Chemical digestion involves enzymes. In the mouth, chemical digestion is initiated when the food comes in contact with saliva, which is secreted by salivary glands. It contains salivary amylase which begins the digestive process by breaking down starch and converting it into maltose. Chemical digestion then further continues in stomach and then finally in the small intestine.

Chemical digestion food starts in the mouth as saliva is secrets from salivary gland which consists salivary amylase enzyme which acts on starch and converts it into the simpler form the churned food particles with saliva is called as the bolus then transferred to the stomach through the esophagus.

Carnivorous animals are meat eating animals. They use canines which are long, pointed teeth near the front of their jaw for tearing of flesh. Other teeth along the side of their jaw, molars and premolars, have uneven edges and are used for shearing the food in smaller pieces.

Pancreas helps in digestion by secreting pancreatic juice in small intestine. However pancreas is a gland and is not a part of alimentary canal. Alimentary canal is a muscular tube which extends from mouth to anus and includes the mouth, pharynx, oesophagus, stomach and the intestines.

Saw fish, Hyla and Bombay duck belong to super class: Pisces and Division: Gnathostomata. Myxine has circular sucking type of mouth belonging to Division: Agnatha.

'Gastrulation' word is derived from Greek word 'gaster' meaning stomach and according to McEwen (1923), gastrulation refers to the formation of the primordial gastric gut or cavity called the archenteron.

Tastes like sweet, salt, sour, bitter are sensed by all the sides of the tongue but the back of the tongue is very sensitive to bitter tastes.

Acetabulum is made up of Parts of ilium, ischium and pubis. It provides articulation for head of femur.

The taste buds for sweet are on the tip of the tongue the salt taste buds are on either side of the front of the tongue. Sour taste buds are behind this and bitter taste buds are at the posterior end

Ampulla of vas deferens, seminal vesicle, prostate gland are the structures found in the abdominal cavity of male.

Digestion of starch starts from the mouth. The salivary gland in the mouth secretes saliva, which mixes with the food that is chewed. This is because to moisten the food. The saliva in the mouth contains the enzyme called amylase that is the starch-digesting enzyme.

'Oesophagus' does not secrete any enzyme.

Stomach: It is a muscular J- shaped thickly walled bag. Stomach churns the food to mix digestive juices. The food in the stomach is churned into semi-solid. The churned semi-solid food is called chime.

All the above options are correct.So, the correct option is 'None of the above'.

Single layered of flattened cells with irregular boundaries constitute the squamous epithelium which is found in walls of blood vessels and air sacs of lungs. The epithelium that lines the oesophagus is stratified epithelium.

• The oesophagus is a hollow, muscular tube that connects the mouth to the stomach and also carries food and liquids to the stomach from the mouth.
• It is usually around 9 to 10 inches in adults which begins at the pharynx and passes behind the trachea or windpipe.
• The upper part of the oesophagus is made up of striated or voluntary muscles.
• The middle part is composed of both striated and smooth or involuntary muscles.
• The lower part is made up of smooth muscles only.
• The oesophagus consists of two sphincters.
• The upper oesophagal sphincter is single ringlike cartilage which is both voluntary and involuntary in nature and it prevents food and liquids from entering the windpipe (trachea,)
• The lower oesophagal sphincter is involuntary and prevents gastric acids from travelling into the oesophagus and it opens into the diaphragm.
  
• So, the correct answer is 'Both voluntary and involuntary'.

• The oesophagus is a hollow distensible muscular part of the alimentary canal.
• The ability to stretch and expand is called distensibility.
• The distensibility of the oesophagus allows any kind of food to pass through it with ease.
• The oesophagus dilates and propels the food from the region of the pharynx to the stomach.
• The stomach is a J shaped distensible bag like structure and is a highly distensible part of the alimentary canal.
• It may take varying shapes and can hold about 1 litre of food.
• The gastric folds in the inner walls of the stomach allow it to get expanded.
• So, the correct answer is 'Stomach'.

