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OCR A level Biology > 2.1.5 - Biological Membranes > Flashcards

2.1.5 - Biological Membranes Flashcards

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1
Q

Phospholipid structure

A

A glycerol molecule
Two fatty acid tails (saturated and unsaturated)
Phosphate group

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2
Q

Properties of phospholipid

A

Phosphate group is polar —> hydrophilic
Fatty acid tails are non polar —> hydrophobic

(Amphipathic)

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3
Q

Why does soap dissolve the membrane easily

A

Membranes are made from lipids

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4
Q

What is selective permeability

A

When what goes in and out of the cell is regulated by only letting certain things in and out

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5
Q

Major molecules in cell membranes

A

Phospholipids

Proteins

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6
Q

Amphipathic

A

The molecule has dual nature (hydrophobic and hydrophilic)

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7
Q

What roles do proteins play in transport

A

Regulation

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8
Q

What kinds of cells have cell walls

A

Plant
Bacterial
Fungal

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9
Q

What are glycoproteins made from

A

Proteins

Sugars

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10
Q

Example of a glycoprotein

A

Antibodies - important in immune response

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11
Q

What are glycolipids made of

A

Fats

Sugars

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12
Q

Why can’t water pass through the phospholipids

A

The inside is non polar

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13
Q

How do proteins assist in transport

A

Allow big things and things that have a charge to move across the membrane

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14
Q

What is a plant cell wall made of

A

Cellulose

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15
Q

What is a bacteria cell wall made from

A

Peptidoglycan

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16
Q

What is a fungal cell wall made from

A

Chitin

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17
Q

Function of chlolesterol in cell membranes

A

Regulates fluidity of membrane by keeping phospholipids slightly apart or pulling them closer
Hydrophilic ends interact w/ heads and hydrophobic end interacts w/ tails; pulls them together
Prevent phospholipids from grouping together too closely and crytsallising

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18
Q

Function of glycoprotein in cell membrane

A

Cell adhesion - binding site for hormones and drugs
Cell signalling to coordinate activities of organisms
Antigens for the recognition of ‘self’
Acts as receptor

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19
Q

Function of glycolipid

A

Form cell markers/ antigens

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20
Q

Function of carbohydrates in cell membrane

A

Hydrophilic molecules that sit on the cell surface membrane and attracts water with dissolved solutes

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21
Q

Carrier protein

A

Changes shape to allow specific molecules in and out of the cell

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22
Q

Channel protein

A

These provide a hydrophilic channel that allows the passive movement of polar molecules down a concentration gradient

Water filled channel inside is lined with hydrophilic amino acids

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23
Q

Integral/ intrinsic proteins

A

Proteins that span the whole membrane

Either channel or carrier proteins

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24
Q

Protein receptor site

A

Acts as receptors to detect hormones and/or drugs

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25
Q

How do carrier proteins work

A

Molecule binds
Carrier protein changes shape
Releases molecules on the other side

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26
Q

When is diffusion rapid

A

Small

Non-polar molecules

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27
Q

Facilitated diffusion

A

Involves carrier and channel proteins within the cell membrane.
These help transport large, polar molecules e.g. glucose, across the membrane

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28
Q

Functions of a cell membrane

A

Can be a site of chemical reactions - contain enzymes
Cell signalling
Create conc. gradient
Has antigens so the immune system recognises it as ‘self’
Separates contents from outside - barrier (cell or organelles)
Regulates transport of molecules in/out of a cell or organelle
Seperates metabolic pathways

29
Q

Factors affecting diffusion

A 
Temperature
Molecule size 
Conc. gradient 
Diffusion distance 
Surface area
30
Q

Cell membrane permeability at higher temps

A

Phospholipids moving around so fluidity and permeability increases (more kinetic energy)
Cholesterol reduces the fluidity
The proteins could denature and the bilayer could be completely permeable

31
Q

What does water dissolve

A

Polar solutes

32
Q

What does ethanol dissolve

A

Membranes, disrupting cells which is why alcohols are used in antiseptic wipes

33
Q

How do solvents affect permeability

A

Non polar or less polar solutes will disrupt membranes as the tails no longer orientate towards the middle. The membrane will become more fluid and more permeable

34
Q

What happens if animal cells are put into pure water

A

Cell bursts open, it is cytolysed

35
Q

What happens if animal cells are put in a solution with low water potential

A

Cell shrinks and appears wrinkled - it is crenated

36
Q

What happens if a plant cell is put in pure water

A

Plant cell wall prevents bursting. Membrane pushes against cell wall - cell is turgid

