1.  What causes ulcers?

 It used to be thought that ulcers were caused by an overproduction of stomach acid (hydrochloric acid).  Then it was found that ulcers of the stomach can be caused by use of some medications, such as aspirin taken on an empty stomach.  Even more recently it has been found that a bacterium, Helicobacter pylori, can cause ulcers.  This bacterium can neutralize stomach acid so it can grow and multiply in the stomach.  Its growth can result in gastritis and ulcers.
 

2.  Where in the digestive system are most digestive enzymes produced?

 Many digestive enzymes are produced in the pancreas & then released into the upper part of the small intestine, the duodenum, where they become active.
 

3.  In what part of the body is most digested food absorbed?

 The majority of digested food is absorbed through structures called villi (villus, singular) located in the small intestine into the blood stream so nutrients can be transported to cells of the body for their use.  First, the nutrient-rich blood from the small intestine is transported to the liver via the hepatic portal vein.  Cells of the liver work to moderate the surge of nutrients in the blood before the blood passes to the rest of the body. This helps prevent sharp increases in blood sugar levels.
 There is some absorption of small molecules, such as water, alcohol & some vitamins that also occurs in the stomach, but most absorption is accomplished in the upper part of the small intestine, the duodenum.  The large intestine is not involved in absorption of nutrients but does absorb water from any remaining undigestible food as it reaches the end of the digestive tract.
 

4.  What is bile?  How does it help digest food?

 Bile is a substance produced by the liver and stored in the gall bladder.  It is NOT a digestive enzyme, but an emulsifier, a substance which has a “detergent action”, breaking large clumps of fat down into smaller clumps of fat*, consequently increasing the surface area available to the actual digestive enzymes.

 *note that this is NOT digestion:  digestion would mean breaking the fats down into fatty acids and glycerol.