AQA · GCSE · Biology
Course version: 8461 · Version from Sept 2018
Digestive enzymes convert food into small soluble molecules that can be…
Full specification wording
The human digestive system: Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream.
Large food molecules cannot pass through the wall of the small intestine, so digestive enzymes break them into small soluble molecules.
Checked against the AQA 8461 specification (opens in a new tab) on .
- Point 9 of 25
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Large food molecules cannot pass through the wall of the small intestine, so digestive enzymes break them into small soluble molecules. Amylase converts starch into sugars, proteases convert proteins into amino acids, and lipases convert lipids into fatty acids and glycerol. These products dissolve and are small enough to be absorbed through the lining of the small intestine into the bloodstream. The blood then carries them to cells for use in respiration and growth. For example, amino acids absorbed from digested protein are used to build new proteins in cells. Absorption happens mainly in the small intestine, whose lining has a large surface area and a good blood supply, features that increase the rate of absorption.
What earns the marks
- Digestive enzymes break large insoluble food molecules into small soluble molecules.
- The products of digestion include sugars from starch, amino acids from proteins, and fatty acids and glycerol from lipids.
- Small soluble molecules can be absorbed through the wall of the small intestine into the bloodstream.
- The bloodstream transports the absorbed products to cells for use in the body.
- The small intestine is adapted for absorption with a large surface area and a rich blood supply.
Common mistakes and how to put them right
Stating that large food molecules are absorbed directly.
Put it right by explaining that enzymes must first break them into small soluble molecules.
Saying that enzymes convert food into energy.
Put it right by stating that enzymes produce small soluble molecules, and energy is released later by respiration in cells.
Naming the stomach as the main site of absorption.
Put it right by stating that absorption occurs mainly in the small intestine.
Exam tips
- Use the phrase small soluble molecules when explaining why digestion is needed for absorption.
- Link each enzyme to its substrate and product so that the conversion step is explicit.
- When explaining absorption, mention the small intestine and one adaptation that increases its rate.
Try the lesson
The start of the The human digestive system: Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream. lesson, made from checked teaching notes for this specification point.
Have a go first
Digestive enzymes convert large food molecules into small, soluble molecules. What is the primary reason this breakdown is necessary?
Listen
Large food molecules cannot pass through the wall of the small intestine, so digestive enzymes break them into small soluble molecules. Amylase converts starch into sugars, proteases convert proteins into amino acids, and lipases convert lipids into fatty acids and glycerol. These products dissolve and are small enough to be absorbed through the lining of the small intestine into the bloodstream. The blood then carries them to cells for use in respiration and growth. For example, amino acids absorbed from digested protein are used to build new proteins in cells. Absorption happens mainly in the small intestine, whose lining has a large surface area and a good blood supply, features that increase the rate of absorption. A strong answer earns marks for these points. Digestive enzymes break large insoluble food molecules into small soluble molecules. The products of digestion include sugars from starch, amino acids from proteins, and fatty acids and glycerol from lipids. Small soluble molecules can be absorbed through the wall of the small intestine into the bloodstream. The bloodstream transports the absorbed products to cells for use in the body. A common slip: Stating that large food molecules are absorbed directly. Instead, explaining that enzymes must first break them into small soluble molecules. Exam tip: Use the phrase small soluble molecules when explaining why digestion is needed for absorption.
Key words
Say what each word means before you turn the card.
Digestion and absorption
Try answering aloud or in your head before turning the card.
Surface area and exchange
Try answering aloud or in your head before turning the card.
Transport in the bloodstream
Try answering aloud or in your head before turning the card.
Molecules for growth and respiration
Try answering aloud or in your head before turning the card.
See every definition
- Digestion and absorption
- Digestive enzymes convert food into small soluble molecules that can be absorbed through the wall of the small intestine into the bloodstream.
- Surface area and exchange
- Absorption happens mainly in the small intestine, whose lining has a large surface area and a good blood supply, features that increase the rate of absorption.
- Transport in the bloodstream
- The blood carries the absorbed products to cells for use in respiration and growth.
- Molecules for growth and respiration
- The bloodstream transports the absorbed products to cells for use in the body, for example amino acids are used to build new proteins in cells.
There is more to this lesson
The full lesson goes on to check your understanding and help you earn the marks. Create a free account to carry on, with your progress saved.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge
Test your understanding of The human digestive system: Digestive enzymes convert food into small soluble molecules that can be absorbed into the bloodstream.
Active recall beats re-reading. Take an instant quiz now to test what you’ve learned and lock it into long-term memory.
A week of Premium from your first lesson · Then the free plan continues · No card, no charge