AQA GCSE Biology - Diseases

Health

A state of physical and mental well-being, not just an absence of disease

Communicable diseases

Diseases that are caused by pathogens or by a toxin made by a pathogen which can be passed from one person to another.

Communicable diseases examples

Tuberculosis, flu, HIV/AIDS

Non-communicable diseases

Diseases that cannot be passed on from one person to another

Non-communicable diseases examples

Arthritis, Heart disease and cancer - any deficiency disease, genetic disorders

Main Factors that can affect health

Diet, Stress and life situations (e.g. ethnic group and financial status)

How health problems interact

Different types of diseases may and often do interact, e.g. viruses in cells can trigger changes that lead to cancer and severe physical illness can lead to depression

Types of pathogens

Bacteria, viruses, protists or fungi

Differences between bacteria and viruses

Viruses are much smaller than bacteria and usually have a regular shape, bacteria are also alive

How pathogens cause disease

Bacteria divide rapidly by splitting into 2 (binary fission) and produce toxins that make you feel ill and they also might directly damage your cells while viruses take over cells of your body. They live and reproduce inside cells, damaging and destroying them

How pathogens are spread

By air, direct contact or by water

Bacteria culture

A place where bacteria are grown in very large numbers so that scientists can see all of the bacteria as a whole

Growing microorganisms in the lab

Must provide them with liquid or gel containing nutrients (culture medium) and warmth and oxygen to optimally grow. Pour hot agar gel into a Petri dish, then leave it to cool.

Contamination

Can come from your skin, the air, the soil, or the water around you

Why do we not want contamination in growing bacteria in the lab?

So we can investigate the effects of chemicals such as disinfectants and antibiotics

Why do we keep the maximum temperature of the cultures at 25C in schools

If you cultured bacteria at 37C (human body temp), there would be a high risk of growing some dangerous pathogens, the lower the temperature, the lower the likelihood of growing pathogens that may be harmful to people.

Sterilising

Kills any unwanted microorganisms, usually by heating or high pressure or ionising radiation

Calculating the number of bacteria in a population

Calculate how many times they will divide in an hour, times by number of hours to calculate number of divisions:

use: bacteria at end = bacteria at beginning x 2^number of divisions

Preventing spread of communicable diseases

Hand-washing, using disinfectants, coughing or sneezing into a handkerchief, physical barriers, isolating, destroying or controlling vectors and vaccination

What type of disease is Measles?

Viral disease

What type of disease is HIV/AIDS?

Viral disease

What type of disease is Tobacco Mosaic Virus?

Viral disease

Measles

Is spread by droplet infection. It causes fever and a rash and can be fatal. There is no cure so patients must be isolated. However, vaccination prevents spread

HIV/AIDS

HIV is spread by sharing needles, sexual contact, and the exchange of bodily fluids that initially causes a flu-like illness. Late stage HIV infection (AIDS), occurs when the body’s immune system is so badly damaged that it can no longer deal with other infections or cancers.

Tobacco Mosaic Virus

Spread by contact and vectors. It damages leaves and, hence, reduces photosynthesis. There is no treatment so spread is prevented by field hygiene and pesticides

What type of disease is Salmonella food poisoning?

Bacterial disease

What type of disease is Gonnorrhoea?

Bacterial disease

Are bacterial diseases common in plants?

No

Salmonella food poisoning

Spread through undercooked food and poor hygiene. Symptoms include abdominal cramps, fever, diarrhoea and vomiting caused by the toxins produced by the bacteria. Poultry is vaccinated to prevent the spreading of this disease

Gonorrhoea

An STD that causes discharge and pain on urination. Treatment involves antibiotics and physical barriers

What type of disease is Rose Black Spot?

Fungal disease

Rose Black Spot

Spread by wind and water. It damages leaves so they drop off, affecting growth as photosynthesis is reduced. Spread is controlled by using chemicals, but that’s still not very effective

Malaria

Caused by parasitic protists and spread by the bite of female mosquitoes, it damages blood and liver cells and can cause fevers which are fatal. Spread is reduced by preventing vectors from breeding and using mosquito nets

Body lines of defence against pathogens

Skin, nose hairs, trachea and bronchi mucus secretion, stomach acid, skin oil and white blood cells

Types of WBCs

Phagocytes and Lymphocytes

Phagocytes

Ingest pathogens, digesting and destroying them

Lymphocytes

Produce antibodies which bond to the antigen on the pathogen, destroying it. Also produce memory cells and antitoxins to counteract the toxins released by the pathogens

