Chapter 2: Cell membranes

Question 1

What is a plasma membrane?

Answer 1

A lipid bilayer composed of molecules that surround and protect the cytoplasm

Question 2

What are the 4 roles of a membrane?

Answer 2

Transport, metabolism, stability, communication and signalling

Question 3

What bonds do phospholipids contain?

Answer 3

Ester bonds

Question 4

Function of the cell plasma membrane?

Answer 4

Separating the inside and the outside contents, cell recognition and signalling, separating the cytoplasm

Question 5

What makes up a phospholipid?

Answer 5

Phosphate head, glycerol and fatty acids

Question 6

2 factors that affect the plasma membrane?

Answer 6

Temperature and solvents (alcohols)

Question 7

What is a glycolipid?

Answer 7

Lipids attached to carbohydrate chains. Called cell markers and are recognised but the cells of the immune system

Question 8

What is a glycoprotein?

Answer 8

Intrinsic proteins. Play a role in cell adhesion. Has receptors that bind to chemical signals

Question 9

What is an intrinsic protein?

Answer 9

Proteins that are embedded through both layers of the membrane and are used for transporting molecules through the membrane

Question 10

What is an extrinsic protein?

Answer 10

Present on one side of the bilayer. Interacts with polar heads of the phospholipids

Question 11

Why is it called a fluid mosaic model?

Answer 11

Fluid = flexible and free to move within the layer
Mosaic = embedded in a variety of shapes and sizes
Model = forms the basis of our understanding

Question 12

What is a channel protein?

Answer 12

Hydrophilic channel that allows movement of polar molecules against concentration gradient. Diffusion.

Question 13

What is a carrier protein?

Answer 13

Important role in active transport into cells

Question 14

What practical can be used to investigate membrane permeability?

Answer 14

By using the beetroot pigment the measure how much has escaped the membrane

Question 15

How does temperature affect membranes?

Answer 15

Increasing the temperature increases the phospholipids kinetic energy. Making the membrane more fluid which causes it to loose its structure and break down. No structure = particles escape easily. Carrier and channel proteins denature

Question 16

How do solvents effect membranes?

Answer 16

The inside of the bilayer is hydrophobic. Organic solvents can dissolve membranes. Pure alcohols are toxic and destroy cells. Non-polar molecules can easily get through the membrane and cause damage. Makes the membrane more fluid as well

Question 17

Diffusion definiton?

Answer 17

The net movement of particles from an area of high concentration to low concentration. It is a passive process.

Question 18

Factors affecting the rate of diffusion?

Answer 18

Temperature - particles have more kinetic energy
Concentration difference
Distance of diffusion - short distances is fast

Question 19

How does diffusion in membranes work?

Answer 19

Non-polar molecules such as O2 diffuse freely down the concentration gradient. Membrane has to be partially permeable

Question 20

Factors affecting rate of diffusion in membranes?

Answer 20

Surface area and Thickness of membrane

Question 21

2 types of diffuion

Answer 21

Simple and facilitated

Question 22

What is facilitated diffusion?

Answer 22

Diffusion across a membrane through channel proteins. Again, with a partially permeable membrane. The more channel proteins, the more diffusion there is

Question 23

What is active transport?

Answer 23

The movement of molecules or ions from an area of low concentration to high concentration. Requires energy and carrier proteins to move against the concentration gradient.

Question 24

How is the energy supplied for active transport?

Answer 24

By ATP

Question 25

What is bulk transport?

Answer 25

‘bulk’ mean ‘a lot at a time’ Another form of active transport. Large molecules cant fit in the carrier proteins so they are moved out by bulk transport.

Question 26

Explain endocytosis?

Answer 26

Bulk transport of material into cells. The membrane invaginates (bends inwards) when in contact with transported material. Folds around it and fuses forming a vesicle. Vesicle then transports it around the cell

Question 27

Explain exocytosis?

Answer 27

Reverse of endocytosis. Contents are usually formed in the golgi apparatus

Question 28

Osmosis definition?

Answer 28

Net movement of water from an area of high water potential to low water potential across a partially permeable membrane. Passive process that will continue until equilibrium is reached

Question 29

What is water potential?

Answer 29

The pressure exerted by water as they collide with a membrane.

Question 30

What is water potential measure in?

Answer 30

Pascals (Pa) or Kilopascals (kPa) The symbol is the Greek letter psi

Question 31

What does cholesterol do?

Answer 31

Regulates fluidity of the membrane, produces hormones like testosterone and oestrogen

Question 31

What are the two types of cholesterol?

Answer 31

High-Density Lipoproteins (HDL) and Low-Density Lipoproteins (LDL)

Question 32

Which cholesterol is considered the ‘bad’ one?

Answer 32

LDL, builds up in the arteries leading to coronary heart disease

Question 33

What does hypotonic mean?

Answer 33

When the cell swells up and bursts as water moves into it

Question 34

What does hypertonic mean?

Answer 34

When the cell shrinks and wrinkles from all the water leaves

Question 35

What is an isotonic solution?

Answer 35

When the cell is functioning at a normal size in solution, no water enter or leave

Question 36

What does ATP stand for?

Answer 36

Adenosine Triphosphate

Question 37

Name a practical to investigate membrane permeability?

Answer 37

Beetroot in different water baths

Question 38

What equipment should you use in the beetroot practical?

Answer 38

Colorimeter, cuvette, test tubes, water baths, mass balance, ruler, scalpel, cutting tile