MOVEMENT OF SUBSTANCES

FLUID

phospholipid molecules move freely and laterally within the phospholipid bilayer

MOSAIC

different proteins are randomly embedded and scattered among the phospholipids

phospholipid structure

hydrophilic phosphate group attatched to the glycerol molecule and 2 hydrophobic fatty acid chains

function of phospholipids

form a barrier between the aqueous environment and cell cytoplasm

cholestrol function

regulate fluidity of cell membrane in animal cells

cholesterol in low temperatures

disturb the close packing of phospholipids and keeps them more fluid

important for organisms living at low temperatures where membranes tend to solidify as cholesterol prevents the membrane from freezing

cholesterol in high temperatures (>35 degrees)

phospholipids tend to gain kinetic energy and move further apart from each other

cholesterol makes the membranes less fluid by restraining the movement of the phospholipids, preventing the membrane from breaking apart

structure of extrinsic/peripheral proteins

loosly bound to membrane, exposed to aqueous medium of extracellular fluid and cytoplasm

found on both sides of bilayer

do not penetrate membrane

structure of intrinsic/integral proteins

embedded within hydrophobic core of phospholipid bilayer

transmembrane protein spans across whole phospholipid bilayer

contains both hydrophobic and hydrophilic regions

channel protein

hydrophilic channels which transport specific hydrophilic substances

carrier proteins

binding sites which bind and transport specific substances down or across a concentration gradient

alternates between two shapes, moving solute across membrane during shape change

glycoprotein 

protein attatched to a short carbohydrate chain

glycolipid

lipid attatched to a short carbohydrate chain

glycoprotein and glycolipid functions

cell to cell recognition

cell-cell adhesion

receptors

cell to cell recognition

cells can recognise and bind to one another, eg. recognition of bacteria by white blood cells

cell-cell adhesion

adjacent cells bind to each other to form a tissue

receptors

bind to molecules for cell signalling

function of cell membrane

boundary

compartmentalisation

selectively permeable barrier

cell membrane boundary

cell surface membrane forms a boundary that separates the cell contents from the external extracellular environment

allows the internal cytoplasm environment of the cell to be kept relatively constant to function optimally

cell membrane compartmentalization

internal cell membranes of organelles enable compartmentalisation of cell contents and prevent mixing
allows for specialisation of cell function by concentrating specific substances needed for metabolic processes

selectively permeable barrier

cell membranes are selectively permeable to prevent interchange of substances

transport of hydrophobic substances

able to diffuse easily through hydrophobic core of the cell membrane

transport of hydrophilic substances

cannot diffuse easily through the hydrophobic core of cell membrane, require transport proteins to move through phospholipid bilayer

importance of transport across membranes

secrete metabolic products

excrete metabolic waste

absorb nutrients

regulate water potential in a cell

passive transport definition

movement of substances down a concentration gradient without the use of energy 

passive transport types

simple diffusion

facilitated diffusion

osmosis

simple diffusion

net movement of substances down a concentration gradient from a region of higher concentration to a region of lower concentration 

what substances can undergo simple diffusion

hydrophobic substances like O2, CO2 and some hormones

what substances can undergo facilitated diffusion 

hydrophilic substances like ions, glucose, amino acids

osmosis definition 

net movement of water molecules down a water potential gradient from a region of less negative water potential to a region of more negative water potential

factors affecting rate of simple diffusion

molecular size

temperature

concentration gradient

distance

surface area to volume ratio

facilitated diffusion definition 

net movement of substances down a concentration gradient from a region of higher concentration to a region of lower concentration with the aid of transport proteins across a selectively permeable membrane

isotonic solution meaning

same water potential as the cytoplasm, no net water molecule movement by osmosis across a selectively permeable membrane

isotonic solution observations

animal cell remains same shape and size

plant cell remains same shape and size (may be slightly flaccid)

hypertonic solution meaning

has a more negative water potential compared to cytoplasm, net movement of water molecules from cytoplasm into solution by osmosis across a selectively permeable membrane

hypertonic solution observations

animal cell shrinks and crenate

plant cell will become plasmolysed, where the plasma membrane pulls away from cell wall

hypotonic solution meaning

has a less negative water potential compared to the cytoplasm, net water molecule movement from solution into cytoplasm by osmosis across a selectively permeable membrane

hypotonic solution observations

animal cell will swell and burst, due to absence of cell wall

define turgor pressure

pressure exerted by the cell wall against the contents of the plant cell

active transport meaning

movement of substances against a concentration gradient, with metabolic energy, from a region of lower concentration to a region of higher concentration across a selectively permeable membrane

bulk transport

used to transport very large substances, energy released from mitochondrion required

endocrytosis meaning

invagination of cell surface membrane to transport very large substances into the cell

exocrytosis meaning

transport of very large substances out of cell