Disease and Bioenergetics


Bacteria Growth

An uncontaminated culture of microorganismscan be grown using sterilised Petri dishes and agar. You sterilise the inoculating loop before use and fix the lid of the Petri dish to prevent unwanted microorganisms from getting in.

Uncontaminated cultures of microorganisms are needed for investigating the action of disinfectants and antibiotics.

Cultures should be incubated at a maximun temperature of 25°C in schools and colleges to reduce the likelyhood of pathogens growing that might be harmful to humans.

Bacteria multiply by simple cell division as often as every 20 minutes if they have enough nutrients and a suitable temperature.

You can investigate the effects of disinfectants and antibiotics on bacterial growth using agar plates and calculating the cross-sectional area of colonies grown or of clear areas of agar.

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Preventing Infections

Ignaz Semmelweis was a doctor in the mid-1850s. He noticed that the fecer was caused by some kind of infectious agent, and therefore insisted medical students washed their hands before delivering babies. This caused immidiate change.

Louis Pasteur showed that microorganisms cause disease and developed vaccines against diseases such as anthrax and rabies.

Joseph Lister started to use antiseptic chemicals to destroy pathogens before they caused infection in operating theatres.

As microscopes improved, it became possible to see pathogens more clearly.

The spread of infectious disease can be prevented by simple hygiene measures, by destroying vectors, by isolation of infected individuals and by vaccination.

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Viral Diseases

Measles virus is spread by droplet infection. It causes a fever rash and can be fatal.

There is no cure to measles. Isolation of patients and vaccination prevents spread.

HIV initially causes flu-like ilness. Unless it is successfully controlled with antiretroviral drugs the virus attacks the body's immune cells.

Late stage HIV infection, or AIDS, occurs when the body's immune system becomes so badly damaged it can no longer deal with other infections or cancers.

HIV is spread by sexual contact, or by the exchange of body fluids such as blood which occurs when drug users share needles.

Tobacco mosaic virus is spread by contact and vectors. It damages leaves and reduces photosynthesis

There is no treatment. Spread is prevented by field hygiene and pest control.

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Bacterial Diseases

Salmonella is spread through undercooked food and poor hygiene.

Sympyoms include fever, abdominal cramps, diarrhoea and vomiting caused by the toxins produced by the bacteria.

In the UK, poultry are vaccinated agains salmonella to control the spread of the disease.

Gonorrhoea is a sexually transmitted disease. Symptoms include discharge from the penis and vagina and pain on urination.

Treatment involves using antibiotics, although many strains are now resistant. Using condoms and limiting sexual partners prevents spread.

There are relatively few bacterial diseases of plants, but agrobacterium tumefaciens causes galls.

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Fungal and Protist Diseases.

Rose black spot is a fungal disease spread in the environment by wind and water.

It damages leaves so they drop off, affecting growth as photosynthesis is reduced. 

Spread us controlled by removing affected leaves and chemical sprays, but it is not very effective.

Malaria is caused by parasitic protists and is spread by the bite of female mosquitos. 

It damages blood cells and causes fevers and shaking. It can be fatal. Some drugs are effective if given early, but protists are becoming resistant.

Spread is reduced by preventing the vectors from breeding and by using mosquito nets to prevent people from being bitten.

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Human Defence Responses

Your skin covers your body and acts as a barrier. It prevents bacteria and viruses reaching the tissues beneath. 

If you damage or cut your skin, the barrier is broken but your body restores it. You bleed and the platelets in your blood set up a chain of events to form a clot.

Your skin produces antimicrobal secretions to destroy pathogenic bacteria.

Healthy skin is covered with microorganisms that help keep you healthy and act as an extra barrier to the entry of pathogens.

Your nose is full of hairs and produces a sticky liquid called mucus. The hairs and mucus trap particles.

The trachea and bronchi also secrete mucus that traps the pathogens from the air. The lining of the tubes is covered in cilia which waft mucus up to the back of the throat.

The stomach produces acid and this destroys the microorganisms in the mucus you swallow as well as the majority of pathogens you take in through your mouth.

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Internal Human Defences

Some white blood cells ingest pathogens, digesting and destroying them to prevent them from making you ill.

SOme white blood cells produce special chemicals called antibodies. These target particular bacteria or viruses and destroy them.

You need a unique antibody for each type of pathogen. When your white blood cells have produced antibodies once against a particular pathogen, they can be made very quickly if that pathogen gets into your body again.

Some white blood cells produce antitoxins. These counteract the toxins released by the pathogen.

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Plant Defence Responces

Plants can be damaged by a range of ion dificiency conditions.

Plant diseases can be detected by a range of symtpoms and identified in a number of ways including laboratory tests involving monoclonal antibodies.

The cellulose wall in a cell helps to resist invasion by microorganisms. This is one reason why the actions of aphids that pierce the cellulose walls are so damaging.

The tough waxy cuticle on the surface of leaves acts as a barrier to the entry of pathogens.

Bark on trees and a layer of dead cells on the outside of stems form a protective layer that is hard for pathogens to penetrate.

Deciduous trees lose their leaves in autumn to lose diseases such as rose black spot.

Some plants produce poisons, or contain thorns, hairy stems or mimic unhealthy plants to deter herbivores from ingesting them. These are known as chemical and mechanical adaptations.

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Vaccination and Antibiotics

If a pathogen enter the body, the immune system tries to destroy the pathogen.

Vaccination involves introducing of small amounts of dead or inactive forms of the pathogen into your body to stimulate the white blood cells to produce antibodies.

If the same live pathogen re-enters the body, the white blood cells respond quickly to produce the correct antibodies, preventing infection.

