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Digestive system

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Lesson notes

Overview of the Digestive System

  • The digestive system breaks down food into small molecules that can be absorbed into the blood.
  • It consists of many organs, each with a specific role in digestion.
  • Enzymes are biological catalysts that speed up chemical reactions in digestion.
  • Some bacteria live in the large intestine; they protect against harmful bacteria and help digest food.

Organs Food Travels Through

  • Mouth: teeth mechanically break food; saliva contains amylase which breaks down starch.
  • Oesophagus: walls squeeze to move food to the stomach.
  • Stomach: muscular walls mechanically break food; contains hydrochloric acid to kill bacteria; protease breaks down proteins.
  • Small intestine: contains villi with a large surface area for absorbing digested food into the blood.
  • Large intestine: absorbs water from undigested food.
  • Rectum: stores faeces (waste material) before it leaves through the anus.

Accessory Organs (Food Does Not Pass Through)

  • Liver: produces bile to neutralise stomach acid.
  • Gall bladder: stores bile and releases it into the small intestine.
  • Pancreas: produces enzymes protease, amylase, and lipase (which breaks down lipids) and releases them into the small intestine.

Enzymes in Digestion

  • Amylase (in saliva and from pancreas) breaks down starch (carbohydrates).
  • Protease (in stomach and from pancreas) breaks down proteins.
  • Lipase (from pancreas) breaks down lipids (fats).
  • Enzymes work best at specific pH conditions; protease works best in acidic conditions in the stomach.

Absorption and Waste

  • Digested food is absorbed in the small intestine via villi, which increase surface area for faster absorption.
  • Water is absorbed in the large intestine.
  • Undigested material forms faeces, stored in the rectum until eliminated.

Diagram

Slides

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Practice questions

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  1. 1.Which organ contains hydrochloric acid that kills bacteria?

    Easy
    • AStomach
    • BSmall intestine
    • CLarge intestine
    • DLiver
  2. 2.Where are villi found and what is their main function?

    Easy
    • ASmall intestine; to absorb digested food
    • BLarge intestine; to absorb water
    • CStomach; to kill bacteria
    • DOesophagus; to move food
  3. 3.In which organ is water absorbed?

    Easy
    • ALarge intestine
    • BSmall intestine
    • CStomach
    • DRectum
  4. 4.Which organ stores faeces before it leaves the body?

    Easy
    • ARectum
    • BAnus
    • CLarge intestine
    • DColon
  5. 5.Which enzyme breaks down starch, and where is it produced?

    Easy
    • AAmylase; mouth
    • BProtease; stomach
    • CLipase; pancreas
    • DAmylase; pancreas
  6. 6.What is the role of bile in digestion?

    Easy
    • ANeutralise stomach acid
    • BBreak down proteins
    • CBreak down carbohydrates
    • DAbsorb water
  7. 7.Enzymes are biological catalysts. What does this mean?

    Easy
    • AThey speed up chemical reactions without being used up
    • BThey are used up in reactions
    • CThey slow down reactions
    • DThey are only found in the stomach
  8. 8.Which organ produces enzymes that are passed into the small intestine, including protease, amylase, and lipase?

    Easy
    • APancreas
    • BLiver
    • CGall bladder
    • DStomach

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