4.1.1: Organisms that cause disease

Question 1

What is a pathogen?

Answer 1

• A microorganism that causes disease.

- Live by taking nutrition from host causing damage in the process.

Question 2

What is a host?

Answer 2

The organism in which a pathogen lives.

Question 3

Bacteria.

• Which kingdom do they belong to?
• Rate at which they multiply?
• How do they cause disease?

Answer 3

• Prokaryotae
• Reproduce rapidly in right conditions.
• Once in host body, multiply rapidly.
• Presence caused disease by damaging cells or by releasing waste products and/or toxins.

Question 4

In plants, where do bacteria often live?

Answer 4

-In vascular tissue, causes blackening and death in these tissues.

Question 5

How can a fungus cause a fungal infection in animals?

Answer 5

• Fungus lives in skin.
• Its hyphae, which form a mycelium, grow under the skin surface.
• The fungus can send out specialised reproductive hyphae which grow to the surface of the skin to release spores.
• This causes redness and irritation.

Question 6

How can a fungus cause a fungal infection in plants?

Answer 6

• Fungus lives in vascular tissue where it can gain nutrients.
• The hyphae released extracellular enzymes, such as cellulase, to digest surrounding tissue, which causes decay.
• Leaves become mottled in colour, curl up and shrivel before dying.
• Fruit and organs, such as tubers (potatoes) will turn black and decay.

Question 7

How can a virus cause disease in animals?

Answer 7

• Invade cells.
• Take over genetic machinery and other organelles of the cell.
• Manufacture more copies of the virus.
• Host cell eventually bursts.
• Releases many new viruses which will infect healthy cells.

Question 8

How do protoctists cause diseases in animals?

Answer 8

• Cause harm by entering host cells and feeding in the contents as they grow.
• Plasmodium has immature forms that feed on the haemoglobin inside red blood cells.

Question 9

Give examples of diseases caused by bacteria

Answer 9

-Tuberculosis
(kills cells and tissues, lungs most often affected)
-Bacterial meningitis
(infection of meninges, membrane becomes swollen causing brain and nerve damage)
-Ring rot
(Ring of decay in vascular tissue of potato tuber or tomato)

Question 10

Give examples of diseases caused by viruses

Answer 10

-HIV/AIDS
(attacks immune system, compromises immune response)
-Influenza
(attacks respiratory system, muscle pains & headaches)
-Tobacco mosaic virus
(causes molting and discolouration of leaves)

Question 11

Give examples of diseases caused by fungi

Answer 11

-Black Sigatoka (bananas)
(causes leaf spots, reduces yield)
-Ringworm (cattle)
(growth of fungus in skin with spore cases erupting through skin causing a rash)
-Athlete's foot. 
(growth under skin of feet)

Question 12

Give examples of diseases caused by protoctistan

Answer 12

-Blight (tomatoes and potatoes).
(affects both leaves and potato tubers)
-Malaria
(parasite in the blood, causes headache, fever, may progress to coma and death)