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AS Biology > 1.3 - Cell Membranes and Transport > Flashcards

1.3 - Cell Membranes and Transport Flashcards

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1
Q

What can phospholipids do?

A

Form bilayers, with sheets opposite eachother.

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2
Q

What is the inner layer of a phospholipid bilayer?

A

Hydrophilic heads pointing towards the cell
Interacts with water in the cytoplasm

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3
Q

What is the outer layer of a phospholipid bilayer?

A

Outer layer has hydrophilic heads pointing outwards
Interacts with water outside the cell

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4
Q

What do the tails do?

A

Hydrophobic tails point towards each other, in centre.
Allows lipid soluable molecules across, not water soluable.

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5
Q

What are hydrophilic heads made of?

A

Polar phosphates

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6
Q

What are hydrophobic tails made of?

A

Non polar fatty acids.

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7
Q

What are the 2 types of proteins found in a phospholipid bilayer?

A

Extrinsic and intrinsic.

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8
Q

What are extrinsic proteins?

A

Either side of the bilayer
Provide structure and form recognition sites

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9
Q

What are intrinsic proteins?

A

Extends across both ends of bilayer
Can use for transport, active transport of ions by forming channels

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10
Q

Who was the fluid mosaic model proposed by?

A

Singer and NIcolson in 1972

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11
Q

What is the meaning behind the fluid mosaic model?

A

Fluid - the individual phosphate molecules can move within a layer relative to another
Mosaic - the proteins vary in shape, size and pattern

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12
Q

What does cholestral do in the bilayer?

A

Makes the membrane rigid and stable

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13
Q

What do glycolipids/glycoproteins do in the bilayer?

A

Transmission of signals and act as hormone receptors

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14
Q

Difference between water and lipid soluable molecules across a membrane?

A

Lipid soluable substances dissolve in phospholipids and can move through the cell membrane easily
Water soluable substances require intrinsic proteins to cross
Proof the bilayer is selectively permeable.

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15
Q

What is the definition of 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, until equilibrium is met.

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16
Q

What is meant by ‘passive’?

A

Not requiring any energy

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17
Q

What 3 things affect diffusion rates?

A
  • Steepness of the concentration gradient
  • Thickness of exchange surface and distance travelled
  • Surface area of the membrane
18
Q

What is the equation for the rate of diffusion?

A

rate of diffusion = surface area x difference in concentration/ length of diffusion path

19
Q

What secondary factors may affect diffusion?

A
  • size of the diffusing molecule
  • nature of the diffusing molecule
  • temperature and kinetic energy
20
Q

What is the definition of facilitated diffusion?

A

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

21
Q

What are channel proteins?

A

molecules with pores lined with polar groups
channels are hydrophilic, so ions can pass through
the channel opens and closes depending on the needs of the cell

22
Q

What are carrier proteins?

A

Diffusion of larger polar molecules such as sugars and amino acids
a molecule attaches to a binding site, the carrier protein changes shape and releases the molecule on the other side of the membrane

23
Q

What is active transport?

A

ions and molecules are moved from a lower to a higher concentration, against the concentration gradient
the process requires energy from ATP
occurs through intrinsic proteins across the membrane

24
Q

How is active transport limited?

A

The number of carrier proteins available for use.

25
Q

What are the 6 steps of active transport?

A

1) molecule combines with carrier protein
2) ATP transfers a phosphate group to the carrier protein
3) the carrier protein changes shape
4) the molecule is released into the cytoplasm
5) phosphate group combines with ADP to form ATP again
6) the carrier protein returns to its original shape

26
Q

What is the definition of osmosis?

A

The passive net diffusion of water molecules across a selectively permeable membrane from a region of higher water potential to a region of lower water potential

27
Q

What is water potential?

A

Psy or trident sign
The tendancy for water to move into a system, water moves from a solution with higher water potential )less negative) to one with a lower water potential (more negative)

28
Q

How is water potential decreased?

A

Decreased by the addition of solute

29
Q

What water potential does pure water have?

A

Zero

30
Q

What happens to plant cells in hypertonic solutions?

A

A plant cell will have its cytoplasm diffuse out, becoming flaccid. The cytoplasm shrinks and moves away from the cell wall (plasmolysis)

31
Q

What happens to plant cells in hypotonic solutions?

A

As osmosis occurs, it will start to take up water and swell. At this stage it can be called turgid. The cell wall stops it from bursting. The hydrostatic pressure rises until internal and external pressures are equal.

32
Q

What happens to a plant cell in an isotonic solution?

A

Incipient plasmolysis is when a cell has lost enough water for the cell membrane to start moving away from the cell wall. This lowers the pressure potential to zero.

33
Q

What happens to an animal cell in a hypertonic solution?

A

Water diffuses out of the cell due to osmosis and the cells shrink. Animal cells must be surrounded by an isotonic solution, which in humans, is the kidney (controls water and salt in blood)

34
Q

What happens to an animal cell in a hypotonic solution?

A

Animal cells swell up and explode, and they do not have a cell wall like a plant does. Instead, when a cell is in danger, organelles called contractive vacuoles will pump water out of the cell.

35
Q

What does it mean if a cell is ‘crenated’?

A

The formation of abnormal notched surfaces on cells as a result of water loss through osmosis. Occurs in hypertonic solutions, the cell shrivels.

36
Q

What is endocytosis?

A

Phagocytosis - uptake of solid material too large to be transported any other way
Pinocytosis - uptake of liquids

37
Q

What happens to membranes in endocytosis?

A

Decreases the surface area

38
Q

What is exocytosis?

A

A vesicle containing a substance is transported through the cell via the cytoskeleton
The vesicle fuses with the cell membrane and releases the product

39
Q

What happens to the membrane in exocytosis?

A

Increase in overall surface area of the cell membrane

40
Q

What 2 things does endo and exocytosis require?

A
  • require energy for cell membranes to change shape
  • require fluidity of the membrane

AS Biology (11 decks)

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