Edexcel Biology Gcse - Communicable Diseases Part 2

The nucleus controls what happens inside the cell. Chromosomes are structures found in the nucleus of most cells. The plural of nucleus is nuclei.

A single-celled organism which does not have a membrane-bound nucleus.

The proteins that surround the DNA of a virus.

A eukaryotic, usually single-celled organism of the kingdom Protista.

Open sores that develop on the lining of the stomach and are usually caused by bacteria.

The spreading of pathogenic disease, for example by touch, food, water.

Substances containing disabled antigens of a particular disease, usually administered via injection. Vaccines stimulate the body to produce antibodies to provide immunity against that disease.

A malaria-carrying mosquito.

An ultramicroscopic infectious non-cellular organism that can replicate inside the cells of living hosts, with negative consequences. plural viruses.

A unicellular fungus used in the brewing and baking industries.

The World Heath Organisation (WHO) is responsible for advising on ways to improve heath around the world. They define health as a state of complete physical, mental and social well-being. This means that being free from disease alone is not necessarily enough to be in good health.

communicable, which can be transferred from one person to another, or from one organism to another, eg in humans, these include measles, food poisoning and malaria.

non-communicable, which are not transferred between people or other organisms

Defects in the immune system mean that an individual is more likely to suffer from infectious diseases. For instance, human immunodeficiency virus infections, known as HIV, which leads to AIDS, affect the immune system and lead to an increase in susceptibility to infectious diseases.

Viruses living in cells can be the trigger for cancers. For instance, the majority of cases of cancer of the cervix are linked with a virus present in the female reproductive system.

The reaction of the immune system to pathogens and other foreign bodies can trigger allergic reactions that lead to skin rashes and asthma. For instance, severe respiratory infections in babies can lead to asthma in later childhood.

Severe physical ill health can lead to depression and other types of mental illness.

Viruses

Bacteria

Fungi

Protists

Viruses

in animals: HIV/AIDS

in plants: Tobacco mosaic virus

Bacteria

in animals: Salmonella

in plants: Agrobacterium

Fungi

in animals: Athlete's foot

in plants: Black rose spot

Protists

in animals: Malaria

in plants: Downy mildew

All types of pathogen have a simple life cycle. They infect a host, reproduce themselves or replicate if it is a virus, spread from their host and infect other organisms. They also all have structural adaptations that make them successful at completing their life cycles, which enable them to cause more disease.

Diseases caused by pathogens are called communicable diseases. This means the disease can be transferred from an infected organism to another organism.

1) Inherited genetic disorders like cystic fibrosis can be passed to offspring but not to anyone else.

2) Deficiency diseases which are caused by a lack of essential vitamins or minerals, such as scurvy which occurs when an individual has insufficient vitamin C.

3) Diseases like cancer that develop as a result of exposure to carcinogens or develop naturally as cell division occurs incorrectly.

Type of transmission: Direct contact

Example: This can be sexual contact during intercourse or non-sexual contact, like shaking hands.

Type of transmission: water

Example: Dirty water can transmit many diseases, such as the cholera bacterium.

Type of transmission: Air

Example: When a person who is infected by the common cold sneezes, they can spray thousands of tiny droplets containing virus particles to infect others.

Type of transmission: Unhygienic food preparation

Example: Undercooked or reheated food can cause bacterial diseases like Escherichia coli which is a cause of food poisoning.

Type of transmission: Vector

Example: Any organism that can spread a disease is called a vector. Many farmers think tuberculosis in their cattle can be spread by badgers.

The life cycle of a virus is the same as other pathogens. They can often survive outside a host for long periods of time. When they do infect a suitable host cell or cells, they replicate themselves within the cell thousands of times. They do not divide and reproduce like cells, but complete the lytic pathway.

1) They replicate their DNA and protein coats.

2) These are then assembled into new virus particles.

3) This causes the host cell or cells to burst. This is called lysis and provides the name of the 'lytic cycle'.

4) Other nearby cells can then be infected with the virus. This process can be as quick as twelve hours in the case of the norovirus or several days for the process of Ebola.

Other types of virus called phages either join their DNA to that of their host or leave small circles of their DNA in the cytoplasm of their host cell or cells. This is called the lysogenic pathway. When these cells divide the DNA is copied. Later in the life cycle the viral DNA is copied and the lytic cycle detailed above begins.

movement

respiration

sensitivity

nutrition

excretion

reproduction

growth

We say 'strains' of virus and not species. Strains are made of a relatively short length of genetic material (DNA) which is surrounded by a protein coat.

Viral infections cannot be treated by antibiotics.

HIV stands for human immunodeficiency virus. This infection is transmitted by body fluids, often during unprotected sex, but also through cuts and injecting drugs using unsterilized needles. Immediately after infection, people often suffer mild flu-like symptoms. These pass and for a period of time infected people might not know they are infected.

AIDS stands for acquired immune deficiency syndrome. Months or years after the infection by HIV, the virus becomes active and attacks the patient's white blood cells. HIV at this point has resulted in AIDS.

There is no cure for HIV/AIDS although scientists are trying to find one. Currently, infected people are given antiviral drugs, which can significantly slow the development of AIDS.