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Biology A LEVEL > Transport across membranes > Flashcards

Transport across membranes Flashcards

1
Q

What is the function of the plasma membrane?

A

To separate the internal and external environment of a cell and control what can enter and exit the cell.

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2
Q

What are the components of phospholipids?

A

A hydrophilic polar head and hydrophobic non-polar fatty acid tails.

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3
Q

What is the role of the phospholipid bilayer?

A

Allows lipid-soluble molecules to pass and prevents water-soluble molecules from entering.

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4
Q

What are intrinsic proteins?

A

Proteins spanning the membrane, functioning as channels or carriers for specific molecules like ions and glucose.

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5
Q

What are extrinsic proteins?

A

Proteins on the membrane surface that may associate with carbohydrates to form glycoproteins.

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6
Q

What are glycoproteins?

A

Carbohydrates attached to proteins, aiding in cell recognition, tissue formation, and receptor function

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7
Q

What are glycolipids?

A

Carbohydrates attached to lipids, involved in cell recognition and providing structural strength.

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8
Q

What is the role of cholesterol in membranes?

A
  • reduces movement of molecules
  • maintains fluidity
  • prevents leakage of water and ions.
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9
Q

Why is the membrane called a “fluid mosaic model”?

A

Phospholipids move freely (fluid), and proteins are distributed unevenly like a mosaic.

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10
Q

Define simple diffusion.

A

Passive movement of molecules from high to low concentration until evenly distributed.

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11
Q

What molecules use simple diffusion?

A

Small, non-polar molecules like oxygen and carbon dioxide.

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12
Q

What factors influence diffusion rate?

A
  • Concentration gradient
  • distance
  • surface area
  • temperature.
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13
Q

What is facilitated diffusion?

A

The passive movement of large or polar molecules via transport proteins from high to low concentration.

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14
Q

How does facilitated diffusion differ from simple diffusion?

A
  • requires specific proteins like carrier or channel proteins
  • only occurs at specific points in the membrane.
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15
Q

What happens during facilitated diffusion when a molecule binds to a carrier protein?

A

The protein changes shape, allowing the molecule to cross the plasma membrane.

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16
Q

What properties allow molecules to pass through the phospholipid bilayer?

A

small, non-polar, and lipid-soluble molecules

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17
Q

What are the functions of membrane-bound proteins besides being carrier proteins?

A

They can act as receptors, enzymes, or provide structural support.

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18
Q

Why do phospholipids form a bilayer in plasma membranes?

A

Due to the aqueous nature of cytoplasm and tissue fluid, hydrophilic heads face outward while hydrophobic tails face inward.

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19
Q

What is passive diffusion and why does it not require ATP?

A

Passive diffusion relies on the natural kinetic energy of particles, NOT external energy.

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20
Q

How do polar and non-polar molecules pass through the membrane?

A

Non-polar molecules diffuse directly through the bilayer, while polar molecules need proteins.

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21
Q

Does simple diffusion require ATP?

A

No, it is a passive process

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22
Q

Why do molecules in simple diffusion move?

A

due to their natural kinetic energy.

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23
Q

What states of matter can undergo diffusion?

A

Liquids and gases, because their particles have kinetic energy

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24
Q

What are the two types of membrane proteins involved in facilitated diffusion?

A

Protein channels and carrier proteins.

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25
Q

How do protein channels work?

A

They are water-filled tubes that allow water-soluble ions and molecules to pass when the correct ions bind.

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26
Q

Why are protein channels selective?

A

They only open when specific ions bind to them.

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27
Q

How do carrier proteins work?

A

Specific molecules bind to the carrier protein, causing it to change shape and transport the molecule across the membrane

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28
Q

Why is facilitated diffusion specific to certain molecules?

A

The molecule must have a complementary shape to bind to the carrier protein.

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29
Q

How is glucose transported across the membrane?

A

Through facilitated diffusion using carrier proteins.

30
Q

What is osmosis?

A

The movement of water from an area of higher water potential to lower water potential through a partially permeable membrane

31
Q

What creates water potential?

A

The pressure created by water molecules

32
Q

What is the unit for water potential, and what symbol represents it?

A

Kilopascals (kPa)

the symbol Ψ

33
Q

What is the water potential of pure water?

A
  • Zero kPa
  • the highest possible water potential.
34
Q

What happens when solutes are dissolved in water?

A

The water potential becomes negative

35
Q

What does a more negative water potential indicate?

A

More solutes are dissolved, creating a more concentrated solution

36
Q

Which side has more solutes: Ψ = -3.1 kPa or Ψ = -0.5 kPa?

A

The side with Ψ = -3.1 kPa has more solutes and is more concentrated.

37
Q

In which direction does water move during osmosis?

