Discuss the Difficulties of Defining the Terms Health and Disease

BIO3: The Search for Better Health

1. What is a healthy organism?

DISCUSS THE DIFFICULTIES OF DEFINING THE TERMS ‘HEALTH’ AND ‘DISEASE’

·  Health is defined by the World Health Organisation as ‘a state of complete physical, mental and social wellbeing and not merely the absence of disease and infirmity’

o  It is possible for a person to be healthy and have a disease at the same time

·  Disease: any change that impairs the functioning of an organism in some way; usually associated with characteristic structural changes to the body and with characteristic symptoms

o  Inherited, nutritional deficiency, infectious and environmental diseases

·  These terms, as used in general conversation, have different meanings to their scientific definitions

OUTLINE HOW THE FUNCTION OF GENES, MITOSIS, CELL DIFFERENTIATION AND SPECIALISATION ASSIST IN THE MAINTENANCE OF HEALTH

·  Genes are units of inheritance which control protein synthesis. Since enzymes and all proteins are crucial for various metabolic processes, the genes which control their production are vital in maintaining health.

·  Genes regulate the cell cycle to stop mitosis when it is not needed. ‘Programmed cell death’ (apoptosis) naturally causes the death of unwanted cells.

o  Mutations in genes can disrupt the normal balance of cell death and reproduction. Too much apoptosis causes degenerative diseases such as Alzheimer’s disease. Too little apoptosis results in uncontrolled cell division, and the undifferentiated cells which result form tumours

§  If a tumour grows and invades healthy tissue, it is called a malignant tumour (cancer)

Proto-oncogenes produce proteins that stimulate cell division. A mutation in a proto-oncogene may change it into an oncogene (a gene that causes cancer). Mutations in tumour-suppressor genes which normally inhibit cell division are also responsible for cancer. Mutations in the DNA repair genes (which produce DNA repair enzymes) can drastically increase rates of mutation.

·  Mitosis is cell division, which produces two daughter cells which are identical to the parent cell.

o  Important for growth and reproduction

o  Also instrumental in repair, when dead or damaged cells are replaced by new cells

·  Cell differentiation is the process whereby new cells formed by mitosis differentiates to become a specialised cell with specialised structure and function

·  Specialisation: many cells have specialised roles in maintaining the health of an organism

o  E.g. specialised white blood cells such as lymphocytes and phagocytes attack pathogenic micro-organisms

USE AVAILABLE EVIDENCE TO ANALYSE THE LINKS BETWEEN GENE EXPRESSION AND MAINTENANCE AND REPAIR OF BODY TISSUES

o  Gene expression: transfer of information from a gene to produce a protein or RNA.

o  If you cut yourself, the genetic code contained in all your cells is used to form the new tissue to repair the damage from the cut

2. Over 3000 years ago the Chinese and Hebrews were advocating cleanliness in food, water and personal hygiene

DISTINGUISH BETWEEN INFECTIOUS AND NON-INFECTIOUS DISEASE

·  An infectious disease is one caused by a pathogen (disease-causing organism), and can be transferred from person to person

o  Transfer of disease may be direct (pathogens passing from person to person) or it may be carried by a vector such as a mosquito

o  Infection refers to a pathogen being present in the host, and doesn’t have to necessarily include disease

·  Non-infectious diseases are diseases that are not caused by pathogens (disease-causing organisms)

o  Inherited, nutritional deficiency, and environmental diseases

IDENTIFY THE CONDITIONS UNDER WHICH AN ORGANISM IS DESCRIBED AS A PATHOGEN

·  A pathogen is an organism that can cause disease

·  If a particular organism has infected a host, but it is not causing damage to host cells, then the organism is not pathogenic

o  E.g. bacterium E. coli is present in large numbers in our alimentary canals. It does no harm to us there, and is therefore not being pathogenic

EXPLAIN WHY CLEANLINESS IN FOOD, WATER AND PERSONAL HYGIENE PRACTICES ASSIST IN CONTROL OF DISEASE

·  Intake of food and water provide an easy way for pathogenic micro-organisms to enter our bodies

o  Therefore, minimising the number of such pathogens in food and water reduces risk of infection

§  Cooking meat to a high temperature

§  Boiling water to kill micro-organisms in it

§  Water treatment of public water supplies to make sure that untreated sewage doesn’t get into our water

