Membrane transport

Question 1

What are the four methods of particle movement across the plasma membrane?

Answer 1

1. Simple diffusion
2. Facilitated diffusion
3. Osmosis
4. Active transport

Question 2

What is simple diffusion and what factors have an effect on its rate?

Answer 2

The movement of particles from a region of high concentration to a region of low concentration, which is the result of the random motion of particles. An equilibrium is reached.

• Temperature (the higher the temp. the higher the rate)
• Surface area (the larger the SA the more molecules diffuse)
• Size of particles (smaller molecules diffuse faster)
• Concentration gradient (the longer the gradient the faster the rate)

Question 3

What is facilitated diffusion and how are potassium channels related?

Answer 3

This process requires channel proteins or carrier proteins. It helps get polar substances across the membrane.

In the process of getting K+ ions in neurons across a membrane, the channels are voltage gated

Question 4

What does voltage-gated mean?

Answer 4

Open and close with changes in the electrical potential to control the movement of K+ ions.

Question 5

What is Osmosis?

Answer 5

The passive movement of water molecules from a region of low solute concentration to a region of high solute concentration across a membrane to dilute it.

Question 6

Why do tissues and organs need to to be placed in isotonic solutions?

Answer 6

• Transplant tissues or organs must be kept in saline solution for storage.
• The osmolarity (solute concentration) of the saline solution must be the same as that in the cytoplasm of the tissue/organ
• This is done to prevent osmosis from occuring

Question 7

What are isotonic, hypertonic and hypotonic solutions?

Answer 7

Isotonic: the concentration of the solutes are equal
Hypertonic: high concentration of solutes outside of the cell (low inside), water will leave the cell
Hypotonic: low concentration of solutes outside the cell (high inside), water will enter the cell

Question 8

What is active transport and how is this connected to sodium-potassium pumps?

Answer 8

• The movement of particles across membrans which requires energy in the form of ATP.
• Against a concentration gradient (low to high concentration)
• Involved in sodium-potassium pumps. The Na+ concentration must be higher outside the neuron and the K+ concentration must be more concentrated inside.
• The protein pump changes shape using ATP energy to expell 3 Na+ to the outside. A phosphate group is donated to the pump.
• The protein pump changes shape using ATP and expells 2 K+ to the inside
• The result of active transport, ADP and a phosphate are produced

Question 9

What is endocytosis?

Answer 9

A method of transport which utilises energy and is highly dependent on the flexibility/fluidity of the plasma membrane. There are two types of endocytosis:
- Pinocytosis: taking in liquid substances ‘drinking’
- Phagpcytosis: absorption of solids ‘eating’
Generally these are processes that takes in substances that come from the outside of the cell
The outside membrane pinches off and becomes the inner layer of the vesicle that forms.

Question 10

What is exocytosis?

Answer 10

Ejection of waste products or useful substances from inside the cell, which uses energy and relies on the flexibility of the membrane. There are two types:
- Excretion: undigested remains are excreted
- Secretion: after protein synthesis by ribosomes proteins are released e.g. enzymes or hormones
The process:
1. After protein synthesis by ribosomes on the RER, the products pass through the golgi apparatus as vesicles where they are processed and packaged
2. They packaged substances are released as vesicles and then fuse with the plasma membrane to secrete the products outside the cell

Question 11

What are vesicles responsible for?

Answer 11

They allow the movement of materials within the cell. Enzymes on the RER produce them as well as the golgi apparatus produce vesicles in the process of exocytosis. (Secretory vesicles and products)

Question 12

How do you estimate the osmolarity in tissues?

Answer 12

Osmolarity is the solute concentration and states the ratio of solutes to water.
Hypotonic (high solute concen. therefore high water potential in cell)
Hypertonic (low solute concen. therefore high water potential in cell)
Independent variable: concentration of solution
Dependent: mass of plant tissue (initial and final)
Control: no. of trials, tissue size and shape, temp. of solution, duration in solution
% change: (final mass - initial mass) / initial mass x100
On a graph, the isotonic point is the osmolarity value where it cuts the x-axis
The higher the concentration, the more water is released and mass decreases.
Cytolisis: burst cell
Plasmolysed: cell shrinks