Absorption moves digested food from the gut into the blood or lymph. Assimilation is what the cells then do with it.
This lesson is part of nutrition and digestion in SPM Biology. Digestion itself is in tracing digestion through the alimentary canal.
What is the where-and-what test?
Ask two questions. Is the substance moving from the gut into the blood or lymph? Then it is absorption.
Is a cell using it, for example in respiration or to build protein? Then it is assimilation.
| Process | Where | What happens |
|---|---|---|
| Absorption | Villi in the small intestine | Glucose and amino acids into blood capillaries; fatty acids and glycerol into the lacteal |
| Assimilation | Body cells | Used for energy, growth or storage |
Worked example: a glucose molecule
An original journey for a glucose molecule from a plate of rice. The starch in the rice has been digested to glucose in the small intestine.
Absorption. Glucose passes through the thin wall of a villus into a blood capillary. The capillary network carries it away, so the concentration in the blood stays low and absorption continues.
Transport. The blood carries glucose through the hepatic portal vein to the liver, then to the body.
Assimilation. In a muscle cell, glucose is used in respiration to release energy. Extra glucose may be stored as glycogen in the liver and muscles.
How is the villus adapted?
The wall is one cell thick, so the diffusion distance is short. The capillary network takes the glucose away, which keeps the concentration gradient steep.
There are many villi, and each has microvilli, which give a large surface area. The lacteal takes in fatty acids and glycerol.
The mistake that swaps the terms
A student writes “assimilation is the movement of glucose into the blood”. The movement into the blood is absorption. Assimilation occurs in the cells.
A second mistake is writing that amino acids are absorbed into the lacteal. Amino acids go to the blood capillaries. Only fatty acids and glycerol enter the lacteal.
A self-check question
Explain what happens to an amino acid from the moment it leaves the small intestine until it is assimilated.
Answer
The amino acid is absorbed through the villus wall into a blood capillary. The blood carries it to the liver and then to body cells. In the cells, amino acids are assimilated: they are joined to build new proteins, such as enzymes or muscle proteins.
How cells release energy from glucose is in cellular respiration. The biological data interpretation trainer has more data questions.
For the next step, see interpreting nutrition information as curriculum data. If absorption and assimilation still swap, SPM Biology one-to-one tuition lets a teacher follow a molecule with you.