Chapter 3B - passive transport

Question 1

Diffusion…

Answer 1

Is the movement of particles down the concentration gradient.

Question 2

Passive transport…

Answer 2

is a process that does not require energy to move things across it

Question 3

Simple diffusion…

Answer 3

is when molecules move from an area of high concentration to an area of low concentration (down the concentration gradient).

• This happens due to the kinetic energy stored in each molecule which causes them to move around and bounce off each other.
• This leads to even dispersion of molecules in an area.

Question 4

Molecules that can freely diffuse across the membrane:

Answer 4

• Non-polar, uncharged or hydrophobic molecules. EG: 02, H2, CO2, lipids
• Small molecules like water are able to slip through the phospholipid bilayer

CAN’T
- Large and hydrophilic molecules (ions, amino acids, proteins, glucose or nucleic acids) will simply bounce off the membrane and be unable to diffuse through

Question 5

Facilitated diffusion…

Answer 5

is the passive movement of molecules down the concentration gradient through membrane bound proteins (protein channels).

• This allows large molecules like glucose and ions to move between the extra- and intracellular environments.

Question 6

What are:
- Protein channels
- Carrier proteins

Answer 6

Protein channels - pores or holes in the membrane that let specific substances through
Carrier proteins - bind to the substance that is being transported and undergoes a conformational change to push the substance down the concentration gradient.

Both channels and carriers are specific to the molecules they transport.
- This contributes to the selective permeability of the plasma membrane.

Question 7

Osmosis…

Answer 7

Is the diffusion of water across a selectively permeable membrane from areas of low solute concentration to areas of high solute concentration
- despite being hydrophilic, water can move through the membrane as it is so small.

Question 8

3 types of tonicity:

Answer 8

Hypertonic - solutions have comparatively higher solute concentrations - so - water moves into the hypertonic solution from adjacent areas with lover solute concentrations.

Isotonic - solutions have equal solute concentrations - so - there is no net movement of water.

Hypotonic - solutions have comparatively lower solute concentrations - so - water moves from a hypotonic solution into adjacent areas with a higher solute concentration.

Hyper - high
Hypo - low

Question 9

The effect of tonicity on cells

Answer 9

Tonicity of a solution will effect cell size.
- If a plant cell cytosol is hypotonic compared to the extracellular fluid, water will move into the cell and cause it to swell and become turgid HOWEVER it won’t burst due to the cell wall
- When water moves out of a plant cell (hypertonic) the cell shrinks and becomes plasmolysed
- Animal cells placed in a hypotonic solution will increase in volume until they lyse. This is because they don’t have a cell wall