Module 2.5 Biological Membranes

Question 1

What are the functions of membranes within the cell

Answer 1

They compartmentalise the cell (substances needed for respiration are inside the mitochondria)
They act as a barrier (only certain things can leave, for example mRNA from the nucleus)
They also act of a site for chemical reactions
Also there are membranes within the cell (organelles)
Can form vesicles for transport

Question 2

What is the function of membranes out of the cell

Answer 2

Partially permeable
Allow recognition by other cells

Question 3

Can you draw the plasma membrane

Answer 3

Question 4

Can water soluble molecules pass through the phospholipid bilayer

Answer 4

No, because the centre of the bilayer is hydrophobic. So water soluble cannot pass through.

But fat soluble ones can

Question 5

Describe what a phospholipid looks like

Answer 5

Hydrophilic head
Hydrophobic tail

Hydrophobic tails face each other whereas the hydrophilic tails point outside towards the water.

Question 6

What the structure and role of cholesterol

Answer 6

Structure- has a flattened shape, allows it fit through bilayer. It is part hydrophobic and part hydrophilic

Function- stabiles the membrane, they control the fluidity. Bind phospholipids more closely to make the membrane more rigid and less fluid

Question 7

What two kinds of proteins are in the cell surface membrane

Answer 7

Extrinsic
Intrinsic

Question 8

What is the role of a carrier and channel proteins

Answer 8

Can transport charged molecules across the bilayer.

Carrier proteins can change shape.
The proteins can be used for specific ions, like a sodium channel

Question 9

What is the role of glycoproteins and lipids

Answer 9

Can help stabilise the membrane by forming hydrogen bonds with water molecules

glycoprotein: Cell communication
glycolipid: Cell recognition

Question 10

Can you draw two molecules of water

Answer 10

Question 11

What two things can affect a membrane permeability

Answer 11

Solvents
Temperature

Question 12

What does a solvent do in the plasma membrane

Answer 12

It dissolves the lipids
So plasma membrane loses structure
Makes membrane more fluid

Question 13

What would happen to the plasma membrane under 0 degree C

Answer 13

Phospholipids packed closely together
Membrane is rigid
Not that much movement
Channel proteins denature
Ice crystals form which pierce membrane when it thaws

Membrane more fluid

Question 14

What happens when the temperature is between 0 and 45 degree C

Answer 14

Kinetic energy increases
Phospholipids vibrate more
Membrane is partially permeable

Question 15

What happens to the membranes permeability above 45 degree C

Answer 15

more kinetic energy so more vibrations
bilayer melts
Membrane becomes more permeable
Proteins denature

Question 16

How do cells communicate with each other

Answer 16

Through cell signalling

Question 17

What would happen if cells could not communicate

Answer 17

Functions in the body would not work properly
Could cause diseases like diabetes, cancer
Cell division would not occur

It would be very bad

Question 18

Explain how cells surface membranes contribute to cell signalling

Answer 18

So a signal is released
Glycoproteins/lipids act as receptors
The receptor is specific to the signal(messenger molecule)
The shape of the receptor and the signal are complimentary
The binding of signal and receptor causes a change in the target cell
Cell surface membrane allows entry of some signal molecules

Question 19

Which component becomes more fluid as temperature increases

Answer 19

Phospholipids bilayer

Question 20

What component of the cell surface membrane becomes denatured when temperature increases

Answer 20

Proteins (channel, carrier)

Question 21

Why is the fluid mosaic model called the fluid mosaic model

Answer 21

Fluid- because the phospholipids bilayer keeps moving
Mosaic- proteins are dotted around

Question 22

The student concluded that yeast cells are killed between 50 °C and 70 °C.
Suggest one way in which the student could have improved the accuracy of this experiment
and one way in which he could have improved the reliability

Exam question

Answer 22

Accuracy

Take temperatures between intermediate temperatures (50 to 70 degree C)

Reliability

Take more readings at each temp

Question 23

Give two examples as hormones as messenger molecules

Answer 23

FSH
Glucagon

Question 24

Explain how glycoproteins can act as receptors

Answer 24

Help with communication between cells
Cell recognition/identification
Work together to trigger a résponse

Question 25

Define diffusion

Answer 25

Net movement of particles down a concentration gradient
Facilitated diffusion requires a protein channel

Question 26

What factors affect diffusion

Answer 26

• Temperature (particles vibrate more)
• Surface area to volume ratio
• Concentration gradient
• distance (thinner the membrane, more diffusion)

Question 27

Define active transport

Answer 27

Movement of particles from an area of low concentration to a high font

• against concentration gradient
• using energy involving protein carriers

Question 28

Define bulk transport

Answer 28

Active transport of large molecules

Question 29

What is endocytosis

Answer 29

-molecule enters cell
-membrane engulfs thing
Examples: phagocytosis, pinocytosis

Question 30

What is exocytosis

Answer 30

• Exit cell
• fuses with cell membrane
• released

Question 31

Define osmosis

Answer 31

• Net movement of water down a water potential gradient
• through partially permeable membrane

Question 32

What happens to an animal and plant cell in a hypertonic solution

Answer 32

Animal- water will leave animal cell through osmosis. The cell will then shrivel up

Plant- water will leave plant through osmosis, the cell will become plasmolysed, plasma membrane detaches from cell wall

Question 33

What will happen to a plant and animal cell in a hypotonic solution

Answer 33

Animal cells- water will move Into cell by osmosis, the cell will burst

Plant cells- water will move into cell by osmosis, the cell will become turgid. Plasma membrane will push against cell wall.