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AQA A Level Biology > Cells > Flashcards

Cells Flashcards

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1
Q

Structure of Nucleus

A
  1. Nuclear envelope: double membrane surrounding nucleus
  2. Nuclear pores: allow the passage of larger molecules (e.g. mRNA), out of the nucleus.
  3. Nucleoplasm: granular, jelly-like material making up the bulk of the nucleus.
  4. Chromosomes: protein-bound, linear DNA.
  5. Nucleolus: small spherical region(s) in nucleoplasm. Manufactures ribosomal RNA and assembles ribosomes.
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2
Q

Function of the nucleus

A
  1. Controls cell’s activities - Controls entry and exit of materials, and contains nuclear reactions.
  2. Retains genetic material in the form of DNA and chromosomes.
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3
Q

Structure of Mitochondria

A
  1. Double membrane surrounding organelle - controls entry and exit of material.
  2. Cristae - extensions of the inner membrane, providing a large surface area for the attachment of enzymes and other proteins during respiration.
  3. Matrix - contains proteins, lipids, ribosomes and DNA matrix contains enzymes for cell respiration.
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4
Q

Function of the Mitochondria

A

site of aerobic respiration

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5
Q

Structure of Chloroplasts

A

Chloroplast envelope - double plasma membrane, highly selective

  1. Grana - stacks of disc-shaped thylakoid membrane.
  2. Thylakoids - contain chlorophyll used in photosynthesis, can be linked by lamellae to other grana.
  3. Stroma - fluid-filled matrix that contains starch grains.
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6
Q

Functions of Chloroplasts

A

site of photosynthesis

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7
Q

Structure of Endoplasmic Reticulum

A

Rough and Smooth ER have folded membranes called cisternae

RER have ribosomes on the cisternae

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8
Q

Function of endoplasmic reticulum

A

RER – protein synthesis

SER- synthesises and stores lipids and carbohydrates

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9
Q

Structure of Golgi Apparatus

A

Flattened sacs and folded membranes making cisternae

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10
Q

Function of Golgi Apparatus

A

Processes, packages and modifies proteins

Stores lipids and proteins and transports them out of the cell

Vesicle- pinches off cisternae and the modified molecule can be transported.

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11
Q

Structure of Lysosomes

A

Vesicles/Bags of digestive enzymes

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12
Q

Functions of Lysosomes

A

Hydrolyse phagocytic cells

Completely break down dead cells (autolysis)

Exocytosis- release enzymes outside of cell to destroy material

Digest worn out organelles for the reuse of materials

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13
Q

Structure of Ribosomes

A

Small organelle made up of proteins and rRNA (ribosomal RNA)

Eukaryotic cells have large ribosomes

Prokaryotic cells, mitochondria and chloroplasts have smaller ribosomes

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14
Q

Functions of Ribosomes

A

Carry out protein synthesis

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15
Q

Structure of Cell Wall

A

Plants- made of microfibrils of cellulose

Fungi- made of chitin, a nitrogenous polysaccharide

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16
Q

Function of Cell Wall

A

Provides structural strength to the cell

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17
Q

Structure of Vacuoles

A
  1. Fluid-filled sac bounded by a single membrane.
  2. Single membrane around it called tonoplast.
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18
Q

Function of vacuole

A

Makes cells turgid and therefore provides support

Temporary store of sugars and amino acids

The pigment may colour petals to attract pollinators

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19
Q

Define Tissue

Give an example

A

A collection of similar cells that work together to perform a specific function.

Example = epithelial tissue - consists of sheets of cells, lining the surfaces of organs, often having a protective or secretory function.

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20
Q

Define eukaryotic cell

A

A larger cell with a true nucleus that is bounded by a nuclear membrane/nuclear envelope.

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21
Q

Define prokaryotic cell

A

A smaller cell which has no true nucleus or nuclear envelope. Organelles are not membrane bound

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22
Q

Can you describe how prokaryotic cells differ from eukaryotic cells?

A

Prokaryotic cells:
- have no nucleus
- smaller 70S ribosomes
- cytoplasm lacks membrane-bound organelles
- much smaller cell
- cell wall contains murein (a glycoprotein)
- plasmids may be found in prokaryotic cells

Eukaryotic Cells:
- have nucleus
- 80S ribosomes
- membrane-bound organelles
- larger cell
- cell wall made of cellulose or chitin
- no plasmids

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23
Q

Can you list other features of prokaryotic cells?

A

Prokaryotic cells can have:
- one or more plasmids
- a slime capsule surrounding the cell
- one or more flagella

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24
Q

What is cell fractionation?

