4.1.1 - Communicable diseases, disease prevention and the immune system

What is a pathogen?

A microorganism that causes disease

What are the 4 types of pathogen?

Bacteria, fungi, virus and protoctist

How do bacteria cause disease? (general)

They multiply rapidly and either damage cells directly or release toxins

How do fungi cause disease? (general)

They often infect skin in animals by forming a mycelium of hyphae. They can release extracellular enzymes for saprotrophic digestion of tissues

How do viruses cause disease? (general)

They take over the host cell in order to make more copies of the virus. This eventually results in the cell bursting

Give 3 examples of diseases caused by bacteria

TB, bacterial meningitis and ring rot

Give 3 examples of diseases caused by viruses

HIV/AIDS, influenza and Tobacco Mosaic Virus

Give 3 examples of diseases caused by protoctista

Malaria and potato/tomato blight

Give 3 examples of diseases caused by fungi

Black sigatoka, ringworm and athlete's foot

Give 2 details about TB

It generally attacks the lungs, but can attack any part of the body such as the kidneys. With treatment it can usually be cured e.g antibiotics

Give 2 details about bacterial meningitis

These bacteria cross the meninges and cause acute inflammation. This can cause fever, headaches and a rash

Give 2 details about ring rot

It is a disease in potato plants that infects the vascular tissue, causing the plant to rot. This produces the characteristic black ring, as the vascular tissue is arranged in this shape.

Give 2 details about HIV/AIDS

HIV damages cells in the immune system, and over time the infected person acquires AIDS due to the progressive depletion of immune cells

Give 2 details about influenza

Influenza viruses infect the cells that line the airways, and can cause a high temp, body aches and fatigue

Give 2 details about Tobacco Mosaic Virus (TMV)

It can infect several plant species, and causes a distinct yellowing of the leaves which produces a mosaic pattern

Give 2 details about malaria

It is spread by mosquitoes, and causes infected individuals to experience fever, chills and fatigue

Give 2 details about potato blight

The pathogen has some fungal characteristics - it is transmitted via spores. The first sign of potato blight are small dark brown marks, which increase and eventually destroy the whole crop

Give 2 details about black sigatoka

It is a fungal disease in bananas, which is spread through the leaves of the plant, reducing its ability to photosynthesise. This eventually causes the leaf to die.

Give 2 details about cattle ringworm

It is a fungal disease that exists on the surface of the skin, and is transmitted by direct contact with infected cattle

Give 2 details about athlete's foot

It is a fungal disease that exists on the surface of the skin, and is transmitted by direct contact with items touched by infected individuals

What is direct transmission (in humans)?

Where no intermediary organism is involved - it spreads directly from host to host

How is direct transmission best prevented?

Basic hygiene and sterilisation

What is indirect transmission (in humans)?

The diseases pass via a vector, which carries the pathogen and is sometimes completely unaffected itself.

Give 3 factors that might increase the risk of disease transmission

Poor sanitation, high population density and limited waste disposal

How does direct transmission work in plants?

It is transmitted through the soil via roots, by the wind, or through leaves if it is in vascular bundles

How does indirect transmission work if it's in plants?

Insect vectors - for example fungal spores and bacteria are transported via insect pests such as beetles

How is climate change affecting disease transmission?

Warmer climates are causing animals and insects to change habitats, therefore affecting what diseases are present

What are the two general types of plant defence?

Passive and active defence

What is passive defence in plants?

Primary defences are present before infection, which aims to prevent pathogen entry and spread

What is active defence in plants?

Plant responds to detection of attack, mostly including fortifying the existing physical defences and producing particular chemicals

Give 3 examples of active defence in plants

Cell walls are thickened with extra cellulose when the plant is attacked, necrosis of the cell using intracellular enzymes to limit pathogen spread, and production of chemicals such as menthol in mint plants

Give 3 examples of passive defence in plants

Bark is both a physical and chemical defence as it contains chemicals such as tannins which are toxic to herbivores, waxy cuticles prevent water droplets containing pathogens from collecting, and cellulose cell wall forms an impenetrable barrier around cells

What are the four key categories of the non-specific immune response?

