Infection and Response (3)

Communicable disease

A disease caused by a pathogen which can be passed between animals or plants eg. flu.

Pathogen

A disease-causing microorganism e.g. bacteria.

How do bacteria cause disease?

Once inside the body, they divide rapidly by binary fission. They kill cells and produce harmful toxins.

How do viruses cause disease?

They invade and reproduce inside living body cells, leading to cell damage.

Ways pathogens can be spread

●By air - flu, tuberculosis and the common cold are spread by droplet infection. ●By water - fungal spores in water spread plant diseases. ●By direct contact - common in plant diseases and sexually transmitted infections.

Ways to reduce the spread of pathogens

●Hygiene - handwashing, disinfectants, tissues. ●Reducing contact with infected individuals - quarantine. ●Removing vectors - use of pesticides and insecticides, removal of habitats. ●Vaccination.

Importance of preventing viral disease spread

Scientists have not yet developed cures for many viral diseases.

Measles

Measles is a serious viral disease that can cause blindness and brain damage. The main symptoms are a fever and a red skin rash.

How is measles spread?

By air - through the inhalation of droplets from coughs and sneezes.

HIV/AIDS

HIV is a virus which attacks and damages the immune system until it can no longer function properly. AIDS is the condition resulting from a long-term HIV infection. There is no cure or vaccine for HIV/AIDS.

How is HIV spread?

Direct sexual contact and the exchange of bodily fluids eg. blood, breastmilk.

Preventing the spread of HIV/AIDS

●Use of condoms ●Screening of blood for transfusions ●Not sharing needles ●Bottle-feeding by HIV-positive mothers ●Use of antiretroviral drugs to prevent the development of AIDS.

Tobacco mosaic virus

A plant pathogen which causes leaf discolouration when cells are damaged. Affected areas cannot photosynthesise, reducing the crop yield. As there is no treatment, farmers grow TMV-resistant crop strains to avoid infection.

How is tobacco mosaic virus spread?

Contact between infected and healthy plants. Insects may act as vectors which transfer the virus between different plants.

Salmonella

A type of bacteria found in raw meat, poultry and eggs. If they enter the body via food poisoning, they can affect natural gut bacteria.

Symptoms of salmonella food poisoning

●Fever ●Abdominal cramping ●Vomiting ●Diarrhoea. May be fatal in very young or elderly populations due the risk of dehydration.

Limiting the spread of salmonella

●Vaccinating animals intended for consumption ●Keep raw meat away from cooked meat ●Disinfect hands and surfaces after contact with raw meat ●Thoroughly cook meat.

Gonorrhoea

Gonorrhoea is a sexually transmitted infection caused by the bacterium Neisseria gonorrhoeae.

Sexually transmitted bacterial infection

An infection caused by unprotected sex with an infected individual, with early symptoms including yellow/green discharge from genitals and painful urination.

Rose black spot

A fungal disease which causes purple or black spots to develop on rose leaves, reducing the area available for photosynthesis and causing leaves to turn yellow and drop prematurely.

Spread of rose black spot fungus

Fungal spores are spread by the wind and in water.

Treatment of rose black spot fungus

Using fungicides and destroying infected leaves.

Malaria

A disease caused by protist pathogens, carried from host to host by mosquitoes, entering the human bloodstream when they feed, with symptoms including fever and shaking.

Reduction of malaria spread

Using insecticides, using insect nets to avoid bites, preventing mosquito breeding by removing stagnant water, and using antimalarial drugs.

Skin's role in pathogen prevention

Acts as a physical barrier, forms scabs after cuts, secretes antimicrobial substances, and has healthy skin flora that compete with pathogens.

Respiratory system's role in pathogen prevention

Nose has hairs and mucus that trap pathogens; trachea and bronchi have mucus that traps pathogens, with ciliated cells moving mucus to the mouth.

Stomach's role in pathogen prevention

Secretes hydrochloric acid that kills any pathogens present.

Phagocytosis

A process where white blood cells (phagocytes) ingest and destroy pathogens to prevent further infection.

Antibody production

White blood cells produce antibodies complementary to specific antigens on pathogens, causing them to clump together for easier destruction.

Antitoxin production

Antitoxins bind to toxins released by pathogens and neutralize them.

Vaccination

Contains a dead or inactivated form of the pathogen, stimulating white blood cells to produce complementary antibodies, with memory cells enabling rapid response to future infections.

Herd immunity

Occurs when a sufficiently high proportion of a population is immune to a disease, limiting its spread.

Advantages of vaccinations

They have eradicated many deadly diseases, such as smallpox.

Disadvantages of vaccinations

Not guaranteed to work - might not protect against multiple strains of a pathogen. May be side effects or adverse reactions.

Antibiotics

Drugs that can kill bacterial pathogens inside the body.

How antibiotics work

Antibiotics, e.g., penicillin, kill bacterial pathogens inside the body, but do not kill human cells. The right antibiotic must be used for specific bacteria.

