Diffusion And Osmosis Flashcards
Permeable vs impermeable
Substances can pass through
Substances cannot pass through
Selectively permeable
Allows some substances to pass through, but blocks others
Selectively permeable in cells
Allow water, CO2, O2 to pass through freely, but not sugars, salts and proteins to pass through easily.
Have specialised mechanisms to allow substances to pass through eg. Glucose for respiration
Biological membranes examples
Cell
Mitochondria
Chloroplasts
Nucleus
Diffusion
The spreading out of molecules from a region of high concentration to a region of low concentration
Active transport
The movement of molecules from a less concentrated to a more concentrated area with the use of energy.
Movement through membranes
Diffusion and active transport
Diffusion in everyday life
Smell of perfume
Bread baking
Stink bomb
Food colouring in water
Teabag in hot water
Diffusion in biology
CO2 and O2 diffusing in and out of leaf
CO2 and O2 diffusing in and out of body cells
Osmosis
The movement of water molecules across a semi-permeable membrane , from a region of high water concentration to a region of low water concentration
- special type of diffusion that does not require energy
- form of passive transport
Solvent
A liquid that dissolves another substance
Solute
A substance that has been dissolved
Solution
Mixture of a solute and a solvent
What happens if pure water is separated from salt water
- water molecules move randomly on both directions
- salt molecules cannot move out so more water moves into the salt solution
Give the three states of osmosis and animal cells
Isotonic, hypertonic, hypotonic
What do animals in the sea have
A cytoplasm with the same salt concentration as sea water
What do land animals have that ensures the blood concentration is the same as the cells cytoplasm
Kidneys
Isotonic medium
If an animal cells is in a solution that is the same concentration as its cytoplasm, water will move in and out at the same rate and the cell remains intact
Hypotonic medium
If an animal cell is in a solution that is less concentrated than its cytoplasm, water will move into the cell
- the cell may burst and die
Amoeba
Single celled organisms that live in freshwater ponds
- have a contractile vacuole
Contractile vacuole
Expels water, to prevent amoeba from bursting
Animals that live in sea water do not have a contractile vacuole
State the steps of contractile vacuole
- Water enters amoeba by osmosis
- Excess water enters contractile vacuole
- Contractile vacuole swells
- Contractile vacuole moves to edge of cell
- Contractile vacuole bursts and expels water
- Cycle is repeated
Hypertonic medium
If an animal cell is in a solution that is more concentrated than its cytoplasm, water will move out of the cell
- the cell will shrivel and possibly die
Cell walls
Plant cells have a membrane surrounded by a cell wall
- cells walls are fully permeable to water, gases and many solutes
How do roots absorb water from the soil
If a plant cell has a higher concentration of solutes than its surroundings, water moves into the cytoplasm and vacuole.
Turgor pressure
Water enters the vacuole of the plant cell, and pushes the cytoplasm against the cell wall
Role of turgor pressure
-Cell wall is rigid and prevents the cell from swelling
- turgor pressure gives plant cells strength
(Plants that do not have wood get strength from their cells being fully turgid)
3 states of plant cells and osmosis
Turgid (hypotonic solution)
Flaccid (isotonic solution)
Plasmolyzed (hypertonic solution)
How do plants become flaccid
If plant cells are surrounded by a more concentrated solution, water moves out from the cells by osmosis
-vacuole and cytoplasm shrivel and the cell membrane moves away from the cell wall.
-the more concentrated solution fills the gaps between the cell membrane and the cell wall.
Cell loses turgor
Plasmolysis
The loss of water and the movement of the cell membrane away from the cell wall
-causes plants to wilt
Examples of food preservation using osmosis
Fish and meat soaked in a salt solution
Fruit is preserved in jams by using a high sugar concentration
Osmosis and food preservation
-bacteria and fungi are the most common cause of food spoilage.
Their cells are enclosed by a membrane
-if food is placed in a salty or sugary solution
Any bacteria or fungi present will lose water from their cells, shrivel and die
