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(HS) Biology 12 > 3.5 Permeability of the Plasma Membrane > Flashcards

3.5 Permeability of the Plasma Membrane Flashcards

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1
Q

What is the function of the plasma membrane?

A

regulates the passage of molecules into and out of the cell

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2
Q

Why is the function of the plasma membrane critical?

A

the life of the cell depends on maintenance of its normal composition

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3
Q

Why can the plasma membrane regulate the passage of molecules into and out of the cell?

A

it is selectively permeable

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4
Q

What does selectively permeable mean?

A

certain substances can move across the membranes while others cannot

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5
Q

In general, what molecules can freely cross the membrane?

A

small, noncharged molecules such as carbon dioxide, oxygen, glycerol, and alcohol

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6
Q

How do molecules cross the membrane?

A

they are able to slip between the hydrophilic heads of the phospholipids and pass through the hydrophobic tails of the membrane

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7
Q

What is concentration gradient?

A

gradual change in chemical concentration between 2 areas of differing concentrations

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8
Q

What does going “down” in concentration gradient mean?

A

most molecules move from an area where the concentration is high to an area where there concentration is low

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9
Q

What does going “up” in concentration gradient mean?

A

some molecules are able to move from an area where their concentration is low to an area where their concentration is high

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10
Q

What is required when going “up” in concentration gradient?

A

energy

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11
Q

Is water polar or nonpolar?

A

polar

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12
Q

Is the membrane polar or nonpolar?

A

primarily nonpolar

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13
Q

Why would water not be expected the readily cross the primarily nonpolar membrane?

A

although the small size of the water molecule may allow some water to diffuse across the plasma membrane, the majority of cells have special channel proteins called AQUAPORINS that allow water to quickly cross the membrane

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14
Q

What molecules are unable to freely cross the membrane?

A

large molecules and some ions and charged molecules

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15
Q

How can large molecules and some ions and charged molecules cross the plasma membrane?

A

through channel proteins, with the assistance of carrier proteins, or in vesicles

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16
Q

What do channel proteins do?

A

form a pore through the membrane that allows molecules of a certain size and/or charge to pass

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17
Q

What are carrier proteins specific for?

A

the substances they transport across the plasma membrane (ie. sodium ions, amino acids, glucose)

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18
Q

What method of crossing a plasma membrane is reserved for macromolecules or even larger materials (ie. virus)?

A

vesicle formation is another way a molecules can exit a cell by exocytosis or enter a cell by endocytosis

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19
Q

Passage of Molecules Into and Out of the Cell

OSMOSIS

  • direction
  • requirement
  • energy required?
  • examples
A
  • direction: toward lower concentration
  • requirement: concentration gradient
  • energy required: no
  • examples: water
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20
Q

Passage of Molecules Into and Out of the Cell

DIFFUSION

  • direction
  • requirement
  • energy required?
  • examples
A
  • direction: toward lower concentration
  • requirement: concentration gradient
  • energy required: no
  • examples: lipid-soluble molecules and gas
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21
Q

Passage of Molecules Into and Out of the Cell

FACILITATED TRANSPORT

  • direction
  • requirement
  • energy required?
  • examples
A
  • direction: toward lower concentration
  • requirement: channels or carrier and concentration
    gradient
  • energy required: no
  • examples: some sugars and some amino acids
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22
Q

Passage of Molecules Into and Out of the Cell

ACTIVE TRANSPORT

  • direction
  • requirement
  • energy required?
  • examples
A
  • direction: toward higher concentration
  • requirement: carrier plus energy
  • energy required: yes
  • examples: sugars, amino acids, and ions
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23
Q

Passage of Molecules Into and Out of the Cell

EXOCYTOSIS

  • direction
  • requirement
  • energy required?
  • examples
A
  • direction: toward outside
  • requirement: vesicle fuses with plasma membranes
  • energy required: yes
  • examples: macromolecules
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24
Q

Passage of Molecules Into and Out of the Cell

ENDOCYTOSIS

  • direction
  • requirement
  • energy required?
  • examples
A
  • direction: toward inside
  • requirement: vesicle formation
  • energy required: yes
  • examples: macromolecules
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25
Q

What is diffusion?

