3.2.3 TRANSPORT ACROSS CELL MEMBRANES Flashcards
(30 cards)
When is there a high water potential?
When the solution has a high water concentration (not much solute dissolved into it)
When is there a low water potential?
The solution has a low water concentration (lots of solute dissolved in it)
What does pure water have a water potential of?
0 kPa, the value decreases as more solute is added
What is osmosis?
The movement of water molecules from an area of high water water potential to an area of low water potential across a semi-permeable membrane, down a water potential gradient
State of an animal cell when there is a high water potential (hypotonic):
Lysis: Swells and bursts in a hypotonic solution because water enters the cell
State of an animal cell when in an isotonic solution:
No change
State of an animal cell in a solution with low water potential (hypertonic):
Cell shrinks and shrivels as water moves out
State of a plant cells when in a hypotonic solution (higher water potential):
Water enters cell, protoplast swells and cell becomes turgid
State of plant cells when in an isotonic solution (same water potential in and outside of the cell):
No water enters or exits the cell, no change in the protoplast, cell is in incipient plasmolysis
State of plant cells when in an hypertonic solution (lower water potential):
Water leaves cell, protoplast shrinks and cell becomes plasmolyed
What is diffusion?
The net movement of particles from an area of high concentration to an area of low concentration, down a concentration gradient, across a semi-permeable membrane
What is facilitated diffusion:
Net movement of particles from an area of high concentration to a low concentration, down a concentration gradient, across a semi-permeable membrane, uses the assistance of carrier proteins and channel proteins- glucose moves by this
What are channel proteins?
Transmembrane proteins that facilitate the movement of substances across a cell membrane, they form a hydrophilic pathway through which specific molecules, typically ions or polar molecules, can pass
What are carrier proteins?
Transmembrane proteins that facilitate the transport of specific substances across a cell membrane. Unlike channel proteins, that provide a continuous pathway, carrier proteins bind to the substance on one side of the membrane, they undergo a conformational change and release the substance on the other side- cam occur through facilitated diffusion
Why is the fluid mosaic model fluid?
Fluid- because the phospholipid molecules in the bilayer are constantly moving
Why is the fluid mosaic model mosaic?
The proteins are all different shapes and sizes
Key components of the fluid mosaic model:
- phospholipid bilayer
- cholesterol- adds stability
- proteins- may be intrinsic and extrinsic
- glycoproteins
- glycolipids
Role of phospholipid bilayer in the fluid mosaic model:
Hydrophilic heads face outwards (towards water) and hydrophobic tails face inwards (away from water
This arrangement creates a hydrophobic centre in the bi-layer so that water soluble substances cannot pass through
However, lipid-soluble substances can dissolve in the bilayer and pass directly through the cell membrane
Role of cholesterol in the fluid mosaic model:
- provide stability to cell membranes
- consist of a hydrophilic and hydrophobic region, the hydrophobic regions bind to phospholipid fatty acid tails, causing them to pack more closely together
- reduces fluidity of the cell membranes
Role of intrinsic proteins in the fluid mosaic model:
- embedded through both sides of the phospholipid bilayer
- these proteins include channel and carrier proteins which transport large molecules and ions across the membrane
Role of extrinsic proteins in the fluid mosaic model:
Only present on one side of the phospholipid bilayer, provide support to the membrane or may be involved in cell signalling
Role of glycoproteins and glycolipids:
- Cell adhesion- attachment of cells to one another
- Cell recognition- allows cells to recognise one another
- Cell signalling- allows communication between cells
Passive/ simple diffusion:
- small lipid soluble molecules (have to get through lipid bilayer without help)
- gradient from high to low (as diffusion) so no energy/ ATP needed
- examples include oxygen diffusing into muscle cells (or respiring cells)
Facilitated diffusion:
- large, water soluble molecules (cannot get through lipid bilayer without help)
- requires channel/ carrier proteins
- gradient is high to low (as diffusion) so no energy/ ATP needed
- examples include glucose diffusing through beta cells
