The human digestive system: The digestive system is an example of an organ system in which several organs work together to digest and absorb food.

The idea

An organ system is a group of organs that cooperate to carry out a major function. In the digestive system, each organ has a specialised role: the mouth chews food and starts starch digestion; the oesophagus moves food by peristalsis; the stomach churns food and digests protein; the small intestine completes digestion and absorbs soluble products; the large intestine absorbs water; the rectum stores faeces before egestion. The liver produces bile, which neutralises stomach acid and emulsifies fats, and the pancreas releases digestive enzymes. Digestion converts large insoluble molecules into small soluble ones that can cross the gut lining, while absorption moves those products into the blood. The system therefore works as an integrated whole, not as isolated organs.

What earns the marks

• Define an organ system as several organs working together to perform a shared function.
• Name the organs of the digestive system and link each to digestion, absorption or transport of food.
• Explain that digestion breaks large insoluble molecules into small soluble molecules that can be absorbed.
• Describe absorption as the movement of soluble products through the gut wall into the blood.
• Explain the roles of the liver, which produces bile, and the pancreas, which produces digestive enzymes.
• Use the idea of cooperation, for example stomach acid and bile working together so small-intestine enzymes function effectively.

Common mistakes and how to put them right

• Saying the digestive system only digests food.

  Put it right: It also absorbs nutrients and water and egests indigestible waste.

• Claiming the liver makes enzymes.

  Put it right: The liver produces bile, while the pancreas produces digestive enzymes.

• Describing absorption as breakdown of food.

  Put it right: Absorption is the uptake of already-digested soluble products into the blood.

Exam tips

• Link each organ to a specific job when answering, rather than listing organs without functions.
• Use the terms digestion, absorption and egestion accurately and in the correct sequence.
• For longer answers, structure your response organ by organ from mouth to anus to show the system working together.