A

the movement of molecules from a higher to lower concentration (down their concentration gradient) until equilibrium is achieved and they are distributed equally

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26
Q

What type of molecule can diffusion be observed with?

A

any type of molecule

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27
Q

Give an example of diffusion.

A

when a crystal of dye (solute) is placed in water (solvent), the dye and water molecules move in various directions, but their net movement (sum of motion) is toward the region of lower concentration

eventually the dye is dissolved in the water, resulting in equilibrium and a coloured solution

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28
Q

What is a solute?

A

the dissolved substance, usually a solid, in a solution

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29
Q

What is a solvent?

A

part of a solution, usually a liquid, that contains solutes

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30
Q

What happens once the solute and solvent are evenly distributed?

A

their molecules continue to move about, but there is no net movement of either one in any direction

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31
Q

What allows only a few types of molecules to enter and exit a cell simply by diffusion?

A

the chemical and physical properties of the plasma membrane

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32
Q

How does oxygen enter cells and carbon dioxide exit cells?

A

gases can diffuse through the lipid bilayer

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33
Q

Why does oxygen diffuse into blood?

A

consider the movement of oxygen from the alveoli of the lungs to the blood in the lung capillaries

after inhalation, the concentration of oxygen in the alveoli is higher than that in blood

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34
Q

What does diffusion also play an important role in?

A

maintaining the resting potential neurons using gradients of potassium and sodium ions

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35
Q

What factors influence the rate of diffusion?

A

temperature (ie. temperature increases, rate increases)
pressure
electrical currents
molecular size

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36
Q

What is osmosis?

A

the diffusion of water across a selectively permeable membrane due to concentration differences

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37
Q

What are percent solutions?

A

grams of solute per 100 mL of solvent (ie. 10% solution is 10 g of sugar with water added to make 100 mL of solution)

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38
Q

Give an example of osmosis.

A

thistle solution containing a 10% solute solution is covered at one end by a selectively permeable membrane and then placed in a beaker containing a 5% solute solution

beaker has a higher concentration of water molecules (lower % of solute) and thistle tube has a lower concentration of water molecules (higher % of solution)

diffusion always occurs from higher to lower concentration therefore a net movement of water takes place across the membrane
from the beaker to the inside of the tube

solute doesn’t diffuse out of the thistle tube because the membrane is not permeable to the solute

as water enters and the solute doesn’t exit, the level of the solution within the thistle tube rises

in the end, concentration of solute in thistle tube is less than 10% because there is now less solute per unit volume of solution

concentration of solute in the beaker is greater than 5% because there is now more solute per unit volume

water enters thistle tube due to osmotic pressure of the solution in thistle tube

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39
Q

What is osmotic pressure?

A

the pressure that develops in a system due to osmosis

THE GREATER THE OSMOTIC PRESSURE, THE MORE LIKELY IT IS THAT WATER WILL DIFFUSE IN THAT DIRECTION

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40
Q

How is osmotic pressure measured?

A

by placing a solution in an osmometer and then immersing the osmometer in pure water which creates the pressure

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41
Q

Where does osmosis also occur?

A

across the plasma membrane

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42
Q

In the body, what is due to osmotic pressure?

A

water is absorbed by the kidneys and taken up by capillaries in the tissues

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43
Q

What is an isotonic solution?

A

solution in which the solute concentration and the water concentration both inside and outside the cell are equal and therefore there is no net gain or loss of water

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44
Q

What does “iso-“ mean?

A

the same as

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45
Q

What does the term tonicity refer to?

A

the osmotic pressure or tension of the solution

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46
Q

Give an example of an isotonic solution?

