Explain why absorbed fatty acids and glycerol enter the lacteals rather than the blood capillaries in the ileum wall.

Cambridge International IGCSE Biology (0610) — 7.5 Absorption · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

1. Fatty acids and glycerol are re‑assembled into triglycerides within enterocytes.
2. Triglycerides are too large to pass through the walls of blood capillaries.
3. Lacteals are lymphatic vessels in the villi that can absorb these large fat droplets.
4. The absorbed fats are carried by the lymphatics into the bloodstream via the thoracic duct.

Examiner tips

Use the term ‘triglycerides’ and ‘lymphatic vessels (lacteals)’. Show the sequence: re‑assembly → size restriction → lacteals → lymph → blood. Keep each point concise to fit the 4‑mark structure.

Common mistakes

Confusing blood capillaries with lacteals; not mentioning the size restriction. Using vague terms like ‘fat’ instead of ‘triglycerides’. Omitting the final step of entry into the bloodstream via the lymphatic system.

Mark scheme (4 marks)

Fatty acids and glycerol are reassembled / recombined into fats after absorption through the epithelial cells.
Fats / lipids are too large to pass into blood capillaries.
Lacteals are lymphatic vessels that can absorb large fat molecules / droplets.
Fats then enter the bloodstream via the lymphatic system.

Key terms in this question

lacteals · fatty acids · glycerol · ileum