Movement Of Substances Flashcards
(28 cards)
What is the criteria for diffusion to take place ?
Can only take place if there is a concentration gradient.
Define ‘diffusion’.
Net random movement of molecules of a substances from a region of higher concentration to a region of lower concentration, down a concentration gradient.
What is concentration gradient?
Difference in concentration of a substance between 2 regions.
What is a partially/selectively permeable membrane?
Membrane which allows some substances to pass but not others.
Define ‘Osmosis’.
Net movement of water molecules from region of higher concentration to region of lower concentration across a partially permeable membrane, down a concentration gradient.
What is osmotic concentration?
Presence of solute in a cell that causes water to move into it.
What is water potential?
Measure of free kinetic energy of water in a system, or tendency for water to leave a system.
What are the factors affecting diffusion rate?
- Thickness of membrane.
- Concentration gradient.
- Surface area.
- Size of molecules and ions.
- Nature of any structure across which diffusion occurs.
What is a hypotonic solution?
Solution with a lower osmotic potential( or high water potential) than another solution.
What is an isotonic solution?
Solutions of equal osmotic potential( or water potential).
What is a hypertonic solution?
Solutions with higher osmotic concentration( or lower water potential) than another solution.
What is endosmosis?
Water enters cell by osmosis.
What happens to a plant cell that is placed into a hypotonic solution?
- Water enters cell into vacuole.
- Presence of cell wall(strong and elastic), it prevents over expansion of cell by exerting opposing pressure preventing further entry of water.
- Cell become turgid.
What is turgor pressure?
Pressure exerted outwards by water on cell wall.
What happens to an animal cell placed in a hypotonic solution?
Cells will swell and may actually burst.
What happens to cells placed in an isotonic solution?
- Exosmosis and endosmosis skes place at equal rates.
- Rate of water equals rate of water gain.
- Thus cells remain in same shape.
What is exosmosis?
Water leaves cell through osmosis.
What happens to animal cells placed in hypertonic solution?
Cells shrink in size(become dehydrated)- crenated cells.
What happens to a plant cell placed in a hypertonic solution?
- Vacuole decreases in size, cytoplasm shrinks away from cell.
- Cell decreases in size and becomes flaccid.
What is plasmolysis?
Shrinkage of cell cytoplasm away from cell wall when cell is immersed in hypertonic solution.
What is incipient plasmolysis?
Stage where protoplasm is just beginning to pull away from cell wall.
How can plasmolysed cells be restored to their original shape?
By placing them into hypotonic solution, cells will be killed if they remain plasmolysed for too long.
What is the importance of turgor in plants?
- Maintains shape of soft tissues in plants.
2. Movement of certain plant parts.
Define ‘Active transport’.
Movement of substances from region of lower concentration to region of higher concentration, against concentration gradient.