A

A method used to isolate different organelles so they can be studied. This enables the individual organelle structures to be studied in an electron microscope

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25
Q

What are the steps of cell fractionation

A
  • Homogenisation
  • Filtration
    -Ultracentrifugation
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26
Q

Why should the solution be isotonic?

A

water potential is the same as the solution which prevents osmosis that could shrink or burst organelles

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27
Q

Why should the solution be buffered?

A

keeps pH constant and avoids damaging the protein structures of the organelle)

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28
Q

Why should the solution be ice cold?

A

reduces enzyme activity that might damage organelles

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29
Q

How does an optical microscope work?

A

A beam of light is condensed to create the image as visible light passes and is bent through the lens system to enable the user to see the specimen

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30
Q

What are the properties of an optical microscope?

A
  • the specimen can be alive
  • Individual cells are transparent, and their components are not distinguishable unless they are coloured with special stains.

Staining usually kills the cells.

Small organelles are not visible, but living samples can be examined and a colour image is obtained

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31
Q

What are the uses of an optical microscope?

A

Most student microscopes are classified as light microscopes.

Max resolution is 0.2 micrometres.

The nucleus and mitochondria can be seen with a light microscope.

The max magnification is around x1,500.

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32
Q

How is an electron microscope used?

A

A beam of electrons that are condensed using electromagnets creating the image. This allows higher magnification and higher resolving power, allowing more detail to be seen with black and white images

Samples must be in a vacuum and non-living

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33
Q

What are the uses of an electron microscope?

A

Max resolution of 0.0002 micrometres. Around1000 times more than light microscopes.

Max magnification is around x1,500,000.

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34
Q

What are the two types of electron microscopes?

A

transmission (TEM) and scanning (SEM) electron microscopes.

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35
Q

How does an SEM work?

A

A beam of electrons moves back and forth across a cell’s surface, creating details of cell surface characteristics.

SEMs knock electrons off the specimen and these electrons come together to form an image.

SEM images can be three-dimensional.

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36
Q

What are the properties of an SEM?

A

-The specimens do not need to be thin, as the electrons are not transmitting through. -Can produce a 3D image

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37
Q

How does a TEM work?

A

Extremely thin specimens are stained and placed in a vacuum

The electron beam penetrates the cell and provides details of a cell’s internal structures.

TEMs use electromagnets to focus the electron beams and are high resolution microscopes.

In thin specimens, you can see the internal structures of organelles such as chloroplasts.

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38
Q

What are the steps in calibrating the eyepiece graticule?

A

Line up the stage micrometre and eyepiece graticule whilst looking through the eyepiece

Count how many divisions on the eyepiece graticule fit into one division on the micrometre scale

For example, each division on the micrometre is 10, so this can be used to calculate one division on the eyepiece graticule at that current magnification. 10/2=5 micrometres

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39
Q

Can you describe the pros and cons of optical microscopes?

A

Pros:
- cheap
- images in colour
- no training required
- live specimens

Cons:
- low magnification x1500
- low resolution
- 2D images

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40
Q

Can you describe the pros and cons of transmission electron microscopes?

A

Pros:
- high resolution images
- high magnification
- visible internal structures

Cons:
- expensive
- training is required
- no colour images
- 2D images
- only thin specimens

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41
Q

Can you describe the pros and cons of scanning electron microscopes?

A

Pros:
- 3D images
- high magnification
- high resolution
- thick specimens

Cons:
- expensive
- training is required
- no colour images

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42
Q

How do you prepare a slide for an optical microscope?

A
  1. Pipette a drop of water onto the slide
  2. Use tweezers to place a thin section of your specimen on top of the droplet
  3. Add a drop of a stain
  4. Add a cover slip - remove all air bubbles
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43
Q

What is the difference between magnification and resolution?

A

MAGNIFICATION - increasing the size of an image. Up until the limit of resolution, an increase in magnification = an increase in detail.

RESOLUTION = minimum distance apart that two objects can be for them to appear as separate items.

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44
Q

Can you describe the principles of cell fractionation and ultracentrifugation in separating cell components?

A
  1. Homogenisation
    - tissue is broken up in a cold, isotonic buffer solution to release the organelles into a solution
  2. Filtration
    - the homogenised cell solution is filtered through a gauze
    - this separates any large cell debris
  3. Ultracentrifugation
    - the cell fragments are poured into a test tube and placed in a centrifuge and spun at a low speed
    - a thick sediment - the pellet - is at the bottom of the tube and the fluid above is the supernatant
    - the supernatant is drained into a new tube and spun again at a higher speed
    - a new pellet forms and again, the supernatant is drained off and spun again at an even higher speed
    - this process is repeated at higher speeds each time until all the organelles are separated out
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45
Q

How are the organelles separated out during centrifugation?