A

From the side with higher water potential (less negative) to the side with lower water potential (more negative)

38
Q

What is an isotonic solution?

A

where the water potential is the same on both sides of the membrane

39
Q

What is a hypotonic solution?

A

A solution with a higher (less negative) water potential compared to the cell.

40
Q

What is a hypertonic solution?

A

A solution with a lower (more negative) water potential compared to the cell.

41
Q

What happens to animal cells in an isotonic solution?

A

No net water movement occurs; the cell remains unchanged

42
Q

What happens to animal cells in a hypotonic solution?

A

Water moves into the cell, possibly causing it to burst (lysis) due to a lack of a cell wall

43
Q

What happens to animal cells in a hypertonic solution?

A

Water leaves the cell, causing it to shrink or shrivel

44
Q

What happens to plant cells in a hypotonic solution?

A

Water moves into the cell, making it turgid due to its strong cell wall

45
Q

What happens to plant cells in a hypertonic solution?

A

Water leaves the cell, causing it to shrink and the cell membrane to pull away from the cell wall (plasmolysis)

46
Q

What is active transport?

A

The movement of molecules from an area of lower concentration to higher concentration (against the concentration gradient) requiring energy from respiration or ATP

47
Q

Why does active transport require energy?

A

It moves substances against the concentration gradient.

48
Q

What type of membrane proteins are used in active transport?

A

Carrier proteins, which act as pumps to move specific molecules across the membrane

49
Q

Why are carrier proteins selective in active transport?

A

Only molecules complementary in shape to the protein can bind to its receptor site

50
Q

How does ATP provide energy for active transport?

A

ATP binds to the carrier protein and is hydrolyzed into ADP and Pi (inorganic phosphate), releasing energy.

51
Q

What happens when ATP is hydrolyzed?

A

The released energy causes the carrier protein to change shape, transporting the molecule to the other side of the membrane

52
Q

What happens after the molecule is transported in active transport?

A

The Pi (inorganic phosphate) is released from the protein, allowing it to revert to its original shape

53
Q

How long can active transport continue?

A

As long as there is a continuous supply of ATP available

54
Q

What is co-transport?

A

A type of active transport where two molecules are transported simultaneously across the membrane

55
Q

Which molecules are involved in co-transport in the ileum?

A

Sodium ions (Na⁺) and glucose.

56
Q

Why is co-transport needed for glucose absorption in the ileum?

A

The epithelial cell already has a high glucose concentration, preventing glucose from entering by facilitated diffusion alone

57
Q

What happens first in co-transport?

A

Sodium ions are actively transported from the epithelial cell to the blood using ATP.

58
Q

What does the active transport of sodium create?

A

A low sodium ion concentration in the epithelial cell, enabling sodium ions from the lumen to enter by facilitated diffusion

59
Q

How does glucose enter the epithelial cell?

A

Sodium ions and glucose bind to a co-transporter protein; when sodium enters, glucose is transported with it

60
Q

What happens to glucose after entering the epithelial cell?

A

It diffuses into the blood capillary down its concentration gradient via facilitated diffusion

61
Q

Why doesn’t glucose accumulate in the blood?

A

The blood constantly flows, carrying glucose away and maintaining the concentration gradient

62
Q

How are epithelial cells adapted for maximum absorption?

A

They have microvilli that increase the surface area, allowing more co-transporter proteins to be embedded in the membrane

63
Q

Why are more co-transporter proteins beneficial?

A

More co-transporter proteins mean more sodium ions and glucose can be absorbed simultaneously

64
Q

How does the co-transporter protein work?

A

Sodium ions bind to their complementary receptor site on the co-transporter protein, enabling glucose to attach and be transported together

65
Q

How is the glucose concentration gradient maintained in the blood?

A

The blood flows continuously, carrying away absorbed glucose, preventing buildup and maintaining the gradient

66
Q

What is the function of microvilli in the epithelial cells of the ileum?

A
  • increases the surface area of the cell membrane
  • allows more co-transporter proteins to be embedded
67
Q

Why is having more co-transporter proteins beneficial?

A

more sodium ions and glucose can be absorbed, maximizing nutrient uptake

68
Q

Why is ATP necessary in co-transport?

A

required to actively transport sodium ions out of the epithelial cell into the bloodstream, enabling co-transport of glucose

69
Q

What causes the carrier protein in active transport to change shape?

A

The hydrolysis of ATP into ADP and Pi, with the inorganic phosphate (Pi) attaching to the carrier protein

70
Q

What happens when the inorganic phosphate (Pi) is released from the carrier protein?

A

The protein returns to its original shape, ready to transport more molecules

71
Q

How are amino acids absorbed in the ileum?

A
  • Through the same co-transport process
  • involves sodium ions and a co-transporter protein

Biology A LEVEL (9 decks)

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