Infection and response

Explain what a pathogen is and how pathogens are spread (inc how viruses, bacteria, protists and fungi are spread in animals and plants)

communicable diseases are caused by microorganisms called pathogens, which include bacteria, viruses, fungi, and protists 

Pathogens can be spread by air (including droplet infections). When you are ill and you expel tiny droplets full of pathogens from your breathing system, another person can inhale the droplets, containg the pathogen. Examples: influenza, tuberculosis and the common cold

Pathogens can be spread by direct contact. This can be between an infected person and a healthy person and is also very common in plant diseases, where a tiny piece of infected plant material left in a field can infect an entire new crop. For humans, diseases including sexually transmitted infections, such as syphillis and chlamydia are spread

Pathogens can be spread by water. Fungal spores carried in splashes of water often spread plant diseases. For humans, eating raw, undercooked or contaminated food can spread diseases. for exmaple: diarrhoeal diseases, cholera, or salmonellosis.

Explain how pathogenic bacteria and viruses cause damage in the body

Bacteria damage the body by rapidly reproducing inside our body and produces toxins to make you feel ill.

Viruses damage the body by rapidly reproducing inside our cells, causing cell damage.

Explain how the spread of diseases can be reduced or prevented

The spread of disease can be reduced or prevented by :

• simple hygiene measures
• by destroying vectors (diseases that are carried and passed on by animals or plants)
• by isolation of infected individuals

• by vaccination.

Describe measles, HIV and tobacco mosaic virus as examples of viral pathogens

• Measles - a virus spread by droplets infection. It causes a fever and a rash that can be fatal. There is no cure. Isolation of patients and vaccination can prevent it from being spread.

• HIV - a virus where until it is successfully controlled with antiretrovial drugs will attack the immune system and could potentially lead to AIDS where your body's immune system is so damaged it can no longer deal with any other infections or cancers. ( Can be spread by sexual contact or by the exchange of body fluids, such as blood) 

• Tobacco mosaic virus - spread by contact and vectors. It damages leaves and reduces photosynthesis. There is no treatment however, the spread can be prevented by field hygeine and pest control.

Describe salmonella food poisoning and gonorrhoea as examples of bacterial pathogens

• salmonella - spread through undercooked food and poor hygeine. Symptoms include fever, abdominal cramps, diarrhoea, and vomiting caused by the toxins produced by the bacteria.In the UK poultry are vaccinated against salmonella to control the spread.

• Gonorrhoea - a sexually transmitted that have symptoms which include: discharges, and pain on urination. Treatment include taking antibiotics. Using protection and limiting sexual partners prevents spread.

Describe the signs, transmission and treatment of rose black spot infection in plants as an example of fungal pathogens

Rose black spot is a fungal disease spread in the enviroment by wind and water. It damages leaves so they drop off, affecting growth due to the reduced amount of photosynthesis. The spread is controlled by removing affected leaves and chemical sprays. Signs of rose black spot include: purple or black spots on leaves. 

Describe the symptoms, transmission and control of malaria, including knowledge of the mosquito vector as an example of a protists pathogen

Malaria is caused by parasitic protists and is spread by the bite of female mosquitos . It damages blood and liver cells and causes fever and shaking. Some drugs are effective if given early however, protists are becoming resistant.The spread is reduced by preventing the vectors from breeding and by using mosquito nets. 

Describe defences that stop pathogens entering the human body (inc skin, nose, trachea & windpipe, stomach)

Defences against the entry of pathogens:

• skin - acts as a barrier and prevents bacteria and viruses from reaching the tissues beneath. The skin also produces antimicrobial secretions to destroy pathogenic bacteria

• The nose - full of hair and produces mucus which trap particles in the air that may contain pathogens.

• The trachea and bronchi - also secrete mucus that traps pathogens from the air. The lining of the tubes is covered in cilia which waft up the mucus up to the back of the throat where it is swallowed. 

• The stomach produces acid which destroys the microorganisms in the mucus you swallow, as well as most of the pathogens you take in through your mouth in your food and drink

Recall the role of the immune system

The main role of the immune system is to protect the body against pathagones and other foreign bodies. The human immune system must identify threats to our health distinguish these threats and then fight against it. One main way the immune system fights against pathogens is by producing white blood cells to fight against pathogens.

Describe how white blood cells destroy pathogens

• Ingesting microorganisms - some white blood cells ingest pathogens, digesting and destroying them so they don't make you ill.

• Producing antibodies - some white blood cells produce special chemicals called anitbodies. These attatch to a specific antigen, depending on the pathogens, and destroy them. When white blood cells have produced certain antibodies once against a perticular pathogen they will be remebered and made quicker the next time.

• producing antitoxins - some white blood cells produce antitoxins. These counteract the toxins released by pathogens 

Describe how vaccination works, including at the population level

vaaccination involves introducing small amounts of dead or inactive forms of a pathogen into your body to stimulate the white blood cells to produce antibodies. If the same live pathogen re-enters the body, the white blood cells respond quickly to produce the correct antibodies, preventing infection.