A

They are separated in order of mass and the order is usually:
- nuclei
- mitochondria
- lysosomes
- endoplasmic reticulum
- ribosomes

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46
Q

Why are virus cells not considered living?

A

They have no nucleus, plasma membrane, cytoplasm, or ribosomes.

They are not made of cells.

They cannot reproduce independently

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47
Q

How do viral cells replicate?

A

Viruses replicate by injecting their nucleic acid into a host cell:

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48
Q

Can you describe the structure of virus particles?

A

no plasma membrane, cytoplasm, ribosomes
- a core of genetic material : DNA or RNA
- capsid surrounding core
- attachment proteins around edge of capsid that are complementary to specific host cells

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49
Q

Outline the differences between mitosis and meiosis.

A

Mitosis results in 2 genetically identical diploid daughter cells.

Meiosis results in 4 genetically different haploid daughter cells.

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50
Q

List the stages of mitosis

A

Prophase
Metaphase
Anaphase
Telophase

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51
Q

outline interphase

A

Precedes Mitosis

  1. Cell is not dividing.
  2. Considerable cellular activity - replication of DNA, two copies on centromere.
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52
Q

outline prophase

A
  1. Chromosomes become more visible, thicken.
  2. Centrioles move to opposite ends of the cell (poles).
  3. Spindle fibres develop from each of the centrioles (spindle apparatus).
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53
Q

outline metaphase

A
  1. Chromosomes seen to be made up of two chromatids.
  2. Microtubules attach to centromere - chromosomes pulled to the cell equator where they line up.
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54
Q

Outline Anaphase

A
  1. Centromeres divide, separating each pair of sister chromatids.
  2. Chromatids pulled to their respective poles as spindles contract, centromeres first - v-shaped.
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55
Q

Outline Telophase

A
  1. Chromosomes reach their opposite poles and then uncoil, become long and thin again
  2. Spindle fibres disintegrate; nuclear envelope and nucleolus reform.
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56
Q

Why is mitosis so important?

A

GROWTH - ensures that all cells growing from original cell of an organism are genetically identical.

REPAIR - Important that replacement cells produced have an identical structure and function to lost cells.

REPRODUCTION - Single-celled organisms divide by mitosis to give 2 new organisms - each new organism is genetically identical to the parent organism.

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57
Q

How does cancer arise?

A

Result of gene damage controlling mitosis and cell cycle.

Mutant cells are structurally and functionally different - most mutant cells die but surviving mutant cells become tumours.

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58
Q

Outline cytokinesis

A

the cytoplasm is divides forming two genetically identical cells

Animal cells: a ‘cleavage furrow’ forms and separates the daughter cells

Plant cells: a ‘cell plate’ forms at the site of the metaphase plate. Once the cell plate reaches the cell walls of the parent cell, new cell walls are produced, separating the new daughter cells

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59
Q

Outline the processes that occur during interphase

A

G1- growth of organelles

S- DNA Synthesis

G2- Growth and preparation for mitosis

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60
Q

Difference between benign and malignant?

A

Malignant - grow rapidly, spread, more likely to be life-threatening.
Benign - grow more slowly, do not spread less likely to be life-threatening

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61
Q

How can cancer be treated?

A

Involves killing dividing cells by blocking a part of the cell cycle - cell division and therefore cancer growth ceases.

Chemo disrupts cell cycle by preventing DNA replication or by inhibiting the metaphase stage of mitosis by interfering with spindle formation.

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62
Q

Outline the process of Binary Fission

A
  1. The circular DNA in the cells replicates and both copies attach to the cell membrane.
    Plasmids also replicate.
  2. The cell membrane then begins to grow between the two DNA molecules and begins to pinch
    inwards, dividing the cytoplasm in two.
  3. A new cell wall forms between the two DNA molecules dividing the original cell. The identical
    daughter cells each have a single copy of the circular DNA and a variable number of copies
    of the plasmids
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63
Q

Outline role of phospholipids in cell-surface membrane structure.

A

Their hydrophilic/hydrophobic interactions lead to the formation of a phospholipid bilayer.

  1. Allow lipid-soluble substances to enter/exit cell.
  2. Prevent water-soluble substances entering and leaving cell.
  3. Make the membrane flexible and self-sealing.
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64
Q

Outline role of proteins in cell-surface membrane structure.

A
  • to aid movement across the
    membrane
  • provide mechanical support
  • act in conjunction with glycolipids as
    receptors.
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65
Q

Outline role of glycolipids in cell-surface membrane structure.

