Communicable Diseases

Question 1

State the types of organism that can act as pathogens

Answer 1

1. Bacteria
2. Viruses
3. Protoctists
4. Fungi

Question 2

Describe bacteria and how they act as pathogens

Answer 2

1. Bacteria are prokaryotic cells
2. They can be identified by different shapes (rod, spherical, comma-shaped, spiral, corkscrew)
3. Bacteria can have gram-negative or gram positive cell wall
4. Bacteria can produce toxins which damage host cells
5. Host organism defences towards the bacteria may also cause damage to host cells and tissues

Question 3

Describe viruses and how they act as pathogens

Answer 3

1. Viruses are not cellular organisms
2. They are infectious structures composed of DNA or RNA surrounded by protein
3. They can infect eukaryotic and prokaryotic cells (depending on the type)
4. They enter host cells and use their organelles to produce more viral particles
5. Which go on to infect more host cells
6. This causes destruction of the infected cells

Question 4

Describe fungi and how they act as pathogens

Answer 4

1. Fungi are eukaryotic organisms that can be uni- or multicellular
2. Fungi are not autotrophic so need to obtain nutrients from their environment
3. They release digestive enzymes onto their host organism
4. And absorb the digestion products in order to grow and carry out respiration
5. Digestion of host cells and tissues causes harm to the host organism
6. Some fungi also produce toxins

Question 5

Describe protoctists and how they act as pathogens

Answer 5

1. Protoctists are unicellular eukaryotic organisms
2. Some protoctists act as pathogens of plant or animal organisms
3. Pathogenic protoctists infect cells and use the cellular contents as their nutrition to grow and multiply
4. They burst out of the host cell and infect other cells

Question 6

Give examples of bacterial pathogens and the diseases they cause

Answer 6

Question 7

Give examples of viral pathogens and the diseases they cause

Answer 7

Question 8

Give examples of fungal pathogens and the diseases they cause

Answer 8

Question 9

Give examples of protoctist pathogens and the diseases they cause

Answer 9

Question 10

State the main types of direct transmission of pathogens between host organisms

Answer 10

1. Direct transmission is when the pathogen is transferred directly from one host body to another. Ways in which direct transmission can occur are:
2. Direct contact, including kissing, skin-to-skin contact, from faeces to hands
3. Inoculation, including through breaks in skin, animal bites, sharing needles
4. Ingestion, including contaminated food or drink, transfer from hands to mouth
5. In plants, direct contact can be from part of an infected plant to another

Question 11

State the main types of indirect transmission of pathogens between host organisms

Answer 11

1. Indirect transmission is the transfer of pathogen from one individual to another, that requires some surface, substance or organism. Examples are:
2. Fomites, inanimate objects such as clothing or door handles that transfer the pathogen between individuals
3. Droplet infection, is where mucus droplets from one infected individual are inhaled by another
4. Vectors are substances or organisms in which the pathogen can be moved from an infected individual to an uninfected one. Examples include:

• Wind
• Water
• Animals
• Human transfer (through clothing, machinery, skin)

Question 12

State the factors which affect the transmission of communicable diseases in animals

Answer 12

1. Overcrowding
2. Poor nutrition
3. Weak or weakened immune system (very young or elderly individuals)
4. Poor waste disposal
5. Climate change
6. Culture and infrastructure
7. Socioeconomic factors

Question 13

State the factors which affect the transmission of communicable diseases in plants

Answer 13

1. Some crop varieties are genetically susceptible to disease
2. Planting too close together
3. Poor mineral supply can reduce plant health
4. Damp, warm conditions may favour pathogens
5. Climate change (more rain, more wind: more vector)

Question 14

Describe how plant cells may detect and make a response to a pathogen

Answer 14

1. Substances produced by the pathogen are detected by the receptor proteins in plant cell membranes
2. Signaling molecules are produced inside the plant cell that alert the nucleus
3. Nucleus activates production of physical or chemical defences
4. This can prevent the spread of pathogen to uninfected parts of the plant

