1.3 infection and response

Communicable diseases

Diseases caused by pathogens that can spread between organisms

Pathogens

Microorganisms that cause infectious disease (viruses, bacteria, protists, fungi)

How pathogens spread

Direct contact, water, or air

Virus structure/action

Enters cells, uses cell machinery to replicate, causes cell to burst and release copies

Effect of viral infection on cells

Cell damage and bursting causes illness

Bacteria reproduction

Rapid binary fission

Bacterial damage

Produce toxins that damage cells

Protists (pathogens)

Some are parasites living in/on hosts causing damage

Fungi (pathogens)

Single-celled or hyphae-based organisms producing spores

Direct contact transmission

Touching infected surfaces, bodily fluids, faeces, infected plants

Water transmission

Drinking or contact with contaminated water

Air transmission

Pathogens spread in droplets via coughing/sneezing/talking

Droplet infection

Spread of pathogens through airborne droplets

Hygiene to prevent disease spread

Handwashing, disinfectants, tissue use, isolating raw meat

Vaccination purpose

Prevents disease before infection (immunity development)

Vector control

Using pesticides, removing habitats, insect nets

Measles symptoms

Fever, red rash, pneumonia, encephalitis, blindness

Measles transmission

Droplet infection

Measles prevention

Vaccination

HIV symptoms

Flu-like symptoms → immune system failure → AIDS

HIV transmission

Sexual contact or exchange of bodily fluids

HIV prevention

Condoms, no needle sharing, screened blood, bottle feeding

HIV treatment

Antiretroviral drugs slow replication

TMV symptoms

Leaf discolouration, reduced photosynthesis, lower yield

TMV transmission

Plant contact or insect vectors

TMV prevention

Resistant strains, good hygiene, pest control

Rose black spot symptoms

Purple/black leaf spots, yellowing leaves, early leaf drop

Rose black spot transmission

Wind or water spores

Rose black spot prevention

Fungicides, removing/burning infected leaves

Malaria cause

Protist in red blood cells

Malaria symptoms

Fever and shaking due to bursting blood cells

Malaria transmission vector

Female Anopheles mosquito

Malaria prevention

Nets, removing stagnant water, antimalarial drugs

Salmonella symptoms

Fever, cramps, vomiting, diarrhoea

Salmonella transmission

Contaminated meat/eggs, poor hygiene

Salmonella prevention

Cooking food, hygiene, vaccination in poultry

Gonorrhoea symptoms

Pain when urinating, thick discharge

Gonorrhoea transmission

Unprotected sexual contact

Gonorrhoea prevention

Condoms, antibiotics (resistance developing)

Non-specific defence system

General protection against all pathogens

Skin defence

Physical barrier, antimicrobial secretions, good bacteria competition

Nose defence

Hairs and mucus trap particles

Trachea/bronchi defence

Mucus traps pathogens, cilia move mucus upward

Stomach defence

Hydrochloric acid kills pathogens

Phagocytosis

White blood cells engulf and digest pathogens

Antibody function

Bind to specific antigens on pathogens

Antigen

Protein on pathogen surface triggering immune response

Immune memory

Faster antibody production on reinfection

Antitoxins

Neutralise toxins produced by pathogens

Vaccination definition

Injection of dead/inactive pathogen to trigger immunity

Herd immunity

Reduced spread due to high population immunity

Antibiotics

Drugs that kill bacteria without harming body cells

Why antibiotics don’t work on viruses

Viruses use body cells to reproduce

Painkillers

Reduce symptoms, not cause of disease

Antibiotic resistance

Mutations make bacteria survive antibiotics

How resistance spreads

Resistant bacteria survive, reproduce, increase population

Preventing resistance

Avoid overuse, complete courses, correct prescribing

Drug testing stages

Preclinical (cells/animals) then clinical (humans)

Placebo

Fake treatment used for comparison

Single blind trial

Patient unaware of treatment

Double blind trial

Patient and doctor unaware of treatment

Peer review

Other scientists check results for reliability

Monoclonal antibodies

Identical antibodies from one immune cell

Hybridoma cells

Mouse lymphocyte + tumour cell (rapid antibody production)

Monoclonal antibody use

Pregnancy tests, diagnosis, research, cancer treatment

Pregnancy test marker

hCG hormone in urine

Pregnancy test result

Blue line indicates hCG present

Cancer treatment using antibodies

Deliver drugs, block receptors, trigger immune attack

Advantages of monoclonal antibodies

Target specific cells, reduce damage to healthy cells

Disadvantages of monoclonal antibodies

Expensive, difficult to attach drugs, immune reactions

Plant disease signs

Spots, stunted growth, decay, discolouration, abnormal growth

Nitrate deficiency effect

Stunted growth (less protein synthesis)

Magnesium deficiency effect

Chlorosis (yellowing leaves)

Plant physical defences

Waxy cuticle, cellulose walls, bark layers

Plant chemical defences

Poisons and antibacterial chemicals

Plant mechanical defences

Thorns, hairs, drooping leaves, mimicry