A

a 0.9% solution of sodium chloride is known to be isotonic in red blood cells therefore intavenous solutions medically administered usually have this tonicity

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47
Q

What do terrestrial animals do to maintain the tonicity of their internal environment?

A

can usually take in either water or salt as needed

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48
Q

How do animals such as oysters, blue crabs, and some fishes able to cope with changes in the salinity (salt concentrations) of their environment?

A

using specialized kidneys, gills, and other structures

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49
Q

Animal Cells:

ISOTONIC

A

there is no net movement of water

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50
Q

Animal Cells:

HYPOTONIC

A

water enters the cell which may burst (cytolysis)

51
Q

Animal Cells:

HYPERTONIC

A

water leaves the cell, which shrivels (crenation)

52
Q

Plant Cells:

ISOTONIC

A

there is no net movement of water

53
Q

Plant Cells:

HYPOTONIC

A

the central vacuole fills with water, turgor pressure develops, and chloroplasts are seen next to the cell wall

54
Q

Plant Cells:

HYPERTONIC

A

the central vacuole loses water, the cytoplasm shrinks (plasmolysis), and chloroplasts are seen in the centre of the cell

55
Q

What is a hypotonic solution?

A

solution that causes cells to swell, or even burst, due to an intake of water

56
Q

What does “hypo” mean and refer to?

A

“less than”

refers to a solution with a lower concentration of solute (higher concentration of water) than inside the cell

57
Q

What happens when an animal cell is placed in a hypotonic solution?

A

water enters the cell and the net movement of water s from the outside to the inside of the cell

58
Q

What solution is hypotonic to red blood cells?

A

any concentration of a salt solution lower than 0.9%

59
Q

What is the difference between cytolysis and hemolysis?

A

cytolysis: refers to disrupted cells
hemolysis: refers to disrupted red blood cells

60
Q

What happens when a plant cell is placed in a hypotonic solution?

A

the cytoplasm expands because the large central vacuole gains water and the plasma membrane pushes against the rigid cell wall

THE PLANT CELL DOES NOT BURST BECAUSE THE CELL WALL DOES NOT GIVE WAY

61
Q

What creates turgor pressure?

A

the swelling of the plant cell in a hypotonic solution

62
Q

Why is turgor pressure extremely important?

A

important to the maintenance of the plant’s erect position, plants wilt due to turgor pressure

63
Q

How do organisms that live in fresh water prevent their internal environment form becoming hypotonic?

A
  • many protozoans (ie, paramecia) have contractile vacuoles that rid the body of excess water
  • fishes have well-developed kidneys that excrete a large volume of dilute urine, they have to take in salt at their gills
64
Q

What is a hypertonic solution?

A

solution that causes cells to shrink or shrivel due to loss of water

65
Q

What does “hyper” mean and refer to?

A

“more than”

refers to a solution with a higher percentage of solute (lower concentration of water) than the cell

66
Q

What happens when an animal cell is placed in a hypertonic solution?

A

water leaves the cell and the net movement of water is from the inside to the outside of the cell

67
Q

What solution is hypertonic to red blood cells?

A

any concentration of a salt solution higher than 0.9%

68
Q

What is crenation?

A

the shriveling of a cell in a hypertonic solution

69
Q

Why are meats sometimes preserved by salting them?

A

the salt kills any bacteria present because it makes the meat a hypertonic environment

70
Q

What happens when a plant cell is placed in a hypertonic solution?

A

the plasma membrane oulls away from the cell wall as the large central vacuole loses water

71
Q

What is plasmolysis?

A

shrinking of the cytoplasm due to osmosis

72
Q

Why might you see dead plants along a salted roadside?

A

they were exposed to a hypertonic solution during the winter

73
Q

How do marine animals cope with their hypertonic environment to prevent losing water?

A
  • sharks increase or decrease the urea in their blood until their blood is isotonic with the environment
  • marine fishes and other types of animals excrete salts across their gills
74
Q

What are carrier proteins required for?

A

facilitated and active transport

75
Q

What is facilitated transport?

