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AS BIO UNIT1 > 1.3 Cell Membranes & Transport > Flashcards

1.3 Cell Membranes & Transport Flashcards

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1
Q

Explain the arrangement of the phospholipid bilayer

A
  • hydrophilic heads interact w water in cytoplasm and with water around the cell
  • hydrophobic tails point inward
  • phospholipid component allows lipid soluble molecules to move across but not water soluble molecules
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2
Q

Extrinsic proteins

A
  • on the surface of the bilayer
  • provide structural support and do cell-cell recognition as well as hormone recognition
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3
Q

Intrinsic protein

A
  • extend both layers of phospholipid
  • include transport proteins (channels and carriers) for non lipid soluble molecules
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4
Q

Permeability of membrane for small molecules, lipid soluble and water soluble

A
  • small: move between phospholipid molecules through diffusion
  • lipid soluble: dissolve and diffuse across easily
  • water soluble: cannot ready diffuse so use intrinsic protein molecules
  • non-polar dissolve in hydrophobic layer and easily diffuse
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5
Q

Why is it called the fluid mosaic model?

A
  • individual phospholipid molecules can move within a layer to one another (fluid)
    -proteins embedded in the bilayer vary in shape and size and in their distribution among phospholipids (mosaic)
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6
Q

What’s the carbohydrate layer around an animal cell called?

A
  • glycocalyx formed from glycoproteins and glycolipids (carbs attach to proteins and phospholipids)
  • acts as an antigen in cell to cell recognition
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7
Q

How does the distribution of charges and uncharged parts determine the position of a protein in a membrane?

A
  • charged groups go to hydrophilic heads (extrinsic)
  • non charged groups go to hydrophobic tails (instrinsic)
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8
Q

Define diffusion

A

The passive movement of a molecule or ion down a concentration gradient from a region of high concentration to a region of low concentration

  • limited to small non-polar or lipid soluble molecules
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9
Q

What 3 main factors influence the rate of diffusion?

A
  • concentration gradient: increased conc difference = increased rate
  • thickness of exchange surface: thinner surface = higher rate
  • surface area of membrane: larger area = more room for molecules to diffuse
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10
Q

What are some other factors impacting rate of diffusion?

A
  • size of diffusing molecule
  • number of diffusing molecules
  • temperature
    —> number of carrier proteins available (Fd)
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11
Q

Rate of diffusion equation

A

Surface area x conc difference
——————————————
Length of diffusion path

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12
Q

Define facilitated diffusion

A

The passive transfer of molecules or ions down a concentration gradient across a membrane by carrier protein molecules in a membrane

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13
Q

Describe channel proteins

A
  • molecules with pores lined with polar groups
  • hydrophilic and therefore ions can pass through
  • able to open or close based on cells need
  • specific to the molecule/ion that they transport
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14
Q

Describe carrier proteins

A
  • diffusion of large polar molecules
  • molecule attaches to binding site of the carrier protein
  • able to change shape to release molecule, then revert
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15
Q

Define active transport

A

The movement of molecules or ions across a membrane against a concentration gradient using energy from the hydrolysis of ATP made in the cell by respiration

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16
Q

Outline some of the features of active transport

A
  • low to high conc
  • anything impacting respiration impacts active transport
  • intrinsic carrier proteins
  • rate is limited by number and availability of carrier proteins
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17
Q

Outline the process of active transport

A
  • molecule or ion combines with specific carrier protein on outside of membrane
  • ATP transfers phosphate group to carrier protein on inside of membrane
  • carrier protein changes shape and carries the molecule/ion across the membrane and into the cell
  • molecule/ion released into cytoplasm
  • phosphate ion is released from carrier molecule back to cytoplasm and combines with ADP to form ATP
  • carrier protein regains original shape
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18
Q

Width of phospholipid bilayer

A

8nm

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19
Q

Why does pigment leakage occur when beetroot discs submerged in ethanol?

A
  • ethanol dissolves/emulsifies lipids and denatures proteins creating holes in the membrane
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20
Q

How does solubility in lipid affect the rate of diffusion?

A
  • increased solubility = increased rate of diffusion
  • lipid soluble substances can diffuse much easier than non-lipid soluble as they dissolve
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21
Q

Describe how molecular size affects the rate of diffusion

A
  • increased size = lower rate of diffusion
  • easier to pass through phospholipid molecules
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22
Q

Suggest two reasons why transport across the membrane is vital to the cell

A
  • obtain nutrients
  • secrete molecules ie enzymes
23
Q

Compare the Davison-Danielli model to the fluid mosaic model

A

S: phospholipid bilayer w same arrangement of hydrophobic/hydrophilic parts. Both have protein
D: proteins not embedded in bilayer in DD - no intrinsic proteins. Absence of glycoalyx in DD

24
Q

Why would the presence of unsaturated fatty acids in the phospholipid increase its fluidity?

