Biology Paper 1 - Communicable Diseases Flashcards
Pathogens
Pathogens are microorganisms that cause infectious disease. Pathogens may be viruses, bacteria, protists or fungi. They may infect plants or animals and can be spread by direct contact, by water or by air.
How Pathogens Are Spread
- By Air - when ill, you expel tiny droplets full of pathogens when you speak, cough, sneeze etc. Other people breathe them in so pick up the disease.
- Direct Contact - common in plant species, where one leaf can infect an entire field of crops. For humans, this is most common through sex.
- By Water - drinking untreated sewage water.
Reducing Spread Of Diseases
- Hygiene - Hand-washing, coughing/sneezing into a tissue and then washing your hands. etc.
- Isolating infected individuals - Fewer people going near infected individuals means that the pathogens are less likely to spread.
- Destroying or controlling vectors - (i.e: mosquitoes carrying malaria, Houseflies, Rats), by controlling the number of vectors, it can be reduced.
Measles
Viral disease showing symptoms of fever and a red skin rash.
The measles virus is spread by inhalation of droplets from sneezes and coughs.
Reduction in spread of Measles, due to improved living conditions in the UK.
HIV/AIDS
Unless successfully controlled with antiretroviral drugs the virus attacks the body’s immune cells. Late stage HIV infection, or AIDS, occurs when the body’s immune system becomes so badly damaged it can no longer deal with other infections or cancers. HIV is spread by sexual contact or exchange of body fluids such as blood which occurs when drug users share needles.
Tobacco Mosaic Virus (TMV)
Tobacco mosaic virus (TMV) is a widespread plant pathogen affecting many species of plants including tomatoes. It gives a distinctive ‘mosaic’ pattern of discolouration on the leaves which affects the growth of the plant due to lack of photosynthesis.
It is spread due to direct contact between plant species’. Good field hygiene can reduce the spread of TMV.
Salmonella
A food poisoning is spread by bacteria ingested in food, or on food prepared in unhygienic conditions - causes an unnatural balance of bacteria in the guts.
Fever, abdominal cramps, vomiting and diarrhoea are caused by the bacteria and the toxins they secrete.
In the UK, poultry are vaccinated against Salmonella to control the spread.
Gonorrhoea
Is a sexually transmitted disease (STD) with symptoms of a thick yellow or green discharge from the vagina or penis and pain on urinating.
If untreated, it can cause long-term pelvic pain, infertility and ectopic pregnancies.
It is caused by a bacterium and was easily treated with the antibiotic penicillin until many resistant strains appeared. It can be spread via sexual contact.
The spread can be controlled by treatment with antibiotics or the use of a barrier method of contraception such as a condom.
Fungal Diseases
- For people - Athlete’s foot
But more common in plants - In plants - Rose Black Spot :
Purple or black spots develop on leaves, which often turn yellow and drop early. It affects the growth of the plant as photosynthesis is reduced.
Spread by wind and water.
Rose black spot can be treated by using fungicides and/or removing and destroying the affected leaves.
Protist Diseases
Protists - a type of single-celled organism that causes a disease in animals and plants.
The pathogens that cause Malaria are protists.
The malarial protist has a life cycle that includes the mosquito.
The protists reproduces sexually in the mosquito and asexually in the human body.
Malaria causes recurrent episodes of fever and can be fatal. The spread of malaria is controlled by preventing the vectors, mosquitos, from breeding and by using mosquito nets to avoid being bitten. + using insecticides.
Skin Defences
- If cut, the skin bleeds and platelets rush towards the cut to form a clot which dries into a scab, stopping pathogens getting in.
- Skin produces antimicrobial secretions.
Nose Defences
- Full of hairs and contains mucus, which both trap particles and pathogens from entering the body.
Trachea And Bronchi
Secretes mucus that traps pathogens from the air.
The lining of the tubes are covered in Cilia - tiny hair-like projections from the cells.
Stomach Defences
Produces acids which destroy microorganisms, in the mucus you swallow.
Antibody Production
These target particular bacteria or viruses to destroy them.
The antigen of the pathogen is complementary to the antibodies of a white blood cell. This means that once they have been combatted, the antibodies can be rapidly made again.