A

the act of a carrier assisting the passage of a molecule such as glucose and amino acids, across the plasma membrane with no expenditure of energy

76
Q

What happens during facilitated transport?

A

a carrier protein speeds the rate at which the solute crosses the plasma membrane toward a lower concentration

77
Q

What happens to the carrier protein during facilitated transport?

A

it undergoes a change in shape as it moves a solute across the membrane

78
Q

Why doesn’t facilitated transport require ATP?

A

the molecules are moving down their concentration gradient in the same direction they tend to move anyways

79
Q

What is active transport?

A

the movement of molecules or ions through the plasma membrane against their concentration gradient and requires ATP

80
Q

What happens during active transport?

A

molecules or ions move through the plasma membrane, accumulating either inside or outside the cell

molecules have moved to the region of higher concentration, exactly opposite of the process of diffusion

ie.
- iodine collects in the cells of the thyroid gland
- glucose is completely absorbed from the gut by the cells lining the digestive tract
- sodium can be almost completely withdrawn from urine by cells lining the kidney tubules

81
Q

What do cells involved primarily in active transport have?

A

a large number of mitochondria near membranes where active transport is occurring because ATP is required for the carrier to combine with the substance to be transported

82
Q

What are proteins involved in active transport often called?

A

pumps because just as a water pump uses energy to move water against the force of gravity, proteins use energy to move a substance against its concentration gradient

83
Q

Give an example of a pump that is active in animal cells.

A

SODIUM-POTASSIUM PUMP

especially active in nerve and muscle cells

moves sodium ions to the outside of the cell and potassium ions to the inside of the cell

84
Q

What allows the carrier to combine alternatively with sodium ions and potassium ions?

A

a change in carrier shape after the attachment of a phosphate group and again after its detachment

85
Q

When is the phosphate group donated by ATP?

A

when it is broken down enzymatically by the carrier

86
Q

What does the sodium-potassium pump result in?

A

both a solute concentration gradient and an electrical gradient for these ions across the plasma membrane

87
Q

Why is the inside of the cell negatively charge compared to the outside?

A

3 sodium ions are carried outward for every 2 potassium ions carried inward

88
Q

How do macromolecules enter and exit a cell?

A

because they are too large to be transported by carrier proteins, macromolecules are transported into and out of the cell by vesicle formation

89
Q

What is vesicle formation called?

A

membrane-assisted transport because membrane is needed to form the vesicle

90
Q

Does vesicle formation require energy?

A

yes, requires an expenditure of cellular energy

91
Q

What is a benefit of vesicle formation?

A

vesicle membrane keeps the contained macromolecules from mixing with molecules within the cytoplasm

92
Q

What is exocytosis?

A

a way substances can exit a cell

93
Q

How does exocytosis work?

A

a vesicle fuses with the plasma membrane as secretion occurs

hormones, neurotransmitters, and digestive enzymes are secreted from cells in this manner

94
Q

What produces the vesicles that carry these cell products to the membrane?

A

Golgi apparatus

95
Q

Why can exocytosis be a normal part of cell growth?

A

during exocytosis, the membrane of the vesicle becomes a part of the membrane which is thereby enlarged

96
Q

What happens to the proteins released from the vesicle during exocytosis?

A
  • adhere to the cell surface

- become incorporated in an extracellular matrix

97
Q

What do pancreatic cells do?

A

produce digestive enzymes or insulin

98
Q

What do pituitary cells do?

A

produce growth hormone, among other hormones

99
Q

What do vesicles do in pancreatic and pituitary cells?

A

secretory vesicles accumulate near the plasma membrane, and the vesicles release their contents only when the cell is stimulated by a signal received at the plasma membrane

100
Q

What is regulated secretion?

A

ie. a rise in blood sugar signals pancreatic cells to release the hormone insulin

vesicles fuse with the plasma membrane only when it is appropriate to the needs of the body

101
Q

What is endocytosis?

