National 5 Biology: KA2: Transport Across Membranes Flashcards
What is the meaning of ‘hydrophillic’?
Water “loving”
What is the meaning of ‘hydrophobic’?
Water “hating”
What is the membrane made up of?
Two types of molecules - phospholipids and proteins
Why do phospholipids arrange themselves into a double layer?
The head and tails are different in their affinity for water
What is the ‘double layer’ called?
Bi-layer
Why is it called the fluid mosaic model?
fluid - phospholipids are able to move around the cell.
mosaic - proteins are in this plasma membrane making it look like a mosaic
Why is the membrane called selectively permeable?
It only allows certain molecules to diffuse into the cell - mainly smaller ones.
Why do larger molecules not get through the membrane?
They find it too difficult. eg glucose and amino acids
Where does the oxygen that enters the cell come from?
The breathing system, delivered by the blood to the extracellular fluid.
Where does the food that enters the cell come from
The digestive system, delivered by the blood to the extracellular fluid.
Waste and carbon dioxide may build up to toxic levels, so what happens?
They have to be removed to extracellular fluid and then to the blood to be carried away.
Define:
Diffusion
Movement of particles from an area of high concentration to an area of low concentration, down the concentration gradient.
What does diffusion result in?
Even distribution of particles
Define:
Passive transport
The cell doesn’t use energy, which includes diffusion and osmosis - going from high to low concentration
Define:
Active transport
The cell does use energy - going from low to high concentration
In the Diffusion of Starch and Glucose Through Visking Tubing experiment, why couldn’t starch get through the tubing?
The starch molecules are too big to pass through the selectively-permeable membrane.
Define:
Osmosis
the movement of water from an area of high concentration to an area of low water concentration through a selectively permeable membrane.
What does LWC stand for?
Low water concentration
What does HWC stand for?
High water concentration
When investigating osmosis in potatoes, why must the potatoes be blotted dry before weighing them?
The excess water would have affected the weight/mass.
Why was the percentage masses compared rather than the actual masses?
The potatoes were different masses before the experiment.
What happens to a cell wall in water? [4]
- large vacuole
- cell membrane pushed against cell wall
- cell wall prevents bursting
- cell is FULLY TURGID
What happens to a cell wall in salt solution? [4]
- small vacuole
- cell membrane shrunken away from cell wall
- cell wall prevents collapse
- cell is PLASMOLYSED.
When lots of cells are plasmolysed, the tissue is described as being what?
Flaccid
Define:
Turgid
Enlarged or swollen with water
Define:
Plasmolysed
Vacuole has shrunk and the membrane has pulled away from the wall due to water loss.
Amoeba experiences an osmotic problem. What is this problem?
It does not have a cell wall and lives in fresh water which means it’s constantly surrounded by a HWC.
What would an average cell do in this situation?
Eventually burst because the amount of water entering by osmosis.
How does amoeba avoid death?
It has a contractile vacuole.
What does ‘contractile vacuole’ mean?
The vacuole will fill with water then squirt it out in a cycle.
Define:
HypERtonic
Refers to a solution which effectively has a LWC because there is a lot of solute dissolved in it.
Define:
HypOtonic
Refers to a solution which effectively has a HWC because there is very little solute dissolved in it.
Define:
Isotonic
Refers to two solutions having the same water concentration.
Define:
Active Transport
When cells go against the concentration gradient - to do this, a cell must use energy
Seaweed needs iodine. How does it get it?
It goes against the concentration gradient. This means it uses energy
