Cholecystokinin (CCK), made by the I cells of the small intestine and secreted into the duodenum, serves to stimulate contraction of the muscular layer of the gallbladder. CCK is generally released within two to three minutes of ingesting food, especially foods that are high in fats and triglycerides. As the gallbladder contracts, it releases bile salts into the duodenum that help solubilize ingested fat for absorption in the jejunum of the small intestine.

Secretin stimulates release of bicarbonate from the pancreas, gastrin stimulates release of acid in the stomach, and chymotrypsin cleaves peptide bonds of ingested proteins. 

Calcitonin is a hormone secreted by the thyroid in response to increased blood-calcium levels. It acts on the cells of bone to inhibit osteoclast activity (bone break down) and promote osteoblast activity (bone synthesis).

Acetylcholine and substance P are both neurotransmitters involved in orad contraction during peristalsis. Nitric oxide is a neurotransmitter involved in caudad relaxation during peristalsis.

The answer to this question is cholecystokinin (CCK). CCK is responsible for the release of bile from the gallbladder. The bile is responsible for fat breakdown and absorption in the small intestine, as the bile acts to emulsify fats so that lipase can effectively digest them.

Gastrin and secretin are also digestive hormones, but serve different functions. Gastrin promotes acid release from parietal cells in the stomach, while secretin suppresses acid release. Renin is not involved in digestion, and is released in response to low blood pressure.

Bile is released by the gallbladder due to secretion of cholecystokinin (CCK) in response to lipid digestion. Cholecystokinin is produced by I cells of the small intestine and has a number of digestive regulation effects, including pancreatic and liver stimulation. The liver produces bile, which is stored in the gall bladder until stimulation with CCK cause gall bladder contraction and bile release.

The vagus nerve indirectly stimulates the parietal cells by releasing the hormone gastric releasing peptide (GRP). GRP then acts on the G cells, stimulating them to secrete gastrin. Gastrin then acts on the parietal cells to promote hydrochloric acid secretion. Since there is no stomach, this cascade cannot proceed, and thus no acid would be secreted.

This question tests your ability to incorporate information from a passage about a fictional organism with many structural and functional similarities to humans to answering a question about similar cellular functions between the two organisms. Ultimately, you are told in the question stem that the new organism contains cells within the stomach called "betts cells" that are very functionally similar to chief cells in the human stomach. Thus, the question is testing your knowledge of the function of human chief cells. The question specifically asks to choose the substance that is produced directly by betts cells, which essentially is asking which substance is produced directly by human chief cells. The only substance listed that is directly produced by the chief cells in the stomach is pepsinogen, which is a zymogen, meaning that it is a precursor to pepsin. Pepsinogen is activated to pepsin when it meets acid in the stomach. Because pepsinogen requires activation outside of the chief cells in order to become pepsin, pepsin is not directly produced by the chief cells, making pepsin an incorrect answer to the question.

Hydrochloric acid is produced by the parietal cells of the stomach, not chief cells.

Gastrin is produced by G cells in the stomach and duodenum, but not chief cells.

Thrombin is a clotting factor found in blood. It is not produce by chief cells.

Calcium plays an important role in many physiological functions, including signal transduction, muscle contraction, and bone formation. Of all of the processes listed in the answer choices, calcium is least directly related to biotin and vitamin K production. Biotin and vitamin K are synthesized by gut flora.  

This question asks us to understand osmolarity and osmosis. Osmosis is the property of water whereby it moves from a high concentration of water to a low concentration of water, while osmolarity refers to the tendency of solutes to affect the draw of water from one area to another. In more practical terms, this means that water moves from areas of low solute concentration to areas of high solute concentration. Fiber is not digestible by humans, thus it cannot be absorbed by the gastrointestinal enterocytes. Additionally, because fiber cannot be absorbed, it cannot affect the absorption of other compounds in the gut to a great extent. Fiber does, however, increase the number of solute particles in the gut, and so draws water from the circulation and tissues via osmosis. Increasing the flow of water into the lumen will add more water to stool and help relieve constipation.

Fat-soluble vitamins include A, D, E, and K. Water-soluble vitamins include B and C. 

While carbohydrates and proteins are digested and absorbed directly into the bloodstream, dietary fats are packaged into chylomicrons and moved into the lacteal. The lymphatic system then transports the dietary fats to the large veins of the body via the thoracic duct. The majority of fats are absorbed by this process, but a smaller minority of shorter fatty acids are able to float freely into the bloodstream.