Topic 2B - Cell Membranes Flashcards

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1
Q

What is the role of the cell-surface membrane?

A

They are a partially-permeable barrier between a cell and it’s environment, controlling which substances enter and leave the cell.

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2
Q

What are cell membranes composed of?

A

Lipids (phospholipids), proteins, and carbohydrates.

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3
Q

Give three properties of the cell membrane.

A

Bilayer, fluid because phospholipids constantly moving. Proteins scattered through the bilayer like tiles in a mosaic. Some can move sideways, others are fixed in position. Cholesterol.

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4
Q

Describe proteins in the membrane and their features.

A

Channel proteins and carrier proteins allow large molecules and ions to pass through the membrane. Receptor proteins on the membrane allow the cell to detect chemicals released from other cells.

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5
Q

What can’t enter through the membrane and why?

A

Water-soluble substances like ions can’t enter because the centre of the bilayer is hydrophobic, so it acts like a barrier.

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6
Q

What is cholesterol? Describe its purpose in the cell membrane.

A

A type of lipid. It is present in all membranes except bacterial cell membranes. They fit between the phospholipids, binding to the tails and causing them to pack closely together. This restricts the movement of the phospholipids, making the membrane less fluid and more rigid. They also help to maintain the shape of animal cells as they don’t have cell walls.

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7
Q

How do you calibrate a colorimeter?

A

Using pure water.

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8
Q

Name some control variables in the experiment about the permeability of membranes.

A

Equally sized beetroot/same mass.
Same volume of water.
Same length of time for beetroot in water.

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9
Q

What is the permeability of a cell membrane like below 0° and why?

A

The phospholipids don’t have much energy and can’t move, so they’re packed close together and make the membrane rigid. However, channel proteins and carrier proteins deform, increasing the permeability. Ice crystals form, and pierce the membrane.

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10
Q

What is the cell membrane permeability like between 0 and 45° and why?

A

Phospholipids have more energy and can move, so they aren’t as packed together. Membrane is partially permeable. As temp increases, phospholipids move more due to more energy, so increases permeability.

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11
Q

What is the permeability of the cell membrane like above 45° and why?

A

Phospholipid bilayer melts. Water inside the cell expands, putting pressure on the membrane. Channel proteins and carrier proteins deform, increasing permeability.

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12
Q

What is diffusion?

A

Net movement of particles from an area of higher concentration to an area of lower concentration.

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13
Q

Name two molecules that can easily diffuse through cell membranes and why.

A

Oxygen and carbon dioxide. They’re small, so they can pass through spaces between the phospholipids. They’re also non-polar, so they are soluble in the hydrophobic lipid bilayer.

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14
Q

Name two large molecules and two charged particles.

A

Amino acids and glucose are large. Ions and polar molecules are charged.

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15
Q

Why can’t charged particles diffuse quickly through the cell membrane?

A

They’re water soluble, and the centre of the bilayer is hydrophobic.

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16
Q

Describe how carrier proteins work.

A

They move large molecules across membranes, down their conc gradients. A large molecule attached to the binding site of the protein, and the protein changes shape. This releases the molecule on the opposite side of the membrane.

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17
Q

Why do we say that carrier proteins and channel proteins are specific.

A

Different carrier proteins facilitate the diffusion of different molecules. Same with channel proteins.

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18
Q

What does simple diffusion depend on?

A

Concentration gradient. Difference in concentration between the two sides of the membrane decreases until equilibrium is reached.
Thickness of exchange surface. Shorter distance travelled the thinner the surface is.
Surface area.

19
Q

What are microvilli?

A

Projections formed by the cell-surface membrane folding up on itself. Increases surface area.

20
Q

What does facilitated diffusion depend on?

A

Conc gradient.
Number of channel and carrier proteins. They become the limiting factor.

21
Q

What are aquaporins?

A

Special channel proteins that allow the facilitated diffusion of water through cell membranes. Some kidney cells are adapted to have a lot of aquaporins.

22
Q

What is osmosis?

A

The diffusion of water molecules across a partially permeable membrane, from an area of high water potential to an area of lower water potential.

23
Q

What is isotonic?

A

Two solutions with the same water potential.

24
Q

What is the rate of osmosis dependent on?

A

Water potential gradient.
Thickness of exchange surface.
Surface area of exchange surface.

25
Q

Describe an example of a serial dilution technique.

A

Add 10cm^3 of 2M sucrose to the first test tube, and 5cm^3 of distilled water to the other four. With a pipette, draw 5cm^3 of the solution from the first test tube, add it to the second and mix. Now you have 10cm^3 of 1M sucrose. Repeat until 0.5M, 0.25M, and 0.125M.

26
Q

In a calibration curve, what does the point where the curve meets the x-axis signify? Y-axis is change in mass and x-axis is conc of sucrose.

