2.3 Transport Across Cell Membranes

Question 1

What are the components of the membrane structure?

Answer 1

Phospholipid bilayer
Intrinsic protein
Extrinsic protein
Glyoprotein
Glycolipid
Cholesterol

Question 2

What is the function of the phospholipid bilayer?

Answer 2

Prevents water soluble substances entering and leaving the cell
Makes the membrane flexible
Allows lipid soluble substances to enter and leave the cell

Question 3

What is the function of the:

Intrinsic protein?
Extrinsic protein?

Answer 3

Acts as a channel to allow water soluble substances across the membrane

Provides structural support
Receptor site for cell recognition

Question 4

What is the function of the cholesterol?

Is cholesterol present in plant cells?

Answer 4

Provides strength to membrane
Prevents loss of water and dissolved ions
Pulls together fatty acids to reduce lateral movement

Cholesterol is not present in plant cells because they have a cell wall which is strengthening enough

Question 5

What is the function of the Glycoprotein and glycolipid?

What is the difference between the two structures?

Answer 5

Acts as a recognition site
Helps cells to attach to each other to form tissues

Glycoproteins are polysaccharides that are attached to proteins
Glycolipids are polysaccharides that are attached to phospholipids

Question 6

Define hydrophilic

Define hydrophobic

Answer 6

Attracts water

Repels water

Question 7

What is the thickness of the cell surface membrane?

Answer 7

7nm

Question 8

Why do phospholipids align themselves in a bilayer?

Answer 8

Phosphate head is polar and line with extracellular fluid containing water and an inner layer aligns polar phosphate headsets intracellular fluid containing water

The non polar fatty acid tails are tucked Inbetween

Question 9

Why is the model called the fluid mosaic model?

Answer 9

Proteins and lipids give a mosaic appearance

Proteins and can move around the lipids making it fluid

Question 10

What property of phospholipids ensure that the membrane remain fluid?

Answer 10

Phospholipids are not bonded together. They are bound by hydrophilic and phobic interactions

Question 11

What factors effect plasma membrane permeability?

Answer 11

Temperature
pH - wrong pH, proteins denature
Ethanol - dissolves fatty acids and cholesterol, creating gaps in membrane

Question 12

Define osmosis

Answer 12

When water moves from a high water potential to a low water potential

Question 13

Define water potential

Answer 13

Concentration of water in a solution

Question 14

Define hypotonic

What occurs to animal cells and plants cells when it is hypotonic?

Answer 14

Lower concentration of solute molecules outside of cell

Animal cell bursts - cellysis

Plant cell doesn’t burst because of cell wall
Becomes turgid

Question 15

Define hypertonic

What occurs to animal cells and plants cells when it is hypertonic?

Answer 15

Higher concentration of solute molecules outside cell

Animal cell shrivels

Plant cell membrane shrinks - plasmolysis
Cell wall does not shrink

Question 16

Define isotonic

What occurs to animal cells and plants cells when it is isotonic

Answer 16

Equal concentration of solute molecules outside cell

Animal cell - nothing

Plant cell - cell membrane is slightly torn away - incipient plasmolysis

Question 17

Describe the phospholipid structure

What does it do, in terms of its function in the cell?

Answer 17

Phosphate head
Polar hydrophilic

2 fatty acid tails
Hydrophobic
Non polar

Forms a bilayer between extracellular and intracellular fluid

Question 18

Define simple diffusion

How is diffusion affected by ficks law?

give an example of a molecule that passes a membrane using simple diffusion

Answer 18

Net movement of particles down the concentration gradient from a high concentration to a low concentration

Rate of diffusion increases with increase in SA, decrease in thickness of exchange surface and increase in concentration gradient

Oxygen

Question 19

Define facilitated diffusion

Answer 19

Movement of particles down concentration gradient using a carrier or channel protein (transport proteins)

Question 20

How does a carrier protein work?

Give 3 examples of molecules that pass through a carrier protein

Answer 20

1. A large molecule attaches to binding site of carrier protein
2. Protein changes shape and releases molecule on the other side. It then assumes its original position

Amino acid
Glucose
Testosterone

Question 21

How does a channel protein work?

What kind of molecule passes through a channel protein? Give an example

Answer 21

Charged particles (ions) diffuse across the channel protein because the pore is lined with polar groups
Channel proteins are specific to one particular ion each
They can open and close

Solute molecule
Sodium

Question 22

Define active transport

Answer 22

Movement of particles against concentration gradient, moving from a low concentration to a high concentration, through a carrier protein, requiring energy