B6.3-part 1 Monitoring and maintaining health

Question 1

Describe the relationship between health and disease

Answer 1

• if a person is in good health, they don’t have any type of disease
• a disease is a condition caused by any body part not functioning properly
• diseases can affect both mental and physical health

Question 2

State the definition, causes and examples of communicable diseases

Answer 2

• diseases that can be spread between organisms
• also called contagious or infectious
• most caused by microorganisms
• most microorganisms cause no harm, but pathogens (microorganisms) cause disease when they enter the organism - these are parasites

Type of pathogen - example of animal disease - example of plant disease

Fungi - athlete’s foot - powdery mildew
Bacteria - tuberculosis - crown gall disease
Viruses - influenza (flu) - tobacco mosaic disease
Protozoa - malaria - coffee phloem necrosis

Question 3

State the definition, causes and examples of non-communicable diseases

Answer 3

• cannot be spread between organisms

Causes:

• a poor diet - vegetable + fruitless diet can result in vitamin and mineral deficiencies
• obesity - can lead to arthritis, type 2 diabetes, heart disease and stroke
• inheriting a genetic condition - e.g. cystic fibrosis
• body processes not operating correctly - uncontrollable cell division may lead to cancer

Question 4

Describe the interactions between different types of disease (HIV and TB; HPV and cervical cancer)

Answer 4

Although most communicable and non-communicable diseases have separate causes, some conditions are linked.

HPV and cervical cancer

• Human papilloma virus causes most forms of cervical cancer
• periphery usually recover from an HPV infection without long term problems
• in some cases, HPV causes cell changes that lead to cervical cancer
• Girls in the UK are now routinely vaccinated against this virus, which has significantly reduced the no. of cases of cervical cancer

HIV and TB

• human immunodeficiency virus, which causes AIDS (acquired immune deficiency syndrome), weakens a person’s immune system, making it much easier for other microorganisms, like the tuberculosis-causing bacteria, to cause disease
• many people with HIV die from tuberculosis

Question 5

Describe how communicable diseases can be spread between animals

Answer 5

Pathogens enter an animal’s body in order to cause harm:

• through cuts in skin - from injury, or insect/animal bites
• through digestive system - foods and drinks shared
• through respiratory system - by inhaling pathogens
• through reproductive system - during sexual intercourse

The closer together organisms live, the greater risk of a disease being passed on

Question 6

Describe how communicable diseases can be spread between plants

Answer 6

• through soil and water in which the plants grow
• vectors, such as insects
• direct contact of sap from an infected plant with a healthy plant. Sap can be released by agricultural damage, or through animals feeding on plants
• the wind. Fungal spores can be blown between plants. Infected seeds can also be blown across large distances, resulting in the spread of a disease

Question 7

Explain how pathogens cause disease

Answer 7

• incubation period - time delay between harmful organisms entering body and you feeling unwell
• during this period, pathogens reproduce rapidly
• as they grow + reproduce they cause cell damage
• some also produce toxic waste products - these toxins cause a range of symptoms like fevers, rashes and sores
• Viruses can not replicate by themselves - they can only reproduce by ‘taking over’ and using a host organism’s cell to make more viruses

Question 8

State the steps of viral replication

Answer 8

• virus attacks a cell
• inserts it’s genes
• ‘tells’ the nucleus to copy its genes
• new viruses are made
• cell bursts, releasing the new viruses and destroying your cell

Question 9

Explain how scientists monitor disease

Answer 9

• for disease outbreaks they normally study the incidence of a disease - rate at which new cases occur in a population over a period of time
• for non-communicable diseases, studies often last for long periods and involve many people
• a typical study may look at the no. of cases per 10000 people, per year, over a 10-year period
• outcomes from studies like these provide scientists with evidence for the effectiveness of disease treatments or prevention techniques

Question 10

Explain how the spread of communicable diseases between humans (animals) can be reduced or prevented

