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2.1.5 Movement Across Membranes (Osmosis (Plant Cells: (Turgid: water…
2.1.5 Movement Across Membranes
Factors affecting membrane permeability
Temperature
decrease in temp
Kinetic energy of molecules decrease; molecules move more slowly.Fatty acids are compressed , and phospholipids are pushed away, maintaining membrane fluidity.
increase in temp
Kinetic energy of molecules increase; molecules move faster. Membrane fluidity and permeability increases
Solvents
dissolve lipids and damage membrane; make it more permeable as holes are created
Diffusion
passive method of movement
requires no energy
Net movement of molecules from an area of high concentration to an area of low concentration across a partially permeable membrane
Factors affecting diffusion
Temperature: more temp means more KE and more diffusion as particles move faster
Diffusion distance: shorter diffusion distance means more diffusion as shorter time for molecules to move across
Surface Area; more surface area means more area for molecules to diffuse across from
Size of Molecule: smaller molecule means molecule is lighter and can move faster. Faster movement of molecule means more KE
Concentration Gradient: steeper concentration gradient means faster rate of diffusion
Stirring: more stirring means faster diffusion rates
Facilitated Diffusion
passive method of movement
no energy
Net movement of molecules from an area of high concentration to an area of low concentration through a protein channel
larger molecules and ions use this type of transport because they are too big to fit in between phospholipid bilayer
cells control what goes in and out
receptors must bind and be complementary
Active Transport
requires ATP
hydrolysis of ATP from respiration
ATP changes shape of protein channel so ions can pass through
Net movement of molecules from an area of low concentration to an area of high concentration across a partially permeable membrane using ATP through a protein carrier
usually used by molecules and ions
ACTIVE, against concentration gradient
Endocytosis
requires ATP
needed to move membrane to form vesicles and to move vesicles around the cell
bulk transport of molecules too large to pass through a cell membrane even via channel or carrier proteins into a cell
phagocytosis
intake of solid matter
pinocytosis
intake of liquid matter
Exocytosis
requires ATP
needed to move membrane to form vesicles and to move vesicles around the cell
bulk transport of molecules too large to pass through a cell membrane even via channel or carrier proteins out of a cell
vesicle containing substance fuses with plasma membrane and exports them out of the cell
Osmosis
Net movement of water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane
value of pure water is 0
Plant Cells:
Turgid: water enters cell and is full of water
Flaccid: water leaves cell and cell is soft
Plasmolysis: detachment of plasma membrane from cell wall; cytoplasm shrinks due to loss of water
don't change shape like animal cells; have cell wall
Animal Cells:
Crenate: state of animal cell when lost water and shrinks
Cytolysis: when animal cell bursts due to too much water going in
Type of Solutions:
Isotonic: water potential outside cell is equal to water potential outside cell; cell doesn't change shape
Hypertonic: water potential outside cell is greater than the water potential outside cell; water moves into cell; cell may undergo cytolysis
Hypotonic: water potential outside cell is less than the water , potential outside cell; water moves out of cell; cell may crenate
water can move through specialised protein channels called aquaporins
Sammer Sheikh