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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
How do protein channels work?
They are water-filled tubes that allow water-soluble ions and molecules to pass when the correct ions bind.
26
Why are protein channels selective?
They only open when specific ions bind to them.
27
How do carrier proteins work?
Specific molecules bind to the carrier protein, causing it to change shape and transport the molecule across the membrane
28
Why is facilitated diffusion specific to certain molecules?
The molecule must have a complementary shape to bind to the carrier protein.
29
How is glucose transported across the membrane?
Through facilitated diffusion using carrier proteins.
30
What is osmosis?
The movement of water from an area of higher water potential to lower water potential through a partially permeable membrane
31
What creates water potential?
The pressure created by water molecules
32
What is the unit for water potential, and what symbol represents it?
Kilopascals (kPa) the symbol Ψ
33
What is the water potential of pure water?
- Zero kPa - the highest possible water potential.
34
What happens when solutes are dissolved in water?
The water potential becomes negative
35
What does a more negative water potential indicate?
More solutes are dissolved, creating a more concentrated solution
36
Which side has more solutes: Ψ = -3.1 kPa or Ψ = -0.5 kPa?
The side with Ψ = -3.1 kPa has more solutes and is more concentrated.
37
In which direction does water move during osmosis?
From the side with higher water potential (less negative) to the side with lower water potential (more negative)
38
What is an isotonic solution?
where the water potential is the same on both sides of the membrane
39
What is a hypotonic solution?
A solution with a higher (less negative) water potential compared to the cell.
40
What is a hypertonic solution?
A solution with a lower (more negative) water potential compared to the cell.
41
What happens to animal cells in an isotonic solution?
No net water movement occurs; the cell remains unchanged
42
What happens to animal cells in a hypotonic solution?
Water moves into the cell, possibly causing it to burst (lysis) due to a lack of a cell wall
43
What happens to animal cells in a hypertonic solution?
Water leaves the cell, causing it to shrink or shrivel
44
What happens to plant cells in a hypotonic solution?
Water moves into the cell, making it turgid due to its strong cell wall
45
What happens to plant cells in a hypertonic solution?
Water leaves the cell, causing it to shrink and the cell membrane to pull away from the cell wall (plasmolysis)
46
What is active transport?
The movement of molecules from an area of lower concentration to higher concentration (against the concentration gradient) requiring energy from respiration or ATP
47
Why does active transport require energy?
It moves substances against the concentration gradient.
48
What type of membrane proteins are used in active transport?
Carrier proteins, which act as pumps to move specific molecules across the membrane
49
Why are carrier proteins selective in active transport?
Only molecules complementary in shape to the protein can bind to its receptor site
50
How does ATP provide energy for active transport?
ATP binds to the carrier protein and is hydrolyzed into ADP and Pi (inorganic phosphate), releasing energy.
51
What happens when ATP is hydrolyzed?
The released energy causes the carrier protein to change shape, transporting the molecule to the other side of the membrane
52
What happens after the molecule is transported in active transport?
The Pi (inorganic phosphate) is released from the protein, allowing it to revert to its original shape
53
How long can active transport continue?
As long as there is a continuous supply of ATP available
54
What is co-transport?
A type of active transport where two molecules are transported simultaneously across the membrane
55
Which molecules are involved in co-transport in the ileum?
Sodium ions (Na⁺) and glucose.
56
Why is co-transport needed for glucose absorption in the ileum?
The epithelial cell already has a high glucose concentration, preventing glucose from entering by facilitated diffusion alone
57
What happens first in co-transport?
Sodium ions are actively transported from the epithelial cell to the blood using ATP.
58
What does the active transport of sodium create?
A low sodium ion concentration in the epithelial cell, enabling sodium ions from the lumen to enter by facilitated diffusion
59
How does glucose enter the epithelial cell?
Sodium ions and glucose bind to a co-transporter protein; when sodium enters, glucose is transported with it
60
What happens to glucose after entering the epithelial cell?
It diffuses into the blood capillary down its concentration gradient via facilitated diffusion
61
Why doesn’t glucose accumulate in the blood?
The blood constantly flows, carrying glucose away and maintaining the concentration gradient
62
How are epithelial cells adapted for maximum absorption?
They have microvilli that increase the surface area, allowing more co-transporter proteins to be embedded in the membrane
63
Why are more co-transporter proteins beneficial?
More co-transporter proteins mean more sodium ions and glucose can be absorbed simultaneously
64
How does the co-transporter protein work?
Sodium ions bind to their complementary receptor site on the co-transporter protein, enabling glucose to attach and be transported together
65
How is the glucose concentration gradient maintained in the blood?
The blood flows continuously, carrying away absorbed glucose, preventing buildup and maintaining the gradient
66
What is the function of microvilli in the epithelial cells of the ileum?
- increases the surface area of the cell membrane - allows more co-transporter proteins to be embedded
67
Why is having more co-transporter proteins beneficial?
more sodium ions and glucose can be absorbed, maximizing nutrient uptake
68
Why is ATP necessary in co-transport?
required to actively transport sodium ions out of the epithelial cell into the bloodstream, enabling co-transport of glucose
69
What causes the carrier protein in active transport to change shape?
The hydrolysis of ATP into ADP and Pi, with the inorganic phosphate (Pi) attaching to the carrier protein
70
What happens when the inorganic phosphate (Pi) is released from the carrier protein?
The protein returns to its original shape, ready to transport more molecules
71
How are amino acids absorbed in the ileum?
- Through the same co-transport process - involves sodium ions and a co-transporter protein

Biology A LEVEL (15 decks)

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