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OCR A-LEVEL Biology > Module 2 Section 5 - Cell Membranes > Flashcards

Module 2 Section 5 - Cell Membranes Flashcards

1
Q

What do membranes control

A

Membranes control what passes through them

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2
Q

What are membranes at the surface of the cell

A

They are barriers between the cell and its environment

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3
Q

What does the membranes at the surface of cells control

A

Controls which substances enter and leave the cell

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4
Q

What is said about the permeability of membranes on the surface of the cell

A

They are partially permeable - they let some molecules through but others not

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5
Q

How would substances typically move across membranes at the surface of cells

A

Diffusion
Osmosis
Active transport

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6
Q

What do membranes on the surface of the cell allow

A

Recognition by other cells
Cell communication

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7
Q

What are membranes within cells

A

The membranes around organelle divide the cell into different compartments. Making functions more efficient.

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8
Q

What can membrane within cells form

A

Vesicles to transport substances between different areas of the cell

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9
Q

What do membranes within cells control

A

Which substances enter and leave the organelle, they are also partially permeable

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10
Q

Can you find membranes within organelles

A

Yes - these act as barriers between the membrane contents and the rest of the organelle

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11
Q

Membranes within cells can be the site of what

A

Site of chemical reactions

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12
Q

Cell membranes have a

A

Fluid mosaic structure

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13
Q

What are all membranes composed of

A

Lipids (mainly phospholipids), proteins and carbohydrates (usually attached to protein or lipids)

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14
Q

In 1972 what was suggested to describe the arrangement of molecules in the membrane

A

The fluid mosaic model

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15
Q

In the fluid mosaic model what forms a continuous double layer (bilayer)

A

Phospholipid molecules

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16
Q

Why is the phospholipid bilayer fluid

A

Because the phospholipids are always moving

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17
Q

What is present within the bilayer

A

Cholesterol

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18
Q

What is scattered throughout the bilayer

A

Protein molecules

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19
Q

What are glycoproteins

A

Some proteins that have a polysaccharide chain attached to it

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20
Q

What are glycolipids

A

lipids that also have a polysaccharide chain attached to it

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21
Q

What are the different components of the cell membrane

A

Phospholipid
Cholesterol
Proteins
Glycolipids
Glycoproteins

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22
Q

Phospholipid molecules have a

A

Head and tail

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23
Q

The Phospholipid head is

A

Hydrophilic - attracts water

24
Q

The phospholipid tail is

A

Hydrophobic - repels water

25
Q

How are the phospholipid molecules arranged

A

They automatically arrange themselves into a bilayer - head face out towards the water on either side of the membrane

26
Q

The centre of the bilayer is

A

Hydrophobic meaning the membrane doesn’t allow water soluble substances through it

27
Q

What does cholesterol give to a cell membrane

A

Gives the membrane stability

28
Q

What is cholesterol

A

A type of lipid

29
Q

Is cholesterol present in all membranes

A

Yes

30
Q

Where does cholesterol fit in

A

Cholesterol molecules fit in between the phospholipids, they bind to the hydrophobic tails causing them to pack more closely meaning the membrane is less fluid and more rigid

31
Q

What do proteins control in the cell

A

Proteins control what enters and exits the cell

32
Q

Some protein form what in the membrane

A

channels in the membrane which allow small or charged particles through

33
Q

Other proteins (carrier proteins) transport what

A

Molecules and ions across the membrane by active transport and facilitated diffusion

34
Q

Proteins can acts as

A

Receptors for molecules in cell signalling, when a molecule binds to the protein a chemical reaction is triggered inside the cell

35
Q

What do glycolipids and glycoproteins do for the cell

A

Act as receptors for messenger molecules

36
Q

How do glycolipids and glycoproteins stabilise the cell

A

They form hydrogen bonds with surrounding water moelcules

37
Q

Glycolipids and glycoproteins are sites where what bind

A

Drugs
Hormones
Antibodies

38
Q

Glycolipids and glycoproteins are also what

A

Antigens

39
Q

Cell signalling is..

A

How cells communicate with each other

40
Q

How do cells communicate with each other

A

Messenger molecules

41
Q

Describe the three steps a messenger molecule makes to communicate with other cells

A

-one cell releases a messenger molecule
-this molecule travels to another cell
-the messenger molecule is detected by the cell because it binds to a receptor on its cell membrane

42
Q

What plays an important role in cell signalling

A

Cell membrane receptors

43
Q

What act as receptors for messenger molecules

A

Proteins in the cell membranes (membrane-bound receptors)

44
Q

What is specific about receptor proteins

A

Their shape

45
Q

What can bind to the receptor proteins

A

Only messenger molecules with a complementary shape can bind to them

46
Q

Different cells have different….

A

Types of receptors - they respond to different messenger molecules

47
Q

What is a cell that responds to a particular messenger molecule called

A

Target cell

48
Q

How do many drugs work

A

By binding to the receptors in cell membranes, they either trigger a response or block the receptor and prevent it from working

49
Q

How can you investigate the permeability of a membrane

A

Beetroot cells contain a coloured pigment that leaks out - the higher the permeability the more pigment leaks out.

50
Q

What affects the permeability of a membrane

A

Temperature
Solvent type
Solvent concentration

51
Q

What happens to the permeability of a membrane if the temperature is below 0°c

A

-The phospholipid pack more closely due to not much energy and the membrane becomes rigid
-The channel and carrier proteins in the membrane deform increasing the permeability
-Ice crystals may form and pierce the membrane further increasing the permeability.

52
Q

What happens to the permeability of a membrane if the temperature is between 0°c - 45°c

A

Phospholipids aren’t as packed because they can move around - the membrane is partially permeable. As the temperature increases the phospholipids move more because they have more energy and this increases permeability

53
Q

What happens to the permeability of a membrane if the temperature is above 45°c

A

The phospholipids start to melt and membrane becomes more permeable. The water inside the cell expands putting pressure on the membrane and channel and carrier proteins deform so they can’t control what enters and exits the cell which increases permeability.

54
Q

What happens to the permeability of a membrane if you surround it in a solvent

A

A solvent such as ethanol increases membrane permeability of the cell membrane

55
Q

Why does surrounding the cells in a solvent increase membrane permeability

A

This is because solvents dissolve the lipids in a cell membrane so the membrane loses its structure

56
Q

What happens to the permeability of a membrane if you increase the concentration of the solvent

A

The permeability of the membrane will increase

OCR A-LEVEL Biology (48 decks)

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