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Causes of Disease

Disease: description of symptoms that suggests a malfunction of body or mind. It is
caused by pathogens, genetics and lifestyle.

For a microorganism to be considered a pathogen, it must:

Gain entry to the host
Colonise the tissues of the host
Resist the defences of the host…

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Enzymes and Digestion

Parts of the Digestive System:
Oesophagus: Transports food from mouth to stomach. Thick muscular wall.
Stomach: Stores and digests food. Muscular sac, releasing enzymes and a
mucus lining.
Small Intestine: Enzymes on the wall secrete enzymes and try to break the food
down. Large surface area filled…

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Structure of an Amino Acid:

Amino Group
Carboxyl Group
Hydrogen Atom
R Group

Formation of a peptide bond:

During a condensation reaction ­ a molecule of water is lost. Can be reduced back to
amino acids by hydrolysis.

A chain of many amino acids is called a polypeptide chain in…

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Cells and movement in and out of them

Cell Fractionation:

The sample would need to be:
Cold: reduce enzyme activity
Buffered: to maintain a constant pH
Isotonic: to minimise movement in or out of the cell and prevent organelles
bursting or shrinking
Homogenized: Release organelles from cells and this will…

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Roles of Lipids:

1. Energy Source
2. Waterproofing
3. Insulation
4. Protection

Emulsion Test:

1. Put 2cm³of sample with 5cm³of ethanol into a clean grease free test tube.
2. Shake test tube thoroughly to dissolve lipid,
3. add 5cm³of water and shake gently

Cloudy white shows presence of lipid…

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CellSurface Membrane


The phospholipid forms a bilayer sheet, where one layer interacts with the water in the
cytoplasm and the other pair interacting with the water surrounding the cells.

Phospholipids functions are to:
Allow lipidsoluble substances to enter and leave the cell
Prevent water soluble molecules entering and leaving…

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Properties to increase the efficiency of absorption:
Increase surface area for diffusion
Thin walled
Move ­ maintain a diffusion gradient
Well supplied with blood to maintain a diffusion gradient

The epithelial lining also contains microvilli.

Role of active transport in absorption:

At best, diffusion only results of concentrations of substances…

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Cell Wall: physical barrier acting against mechanical damage and excludes certain

Capsule: Allows bacteria to stick together for further protection

CellSurface Membrane: Controls entry and exit from cells

Flagellum: Aids movement of the bacteria

Circular DNA: Posses the genetic information for the bacterium to replicate

Plasmid: Posses the…

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Treatment of Diarrhoea:


What Causes Disease:

Damage to epithelial cells lining the intestine
Loss of microvilli due to toxins
Excessive secretion of water due to toxins

What is ORT?

As diarrhoea results in dehydration, you need to replace fluid lost. Just drinking water
alone is ineffective because:

Water is…


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