Chapter 5 - Plasma Membranes

Question 1

Characteristics of cell surface membrane

Answer 1

Made up of phospholipids
That have hydrophilic heads and hydrophobic tails
That allow non polar molecules through and some small polar molecules ( water)

Question 2

What is the fluid mosaic model

Answer 2

Idea that phospholipids are free to move like a fluid

The proteins embedded in the bilayer vary in shape size and position like tiles in a mosaic

Question 3

What is the structure of glycoprotein

Answer 3

Protein with a branching carbohydrate portion of a protein which acts as a recognition site for chemicals

Question 4

Structure of glycolipid

Answer 4

Carbohydrate chain attached to the membrane, not a protein recognition site

Question 5

What is an intrinsic protein (examples)

Answer 5

Transmembrane proteins that are embedded through both layers of a membrane
Amino acids have hydrophobic r groups that interact with hydrophobic core

Channel protein
Carrier protein
Glycoprotein

Question 6

Extrinsic proteins

Answer 6

Peripheral proteins that are only present on either side of the bilayer

Have hydrophilic r groups that interact with the polar heads

Question 7

What is the role of cholesterol

Answer 7

Regulates the fluidity of the membrane

Adds stability - doesn’t let them touch and crystallise, pulls them together

Question 8

How does temperature affect the membrane structure?

Answer 8

Phospholipids are always moving
Increases kinetic energy
Moves faster - loses structure - increases fluidity
Loss of structure increases permeability - easier for particles to cross

At high temperatures carrier and channel proteins will denature - involved in transport of proteins

Question 9

How does solvents affect membrane structure

Answer 9

Organic substances that are less polar than water or non polar will dissolve membranes

Non polar alcohol can enter membrane and disrupt the structure of phospholipids - making the membrane more fluid and permeable

Question 10

A practical to investigate the permeability of membranes

Answer 10

Beetroot

Put equal amounts of beetroot in tube and increase the water bath at intervals of ten - measure absorbance of each sample 5 minutes after temperature is reached
Using colorimeter with blue filter
Pigment is releases from cell

More pigment molecules absorb more light, light transmitted decreases

Question 11

What is diffusion

Answer 11

The net movement of particles from a region of high concentration to a region of low concentration

Question 12

Factors affecting the rate of diffusion

Answer 12

Temperature
- more kinetic energy - move at faster speeds

Concentration difference
- overall movement from high to low is larger

Question 13

Practicals to find the rate of diffusion and surface area

Answer 13

Distance travelled / time

Volume filled / time

Question 14

Factors that affect rate of diffusion across membranes

Answer 14

Surface area
- larger the area of a exchange surface

Thickness of membrane
- when particles move over a long distance, collisions are more likely, which will slow the rate of reaction

Question 15

What is facilitated diffusion

Answer 15

Diffusion across a membrane through a protein channel

Question 16

What is the rate of facilitated diffusion dependent on

Answer 16

Temperature 
Concentration gradient 
Surface area 
Cell membrane thickness 
Number of channel proteins present

Question 17

Practical to investigate the factors affecting diffusion rates in model cells

Answer 17

Placed in different concentrations/ temperatures

Using dialysis tubing with pores

• water can pass through
• glucose can - use Benedict’s solution to test
• starch can’t - iodine test

Question 18

What is active transport

Answer 18

The movement of molecules from a region of low concentration to a region of high concentration
Requires energy and carrier proteins - atp

Question 19

How does active transport happen with Carrier proteins

Answer 19

• molecule binds to receptors on channel / carrier protein ( outside of cell)
• (inside of cell) atp binds to carrier protein and is hydrolysed into Adp and a phosphate
• when phosphate binds to carrier protein the protein changes shape, opening up to the inside of the cell
• molecule is released into the cell
• phosphate is released and recombined to adp to make atp
• Carrier protein returns

Question 20

What is bulk transport

Answer 20

Another form of transport where large molecules or cells are moved into or out of a cell by enocytosis and exocytosis

Enzymes , hormones , bacteria

Question 21

What is endocytosis

Answer 21

Bulk transport of material into cells

• phagocytosis - solids
• pinocytosis - liquids
• the cell surface membrane invaginate, bends inwards when it comes into contact with material
• membrane enfolds material until fuses and forms a vesicle
• vesicles pinches off and moves into the cytoplasm to transfer material

Question 22

What is exocytosis

Answer 22

Vesicles formed by the Golgi apparatus moves towards and fuses with the cell surface membrane - contents of vesicles are released

• energy atp is required to move the vesicles along the cytoskeleton, changing the shape of cells to engulf and fusion of membrane

Question 23

What is water potential

Answer 23

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

Pure water = 0 water potential
The more concentrated the more negative the water potential

Question 24

What are the effects of osmosis on plants and animals cells

Answer 24

The increase of volume into a cell results in the increase in hydrostatic pressure

Question 25

Cytolysis

Answer 25

Animal cells swell with water

• increases hydrostatic pressure
• the cell surface membrane can’t stretch to withstand the pressure

Question 26

Crenation

Answer 26

Reduction in the volume of the cell

Shrivel

Question 27

What do animal cells have to prevent cytolysis and crenation

Answer 27

Have control mechanisms - blood plasma

Makes sure they are surrounded by isotonic solutions

Question 28

Why do plant cells have cell walls

Answer 28

They can’t control the water potential around them

Need strong cellulose walls

Question 29

Turgid

Answer 29

Plant cells swell

Increased hydrostatic pressure pushes the membrane against the rigid walls

Question 30

Plasmolysed

Answer 30

Plant cells shrivel

Reduction in volume of cytoplasm
Pulls the plasma membrane away from cell wall

Question 31

What do channel proteins do

Answer 31

Hydrophilic channel

Allows passive movement of polar molecules and ions
Down a concentration gradient

Held in position by interactions between hydrophobic r groups on outside of protein and hydrophobic core of membrane

Question 32

Carrier proteins

Answer 32

Passive and active transport

Involved changing of shape

Question 33

Glycoproteins

Answer 33

Have receptors
That elicits response from the cell

Cell communication/signalling - responds to its environment

Cell adhesion - when cells join to form tight junctions in tissues

Question 34

Insulin glucagon example for glycoproteins

Answer 34

Receptor for hormones insulin and glucagon

Affect uptake and storage of glucose by cells

Question 35

Glycolipid

Answer 35

Cell markers/ antigens

Can be recognised by the immune system as self or non self

Question 36

What can pass through a phospholipid bilayer

Answer 36

Non polar molécules - oxygen

Small Polar molecules - water / glucose
Only

Not ions

Question 37

Partially permeable

Selectively permeable

Answer 37

Only allows certain types of molecules through but not all

Plasma membranes with protein channels that only allow specific substances to cross