Biology-Revision Notes

Pathogens
Microorganisms are a general term for single celled organism.
They include bacteria and viruses

Some microorganisms cause disease these are known as Pathogens
If a microorganism is to be called a pathogen it must:
Gain Entry
Colonise Tissues
Resist the Defences
Cause Damage to host tissues
Pathogens include viruses, bacteria and fungi
If a pathogen gets into the host and colonises its tissue an infection can occur.

How quickly pathogen causes damage is related to how rapidly the pathogen divides. Some divide every 30 minutes and some longer…

Pathogens cause disease in two main ways:
1. By Damaging Host Tissues sheer Number of pathogens & viruses inhibit the synthesis of DNA, RNA and proteins. Some break down the membranes of the host cell.
2. By Producing Toxins Bacterial pathogens produce toxins. The Cholera bacterium produces a toxin that leads to water loss.

Genetic Variation in Bacteria

Adaption increases the long-term reproductive success of a species by helping its members to survive long enough to breed. Adaption and Selection are major features in evolution.
Changes in DNA can result in two ways:
1. Changing the quantity or structure of the DNA of an organism. This is known as mutation.
2. Recombining the existing DNA of two individuals. This occurs due to sexual reproduction.
DNA is the genetic material in bacteria. DNA is changing by mutations and conjugation.

Mutations
-Changes in DNA that result in different characteristics
-One of more bases in DNA sequence may be added, deleted or replaced by others during replication
-Triplet of bases on a DNA molecule codes for a single amino acid. Any differences in the base sequence of a DNA molecule may result in a difference sequence of amino acids. This will lead to a difference polypeptide and hence a protein.
-If this Protein is an enzyme it is likely to disrupt the metabolic pathway leading to the production of other substances, including proteins.
-As proteins are responsible for the characteristics of an organism, it follows that changes to DNA are likely to alter an organisms characteristics.

Conjugation
-Occurs when one bacterial cell transfers DNA to another bacteria cell.
1. One cell produces a thin projection that meets another cell and forms a thin conjugation tube between the two cells.
2. The donor cell replicated one of its small circular pieces of DNA plasmid
3. The Circular DNA is broken to make it linear before in passes along the tube into the recipient cell.
4. Contact between the cells is brief, leaving only time for a portion of the donors DNA to be transferred.
5. In the way the recipient cell acquires new characteristics from the donor cell.

The Digestive System
Glands produce enzymes that break down large molecules into smaller ones

Physical Break down
-Broken down by the teeth into smaller pieces this Is easier to digest but also provides a larger surface area for chemical digestion.

Chemical Break down
-Large Insoluble Small Insoluble
-All digestive enzymes function by hydrolysis
-Hydrolysis= splitting of molecules by adding water
-Enzymes are specific and therefore a large molecule may need a few enzymes to break it down.

Carbohydras Breakdown carbohydrates, ultimately to monosaccharide’s
Lipase break down lipds into glycerol and fatty acids
Protease break down proteins, ultimately to amino acids

These are then absorbed by the small intestine and into the blood.
They are carried to different parts of the body and the molecules build up again , they are not necessarily the same molecules they were originally. The molecules are incorporated into the body tissues and/or used within the body.  Assimilation

Major parts of the digestive system
The Oesophagus
Carries food from the mouth to the stomach
Therefore it's adapted for transport rather than for digestion or absorption
Made up of a thick muscular wall
The Stomach
Muscular sac
Inner layer produces enzymes
Role = store and digest