AQA AS BIOLOGY UNIT 1 CAUSES OF DISEASE

Pathogens - single celled micro-organisms that cause disease (bacteria, fungi, virus) they: gain entry to host, colonise tissue of host, resist defences and damage tissues.

Gain entry through: Interface between two systems, gas exchange surfaces and digestive system.

Pathogens effect the body by:

• Damaging host tissue, their large numbers cause damage by preventing tissues from functioning and breaking down membranes of cells.
• Produce toxins, bacterial pathogens do this.

The speed at which a pathogen causes damage depends on how quickly it replicates. Preventing Pathogens getting into the body:

• Mucus layer covering exchange surface with thick sticky barrier.
• Production of enzymes breaks down the pathogens.
• Stomach acid kills the micro-organisms.

Prokaryotic Cell -

• Flagellum - aids movement
• Cell surface membrane - entry & exit
• Cell Wall - physical barrier, protecting against damage
• Capsule - protection from other cells & sticks to other bacteria
• Plasmid - contains genes & aids survival of bacteria (e.g. produces enzymes)

• No true nucleus (nuclear material not in envelope)
• No nucleolus (RNA)
• Circular strands of DNA
• No membrane bound organelles
• Small ribosomes
• Cell wall

Cholera -

Transmission: unpurified drinking water, water contaminated with faeces from untreated sewage, food contamination, organisms which have fed on untreated sewage.

Most bacteria are killed by the stomach acid, those that survive propel through the lining of the intestine wall.

Causes severe muscle/stomach cramps, vomiting & diarrhoea.

1. Cholera bacterium produce poisonous toxin, choleragen.

2. Molecules of the toxin bind to the cell surface membrane of the epithelial cells lining the small intestine, the protein channels for chloride ions open.

3. There is a huge increase of active transport of chloride ions out of the cells & into the lumen.

4. Low water potential in lumen.

5. Water moves out of the blood, through epithelial cells and into the lumen by osmosis. (High WP -> Low WP) = DIARRHOEA

Oral Rehydration Therapy -

Cannot just give water - will not be absorbed and does not contain ions lost that are being lost from the cells. Co-transport proteins are not effected.

Rehydration solution contains:

Glucose & Sodium - make use of the co-transport proteins to stimulate uptake of sodium & glucose ions back into the cells - WP falls in the cells (MORE SOLUTE), WP higher in the lumen, water moves from the lumen (HIGH WP) into the cells (LOW WP) by osmosis.

Water - to rehydrate tissues

Potassium - replace lost ions and stimulate appetite

Other ions - to help prevent imbalance of ions

Analyzing and Interpreting Data on Disease

Epidemiology - studies the number of cases and pattern of a disease with a view to finding the means of preventing and controlling it. Suggests connections between the cases of the disease and other factors such as lifestyle.

Quantitative Data ( Very specific numbers) - can be gathered from these studies.

Correlation - positive, one increases and the other increases.

Negative correlation, one increases and the other decreases.

The need for a placebo - acts like a control experiment, changes in the patient taking the real drug can be compared with the patients taking the placebo, to see whether the changes are due to the drug or some other factor.

The need for a double-blind trial - ensures thats there's no risk of any deliberate bias by the patients of the scientist, those knowing they are on the real drug might wrongly attribute their symptoms to the drug.