Physical, cellular, chemical and commensal organisms (harmless bacteria and fungi that are present on and in the body)

What makes up the first line of defence in the non-specific immune response?

Skin, blood clotting, wound repair, inflammation, expulsive reflexes and mucous membranes

How does the skin act as a defensive layer

The epidermis is composed of layers of cells, with a hardened outer layer of cells filled with keratin. This layer acts as a physical barrier to pathogens

How does blood clotting act as a defensive layer?

Damaged tissue and platelets release clotting factors which then form a scab to prevent pathogen entry and stop blood loss

How does wound repair act as a defensive layer?

When the scab dries out, the gap shrinks and pulls the skin back together. New skin underneath is formed by mitosis and the scab is released once the new skin is completed

How does inflammation act as a defensive layer?

Specialised mast cells detect infection and then release histamines. This can cause vasodilation, meaning excess tissue fluid leaks into the lymphatic system and comes into contact with lymphocytes, triggering a specific immune response

How do expulsive reflexes at as a defensive layer?

When a pathogen irritates the lining of an airway it can trigger a cough or a sneeze - this expelled air contains secretions from the respiratory tract and help to remove the pathogen

How do the mucous membranes act as a defensive layer?

Mucous membranes line the gut, airways and reproductive system. In the airways mucus can trap viruses, bacteria and pollen, and these are then moved back out of the body by cilia

What is an antibody?

A protein produced in response to an antigen

What is an antigen?

A protein that binds to an antibody

Why do antibodies have a variable region?

So they can be specific to the antigen

What are phagocytes?

White blood cells that are produced continuously in the bone marrow

What are the two main types of phagocytes?

Neutrophils and macrophages

What are opsonins?

Chemicals which bind to pathogens and tag them for ingestion and destruction by phagocytes. Phagocyte receptors bind to opsonins.

What is phagocytosis a type of?

Endocytosis

Outline the steps in phagocytosis

Chemotaxis and adherence of microbe to phagocyte, ingestion of microbe by phagocyte, formation of a phagosome, fusion of phagosome with a lysosome to form a phagolysosome, digestion of ingested microbe by enzymes, formation of residual body and discharge of waste materials

What is a phagolysosome?

The structure that results from the fusion of a phagosome and a lysosome.

What is a phagosome?

a phagocytic vesicle

What are the most common types of phagocytes?

Neutrophils

Describe a neutrophil

A type of phagocyte that can squeeze through capillary walls to reach tissues. They are short lived and have a distinctive multi-lobed nucleus

Describe a macrophage

A type of phagocyte which is made in the bone marrow and travel to blood in organs and lymphs nodes. They initiate the immune response by acting as antigen-presenting cells

How do neutrophils work?

Chemotaxis attracts neutrophils to the site, neutrophils move to the pathogen and attach to the opsonin. They then engulf the pathogen by endocytosis and form a phagosome. Digestive enzymes produced in a lysosome fuse with the phagosome and form a phagolysosome. The pathogen is destroyed and the neutrophil now dies

How is pus formed?

Dead neutrophils collect in the area of infection and form pus

How do macrophages work?

Macrophages travel in the blood as monocytes and then enter body tissues where the mature to macrophages. They engulf pathogens, but rather than completely destroying them they retain the antigen and display it on a protein complex in their cell membrane. This activates the specific response, and is called antigen presentation.

What does antigen presentation stimulate?

T cells and B cells

What are T cells and B cells?

Types of lymphocytes

Give 2 ways the specific immune response is activated

Clonal selection and cytokine coordiation

How does clonal selection work?

B and T cells with the correct recognition site for the antigen present have to come into contact with the pathogen directly (for B cells) or an antigen being presented (for T cells). This then triggers the full immune response

What is clonal expansion?

Interleukines are released by T cells and macrophages to stimulate proliferation and differentiation of B and T cells

How does cytokine coordination work?

Monokines are released by macrophages to attract neutrophils and stimulate B cell differentiation and antibody release. Clonal expansion occurs, and interferon is released by many cells to simulate T killer cells and inhibit virus replication

What are cytokines

Hormone-like chemicals which coordinate and stimulate the entire immune response

What are the two different types of lymphocytes?

