2.5 Plasma membrane

Question 1

What does the cell surface membrane do?

Answer 1

Acts as a barrier, controls movement in and out of cell

Question 2

What is compartmentaillsation?

Answer 2

formation of separate membrane bound areas in a cell,

Question 3

What can compartmentalisation be used for?

Answer 3

incompatible reactions, so allows for specific conditions of the reactions

Question 4

What is a phospholipid

Answer 4

Hydrophilic phosphate head, hydrophobic fatty acid tails

Question 5

What is the phospholipid bilayer, draw it

Answer 5

2 phospholipids, Phosphate heads face outwards, tails point inwards

Question 6

What are the properties of phospholipids that makes it suited to be in the membrane

Answer 6

cells exist in aqueous environments, and are also aqueous, , heads can interact with water

Question 7

Why is the phospholipid bilayer a theory

Answer 7

Membrane is seen as two black lines during electron microscopy

Question 8

What is the fluid mosaic model?

Answer 8

Shows the components of a plasma membrane

Question 9

Compare intrinsic and extrinsic proteins

Answer 9

Intrinsic - embedded through BOTH layers of phospholipids
Extrinsic - proteins that are present on only one side of bilayer, some can move between layers

Question 10

What are channel proteins?

Answer 10

Intrinsic protein, with hydrophobic channel that allows for diffusion of polar molecules

Question 11

What are carrier proteins?

Answer 11

Intrinsic proteins that are part of active transport, they change shape

Question 12

What are glycoproteins

Answer 12

Intrinsic proteins, that have a carbohydrate chan. Play a role in cell adhesion (two cells join to form a junction), and receptors in cell signalling (chemical binds to receptor, causing a response)

Question 13

What are glycolipids

Answer 13

lipid with a carbohydrate tail attached, act as cell markers, so a cell can be recognised

Question 14

What is cholesterol

Answer 14

lipid with a hydrophilic end and hydrophobic end, regulates the fluidity of the membrane, adding stability

Question 15

How does temperature impact membrane structure?

Answer 15

temperature is increased, so phospholipids move more, making the membrane loose it’s structure, so molecules can pass easier

if temp gets too high, eventually breaking down Carrier and channel proteins will denature, decreasing permeability

Question 16

How does solvents impact membrane structure?

Answer 16

Organic solvents (less polar then water) will dissolve membranes. making it more fluid/permeable
Pure alcohol will destroy cells, non-polar alcohol disrupts the membrane, making it more fluid/permeable

Question 17

What is diffusion?

Answer 17

Net, passive movement of particles from a high concentration to a low concentration. until there is an equilibrium

Question 18

What are the factors effecting the rate of diffusion?

Answer 18

Temperature - higher temp = faster diffusion (particles have high kinetic energy)
Concentration difference. (greater difference the faster the rate of diffusion

Question 19

What is simple diffusion

Answer 19

Absence of a barrier or membrane

Question 20

What molecules can diffuse across a partially permeable membrane? Why?

Answer 20

non polar molecules (no charges)
Hydrophobic tails repels substances with positive or negative charges
Small polar molecules can pass through easier then large ones

Question 21

What is the rate of diffusion across a membrane affected by?

Answer 21

Surface area - larger exchange surface = higher rate of diffusion
Thickness of membrane - thinner exchange surface = higher rate of diffusion

Question 22

What is facilitated diffusion? What does this allow for?

Answer 22

Diffusion with involve carrier proteins (without the need for energy) or channel proteins. Allows for movement of polar molecules and ions

Question 23

What is facilitated diffusion impacted by?

Answer 23

Temperature, Concentration gradient, membrane surface area and thickness, and number of protein channels
More protein channels = higher rate

Question 24

What is active transport

Answer 24

A selective, active movement of molecules from a low concentration to a high concentration. Requiring energy

Question 25

Explain active transport

Answer 25

Molecule binds to the channel of the carrier protein. ATP binds to the carrier protein and gets hydrolysed. This causes the carrier protein to change shape, opening to the inside of the cell. ADP and P group bond to form ATP, the carrier

Question 26

What is bulk transport

Answer 26

Active transport of large molecules are transported in and out of a cell. Like enzymes, hormones and bacteria

Question 27

What is endocytosis

Answer 27

Bulk transport into cells

Question 28

What is phagocytosis?
What is pinocytosis?

Answer 28

Phagocytosis - Endocytosis of solids
Pinocytosis - Endocytosis of liquids

Question 29

Explain endocytosis

Answer 29

Cell surface membrane bends inwards as it comes into contact with material. Membrane enfolds the material, forming a vesicle, Which pinches off and moves into the cytoplasm

Question 30

What in endocytosis

Answer 30

Vesicles (formed by the Golgi apparatus) move towards and forms with the cell surface membrane, contents of the vesicle are released to the outside of the cell

Question 31

Why does Bulk transport require energy?

Answer 31

ATP is needed for the movment of vesicles along the cytoskeleton, changing shape of cells to engulf materials, fusion of cell membranes as vesicle or as they meet the cell surface membrane

Question 32

What is osmosis

Answer 32

the passive diffusion of water across a partially permeable membrane

Question 33

What is water potential?

Answer 33

the pressure exerted by water molecules as they collide with a container or membrane

Question 34

What is water potential measured in

Answer 34

Pascals (Pa) Killa Pascals (KPa) ψ

Question 35

What is pure water measured as. What is other water measured as?

Answer 35

0Kpa, all other solutes have a negative water potential (more concentrated, the more negative)

Question 36

In a closed system, what does the diffusion of water into a solution lead to

Answer 36

Hydrostatic pressure

Question 37

What is the effect on an animal cell if it is placed in a solution that has a higher water potential then the cytoplasm

Answer 37

Water moves into the cell, cell may burst (cytolysis)

Question 38

What happens is an animal cell is placed in a solution that has a lower water potential then the cytoplasm?

Answer 38

Cell looses water, causing a shrunken or shrivelled (crenation)

Question 39

What is the effect on a plant cell if it is placed in a solution that has a higher water potential then the cytoplasm

Answer 39

Water enters the cell, increased hydrostatic pressure, pushing the membrane against the rigid cell wall, (pressure is called turgor), the turgor resists entry of further water (turgid)

Question 40

What happens to a plant cell if it is placed in a solution that has a lower water potential then the cytoplasm?

Answer 40

Water is lost, the cytoplasm looses volume, causing the cell surface membrane away from the cell wall (plasmolysed)