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BIOLOGY A LEVEL > CHAPTER 5 - PLASMA MEMBRANES > Flashcards

CHAPTER 5 - PLASMA MEMBRANES Flashcards

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1
Q

What is compartmentalisation?

A

Formation of separate membrane-bound areas in a cell

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2
Q

Why is compartmentalisation vital to the cell

A

Separates many different and often incompatible reactions

Allows specific conditions required for cellular reactions

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3
Q

What are Membranes formed from

A

Phospholipid bilayer (two sets of phospholipids with a hydrophilic head and a hydrophobic tail)

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4
Q

What is a fluid-mosaic model and why is it called that

A

a model used to show the structure a bilayer

Fluid as things are free to move, flexible, varied shape size and position

Randomly scattered

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5
Q

What types of membrane proteins are there?

A

Intrinsic and Extrinsic

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6
Q

What are intrinsic proteins?

A

Intrinsic (or integral) proteins are transmembrane proteins that are embedded through both layers of membrane

They have amino acids with hydrophobic R-groups on their external surfaces, which interact with the hydrophobic core of the membrane

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7
Q

What do Channel proteins and carrier proteins do

A

Both Intrinsic

Channel proteins provide a hydrophilic channel that allows the passive movement of polar molecules and ions down a concentration gradient

Carrier proteins do both passive and active transport into cells, usually involving the change of protein shape

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8
Q

What are glycoproteins

A

Proteins embedded in the cell-surface membrane with attached carbohydrate (sugar) chains with varying lengths and shapes

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9
Q

What are the role of glycoproteins

A

Receptors for chemical signals

aids in Cell Adhesion

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10
Q

What is cell signalling?

A

A direct response from a cell, setting off a cascade of events as a result of a chemical binding to a receptor

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11
Q

What are some examples of cell signalling?

A

Receptors for neurotransmitters such as acetylcholine at nerve cell synapses. The binding of the neurotransmitters triggers or prevents an impulse in the next neurone

Receptors for peptide hormones, including insulin and glucagon, which affect the uptake and storage of glucose by cells

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12
Q

What are glycolipids?

A

Lipids attached to carbohydrate (sugar) chains

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13
Q

What do Glycolipids do?

A

Cell markers (antigens) which identify the cells as self or non-self

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14
Q

What are Extrinsic (peripheral) proteins and what part of their structure allows them to be where they are?

A

Proteins that reside in one side of the bilayer

Hydrophilic R-groups on outside surface which interact with the polar phospholipid heads

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15
Q

What is cholesterol and what does it do?

A

A Lipid with a hydrophilic and hydrophobic end

Regulates fluidity of membranes

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16
Q

Where is cholesterol located and how does it work?

A

Between phospholipids in a membrane bilayer, with the hydrophilic end interacting with the heads, hydrophobic end interacting with the tails, pulling them together

Adds stability without making them too rigid

Stops molecules grouping too close and crystalising

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17
Q

Define the term ‘compartmentalisation’

A

Membranes form cells and separate areas within cells

Isolating each area from its external
environment

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18
Q

Describe the difference between intrinsic and extrinsic proteins. State two examples of each

A

2 Intrinsic protein – embedded in both sides of the bilayer

for example a channel protein or
carrier protein

Extrinsic protein – embedded in one side of the bilayer

for example a
glycoprotein or enzyme

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19
Q

Alcohol, Caffeine and nicotine are all lipid-soluble molecules - they have an almost instant and widespread effect on the body. Explain why.

A

Lipid soluble molecules can pass through membranes

(by) simple diffusion

(so) diffuse
quickly through (whole) body

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20
Q

Membranes, particularly those present within mitochondria, are often highly folded. Suggest what advantages this folding provides

A

4 Process occur within/across, membranes

process is enzyme controlled

folding gives
increased surface area

(so) more enzymes

increased rate of reaction(s)

and therefore an
increased rate of ATP production

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21
Q

What factors affect membrane structure?