Question 15

Describe the physical defences of plant cells to pathogens

Answer 15

1. Plant cells deposit more of the carbohydrate callose between cell walls
2. Callose blocks the sieve plates in the phloem
3. Callose blocks the plasmodesmata between plant cells
4. This prevents uninfected cells from getting infected
5. Lignin is then also deposited in the cell walls
6. These processes strengthen barriers between cells to prevent the spread of the pathogen

Question 16

Describe the chemical defences of plants

Answer 16

1. Chemical defences are substances produced by plants that act against the sources of infection or damage
2. Examples include:

• Insect repellents
• Insecticides
• Antibacterial compounds
• Antifungal compounds
• Anti-oomycetes (act against protoctist pathogens)
• General toxins (produced at levels only harmful to pathogens)

Question 17

Describe the non-specific defences of animals that prevent the entry of pathogens

Answer 17

1. Skin, a physical barrier that prevents pathogens from accessing living cells and tissue underneath
2. Mucous membranes which:
3. Lysozyme is present in body fluids such as tears, urine
   
   1. Trap and remove pathogens in mucus
   2. Release lysozyme to break down pathogen cell walls
   3. Contain many phagocytes
4. Gut and skin bacteria that prevent the survival of pathogens
5. Highly acidic environment in the stomach
6. Expulsive reflexes that allow removal of pathogens trapped in mucus

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Question 18

Describe how blood clotting reduces the risk of infection

Answer 18

1. A cut to the skin breaks open a blood vessel
2. Exposed collagen fibres activate platelets in the blood
3. Activated platelets release thromboplastin
4. Thromboplastin causes prothrombin (inactive) to be converted into thrombin (active)
5. Thrombin converts soluble fibrinogen into insoluble fibrin
6. Creating a mesh of fibrin that traps erythrocytes and more platelets that forms a clot
7. This seals the skin, and prevents the entry of pathogens into the blood
8. Epidermal cells divide and move to reform the skin

Question 19

Describe how an inflammatory response reduces the risk of infection

Answer 19

1. Damage or pathogens are detected by mast cells in the tissue
2. Mast cells release histamine
3. Histamine causes vasodilation, increases blood flow to area
4. Histamine causes capillaries to become more permeable
5. Plasma and phagocytes exit the blood (neutrophils and macrophages)
6. Phagocytes internalise and digest pathogen (phagocytosis)
7. Increased fluid in tissue drains pathogens into lymphatic system, to be destroyed at lymph nodes

Question 20

Describe the events of phagocytosis

Answer 20

1. Phagocytes are neutrophils and macrophages
2. Phagocytes are activated by detection of non-self antigens
3. Phagocytes engulf pathogens by extending their cell surface membrane around them
4. This forms a compartment inside the phagocyte called the phagosome
5. Lysosomes then combine with the phagosome, forming the phagolysosome
6. Digestive enzymes then break up the pathogen into smaller, harmless fragments
7. These fragments (antigens) are then presented on the surface of the phagocyte
8. Phagocytes are then acting as antigen-presenting cells (ready to activate the specific immune response)

Question 21

Describe the identifying features of blood cells

Answer 21

Question 22

Describe how cytokines are involved in the functioning of phagocytes

Answer 22

1. Phagocytes can release cytokines
2. Cytokines act as cell signalling molecules
3. Cytokines act to recruit and activate more phagocytes in the local area
4. Cytokines can raise the body temperature
5. Cytokines can also activate cells of the immune system

Question 23

Describe the role of opsonins in the non-specific defences of mammals

Answer 23

1. Opsonins are molecules that can bind non-self antigens as well as phagocytes
2. They therefore help the process of phagocytosis to occur more effectively

