Plasma Membranes

Question 1

What is the structure of a lipid?

Answer 1

• made of one glycerol and three fatty acids
  -Ester bonds

Question 2

What is a phospholipids?

Answer 2

When the phosphate replaces the fatty acids

Question 3

What types of membranes do eukaryotes have?

Answer 3

• cell surface membrane
• membrane bound organelles

Question 4

What types of membranes do prokaryotes have?

Answer 4

• cell surface membrane
• no membrane bound organelles

Question 5

What are the roles of cell membranes?

Answer 5

• compartmentalisation
  - contains reactions in separate parts of cell
  - separates cell contents from environment
  - keeps harmful substances separate
• cell signalling and recognition
• control what enter and leaves cell
• site of chemical reactions- photosynthesis

Question 6

What are the components of cell membranes?

Answer 6

• phospholipid
  - hydrophilic head
  - hydrophobic tail
• phospholipid form a bilayer (basic structure of a membrane)

Question 7

What is in a fluid mosaic model?

Answer 7

• free moving phospholipids within the layer, relative to each other - gives it flexibility
• proteins are embedded which vary in shape, size and position, like a mosaic

Question 8

What are the functions of channel protein (intrinsic)?

Answer 8

Provides a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient through membranes

Question 9

What is the function of carrier proteins (intrinsic)?

Answer 9

Passive transport and active transport into cells. Involves shape of protein changing

Question 10

What is the function of glycoproteins (intrinsic)?

Answer 10

• cell adhesion and as receptors for chemical signals
• cell communication/ signalling
• cell to cell recognition

Question 11

What is the function of extrinsic proteins?

Answer 11

To interact with heads of phospholipids or intrinsic proteins

Question 12

What is an intrinsic protein?

Answer 12

When the protein goes through both layers of the bilayer

Question 13

What is an extrinsic protein?

Answer 13

Proteins that only sit in one layer of the bilayer

Question 14

What is the function of cholesterol?

Answer 14

• regulates fluidity of membrane
• adds stability without making them rigid
• prevents them becoming too solid by stopping phospholipids grouping too closely and crystallising

Question 15

What is the function of glycolipids?

Answer 15

Contains cell markers/antigens and can be recognised by cells of immune system as self or non self

Question 16

All membranes are _______________ permeable?

Answer 16

Partially

Question 17

What is cell signalling?

Answer 17

A complex system of intracellular communication

Question 18

What are the three mechanisms of cell signalling?

Answer 18

1) receptor acts as ion channel
2) receptor activates a G protein
3) receptor acts as an enzyme

Question 19

Signal molecules fit into __________ molecules on the cell surface ___________?

Answer 19

• receptor
• membrane

Question 20

What molecules could the signal molecules be?

Answer 20

Neurotransmitters

Question 21

What structures in the membrane could the signalling molecules be?

Answer 21

Glycolipids, glycoproteins

Question 22

What is diffusion?

Answer 22

Net movement of particles from an area of high to low concentration until there is an equilibrium

Question 23

What type of process is diffusion?

Answer 23

Passive process

Question 24

What is a concentration gradient?

Answer 24

Difference in concentration between two areas

Question 25

Why does increasing temperature increase the rate of diffusion?

Answer 25

An increase in temperature increases the kinetic energy of the particles which increases collision rate. This increases the rate of diffusion

Question 26

What factors of cells can affect the rate of diffusion?

Answer 26

- surface area- the larger the area if an exchange surface the higher the rate of diffusion -thickness of membrane- thicker exchange surface the higher the rate of diffusion

Question 27

What can diffuse through a phospholipid bilayer and why?

Answer 27

- non-polar molecules - very small molecules - small polar molecules e.g. water as it slowly diffuses through lipid based molecules

Question 28

Why can ions now pass through the phospholipids bilayer?

Answer 28

The hydrophobic interior repels ions so they cannot pass through

Question 29

What is facilitated diffusion?

Answer 29

The movement of molecules from an area of high to low concentration

Question 30

What factors affect the rate of diffusion?

Answer 30

- temperature- higher temp=faster diffusion - surface area- larger surface=faster diffusion - concentration gradient- higher gradient=faster diffusion - size of particles- smaller particles=faster diffusion - diffusion medium- solid=slowest - liquid=faster - gas=fastest

Question 31

What are some factors that affect the rate of facilitated diffusion?

