4.1.1 - Communicable Diseases, Disease Prevention and the Immune System

Question 1

What are the 4 different pathogens?

Answer 1

• Bacteria
• Virus
• Fungi
• Protoctista

Question 2

Which diseases are caused by bacteria?

Answer 2

• Tuberculosis
• Bacterial meningitis
• Ring rot (potatoes and tomatoes)

Question 3

Which diseases are caused by viruses?

Answer 3

• HIV/AIDS
• Influenza
• Tobacco Mosaic Virus

Question 4

Which diseases are caused by protoctista?

Answer 4

• Malaria
• Potato/tomato late blight

Question 5

Which diseases are caused by fungi?

Answer 5

• Black Sigatoka (bananas)
• Ringworm (cattle)
• Athlete’s foot

Question 6

How are pathogens directly transmitted in animals?

Answer 6

• Direct contact - touching, kissing, contact with cuts in skin and sexual contact
• Inoculation - animal bites, sharing needles and cuts in skin
• Ingestion - drinking and eating contaminated water and food

Question 7

How are pathogens indirectly transmitted in animals?

Answer 7

• Vectors - animals that pass the pathogen to humans such as mosquitoes
• Droplets - pathogens transmitted in droplets of water such as saliva
• Fomites - dirty bedding, socks and cosmetics

Question 8

How are pathogens directly transmitted in plants?

Answer 8

• Direct contact between different plants

Question 9

How are pathogens indirectly transmitted in plants?

Answer 9

• Contaminated soil - pathogens and their spores can remain in the soil and infect the roots
• Vectors - wind, water, animals and humans can carry pathogens and spores from one plant to another

Question 10

How can the transmission of communicable diseases be increased in humans?

Answer 10

By social factors such as poorer sewage infrastructure, a lack of fresh water and food, poorer sanitation and overcrowding. Medicines and vaccines being less readily available to prevent the spread.

Question 11

How can the transmission of communicable diseases be increased in plants?

Answer 11

Hot climates provide more kinetic energy for chemical reactions and reproduction

Question 12

What are plant defences against pathogens?

Answer 12

• Barriers to prevent entry such as bark or waxy cuticles
• Antibacterial chemicals and proteins as a defence against bacterial infections which can repel insects and kill pathogens
• Physical defences to prevent pathogens from spreading between their cells such as producing callose which blocks the pores in phloem sieve plates between phloem sieve tubes

Question 13

What are primary non specific animal defences against pathogens?

Answer 13

• Skin - tough waterproof outer layer made up of dead keratinocytes
• Mucous membranes - lined with mucus which traps pathogens and the cilia sweep the mucus away
• Chemical defences - lysozyme in tears, hydrochloric acid in the stomach
• Blood clotting - a mesh of protein fibres and blood cells form a scab to prevent pathogen entry through broken skin
• Inflammation - mast cells release histamines which causes capillaries to dilate and attract white blood cells to the affected area
• Wound repair - cells at the wound edge divide to repair damage to the skin
• Expulsion reflexes - coughing and sneezing in response to irritation of the airways

Question 14

What are the two types of phagocytes?

Answer 14

• Neutrophils - multi lobed nucleus, short lived, found in large numbers during infections
• Macrophages - larger than neutrophils, can display pathogen antigens on their surfaces after phagocytosis and become antigen-presenting cells

Question 15

What happens during phagocytosis?

Answer 15

• Damaged cells and pathogens release cytokines that attract the phagocytes to the site of the infection
• Opsonins attach to pathogens to mark them and make it easier for neutrophils and macrophages to engulf them
• Phagocytes have receptors which can attach onto chemicals on the surface of pathogens
• The phagocyte then engulfs the pathogen into a vesicle to create a phagosome
• Within the phagocytes there are lysosomes which contain hydrologic lysozyme enzymes
• The lysosome fuses with the phagosome to expose the pathogen to the lysozyme. The lysozyme hydrolyses the pathogen and any soluble useful molecules are absorbed into the cytoplasm of the phagocyte
• Macrophages will present the antigen of the digested pathogen on their surface called antigen presenting cells
• The phagocyte secretes cytokines which act as messenger molecules attracting more phagocytes to the area

Question 16

What are the two types of lymphocytes?

Answer 16

• T lymphocytes
• B lymphocytes

Question 17

Where are T and B lymphocytes produced?

Answer 17

They are both produced in the bone marrow but T cells mature in the thymus and B cells mature in the bone marrow.

Question 18

What happens during the cell mediated response?

Answer 18

• The antigen presenting cell presents the pathogen’s antigens to T helper cells
• The antigens bind to complementary receptors on one type of T helper cell which is clonal selection
• Once attached interleukins are produced which activates the T helper cells to divide by mitosis to replicate and make large numbers of clones which is clonal expansion
• T helper cells produce interleukins to activate B lymphocytes or to stimulate macrophages to perform more phagocytosis
• T helper cells differentiate into T memory cells, T killer cells which destroy abnormal cells by making holes in their cell surface membranes or T regulator cells which suppress the immune response by inhibiting cytokine production to ensure the cell mediated response only occurs when pathogens are detected

Question 19

What happens during the humoural response?