A
  • acts as a cell surface receptors for
    certain molecules
  • allow cells to
    adhere to one another to form tissues.
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66
Q

Outline the role of glycoproteins in cell-surface membrane structure

A
  • carbohydrates that attach to extrinsic proteins and acts
    a cell surface receptors and
    neurotransmitters.
  • allow cells to recognise one another as well as attach to
    form tissues.
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67
Q

Comment on the permeability of the cell-surface membrane.

A

Controls the movement of substances into/out of the cell.

Most molecules don’t freely diffuse across it because many are:

  1. Not lipid-soluble
  2. Too large to pass through
  3. Same charge as protein channel charges - repelled even if small
  4. Charged/polar - can’t pass through the non-polar hydrophobic tails in the phospholipid bilayer.
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68
Q

Explain the “fluid-mosaic” model of the cell-surface membrane structure.

A

The “mosaic” term of this model refers to the mixture of lipids and intrinsic proteins in the membrane. These boundaries are also “fluid” because their components can move flexibly

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69
Q

Define Diffusion

A

the net movement of particles from an area of high concentration to low concentration until an even distribution is maintained.

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70
Q

How does concentration gradient affect diffusion?

A

the greater the concentration gradient, the faster the rate of diffusion.

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71
Q

How does membrane thickness affect diffusion?

A

The thinner the membrane, the faster the rate of diffusion and thin membranes reduce the distance that particles have to travel

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72
Q

How does surface area affect diffusion?

A

The larger the surface area, the faster the rate of diffusion and increasing the surface area means more particles can be exchanged in the same amount of time.

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73
Q

How does temperature affect diffusion?

A

The higher the temperature, the faster the rate of diffusion and particles will have more kinetic energy so will be able to move around faster

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74
Q

Give an example of a molecule which can use simple diffusion to pass through the membrane

A

small, non polar e.g. oxygen and carbon dioxide

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75
Q

What is facilitated diffusion?

A

passive transport that uses specialized proteins, such as channel proteins and carrier proteins, to help large molecules move across a cell membrane faster

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76
Q

What are channel proteins?

A

a protein that allows the transport of specific substances across a cell membrane.

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77
Q

What are carrier proteins?

A

Carrier proteins can change their shape to move a target molecule from one side of the membrane to the other.

78
Q

How do carrier channels help in facilitated diffusion?

A

Carrier proteins can change shape to assist the movement of substances across the membrane. They have specific binding sites which allows them to selectively “help” substances through

79
Q

How do channel proteins help in facilitated diffusion?

A

channel proteins form open pores through the membrane, allowing the free diffusion of any molecule of the appropriate size and charge

80
Q

What factor affects the rate of facilitated diffusion?

A

number of channel or carrier proteins

81
Q

How does the number of channel or carrier proteins affect the rate of facilitated diffusion?

A

The greater the number of channel or carrier proteins in the plasma membrane the faster the rate of facilitated diffusion.​

This is true up to a certain point, once all the proteins in the membrane are in use facilitated diffusion can’t happen any faster even if you increase the concentration gradient. So, it becomes a limiting factor.

82
Q

what types of molecules would transported using facilitated diffusion across the membrane?

A

Large, polar, water-soluble (e.g. glucose, amino acids)

83
Q

Protein molecules on the cell-surface membrane enable the immune system to identify:

A
  1. Pathogens.
  2. Cells from other organisms of the same species - non-self material (different genes).
  3. Toxins (produced by pathogens - leads to chemotaxis)
  4. Abnormal body cells - such as cancer cells.
84
Q

Define an antigen

A

A specific protein on the surface of a pathogen that triggers an immune response

85
Q

Describe the effect of antigen variability

A

Enables the pathogen to avoid the immune response in its current host, but also allows re-infection of previously infected hosts

86
Q

Give an example of a disease with antigen variability and how it is prevented

A

Influenza virus

Influenza vaccine changes yearly -> new immunologically distinct strains not recognised by memory cells circulate in population.

87
Q

Define Immunity

A

The ability of organisms to resist infection by protection against pathogens

88
Q

Outline the process of phagocytosis

A
  1. The phagocyte is attracted to the pathogen as it releases chemicals, leaving a chemical trail
  2. Receptors on the phagocyte allow it to attach to the pathogen via its antigen
  3. It engulfs the pathogen and forms a phagosome
  4. Lysosomes contain a digestive enzyme called lysozymes. The lysosomes move towards the phagosome and bind with it, releasing the lysozyme
  5. Lysosomes hydrolyse the pathogen, and the debris is absorbed by the cell
  6. ★ Once a phagocyte has engulfed and hydrolysed a pathogen. It presents part of the pathogen (usually a small part of a protein) on its cell surface membrane; making it now an APC (antigen presenting cell)
89
Q

why do some pathogens exhibit antigen variability?