A

Temperature

Solvents

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22
Q

How does temperature affect membrane structure

A

Increase in Kinetic energy, means phospholipids will move more

lose structure, loss of permeability

Carrier proteins will be denatured

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23
Q

How do pure/strong solvents effect membrane structure

A

most organic solvents are less polar than water eg. alcohols, benzene

Organic solvents will dissolve membranes, disrupting cells

eg. alcohols rubbed onto a wound dissolve membranes of bacteria, killing them

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24
Q

How do less concentrated solvents affect the body

A

(Found in alcoholic drinks)

Enters and disrupts membrane

Becomes more permeable and fluid

Some cells need intact membranes for specific functions eg. transmission of nerve impulses by neurones

Cannot transmit if membranes are disrupted

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25
Q

Describe an experiment investigating membrane permeability

A

Cut 5 small pieces of beetroot using cork borer

wash with running water

place in 100ml distilled water in varying degrees of water bath (10,20,30,40,50) for 5 minutes

Measure absorbance of each using a colorimeter with a blue filter

Repeat 3 times with fresh pieces, calc mean, plot graph

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26
Q

Why would a student use beetroot cells to investigate membrane permeability?

A

Contains betalain - red pigment

when cell membranes are disrupted, pigment is released into solution, colouring it

amount of pigment is correlated to disruption of cell membranes

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27
Q

Suggest, in the experiment investigating membrane permeability, why

1) the beetroot places were washed in running water
2) Samples of water containing beetroot were taken five minutes after the temperature was reached
3) Experiment was repeated 3 times
4) Colorimeter used a blue filter

A

1) to release pigment on surface from damaged cells
2) Allow for mixture to equilibrate
3) For Repeatability
4) Pigment is red

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28
Q

The absorbency solution can be calculated from the amount of light transmitted. Suggest house and explain why the absorbance would change as the amount of pigment increases.

A

more pigment molecules absorb more light

light transmitted decreases

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29
Q

suggest how you could carry out an investigation to see the effects of organic solvents on membrane permeability

A

Same procedure except temperature constant

different (organic) solvents used
e.g., ethanol

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30
Q

Explain why solvents like water do not disrupt cell membranes

A

water is a polar solvent

phospholipids will not dissolve in water

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31
Q

describe how the absorbance of light could be measured quantitatively as the concentration of released pigment increased with increasing temperature.

A

use of colorimeter

use of filter

range of readings taken (at different temperatures

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32
Q

Suggest how an excessive consumption of alcohol could lead to liver cell death and ultimately be fatal

A

Alcohol is lipid soluble and dissolves in membrane bilayer

this disrupts the bilayer and stops/reduces transport of materials

preventing the normal functioning and may cause cell death.

The liver is particularly affected due to its role in filtering substances from the blood

this may ultimately be fatal if the liver function is destroyed

or if impulse transmission is depressed, prevent involuntary reflexes

such as breathing and the gag reflex (which prevents choking).

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33
Q

What is Diffusion?

A

The net movement of particles from a region of higher concentration to a region of lower concentration through a partially (or selectively) permeable membrane

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34
Q

Why does diffusion occur?

A

Particles in a gas or liquid have kinetic energy

Movement is random and an unequal distribution will eventually become an equal distribution

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35
Q

Why are many small cells beneficial for diffusion as opposed to a larger cell the same size?

A

Large cell would slow rates of diffusion

More collisions, slowing down diffusion

(ATP would be supplied too slowly, reactions wouldn’t be complete)

36
Q

What factors affect rate of diffusion

A

Temperature

Concentration

Surface area

Thickness of membrane

37
Q

How does temperature affect rate of diffusion

A

Higher temperature leads to higher rates of diffusion, particles have higher KE so move at higher speeds

38
Q

How does concentration affect rate of diffusion

A

Greater difference in concentration between the two regions, the faster the rate of diffusion will be, as there will be more overall movement from the higher to the lower conc

39
Q

What is simple diffusion

A

Diffusion in the absence of a barrier

40
Q

Describe an experiment to measure rate of diffusion and surface area

A

Using different sized agar blocks (pale colour), with Phenolphthalein indicator which turns pink in presence of alkali

Immerse blocks in solution of NaOH for 10 minutes

Remove blocks and cut open, measure distance diffused with ruler

41
Q

What type of molecules can diffuse across a membrane?

