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Biology Year 12 > 5 - Plasma membrane > Flashcards

5 - Plasma membrane Flashcards

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1
Q

Roles of membranes within and surface of cells?

A
  • partially permeable barriers between cell and its environment, between organelles, and within organelles.
  • controls which substances enter and leave cells.
  • sites of chemical reactions
  • sites of cell communication.
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2
Q

What is compartmentalisation?

A

formation of separate membrane-bound areas in a cell.

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3
Q

Why is compartmentalisation important?

A
  • metabolism includes many different and often incompatible reactions.
  • allows the specific conditions required for cellular reactions.
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4
Q

What model was used to describe the cell surface membrane?

A

fluid-mosaic model

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5
Q

Why is the fluid-mosaic model used to describe the cell surface membrane?

A
  • the phospholipids are free to move within the layer relative to each other (fluid).
  • proteins embedded in the bilayer vary in size, shape, position.
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6
Q

How is the cell surface membrane a … bilayer?

A

phospholipid bilayer.

  • hydrophilic phospholipid heads (polar) face the aqueous environment
  • hydrophobic fatty acid tails (non-polar) face inwards away from the aqueous environment.
  • both tissue fluid and cytoplasm are aqueous
  • molecules arrange themselves to form a bilayer.
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7
Q

What kind of molecules can pass through the cell membrane with ease?

A

fat-soluble substances.

  • due to hydrophobic bilayer centre, the bilayer acts as a barrier to water-soluble substances.
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8
Q

phospholipid

A
  • hydrophilic phosphate ‘head’
  • hydrophobic fatty acid ‘tail’
  • molecules arrange to form a bilayer.
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9
Q

cholesterol

A
  • lipid with a hydrophilic end and hydrophobic end
  • positioned between phospholipids in the bilayer.
  • regulates the fluidity of membranes.
  • stabilises the membrane
  • prevents phospholipid molecules from grouping too closely and crystallise.
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10
Q

what is cell signalling?

A

Communication between cells to trigger a response inside the cell.

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11
Q

thickness of the cell surface membrane?

A

7nm

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12
Q

What are intrinsic proteins and some examples?

A
  • proteins that span the whole width of the membrane.
  • channel proteins
  • carrier proteins
  • glycoproteins
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13
Q

What are extrinsic proteins and some examples?

A
  • proteins that are present in one side of the bilayer.

- peripheral proteins

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14
Q

channel proteins?

A
  • intrinsic protein
  • hydrophilic channel
  • allows passive movement of small, uncharged, or charged/polar particles down a conc gradient.
  • e.g oxygen
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15
Q

Carrier proteins?

A
  • intrinsic protein
  • transports molecules and ions across membrane by active transport, facilitated diffusion.
  • e.g sodium ion
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16
Q

glycoproteins?

A
  • intrinsic protein
  • proteins with attached carbohydrate chain.
  • act as receptors for cell signalling
  • when molecule binds to glycoprotein, chemical reaction is triggered in the cell.
  • stabilises membrane by forming hydrogen bonds with surrounding water molecule.
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17
Q

glycolipids?

A
  • lipids with an attached carbohydrate chain.
  • act as cell antigens.
  • can be recognised by cells of immune system as self or non-self.
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18
Q

What acts as membrane bounds receptors and what is their role?

A
  • glycoprotein
  • glycolipids
  • membrane-bound receptors are sites where drugs and hormones can bind.
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19
Q

How do drugs work?

A
  • bind to receptors in cell membranes
  • triggers a response in the cell
  • or blocks the receptor and prevents it from working.
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20
Q

What factors affect membrane structure and permeability?

A
  • temperature

- solvents.

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21
Q

How does temperature affect membrane structure and permeability?

A
  • increase in temperature, phospholipids have more kinetic energy and will move more. Gaps are created.
  • membrane becomes more fluid and starts to lose its structure. Permeability increases.
  • carrier and channel proteins are denatured, cannot control what enters/leaves cell. Increases permeability.
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22
Q

How do solvents affect membrane structure and permeability?

A
  • many organic solvents like ethanol are non-polar and dissolve membranes.
  • strong alcohol solutions are toxic (destroy cells). Lower conc alcohols do not dissolve membranes but still cause damage.
  • as solvent concentration increases, membrane permeability also increases.
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23
Q

What happens when a membrane is disrupted?

A
  • becomes more fluid

- becomes more permeable.

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24
Q

How does alcohol affect membrane structure?

A
  • non-polar alcohol molecules enter cell surface membrane and fit between the phospholipids.
  • this disrupts the structure, increasing membrane permeability.
25
Q

What are the two passive transport methods?

A
  • diffusion

- facilitated diffusion

26
Q

What is the definition of diffusion?

A

The net movement of particles from an area of higher concentration to an area of lower concentration.

  • passive process
  • continues until there is a concentration equilibrium between the two areas.
27
Q

What does it mean by ‘passive process’?

A
  • no external energy is needed for the process to happen.
28
Q

What does it mean by ‘concentration gradient’?

A
  • path from an area of higher concentration to an area of lower concentration.
29
Q

Why does diffusion occur?

A
  • particles have kinetic energy

- the random movements of particles.

30
Q

factors affecting rate of diffusion?

A
  • temperature (higher)
  • steepness of concentration gradient (steeper)
  • surface area (greater)
  • thickness of exchange surface (thinner)
31
Q

How does surface area affect rate of diffusion?

