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OCR A level biology > Cell membranes > Flashcards

Cell membranes Flashcards

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1
Q

State 4 functions of plasma membranes

A

Options:

  • recognition of other cells
  • separates cell contents from the outside (barrier between cells and its environment)
  • controls the passage of materials in and out
  • allow cell communication
  • phagocytosis
  • cell to cell attachment
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2
Q

State 4 functions of membranes inside cells

A

Options:

  • isolates DNA
  • acts as an intracellular transport system
  • compartmentalises reactions
  • can be the site of chemical reactions
  • ribosomes attach
  • protection from lysosomes
  • forms vesicles
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3
Q

Define compartmentalisation

A

The formation of separate membrane-bound areas

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4
Q

Why is compartmentalisation useful in cells?

A
  • incompatible reactions occur within the cell
  • isolates reactions making them more efficient
  • allows reaction conditions to be maintained (e.g chemical gradients)
  • protects cell components
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5
Q

Define partially permeable

A

A membrane that allows some substances to cross but not others

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6
Q

Define cell signalling

A

A complex system of intercellular communication

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7
Q

Define phospholipid bilayer

A
  • arrangement of phospholipids found in cell membranes
  • the hydrophilic phosphate heads form the inner and outer surface of a membrane ,
  • sandwhiching the fatty acid tails to form a hydrophobic core
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8
Q

Why are membranes referred to as having a ‘fluid-mosaic structure’ ?

A
  • the phospholipids are able to move freely relative to each other (fluid)
  • the proteins embedded in the bilayer vary in shape, size, and position (mosaic)
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9
Q

Define glycoprotein

A

Extrinsic membrane proteins with attached carbohydrate molecules of varying lengths and shapes

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10
Q

Define glycolipid

A

Cell-surface membrane lipids with attached carbohydrate molecules of varying lengths and shapes

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11
Q

Define phospholipid

A

Modified triglycerides, where one fatty acid has been replaced with a phosphate group

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12
Q

What are channel proteins?

A

Membrane proteins that provide a hydrophilic channel through a membrane

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13
Q

What are receptor proteins?

A

Extrinstic glycopoteins that bind chemical signals, triggering a response by the cell

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14
Q

What are carrier proteins?

A

Membrane proteins that play a part in the transport of substances through a membrane

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15
Q

What is the approximate width of an animal cell plasma membrane?

A

7nm

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16
Q

What are the functions of cholesterol in cell surface membranes?

A
  • regulates fluidity and adds stability to membranes

- prevents phospholipids from crystallising

17
Q

What are the functions of phospholipids in cell surface membranes?

A
  • forms basic structure
  • acts as partially permeable barrier
  • allows the passage of lipid soluble molecules
  • prevents water soluble molecules from moving across
18
Q

What are the functions of glycoproteins in cell surface membranes?

A
  • receptors for chemical signals
  • cell adhesion
  • when chemical binds to the receptor, events inside the cell are set off
  • binding sites for chemical e.g hormones
  • Hydrogen bonds to water to stabilise membrane
19
Q

What are the functions of glycolipids in cell surface membranes?

A
  • act as antigens that can be recognised by the immune system
  • form hydrogen bond with water molecules to stabilise membrane
20
Q

What are the functions of carrier proteins in cell surface membranes?

A
  • have an important role in both passive movement of polar molecules and ions down a concentration gradient
  • this involves the shape of the protein changing
21
Q

What are the functions of channel proteins in cell surface membranes?

A

-provide a hydrophillic channel that allows passive movement of polar molecules and ions down a concentration gradient

22
Q

What are the functions of extrinsic proteins in cell surface membranes?

A

-can attach to the cytoskeleton

23
Q

Define cell adhesion

A

The process by which cells make contacts with each other

24
Q

Describe 2 ways in which cholesterol regulates membrane fluidity

A
  • hydrophillic end of cholesterol interact with phosphate heads
  • hydrophobic end of cholesterol interacts with fatty acid tails
  • pulling the phospholipids together
  • prevents membranes from becoming too solid and crystallising by preventing the phospholipids from getting too close together
25
Q

What 3 factors affect membrane structure?

A

Temperature
Solvents
Cholesterol

26
Q

How does an increase in temperature affect cell membranes?

A
  • increases membrane fluidity
  • increases membrane permeability
  • carrier and channel proteins are denatured at higher temperatures
  • membrane loses its structure
27
Q

Why does an increase in temperature increase membrane permeability?

A
  • more temperature means phospholipids move more
  • because they have a higher kinetic energy
  • makes it easier for things to pass through
28
Q

How do solvents affect cell membranes?

A
  • membrane loses structure

- increases permeability

29
Q

Why do solvents increase membrane permeability?

A

-solvents dissolve phospholipids

30
Q

Give an example of a solvent that can dissolve phospholipids

A

Ethanol, Methanol etc.

31
Q

Outline how the effect of temperature on membrane permeability can be investigated

A
  • beetroot cells contain betalain
  • when membranes are disrupted the red pigment is released
  • pieces of equal size beetroot are placed in water and heated in waterbaths at different temperatures for the same amount of time
  • the solutions are placed in a colorimeter
32
Q

How can a colorimeter show the permeability of membranes?

A
  • more permeable means more betalain leaks out

- more betalain means less light is absorbed by the detector

33
Q

Outline how the effect of solvents on membrane permeability can be investigated

A
  • beetroot cells contain betalain
  • when membranes are disrupted the red pigment is released
  • pieces of equal size beetroot are placed in different concentrations of a solvent for the same amount of time
  • the solutions are placed in a colorimeter
34
Q

Suggest 3 improvements of the design of the experiment

A
  • cut pieces from same place in beetroot
  • blot surface of beetroot before experiment
  • use same volume of water

OCR A level biology (44 decks)

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