·  Good personal hygiene also assists in control of disease, by ensuring that pathogens cannot enter our body

o  Keeping wounds on the skin clean and covered

o  Washing hands after going to the toilet, to wash away any pathogens that have been transferred to one’s hands. Otherwise, these pathogens may inadvertently be transferred to mouth/nose, and into the body

o  Personal hygiene with regard to sex and childbirth reduces transmission of pathogens

GATHER, PROCESS AND ANALYSE INFORMATION FROM SECONDARY SOURCES TO DESCRIBE WAYS IN WHICH DRINKING WATER CAN BE TREATED AND USE AVAILABLE EVIDENCE TO EXPLAIN HOW THESE METHODS REDUCE THE RISK OF INFECTION FROM PATHOGENS

·  Flocculation: Iron chloride FeCl3 is added to water. It reacts with water to form an iron hydroxide Fe(OH)3 precipitate.

o  Some bacteria adsorb onto these clumps, which can then be removed upon settling

·  Filtration using sand beds, or sometimes membrane filters, removes any pathogens which are larger than the pore size

o  Especially effective at removing macroparasites

o  Microscopic membrane filters, if used, have smaller pore sizes and can remove smaller sized pathogens from drinking water

·  Chlorination using chlorine gas or monochloramine: chlorine forms hypochlorous acid in solution, which is a disinfectant and bactericide that can kill many pathogens in the water

·  Although ozone is not yet widely used in NSW, ozone can also be used as an effective disinfectant

·  In NSW, water samples are tested for the presence of E. coli, Cryptosporidium, and Giardia

IDENTIFY DATA SOURCES, PLAN AND CHOOSE EQUIPMENT OR RESOURCES TO PERFORM A FIRST-HAND INVESTIGATION TO IDENTIFY MICROBES IN FOOD OR IN WATER

3. During the second half of the nineteenth century, the work of Pasteur and Koch and other scientists stimulated the search for microbes as causes of disease

DESCRIBE THE CONTRIBUTION OF PASTEUR AND KOCH TO OUR UNDERSTANDING OF INFECTIOUS DISEASES

Louis Pasteur:

·  Disproved the theory of spontaneous generation, that maggots and fungi grew naturally from non-living material

o  Broth kept in a open flask spoiled over time, whereas broth kept in a swan-necked flask did not spoil

§  Proved the spoiling was caused by micro-organisms, which could not pass the swan-neck section of the flask

o  Showed that micro-organisms came from pre-existing micro-organisms

o  Contributed to our understanding that infectious diseases can be reduced by preventing the responsible micro-organisms from entering our body

o  Showed that heating to 55⁰C for 30 minutes could kill the micro-organism responsible for souring wine. Applied this technique (pasteurisation) to milk and other fluids

·  Germ theory of disease, opposed the prevalent Miasma theory of disease that disease was caused by ‘bad air’

o  Determined that diseased silkworms contained a parasite, and farmers could eliminate the disease by using only disease-free worms

·  Developed vaccination

o  Found that chickens which had suffered a mild attack of cholera survived an injection of a highly virulent strain

o  Developed a vaccine against rabies

Robert Koch:

·  Some people argued that bacteria found in sick animals followed the infection rather than causing it

o  Koch proved that microscopic pathogens caused disease, by showing that a specific microorganism caused anthrax in sheep

·  Koch observed microscopic rods in the blood of sheep that had died from anthrax, and noticed that these rods were not found in the blood of healthy animals

·  Found that mice died when injected with blood from an animal that had died from anthrax

o  Therefore, blood of an infected animal contained the disease-causing agent

·  Koch grew pure cultures of the anthrax bacterium

o  Placed a tiny piece of spleen from a mouse killed by anthrax, with vitreous humour from an ox’s eye, on a cover slip.

o  Used a microscope to observe the small rods growing,, proving they were alive

·  Injected some of this culture into a healthy mouse. The mouse died from anthrax.

o  Therefore, the micro-organisms caused anthrax

·  Koch took some spleen from this experimentally infected mouse, and cultured it to grow micro-organisms identical to those of the previously infected mice

·  Koch’s postulates: a series of steps needed to prove that a particular micro-organism caused a particular disease

o  Suspect organism must be present in all infected hosts and absent in uninfected individuals

o  A pure culture of the suspect organism must be obtained

o  When a healthy organism is infected with the pure culture, it must develop the disease

o  The suspect organism must be isolated from the experimentally infected host, grown in pure culture and proven to be identical to the first culture

