plasma membranes

Question 1

what are the key components od the plasma membrane

Answer 1

Phospholipid bilayer- This is made up of phospholipids with hydrophilic heads and hydrophobic tails.

Cholesterol- This adds stability.

Proteins- These may be intrinsic and extrinsic proteins.

Glycoproteins- These are proteins attached to a carbohydrate.

Glycolipids- These are lipids attached to a carbohydrate.

Question 2

what does the phospholipid bilayer contain

Answer 2

Each phospholipid molecule is made up of a hydrophilic ‘head’ and a two hydrophobic ‘tails’.

Question 3

what does the phospholipid bilayer arrangement make them do

Answer 3

This causes phospholipids to arrange themselves into a bilayer so that the hydrophilic heads are facing out (towards water) and the hydrophobic tails are facing in (away from water).

This arrangement creates a hydrophobic centre in the bilayer so that water-soluble substances cannot pass through.

Question 4

what does cholesterol do

Answer 4

provide stabilty and maintain the permeability

Question 5

how does the cholestorol reduce the fluidity in the membrane

Answer 5

Cholesterol molecules consist of a hydrophilic and hydrophobic region. The hydrophobic regions bind to phospholipid fatty acid tails, causing them to pack more closely together.

This reduces the fluidity of the cell membrane

Question 6

what are the types of proteins

Answer 6

intrinsic and extrinsic

Question 7

what are insintric proteins and what does it do

Answer 7

Intrinsic (or integral) proteins are embedded through both sides of the phospholipid bilayer.

These proteins include channel and carrier proteins which transport large molecules and ions across the membrane.

Question 8

what are extrinsic proteins and what do they do

Answer 8

Extrinsic (or peripheral) proteins are present on only one side of the phospholipid bilayer.

These proteins provide support to the membrane or may be involved in cell signalling.

Question 9

what are glycoproteins and glycolipids

Answer 9

Glycoproteins consist of intrinsic proteins attached to carbohydrates, whereas glycolipids consist of lipids attached to carbohydrates.

Question 10

what are glycoproteins and glycolipids involved in

Answer 10

Cell adhesion- This is the attachment of cells to one another.

Cell recognition- This allows cells to recognise one another.

Cell signalling- This is communication between cells.

Question 11

what are the two types of membrane

Answer 11

cell surface membrane
membrane around organelles

Question 12

what are the roles of both types of membrane

Answer 12

Cell-surface membranes- These surround cells to act as a barrier between the cell and its environment, controlling which substances enter and leave the cell.

Membranes around organelles- These surround organelles (e.g. mitochondria) to act as a barrier between the organelle and the cytoplasm, dividing the cell into different compartments (this is sometimes called compartmentalisation).

Question 13

what are the factors that affect the permeability of membrane

Answer 13

temperature
solvent
length of the tails
cholesterol

Question 14

,

Question 15

what does temperature affect the permeability

Answer 15

At low temperatures (below 0°C)- Phospholipids do not have much kinetic energy. They are packed closely together to form a rigid cell membrane, decreasing the permeability of the membrane.

At medium temperatures (0 - 40°C)- As temperature increases, phospholipids have more kinetic energy so they move faster and aren’t packed as closely together. This increases the permeability of the membrane.

At high temperatures (above 40°C)- The phospholipid bilayer breaks down. Channel and carrier proteins denature, meaning they cannot control what enters or leaves the cell. These effects increase the permeability of the membrane.

Question 16

how does solvent affect the permeabilty

Answer 16

Solvents are liquids that have the ability to dissolve substances.

When cells are placed in a solvent such as ethanol, thephospholipids dissolve, causing the membrane to become morefluid. Thisdisrupts the structureof the cell membrane to make itmore permeable.

Increasing theconcentrationof the solvent will furtherincrease the permeabilityof the cell membrane.

Question 17

what is diffusion

Answer 17

Diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration.

Question 18

is diffusion a passive process

Answer 18

yes

Question 19

what are the types of diffusion

Answer 19

Simple diffusion

Facilitated diffusion

Question 20

what is simple diffusion

Answer 20

Some molecules can diffuse directly across cell membranes in a process known as simple diffusion.

Question 21

why can oxygen and carbon dioxide diffuse by simple diffusion

Answer 21

Small- This means that they can pass through the spaces between phospholipids.

Non-polar-This means that they can dissolve in the hydrophobic core of the cell membrane.

Question 22

what is facilitated diffusion

Answer 22

Large or polar molecules can cross cell membranes in a process known as facilitated diffusion.

Question 23

what are the two types of proteins that facilitated diffusion involves

Answer 23

Carrier proteins

Channel proteins

Question 24

how do carrier proteins work

Answer 24

A large molecule attaches to a carrier protein.

