2.5 Cell Membranes

Question 1

Roles of membranes

Answer 1

• Surface of cells (plasma membrane)

- within cells

Question 2

Surface of cells (Plasma membrane)

Answer 2

• barrier - control of substances entering and leaving- partially permeable
  (diffusion, osmosis, active transport)
• Communication/ cell Signalling
• recognition (immune system)

Question 3

Within the cell

Answer 3

• Compartmentalisation
• Surface area for reactions
• vesicles

Question 4

Fluid Mosaic Model

Answer 4

• Model of cell membrane structure
• Lipid molecules give fluidity
• Proteins give a mosaic appearance

-2 layers of phospholipids and easily flow over each other

Question 5

Cell Signalling

Answer 5

• Communication between cells using chemical messengers

- Drugs, hormones which travel to other cell and bind to receptor on cell membrane

Question 6

Cell Membrane Receptors

Answer 6

• Complementary shape to a messenger molecule binds with Receptor

Question 7

Components of Cell Membranes

Answer 7

• Phospholipids
• Cholesterol
• Proteins
• Glycolipids
• Glycoproteins

Question 8

Phospholipid bilayer

Answer 8

• form a barrier to dissolved substances
• partially permeable
• Rows of phospholipids naturally arrange themselves into a bilayer
• head is hydrophilic- attracts water
• tail is hydrophobic- it repels water
• hydrophobic centre of bilayer- membrane

Question 9

Cholesterol

Answer 9

• gives membrane stability
• between phospholipid bilayer
• made of lipid
• controls membrane fluidity
• bind to hydrophobic tails of phospholipids
• causing them to pack more closely together
• making membrance less fluid
• and more rigid

Question 10

Proteins

Answer 10

• channel and carrier proteins in membrane

- receptors on cell membrane

Question 11

Channel proteins

Answer 11

• ## form pores in the membrane for charged particles to diffuse through

Question 12

Carrier proteins

Answer 12

• move large molecules out of Cell
• large molecule attaches to carrier protein in membrane
• protein changes shape
• releases molecule on opposite side of membrane

Question 13

Receptors in proteins

Answer 13

• receptors cell signalling

- when molecule binds to protein, chemical reaction takes place in cell

Question 14

Glycolipids

Answer 14

• carbohydrate on a lipid
• stabilise membrane by forming hydrogen bonds with surrounding water molecules
• sites where drugs, hormones and antibodies bind
• receptors for cell signalling
• antigens- involved in immune system

Question 15

Glycoproteins

Answer 15

• carbohydrate on a protein
• stabilise membrane by forming hydrogen bonds with surrounding water molecules
• sites where drugs, hormones and antibodies bind
• receptors for cell signalling
• antigens- involved in immune system

Question 16

Temperature

Answer 16

Increasing temperature increases membrane fluidity

Question 17

1. Temperatures below 0°C

Answer 17

• Phospholipids don’t have much energy so they can’t move much
• Packed closely together and the membrane is rigid
• Ice crystals form and pierce membrance making it highly permeable
• Carrier and channel proteins deform increasing permeability

Question 18

2. Temperatures between 0 and 45°C

Answer 18

• Phospholipids can move and aren’t packed as tightly together
• membrane is partially permeable
• as temperature increases, phospholipids move more as they have more energy
• increases permeability of membrane

Question 19

3. Temperatures above 45°C

Answer 19

• phospholipid bilayer starts to break down
• membrane becomes more permeable
• water inside the cell expands, putting pressure on the membrane
• Channel and carrier proteins denature
• increases permeability of membrane

-

Question 20

Types of transport across cell membranes

Answer 20

• Diffusion
• Osmosis
• Active transport
• Bulk transport

Question 21

Diffusion

Answer 21

1) the net movement of molecules from an area of high concentration to an area of low concentration down a concentration gradient

2) molecules diffuse both ways but net movement will be to area of lower concentration.
- This continues until particles are evenly distributed

• Concentration gradient
• passive

Question 22

What factors affects the Rate of Diffusion?

Answer 22

-temperature

-

Question 23

What factors affects the Rate of Diffusion?

Answer 23

• Temperature
• Concentration gradient
• Movement
• Surface area
• Distance

Question 24

Temperature affecting rate of diffusion

Answer 24

• the warmer
• the faster rate of diffusion
• particles have more kinetic energy so they move faster

Question 25

Temperature affecting rate of diffusion

Answer 25

- as temperature increases - the faster rate of diffusion - particles have more kinetic energy - they move faster

Question 26

Surface area affecting rate of diffusion

Answer 26

-

Question 27

Surface area affecting rate of diffusion

Answer 27

- larger surface area of membrane | - faster rate of diffusuon

Question 28

Distance affecting rate of diffusion

Answer 28

- The thinner the exchange surface - The shorter the distance molecules have to travel - The faster the rate of reaction

Question 29

Facilitated diffusion

Answer 29

- Diffuse through channel proteins or carrier proteins in cell membrane - Large molecules, ions and polar molecules don't diffuse directly through phospholipid bilayer - Doesn't use energy- passive

Question 30

Osmosis | Diffusion of water

Answer 30

-Movement of water from an area of high water potential to an area of low water potential down its water potential gradient

Question 31

Water potential c (negative) (Ψ) kiloPascals (kPa)

Answer 31

Measure of how much water there is - potential of water molecules to diffuse out of or into a solution - measure of the tendency of water molecules to diffuse from one region to another

Question 32

pure water

Answer 32

- highest water potential - All solutions have a lower water potential than pure water - water potential of zero kPa

Question 33

Lower water potential

Answer 33

- Large amount of solute dissolved | -

Question 34

Hypotonic

Answer 34

- Solution with a higher water potential than the cell - Net movement of water molecules is into the cell - in Animal cell, cell bursts (lysis) - in Plant cell, vacuole swells - vacuole+cytoplasm push against cell wall - Cell becomes turgid (swollen)

Question 35

Isotonic

Answer 35

- Solution with the same water potential as the cell - water molecules pass into and out of the cell in equal amounts - the cell stays the same

Question 36

Hypertonic

Answer 36

- Solution with a lower water potential than the cell - Net movement of water molecules is out of the cell - in Animal cell, cell shrinks (shrivel) - in Plant cell, Cell becomes flaccid (limp) - cytoplasm and membrane move away from the cell wall - this is called plasmolysis

Question 37

Active transport

Answer 37

- Against concentration gradient - Active - energy used from ATP - Use carrier and channel proteins

Question 38

Active transport process

Answer 38

- molecule attaches to Carrier protein - Protein changes shape - moves molecule across Membrane - releasing it on the other side -energy used to move Solute against Concentration gradient

Question 39

Bulk transport

Answer 39

- Endocytosis- in - Exocytosis- out - Pinocytosis- liquid - Phagocytosis- solid

Question 40

Endocytosis

Answer 40

How large particles are brought into cell Segment of plasma membrane surrounds and encloses particle -brings it into the cell, enclosed in a vesicle

Question 41

Exocytosis

Answer 41

- How large particles are exported out of cells - Substance to be exported out of cell is moved towards and fuses with plasma membrane - Fused site opens releasing contents of vesicle