The human digestive system

Diffusion and exchange surfacesOsmosisActive transportThe human digestive systemEnzymesThe human respiratory systemThe human circulatory systemPlant tissuesPlant transport systems

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Objectives

Purpose of the digestive system

Breaks down large, insoluble food molecules into smaller, soluble ones that can be absorbed into the bloodstream.

Made up of several organs working together for digestion and absorption.

The digestive process

Mouth:

Food is physically broken down by teeth.
Saliva contains amylase (carbohydrase) to start breaking down starch.

Oesophagus (Gullet):

Transports food to the stomach.

Stomach:

Produces hydrochloric acid to kill pathogens and create the optimum pH for protease enzymes.
Protease enzymes break down proteins into amino acids.

Small Intestine (made up of the duodenum and ileum):

Digestive enzymes (amylase, protease, lipase) complete the breakdown of food.
Bile (from the liver) neutralises stomach acid and emulsifies fats for easier breakdown by lipase.
Digested nutrients are absorbed into the bloodstream.

Large Intestine:

Absorbs excess water.

Rectum and Anus:

Undigested material is expelled as faeces.

Organs in the human digestive system

Enzymes in the digestive system

Carbohydrases:

Break down carbohydrates into simple sugars.
Example: Amylase (produced in the salivary glands, pancreas, and small intestine) breaks down starch into maltose.

Proteases:

Break down proteins into amino acids.
Produced in the stomach, pancreas, and small intestine.

Lipases:

Break down lipids (fats) into glycerol and fatty acids.
Produced in the pancreas and small intestine.

Bile:

Produced in the liver, stored in the gall bladder, and released into the small intestine.
Neutralises stomach acid and emulsifies fats to increase the surface area for lipase activity.

Testing for different foods experiment method

Test for Sugars (Benedict’s Test):

Method:
- Prepare the sample by grinding the food sample using a pestle and mortar before testing.
- Place the sample in a boiling tube with 5 cm³ of Benedict’s reagent.
- Boil the tube in a water bath for 5 minutes.
Results:
- Negative: Stays blue.
- Positive: Turns brick red.

Test for Starch (Iodine Test):

Method:
- Prepare the sample by grinding the food sample using a pestle and mortar before testing.
- Add the sample to a test tube.
- Add a few drops of iodine solution.
Results:
- Negative: Stays orange.
- Positive: Turns black.

Test for Proteins (Biuret Test):

Method:
- Prepare the sample by grinding the food sample using a pestle and mortar before testing.
- Place the sample in a test tube with 5 cm³ of Biuret reagent.
- Swirl the sample for 1 minute.
Results:
- Negative: Stays blue.
- Positive: Turns purple.

Test for Lipids (Ethanol Emulsion Test):

Method:
- Prepare the sample by grinding the food sample using a pestle and mortar before testing.
- Add the sample to a test tube with ethanol.
- Seal the tube with a bung and shake for 1 minute.
- Slowly dribble water down the side of the tube.
Results:
- Negative: Stays colourless and clear.
- Positive: Turns milky white.

GCSE Biology

Topic 2: Movement within organisms