Infection and response

What are pathogens?

Disease causing microorganisms, like virus, protist, fungi and bacteria

What are communicable diseases?

Diseases that can spread from one living thing to another

What is virus?

• Microorganism that are not cells, but live and reproduce quickly inside cells

• This damages cells

• Examples of viral diseases are measles and flu

What is bacteria?

• Cells that reproduce quickly inside body

• Release toxins that damages cells which makes us feel ill

What is malaria?

• Parasitic protists (need a host to survive) cause malaria

• When mosquitoes feed on animal, it sucks up blood which contains malaria parasites

• When mosquitoes feed on human, malaria parasites enter human

What are symptoms of malaria?

Fever, headaches and exhausting sweats

How to prevent malaria?

• Using mosquito nets

• Wear long sleeved clothes

• Killing mosquitoes using insecticides

What is a vector?

An organism that transmits a pathogen, e.g.mosquitoes transmit parasitic protist which causes malaria

What is an example of fungi disease?

• Rose black spot

• Purple or black spots develop on leaves, causing them to turn yellow and drop early

• This reduces photosynthesis and therefore growth

• spread through environment in water or by the wind

How to treat rose black spot?

• Use fungicides

• Remove infected leaves

What is measles?

• a viral disease that is spread by droplets from an infected person’s cough and sneeze

• Symptoms are red skin rash and fever

How to treat and prevent measles?

Drink lots of water and sleep more to treat, vaccinate to prevent

What is HIV?

• a viral disease that is caused by sexual contract or exchange of blood (sharing needles when taking drugs)

• Initially there are flu like symptoms, but virus are attacking the immune cells already

• Then it may turn into AIDS, which one may experience rapid weight loss and night sweats

How to treat and prevent HIV?

• treat by taking antiretroviral drugs to stop the virus replicating in the body

• prevent by not sharing needles and use barrier methods like condoms during intercourse

What is Tobacco mosaic virus (TMV)?

• a viral disease that causes plants to produce less chlorophyll, which causes leaf decolorisation

Explain why plants with TMV have stunted growth?

• this is because plants produce less cholorophyll

• meaning less photosynthesis happens

• less glucose is made from photosynthesis

• means that less energy is released for growth via respiration

• also less glucose is combined with nitrate ions to form amino acids for growth

What is salmonella?

• bacterial diseases that cause food poisoning

• can get by eating food that’s has been contaminated with salmonella bacteria/prepared in unhygienic conditions

• Symptoms may be diarrhoea and fever

How to prevent and treat salmonella?

• Treat by resting and drinking water, taking antibiotics if it’s severe

• Prevent by cooking food throughly and storing food correctly

What is gonorrhoea?

• Bacterial disease passed on by sexual contacts

• Symptoms may be pain when urinate or thick yellow discharge from vagina/penis

How to treat and prevent gonorrhoea?

• treat by taking antibiotics, like penicillin

• however bacteria is becoming resistant to penicillin

• Prevent by using barrier methods during intercourse like condoms

How do non-specific defence systems of the human body fight against pathogens?

• Skin contains antimicrobial substances that kill pathogens

• Nose contains hairs and mucus which traps pathogens from entering lungs

• Trachea and bronchi are lined with mucus, which traps pathogens

• Cilia move mucus up the the throat, mucus is coughed out which removes trapped pathogens from respiratory system

• Stomach contains hydrochloric acid which kills many pathogens

How do white blood cells in immune system help defend against pathogens?

• Phagocytes - white blood cells engulfing and digesting pathogens

• Lymphocytes - white blood cells recognising antigens on surface of pathogens

• Lymphocytes produce antibodies, which are specific to specific antigen to destroy pathogens for phagocytes to engulf

• White blood cells also produce antitoxins to neutralise toxins produced by bacteria cells

How does vaccination work?

• inject dead or inactive pathogens which carry antigens

• At first, the lag phase (time to produce antibodies) is slower

• And less antibodies are produced

• Next time the lag phase is shorter because there are memory cells which quickly recognise antigens

• And more antibodies are produced

What are the disadvantages of vaccination?