Answer 10

• covering your mouth + nose when coughing/sneezing - use a tissue and immediately discard it
• not touching infected people or objects - e.g. chicken pox and mumps
• using protection - e.g. condoms to help prevent STIs being transferred (body fluids prevents from being exchanged during sex)
• not sharing needles - needles used to inject drugs should be disposed of immediately after single use - e.g. HIV and hepatitis can be passed on in blood on the needle

Being hygienic:

• washing your hands - before eating
• cooking food properly - some animals contain bacteria (E.coli, salmonella) which could cause food poisoning - thorough cooking kills bacteria
• drinking clean water - untreated water contain microorganism that cause diseases like cholera and typhoid. Boil water / use sterilisation tablets
• protect yourself from animal bites - use insect-repellent sprays

Question 11

Explain how the spread of communicable diseases between animals and plants can be reduced or prevented

Answer 11

First, diseases are identified by changes to an organism’s appearance, or through identifying the pathogen by its DNA or antigens (proteins on surface of microorganism). Once identified:

• diseased plant material is normally burnt to prevent disease spreading
• animals may be treated using drugs although some communicable diseases require whole herds to be slaughtered
• livestock cannot be moved
• chemical dips are installed on farms to kill pathogens on footwear
• farmers also spray plants with fungicides to prevent fungal disease
• get their animals vaccinated against some pathogens

Question 12

Describe common fungal infections (athlete’s foot)

Answer 12

Athlete’s food

• caused by a group of parasitic fungi called dermatophytes
• feet provide a warm, humid environment, ideal for dermatophytes to live and multiply in
• symptoms (effects of disease) are cracked, flaking itchy skin
• normally treated using an anti-fungal cream
• very contagious - spread through direct and indirect contact

Question 13

Describe common bacterial diseases (food poisoning)

Answer 13

Food poisoning

• caused by growth of microorganisms in food
• most serious types are caused by bacteria and the toxins they produce

3 main groups:

• Campylobacter - found in raw meat, unpasteurised milk and untreated water
• Salmonella - raw meat, eggs, raw unwashed vegetables and unpasteurised milk
• E.coli - only some types cause food poisoning - found in raw and undercooked meats, and unpasteurised milk and dairy products
• all these bacteria can survive refrigeration and freezer storage, but thorough cooking kills them
• common symptoms - stomach pains, diarrhoea, vomiting and fever
• most get better within a few days
• in some cases, doctors may need to use a drip to replace fluids
• in rare cases it can kill

Question 14

Describe some examples of sexually transmitted diseases

Answer 14

STIs are passed on between people through unprotected sex or genital contact - passed on through bodily fluids or by skin on skin contact

• people use condoms to protect themselves
• many diseases initially don’t have symptoms so makes their spread more likely as people are unaware that they are infected

Infection - cause - symptoms - treatment
Chlamydia - bacteria - pain when urinating, discharge from penis/vagina - antibiotics
Gonorrhoea - bacteria - burning pain when urinating, vaginal discharge - antibiotics
Genital herpes - virus - painful blisters or sores - no cure
HIV - virus - weakened immune system, often resulting in AIDS - no cure, symptoms controlled with antiretroviral drugs. Lifetime treatment required

Question 15

Explain the difference between HIV and AIDS

Answer 15

• HIV invaded WBC and reproduces inside cells
• this weakens your immune system as affected cells show be producing antibodies to defend against disease but cannot
• without them, body becomes target of everyday infections and cell changes that cause cancer
• AIDS is final stage of HIV infection, when body can no longer fight life-threatening infections like cancer

Question 16

Describe a viral plant disease (tobacco mosaic virus)

Answer 16

• virus attacks leaves, making them mottled/discoloured - does this by preventing chloroplasts from forming, which stunts growth of plant
• virus almost never kills plants, but lowers quality + quantity of crop produced
• to prevent spread, infected plants should be removed, and hands and equipment washed between panting
• to avoid soil re-infecting the flowing year’s plants, crops that are resistant to the tobacco mosaic virus should be planted in previously infected areas

Question 17

Describe a bacterial plant disease (crown gall disease through A. tumefacians)