A

The antigens present on their surface change frequently due to genetic mutations

90
Q

Define Antigen-presenting cell

A

A cell that displays foreign antigens on their surface.

91
Q

Comment on the specificity of T-cells.

A

Receptors on each T-cell are complementary to and respond to only one antigen.

92
Q

Describe how T-lymphocytes can distinguish antigen-presenting cells from normal cells

A
  1. Phagocytes that have hydrolysed pathogen present its antigens on their own cell-surface membrane.
  2. Body cells invaded by a virus present some of the viral antigens on their own cell-surface membrane.
  3. Transplanted cells have different antigens on their cell-surface membranes.
  4. Cancer cells are different from normal body cells and present antigens on their own cell-surface membranes.
93
Q

Define Cell-Mediated Immunity

A

T-lymphocytes respond only to antigens that are presented on a body cell

94
Q

Outline the process of Cell-Mediated Immunity

A

Phagocyte engulfs and hydrolyses the pathogen (phagocytosis)

Phagocyte presents an antigen on its cell surface membrane becomes an APC

A specific T-helper cell with a complementary receptor binds to the presented antigen

This activates the T-helper cells, and it undergoes mitosis to form identical copies of itself (clonal selection)

95
Q

What do these cloned T- cells become:

A

Memory T-cells

Plasma cells

Stimulate the production of B cells

Stimulate phagocytosis

Activate cytotoxic T-cells

96
Q

How do cytotoxic T cells kill abnormal cells?

A

by producing a protein called perforin that makes holes in the cell-surface membrane which causes the cell to become freely permeable and die (as contents leak out of the cell)

97
Q

What is the role of T-Helper Cells?

A

involved in cell recognition and they bind to APC’s and stimulate other immune processes

98
Q

What is an antibody?

A

A specific protein found in the blood that is produced by plasma cells

99
Q

What are plasma cells?

A

Cells which secrete antibodies (usually) into blood plasma. They only survive for a few days - lead to destruction of pathogen

100
Q

Define humoral immunity

A

This involves B-cells and antibodies, soluble in blood and tissue fluids of body. The B-cells produce specific antibodies, specific to one antigen.

101
Q

What are memory cells?

A

Cells which circulate in blood and tissue fluid - divide rapidly into plasma cells and more memory cells -> more antibodies at a faster rate (faster response).

102
Q

Outline the process of humoral immunity

A
  1. Invading pathogen has an antigen that is complementary to a receptor on the B-cell
  2. The pathogen enters the B cell by endocytosis and the B cell presents an antigen on its cell surface membrane
  3. An activated T-helper cell binds to the presented antigen
  4. The T-helper cells stimulate the B cell to divide through mitosis (clonal selection)
  5. In each clone of B cells, the cells develop into one of two types of cells: plasma cell or memory B cell

Antibodies attach to antigens on the pathogen which leads to destruction. The antibodies act as markers for phagocytosis and clump multiple pathogens together in a process called agglutination

103
Q

What is the primary immune response?

A

Production of antibodies and memory cells from new B-cells, after antigen enters body for the first time.

104
Q

What is the secondary immune response?

A

Secondary response is much faster, and produces more antibodies

105
Q

What is antibody?

A

a specific protein secreted by a plasma cell

106
Q

The structure of an antibody

A
  • 4 polypeptide chains
  • antigen-binding sites.
  • constant and variable regions (variable region dependant on antibody).
  • receptor binding site.
107
Q

Outline how antibodies help to destroy pathogens

A

Their 2 binding sites mean that antibodies can cause agglutination of the bacterial cells.

This makes it easier for phagocytes to locate them, as not spread out throughout the body.

They then serve as markers, stimulating phagocytes to engulf and destroy the bacterial cells to which the antibodies are attached.

108
Q

Define Monoclonal Antibodies

A

Antibodies with the same tertiary structure produced from a single clone of B cells

109
Q

List uses of monoclonal antibodies

A
  • Cancer treatment
  • Pregnancy tests
  • Detecting antigens or antibodies in blood (ELISA test)
110
Q

Outline how monoclonal antibodies are used in targeting cancer drugs

A
  1. Monoclonal antibodies can be made that will bind to tumour markers (cancer cell antigens), with anti-cancer drugs attached to antibody.
  2. So, antibodies will bind to tumour markers - drug will only accumulate in areas of body where there are cancer cells.
  3. Therefore, side-effects of an antibody-based drug are lower than other drugs because they accumulate near specific cells
111
Q

What is the advantages of using monoclonal antibodies in cancer treatments rather than chemotherapy?

A

Less side effects than chemotherapy as they target the cancer with destroying healthy body cells

112
Q

What is the disadvantages o using mAb’s for cancer treatment?