Answer 31

- temperature - concentration gradient - surface area - membrane thickness -number of channel proteins present

Question 32

What is meant by the term ‘model cell’?

Answer 32

A human-made set up that represents a cell

Question 33

Describe the differences between dialysis tubing ans cell membranes with reference to transport across a membrane?

Answer 33

- Dialysis tubing doesn’t have proteins - no energy in a model cell

Question 34

Explain why some ions can pass through dialysis tubing by diffusion but can only pass through the cell membrane by facilitated diffusion?

Answer 34

- no hydrophobic interior so cannot repel ions - permeability of viskin tubing is determined by the size of the particles

Question 35

What is active transport?

Answer 35

The movement of molecules of ions from an area of low to high concentration (against concentration gradient)

Question 36

What uses active transport?

Answer 36

- large and charged molecules - anything that needs to go the opposite way

Question 37

What is bulk transport?

Answer 37

The movement of large enzymes into or out of the cell

Question 38

What are the four types of bulk transport?

Answer 38

- endo - exo - pino - phago

Question 39

What happens in endocytosis?

Answer 39

- bulk transport into cell - cell surface membrane invaginates - vesicles are formed - vesicles pinched off into the cytoplasm

Question 40

What happens in exocytosis?

Answer 40

- bulk transport out of cell - vesicles move to and fuses with the cell surface membrane - releases contents to outside of cell

Question 41

Active or passive?: 1) diffusion 2) facilitated diffusion 3) active transport 4) bulk transport

Answer 41

1) passive 2) passive 3) active 4) active

Question 42

Is ATP needed?: 1) diffusion 2) facilitated diffusion 3) active transport 4) bulk transport

Answer 42

1) no 2) no 3) yes 4) yes

Question 43

Is protein needed?: 1) diffusion 2) facilitated diffusion 3) active transport 4) bulk transport

Answer 43

1) no 2) yes 3) yes 4) no

Question 44

what is compartmentalisation?

Answer 44

the formation of separate membrane-bound areas in a cell

Question 45

what types of environments do cells usually exist in?

Answer 45

aqueous environments

Question 46

why are phospholipid bilayers suited for aqueous environments?

Answer 46

the outer surfaces of the hydrophobic phosphate heads can interact with water

Question 47

what do intrinsic proteins contain?

Answer 47

amino acids with hydrophobic R-groups on their external surfaces, which interact with the hydrophobic core of the membrane, keeping them in place

Question 48

what are the intrinsic proteins?

Answer 48

- channel proteins - carrier proteins - glycoproteins

Question 49

what is cell signalling/ communication?

Answer 49

when the chemical binds to the receptor, it elicit a response from the cell. this may cause a direct response or set off a cascade of events inside a cell

Question 50

What is the movement of water molecules in osmosis?

Answer 50

Random - move in both directions - if moving on one side, then the net movement is high to low water potential

Question 51

Why is equilibrium needed in osmosis?

Answer 51

To ensure cells are normal so they can function

Question 52

What liquid has the highest water potential?

Answer 52

Distilled water

Question 53

What is water potential measured in?

Answer 53

Pascals (Pa) - unit of pressure

Question 54

Describe the process of osmosis when a cell is in water?

Answer 54

Water moves by osmosis from an area of high water potential outside the cell to an area of low water potential inside the cell- this causes the cell to burst (lyses/lysis)

Question 55

Describe the process of osmosis when the cell is in a solution?

Answer 55

Water moves by osmosis from an area of high water potential inside the cell to an area of high water potential outside the cell- causes cell to shrivel

Question 56

What is the definition of osmosis?

Answer 56

The net movement of water molecules across a partially permeable membrane from an area of high to low concern traction as a result of random motion

Question 57

What is the term for high solute concentration?

Answer 57

Hypertonic

Question 58

What is the term for low solute concentration?

Answer 58

Hypotonic

Question 59

What is the term for when the solute is at equilibrium with concentration.

Answer 59

Isotonic

Question 60

What is the term for a shrivelled cell?

Answer 60

Plasmolyzed

Question 61

What is the term for a cell with water equilibrium?

Answer 61

Flaccid

Question 62

What is the term for a cell that’s about to burst/ has burst?

Answer 62

Turgid