Question 24

Describe the key steps involved in developing cell-mediated immunity

Answer 24

1. A T helper cell, with a T cell receptor complementary to a specific antigen on the antigen-presenting cell is activated (clonal selection)
2. The activated T helper cell undergoes many cycles of mitosis producing many copies of that particular T helper cell (clonal expansion)
3. Some T helper cells also differentiate into different T cell types:
4. T killer cells, which identify and kill infected cells
5. T memory cells, which have a longer lifespan and allow a quicker response if reinfection occurs
6. The T killer cells use their TCR to identify infected cells
7. Once they bind to an infected cell, they release chemicals to kill that cell
8. Preventing further growth and multiplication of the pathogen
9. T cells can also stimulate phagocytosis and raise body temperature by releasing cytokines

Question 25

Describe the key steps involved in developing humoral immunity

Answer 25

1. A range of B cells exist, each displaying a different antigen on their surface 2. An activated T helper cell (with a complementary TCR) will bind a particular clone of B cell (clonal selection) 3. The T helper cell releases interleukins to stimulate mitosis and differentiation of that B cell (clonal expansion) 4. The B cells differentiate into: 1. plasma cells that produce a specific type of antibody towards the antigen 2. B memory cells that have a longer lifespan and can make a quicker response if reinfection occurs 5. Antibodies produced by the plasma cells act to neutralise or destroy the pathogen

Question 26

Describe the structure of antibodies

Answer 26

1. Antibodies are globular proteins 2. They have a quaternary structure of 4 polypeptides 3. Two heavy chains 4. Two light chains 5. Connected by disulfide bonds at the hinge region 6. The two variable regions are made up of both heavy and light chains and are specific and complementary to a particular antigen 7. The constant region is made of the two heavy chains and bind receptors on phagocytes

Question 27

Describe the function of antibodies

Answer 27

1. Antibodies act to neutralise or cause the destruction of pathogens 2. Their variable region is responsible for specific binding to particular antigens 3. Their constant region is for binding to phagocytes and stimulating phagocytosis 4. They act in a number of ways: 1. By binding to surface proteins of pathogens they prevent them from infecting cells (neutralisation) 2. Each antibody can bind multiple pathogens and cause their ‘agglutination’. This neutralises them. 3. By binding to phagocytes, antibodies can increase the phagocytosis of pathogen (opsonins) 4. By binding to toxins, antibodies can reduce their toxic effects (antitoxins)

Question 28

Describe and explain the differences between primary and secondary immune responses

Answer 28

1. Primary immune response occurs upon first exposure to an antigen 2. The clonal selection and clonal expansion processes take time 3. So the generation of antibodies occurs after a delay, and the quantity produced is small 4. Symptoms of disease and fever may be experienced 5. The secondary immune response is made by T memory and B memory cells 6. They are able to make a bigger and faster response to the antigen 7. Symptoms of disease and fever may not be experienced

Question 29

Describe active and passive immunity

Answer 29

1. Active immunity involves the activation of the specific immune response including the production of antibodies towards a non-self antigen. 2. Active Immunity provides long term protection 3. Passive immunity is the immunity conferred by the presence of antibodies that were not made by the individual, but acquired from a different individual or organism 4. Passive immunity provides short term protection

Question 30

Describe natural and artificial immunity

Answer 30

1. Natural immunity is the immunity (presence of antibodies) that has occurred through naturally occurring life processes 2. Artificial immunity is the immunity (presence of antibodies) that has occurred through non-natural processes

Question 31

Give examples of each type of immunity

Answer 31

Question 32

Describe and give examples of autoimmune diseases

Answer 32

1. A dysfunction of the immune system 2. Where self-antigens are mistaken for non-self antigens 3. An immune response is mounted to certain cells and tissues, resulting in them not working properly 4. Examples are: 1. Type I diabetes, where beta cells of the pancreas are destroyed 2. Rheumatoid arthritis, in which the joint tissues are affected 3. Lupus, where are range of body tissues and organs can be affected

