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Transport across membranes Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What kind of transport is simple diffusion known as?

A

Simple

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2
Q

Why is simple diffusion known as passive transport?

A

The energy for the movement comes from the natural, inbuilt motion of particles, rather than other sources such as ATP

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3
Q

Define some necessary details of particles

A
  • All particles are constantly in motion due to the kinetic energy they posess
  • This motion is random
  • Particles are constantly bouncing off one another as well as other objects
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4
Q

What will particles that are concentrated together in a closed vessel do?

A

Distribute themselves evenly throughout the vessel as a result of diffusion

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5
Q

What is diffusion?

A

The net movement of molecules or ions from a region where they are more highly concentrated to one where their concentration is lower until evenly distributed

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6
Q

Which molecules can easily pass through the cell-surface membrane?

A

Small, non-polar molecules e.g. water and carbon dioxide

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7
Q

Why do charged ions and polar molecules not diffuse easily across a cell-surface-membrane?

A

Due to the hydrophobic nature of the fatty acid tails

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8
Q

How is the movement of charged ions and polar molecules made easier?

A

Through facilitated diffusion. The movement is made easier by transmembrane channels and carriers that span the membrane

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9
Q

What kind of process is facilitated diffusion?

A

Passive
It relies only on the inbuilt motion of the diffusing molecules. No external input of ATP from respiration

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10
Q

Where does facilitated diffusion occur?

A

It occurs down a concentration gradient but it occurs at specific points on the plasma membrane where there are special protein molecules

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11
Q

Which types of proteins are involved in facilitated diffusion?

A

Protein channels and carrier proteins

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12
Q

How do protein channels help in facilitated diffusion?

A

These proteins form water-filled hydrophilic channels across the membrane

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13
Q

What do protein channels allow to diffuse across?

A

Specific water-soluble ions
The channels are selective, each opening in the presence of a specific ion. If the particular ion is not present, the channel remains closed

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14
Q

What do protein channels allow for in cell-surface membranes?

A

They allow for control over the entry and exit of ions. The ions bind with the proteins causing it to change shape in a way that closes it to one side of the membrane and opens it to the other

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15
Q

What is an alternative way, aside from protein channels, for facilitated diffusion?

A

Another way involves carrier proteins that span the plasma membrane

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16
Q

How do carrier proteins carry out facilitated diffusion?

A
  • When a molecule such as glucose that is specific to the protein is present, it binds with the protein
  • This causes it to change shape so that the molecule is released to the inside of the membrane
  • No external energy is needed
  • The molecules move from a region where they are highly concentrated to one of lower concentration, using only the kinetic energy of the molecules themselves
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17
Q

How can cells be adapted for rapid transport across their internal or external membranes?

A

By an increase in surface area, or by an increase in the number of protein channels and carrier molecules in their membranes

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18
Q

What is osmosis?

A

The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane

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19
Q

What does selectively permeable mean?

A

Permeable to water molecules and a few other small molecules, but not larger molecules (cell - surface membranes and other plasma membranes are selectively permeable)

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20
Q

What is a solute?

A

Any substance dissolved in a solvent

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21
Q

What do the solute and the solvent form together?

A

A solution

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22
Q

What is water potential and what is it measured in?

A

It is the pressure created by water molecules and it is measured in units of pressure (usually kPa)
It is represented by the greek letter psi

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23
Q

When does pure water have a potential of zero?

A

Under standard conditions of temperature and pressure (25 degrees celsius and 100 kPa)

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24
Q

What will lower the water potential of pure water?

A

The addition of solute

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25
Q

What value must the water potential of a solution always be?

A

A negative value - less than zero

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26
Q

If you add more solute to a solution, what will happen?

A

Its water potential will get lower

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27
Q

How do you find the water potential of cells or tissues?

A
  • Place them in a series of solutions of different water potentials
  • When there is no net gain or loss of water from the cells or tissues, the water potential inside the cells/tissues is the same externally
28
Q

What do animal cells contain in their watery cytoplasm?

A

A variety of dissolved solutes

29
Q

What will happen if a RBC is placed in pure water?

A

It will absorb water by osmosis as it has a lower water potential

30
Q

Why will the cell surface membrane break is a RBC is placed in pure water?

A
  • They are very thin and although they are flexible, they cannot stretch to any great extent
  • It will therefore break, bursting the cell and releasing its contents
  • In RBC’s, this is called haemolysis
31
Q

How is the bursting of animal cells prevented?

A

They normally live in a liquid which has the same water potential as the cells

32
Q

What will happen if a RBC is placed in a solution with a water potential lower than its own?

A

Water leaves by osmosis and the cell shrinks and becomes shrivelled

33
Q

What is the protoplast?

A

It consists of the outer cell-surface membrane, nucleus, cytoplasm and the inner vacuole membrane

34
Q

What happens when a plant cell is placed in pure water?

A
  • Water is absorbed by osmosis
  • So the protoplast swells and presses on the cell wall
  • The cell wall is only capable of very limited expansion and so a pressure builds up on it that resists the entry of further water
  • So, the protoplast is kept pushed against the cell wall
  • And the cell is said to be turgid
35
Q

What happens when a plant cell is placed in a solution with the same water potential as itself?

A

No water leaves or enters by osmosis
The cell is said to be at incident plasmolysis

36
Q

What happens when a plant cells is placed in a solution with a lower water potential than itself?