Chlorosis

Yellowing of leaves due to lack of magnesium ions, prevent by using fertilisers which replace lost minerals

Detecting plant disease

stunted growth, spots on leaves, areas of decay, growths, malformed stems, discolouration and presence of visible pests

Plant physical barriers

cell walls strengthen plant cells, waxy cuticle bark on trees and leave fall that ensures the infected leaves are taken away

Plant chemical barriers

Produce antibacterial chemicals that protect them against invading pathogens

Plant defence against herbivores

Poisons, thorns, hairy stems, drooping or curling when touched and mimicry

Vaccination

Involves introducing small amounts of dead or weakened pathogens to the body to stimulate WBCs to produce antibodies. The WBCs respond quickly to prevent, when the pathogen arrives, to destroy it

Herd immunity

When a large proportion of a population is vaccinated against a disease, making it difficult for the pathogen to spread

Paracetamol and Aspirin

Used as painkillers - don’t get rid of pathogen, just soothes the feeling of pain

Antibiotics

Cure bacterial diseases

Penicillin

by Alexander Fleming in 1928 involved him noticing mould (Penicillium) killing bacteria on a contaminated Petri dish, leading to the first antibiotic

What defines a good medicine?

How effective it is, if it’s safe, stable and successfully taken in and out of the body so it doesn’t overdose

Efficacy

How well a new medicine works to cure a disease or relieve symptoms

Toxicity

How harmful a new medicine is, checking for dangerous side effects or cell damage

Dosage

the specific amount of a medicine needed for it to be effective without being harmful

Preclinical trials

To assess if a drug is toxic (harmful) and has potential before human testing. Test on human cells and tissue in labs as well as live animals

Phase 1 - Clinical trials

Very low dosage is given to healthy volunteers to check for safety and side effects

Phase 2 - Clinical trials

Trials continue to find the optimum (best) dose.

Phase 3 - Clinical trials

Tested on patients with the illness to see if it works (efficacy).

Double blind trial

To reduce bias, some patients get the drug, others get a placebo, neither patients nor doctors know who gets what.

Placebo

A fake treatment (like a sugar pill) that looks identical to a real drug but has no active ingredients

How are monoclonal antibodies produced?

inject an animal with an antigen, collect its lymphocytes, fuse them with tumour cells to create hybridomas, clone these hybridomas, and then collect and purify the identical (monoclonal) antibodies they produce, which are specific to one target. 

Hybridomas

A fused cell made from a mouse lymphocyte (which makes a specific antibody) and a tumour cell (which divides rapidly)

Uses of monoclonal antibodies

Pregnancy tests, diagnosis of disease, measuring and monitoring levels of blood/hormones, research and treating disease

How do monoclonal antibodies treat disease

They have been developed against the antigens on cancer cells, if a monoclonal antibody is bound to a radioactive substance, it will deliver the substance to the cancer cells without harming other cells in the body.

Advantages of monoclonal antibodies

They only bind to specific diseased or damaged cells

Disadvantages of monoclonal antibodies

Very expensive and they have created more side effects than expected

Risk factors for non-communicable diseases

Aspects of your life (smoking, exercise) and exposure to ionising radiation

Carcinogens

A chemical that leads to a mutation in cells

Benign tumours

Growths of abnormal cells contained in one place, not spreading to other tissues

Malignant tumours

Are cancers, they invade neighbouring tissues and may spread to different parts of the body in the blood where they form secondary tumours

Tumour

Result of abnormal, or uncontrolled cell division

Causes of cancer

Genetic factors, mutations from chemicals, exposure to ionising radiation

Radiotherapy

When cancer cells are destroyed by targeted doses of radiation

Chemotherapy

Chemicals are used to either stop the cancer cells dividing or make them “self-destruct”

Smoking during pregnancy

is a major risk factor for complications like premature birth, low birth weight, miscarriage, stillbirth, and birth defects because carbon monoxide reduces oxygen to foetus

Nicotine

Addictive drug found in tobacco smoke, it produces a sensation of calm, well-being

Carcinogens effects

Cilia in trachea and bronchi become weaker, so pathogens are more likely to enter the body and cause illness.

Cirrhosis

A disease that destroys liver tissue, liver cells are replaced with scar tissue that cannot carry out the same function.

Examples of carcinogens

Alcohol, smoking and ionising radiation.