an animal cell is put in it a hypertonic solution
The water moves out of cell into solution and so cell shrinks
What happens when an animal cell is put in a hypotonic solution
The cell undergoes lysis (bursts) as water moves from the solution into the cell
What happens when a plant cell is placed in a hypertonic solution
Cell is plasmolysed as the water leaves the cell and the protoplasm pulls away from the cell wall
