Once the undigested and unabsorbed substances enter the caecum, their backflow is prevented by-
Sphincter of Oddi
Ileo - caecal valve
Gastro - oesophageal sphincter
Pyloric sphincter
The correct answer is: Option 2) Ileo-caecal valve
The ileo-caecal valve is a one-way valve located between the ileum (the last part of the small intestine) and the caecum (the first part of the large intestine). It prevents the backflow of undigested and unabsorbed substances from the caecum back into the ileum, ensuring that the materials move in the correct direction through the digestive system.