4.1 communicable diseases

Question 1

What is a pathogen?

Answer 1

disease-causing organism

Question 2

What is a host body?

Answer 2

The environment in which the pathogens live. They live by taking nutrition from the host and cause damage in the process

Question 3

How do protoctista cause disease?

Answer 3

They cause harm by entering the host cells and feeding on the contents as they grow.

Question 4

How viruses cause infection

Answer 4

They Invade cells and take over the genetic machinery and organelles of the cell. The viruses make copies of themselves until the cell bursts and releases the virus to infect other cells.

Question 5

How do fungi cause infection in plants?

Answer 5

Fungi infect vascular tissue and extract nutrients by releasing extra cellular enzymes that digest surrounding tissues

Question 6

How do fungi cause disease in animals?

Answer 6

Most common fungal infections are where the fungal hyphae form a mycelium under the surface of the skin. These can grow to release spores, which cause irritation and redness.

Question 7

How do bacteria cause disease?

Answer 7

In the right conditions, bacteria can reproduce every 20mins. Once in a host, they cause disease by damaging cells or by releasing waste products or toxins that are toxic to the cell

Question 8

What is direct transmission?

Answer 8

Passing a pathogen from host to new host, with no intermediary. This can happen via droplet infection, sexual inter course or touching an infected oerson

Question 9

What is indirect transmission?

Answer 9

Passing a pathogen from host to new host, via an intermediary. Such as air, water, food or a vector.

Question 10

How does the blood clot?

Answer 10

Clotting Factors are released. Platelets bind to the collagen and a temporary plug is formed. Inactive thrombokinase in the blood becomes active and the presence of this means prothrombin in the blood becomes active thrombin. this means soluble fibrinogen in the plasma becomes insoluble fibrin. Fibres attach to the platelets forming a plug and the blood clots.

Question 11

How does callous help in a plant?

Answer 11

It is a large polysaccharide that is deposited in the sieve tubes at the end of the growing season. deposited around the sieve plates and blocks the flow in the sieve tube. this can prevent the pathogen spreading around the plant is also deposited between plasmodesmata.

Question 12

How does tylose formation help a plant?

Answer 12

This is balloon like swelling that fills the xylem vessels so that it can no longer carry water. this prevents the spreading through the vessel. the tylose also contains a high concentration of chemicals toxic to pathogens

Question 13

What are defensins?

Answer 13

Small cysteine rich proteins with broad antimicrobial action. they act on molecules in the plasma membrane of pathogens

Question 14

What is an alkaloid?

Answer 14

N containing compounds e.g. caffeine. it gives it a bitter taste to inhibit herbivore feeding and inhibit/activate enzyme action. helps reduce damage from pathogens that enter after grazing

Question 15

What are phenols?

Answer 15

Antibiotic/antifungals. Tannins inhibit attack by insects. they bind to salivary proteins and digestive enzymes to deactivate them. insects that ingest large volumes of tannins do not grow and will eventually, die thereby reducing transmission by pathogens

Question 16

What are terpenoids?

Answer 16

A range of essential oils that have antibacterial and anti-fungal properties. Eg menthols produced by mint plants

Question 17

How does the skin prevent disease?

Answer 17

The cells at the surface cells dry out and the cytoplasm is replaced by keratin known as keratinisation. The dead cells act as a barrier.

Question 18

How does blood clotting prevent disease?

Answer 18

Clotting temporarily seals wounds. Clotting factors activate an enzyme cascade that makes insoluble fibrin.

Question 19

How does the mucous membrane prevent disease?

Answer 19

Goblet cells in epithelial cells produce mucus to trap pathogens. Ciliated epithelium waft the mucus up the trachea to the top of the oesophagus. Pathogens in mucus swallowed into the digestive system

Question 20

How do expulsive reflexes prevent disease?

Answer 20

Sudden expulsion of air carried away irritation micro organisms

Question 21

How does inflammation prevent disease?

Answer 21

Specialised cells release cell signalling histamine which causes vasodilation, capillaries become more permeable to white blood cells which enter tissue fluid and cause swelling.

Question 22

What are the 3 regions of an antibodies and what do they do?

Answer 22

Variable region has a specific shape that is complimentary to the antigens. The constant region is the same in all antibodies, it has an easy binding site for phagocytic cells. The hinge region makes it more flexible.

Question 23

What are opsonins?

Answer 23

They bind to antigens. Phagocytes can bind to the constant region of the antibody and phagocytosis can occur.

Question 24

What are agglutinins?

Answer 24

As there are two binding sites of the variable region, it is able to cross link pathogens by binding an to two antigens.

Question 25

What are antitoxins?

Answer 25

Some antibodies attach to molecules released by pathogenic cells. These molecules may be toxic and in such renders the toxin harmless.

Question 26

What is herd immunity?

Answer 26

When the majority of the population has been vaccinated, which provides protection for those who haven’t been vaccinated as the pathogen cannot spread.

Question 27

How does a vaccination work?

Answer 27

An attenuated version of the pathogen is injected into someone. A macrophage engulfs the pathogen to form a phagosome and digest it. The phagosome becomes an antigen presenting cell which triggers the immune response and memory cells are made.

Question 28

What is natural active immunity?

Answer 28

Immunity provided by antibodies made by the immune system from an infection

Question 29

What is artificial active immunity?

Answer 29

Immunity provided by antibodies made in the immune system from vaccinations.

Question 30

What is natural passive immunity?

Answer 30

Immunity provided by breast milk or via the placenta. This makes the baby immune to diseases that the mother is immune to.

Question 31

What is artificial passive immunity?

Answer 31

Immunity provided by an injection of antibodies made by another individual.

Question 32

What is the specific immune response?

Answer 32

Macrophages will fight off the pathogen and from an antigen presenting cell. An opsonin attaches to the pathogen and monokines cause T cell differentiation (colonal selection). Then T helper cells signal to active B cells via interleukins.