A

Where the water potential of the sucrose solution is the same as the water potential of the potato cells.

27
Q

What is the definition of active transport.

A

Using energy to move molecules and ions across membranes against a concentration gradient.

28
Q

What is ATP and what is the reaction that releases energy?

A

It is a source of energy in the cell produced by respiration. ATP undergoes a hydrolysis reaction, forming ADP and Pi.

29
Q

Which protein in the cell membrane can use active transport and which doesn’t?

A

Carrier proteins are involved in active transport. Channel proteins are not.

30
Q

What are Co-transporters and how do they work?

A

They are a carrier protein. They bind two molecules at a time, and the concentration gradient of one of the molecules is use to move the other molecules against its concentration gradient.

31
Q

What are the 3 factors affecting the rate of active transport? What doesn’t affect active transport?

A

A decreasing concentration gradient doesn’t affect rate of active transport.
Speed of individual carrier proteins, number of carrier proteins, and rate of respiration in the cell and availability of ATP affect rate of active transport.

32
Q

Describe the processes occurring in the mammalian ileum.

A

Sodium ions are actively transported out of the ileum epithelium cells into the blood by the sodium-potassium pump, creating a concentration gradient where there is a higher concentration of sodium ions in the lumen of the ileum than inside the cell. Sodium ions diffuse from the lumen of the ileum into the epithelial cell, down their conc gradient via sodium-glucose Co-transporter proteins. Glucose is carried too, which increases the concentration of glucose inside the cell, so it can then diffuse out of the cell into the blood down its concentration gradient through a channel protein.

33
Q

Why might both CO2 and H2O be able to enter an aquaporin channel protein?

A

They are both small so fit channel. They both have similar shapes so bind to channel.

34
Q

Why does surrounding cells in alcohol increase membrane permeability?

A

The solvent dissolves the lipids in the cell membrane, causing it to lose its structure.

35
Q

Explain the function of ATP hydrolase in reference to the sodium potassium pump.

A

Breaks down ATP into ADP and Pi to release energy to allow the active transport of ions.

36
Q

The movement of substances across cell membranes is affected by membrane structure. Describe how (5)

A

Phospholipid bilayer allows diffusion of non-polar/lipid-soluble substances.
Phospholipid bilayer prevents diffusion of polar/lipid-insoluble/water-soluble substances.
Carrier proteins allow active transport.
Channel/carrier proteins allow facilitated diffusion/co-transport
Shape/charge of channel/carrier determines which substances move.
Number of channels/carriers determines how much movement.
Cholesterol affects fluidity.

37
Q

Why was it important that the same volume of water is in each tube in the beetroot experiment?

A

Too much water would make the concentration of water lower.
So results from different temperatures are comparable.

38
Q

Suggest how the increase in temperature of the water causes the release of the red pigment (2)

A

Damage to the cell surface membrane. Proteins denature. Increased fluidity.

39
Q

Suggest and explain two ways the cell-surface membranes of the cells lining the uterus may be adapted to allow rapid transport of nutrients (2)

A

Lots of carrier and channel proteins for for active transport/facilitated diffusion/ co-transport (all 3 reasons give marks).
Membrane folded so large surface area.

40
Q

NHE3 actively transports one sodium ion into the cell in exchange for one proton out of the cell. How? (3)

A

Co-transport.
Uses hydrolysis of ATP.
Sodium ion and proton bind to the protein.
Proteins changes shape.

41
Q

The mean mass of contents in the gut in the group with tenapanor (which reduces gut absorption) is 4.1g and the group without is 2.0g. The p value is less than 0.05. Explain how they reached this conclusion (4)

A

There is a significant different between A and B
There is a less than 0.05 probability that the difference is due to chance. Water potential in gut is reduced. Water moves into the gut by osmosis.

42
Q

High absorption of salt from the diet can result in a higher than normal concentration of salt in the blood plasma entering capillaries, which can lead to a build-up of tissue fluid. Explain how (2)

A

Higher salt results in lower water potential of tissue fluid, so less water returns to capillary by osmosis at the venule end.

43
Q

Compare and contrast the processes by which water and inorganic ions enter cells. (3)

A

Both move down concentration gradient. Both move through channels in membrane. Ions can move against a concentration gradient by active transport but water can’t.

44
Q

Group A had a substance that inhibited respiration and group B did not have that substance added. Explain the graph (the total uptake of chloride ions graph for B is greater than A) (4)

A

Group A is diffusion only so initial uptake slower. Group A levels off because same concentrations inside cells and outside cells. Group B has faster uptake because by diffusion plus active transport.
Group B fails to level off because uptake against gradient.
Rate slows for group B because fewer chloride ions in external solution.