A

non-polar molecules (eg oxygen) can move freely

Polar molecules (eg water) with partial charges can diffuse through, but at a very slow rate

(small molecules move through easier than larger ones)

Membranes called partially permeable

42
Q

How does Surface area affect rate of diffusion

A

The larger the area of an exchange surface, the higher the rate of diffusion (more contact/exchange surface)

43
Q

How does membrane thickness affect the rate of diffusion

A

The thinner the exchange surface, the higher the rate of diffusion (less distance to travel)

44
Q

What determines if a membrane is partially or selectively permeable?

A

If protein channels are present/in action

45
Q

What is facilitated diffusion?

A

Diffusion of polar molecules or ions through a membrane using a channel (and sometimes carrier) protein

46
Q

Is diffusion an active or passive process and why?

A

Passive

No energy is required

47
Q

What is the rate of facilitated diffusion dependant on

A

Temperature, conc gradient, membrane SA, membrane thickness and number of channel proteins present

48
Q

Describe an investigation into the factors affecting diffusion rates in a model cell

A

Use dialysis tubing as it is partially permeable with pores similar to those on a membrane, so small molecules can pass, but not large ones like starch

Fill tubing with various concentrations or sizes of solutions containing solute molecules eg glucose and starch

After set time in various conditions of temperature, benedicts test for glucose, iodine for starch, rate of diffusion can be calculated

49
Q

Explain why benedict’s test is both qualitative and quantitative

A

qualitative detects the presence of, reducing sugar / glucose

quantitative colour change is estimate of concentration (of reducing sugar / glucose

50
Q

Explain what is meant by the term model cell

A

tied dialysis tubing is, simplified / practical, representation of real cell

(tied dialysis tubing) has the same properties as membrane (of cell)

demonstrates diffusion across (cell) membrane

51
Q

Describe the differences between dialysis tubing and cell membranes with reference to transport across membranes

A

cell membranes more complex ORA (or reverse argument)

(cell membranes) have, carrier proteins / channel proteins ORA

active transport and diffusion across (cell) membranes (1);

(cell membranes) have hydrophobic core (1); ORA

(cell membrane permeability) determined by size and, polarity / charge

52
Q

Explain why rate of diffusion increases as temperature increases

A

Increased temperature increases the kinetic energy of particles

causing the particles to move at increased speed

53
Q

explain why some ions can pass through dialysis tubing by diffusion but can only pass through cell membranes by facilitated diffusion

A

dialysis) tubing permeability based on pore size

dialysis tubing is not a barrier to (small) ions

phospholipid bilayer (of cell membrane) is barrier to ions

ions diffuse through channel proteins (in membrane)

54
Q

State two changes to the structure of a cell membrane that would increase the rate at which polar molecules diffuse into a cell

A

Increased surface area

and reduced thickness

55
Q

Movement requires energy and yet the movement if molecules in diffusion is described as passive (not requiring energy). Explain statement and state the source of the energy involved in diffusion.

A

Diffusion is described as passive because it does not require an external (metabolic) energy source

diffusion relies on the energy from the natural random movement of particles

56
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

57
Q

Why is Active Transport an active process

A

Energy is required to go against the concentration gradient (ATP)

58
Q

What Is a pump?

A

A carrier protein which pumps out ions and molecules

59
Q

Describe active transport outside-inside of the cell

A

The molecule or ion binds to receptors in the channel of a carrier

ATP on inside of cell binds to carrier protein and hydrolyses to ADP and Pi

This causes change in shape opening up to the inside of the cell

Molecule is released inside the cell

Phosphate is released and adds to ADP to form ATP

Carrier protein returns to original shape

60
Q

What is bulk transport?

A

Active process of moving large molecules such as enzymes, hormones and whole cells eg bacteria in or out of a cell because they are too large to fit through a channel or carrier protein

61
Q

What are the two forms of bulk transport

A

Endocytosis

Exocytosis

62
Q

What is Endocytosis

A

The bulk transport of material into cells.

There are two types of endocytosis, Phagocytosis for solids and pinocytosis for liquids

63
Q

How does Endocytosis work?

