Pathogens, Digestive System Notes for AQA

Chapter 1 and 2 notes for AQA biology AS level From textbook.

  • Created by: Jenessa
  • Created on: 24-05-10 10:33


What is disease?

It suggests a malfunction of body or mind which has an adverse effect on good health.

Microorganisms as pathogens

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 tissues

If the pathogen gets into the host and colonises its tissue an infection results.

When a pathogen is transferred from one individual to another it is known as transmission.

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How do microorganisms get into the body?

- through the gas-exchange system e.g. pathogens that cause tuberculosis.

- through the digestive system e.g. pathogens that cause cholera.

The body's natural defences

- a mucous layer that covers the exchange surfaces and forms a thick sticky barrier.

- the production of enzymes that break down the pathogens.

- the production of stomach acid, which kills microorganisms.

How do pathogens cause disease?

- by damaging the host tissues

- by producing toxins

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Enzymes and Digestion

Major parts of the digestive system

oesophagus: carries food from mouth to stomach. Made up of a thick muscular wall.

stomach: a muscular sac, producing enzymes. It stores and digests food (proteins). Glands in stomach wall produce mucus. Mucus prevents stomach being digested by its own enzymes.

small intestine: a long muscular tube, to further digest food, by enzymes, produced by its walls. Walls of small intestine, folded into villi, for large surface area. There are microvilli on the epithelial cells of each villus.

large intestine: absorbs water from secretions of digestive glands. The food thickens to form faeces.

rectum: final section of intestines. Faeces are stored and removed by egestion.

salivary glands: pass secretions to the mouth. Secretions contain amylase which breaks down starch into maltose.

pancreas: large gland, below the stomach. Produces pancreatic juice, containing protease, lipase and amylase.

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Enzymes and Digestion

Two stages of digestion

1) Physical breakdown: large food is broken down into smaller pieces by teeth. It provides a large surface area for chemical digestion.

2) Chemical breakdown: breaks down large, insoluble molecules into smaller soluble ones by the use of enzymes with a process called hydrolysis.

- Carbohydrases - carbohydrates into monosaccharides in the small intestine.

- Lipases - lipids into glycerol and fatty acids in the small intestine.

- Proteases - proteins into amino acids in the stomach/small intestine.

- Amylase - starch into glucose and maltose in the mouth/small intestine.

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