Answer 19

• T helper cells bind to the antigens, stimulate B cells to divide by mitosis and differentiate into short lived plasma cells and long lived memory cells
• The plasma cells produce complementary antibodies to the antigens which is the primary immune response and the infected person will show symptoms until the pathogen is destroyed
• When the memory cells come into contact with the antigen again they divide rapidly to form plasma cells and memory cells.
• The plasma cells rapidly produce high levels of antibodies so the pathogen is destroyed before the person feels unwell which is the secondary immune response

Question 20

What is the structure of an antibody?

Answer 20

• Globular quaternary proteins that have binding sites complementary in shape to antigens
• They are made up of four polypeptide chains, two heavy and two light
• They are arranged in a Y shape and held together by disulphide bridges
• The binding site is the variable region where the antibody binds to a complementary shaped antigen
• The rest of the antibody is the constant region

Question 21

What are the 3 functions of antibodies?

Answer 21

• Agglutination which is the clumping together of pathogens to make it easier for phagocytes to locate and engulf them
• Neutralisation which blocks the adhesion of bacteria and docking of viruses to cells blocking activity of toxins
• Opsonisation which is coating antigens with antibodies making them more susceptible to phagocytosis

Question 22

What is natural immunity?

Answer 22

The body’s ability to recognise, neutralise or destroy non-self substances

Question 23

What is artificial immunity?

Answer 23

Gained through deliberate exposure to antigens or antibodies

Question 24

What is active immunity?

Answer 24

Immunity gained through activation of the immune system creating memory cells

Question 25

What is passive immunity?

Answer 25

Immunity gained through antibodies which have been made externally

Question 26

What is an example of natural active immunity?

Answer 26

Natural exposure to the antigens on pathogens and making memory cells

Question 27

What is an example of natural passive immunity?

Answer 27

Antibodies transferred from mother to baby via breast milk and placenta

Question 28

What is an example of artificial active immunity?

Answer 28

Immune response by exposure to a dead or weakened pathogen and production of memory cells

Question 29

What is an example of artificial passive immunity?

Answer 29

Antibodies made by another organism

Question 30

What is an autoimmune disease?

Answer 30

When your immune system identifies your own body cells as foreign which results in your white blood cells attacking your own body cells

Question 31

What are two examples of autoimmune diseases?

Answer 31

• Rheumatoid arthritis - the immune system attacks the cartilage in joints which can cause inflammation and pain
• Lupus - causes inflammation to joints, skin and organs and causes fatigue

Question 32

What is a vaccination?

Answer 32

The introduction of a substance containing appropriate antigens into the body to stimulate artificial active immunity against a pathogen

Question 33

What are routine vaccinations?

Answer 33

They are vaccinations given to babies starting at 8 weeks of age with the 6 in 1 vaccine for diphtheria, whooping cough, hep B, polio, tetanus and flu

Question 34

When are vaccination programmes introduced?

Answer 34

Some pathogens cause a pandemic which is a large scale global outbreak so vaccination programmes are set up to target those people most at risk

Question 35

Why do new vaccines need to be developed?

Answer 35

Some pathogens mutate and change their antigens. When this happens a new vaccine needs to be developed against the new strain of pathogen to ensure antibodies are made for the new antigen.

Question 36

What are possible sources of medicines?

Answer 36

Many microorganisms and plants are sources of medicines such as aspirin from willow bark so maintaining biodiversity is key.

Question 37

What are personalised medicines?

Answer 37

When a person’s genotype is used to choose the best treatment. DNA sequencing and clinical information can provide individual treatment plans using medicines and lifestyle choices.

Question 38

What is synthetic biology?

Answer 38

It involves using genetically modified bacteria or animals and nanotechnology to produce drugs that might be rare, expensive or difficult to make.

Question 39

How do antibiotics kill bacteria?

Answer 39

• Preventing cell wall synthesis by inhibiting the enzymes responsible for making molecules in the cell walls. The bacteria die from the leakage of contents or from too much water entering
• Disrupting cell membranes by binding to the phospholipids to distort the structure and make the membrane too permeable
• Interfering with protein synthesis by attaching onto the bacterial ribosomes which prevents protein synthesis

Question 40

What factors contribute to bacteria becoming resistant to antibiotics?

Answer 40

• Using antibiotics to treat minor ailments
• Patients not completing courses of antibiotics
• Doctors prescribing antibiotics unnecessarily in response to patient demand
• Use of antibiotics in intensive farming to prevent infections

Question 41

What is an example of an antibiotic resistant infection?

Answer 41

MRSA