If a large proportion of the population is immune to a pathogen, the spread of this pathogen is greatly reduced.

Antibiotics cure bacterial diseases by killing the bacterial pathogens inside your body.

The use of antibiotics has greatly reduced deaths from infectious diseases.

The emergence of strains of bacteria resistant to antibiotics is a great concern.

Antibiotics do not destroy viruses because the viruses reproduce inside the cells. A drug that attacks the virus directly would likely damage your cells consequently.

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Discovering and Developing Drugs

Traditionally drugs were extracted from plants, for example, digitalis, or from microorganisms, for example, penicillin.

Penecillin was discovered by Alexander Fleming from the Penicillium mould.

Most new drugs are synthesised by chemists in the pharmaceutical industry. However, the starting point may still be chamically extracted from a plant.

New medical drugs are extensively tested for efficacy, toxicity and dosage.

New drugs are tested in the laboratory using cells, tissues and live animals.

Preclinical testing of new drugs takes place in a laboratory on cells, tissues and live animals. Clinical trials use healthy volunteers and patients.

Low deses are used to test for safety, followed by high doses to test for optimum dose.

In double blind trials, some patients are given a placebo.

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Making Monoclonal Antibodies

B lymphocyted make sprecific antibodies but do not divide. Timor cells do not make antibodies but rapidly divide.

A hybridoma cell combines B lymphocites and tumour cellsm that male specific antobodies and divide rapidly.

These cells are cloned and monoclonal antibodies are seperated and purified so they can be used.

Antigens are protein molecules that are often found on the surface of cells, although free protein molecules can also act as antigens.

Each type of antibody is specific to one binding site on a specific protein antigen so they can target specific cells.

Monoclonal antibodies are used for diagnosis in pregnancy tests, measuring hormones and other chemicals in the blood to detect pathogens for research, and to identify or locate specific molecules in cells or tissue.

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Using Monoclonal Antibodies

Monoclonal antibodies block receptors on the surface of a cancer cell to stop the cells growing and dividing.

Monoclonal antobodies can be used to carry toxic drugs or radioactive substances for radiation therapy, or chemicals that stop cells growing and dividing to attack the cancer cell directly without harming other cells in the body.

Monoclonal antibodies have created more side effects than exprected and are not yet as widely used as hoped when they were first developed.

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Cancer and Smoking

A non-communicable disease cannot be passed from one individual to another.

Risk factors are aspects of a persons lifestyle, or substances present in a persons body.

Benign and malignant tumors result from abnormal, uncontrolled cell division.

Benigh tumors form in one place and do not spread to other tissues. Malignant tumours are cancers. They invade neighbouting tissues and may spread elsewhere in the body.

Lifestyle risk factors for various types of cancer include smoking, obesity, common viruses and UV esposure. There are also genetic risk factors for some cancers.

Smoking causes cardiovascular disease including coronary heart disease, lung cancer and lung diseases such as bronchitis and COPD.

A foetus exposed to smoke has restricted oxygen, which can lead to premature birth, low birthweight and even stillbirth.

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Diet, Alcohol and Carcinogens

Alcohol can damage the liver and cause cirrhosis and liver cancer.

Alcohol can cause brain damage and death, and affect the development of babies.

Diet affects your risk of developing cardiovascular and other diseases directly through colesterol levels and indirectly through obesity.

Exercise leves affect the likelihood of developing cardiocascular disease.

Obesity is a strong risk factor for type 2 diabetes.

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Photosynthesis is an endothermic reaction.

During photosynthesis, energy is transfered from the environment to the chloroplasts by light. It is used to convers carbon dioxide and water into sugar.

Oxygen is also formed and released as a by product of photosynthesis.

Carbon dioxide + water     ----light---->     glucose + oxygen

Leaves are well adapted to allow the maximum amount of photosyhthesis to take place.

The rate of photosynthess may be affected by light intensity, temperature, level or carbon dioxide and the amount of chlorophyll.

Plants and algae use the glucose produced for respiration, to convert into insoluble starch for storage, to produce fats or oils for storage, to produce cellulose to strengthen walls and to produce amino acids for protein syntheses.

Plants and algae need nitrate ions from the soil to make amino acids.

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Respiration and Response to Exercise

Cellular respiration is an exothermic reaction that occurs continuously in living cells.

Aeriobic respiration is summarised as: glucose + oxygen    ----->    carbon dioxide and water.

The energy transfered supplies all the energy needed for living processes.

The energy transfered in respiration enables the muscles to contract. The human body responds to the increased demands in energy during exercise.

Heart rate and breathing rate increases to get blood to your muscles faster.

Glycogen stores in the muscles are converted to glucose for cellular respiration.

These responces act to increase the rate of supply of glucose and oxygen to the muscles and the rate of removal of carbon dioxide from the muscles.

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Anaerobic Respiration and Metabolism

If muscles work hard for a long time, they become fatigued and don't contract efficiently. If they don't get enough oxygen, they will respire anaerobically.

Anaerobic respiration is respiration without oxygen. When this takes place in animal cells, glucose is incompletely broken down to form lactic acid.

The anaerobic breakdown of glucose transfers less energy than aerobic respiration.

After exercise, oxygen is still needed to break down the lactic acid that has built up. The amount of oxygen needed is known as the oxygen debt.

Anaerobic respiration in plant cells and some microorganisms, such as yeast, results in the production of ethanol and carbon dioxide.

The energy transfered by respiration is used for the continual enzyme process of metabolism, which converts glucose to starch, glycogen and cellulose, as well as forming proteins and amino acids.

Blood flow through the muscles transports lactic acid to the liver where it's converted to cellulose.

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