communicable diseases SLOP

Question 1

State the kingdom of organism that causes each of the following diseases: tuberculosis, Black Sigatoka, Athlete’s foot, malaria

Answer 1

Bacteria, fungi, fungi, protoctists

Question 2

State the kingdom of organism that causes each of the following diseases: blight, ringworm, ring rot, bacterial meningitis

Answer 2

Protoctists, fungi, bacteria, bacteria

Question 3

Give one plant disease caused by each of the following: viruses, bacteria and fungi

Answer 3

Tobacco mosaic virus, ring rot, black sigatoka

Question 4

State three factors that would affect the speed of disease transmission in plants

Answer 4

Overcrowding; poor mineral nutrition; damp, warm, humid conditions; climate change

Question 5

State how the influenza virus is most likely to be transmitted between different humans

Answer 5

Respiratory droplets (inhalation)

Question 6

State four different types of vector that can be used to transmit a communicable disease

Answer 6

Water (e.g. diarrhoeal diseases); animals (e.g. mosquito transmits Plasmodium); wind (carries spores); humans (hands, clothing etc.)

Question 7

State three passive physical defences that prevent plants being infected by a pathogen

Answer 7

Bark, waxy cuticle, thorns, spines, lignified cell walls, cellulose etc.

Question 8

State three active physical defences a plant would employ against an invading pathogen

Answer 8

Callose synthesised and deposited between plasma membrane and cell wall; callose blocks sieve plates in phloem; callose deposited in plasmodesmata between infected cells and their neighbours; lignin added to cell walls; tyloses block xylem vessels

Question 9

State three chemical defences a plant would employ against an invading pathogen

Answer 9

Antibacterial compounds like phenols, alkaloids; terpenes; hydrolytic enzymes like glucanases and chitinases; caffeine; tannins etc.

Question 10

Describe the role of the skin as a primary non-specific defence

Answer 10

Dead outer layer of keratin prevents pathogen entry; skin flora outcompete pathogens for space; oil secretions inhibit pathogenic growth

Question 11

Describe the role of mucous membranes as a primary non-specific defence

Answer 11

Mucus traps pathogens and contains lysozymes; phagocytes engulf and digest pathogens in mucus

Question 12

Which enzyme catalyses the conversion of prothrombin to thrombin

Answer 12

Thromboplastin (thrombokinase)

Question 13

Describe the role of thrombin in the clotting process

Answer 13

Causes the conversion of soluble fibrinogen into insoluble fibrin fibres

Question 14

Describe the process of inflammation as a secondary non-specific response

Answer 14

Mast cells release histamines; histamines increase permeability of capillaries meaning plasma leaks into tissue fluid (pain and swelling); vasodilation of arterioles so more blood reaches infected area (heat and redness); neutrophils attracted to area for enhanced phagocytosis

Question 15

Describe the process of phagocytosis

Answer 15

Phagocyte engulfs pathogen into a phagosome; lysosomes fuse with phagosome to form a phagolysosome; enzymes, hydrogen peroxide and nitric acid break down the pathogen

Question 16

Describe how macrophages process antigens for presentation on their cell surface membrane

Answer 16

Antigen fragments combined with MHC (special glycoproteins in cytoplasm)

Question 17

What name is given to small protein molecules that act as cell-signalling compounds?

Answer 17

cytokines

Question 18

Describe how neutrophils are specialised for their role

Answer 18

Plasma membrane contains receptors for opsonins, well developed cytoskeleton for phagocytosis, many mitochondria for respiration, many ribosomes to make enzymes, many lysosomes, many Golgi

Question 19

Opsonins are non-specific. Explain why

Answer 19

Opsonins can attach to many types of pathogen and help the process of phagocytosis, by giving the phagocyte something to bind to. They must be non-specific, so they can attach to many different pathogens.

Question 20

Where do B lymphocytes and T lymphocytes mature?

Answer 20

Bone marrow and thymus respectively

Question 21

What is meant by the term ‘autoimmunity’ and give two examples of autoimmune diseases

Answer 21

Destruction of self-tissue; rheumatoid arthritis, lupus, type I diabetes

Question 22

What is the role of T regulatory cells?