A
  • unsaturated have double carbon bond
  • kink in chain
  • less packing/compact so less energy to break intermolecular forces
25
Q

Position of cholesterol molecules in bilayer

A

By fatty acid tails

26
Q

Role of cholesterol molecules in the phospholipid bilayer

A
  • regulate fluidity of membrane, located by fatty acids
  • not enough makes it fluid
  • too much makes it rigid
27
Q

Where would hydrophilic parts with charged/polar R groups be located?

A

Around the phospholipid heads

28
Q

Where would the hydrophobic parts with non-polar R groups be found?

A

Arranged between hydrophobic tails

29
Q

Beetroot prac - what happens when temp is below 40°C?

A
  • increased KE of phospholipid and proteins will cause them to move more which creates gaps in the phospholipids
  • pigment will diffuse at greater rate as it has more KE
30
Q

Beetroot prac - what happens above 40°C?

A
  • protein components of membrane begin to denature forming pores that the pigment can diffuse out of more easily
    —> graph levels off as membrane becomes fully permeable
31
Q

Define osmosis

A

Net movement of water molecules from an area of high water potential to an area of low water potential across a selectively permeable membrane

32
Q

Define water potential

A

A measure of the free energy of water molecules and the tendency of water to move
- the higher the concentration of solute in a solution or cell, the lower the water potential.

33
Q

Explain hypotonic, isotonic and hypertonic solutions

A
  • hypotonic solution has a lower solute concentration outside cell than inside
  • isotonic solution has the same concentration of solute and the same water potential.
  • hypertonic solution has a higher concentration of solute outside the cell than inside
34
Q

Animals cells in hypotonic solutions

A
  • net movement of water is from the higher water potential of the solution to the lower water potential in the cells, by osmosis.
  • the cells will expand and as they lack a cell wall, they will burst because of the increased pressure in the cells.
  • called haemolysis.
  • red pigment is released into the surrounding solution.
35
Q

Animal cells in hypertonic solutions

A
  • net movement of water is from the higher water potential in the cells to the lower water potential in the solution by osmosis.
  • this makes the cells shrivel, and is termed crenating.
36
Q

Animal cells in isotonic solutions

A
  • no change as no net movement
37
Q

Plant cells in solution with a lower water potential

A
  • water leaves the cells by osmosis, from a higher water potential inside the cell to a lower water potential in the solution.
  • the vacuole and cytoplasm shrink because of the loss of water and the cytoplasm pulls away from the cell wall.
  • plasmylosis (plasmolysed cells)
38
Q

Plant cells in solution with a higher water potential

A
  • become turgid
  • water enters by osmosis and the cytoplasm and vacuole expand.
  • when it is not physically possible for any more water to enter the cell, the water potential of the cell is 0
39
Q

What is the water potential of pure water?

A

0kPa

40
Q

Water potential of a cell =

A

Solute potential + pressure potential

41
Q

What is pressure potential?

A
  • pressure exerted in the cell contents by its cell membrane
  • usually +ve, cell trying to push H2O out
42
Q

What is incipient plasmolysis?

A

The point at which the cell membrane just begins to move away from the cell wall
—> pressure potential is a,ways 0

43
Q

What is the water potential during incipient plasmolysis?

A

= to solute potential

44
Q

How can you identify incipient plasmolysis in a microscope?

A

When half of the visible cells are plasmolysed

45
Q

2 factors that affect the rate of FD

A
  • temp
  • amount of carrier proteins
46
Q

Function of channel protein

A

To allow FD

47
Q

What is meant by the term lipid bilayer?

A

Two layers of phospholipids

48
Q

Rate of diffusion is proportional to…

A

Concentration

49
Q

Describe enodcytosis

A

The cell membrane engulfs particle to from a vesicle around it

50
Q

Use your knowledge of osmosis to explain why contractile vacuoles are necessary for the survival of amoeba

A
  • cytoplasm of amoeba has lower water potential than surrounding solution
  • water move into cell by osmosis
  • water move from cytoplasm to vacuole by osmosis
  • water then expelled to prevent bursting and therefore keep amoeba alive
51
Q

How does the cell wall result in pressure potential?

A

Generated as a result of cell walls resistance to expansion

52
Q

Explain arrangements of phospholipids in water

A
  • hydrophilic heads in water as attracted
  • hydrophobic tails away as repel
53
Q

Why would seed growth be stunted by no O2 (active transport link)

A
  • oxygen needed for atp synthesis to enable active transport
  • no atp means no active transport means stunted growth because plant can’t get enough phosphate/calcium/magnesium

AS BIO UNIT1 (6 decks)

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