Chapter 5: Communicable Diseases

Question 1

Health and Disease

Answer 1

• Health is the state of physical and mental well-being
• Diseases, both communicable and non-communicable, are major cause of ill health
• Other factors including diet, stress, and life situations may have a profound effect on both mental and physical health
• Different types of diseases may and often do interact

Question 2

Pathogens and Disease

Answer 2

• Communicable diseases are caused by microorganisms called pathogens, which include bacteria, virus, fungi and protists
• Bacteria and viruses reproduce rapidly inside your body. Bacteria can produce toxins that make you feel ill
• Viruses live and reproduce inside your cells, causing cell damage
• Pathogens can be spread by direct contact, by air (including droplet infection), or by water

Question 3

Growing Bacteria in the lab

Answer 3

• An uncontaminated culture of microorganisms can be grown using a sterilised petri dish and agar. You sterilise the inoculating loop before use and fix the lid of the petri dish to prevent unwanted microorganisms getting in.
• Uncontaminated cultures of microorganisms are needed for investigating the action of disinfectants and antibiotics
• Cultures should be incubated at a maximum temperature of 25 degrees C in schools and colleges to reduce the likelihood of pathogens growing that might be harmful towards humans

Question 4

Preventing bacterial growth

Answer 4

• Bacteria multiply by simple cell division every 20 minutes if they have enough nutrients and a suitable temperature
• You can investigate the effects of disinfectants and antibiotics on bacterial growth using agar plates and calculating the gross sectional area of colonies frown or of clear areas of agar
• Bacteria at end of growth period = bacteria at beginning of growth period x 2^number of divisions

Question 5

Preventing infections

Answer 5

• The spread of disease can be prevented by simple hygiene measures, by destroying vectors, by isolating infected individuals, and by vaccination
• Hygiene: hand washing, using disinfectants, keeping raw meet away from food that is going to be eaten, coughing or sneezing into a tissue, maintaining hygiene to prevent spread of diseases
• Isolation: if infected be do not come into contact with healthy people the disease will not be spread
• Destroying vectors: means to kill off insects and animals that can spread the disease, like mosquitoes, houseflies, rats, etc.
• Vaccination: gives body a small amount of an inactive pathogen so that the body can find antibodies for the pathogen and become immune to it

Question 6

Viral Diseases

Answer 6

• Measles virus is spread by droplet infection. It causes fever and rash and can be fatal. There is no cure. Isolation of patients and vaccination prevents spread
• HIV initially cause flu-like illness. Unless it is successfully controlled with antiretroviral drugs the virus attacks the body immune cells. Late stage HIV infection, or AIDS, occurs when the bodies immune system is so badly damaged that it can no longer deal with other infections or cancers. HIV is spread by sexual contact or by the exchange or body fluids, such as, blood, which occurs when drug users share needles

Question 7

TMV

Answer 7

• Tobacco mosaic virus is spread by contact and vectors. It damages leaves and reduces photosynthesis. There is no treatment. spread is prevented by field hygiene and pest control.
• TMV causes a distinctive mosaic pattern of discoloration on the leaves where the virus has destroyed chlorophyll.
• This affect the growth of the plant as these cells can no longer photosynthesise and cannot produce glucose for respiration, so they produce enough energy to grow cannot grow.
• It can seriously reduce the yield of a crop.
• Can remain infectious in the soil for about 50 years

Question 8

Bacterial Diseases

Answer 8

• Salmonella is spread through undercooked food or poor hygiene. Symptoms include fever, abdominal cramps, diarrhoea and vommitting caused by the toxins produced by the bacteria. In the UK, poultry are vaccinated against salmonella to control the spread of the disease
• Gonorrhoea is a STD. Symptoms include discharge from the penis or vagina and pain on urination. Treatments involve using antibiotics, but many strains of gonorrhoea are now resistant. Using condoms and limiting sexual partners prevents spread
• There are relatively few bacterial diseases of plants but agrobacterium tumefaciens causes galls – a mass of unspecialised cells that often grow at the join between the root and the shoot in infected plants.

Question 9

Diseases caused by fungi and protists

Answer 9

• Rose black spot is a fungal disease spread in the environment by wind and water. It damages leaves so they drop off, affecting growth as photosynthesis is reduced. Spread is controlled by removing infected leaves and chemical sprays, but is not very effective
• Malaria is caused by parasitic protists and is spread by the bite of female mosquitos. It damages blood and liver cells, causes fevers and shaking, and can be fatal. Some drugs are effective if given early, but protists are becoming resistant. Spread is reduced by preventing the vectors from breeding and by using mosquito nets to prevent people from being bitten

Question 10

Human defence responses

Answer 10

• Your body has several lines of defence against the entry of pathogens. These include the skin (barrier and antimicrobial), the nose, the trachea, the bronchi, and the stomach
• Your white blood cells help to defend against pathogens by ingesting them and by making antibodies and antitoxins

See picture in documents

Question 11

More about plant diseases

Answer 11

• Plants can be infected by a range of viral, bacterial and fungal pathogens as well as insect pests
• Plants can be damaged by a range of ion deficiency conditions
• Plant diseases can be detected by a range of symptoms like stunted growth, spots on leaves, areas of decay or rotting, growths, malformed stems and leaves, discoloration, presence of visible pests and identified in several ways including gardening manuals and lab tests, some involving monoclonal antibodies

Question 12

Plant defence response

Answer 12

• 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 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 (like drooping to mimic unhealthy plants or mimic butterfly eggs on their leaves)