Transport Across Membranes Flashcards
(14 cards)
Describe diffusion
Net movement of particles from an area of higher concentration to an area of lower concentration.
Continues until particles are evenly distributed.
Passive process.
What are the factors that affect rate of diffusion?
- Concentration gradient
- *Thickness *of exchange surface
- Surface area
- *Temperature *
- Size of molecule
Osmosis definition.
Diffusion of water molecules across **partially permeable membrane **down water potential gradient.
Describe meaning of water potential.
Likelihood of water molecules to diffuse in/out of solution.
Pure water has water potential of zero.
Solutes lower water potential.
More **negative **water potential is, the stronger the concentration of solutes is in solution.
Describe facilitated diffusion.
Net movement of particles from area of higher concentration to area of lower concentration.
Uses carrier proteins to aid diffusion of large molecules through plasma membrane.
Uses channel proteins to aid diffusion of smaller molecules.
Passive process.
Describe active transport.
Uses energy to move molecules and ions across plasma membrane against concentration gradient.
Involves carrier proteins
Describe animal cells in a hypertonic solution.
Water potential of the external solution is lower than the solution inside the cell.
Water moves out the cell by osmosis.
Cell loses volume.
Crenation.
Describe animal cells in a isotonic solution.
The water potential of the external solution is equal to the solution in the cell.
No net movement of water.
Cell shape has not changed.
Describe animal cells in a hypotonic solution.
The water potential of the external solution is higher than in the cell.
Water moves in by osmosis.
The cell swells and bursts.
Cytolysis.
Describe plant cells in a hypertonic solution.
The water potential of the external solution is less than the solution outside the cell.
Water moves out by osmosis.
Cytoplasm loses volume and protoplast pulls away.
Cells become plasmolysed.
Describe plant cells in an isotonic solution.
The water potential of the external solution is equal to the solution inside the cell.
No change in the protoplast.
Describe plant cells in a hypotonic solution.
The water potential of the external solution is higher than the solution inside the cell.
The protoplast swells and exerts an increased pressure on the inelastic cellulose wall.
Cell becomes turgid.
What does flaccid mean?
the state of a plant cell when it lacks water = limp or wilted
cells have drawn in and pulled away from the cell wall
Concentrated solution
What does turgid mean?
Swollen and hard
pressure inside the cell rises, eventually the internal pressure of the cell is so high that no more water can enter the cell.
dilute solution