T cells and B cells

What is the function of a B lymphocyte

They are specific for one antigen and can produce only one antibody type

How does a B lymphocyte work?

When a B cell is selected by complementary antigen cells on a pathogen, they divide by mitosis to form plasma cells (antibody producing) or memory cells

What are the two key types of T lymphocytes?

T killer cells and T helper cells

What is the function of a T killer lymphocyte?

They target cells that have been infected. They attach to the infected cell and secrete toxic substances to kill it

What is the function of a T helper lymphocyte?

They release cytokines to stimulate B cell division and macrophage action

What do both types of T lymphocytes produce?

Memory cells

How are antibodies structured?

They are Y-shaped protein molecules composed of four polypeptides. Two identical 'heavy chains' and two identical 'light chains'. Disulfide bridges attach the polypeptides together

What is the variable region on an antibody?

It determines the antibodies' specificity

What are the three principal mechanisms for antibody function?

Opsonisation, aggultination and anti-toxin

What is opsonisation?

When certain antibodies (opsonins) bind to a pathogen's antigens and thereby mark the pathogen for destruction by phagocytes

What is aggultination?

Antibodies have two identical binding sites and so one antibody can bind to two pathogens. When many antibodies do this, it causes a clumping of pathogens

How does agglutination help?

Agglutinated pathogens are too big to enter host cells so they are an easy target for phagocytes and are effectively neutralised

How do antibodies act as anti-toxins?

They bind to and neutralise toxin molecules released by pathogens

How does the primary immune response work?

When a pathogen enters for the first time, the antigens on its surface activate the immune system. It is slow, because there aren't many B lymphocytes that can make the antibody needed to bind to it. After being exposed to the antigen, T and B lymphocytes produce memory cells and the person is now immune ie their body can respond quickly to a second infection

How does the secondary immune response work?

If the same pathogens enter the body again, clonal selection happens faster and memory T cells are activated so it often gets rid of the pathogen before you show any symptoms

Define vaccination

Deliberate exposure to antigenic material that has been rendered harmless

Name the 5 types of antigenic material that could be used in vaccines

Harmless version of the pathogen, dead pathogen, antigens from the pathogen, toxoid (harmless version of a toxin) or whole, live microorganisms

What are the two main vaccination strategies?

Herd vaccination and ring vaccination

How does herd vaccination work?

A vaccine is used to provide immunity to all, or almost all of a population at risk. When a sufficient number are vaccinated, the disease can no longer spread

How does ring vaccination work?

You vaccinate everyone in the vicinity of a new case - this is often used for livestock diseases or novel outbreaks

Is vaccination that same as immunisation?

No - vaccination is the administration of a substance designed to stimulate the immune system. Vaccination causes immunisation

Why do we have a slightly different flu vaccine every year?

Mutations can cause the shape of the antigen protein to change so it can evade immunity provided by vaccines. In flu, the rate of mutation is very high and so a slightly different vaccine is needed every year

What are the two overarching types of immunity?

Active immunity and passive immunity

What is natural active immunity?

Immunity provided by antibodies made in the immune system as a result of infection

What is artificial active immunity?

Immunity provided by antibodies made in the immune system as a result of vaccination

What is natural passive immunity?

Antibodies provided via the placenta or breast milk make the baby immune to the diseases the mother is immune to

What is artificial passive immunity

Immunity provided by injection to antibodies made by another individual

Are memory cells produced by passive immunity?

No

List four ways new medicines could be discovered

Accidental discovery e.g penicillin, traditional remedies, observation of wildlife and plants

Give an example of a medicine that has come from plants

Morphine is found in the opium harvested from the opium poppy seed capsules. Aspiring also comes from plants

What is personalised medicine?

Medicines tailored to an individuals dna

What is synthetic biology?

Uses technology for design & synthesis of new medicines.

Give two examples of antibiotic resistant bacteria

MRSA, C. difficile

How is C.difficile resistant to antibiotics?

C.difficile infects the digestive system. It is thought that the harmless bacteria in the digestive system are killed by the antibiotics which C.difficile is resistant to, allowing it to flourish and produce a toxin