A
  • Loss of water by osmosis will cause the cell contents to shrink and the protoplast will pull away from the cell wall
  • The cell is said to be plasmolysed
37
Q

What is active transport?

A

The movement of molecules or ions into or out of a cell from a region of lower concentration to a region of higher concentration using ATP and carrier proteins

38
Q

What is ATP used for in active transport?

A
  • To directly move molecules
  • Individually move molecules using a concentration gradient which has already been set up by (direct) active transport (known as co-transport)
39
Q

How does active transport differ from passive transport?

A
  • Metabolic energy in form of ATP is needed
  • It’s against a concentration gradient
  • Carrier protein molecules which act as ‘pumps’ are involved
  • The process is very selective, with specific substances being transported
40
Q

What do carrier proteins do in terms of active transport?

A

They span the plasma membrane and bind to the molecule or ion to be transported on one side of it

41
Q

What does the molecule/ion do at the beginning of active transport?

A

It binds to receptor sites on the carrier protein

42
Q

What does ATP cause to happen on the inside of the cell at the beginning of active transport?

A
  • ATP binds to the protein
  • It splits into ADP and a phosphate molecule
  • As a result, the tertiary structure of the protein molecule changes shape and opens to the opposite side of the membrane
43
Q

What happens as a result of the protein changing shape in active transport?

A

The molecule/ion is then released to the other side of the membrane

44
Q

What happens to the phosphate molecule bound to the carrier protein after active transport?

A
  • It is released from the protein which causes the protein to revert to its original shape, ready for the process to be repeated
  • The phosphate molecule then recombines with the ADP to form ATP during respiration
45
Q

Can more then one molecule/ion be moved in the same direction at the same time in active transport?

A

Yes

46
Q

Can a molecule/ion move into a cell at the same time as a different one is moving out of the cell in active transport?

A

Yes

47
Q

What is the sodium-potassium pump?

A

Sodium ions are actively removed from the cell/organelle while potassium ions are actively taken in from the surroundings

48
Q

Why is the sodium-potassium pump an important process?

A

It is essential to a number of important processes in the organism, including the creation of a nerve impulse

49
Q

What do the epithelial cells lining the ileum possess that increases the rate of transport?

A

Microvilli

50
Q

What are microvilli?

A

Finger like projections of the cell-surface membrane about 0.6 micrometers in length

51
Q

What are microvilli collectively termed as?

A

A ‘brush border’
(when viewed under a microscope, they look like the bristles on a brush)

52
Q

How do microvilli increase transport across membranes?

A

They provide more surface area for the insertion of carrier proteins

53
Q

Apart from increased surface area, what mechanism can also be used to increase transport across membranes?

A

Increase the number of protein channels and carrier proteins in any given area of membrane

54
Q

Why is there normally a greater concentration of glucose and amino acids in the ileum than in the blood?

A

Carbohydrates and proteins are being digested continuously

55
Q

How does glucose move into the blood from inside the ileum?

A

There is a concentration gradient so it moves down by facilitated diffusion

56
Q

What is the effect of constant circulation of blood on glucose?

A
  • As it is constantly circulated, the glucose moved into it is continuously being removed by the cells as they use it up during respiration
  • This helps to maintain the concentration gradient between the inside of the ileum and the blood
  • So the rate of movement by facilitated diffusion is increased
57
Q

Why can’t all the available glucose and amino acids be absorbed into the blood by diffusion?

A
  • Diffusion only results in the concentrations either side of the intestinal epithelium cell becoming equal
  • Not all is absorbed into the bloodstream and some may pass out of the body
58
Q

How else are amino acids and glucose absorbed into the blood aside from diffusion?

A

By active transport

59
Q

What is the actual mechanism for the absorption of glucose and amino acids into the blood from the small intestine?

A

It is an example of co-transport

60
Q

Why is the term co-transport used for the absorption of glucose and amino acids into the blood from the small intestine?

A

As either glucose or amino acids are drawn into the cells along with sodium ions that have been actively transported out by the sodium-potassium pump

61
Q

How is a much higher concentration of sodium ions in the lumen of the intestine than inside the epithelial cells maintained?

A
  • Sodium ions are actively transported out of epithelial cells, by the sodium potassium pump, into the blood
  • This takes place in one type of protein carrier molecule found in the cell surface membrane of epithelial cells
62
Q

How do the sodium ions help glucose molecules to move into the epithelial cells?

A
  • Sodium ions diffuse into the cells down this concentration gradient through a different type of protein carrier (co-transport protein) in the cell-surface membrane
  • As the sodium ions diffuse in through this second carrier protein, they carry either amino acids or glucose into the cell with them
  • They carry amino acids/glucose/galactose/fructose with them as otherwise, they can’t diffuse in as the channel proteins will not permit it
63
Q

How do the glucose/amino acid molecules travel into the blood after being taken into the epithelial cells by the sodium ions?

A

Through facilitated diffusion using another type of carrier

64
Q

What kind of active transport is the absorption of glucose molecules into the blood from the intestinal lumen known as?

A

Indirect active transport

65
Q

Why is this known as indirect active transport?
(What kind of active transport is the absorption of glucose molecules into the blood from the intestinal lumen known as?)

A
  • Both sodium ions and glucose/amino acids move into the cell, but sodium ions move down a concentration gradient whilst glucose/amino acids move against a concentration gradient
  • It is the sodium ion concentration gradient, rather than ATP directly, that powers the movement of glucose/amino acids into the cells

Biology (13 decks)

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