Antibiotics and viral diseases

Antibiotics have no effect on viral pathogens as they live inside the host's (human) cells.

Antibiotic resistance

Occurs when mutations lead to individual bacteria being resistant to an antibiotic, allowing them to survive, reproduce, and pass on their alleles.

Preventing antibiotic resistance

Avoid overuse and unnecessary use of antibiotics, and finish antibiotic courses to ensure all bacteria are killed.

Effect of painkillers on infectious diseases

Painkillers can only treat the symptoms but do not kill pathogens.

Digitalis

A heart drug extracted from foxgloves.

Aspirin

A painkiller that originates from a compound found in willow bark.

Penicillin

An antibiotic discovered by Alexander Fleming from a type of mould.

Qualities of a good medicine

Effective, Safe, Stable, Able to be taken in and removed easily.

Factors tested in drug development

Toxicity, Efficacy, Dose.

Preclinical testing

Carried out in a laboratory using cells, tissues, and live animals.

Clinical testing

Uses healthy volunteers and patients, testing at low doses initially and then on a larger scale.

Single-blind trial

Only the doctor knows whether the patient is receiving the drug or the placebo.

Double-blind trial

Neither the patient nor the doctor knows which group receives the drug or placebo, helping to remove bias.

Peer review

Where the results of drug trials are checked over by scientists knowledgeable in this field.

How do aphids cause damage to plants?

They use their sharp mouthparts to extract sap from the plant phloem, weakening the plant, and can transfer pathogens from diseased plants to healthy plants.

How can we reduce the number of aphids?

Using chemical pesticides and biological pest control, such as ladybirds.

Why do plants need a good supply of nitrate ions?

Nitrate ions are required to convert sugars into proteins necessary for plant growth; inadequate supply stunts growth.

Why do plants need a good supply of magnesium ions?

Magnesium ions are required to synthesize chlorophyll, which is essential for photosynthesis; a deficiency causes leaves to turn yellow (chlorosis).

What are the symptoms of disease in plants?

Symptoms include stunted growth, spotted leaves, decay/rotting, growths, malformation of stems/leaves, discolouration, and presence of pests.

What are three ways in which plant disease can be identified?

Identification methods include reference to gardening websites or manuals, laboratory testing, and monoclonal antibody test kits.

Give examples of physical defence responses used by plants.

Examples include cellulose cell walls, tough waxy cuticle on leaves, outer layer on stems/bark, and leaf fall.

Give examples of chemical defence responses used by plants.

Examples include antibacterial chemicals and poisons.

Give examples of mechanical defence responses used by plants.

Examples include thorns and hairs to deter animals, leaves that droop/curl on contact, and mimicry to trick animals.

What are monoclonal antibodies (mAbs)?

Antibodies that are clones from one parent cell, specific to one type of antigen.

How are monoclonal antibodies produced?

1. Specific antigen injected into an animal (e.g. mouse). 2. B-lymphocytes producing complementary antibodies extracted. 3. B-lymphocytes fuse with myeloma cells to form hybridoma cells. 4. Hybridoma cells cultured. 5. Monoclonal antibodies collected and purified.

What are the uses of monoclonal antibodies?

Detection of pathogens, location of cancer cells and blood clots, treatment of cancer, and used in pregnancy test kits.

What are myeloma cells?

A type of tumour cell.

What do pregnancy kits test for?

hCG in urine.

What does a pregnancy test consist of?

A stick containing monoclonal antibodies (mAbs) specific to hCG, with mAbs attached to a blue bead and mAbs fixed to the test stick.

What happens to the test stick if a woman is pregnant?

hCG in urine binds to mAbs attached to a blue bead, mAbs with hCG diffuse up dipstick, mAbs fixed to the stick bind to hCG, and a blue line forms.

What happens to the test stick if a woman is not pregnant?

No hCG in urine so a blue line is not formed.

What is the advantage of using monoclonal antibodies to test for pathogens?

Specific to one particular antigen, very accurate, and provide quick results.

Why can monoclonal antibodies be used to target cancer cells?

Cancer cells have specific antigens called 'tumour markers' on their membranes, and mAbs can be targeted to these without damaging other cells.

How can monoclonal antibodies be used to diagnose cancer?

mAbs tagged to a radioactive substance are injected into the bloodstream, bind to 'tumour markers' on cancer cells, and emitted radiation is detected to locate cancer cells.

How can monoclonal antibodies be used to target drugs to cancer cells?

mAbs attached to an anti-cancer drug are injected into the bloodstream, bind to 'tumour markers' on cancer cells, and the drug destroys the cancer cells.

Why are cancer treatments that use monoclonal antibodies favored over traditional treatments?

They only target cancer cells, reducing damage to normal cells, unlike radiotherapy and chemotherapy which damage healthy rapidly dividing cells.

How can monoclonal antibodies be used to locate blood clots?

mAbs tagged to a radioactive substance target and bind to specific proteins in blood clots, and the emitted radiation is detected to identify the location of blood clots.