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Topic 2-Transport Across Membranes Flashcards

1
Q

What are the three different wasys substanves can cross membranes?

A

Diffusion
Osmosis
Active Transport

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2
Q

Describe the arrangment of the components of a cell membrane

A

Phospholipids form a bilayer- Its fatty acids tail face inwards and phosphate heads face outwards
Proteins- Intrinsic proteins span bilyare whereas extrinisc proteins on surface of membrane
Glycolipids are found on exterior surface
Glycoprotein are found on exterior surface
Cholestrol which is sometimes present bond to phospholipid hrdrophobic fattly acid tails

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3
Q

How can cell membranes be seen? (under what conditions)

A

Electron Microscope at very high magnification

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4
Q

What three things does the fluid mosaic model help to explain?

A

-Passive & active movement between cells and their surroundings.
-Cell to cell interactions
-Cell signalling

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5
Q

Describe the structure of phospholipipids

A

It has a hydrophilic head and two hydrophobic tails.

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6
Q

What model was suggested to describe the arrangment of molecules in a membrane?

A

Fluid Mosaic model

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7
Q

What is the function of receptor proteins on cell-surface membranes?

A

To allow cell to detect chemicals released from other cells

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8
Q

Name the two types of proteins scattered through the bi-layer

A

Channel proteins
Carrier proteins

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9
Q

What is the name of proteins with carbohydrates attached?

A

Glycoproteins

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10
Q

What is the name of lipids with carbohydrates attached?

A

Glycolipids

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11
Q

Why is the centre of the bilayer hyrophobic?

A

So it does not allow water soulble substances like ions and polar molecules to diffuse through

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12
Q

Give an example of a small non polar substance that can diffuse through the membrane

A

Carbon dioxide

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13
Q

What type of cell membrane is cholestral not present in?

A

Bacterial cell membranes

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14
Q

How does cholestrol provide the cell with stability?

A

It fits between the phospholipids binding their hydrphobic tails together causing the to pack more closely together. This restricts the movement of the phospholipids making the membrane less fluid and more rigid.

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15
Q

Why is cholestral able to barrier polar substances coming through the membrane?

A

It has hydrohobic regions

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16
Q

Why cant phospholipids move very much at temperature below 0 degrees?

A

They dont have much energy and are packed close together with a rigid membrane.

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17
Q

What happens to the permeability of the membrane below 0 degrees and why?

A

Permeability will invrease because channel and carrier proteins denature increasing permability of the membrane. Ice crystals may form and pierce membrane making it higky permeable when it thaws.

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18
Q

What happens to the mebrane at temperatures between 0-45 degrees?

A

Phospholipids arent as tightly packed andhave energy to move incresing permeablility making membrane partially permable.

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19
Q

Describe what happens to the cell membrane at temperature above 45 degrees

A

The phospholipid bi-layer starts to melt and membrane becomes more permeable. Water inside the cell expands putting pressure on the membrane. Channel and carrier proteins denature so cannot control wht moves in an out of cell therefore increasing permeability of the cell.

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20
Q

What is a colourmeter and its function?

A

A machine that passes light of a specific wavelength through a liquid and measures how much of that liquid is absorbed.

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21
Q

Name 3 variables that should be controlled when investigating cell membrane permability

A

-size of beetroot cubes
-Volume of liquid
-amount of time

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22
Q

What two things need to be done to colourimeter before it is used to measure absobance?

A

Calibrated to zero
Allowed 5 minutes to stablize itself

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23
Q

What are the 6 structure in the mebrane?