A
  • Allergic reactions are common
  • Doesn’t work on all cancer types
  • Long term effects aren’t well known
  • Most mAb’s are in the clinical trial stage
  • Some mAb’s can have side effects related to the antigen they target
113
Q

Outline how monoclonal antibodies are used in pregnancy testing (Medical Diagnosis)

A
  1. Sample pad absorbs urine
  2. Urine travels to reaction zone. This contains mobile mAbs with a blue dye attached which are complementary to hCG
  3. Travels up the stick to the result window. This contains immobilised mAb’s which are also complementary to hCG
  4. The mobile mAb’s continue moving to the control window. This contains immobilised mAb’s complementary to the mobile mAb’s from the action zone (prevents a false negative)
114
Q

Outline what an ELISA test is and how it works

A

An ELISA test is an enzyme linked immunosorbent assay

It uses monoclonal antibodies to detect the presence and quantity of proteins in blood plasma. It detects the presence of antigens or antibodies

115
Q

Outline how monoclonal antibodies are used in the ELISA test to find antigens

A
  1. Apply blood serum to well in a plate (plate already has attached antibodies)​
  2. Wash (removes any unbound antigens)​
  3. Add 2nd antibody (binds to antigen and has enzyme attached)​
  4. Wash (removes unbound antibody)​
  5. Colourless substrate added which binds to enzyme. Enzyme catalyses it forming a coloured substrate.​

Concentration of protein present indicated by intensity of colour

116
Q

Explain why the ELISA test does NOT diagnose AIDS

A

AIDS is a degenerative disease caused by HIV when T-cell count has declined below a certain level.

Having HIV does not = having AIDS - takes years to develop AIDS.

117
Q

Outline the ethical issues of monoclonal antibody use.

A
  1. Involves inducing cancer in mice to produce antibodies —> some have reservations, despite guidelines to minimise suffering.
  2. Successfully used to treat many diseases such as cancer and diabetes, BUT some deaths have been associated with their use in MS treatments.
  3. Testing for the safety of new drugs presents new dangers —> 2006 trial, London.
118
Q

Define antigen-presenting cell.

A

Cells that display foreign antigens on their surface.

119
Q

Comment on the specificity of T-cells.

A

Receptors on each T-cell are complementary to, and respond to only one antigen.

There are a vast number of different T-cells with each one responding to a different antigen.

120
Q

T-cell action is most effective against which type of pathogen? Why?

A

Most effective against viruses, as they need host cells to survive and replicate.

121
Q

Which type of cells are most involved with humoral immunity? Where do they mature?

A

B-cells.

Bone marrow.

122
Q

An ELISA test is carried out to detect the presence of malaria antibodies in the blood. There is no colour change. Explain what this means.

A

Negative result - not infected with malaria. No antibodies in blood to bind with antigen in well. Therefore first and second antibodies have nothing to attach to. Substrate cannot bind to enzyme as not present.​

123
Q

A coloured line appears on the test and control window of a pregnancy test. Explain what this means.

A

Positive test result - pregnant. hCG (pregnancy hormone) has bound to Ab with blue dye attached. This antibody binds to immobilised Abs in test and control window.​

124
Q

What are the body’s specific defence mechanisms (hint: involving lymphocytes)

A
  • cell mediated response involving T-lymphocytes
  • humoral responses involving B-lymphocytes
125
Q

what are the characteristics of specific defence mechanisms?

A
  • specific to each pathogen
  • slower
  • longer lasting
126
Q

How is the body able to be defended from invasion?

A

lymphocytes are able to distinguish the body’s own cells and molecules from those that are foreign

127
Q

what is a non specific defence mechanism?

A

response that is immediate and the same for all pathogens

128
Q

what are the two non specific defence mechanisms?

A
  • physical barrier e.g. skin
  • phagocytosis
129
Q

State two differences between
a specific and a non-specific
defence mechanism

A

non-specific mechanisms repel all microorganisms equally, while the specific immune responses are tailored to a specific pathogen

130
Q

After a pathogen gains entry
to the body it is often a
number of days before the
body’s immune system
begins to control it. Suggest a
possible reason why this is so.

A

The lymphocytes that will finally control the pathogen need to build up their numbers and this takes time.

131
Q

Why would it be inaccurate to say the body takes days to ‘respond’ to the pathogen.

A

The body responds immediately by ‘recognising’ the pathogen (and by phagocytosis). The delay is in building up numbers of lymphocytes and therefore controlling the pathogens.

132
Q

what are the body’s physical defences?

A
  • skin
  • scab formation
  • membranes that line the trachea
133
Q

what are the body’s chemical defences?

A
  • lysozymes in the eyes produced in tears/fluids
  • stomach acid
  • chemical secretions in the skin
134
Q

what is cell recognition?

