Correct Answer :- a

Explanation : Pepsin is one of three principal protein-degrading or proteolytic, enzymes in the digestive system. Pepsin is most active in acidic environments. Its primary site of synthesis and activity is in the stomach pH of 1.5 to 2. Pepsin exhibits maximal activity at pH 2.0 and is inactive at pH 6.5 and above.

Trypsinogen is converted to active trypsin by the enzyme enterokinase which is secreted by the intestinal mucosa. Option C is the correct answer.

Stomach in vertebrates is the main site for digestion of proteins. Pepsin is the chief proteolytic enzyme of stomach secreted in the inactive form called as pepsinogen. The pepsinogen is activated to pepsin in presence of hydrochloric acid secreted in stomach by oxyntic or parietal cells. The optimum pH for activity of pepsin is 1.8.

Cholecystokinin plays a key role in facilitating digestion within the small intestine. It is secreted from mucosal epithelial cells in the first segment of the small intestine (duodenum), and stimulates delivery into the small intestine of digestive enzymes from the pancreas and bile from the gallbladder.

Function of HCl in stomach:

1)It kills pathogens in our body

2)It kills microbes in food

Rabbits are herbivorous animals. The digestive system is made up of an  oesophagus, stomach, and intestinal tract like other mammals. However, since their intake consists large quantities of fibre, rabbits are characterised by hind gut fermentation similar to horses. This helps to break down the indigestible materials into their chemical form. The presence of villi in the intestine distinguishes it from the stomach.

So, the correct answer is option B.

Sweet tasting carbohydrates are called sugars, e.g., glucose and fructose. Starch is a storage polymer of glucose and is tasteless till it is broken down into monomer glucose molecule. Lactose is milk sugar. Proteins are polymers of amino acids which are tasteless except for some like aspartic acid. Saccharine is an artificial sweetener. Saccharin is more sweet than common table sugar or sucrose but has a bitter after taste.

Alkaline intestinal juice (pH 7.8 to 8.0) assists in raising the pH of the intestinal contents to between 6.5 and 7.5. Sucrase, maltase and lactase complete the digestion of carbohydrates by converting disaccharides such as sucrose, maltose and lactose to monosaccharides in the intestine.

Glucose is a simple monosaccharide sugar. It is a hexose sugar. It is an aldose sugar. Ingested carbohydrates are broken down into monosaccharides which are absorbed in the intestine. Glucose is absorbed in intestine. Glucose is also chief form of sugar in blood and circulates in blood to supply energy to visceral organs.

Liver along with muscles stores excess glucose as glycogen, which can be used in times of starvation to maintain blood glucose levels. Excess carbohydrates are also stored as fat in adipose tissue around visceral organs and underneath the skin. During starvation the fat in the adipose tissue can be metabolised to derive energy.

So, the correct answer is 'Liver and adipose tissue'

Enterokinase helps in conversion of trypsinogen into trypsin in small intestine, which is an endoproteolytic enzyme and hydrolyses the peptones and proteoses into peptides.

(D) is correct.because in it pancreas and gallbladder secretions are released and also succus entericus is released here so maximum digestion of food occurs in dudonem.

Bile salts helps in emulsification of fats so in absence of these salts fats does not digest.

The hypothalamus is a mass of grey matter present at the base of the cerebrum. The center for thirst and drinking regulation is present in lateral hypothalamus while that for hunger and satiety is present in the arcuate nucleus, ventral nucleus and lateral hypothalamic area. This makes option C correct.

The common bile duct opens into the pancreatic duct and they join together to form the hepato-pancreatic duct that opens onto the duodenum. Hence, duodenum receives bile as well as pancreatic juice and it itself is the part of the intestine. Therefore, in the small intestine the bile, pancreatic juice and intestinal juice meet and act together over their respective substrates.

Enterogastrone is transported by the bloodstream to the glands and muscles of the stomach, where it inhibits gastric movements and secretions, possibly by blocking the production or activity of gastrin, the hormone that initially causes these functions.

Lipase is an enzyme, that hydrolyzes lipids, the ester bonds in triglycerides, to form fatty acids and glycerol. Lipases perform essential roles in the digestion, transport and processing of dietary lipids (e.g., triglycerides, fats, oils).

Of the options given only rennin is an enzyme, rest three are hormones. Rennin is a proteolytic enzyme found in gastric juice of infants, which helps in the digestion of milk proteins.

Correct option is D bcoz it is the hormone which secreted by some specialised cells of duodenum.

Secretin functions as a type of fireman; it helps in releasing acid from small intestine and stimulates the pancreas and bile ducts to release a flood of bicarbonate base, which neutralizes the acid.

Secretin is a hormone of the gastrointestinal tract. It is secreted by the duodenal wall of the small intestine when hydrochloric acid passes from the stomach into the duodenum, secretin is released into the bloodstream. This hormone stimulates pancreas for synthesis and secretion of non enzymatic part of pancreatic juice. It also stimulates liver for secretion of bile juice and inhibit the gastric acid secretion in stomach and reduce rate of contraction of stomach.

The pancreas secretes lipase enzymes, that act upon dietary fat molecules. Most dietary fat molecules are in the form of triglycerides. The cells lining the small intestine cannot absorb the large triglyceride molecules, so pancreatic lipase breaks the triglyceride into a smaller monoglyceride molecule and two free fatty acids. The cells lining the small intestine, then absorb the monoglycerides and fatty acids to use for energy production.

The percentage of lactose in milk varies with species. Human milk has a high lactose content, the percentage of lactose in human milk ranges from 6.5 to 7.5%. Unprocessed cow milk has about 4.7% lactose, unprocessed goat milk has about 4.7% lactose, unprocessed buffalo milk has about 4.86% lactose. The average in cow and goat milk is less than 5% and vary according to the breed. When human babies are reared on cow or goat milk, it is customary to add lactose, sucrose, glucose, or malto-dextrin in their feed.

Only some chemicals medicines and alcohol are absorbed in oro pharyngeal cavity. In the stomach, absorption of water, some salts, alcohol and glucose takes place, complete absorption of alcohol takes place in the stomach. Thus, carbohydrates, proteins and fats will remain in alimentary canal for complete digestion and when broken down completely in small intestine then only they will be absorbed in the intestine but beer will not be digested in alimentary canal and directly absorbed in the stomach. 

Carbohydrates are broken down in the body into glucose, an immediate source of energy. Excess glucose gets stored in the liver as glycogen or, with the help of insulin, converted into fatty acids, circulated to other parts of the body and stored as fat in adipose tissue.So, carbohydrates are responsible for the excess fat in the body.