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A Level Biology Year 1 > Chapter 4 - Transport across cell membranes > Flashcards

Chapter 4 - Transport across cell membranes Flashcards

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1
Q

What are cell-surface membranes?

A

A partially permeable barrier between the cell and its environment, which controls what enters and leaves the cell

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2
Q

What is a plasma membrane?

A

A membrane anywhere in the cell, including those that surround the organelles

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3
Q

What three things is a cell membrane made of?

A

Lipids, proteins and carbohydrates

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4
Q

What are the two components of a phospholipid?

A

A hydrophobic tail and a hydrophilic head

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5
Q

How are phospholipids organised in the bilayer?

A

With the hydrophilic heads pointing out and the hydrophobic tails pointing in

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6
Q

What type of molecules CAN’T get through the bilayer?

A

Large or charged (e.g. ions or glucose)

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7
Q

Functions of phospholipids (3)

A

Allow lipid-soluble substances in and out of the cell
Prevent water-soluble substances from entering or leaving
Make the membrane flexible

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8
Q

What are the functions (2) of the proteins that only occur on the surface of the membrane?

A

Mechanical support to cell

Cell receptors

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9
Q

A function of protein channels

A

Water filled tubes which allow water-soluble ions to diffuse across the membrane

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10
Q

What are carrier proteins?

A

Proteins which bind to ions or molecules and change shape in order to move them across the membrane

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11
Q

Main functions of proteins in the cell membrane (3)

A

Structural support
Cell surface receptors
Allow substances to cross the membrane

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12
Q

Where are cholesterol molecules found?

A

Between the phospholipids

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13
Q

Functions of cholesterol

A

Structural support
Make the membrane less fluid
Prevent leakage of fluids from cell

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14
Q

How does cholesterol stop the membrane being so fluid?

A

It binds to the hydrophobic tails and causes them to pack closely together, which restricts the movement of the phospholipids

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15
Q

What are glycolipids?

A

A carbohydrate bonded to a lipid

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16
Q

Function of glycolipids (3)

A

Recognition sites
Keep the membrane stable
Help cells attach to eachother

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17
Q

What are glycoproteins?

A

Carbohydrate chains attached to extrinsic proteins

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18
Q

Functions of glycoproteins (2)

A

Recognition sites

Allow lymphocytes to distinguish between cells

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19
Q

What name is given to the current model of the cell membrane?

A

Fluid mosaic

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20
Q

Why is the current model of the cell membrane described as fluid?

A

The phospholipids can move relative to eachother

21
Q

Why is the current model of the cell membrane described as a mosaic?

A

The proteins embedded in the structure fit together like tiles in a mosaic

22
Q

Why does a higher temperature mean the cell membrane is more permeable?

A

The phospholipids move more and create gaps in the membrane

23
Q

What is diffusion?

A

The passive net movement of particles from a high to a low concentration until they are evenly distributed

24
Q

What is facilitated diffusion?

A

The passive movement of large or charged molecules across a cell membrane using channel or carrier proteins

25
Q

How do channel proteins work?

A

These create pores in the membrane across which water-soluble ions can pass. A different channel is needed for each charged particle

26
Q

How do carrier proteins work?

A

A large molecule attaches to a carrier protein in the membrane
The protein changes shape
The molecule is released on the other side of the membrane

27
Q

Three things simple diffusion depends upon

A

A high concentration gradient
A thin exchange surface
A large surface area, perhaps provided by microvilli

28
Q

Two things facilitated diffusion depends upon

A

A high concentration gradient

The number of channel or carrier proteins

29
Q

What is osmosis?

A

The movement of water from an area of higher water potential to an area of lower water potential

30
Q

What do water molecules have to pass through in osmosis?

A

A partially permeable membrane

31
Q

3 things the rate of osmosis depends upon

A

The concentration gradient (higher = faster osmosis)
The thickness of the cell membrane
The surface area of the exchange surface

32
Q

What is the water potential of pure water?

A

0kPa

33
Q

From what water potential will water move?

A

From a less negative water potential to a more negative water potential

34
Q

Explanation of osmosis:

A

The solution on one side has a low concentration of solute and a high concentration of water molecules. These both have kinetic energy and so move around rapidly. The partially permeable membrane only allows water molecules, not solute molecules, to cross. The water molecules diffuse from the side with the higher water potential to the side with the lowest water potential until an equilibrium is reached.

35
Q

Why won’t plant cells burst?

A

The vacuole stores water and the cell wall provides extra support to prevent bursting

36
Q

What is active transport?

A

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

37
Q

How does active transport work?

A

Carrier proteins span the membrane
The molecule attaches to the receptor site on the protein
On the inside of the cell, ATP attaches to the carrier protein, releasing the energy needed for it to change shape
The carrier protein opens the other side of the membrane
The molecule is allowed into or out of the cell

38
Q

What is the difference between active transport and facilitated diffusion?

A

Facilitated diffusion doesn’t require an energy input from ATP

39
Q

How does ATP release energy?

A

It undergoes a hydrolysis reaction to produce ADP and phosphate group, which also releases energy

40
Q

What are co transporters?

A

A type of carrier protein which can bind to two molecules at a time

41
Q

How does co transport of glucose work?

A

Sodium ions are actively transported out of the epithelial cells lining the ileum by a sodium-potassium pump
This creates a steep concentration gradient
Sodium ions attached to a glucose molecule diffuse into the lumen of the epithelial cells, down the concentration gradient via the co transporter proteins
The concentration of glucose inside the cell is high
Glucose diffuses out of the cell and into the blood by facilitated diffusion

42
Q

3 things needed for efficient active transport

A

Fast carrier proteins
Lots of carrier proteins
The rate of respiration in the cell and the availability of ATP

43
Q

Why is co transport described as indirect?

A

Rather than ATP fuelling the movement of glucose, it is the movement of sodium ions

44
Q

What is Oral Rehydration Therapy?

A

A way of treating the dehydration caused by severe diarrhoea

45
Q

What four things does an ORT sachet include?

A

Water
Sodium ions
Glucose
Potassium ions

46
Q

Why will the length of a potato cylinder increase when you put it in distilled water?

A

The potato has a more negative water potential, so water will move into the potato by osmosis, which causes the cells to extend and become turgid

47
Q

What is important to remember about the proteins associated with active transport?

A

Active transport only uses carrier proteins, not channel

48
Q

How do sodium and glucose move into a cell by co-transport?

A

Facilitated diffusion

A Level Biology Year 1 (21 decks)

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