Decide which digestive organ churns food with muscular contractions and also contains strong acid?

The digestive organ that churns food with muscular contractions and also contains strong acid is the stomach.

Here are the steps to arrive at this answer:

1. Digestion begins in the mouth where food is broken down into smaller pieces by chewing and mixed with saliva. However, the mouth does not churn food with muscular contractions or contain strong acid.

2. The food then travels down the esophagus through peristalsis, a series of wave-like muscle contractions. But, the esophagus does not contain strong acid.

3. The food then enters the stomach. The stomach has three mechanical tasks. First, it stores the swallowed food and liquid. To do this, the muscle of the upper part of the stomach relaxes to accept large volumes of swallowed material. The second job is to mix up the food, liquid, and digestive juice produced by the stomach. The lower part of the stomach mixes these materials by its muscle action. The third task of the stomach is to empty its contents slowly into the small intestine.

4. The stomach secretes acid and enzymes that digest food. The stomach muscles contract periodically, churning food to enhance digestion. The pyloric sphincter is a muscular valve that opens to allow food to pass from the stomach to the small intestine.

So, the stomach is the digestive organ that churns food with muscular contractions and also contains strong acid.