A

Protein chanel
glycoproteins
phospholipids
glycolipids
proteins
cholestrol

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24
Q

Define hydrophobic

A

repels water

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25
define hydrophilic
attracts water
26
Why is phospholipid bi layer described as fluid?
phospholipids are constanlty moving
27
Describe the distribution of proteins within the bilayer
They are scattered throughout bilayer, some are able to move sideways whilst others are in a fixed position.
28
Define diffusion
The net movement of particles (molecules or ions) from an area of higher concentration to lower concentration.
29
What is the concentration gradient?
The path from an area of higher concentration to lower concentration that particles diffuse down
30
What are the 5 factors that affect rate of diffusion?
Concentration gradient Temperature Thickness of exchange surface Surface area Properties of molecules/ions
31
How does concentration gradient affect the rate of diffusion?
The greater the different in the concentration, means a greater difference in the number of molecules passing in the two directions therefore a faster rate of diffusion.
32
How does temperature affect the rate of diffusion?
Higher temperatures mean higher rates of diffusion because the molecules and ions have more kinetic energy at higher temperatures, they move faster.
33
How do the properties of molecules and ions affect rate of diffusion?
Large molecules diffuse more slowly than smaller ones as they require more energy to move. Uncharged and non polar molecules diffuse directly across phospholipid bilayer, non polar diffuse more quickly because they are soluble in the non-polar phospholipid bilayer.
34
How does surface are affect the rate of diffusion?
The greater the surface area, the greater the number of molecules or ions that can cross at any one moment and therefore the faster diffusion occurs.
35
How does thickness of the membrane affect the rate of diffusion?
The membrane has to be thin in order to provide the shortest distance for subsatnces to diffuse therefore, thicker membranes have a slower rate of diffusion.
36
What two types of substances can simply diffuse across a membrane?
Non-polar molecules(lipid soluble) Very small molecules and ions e.g co2
37
Define osmosis
The net movement of water molecules from a region of higher water potential to a region of lower water potenetial through a partially permaeable membrane.
38
What is water potential?
The tendency of water to move out of a solution.
39
What type of solution will have a higher water potential?
A dilute solute solution
40
What is the water potential of pure water?
0kPa
41
What will happen to the movement of water and why if a plant cell is placed in pure water?
Water enters plant cell through partially permeable membrane by osmosis as the pure water has higher water potemntial than the plant cell.
42
Describe the process of osmosis in a plant cell placed in a solution with a higher water potential.
Water enters the vacuole of a cell and the volume of the cell increases. This expands the protoplast which pushes againts the cell wall causing pressure to build up in the cell. Plant cell inflated with water becomes inflated with water and fully turgid.
43
What are the properties prevent cell from busting when water entering it?
The cell wall is inelastic and the pressure created by the cell wall stops too much water entering and bursting.
44
Why is a plant cell being tugid important?
It provides support and strength for plants so it can stand upright with levaes to catch sunlight, otherwise plant wilts.
45
Describe the osmosis that occurs when a plant is placed in a solution with low water potential.
Water will leave by osmosis , water will leave the vacuole and the volume of the plant the cell decreases. The protoplast gradually shrinks not exerting pressure of cell wall.
46
What is the name given to the process of the protoplast shrinking and not exerting pressure on cell wall?
Plasmolysis
47
Why is loss and gain of water more severe in an animal cell compared to a plant cell?
Animal cells dont have a supporting cell wall
48
Describe a hypertonic environment
When the solution outside a cell has a higher solute concentration than in the cell
49
Explain the arrangent of phospholipids in a cell membran
The bilayer has water present on either side, Hydrophobic fatty acid tails repel water so point away from the water and hydrophillic phosphate heads are attracted to water so point towards the water
50
Describe how movment across membranes occurs by simple diffusion
Lipid soluble or non polar small substances move from an area of high to low conc down conc gradient across phospholipid bilayer. This processes is passive and does not require energy
51
Descibe how movement across membranes occurs by facilitated diffusion
These are water soluble (polar) or slightly larger substances and they move down a conc gradient through carrier proteins. The processes is passive and does not require ATP
52
Explain the role of carrier and channel proteins in facilitated diffusion
The shape/charge of protein determines which substances move. Channel proteins facilitate diffusion of water soluble substances, it acts as a pore that lets water molecules or small ions through quickly, there are gated channels that can be opened and closed, these gated channels have specific binding dsite for given molecule or ion Carrier proteins facilitate diffusion of larger substances, the complementary substance attaches to the binding site the protein changes shape to transport substance.
53
Describe how movement across membranes occur by active transport
Substances move from areas of lower to higher concentration - against conc gradient, this requires the hydrolysis of ATP and specific carrier protiens
54
Describe the role of carrier proteins and the importance of the hydrolysis of ATP in active transport
Complementary sybstance binds to specific carrier protein ATP binds and is hydrolysed into ADP + Pi releasing energy Carrier protein shape changes releasing substance on the side with higher concentration Pi released and protein returns to original shape
55
Descibe how movement across membranes occurs by co- transport
Two different substances bind and move simulatneoulsy via co- transporter protein, movement of one substance against its concentration gradient coupled with the movemnt doen another conc gradient
56
Descibe how the number of channel/ carrier prteins affext rate of facilitated diffusion
There will be an increasing cocn gradient u til channel and carrier proteins becomes are all in use/saturated as they are limiting factor
57
Explain the adaptations of some specialised cells in relation to the rate of transport across their internal and external memebranes
- Membrane folded e.g in ileum to increas SA -Mpore protein channel/carriers for facilitated diffusion -Large no. mitrochondria to make more ATP by aerobic respiration for active transport
58
Describe a method to produce of a calibration curve with which to identify the water potential of plant tissue (eg. potato)
Create a series of dilutions usind a 1 mol/dm-3 solution and mantain the volume of each solution. Use a cork to cut potatoes into identical cylinders. Blot with a piece od paper towl to remove excess weight and record initial mass of each piece, Immerse one chip in each solution for a set amount of time and the same temp, regularly stir to ensure all suraces exposed. Blot with dry paper after to remove excess weight amd record madd of cylinder. Repeat 3 or more times
59
How would you process data from experiment used to identify water potential of a plant?
Calculate % change in mass = (final - initial mass)/ initial mass Plot a graph with concentration on x axis and percentage change in mass on y axis (calibration curve) Must show positive and negative regions Identify concentration where line of best fit intercepts x axis (0% change) Water potential of sucrose solution = water potential of potato cells Use a table in a textbook to find the water potential of that solution
60
Describe the experiment used to investigate the effect of temperature on the permeability of cell- surface membranes
Cut equal sizes of beetroot of the same type and age. Rinse and blot on paper to removes pigment and extra mass. Add same no. cubes to different test tubes contsining same vol of water. Place them at the same time in different temperatures of water bath. Leave for the sma eamount of time. Remove beetroot and measure intensity of colour of surrounding solution semi quantitively- Usingf a known conc of extrazct and distilled water and comparing to estimate. Or quantitively which ks using a colourimemter to measure absorbance of light and =draw a calibration curve with loine of best fit. Absorbance for each sample used to find associated exact conc
61
What would a high absorbance tell you about the cell membrane?
It is very permable or damaged as more pigment leaks ot making solution darker
62
Explain how pH affects the premaebility of cell- surface membranes
High or low pH increases permeability as transport proteins denature as hydrogen and ionic bonds break changing tertiary structure
63
Explain how lipid soluble slovents affect the peromeability of cell surface membranes
It increases the permeability as a lipid soluble solvent may dissolev phopholipid bi liyaer so gaps form
64
Explain how temperature affects the permeability of cell- surface membranes
As temp increases, permeability increases this is because phospholipids gain kinetic energy and fluidity increases, in addition transport proteins denature as hydrogen bonds breakl changing their tertairy structure. At very low temp the permeability also increases as ice crystals form and pierce cell membrane

Biology (13 decks)

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