Question 33

Explain how a vaccine gives long term immunity

Answer 33

1. A harmless version of pathogen or ‘safe antigens’ are injected into the blood 2. A primary immune response is made 3. Antibodies and memory cells are produced 4. If infected by the actual pathogen 5. The memory T and B cells are used to make a faster and greater secondary response 6. To clear the pathogen before it causes symptoms

Question 34

State the ways in which the antigens of pathogens can be made safe

Answer 34

1. Heat or chemically denatured bacteria or virus 2. Attenuated (weakened) live bacteria or virus 3. Inactivated toxins released by the pathogen 4. Isolated specific antigens of the bacteria or virus such as surface proteins 5. Genetically created antigens, designed to be similar to actual antigens

Question 35

Explain how vaccination programs can prevent epidemics

Answer 35

1. A large number of people must be vaccinated 2. Each person vaccinated has long term immunity 3. People who are immune cannot transmit the disease 4. If a high enough proportion of the population are immunised, the transmission of a disease can be limited 5. So that even non-immunised people are ‘protected’ from the disease 6. This is known as herd immunity

Question 36

Explain why many immunisations need to be routinely administered

Answer 36

1. Immunity is not lifelong 2. Memory cells have a very long but limited lifespan 3. Pathogens undergo mutation and other processes which change their antigens so they are no longer recognised by memory cells 4. Pathogens need to be monitored, and vaccines updated to match their antigens

Question 37

Summarise how living organisms can be sources of medicines (and therefore why it’s important to maintain Earth’s biodiversity)

Answer 37

1. Living organisms produce chemical substances that increase their chance of survival in their habit and community 2. Some of these substances also have beneficial impact on human/animal health 3. Sources can include microorganisms (bacteria and fungi), plants and animals 4. Many of these may not yet have been discovered 5. Therefore it is important that species diversity is maintained, so we do not lose species with medicinal value

Question 38

Give examples of naturally sourced medicines

Answer 38

Question 39

Describe the various research-based approaches to drug design

Answer 39

1. Genetic analysis of pathogen genomes can identify proteins that could be targeted for inhibition 2. Computers/software can be used to design molecules that will complement the 3D shape of pathogen proteins to inhibit their growth 3. Use of a person’s genetic information to determine the drug treatment that will be most effective (personalised medicine) 4. Synthetic biology is genetic manipulation of biological systems for drug production

Question 40

State the benefits of using antibiotics

Answer 40

1. Antibiotics disrupt the metabolic activity of bacteria preventing their growth and reproduction, so can be used to treat bacterial diseases 2. They have selective toxicity, which means they affect bacteria without causing harm to humans 3. They are relatively cheap to produce and widely available 4. There are various types which can be used to target many different pathogenic bacteria

Question 41

Describe the ways in which antibiotics can work

Answer 41

Antibiotics, depending on their type can: 1. Weaken bacterial cell walls 2. Disrupt the metabolic reactions 3. Inhibit protein synthesis 4. Make holes in the cell membrane

Question 42

Explain how abuse of antibiotics can result in antibiotic resistance

Answer 42

1. Abuse of antibiotics exposes populations of bacteria to a selection pressure 2. Many bacteria may be killed but due to genetic variation, some bacteria may have partial resistance 3. As many non-resistant bacteria are killed, there is much less competition for the remaining bacteria 4. Partially resistant bacteria can now freely reproduce, increasing the number of resistant bacteria 5. Continual exposure to the antibiotic will thus increase the level of resistance in the bacterial population 6. For example methicillin-resistant staphylococcus aureus 7. For example clostridium difficile which undergoes overproliferation in the gut when other gut bacteria are killed by antibiotics

Question 43

Describe how the problem of antibiotic resistance is being addressed

Answer 43

1. Minimising the use of antibiotics 2. Ensuring the completion of courses of antibiotics 3. Extra hand-washing in hospitals to prevent transmission and growth of bacterial populations 4. Searching for new antimicrobial compounds 5. Testing for bacterial infections, so the right antibiotics are used in each treatment regime