• doesn’t always work

• Side effects

What does herd immunity mean?

• large proportion of population are vaccinated and are immune to a disease

• Reduce spread

• Therefore protects people who aren’t immune

Why do most drugs that kill bacteria cannot be used to treat viral infections?

• Viruses live inside cells

• This makes them inaccessible to drugs

• Furthermore drugs may damage body cells or tissue when trying to damage viruses

Why has there been a large increase in number of antibiotic resistant bacteria?

• Random mutations occur in some bacteria, making them resistant to an antibiotic

• When antibiotics are used, non resistant bacteria are killed and resistant bacteria survive

• Reduced competition with other bacteria for oxygen

• therefore able to survive and reproduce quickly, passing the resistance genes to the offspring

Why do painkillers not cure infectious diseases?

It only reduces the symptoms but doesn’t kill the pathogen

What do antibiotics do?

Specific antibiotics kill specific bacteria cells inside the body

Describe the process of developing and launching drugs

• Computer modelling on drugs

• Preclinical trials - testing on at least 2 different mammals

• Clinical trials - give low dose of drugs to small number of healthy individuals, then small number of sick patients, then large number of sick patients

• Drug gets a license card and is manufactured and sold

Explain why a new drug is tested on a small number of healthy volunteers, then a small number of patients, and finally a large number of patients.

• Healthy volunteers are tested first to check the drug is safe and identify side effects (testing toxicity)

• A small number of patients are then tested to see if the drug is effective (testing efficacy)

• A large number of patients are tested to confirm effectiveness, find the optimum dose, and identify rare side effects.

Give three examples of drugs that originally came from plants.

• Penicillin (an antibiotic) was discovered by Alexander Fleming from the Penicillium mould

• The painkiller aspirin originates from willow

• The heart drug digitalis originates from foxgloves

What are some patients given a placebo (fake drug)?

To compare the effects of the treatment with no treatment

What are monoclonal antibodies?

• identical copies of one type of antibody

• Have high specificity - only bind to one specific antigen on pathogen

How to produce monoclonal antibodies?

• Antibodies are produced by B-lymphocytes in an organism

• Collect the B-lymphocytes and fuse with tumour cells (which can divide easily)

• To form hybridoma

• Clone identical hybridoma to produce lots of monoclonal antibodies

How are monoclonal antibodies used in pregnancy tests?

• as urine passes through the reaction zone

• The HCG hormone in the urine binds to the mobile HCG antibody in the reaction zone, which have blue dye attached to them

• HCG hormone passes up the stick and binds to the immobilised HCG antibodies in the results zone, resulting a blue colour change

• The other antibodies from reaction zone bind to antibodies in control zone, resulting in a blue colour change

• Blue dye appears in both control and result zone means the result is positive

How can monoclonal antibodies treat cancers?

• Monoclonal antibodies may be given to patients through a drip

• Monoclonal antibodies can bind to tumour cells which have specific antigens

• This stops the tumour cells from growing

• Without killing other normal body cells

What are symptoms of plant diseases?

• Stunted growth

• Discolouration on leaves

• Malformed leaves or stems

• Spots on leaves

How can you diagnose plant diseases?

• reference to a gardening manual or website

• taking infected plants to a laboratory to identify the pathogen by looking under microscopes

What insects transmit diseases to plants?

Aphids

Give two ion deficiency on plants

• Lack of nitrate ions means stunted growth (photosynthesis when combined with glucose)

• Lack of magnesium ions means less chlorophyll is made, therefore yellow leaves and less photosynthesis which leads to stunted growth (less glucose)

Give examples of physical defences that stop pathogens entering plants.

• Cellulose cell walls

• Tough waxy cuticle on leaves

• Layers of dead cells on a bark tree

Give examples of chemical defences in plants

• Plants creating poisons to prevent herbivores eating

• Contains antibacterial chemicals which kill pathogens

Give examples of mechanical defences in plants

• thorns to stop herbivores eating

• leaves that curl if insects land on them to prevent getting eaten