A

how body cells communicate to recognise each other or recognise foreign material in the body

135
Q

what is a pathogen?

A

a microorganism that causes disease

136
Q

how are phagocytes specialised?

A
  • contain lysosomes which are granules that contain lysozymes
  • lobed nucleus allows cell to be flexible and move freely around pathogens
137
Q

where do T-cells mature?

A

In the thymus

138
Q

What are the body cells that T cells recognise?

A
  • phagocytes as they can become antigen presenting
  • Body cell’s invased by a virus as they oresent viral antigens
  • Transplanted cells that have antigens
  • Cancerous/abnormal cells as they have different antigens
139
Q

Phagocytes and lysosomes are involved in destroying microorganisms. Describe how

A
  • phagocytes engulf the pathogen and form a phagosome around the pathogen
  • lysosomes contain lysozymes (an enzyme) which hydrolyse the microorganism
140
Q

What are the characteristics of a B-cell?

A

Involves ‘free floating’ pathogens within bodily fluids

B-lymphocytes produce antibodies which are soluble in bodily fluids

Directly attack the pathogen itself

141
Q

What is endocytosis?

A

The process of bringing substances into a cell where a vesicle forms around the ingested material

142
Q

Why is the secondary response larger?

A

more B-cells are cloned in secondary response which equals more antibodies secreted

143
Q

Outline the role of cholesterol in the cell surface membrane

A
  • make the membrane more rigid and
    reduce the lateral movement of the
    phospholipids
  • prevents the leakage
    of water and dissolved ions from the cell
144
Q

What is the role of intrinsic proteins?

A

Intrinsic proteins include carrier proteins which allow
substances to cross the membrane.

145
Q

What is osmosis?

A

The diffusion of water molecules from an area of high water potential to an
area to low water potential through a partially permeable membrane.

146
Q

What is the role of the antigen added to the well plate?​

A

detects specific antibodies in the blood serum

147
Q

What is the role of the second (enzyme-linked) antibody that is added?​ (ELISA test)

A

binds to antigen and has enzyme attached

148
Q

Why is washing (step 2 and step 4) important?

A

removes any unbound antibodies and antigens

149
Q

What is the purpose of the attachment protein?

A

binds to complementary receptor

150
Q

What is the role of reverse transcriptase?

A

converts RNA to DNA

151
Q

Outline the steps of HIV Replication

A
  1. After infection, HIV circulates the body in the bloodstream​
  2. One of the attachment proteins binds to a CD4 protein on a T helper cell.​
  3. The lipid envelope fuses with the cell membrane, allowing RNA and enzymes to enter the cell.​
  4. The viral RNA is converted to DNA.​
  5. The newly formed DNA is moved to the cells’ nucleus and inserted into its own DNA.​
  6. mRNA is produced that contains instructions for making new viral proteins.​
  7. Protein synthesis occurs.​
  8. HIV particles break away from helper T cells, using part of the cells’ surface membrane to form a new lipid envelope
152
Q

How do doctors determine if someone has AIDS?

A

Someone with AIDS may only have 200 per mm3​ of T helper cells in the blood compared to 800-1200 in a normal persons blood

153
Q

How do people with AIDS develop a reduced immune response?

A

Low TH cell numbers​

So less stimulation of B cells (less plasma cells = less antibodies)​

Less stimulation of cytotoxic T cells​

Memory cells can also become infected by virus and thus destroyed​

154
Q

Why are antibiotics ineffective against viruses?

A

Viruses are surrounded by a protective protein coating; they don’t have cell walls that can be attacked by antibiotics like bacteria does.

155
Q

How is HIV treated?

A

The treatment for HIV is called antiretroviral therapy (ART). It involves taking a combination of HIV medicines every day. ​

ART is recommended for everyone who has HIV. ​

ART cannot cure HIV, but HIV medicines help people with HIV live longer, healthier lives.​

156
Q

How does HIV medicine work?

A

Prevents HIV from multiplying (making copies of itself), which reduces the amount of HIV in the body (called the viral load).

Having less HIV in the body gives the immune system a chance to recover and produce more CD4 cells.​

157
Q

What is the difference between HIV and AIDS?

A

HIV is the virus that causes AIDS. You cannot get AIDS without having HIV

158
Q

what is immunity?

A

the ability of organisms to resist infection, by protecting against pathogens and toxins.​

159
Q

What is passive immunity?

A

Antibodies obtained from an outside source/no direct contact with antigen.​

160
Q

Give an example of natural passive immunity

A

During breastfeeding, antibodies produced by the mother are passed on to the infant within breastmilk. ​

161
Q

Give an example of artificial passive immunity

A

A dog is taken to the vets with the symptoms of a spider bite. The vet administers an antivenom and the dog recovers within a few hours.​

162
Q

What is active immunity?