37
Q

What happens if a plant cell is put in a solution with very low water potential

A

Plasma membrane pulls away from the cell - it is plasmalysed

38
Q

Water tendency

A

Measure of the tendency of water molecules to diffuse from one region to another

Measured in kPa

39
Q

What is water potential affected by

A

The amount of solute it contains

The greater the amount of solute it contains, the lower or more negative the lower water potential

40
Q

Osmosis

A

The passive movement of water from an area of high water potential to an area of low water potential across a partially permeable membrane

41
Q

Active transport

A

Movement of substances from low to high conc. across a cell membrane, using ATP and protein carriers (against a conc. gradient)

42
Q

What do carrier proteins combine reversibly with

A

Specific solute molecules or ions. They also have a region that binds to and allows the hydrolysis of a molecule of ATP to release energy

43
Q

Sodium potassium pump

A

Carrier proteins binds 3 Na+ ions and 1 ATP

ATP is hydrolysed to release energy and the carrier protein changes shape

44
Q

Tonicity

A

How much solute is in the solution

45
Q

Hypotonic

A

Less solute

Higher water potential

46
Q

Hypertonic

A

More solute

Lower water potential

47
Q

Highest water potential

A

0 kPa

Pure water - no solute dissolved

48
Q

Endocytosis

A

Taking in large particles into the cell using vesicles and ATP
Csm invaginates when it comes into contact w/ substance
Enfolds membrane til it fuses –> forms vesicle
Vesicle pinches off and moves into cytoplasm to necessary organelle

49
Q

Phagocytosis

A

Endocytosis carries out by phagocytic cells

50
Q

Pinocytosis

A

Taking in liquid into the cell

51
Q

Passive transport

A

Diffusion
Facilitated diffusion
Osmosis

52
Q

Bulk transport

A

Movement of molecules through a membrane by the action of vesicles

53
Q

Thickness of plasma membrane

A

7.5 nm

54
Q

How factors affect the rate of diffusion

A

(Temp x SA x Conc. diff)/(diffusion distance x size of particle)

55
Q

Receptor mediated endocytosis

A

Transports LDLs and viruses into the cell only

Requires ATP

56
Q

Investigating cell membrane permeability

A

Cut 5 equally sized beetroots w/ a cork borer
Rinse and dry - to remove all pigment
Add beetroots to diff test tubes w/ 5cm^3 of water
Add each tt to a diff water bath w/ diff temp for same amount of time
Remove beetroot and using a pipette transfer remaining sol. to cuvette until 3/4 full
Use blue filter and measure abs
High abs, more pigment released, more permeable

57
Q

Investigating water potential of plant cells

A

Prepare sucrose sol. of diff conc.
Use cork borer to get identically sized potato cylinders
Measure mass w/ mass balance
Place each cylinder is diff conc. solution for same amount of time
Calculate % change in mass
Plot conc. on x and % change on y to find when conc. was isotonic

58
Q

Examples of model cells

A

Agar jelly
Visking tubing
Gelatine cubes

These have a similar cytoplasm to our cells

59
Q

Investigating diffusion using model cells (conc.)

A

Prepare agar jelly / indicator and alkali (pink)
Prepare tt w/ diff conc. of acid
Cut equal sized cubes from agar jelly and place into tt
Use stopwatch and record time taken to go colourless
Higher conc. of acid = less time to go colourless
Repeat at least 3x and calculate mean

60
Q

Why do we do repeats

A

Calculate mean

Reduce effect of random error

61
Q

Precision

A

Having all your values close to EACH OTHER

62
Q

Accuracy

A

Having all your values close to the TRUE VALUE

63
Q

Why does facilitated diffusion not use ATP

A

Molecules have their own kinetic energy

Uses gradient

64
Q

Which type of fatty acid tail contributes most to fluidity

A

Unsaturated

65
Q

Intrinsic proteins

A

Channel proteins
Carrier proteins
Glycoproteins

66
Q

Extrinsic proteins

A

Present in one side of bilayer
Hydrophilic R groups on outer surface
Can be present in either layer and some move between layers

67
Q

Process of active transport

A

Molecule binds to receptor in channel of carrier protein
Binding of phosphate causes proteins to change shape - opening up to the inside
Molecule released to inside of cell
Phosphate released and recombines w/ ADP
Carrier protein returns to orig shape

68
Q

Processes requiring ATP as an immediate source of energy

A

Active transport
Exocytosis
Endocytosis

OCR A level Biology (25 decks)

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