4.1 Communicable diseases

What is a pathogen?

Organisms that cause diseases

Examples of pathogens

Bacteria

Fungi

Virus

Protoctista

How can bacteria cause diseases?

Damages cells

Releasing waste products or toxins

How can fungi cause diseases

Lives in skin of animals where hyphae, forming mycelium grows under skin surface.

Produces specialised reproductive hyphae which grows to skin surface and release spores, causing redness and irritation.

Where do bacteria and fungi live in plants usually?

vascular tissue

How can fungi cause diseases in plants

Hyphae releases extracellular enzymes to digest surrounding tissue, causing decay

How can viruses cause diseases

Invade cells and takes over the genetic machinery and other organelles of the cell

Cause the cell to reproduce more copies of the virus

The host cell will burst, releasing new viruses which will infect healthy cells.

How can protoctista cause diseases

Enters host cells and feeds on the content as they grow

Characteristics of Bacterial meningitis

Infection of the meninges

Membrane becomes swollen

May cause damage to brain and nerves

Characteristic of Ring rot

ring of decay in the vascular tissue of a potato or tomato tubers

Leaf wilting

Characteristic of HIV/AIDS

attacks cells in immune system

weakens body’s ability to fight off diseases

Characteristics of Influenza

attacks respiratory system

causes muscle pain and headaches

Characteristics of Tobacco mosaic virus

causes discolouration of leaves

mottling

Characteristics of Black sigatoka

causes leaf spots on banana plants reducing yield

Characteristics of Blight

affects both leaves and potato tubers

Characteristics of Ringworm

Growth of fungus in skin with spore cases erupting through skin to cause a rash

Characteristics of athlete’s foot

growth under skin of feet

Characteristics of malaria

parasite in blood that causes headache and fever

may progress to coma and death

Life cycle stages

Travel from one host to another

Entering host’s tissues

Reproducing

Leaving host’s tissues

Two ways of transmission between animals

Direct

Indirect

Examples of direct transmission

Direct physical contact with a contaminated person or surface

Eating contaminated food or water

Droplet infection

Transmission by spores

How to limit direct transmission

Hygiene

Treatment of waste water and drinking water

Thorough washing of fresh food

Washing skin water contact with soil

Social factors that affect transmission

Overcrowding

Poor ventilation

Poor health

Poor diet

Homelessness

Living with people from higher risk disease areas

How are pathogens transmitted indirectly

Via a vector

What is a vector

organism that transfers disease-causing agent from one host to another

How do pathogens in the soil infect plants

by entering the roots

Describe one method by which fungal pathogens can be transmitted over long distances.

carried in the wind-airborne transmission

How does indirect transmission of plant pathogen occur

Insect attack

How does climate change affect transmission of diseases

Many protoctists, bacteria and fungi can grow and reproduce more rapidly in warm and moist conditions

How do plants defend themselves from pathogens

Passive defences

Active defences

What are passive defences

Prevents entry and spread of pathogen

Include physical barriers and chemicals

Physical defences in plants

Cellulose cell wall

Lignin thickening of cell walls

Waxy cuticle

Bark

Stomatal closure

Callose

Tylose

Characteristics of lignin thickening of cell walls

Waterproof

Indigestible

Characteristics of waxy cuticle

Prevents water collecting on cell surface.

Water is needed for organisms to survive

Characteristics of bark

Contains variety of chemical defences

Characteristics of stomatal closing

When pathogens are detected, guard cells will close the stomata

Characteristics of callose

It is deposited around sieve plates and blocks the flow in sieve tube, preventing pathogen from spreading around plant

Characteristics of tylose

It plugs the xylem vessel so it can no longer carry water, preventing spread of pathogen.

Contains high concentration of chemicals

When are chemicals produced in a plant

Some a produced before infection

Most are produced when plant detects an infection as it requires a lot of energy.

Characteristics of cellulose cell wall

Contains chemicals that can detect pathogens

Active defences in plants

Cellulose cell walls become thickened and strengthened with more cellulose

Deposition of Callose between plant cell wall and plasma membrane near invading pathogen. Strengthen cell wall and blocks plasmodesmata

An increase in production of chemicals

Oxidative burst that produce highly reactive oxygen molecules that damage cells of pathogens

Name 5 chemicals in plants

Terpenoids

Phenols

Alkaloids

Defensins

Hydrolytic enzyme

Action of terpenoids

Have antibacterial and antifungal properties

Action of phenols

Antibiotic and antifungal properties

What is necrosis

Deliberate cell suicide

How does Necrosis help plants

By killing cells surrounding infection, plants can limit the pathogen’s access to water and nutrients, preventing further spread.

How is necrosis bought about

By intracellular enzymes that are activated by injury.

They destroy damaged cells and produce brown spots

What is canker

A sunken necrotic lesion in woody tissue.