A

Direct contact with antigen which stimulates production of antibodies.

163
Q

Give an example of artificial active immunity

A

Vaccination

164
Q

Give an example of natural active immunity

A

A young child contracts a cold from his friends at school and has the common symptoms. His symptoms are gone within a few days.

165
Q

What are the characteristics of active immunity?

A

Antibodies made by immune system​

Long term immunity​

Memory cells produced​

Resistance to disease develops slowly (lag time)​

166
Q

What are the characteristics of passive immunity

A

Immediate resistance to disease​

Short term immunity (Abs are broken down)​

No memory cells​

167
Q

What is a vaccine?

A

a small amount of attenuated pathogen administered into the body that stimulates and immune response ​

168
Q

What is meant by attenuated?

A

still alive/active but doesn’t cause any symptoms of the disease

169
Q

Why does the individual not experience symptoms of the disease within a vaccine? ​

A

Only a small amount of antigens are present

170
Q

Outline the process of vaccination

A

Vaccine administered, containing antigen from a particular pathogen​

Antigen is presented by phagocyte​

Specific helper T cell detects antigen and stimulates specific B cell​

B cell divides and forms plasma cells​

Plasma cells produce antibody ​

Memory cells form​

171
Q

What is herd immunity?

A

occurs when the vaccination of a significant portion of a population provides a measure of protection for individuals who have not developed immunity.​

172
Q

Why might a vaccine not eliminate a disease?

A

Can develop disease right after vaccination (harvesting the pathogen)​

Doesn’t induce immunity in everyone (e.g. defective immune system)​

Pathogen mutates (antigenic variability)​

Varieties of pathogens (e.g. malaria sub-species)​

Pathogens that ‘hide’ in cells or in out of reach places (e.g. intestines)

173
Q

What is meant by antigen variability?

A

Pathogens DNA can mutate frequently ​. If a mutation occurs in the gene which codes for the antigen, then the shape of the antigen will change​

Any natural or artificial immunity will no longer be effective due to the memory cells not being complementary anymore

174
Q

What is the net movement of osmosis determined by?

A

water potential

175
Q

What is water potential?

A

the tendency of water molecules in a system to move. measured in kilopascals

176
Q

What is the water potential of a solution determined by?

A

The amount of solute it contains. The greater the amount of solute, the lower the water potential

177
Q

What is pressure potential?

A

The greater the pressure, the higher the water potential.

In plants, the pressure potential is the result of the cell wall exerting pressure on the cytoplasm

178
Q

How is water potential calculated?

A

solute potential + pressure potential

179
Q

What substance has the highest water potential?

A

Pure water has the highest water potential, and has a value of 0 kPa.
Solutions that have a lower water potential than pure water, and have a negative water potential.

180
Q

Cell A has water potential of -200kPa, cell B has a water potential of -250 kPa, which cell will the water move towards?

A

Cell B as water molecules always move from a region of high water potential to a region of low (more negative) water potential.​

181
Q

How do animal cells react to osmosis?

A

Red blood cells placed in a solution with a higher water concentration compared to their contents (eg pure water) will gain water by osmosis, swell up and burst.

182
Q

What is an isotonic solution?

A

Isotonic solutions have the same solute concentration as the cytoplasm of the cell​

183
Q

What is a hypertonic solution?

A

Hypertonic solutions have a higher solute concentration than the cytoplasm of the cell​

184
Q

What is hypotonic solution?

A

Hypotonic solutions have a lower solute concentration than the cytoplasm of the cell​

185
Q

How do plant cells react to osmosis?

A

Osmosis can affect plant cells by causing them to become turgid or flaccid.
If a plant cell is surrounded by a solution with a higher concentration of solutes than the cytoplasm of the cell (Hypertonic) water will move out of the cell and it will become flaccid

186
Q

What happens if you place an onion cell in a hypertonic solution?

A

full plasmolysis

187
Q

What happens if you place an onion cell in a hypotonic solution?

A

the cell is turgor (makes living plant tissue rigid); may busrt

188
Q

What happens if you place an onion cell in isotonic?

A

incipient plasmolysis (when half of the cells are plasmolysed and half are not plasmolysed.)

189
Q

What is plasmolysis?

A

The process of contraction or shrinkage of the protoplasm of a plant cell and is caused due to the loss of water in the cell.

190
Q

What does crenate mean?

A

shrivel

191
Q

What does flaccid mean?

A

cell lacking turgidity- looks floppy and loose

192
Q

What does protoplast mean?

A

the entire cell, excluding the cell wall

AQA A Level Biology (8 decks)

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