Biology (4.1): Communicable diseases

pathogen

pathogen

microorganism that causes disease

Types of pathogen

1. bacteria

2. fungi

3. viruses

4. protoctista

bacterium

prokaryotic single-celled organism

How do bacteria cause disease?

in host body, they multipy rapidly and damage cells or release waste products and toxins

bacteria examples (3)

1. tuberculosis

2. bacterial meningitis

3. ring rot

What are the two ways fungal infections live in the skin of animals

1. mycelium grows under skin surface

2. specialised reproductive hyphae release spores

How do fungi cause disease in plants?

live in vascular tissue where the hyphae release extracellular enzymes that digest surrounding tissue and cause decay

fungi examples (3)

1. black sigatoka

2. ringworm

3. athlete’s foot

What are viruses?

non-cellular, but are nucleic acids surrounded by protein capsid

How do viruses cause disease?

invade cells, take over the genetic machinery, cause the cell to replicate virus, host cell bursts and releases many new viruses which infect healthy cells

Virus examples (3)

1. HIV

2. influenza

3. tobacco mosaic virus

protoctista

single eukaryotic cells

How do protoctista cause disease?

by entering host cells and feeding on the contents as they grow

Protoctista examples (2)

1. malaria

2. blight

Tuberculosis

kills cells and tissues (lungs are the most affected)

Bacterial meningitis

infection of the meninges (membranes get swollen and cause damage to brain and nerves)

Ring rot (plants)

ring of decay in vascular tissue of a potato tuber or tomato, accompanied by leaf wilting

HIV/AIDS

attacks cells in the immune cell and compromises the immune response

Influenza

attacks respiratory system and causes muscle pains and h

Tobacco mosaic virus

causes mottling and discolouration of leaves

Black sigatoka (bananas)

causes leaf spots on banana plants reducing yield

Blight (tomatoes and potatoes)

affects both leaves and potato tubers

ringworm (cattle)

growth of fungus in skin with spore cases erupting though skin to cause a rash

Athlete’s foot (humans)

growth under skin of feet (particularly between the toes)

Malaria

parasite in the blood that causes headache and fever and may progress to coma and death

transmission

passing a pathogen from an infected individual to an uninfected individual

types of transmission

direct and indirect

Life-cycle of pathogens (4)

1. transmission

2. entering host’s tissues

3. reproducing

4. leaving host’s tissues

direct transmission

passing a pathogen from host to new host with no intermediary

Means of direct transmission (4)

1. physical contact

2. faecal-oral

3. droplets

4. spores

Social factors affecting transmission (6)

1. overcrowding

2. poor ventilation

3. poor health

4. poor diet

5. homelessness

6. living or working with people who have migrated from areas where a disease is more common

How can you reduce the transmission of disease by physical contact?

hygiene (washing hands regularly, cleaning, disinfecting and sterilisation)

How can you reduce faecal-oral transmission of disease?

treatment of waste water and

How can you reduce faecal-oral transmission of disease?

treatment of waste and drinking water and washing all fresh food

How can you reduce transmission of disease via droplets?

catch it - bin it - kill it

How can you reduce transmission of disease via spores?

use a mask and wash skin after contact with soil

Indirect transmission

passing a pathogen from

Life cycle of Plasmodium

1. a person with malaria

2. gametes of Plasmodium in blood

3. female mosquito sucks blood

4. Plasmodium develops and migrates to a mosquito’s salivary glands

5. an uninfected person is bitten

6. Plasmodium migrates to liver

7. Plasmodium migrates to blood

What does indirect transmission of plant pathogens often occur as a result of?

an insect attack

How does climate affect transmission of disease?

pathogens grow and reproduce more rapidly in warm and moist conditions

Types of defences in plants

passive and active

Types of passive defences

physical and chemical

Physical defences in plants (7)

1. cellulose cell wall

2. lignin thickening of cell walls

3. waxy cuticles

4. bark

5. stomatal closure

6. callose

7. tylose formation

How does the cellulose cell wall act as a physical defence?

acts as a physical barrier and contains chemical defences

How does lignin act as a physical defence?

waterproof and indigestible

How do waxy cuticles act as a physical defence?

prevent water collecting on cell surfaces

How does bark act as a physical defence?

contains a variety of chemical defences that work against pathogenic organisms

How does stomatal closure act as a physical defence?

pathogens enter through stomata, so when pathogens are detected, the guard cells close the stomata

How does callose act as a physical defence?

