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AS/ A-Level Biology: Digestive System

Chapter 1.2 Digestive System

· AS A-Level,Biology,Digestive System

In this chapter of AS/ A-Level Biology, we will learn about different organs within the Digestive System and their functions.

Oesophagus

  • The tube that takes food from the mouth to the stomach using waves of muscle contractions called peristalsis; the muscle layer is thick to help with this
  • Mucus is secreted from tissues in the walls, to lubricate the food’s passage downwards
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Stomach

  • A small sac with many folds which allow it to expand
  • The entrance and exit are controlled by the sphincter muscles
  • The gastric juice produced here help digest food
  • It consists of hydrochloric acid, pepsin, and mucus
  • Pepsin hydrolyses proteins into smaller polypeptide chains and only works in acidic conditions
  • The mucus protects the stomach from acid damage and pepsin
  • Peristalsis of the stomach churns the food in a fluid called chyme
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The Small Intestine

  • In AS/ A-Level Biology, it has two main parts: duodenum and ileum
  • Chyme is moved along it by peristalsis
  • In the duodenum, bile (an alkali) and pancreatic juice neutralises the chyme and breaks it down
  • Small, soluble molecules are absorbed in the ileum through the villi in the gut wall by diffusion, facilitated diffusion and active transport; the villi increase surface area so that soluble molecules are absorbed quickly
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The Large Intestine

  • Absorbs water, salt and minerals
  • Has a folded wall for larger surface area for increase absorption
  • Bacteria can decompose some undigested nutrients

Rectum

  • Faeces are stored here and then pass through sphincter muscles at the anus during defecation

This is the end of this topic~

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