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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
Cause damage to the host
How do microorganisms get into the body?
Gasexchange System: Influenza, TB and Bronchitis
Digestive System: Cholera, Typhoid and Dysentery
How do pathogens cause disease?
1. Damaging Host Tissues
2.…read more

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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 with microvilli.
Large Intestine: Absorbs water.…read more

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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 a process called
Primary Structure: Polypeptide chain
Secondary Structure: alphahelix and betapleated sheet formed as a result of
hydrogen bonds.
Tertiary Structure: 3D structure formed because of disulphide bonds, ionic bonds and
hydrogen bonds.…read more

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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 be filtered to remove
any debris
Electron Microscopes:
Short wavelength and provide better resolution than light electrons.…read more

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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 and clear indicates none.…read more

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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.…read more

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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 being equal each side of
the cell. Therefore, not all the available glucose would be absorbed. Instead, glucose is
absorbed by indirect active transport.…read more

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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 genes for the bacterium to survive in adverse conditions
Bacterial Cells will also smaller ribosome than eukaryotic cells.…read more

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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 not actually being absorbed
Water alone does not replace electrolytes.
It is possible to replace water and electrolytes by IV but it requires trained personnel.…read more


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