It is deposited around the sieve plates and blocks the flow in the sieve tube to prevent a pathogen spreading around the plant

Callose

a large polysaccharide deposit that blocks old phloem sieve tubes

How does tylose formation act as a physical defence?

plugs the xylem vessel so it can’t carry water which prevents the spread of pathogens through the heartwood

Tylose

a balloon-like swelling or projection that fills the xylem vessel

Active defences in plants

1. additional cellulose

2. deposition of callose

3. oxidative bursts

4. increase in production of chemicals

What do oxidative bursts in plants do?

producing highly reactive oxygen molecules (damage cells of invading organisms)

What does additional cellulose do to the cell walls of plants?

thicken and strengthen them

What does deposition of callose between the plant cell wall and cell membrane near the invading pathogen do? (2)

1. impede cellular penetration and site of infection

2. block plasmodesmata

Chemicals released in active defences in plants (5)

1. terpenoids

2. phenols

3. alkaloids

4. defensive proteins (defensins)

5. hydrolytic enzymes

Terpenoids (2)

1. oils that have antibacterial and antifungal properties

2. create scent

Phenols (e.g. tannins) (3)

1. antibiotic and antifungal properties

2. inhibit insects attacking

3. bind to salivary proteins and digestive enzymes, deactivating them

Alkaloid examples

caffeine, nicotine, cocaine, morphine, solanine

Alkaloids (3)

1. nitrogen containing compounds that give a bitter taste to inhibit herbivores from feeding

2. inhibit enzymes used in metabolic reactions

3. inhibit protein synthesis

Defensive proteins/ defensins (2)

1. small cysteine-rich proteins with anti-microbial activity

2. act on molecules in plasma membrane of pathogens inhibiting action of ion transport channels

Where are hydrolytic enzymes found

in spaces between cells

Hydrolytic enzymes examples

1. chitinases

2. glucanases

3. lysozymes

chitinases

break down chitin in fungal cell walls

glucanases

hydrolyse the glycosidic bonds in glucans

lysozymes

degrading bacterial cell walls

necrosis

deliberate cell suicide

How does necrosis prevent disease from spreading?

kills cells surrounding infection to limit pathogen’s access to water and nutrients and stop it spreading further around the plant

canker

sunken necrotic lesion in the woody tissue (main stem or branch) that causes death of cambium tissue in the bark

primary defences in animals

1. skin barrier

2. blood clotting and wound repair

3. mucous membranes

4. coughing and sneezing

5. inflammation

6. phagocytosis

primary defences

those that prevent pathogens entering the body

How does the skin act as a primary defence?

dried dead cells full of keratin act as a barrier to pathogens

How do blood clots and wound repair act as a primary defence?

1. platelets stick to existing collagen forming a plug and release chemicals that cause fibrinogen in blood plasma to convert to insoluble fibrin

2. strengthens the platelet plug

3. collagen repairs underneath and seals the skin

mucous membranes

specialised epithelial tissue that is covered by mucous

What are mucous secreting cells called?

goblet cells

What are cilia?

tiny, hair-like organelles that can move

What do cilia do?

waft mucus along to the top of the trachea where it enters the oesophagus and is swallowed so pathogens can be skilled by stomach acid

How does coughing and sneezing act as a primary defence?

the sudden expulsion of air carries the microorganisms causing the irritation with it

How does inflammation act as a primary defence?

histamine released from damaged cells, causes vasodilation so phagocytes can leak out of blood vessels to destroy pathogens

What do mast cells release?

histamine

What do histamines do?

cause vasodilation to make capillary walls more permeable to white blood cells, leading to increased production of tissue fluid that causing swelling

How are eyes protected (primary defences)?

by antibodies and enzymes in the tear fluid

How are ears protected (primary defences)?

ear canal lined by wax, which traps pathogens

Secondary defences

used to combat pathogens that have entered the body

How are pathogens recognised as foreign when they enter the body?

antigens that are specific to the organism

What are antigens?

proteins or glycoproteins intrinsic to the plasma membrane

opsonins

proteins that bind to the antigen on a pathogen and then allow phagocytes to bind

What is the first line of secondary defence in animals?

phagocytosis

Types of phagocytes

neutrophils and macrophages

neutrophil

a type of white blood cell that engulfs foreign matter and traps it in a large vacuole (phagosome) which fuses with lysosomes to digest the foreign matter

How do you recognise a neutrophil?

multi-lobed nucleus

Where are neutrophils manufactured?

bone marrow

What do neutrophils contain a large number of?

lysosomes

How is pus formed?

When dead neutrophils collect in an area of infection

Steps of phagocytosis (4)

1. neutrophil binds to opsonin attached to antigen of pathogen

2. pathogen engulfed by endocytosis forming phagosome

3. lysosomes fuse to phagosome and release lytic enzymes into it

4. after digestion, harmless products can be absorbed into the cell

macrophages

become antigen-presenting cells so that other cells in the immune system can recognise the antigen

antibodies

specific proteins released by plasma cells that can attach to pathogenic antigens

B memory cells

cells that remain in the blood for a long time, providing long-term immunity

clonal expansion

an increase in the number of cells by mitotic cell division