If a large proportion of the population is immune to a pathogen, the spread of the pathogen is much reduced. This is achieved via a technique called Herd Immunity 

Explain how antibiotics and painkillers are used to treat diseases, including their limitations

painkillers and other medicines treat the symptoms of the diseasse but they do not kill the pathogen that cause it.

Antibiotics cure bacterial diseases by killing the bacterial pathogens inside your body. However,  the emergence of strains of bacteria resistant to antibiotics is a topic of concern

Antibiotics do not destroy viruses because viruses reproduce inside the cells. it is difficult to develop drugs that can destroy viruses without damaging your cells. 

Describe how sources for drugs have changed over time and give some examples

Traditionally drugs were extracted from plants, for example, digitalis or from microorganisms, for example, penicillin (discovered by Alexander Fleming from the penicillium mould).

Most new drugs are synthesised by research chemists in the pharmaceutical industry. an example of this is the noni fruit which is used in traditional medicine in many countries to treat both infections and non-communicable diseases. 

Describe how new drugs are tested, including pre-clinical testing and clinical trials (inc double blind trials and placebos)

New drugs, being tested in the laboratory using cells, tissues, and live animals, are being tested for efficacy, toxicity, and dosage. 

Preclincal testing of new drugs takes place in a laboratory on cells, tissues, and live animals. Clinical trials use healthy volunteers and patients. Low doses are used to test for safety, followed by higher doses to test for optimum dose. 

In double blind trials a group of patients with the target disease are tested by giving some a placebo that doesn't contain the drug and others are given the new medicine.

Bio & HT ONLY: Describe what monoclonal antibodies are and why they are useful

Monoclonal antibodies are a form of medical treatment that relies on the immune system. Monoclonal antibodies are proteins that are produced to target particular cells or chemicals in the body. 

Monclonal anitbodies are useful because they can be used for:

• for diagnosis in pregnancy tests
• in labs to measure the levels of hormones and other chemicals in the blood to detect pathogens for research
• to identify or locate specific molecules in cells or tissue.

Bio & HT ONLY: Describe how monoclonal antibodies are produced

Monoclonal antibodies are produced from a single clone of cells. Each type is specific to one bingding site on a specific protein antigen so they can target specific cells in the body or specific chemicals.

Monoclonal anitbodies are produced by stimulating mouse lymphocytes to make a specific antibody. Large amounts of the specific monoclonal antibody can be collected and purified.

Bio & HT ONLY: Explain how monoclonal antibodies are used for diagnosis, research, chemical testing and disease treatments

diagnosis - monoclonal antibodies are made to bind to specific antigens found on pathogens, or on blood clots, or on cancer cells.

research - research scientists use monoclonal antibodies to locate or identify specific molecules in a cell or tissue. Scientists produce monoclonal antibodies linked to a molecule of a fluorescent dye. When these bind to desired molecules  scientists can see what has happened by observing the build-up of fluorescence.

treating disease - used to directly trigger the immune system, block receptors on the surface of cancer cells, and to carry toxic drugs or radioactive substances for radiation therapy.

Bio & HT ONLY: Evaluate the advantages and disadvantages of monoclonal antibodies (inc side effects)

Advantage:

If a monoclonal antibody is bound to a radioactive substance, a toxic drug, or a chemical that stops cells growing and dividing, it will deliver the substance to the cancer cells without harming other cells in the body. 

Disadvantages:

Monoclonal antibodies have created side effects than expected and are not yet as widely used as hoped when they were first developed. 

Bio & HT ONLY: Describe some observable signs of plant disease, and how plant diseases can be identified

Plants can be infected by a range of viral, bacterial, and fungal pathogens as well as insect pests and can be damaged by a range of ion deficiency conditions.

Plants diseases can be detected by a range of symptoms and identified in a number of ways, including gardening manuals and laboratory tests, some involving monoclonal antibodies.

Bio ONLY: Give examples of plant pathogens

Virus: Tobacco mosaic virus

Bacteria: Agrobacterium

Fungi: Rose Black Spot

Protists: Downy mildew

Bio ONLY: Give examples of plant ion deficiencies and their effects

Plants take magnesium ions from the soil to make the chlorophyll needed for photosynthesis therefore if there is a low level of magnesium in the soil the plant won't be able to make enough chlorophyll. Therefore the leaves will yellow due to the lack of magnesium, this is known as chlorosis.

Plants also need a good supply of nitrate otherwise there won't be enough protein for growth in protein synthesis and the growth will be limited and stunted 

Bio ONLY: Describe physical, chemical and mechanical defence responses of plants

Physical plant defences against invasion by microorganisms include cellulose cell walls, tough waxy cuticles, and layers of bark or dead cells (or dead leaves). which fall off. 

Chemical plant defences include antibacterial chemicals and poisons to deter herbivores. 

Many plants have mechanical adaptations against herbivores such as thorns, and hairs, leaves that droop or curl when touched, and mimicry to trick animals