This causes the carrier protein to change shape.

The carrier protein releases the molecule on the opposite side of the membrane.

Question 25

what are channel proteins

Answer 25

Channel proteins transport ions across the cell membrane.  These proteins form pores in the cell membrane, which ions can travel through. 

Question 26

what are the factors that affect the rate of diffusion

Answer 26

Temperature - At higher temperatures, particles have more kinetic energy and diffuse faster.  Concentration gradient - The steeper the concentration gradient, the faster the rate of diffusion.  Thickness of membrane - The particles travel shorter distances through thin exchange surfaces, so diffuse faster.  Surface area - Larger surface areas mean more particles can cross the membrane at once, making diffusion faster. Number of carrier or channel proteins - The more of these proteins, the faster the rate of facilitated diffusion.

Question 27

what is a solution

Answer 27

Solutions are mixtures made up of a solute (e.g. glucose), dissolved in a solvent (e.g. water). 

Question 28

what is water potential

Answer 28

Water potential (Ψ) is the pressure exerted by water molecules on the membrane (or container) surrounding a solution. It is measured in kiloPascals (kPa

Question 29

what does high and low water potential mean

Answer 29

High water potential - This means the solution has a high water concentration (so not very much solute dissolved in it). Low water potential - This means the solution has a low water concentration (so lots of solute dissolved in it).

Question 30

what is osmosis

Answer 30

Osmosis is the diffusion of water molecules across a partially permeable membrane from an area of higher water potential to an area of lower water potential. 

Question 31

what happens when to the animal cell when put in a solution depending on the water potential

Answer 31

Hypotonic solutions: A hypotonic solution has a higher water potential than the cell. Water molecules move into the cell. The cell swells and bursts. Isotonic solutions: An isotonic solution has the same water potential as the cell. There is no net movement of water into or out of the cell. The cell stays the same size. Hypertonic solutions: A hypertonic solution has a lower water potential than the cell. Water molecules move out of the cell. The cell shrinks.

Question 32

what happens in plant cells when placed in a solution depending on its water potential

Answer 32

Hypotonic solutions: A hypotonic solution has a higher water potential than the cell.  Water molecules move into the cell.  The cell swells and becomes turgid.  Isotonic solutions: An isotonic solution has the same water potential as the cell.  There is no net movement of water into or out of the cell.  The cell stays the same size. Hypertonic solutions: A hypertonic solution has a lower water potential than the cell. Water molecules move out of the cell.  The cell shrinks and becomes plasmolysed.

Question 33

what are factors affecting the rate of osmosis

Answer 33

Temperature - At higher temperatures, water molecules have more kinetic energy and diffuse faster. Water potential gradient - The steeper the gradient, the faster the rate of osmosis.  Thickness of membrane - Water molecules travel shorter distances through thin exchange surfaces, so diffuse faster. Surface area - Larger surface areas mean more water molecules can cross the membrane at once, making osmosis faster.

Question 34

what is active transport

Answer 34

Active transport is the movement of particles from an area of lower concentration to an area of higher concentration. This process requires energy from respiration in the form of ATP. 

Question 35

how does carrier proteins work in active transport

Answer 35

The molecule or ion binds to the carrier protein. ATP binds to the carrier protein. Hydrolysis of ATP to ADP and phosphate (Pi) causes the carrier protein to change shape. This releases the molecule or ion on the opposite side of the membrane. The phosphate (Pi) is released from the carrier protein, causing the carrier protein to return to its original shape, ready to be used again.

Question 36

what are factors that affect the rate of active transport

Answer 36

Temperature - At higher temperatures, particles have more kinetic energy and travel faster. Respiration also increases with temperature. Very high temperatures denature carrier proteins, decreasing the rate of active transport. Thickness of membrane - Particles travel shorter distances through thin exchange surfaces, so travel faster.  Number of carrier proteins - The more of these proteins, the faster the rate of active transport. Rate of respiration - The more respiration, the more ATP available for active transport. 

Question 37

what is bulk transport

Answer 37

Large molecules such as enzymes or hormones cannot be transported through channel or carrier proteins. Instead, they are moved into and out of cells using another form of active transport, known as bulk transport. 

Question 38

what are the 2 types of bulk transport

Answer 38

Endocytosis - This transports materials into cells.  Exocytosis - This transports materials out of cells. 

Question 39

what is endocytosis

Answer 39

Endocytosis is the process in which large molecules, or many molecules at once, are transported into cells. 

Question 40

what is endocytosis

Answer 40

Endocytosis is the process in which large molecules, or many molecules at once, are transported into cells.