Answer 17

Agrobacterium tumefaciens

• has large plasmid, known as a tumour-inducing plasmid - containing genes that cause crown gall disease
• affects many plants (roses, fruit and nut trees)
• bacteria enters plant through wound
• plasmid integrates into host’s genome, and causes production of greater amounts of growth chemicals than normal
• leads to production of large tumour-like growths called galls
• as disease progresses, falls can totally encircle the plant’s stem/ trunk, cutting off the flow of sap - causes stunted growth and eventual death
• to prevent its spread, infected plants must be destroyed + removed
• planting other susceptible plants in are should also be avoided for 2 year, until bacteria die out for lack of host plant

Question 18

Describe a fungal plant disease (Powdery mildew)

Answer 18

• Powdery mildew - fungi dies see affecting wide range of plants
• caused by many different species of fungi
  E.g. Erysiphe graminis causes barley powdery mildew
• infected plants display white powdery spots (fungal growth) on leaves + stems
• fungus reduces growth, and makes leaves drop off early, reducing crop yield by 10-15%
• powdery mildew grows well in areas of high humidity + moderate temps
• survives between seasons on plant residues
• it then releases spores, which are spread by wind to infect the new crop
• can be controlled by spraying crop with a fungicide

Question 19

Describe physical plant defence responses to disease

Answer 19

Cuticle

• epidermal cells of most parts of the plant above the ground are covered in a waxy cuticle
• prevents water loss from plant
• prevents pathogens from coming into direct contact with epidermal cells, limiting chance of infection
• Cuticles can be relatively thin (aquatic plants), or extremely thick (cactus)
• the hydrophobic (water repelling) nature of cuticle prevents water from collecting on leaf surface
• this is an important defence against many fungal pathogens, as most require standing water on leaf surface for spore germination

Cell wall

• major defence against fungal + bacterial pathogens
• provides excellent structural barrier
• all plants cells have a primary cell wall that provides structural support - composed of mainly cellulose fibres, giving strength + flexibility
• these fibres cross-link with other substances like pectin - forms a gel that helps to cement neighbouring cells together
• many cells also form a secondary cell wall, which develops inside primary cell wall - provides further structural barrier
• cell walls also contain a variety of chemical defence that can be activated rapidly when cells detect pathogens

Question 20

Describe chemical plant defence responses

Answer 20

• insect repellents to repel insect vectors that carry disease (e.g. pine resin, citronella from lemon grass)
• insecticides to kill insects (pyrethrins made from chrysanthemums)
• antibacterial compounds to kill bacteria (e.g. phenols disrupt bacterium’s cell wall, defending disrupt cell membrane)
• antifungal compounds to kill fungi (chitinases - enzymes that break down chitin in fungal cell walls; caffeine - toxic to fungi + insects)
• cyanide - some plants make chemicals that break down to form cyanide compounds when the plant cell is attacked - toxic to most living things

Question 21

Describe how plant diseases can be detected in the field

Answer 21

Observation
- most plants have visual symptoms
E.g.
- strawberry mottle disease - viral - discoloured leaves
- bacterial soft rot - bacteria - rotting of plant’s leaves/fruit
- powdery mildew - fungal - White, powdery deposit on plant - repeated infection weaken tree and reduce its yield

Microscopy

• often symptoms of many plant diseases are similar
• plant pathologists use microscopy to identify pathogen e.g. identify species of bacteria by their shape
• electron microscopes sometimes required for accurate diagnosis (identifying existence of disease)
• but plant disease can only be identified in field once an infection had taken hold, and symptoms become apparent

Question 22

Describe how plant diseases can be detected in the laboratory

Answer 22

DNA analysis

• every plant pathogen has unique genome - identified using DNA fingerprinting
• map of genome produced - profile
• scientists compare unknown plant pathogen’s genome to a known DNA profile
• if match is found, accurate diagnosis can be made
• DNA profiles can be used to identify individual strains of microorganism

Identification of antigens

• plant pathogens carry specific antigens (proteins) on their surfaces
• these can be identified through chemical analysis, so the pathogen can be identified
• scientists have developed diagnostic kits to enable farmers to identify common crop pathogens
• key advantage of both lab-based techniques is the potential to identify a plant pathogen before it causes significant damages to a crop