Final answer:
Whales have a sphincter at the stomach end of the esophagus to prevent stomach contents from re-entering the esophagus and to facilitate efficient digestion.
Step-by-step explanation:
Whales, like many animals, have a sphincter around the esophagus known as the gastro-esophageal or cardiac sphincter. This sphincter is a ring-like muscle that acts as a valve at the stomach end of the esophagus. When a whale swallows, the pressure of the food bolus triggers the sphincter to open, allowing the bolus to enter the stomach. After swallowing, the sphincter closes to prevent the contents of the stomach from flowing back into the esophagus, which is particularly important in preventing acid reflux. This mechanism is essential for maintaining an efficient digestive process and protecting the esophagus from the harsh acidic environment of the stomach.