A

Cell surface membrane invaginates (bends inwards) when in contact with material to be transported

Membrane enfolds, fuses and forms a vesicle

Vesicle pinches off and moves to cytoplasm for further processing eg. bacteria in vesicles are moved towards lysosomes to be digested

64
Q

What is exocytosis

A

The bulk transport of materials out of a cell

65
Q

How does exocytosis work?

A

Vesicles formed by golgi move towards and fuse with cell surface membrane.

Contents of vesicle are then released outside of the cell

66
Q

Why is bulk transport an active process

A

Energy/ATP is required to move vesicles along cytoskeleton and change shape of cells

67
Q

Explain why facilitated diffusion is not a form of active transport

A

Diffusion is always a passive process, it does not require a metabolic energy source

facilitated diffusion a channel/co-transport protein aids diffusion

68
Q

Cells that carry out active transport usually have more mitochondria than cells that do not. Explain why

A

Active transport requires metabolic energy in the form of ATP

produced in the mitochondria

69
Q

plant roots take up mineral ions from the soil. The concentration of mineral ions in the soil is very low. Suggest why active transport is very important in root hair cells

A

Plants need mineral ions

concentration of mineral ions higher in root hair cells (than soil solution)

mineral ions will diffuse out of root hair cells

energy required to move mineral ions
against concentration gradient

70
Q

What is osmosis

A

The net movement of water molecules from a region of higher concentration to a region of lower concentration through a partially permeable membrane

71
Q

What is a solute and what is a solvent

A

Solute is something that is dissolved (eg in water)

Solvent is the dissolving agent (eg water) (my term not official)

72
Q

What is water potential

A

The pressure exerted by water molecules as they collide with a membrane or container

73
Q

What are the units for water potential

A

Psi (Trident looking)
Pascals or KiloPascals

74
Q

What is the water potential of pure water at standard temperature and atmospheric pressure (25 degrees C and 100kPa)

A

0kPa

75
Q

What happens to water potential when more solutes are dissolved in it?

A

Decreases

76
Q

What happens when two solutions of different concentrations/water potentials are separated by a partially permeable membrane

A

There will be a net movement of water from the higher water potential (less conc) to the lower water potential (more conc) so the water potential will become equal on both sides

77
Q

What is Hydrostatic pressure

A

The pressure exerted by water upon a cell

78
Q

What happens when animal cells are placed in a solution with higher water potential than its cytoplasm

A

Water will enter cell by osmosis to even out water potential

No cell walls are present, membrane cannot stretch

Cell bursts - cytolysis

79
Q

What happens when animal cells are placed in a solution with lower water potential than its cytoplasm

A

Water leaves cell by osmosis

Causes reduction in volume

Cell surface membrane puckers - called crenation

pg115 for table

80
Q

What is turgor pressure

A

When the hydrostatic pressure pushes the membrane up against the rigid cell wall of a plant

81
Q

What happens when plant cells are placed in a solution with higher water potential than its cytoplasm (normal plant environment)

A

Water enters cell by osmosis

Membrane pushes up against cell wall, increasing turgor pressure

Increased Turgor resists the entry of further water, cell is turgid

82
Q

What happens when plant cells are placed in a solution with lower water potential than its cytoplasm

A

Water leaves the cell by osmosis

Reduction in volume of cytoplasm

Pulls Cell-surface membrane away from the cell wall, cell is said to be plasmolysed

pg116 table

83
Q

Describe an investigation to see different solutions effect on osmosis

A

Core potato/onion (or use shell-less eggs)

Weigh mass

Place in sugar and salt solutions with different concentrations - hence different water potentials (use sugar syrup for eggs)

Water will move in/out of cell

Weigh mass

84
Q

Explain why it is not possible to have a positive water potential

A

The water potential of pure water is zero

addition of solute decreases water potential

therefore all solutions have negative water potential.

85
Q

Explain why it is important to keep concentrations of electrolytes (solutes) in body tissues at the correct level to ensure proper hydration

A

Electrolytes/solutes/minerals are necessary for many body processes

and help prevent excess
water loss by osmosis

to help maintain correct fluid balance for reactions

BIOLOGY A LEVEL (24 decks)

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