A
  • greater surface area
  • means there is more area for diffusion to occur simultaneously
  • rate increases.
32
Q

Why can small molecules travel across the membrane and what is this called?

A
  • diffusion
  • small molecules like oxygen and CO2 are small enough to fit through the phospholipids and diffuse across the membrane.
  • even though water molecules are polar, they are small enough to fit through the phospholipids and diffuse across the membrane.
33
Q

Why are membranes described as partially permeable?

A
  • small, non polar molecules (and water (small)) are able to diffuse through freely.
  • large and polar molecules cannot.
34
Q

What is facilitated diffusion?

A
  • the diffusion across membranes through carrier and channel proteins is called facilitated diffusion.
  • movement of particles is down a concentration gradient.
  • passive process
35
Q

How can carrier proteins be involved in facilitated diffusion? (can also be used for active transport)

A
  • when a specific molecule (large) binds to the carrier protein, it causes it to change shape.
  • the molecule is then released on the opposite side of the membrane.
36
Q

How can channel proteins be involved in facilitated diffusion?

A
  • provide hydrophilic channels

- for charged particles to diffuse through

37
Q

What affects rate of facilitated diffusion?

A
  • temperature
  • surface area
  • concentration gradient
  • thickness of exchange surface (membrane)
  • number of channel proteins present in the membrane.
38
Q

What is active transport?

A
  • movement of molecules or ions from into/out of a cell from an area of lower concentration to an area of higher concentration.
  • active process
  • energy is supplied by ATP
39
Q

Which protein in the cell surface membrane is involved with active transport?

A
  • carrier proteins.
40
Q

steps of active transport?

A
  • molecule/ion binds to carrier protein
  • ATP binds to carrier protein on inside of cell and is hydrolysed to ADP and phosphate.
  • phosphate ion binds to carrier protein and causes shape of protein to change.
  • molecule/ion is released into the cell.
  • phosphate molecule is released and recombines with ADP to form ATP.
  • carrier protein returns to original shape.
  • metabolic energy is supplied by ATP.
41
Q

define ‘bulk transport’

A
  • another form of active transport.

- large molecules such as proteins are too large to moved by carrier proteins.

42
Q

steps of endocytosis

A
  • cell surface membrane invaginates when substance approaches.
  • membrane fuses to form a vesicle.
  • vesicle pinches off and moves into cytoplasm and transports the substances.
  • ATP is the energy source.
  • eg phagocytosis.
43
Q

steps of exocytosis

A
  • vesicles containing substances are formed by Golgi apparatus.
  • vesicles move towards the cell surface membrane.
  • vesicles fuse with the cell surface membrane.
  • contents are released outside the cell.
  • ATP is the energy source.
44
Q

Why is ATP energy needed in bulk transport?

A
  • movement of vesicles along cytoplasm
  • changing the shape of cells (to engulf)
  • fusion of cell membranes with vesicles or when vesicles form.
45
Q

What is osmosis?

A
  • The movement of water molecules from an area of higher water potential to an area of lower water potential across a partially permeable membrane.
46
Q

what is the water potential of pure water?

A

0kPa

47
Q

What is the water potential of solutions compared with pure water?

A

negative

48
Q

what is the symbol for water potential?

A

psi, Ψ

49
Q

define ‘water potential’

A
  • the likelihood of water molecules to diffuse out of or into a solution.
50
Q

What is a hypotonic solution?

A
  • a solution with more water than solute, compared to another solution.
  • has higher water potential than another solution
51
Q

What is a hypertonic solution?

A
  • a solution with more solute than water, compared to another solution.
  • has lower water potential than another solution.
52
Q

What are isotonic solutions?

A

two solutions/cells with the same water potential.

53
Q

What happens to an animal cell in hypotonic solution (higher water potential outside)?

A
  • outside environment of cell has a higher water potential.
  • water enters the cell by osmosis via the partially permeable membrane.
  • hydrostatic pressure inside the cell increases.
  • cell-surface membrane cannot withstand pressure increase.
  • animal cell bursts.
  • cytolysis.
54
Q

What happens to an animal cell in hypertonic solution (lower water potential outside)?

A
  • outside environment of cell has lower water potential.
  • water leaves the cell by osmosis via the partially permeable membrane.
  • hydrostatic pressure inside the cell decreases.
  • difference in pressure inside and environment causes cell to shrink and shrivel.
  • crenation.
55
Q

What happens to an plant cell in hypotonic solution (higher water potential outside)?

A
  • outside environment of cell has higher water potential.
  • water enters the cell by osmosis via the partially permeable membrane.
  • hydrostatic pressure inside cell increases.
  • cell surface membrane pushes against the cell wall.
  • cell does not burst due to cell wall.
  • cell is now turgid.
56
Q

What happens to an plant cell in hypertonic solution (lower water potential outside)?

A
  • outside environment of cell has lower water potential.
  • water leaves the cell by osmosis via the partially permeable membrane.
  • hydrostatic pressure inside the cell decreases.
  • cell surface membrane pulls away from the cell wall due to difference in pressure.
  • cell is now plasmolysed.
57
Q

What happens if a cell is in an isotonic solution?

A

The net movement of water molecules into and out of the cell is the same.

58
Q

factors affecting osmosis?

A
  • water potential gradient
  • thickness of exchange surface
  • surface area of exchange surface. (more area for water molecules to cross the membrane at the same time).

Biology Year 12 (11 decks)

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