Answer 22

Dampen down the immune response; prevents destruction of self tissue (autoimmunity)`

Question 23

Describe how an antigen presenting cell leads to large numbers of T helper cells

Answer 23

APC binds specifically to a T helper cell (clonal selection). This selected T helper cell then proliferates by mitosis (clonal expansion)

Question 24

Describe how B lymphocytes are activated and the role of activated B lymphocytes

Answer 24

The cell binds specifically to B lymphocyte; B lymphocyte differentiates into a plasma cell. Plasma cells release antibodies specific to the particular antigen

Question 25

Describe how T killer cells destroy a virally infected cell

Answer 25

Release perforins which punch holes in the membrane of the cell; T killer cell inserts channels through which it floods hydrogen peroxide/nitric acid/hydrolytic enzymes

Question 26

Distinguish clearly between an antigen and an antibody

Answer 26

An antigen is a cell-surface molecule that is specific to the cell (and a particular antibody); an antibody is an immunoglobulin manufactured by the plasma cells (which binds specifically to an antigen).

Question 27

Antibodies are made by plasma cells. Explain how plasma cells are specialised for their role

Answer 27

Plasma cells have a lot of ribosomes, rough endoplasmic reticulum, Golgi apparatus and mitochondria.

Question 28

Describe how opsonins function

Answer 28

Opsonins bind specifically to an antigen on a pathogen (via the variable region), clearly marking the pathogen for destruction by a neutrophil. A neutrophil will bind to the constant region of the opsonin and destroy the pathogen by phagocytosis

Question 29

Describe how agglutinins function

Answer 29

Agglutinins cross link pathogens by binding specifically via their variable regions. Pathogens are clumped together (agglutinated), meaning they cannot enter host cells and are easier to phagocytose

Question 30

Describe how antitoxins function

Answer 30

Neutralise toxin molecules released by a pathogen through direct binding

Question 31

Describe how the structure of an antibody enables it to perform its function

Answer 31

• The variable region is specific to the antigen
• it has a shape that is complementary to the shape of the antigen
• the disulfide bridges hold the four polypeptide chains together
• the hinge region allows some flexibility so that the molecule can bind to more than one antigen
• the constant region may have a shape that can be recognised by the neutrophils.

Question 32

Explain why it may take several days for the primary immune response to become effective

Answer 32

After infection, the pathogen must be detected and attacked by macrophages; antigen presentation occurs to select the correct B and T cells (clonal selection); these cells must reproduce in clonal expansion; then they must differentiate to form plasma cells; the plasma cells must start to produce the antibodies – each step takes time.

Question 33

Explain why a secondary immune response is so much faster than a primary immune response

Answer 33

B memory and T memory cells are circulating in the blood. On second encounter with a pathogen, the correct B/T memory cell is clonally selected and can very quickly differentiate into correct specific T helper/T killer/plasma cell. Plasma cells can produce antibodies faster, sooner and in much greater quantity. Pathogens are wiped out before symptoms are experienced; level of antibody stays higher for longer

Question 34

Give an example of both natural active immunity and natural passive immunity

Answer 34

Natural active - antibodies made by immune system in response to infection; natural passive - antibodies provided via placenta/breast milk (useful in developing immune system)

Question 35

Explain why passive immunity only provides short-term immunity

Answer 35

Passive immunity is provided by an external supply of antibodies – these are proteins and will not last long in the body. They may even act as antigens and be attacked by antibodies from our immune system.

Question 36

Give an example of artificial active immunity

Answer 36

Immunity provided by antibodies made in response to vaccination (dead/inactive pathogens injected)

Question 37

Define the term epidemic

Answer 37

A rapid spread of disease through a high proportion of a population (usually within a country)

Question 38

Describe the difference between herd vaccination and ring vaccination

Answer 38

Herd vaccination is where everyone, or almost everyone, is vaccinated. Ring vaccination is vaccinating people around the site of the outbreak, so that the pathogen will not be transmitted across that ring to the whole population.

Question 39

Describe how a microorganism can become resistant to an antibiotic

Answer 39

Bacteria that survive a treatment will be slightly resistant to the antibiotic and the antibiotic acts as a selective force which selects the resistant individuals. When they reproduce, some of their offspring may be more resistant, thus resistance evolves.

Question 40

what is the difference between b cells and t cells

Answer 40

• T cells are responsible for cell-mediated immunity.
• B cells, which mature in the bone marrow, are responsible for antibody-mediated immunity.
• The cell-mediated response begins when a pathogen is engulfed by an antigen-presenting cell, in this case, a macrophage.