cell membrane
TRANSCRIPT
The Cell Membrane and The Cell Membrane and Transport SystemsTransport Systems
The Cell Membrane The boundary of all living cells is a cell
membrane which controls the entry of dissolved substances into and out of the cell.
A cell membrane consists of both lipid and protein.
The membrane is formed of a double – layer of lipids.
Proteins are embedded in this layer forming channels that allow water – soluble substances pass through
The Cell Membrane Phospholipid bi-layer
The Cell Membrane
Crossing The Membrane All cells must be able to take in &
expel various substances in order to survive, grow & reproduce.
As a cell membrane only allows some dissolved substances to cross it, it is described as being semi – permeable OR partially – permeable.
Main Types of Transport Passive Transport: diffusion & osmosis Active Transport Endocytosis and Exocytosis
Passive – movement across membranes that does not require any energy
Active – movement across membranes that does require energy
Diffusion Net movement of particles from a
region of high concentration to a region of low concentration.
Diffusion Difference in concentration between
two regions = concentration gradient Diffusion occurs when a gradient
exists and continues until equilibrium Factors can effect the rate of diffusion
when the concentration gradient is large when heat is applied when molecules are smaller when movement occurs through a
gaseous membrane
Diffusion Water, carbon dioxide and other
small uncharged particles
Osmosis Net movement of a solvent,
(usually water) across a differentially permeable membrane from a region of low solute concentration to high solute concentration.
That is, water molecules move from a region of high solvent concentration to low concentration.
Osmosis
Osmosis in Animal Cells Isotonic – when the extracellular fluid and
intracellular fluids are at equal concentrations.
Hypotonic – when the extracellular fluid has a higher water concentration than the intracellular fluid.
Hypertonic – when the intracellular fluid has a higher water concentration than the extracellular fluid.
Osmosis
Partially permeable membrane
Water molecules Solute molecules cannot pass through the partially permeable membrane
There is a net movement of water molecules towards the less concentrated side (in terms
of water molecules) until water concentrations equalize.
High Water Concentration
means the solution is Hypotonic
Loses water by osmosis
Low water concentration means
the solution isHypertonic
Gains water by osmosis
Osmosis in Animal Cells
Osmosis in Animal Cells
Isotonic solutionNo net movement of solvent = equilibrium
Red blood cell = 0.9% saline
Solution = 0.9% saline
Osmosis in Animal Cells
Hypotonic solution Solvent moves into the cell
Red blood cell = 0.9% saline
Solution = 0.4% saline
Osmosis in Animal Cells
Hypertonic solution Solvent moves out of the cell into the solution
Red blood cell = 0.9% saline
Solution = 1.2% saline
Osmosis in Plant Cells Different to animal cells because of the cell wall
Osmosis in Plant Cells
Isotonic solutionNo net movement of solvent = equilibrium
Cell placed in solution that has the same concentration as the cell sap
Osmosis in Plant Cells
Hypotonic solutionPlant cell placed in solution that has a lower concentration than the cell sap
•Water enters the vacuole
•The vacuole expands
•Cytoplasm is pushed outwards
•‘Turgid’ cell
Osmosis in Plant Cells
Hypertonic solutionPlant cell placed in solution that has a higher concentration than the cell sap
•Water exits the vacuole
•Vacuole shrinks
•Cytoplasm moves inwards
•‘Plasmolysis’
Active Transport Diffusion is very slow & it moves substances
down a concentration gradient.
Many substances are needed by organisms in much greater amounts than what can be provided by diffusion alone. Additionally, some substances need to be accumulated in cells against the concentration gradient.
In order for this to occur, energy must be used to move the needed substances across the cell membrane.
Active TransportActive transport occurs through protein channels.