·  Koch’s postulates can be used to identify the causative organism of an infectious disease, by finding microorganisms which are present in the blood of all sufferers and absent in the blood of healthy individuals

o  A suspected causative organism can be confirmed by infecting a test organism

·  Koch extended his work and discovered tuberculosis bacillus and cholera bacillus

PERFORM AN INVESTIGATION TO MODEL PASTEUR’S EXPERIMENT TO IDENTIFY THE ROLE OF MICROBES IN DECAY

IDENTIFY THE ROLE OF ANTIBIOTICS IN THE MANAGEMENT OF INFECTIOUS DISEASE

·  Antibiotics: naturally occurring compounds produced by some bacteria/fungi that prevent the growth of bacteria, e.g. penicillin

·  Sensitivity tests for drugs: Bacteria are spread across the surface of a nutrient plate, and small discs containing antibiotics are added. Size of clear zone around each disc shows effectiveness of the antibiotic.

·  Before the discovery of antibiotics, many people died of what we now think of as simple infections. Therefore, antibiotics play an important role in the management of infectious diseases.

PROCESS INFORMATION FROM SECONDARY SOURCES TO DISCUSS PROBLEMS RELATING TO ANTIBIOTIC RESISTANCE

·  Bacteria that survive exposure to antibiotics are those that are resistant to the particular antibiotic used. These resistant bacteria reproduce, and so proportion of bacteria with antibiotic-resistance increases. This makes subsequent antibiotic treatments less effective.

o  E.g. vancomycin resistant golden staph

·  Overuse of antibiotics in modern times has resulted in decreased potency of antibiotics, as pathogens have developed a greater incidence of drug resistance.

o  Scientists keep developing new antibiotics to deal with multi-resistant bacteria.

·  Examples:

o  In some farm industries, human antibiotics are added into the feed of animals to prevent infections. This increases the proportion of antibiotic resistant bacteria, and may reduce our ability to effectively treat these human diseases with antibiotics.

o  Many household products and cleaning agents contain antibiotics, which also act as a selecting agent for resistant bacteria.

·  Strategies to Combat Antibiotic Resistance:

o  Using a mixture of antibiotics, minimising probability that any bacteria are resistant to all the antibiotics used and survive the treatment.

o  Synthetic drugs which block certain metabolic pathways or mechanisms in bacteria.

o  Completing a course of antibiotics even after symptoms are gone, to ensure that bacteria have been completely destroyed. Not finishing antibiotics can lead to selection of resistant strains.

DISTINGUISH BETWEEN:

-  PRIONS

-  VIRUSES

-  BACTERIA

-  PROTOZOANS

-  FUNGI

-  MACRO-PARASITES

AND NAME ONE EXAMPLE OF A DISEASE CAUSED BY EACH TYPE OF PATHOGEN

Prions:

·  A prion is a protein with the chain of amino acids folded in an abnormal way.

o  When a prion comes into contact with a normal protein, it alters the other protein’s structure to make it a prion too

o  The change spreads like a chain reaction, producing more prions

o  Prions eventually cause a cell to burst, and are then free to infect other cells. Bursting of nerve cells results in holes seen in infected brains

·  Prions are extremely resistant to heat and chemical agents

·  Cause degenerative neurological diseases

Prion Diseases:

·  Bovine spongiform encephalopathy (BSE) in cattle, also known as ‘mad cow disease’

o  Cows which were fed the ground remains of diseased cattle and sheep, developed BSE

·  Creutzfeldt-Jakob Disease (CJD) in humans

o  Humans can get CJD from eating cow meat with BSE, receiving human growth hormone from cadaver pituitary glands, and from brain lining grafts

o  In a tribe in New Guinea, people contracted CJD (then known as kuru) from eating body parts of dead relatives

o  In autopsy, the brains of people with CJD showed extensive damage due to bursting of nerve cells

o  Australia has introduced bans against European beef and beef products

Viruses:

·  Consist of DNA or RNA enclosed inside a protein coat

·  Viruses need to enter a host cell to reproduce

·  A bacteriophage is a virus that infects bacteria

o  The protein coat of the virus becomes attached to the bacterial wall, and its DNA is injected into the cell

o  Phage DNA uses energy from mitochondria and material within the cell to make protein coats and viral DNA within the bacteria

o  New bacteriophages are assembled inside the cell, until the host bacterial ruptures, releasing the new viruses to infect other cells