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Material transfer across the cell membrane - Coggle Diagram
Material transfer across the cell membrane
Diffusion
Net movement of substances ,
down the concentration gradient
Small
Polar/ ions
Through channel protein
Non- polar
Through the phospholipid bilayer
Large
Can't go through cell membrane
Until equilibrium state
Rate of diffusion
Steeper concentration gradient
Faster
Larger surface area
Shorter distance
Higher temperature
Smaller particles
Non-polar substances
No energy needed
Phagocytosis
Engulfed with cell membrane, absorbed through food vacuole
Importance
Some unicellular organisms engulf food particles
Some human white blood cells engulf harmful microorganisms
body defence
Meaning: uptake of large molecules into cells by packing into vacuoles
Active transport
Through cell membrane ,
against the concentration gradient
By changing shape of protein using energy
Energy required
Carrier protein
Importance
additional useful substances
Absorption of nutrients
e.g. human small intestine
Absorption of minerals
e.g. plant roots
Osmosis
Net movement of water molecules,
down the water potential gradient
Through a differentially permeable membrane
Hypotonic
Water enters the cells
Animal: Swell and bursts
Plants: Turgid
Support the plant
Isotonic
No net movment
Animal:
No change
Plants:
Hypertonic
Water leaves the cells
Animal: Shrink and become wrinkled
Plant: Become flaccid and plasmolysed vacuoles shrink
Cell membrane pulled away from cell wall (plasmolysis)
Leaves droop
Importance
Water enters and leaves cells in all organisms
Cell membrane is differentially permeable
Factors affecting it
Temperature
Phospholipid molecules in the bilayer move faster, pack less closely together
Boiling
Fully permeable
Organic solvents
Dissolves the membrane
Permeability increases
Structure
Phospholipid molecules
Arranged in a bilayer
Triglyceride molecule (non-polar, hydrophobic)
Replace 1 fatty acid molecules with a phosphate group
Phospholipid molecules
Hydrophilic "head"
Polar phosphate group and glycerol
Point outwards, in contact with the aqueous solutions
Hydrophobic "tails"
Non-polar fatty acids
Point inwards
Can move laterally (Thus called"fluid")
Protein molecules
Interspersed among the bilayer in a mosaic pattern(Thus called "mosaic")
Attached to the surface of the bilayer
Embedded half-way through the bilayer
Span the entire bilayer
Types of proteins
Channel proteins
Provide channels (e.g. ions)
Carrier proteins
Bind to certain substances and transport then to the other side of the membrane
Receptors
Bind to certain chemical messages
Turn on certain activities
Antigens
Are glycoproteins for cell recognition
Enzymes
Speed up chemical reactions
To notes "Enzymes" (Ch4)
Carbonhydrates are attached to some to form glycoproteins
Development of the cell membrane model
1925 Gorter and Grendel -The bilayer model
1935 Davson and Danielli - The 'sandwich' model
1972 Singer and Nicolson - The fluid mosaic model
Limit: The extracted proteins were mainly hydrophobic , and shouldn't be in contact with water
Limit: No proteins
Cell membrane is fluid in nature
Allowing to change shape and fuse
cell division