A

a way substances can enter a cell

102
Q

How does endocytosis work?

A

cells take in substances by vesicle formation, a portion of the plasma membrane folds in on itself to envelop the substance and then the membrane pinches off to form an intracellular vesicle

103
Q

What are the 3 ways in which endocytosis can occur?

A
  • phagocytosis
  • pinocytosis
  • receptor-mediated cytosis
104
Q

What is phagocytosis?

A

process in which the material taken in by endocytosis is large, such as viruses, food particles, or another cell

105
Q

Where is phagocytosis common?

A

unicellular organisms such as amoebas

106
Q

Where does phagocytosis occur in humans?

A

certain types of human white blood cells are amoeboid (mobile like amoeba) and are able to engulf debris such as worn-out red blood cells or viruses

107
Q

When does digestion occur?

A

when an endocytic vesicle fuses with a lysosome

108
Q

What is pinocytosis?

A

occurs when vesicles form around a liquid or around very small particles

109
Q

Give examples of what use pinocytosis.

A
  • blood cells
  • cells that line the kidney tubules or the intestinal wall
  • plant root cells

all use pinocytosis to ingest substances

110
Q

What microscope can phagocytosis be seen with?

A

light microscope

111
Q

What microscope can pinocytic vesicles be seen with?

A

electron microscope (they are no larger than 0.1 - 0.2 micrometers)

112
Q

Why does pinocytosis involve a significant amount of the plasma membrane?

A

it occurs continuously

113
Q

What is the loss of plasma membrane due to pinocytosis balanced by?

A

the occurrence of exocytosis

114
Q

What is receptor-mediated endocytosis?

A

a form of pinocytosis that is quite specific because it uses a receptor protein shaped so that a specific molecule (ie. vitamin, peptide hormone, lipoprotein) can bind to it

115
Q

Where are the receptors found?

A

at one location in the plasma membrane called a COATED PIT because there is a layer of protein on the cytoplasmic side of the pit

116
Q

Once formed, what happens to the vesicle? (receptor-mediated endocytosis)

A

vesicle becomes uncoated and may fuse with a lysosome

117
Q

When the coated pit is empty, what happens to the vesicles and the receptors?

A

used vesicles: fuse with the plasma membrane

receptors: return to their former location

118
Q

Why is receptor-mediated endocytosis selective and much more efficient than ordinary pinocytosis?

A

it is involved in uptake and also in the transfer and exchange of substances between cells

ie. such exchanges take place when substances move from maternal blood into fetal blood at the placenta

119
Q

The importance of receptor-mediated endocytosis is demonstrated by a genetic disorder called familial hypercholesterolemia. Describe it.

A

cholesterol is transported in the blood by a complex of lipids and proteins called low-density lipoprotein (LDL)

usually, body cells take up LDL when LDL receptor gather in a coated pit but in some individuals, the LDL receptor is unable to properly bind to the coated pit and the cells are unable to take up cholesterol

instead, cholesterol accumulates in the walls of arterial blood vessels, leading to high blood pressure, blocked arteries, and heart attacks

120
Q

When does phagocytosis occur?

A

when the substance to be transported into the cell is large

amoebas ingest by phagocytosis

digestion occurs when the resulting vacuole fuses with a lysosome

121
Q

When does Pinocytosis occur?

A

when a macromolecule such as a polypeptide is transported into the cell

the result is a vesicle (small vacuole)

122
Q

What happens during receptor-mediated endocytosis?

A

(a form of pinocytosis) molecules first bind to specific receptor proteins, which migrate to or are already in a coated pit

the vesicle that forms contains the molecules and their receptors

123
Q

Describe exocytosis.

A

vesicle fuses with plasma membrane as secretion occurs

(Golgi apparatus produces vesicles that carry cell products to membrane)

membrane of vesicle becomes part of plasma membrane which is thereby enlarged

proteins released from vesicle adheres to cell surface or becomes incorporated in extracellular matrix

(HS) Biology 12 (46 decks)

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