Transport in Cells

Question 1

Diffusion

Answer 1

Movement of particles from an area of high concentration to an area of low concentration

Down a concentration gradient until dynamic equilibrium is reached

Passive (caused by natural kinetic energy of molecules)

Question 2

Passive Transport Methods

Answer 2

Diffusion
Facilitated diffusion
Osmosis

Question 3

Properties of Molecules that affect transport

Answer 3

Size of molecule
Solubility in lipids and water
Polarity (charge)

Small, non-polar (oxygen, carbon dioxide)
-Rapidly diffuse across a membrane

Small, polar (water, urea)
-Diffuse across a membrane but slower

Charged particles (Ions)
-Cannot diffuse across a membrane, no matter size

Question 4

Carrier Proteins

Answer 4

Can switch between two shapes
Binding site can be open to one side of membrane first and then open to the other side of the membrane
Specific

Question 5

Channel Proteins

Answer 5

Water filled pores
Fixed shape
Specific

Question 6

Phospholipids

Answer 6

Form a bilayer (two layers of phospholipid molecules)

Hydrophobic tails (fatty acid chains) point in towards the membrane interior

Hydrophilic heads (phosphate groups) point out towards the membrane surface

form a barrier to anything which is not lipid-soluble

Question 7

Cholesterol

Answer 7

Are absent in prokaryotes membranes

Control fluidity of a membrane

Fits between phospholipid molecules

Increases fluidity at low temperatures
Decreases fluidity at high temperatures

Question 8

Glycolipids & glycoproteins

Answer 8

Cell recognition
Cell signalling
Receptor binding sight

Question 9

Facilitated Diffusion

Question 10

Active Transport

Answer 10

Active transport moves molecules against their gradient, from low to high concentration.

This involves a carrier protein which carries the molecule from one side of the membrane to the other.

It is an active process and uses ATP to release energy.

An example is the transport of glucose from the villi of the intestine into the bloodstream.

Cotransporters are a special type of carrier protein which can bind to two molecules at a time. The concentration gradient of one molecule is used to transport the other molecule against its gradient.

Rate of active transport depends on:
-The number of carrier proteins in the membrane
-The speed of each carrier protein
-The rate of respiration

Question 11

Fluid Mosaic Model

Answer 11

‘fluid’ because the phospholipids are constantly moving around
‘mosaic’ because both protein and phospholipids are arranged together

Question 12

Extrinsic and Intrinsic Proteins

Answer 12

Intrinsic:
-Span whole membrane
-Facilitated diffusion

Extrinsic:
-surface of the plasma membrane
-function as enzymes