Causes death of cambium tissue in the bark

What is primary defences

The mechanisms that have evolved to prevent the entry of pathogenic organisms

Non-specific as they prevent entry of any pathogens.

What is the main primary defence

The skin

Structure of the skin

Outer layer- epidermis consists of kerstinocytes

How are keratinocytes produced

Mitosis at the base of the epidermis

What is keratinisation

When keratinocytes migrate out to the surface of the skin, they dry out and cytoplasm is replaced by keratin

how does the keratinised layer of skin protect against pathogens

consists of dead cells that act as a physical barrier.

by the time skin cells reach the surface, they are no longer alive.

this layer prevents pathogen entry and eventually sheds off removing any attached microbes

why must blood clotting be a carefully controlled process

to prevent clots forming in blood vessels where they are not needed

why ions and substances are involved in the blood clotting process

calcium ions and at least 12 clotting factors, which are released by platelets and damaged tissues

what activates the clotting process

enzyme cascade

what happens after a blood clot forms

the clot dries to form a scab that shrinks as it dries, pulling the sides of the cut together

what is the 1st stage of tissue repair under the scab

deposition of fibrous collagen under the scab

how is new skin formed during wound healing

stem cells in the epidermis divide by mitosis and migrate to the edges of the cut differentiating into new skin cells

what helps supply oxygen and nutrients during skin repair

new blood vessels grow to support the regenerating tissue

what helps draw the edges of a cut together during repair

the tissue contracts to help close the wound

what happens to the scab once the skin is fully repaired

the scab is released

What is vaccination

provides immunity to specific diseases

how is a vaccine usually given to a person

Antigenic material is injected or taken orally.

What happens to the immune system as it detects the pathogen

The immune system produces antibodies and memory cells.

Types of antigenic material

whole live microorganisms- not as harmful as the real disease but have similar antigens.

weakened version 

dead pathogen

a preparation of antigens from a pathogen

a toxoid (harmless version of a toxin)

2 types of vaccination

Herd vaccination

Ring vaccination

What is herd vaccination

a vaccine to provide immunity to all/almost all of the population at risk. Disease cannot be spread once enough people are immune.

Achieve ‘herd immunity’

What is ring vaccination

vaccinating those who are most likely to be infected immediately

Why is herd immunity important

 if everyone has been vaccinated and is immune to the disease, then the disease would not be able to spread.

How to control an epidemic

first vaccine those who are at a higher risk

improving hygiene

educating

environmental controls

isolation

why cant communicable diseases such as malaria and HIV not be prevented by vaccination?

• Malaria: The pathogen (Plasmodium) has a complex life cycle and many different stages in the human body, each with different antigens, making it hard to target with one vaccine.

  HIV: The virus mutates rapidly and has a high antigenic variability, which allows it to evade the immune system and makes it difficult to create a long-lasting, effective vaccine.

different types of immunity

natural

artificial

active

passive

what is natural immunity

achieved through normal life processes

what is artificial immunity

achieved through medical intervention

what is active immunity

achieved when immune system is activated and produces its own antibodies

what is passive immunity

achieved when antibodies are supplied from another source

What are the lungs, airways, digestive system protected by

Mucous membranes

What secrets mucus

goblet cells

Function of cilia

waft mucus up to the top of trachea

enter oesophagus and swallowed.

killed by acidity of stomach

What reflexes are triggered by irritation from microorganisms or their toxins?

coughing

sneezing

vomiting

what is inflammation

when tissue is infected causing swelling and redness

what do mast cells detect.

microorganisms in tissue

what do mast cells release

cell signalling substance called histamine

what effect does histamine have on blood vessels during an immune response

causes vasodilation

increase capillary permeability

what leaves the blood and enters the tissue fluid due to histamine action

blood plasma

WBC

what causes swelling during an inflammatory response

increased tissue fluid due to plasma and WBCs entering the tissue

where does excess tissue fluid go after an immune response begins

drained into the lymphatic system

how does the lymphatic system contribute to the specific immune response

stores lymphocytes which may come into contact with pathogens and initiate specific immune responses

other primary defences

eyes are protected by antibodies and enzymes in tear fluid

ear canal is lined by wax which traps pathogens

female reproductive system is protected by a mucus plug in the cervix by maintaining the relatively acidic conditions in the vagina

what are secondary defences

Defences that combat pathogens that have entered the body.

How does the body recognize a pathogen as foreign?

By detecting chemical markers on its outer membrane called antigens

What are antigens made of?

Proteins or glycoproteins intrinsic to the plasma membrane

Are antigens specific to each organism?

Yes, antigens are specific to each organism.

what are opsonins

proteins molecules that attach to antigens on the surface of a pathogen

what type of molecule are opsonins

type of antibody

are all opsonins specific to certain pathogens

no some opsonins are not very specific

can attach to a variety of pathogens

what is the role of opsonins in the immune response

to enhance the ability of phagocytic cells to bind to and engulf pathogens

what is the first line of secondary defence

phagocytosis