The gastric juice is made up of hydrochloric acid, pepsinogen and other digestive enzymes, gastrin, mucus, and bicarbonates. It has a pH ranging from 1 to 2. Its low pH is essential in activating digestive enzyme such as pepsinogen and convert it into the active pepsin, a Proteolytic activity of pepsin and in destroying various pathogens. 

The stomach wall consists gastric gland which secretes gastric juice for digestion of food. The gastric juice is made up of hydrochloric acid, pepsinogen and other digestive enzymes, gastrin, mucus, and bicarbonates. It has a pH ranging from 1 to 2. Its low pH is essential in activating many digestive enzymes and in destroying various pathogens. Thus, the correct answer is option C.

According to the body's needs, the stomach decides what to do with the food. If the small intestine is full and busy absorbing molecules from a previous meal, for instance, the stomach temporarily stores the food. On the other hand, if the body is in need of nutrients and the small intestine is ready for absorption, the stomach begins to break down the macromolecules found in the food and creates a semi-liquid mixture called chyme. This decision-making step of the stomach helps control the pace of the digestive system. The stomach of vertebrates is able to break down macromolecules due to its highly acidic environment, which causes molecular bond stress and forces them to break. So, the original function of the vertebrate stomach was storage but, due to acidic medium it also breaks down the food. Thus, option A is correct.

During digestion process fist food is ingested by mouth where chewing churning and mixing of food take place and make semi solid paste of food called as a bolus. Bolus then enters into the oesophagus where food moves through peristaltic movement and enters into the stomach. Thus, the correct answer is option C.

The stomach wall secretes gastric juices and a mixture of HCl, pepsinogen and mucous. HCl increases the pH of the stomach due to which pepsinogen gets activated and gets converted into the active form pepsin which digests the protein molecule. Thus, the correct answer is option D. 

The stomach is a J-shaped, hollow organ located just inferior to the diaphragm in the left part of the abdominal cavity. It is located between the oesophagus and connects with the duodenum. It has two parts fundus and pyloric. 

The gastric glands of stomach produce gastric juice, which contains pepsinogen, HCl, and mucus. HCl imparts highly acidic pH to stomach which in turn supports conversion of inactive pepsinogen into active pepsin. The proper acidic environment of stomach triggers the opening of one way pyrrolic sphincter which in turn allow the chyme to move into the small intestine for further digestive processes. Thus, the correct answer is option C.

Parietal cells in the mucosa are found in the inner lining of the stomach which secrete hydrochloric acid (HCl) into the stomach lumen, or cavity. It decreases the pH of the stomach and has corrosive nature hence can harm the stomach wall. The gastric juice consists mucous also. It gets deposits on the inner wall of the stomach to protect it from the corrosiveness of HCl.

Gastric glands are numerous microscopic tubular glands formed by the epithelium of stomach. The parietal cells (oxyntic cells) are large and most numerous on the sidewalls of gastric glands. They secrete hydrochloric acid and castle intrinsic factor. The peptic cells (zymogen) cells of gastric glands secrete gastric digestive enzymes as proenzymes-pepsinogen and prorennin and a small amount of gastric amylase and gastric lipase. The hydrochloric acid maintains a strongly acidic pH of about 1.5 to 2.5 in the stomach. HCl converts pepsinogen and prorennin to pepsin and rennin respectively. 

• Parietal cells in the stomach secrete roughly two litres of acid a day in the form of hydrochloric acid. 
• The acid in the stomach functions to kill bacteria, and to help digestion by solubilizing food. 
• The acid is also important to maintain the optimal pH (between 1.8-3.5) for the function of the digestive enzyme pepsin. Hence, the acidic region of the gastrointestinal tract is the stomach.

(i) stomach

• In humans starch is digested in the buccopharyngeal cavity, protein is digested in the stomach and fat in the small intestine.
• In Humans cellulose is not digested because in humans cellulose-digesting enzyme is absent.
• In Humans fats are digested in the stomach and the cellusose digesting enzyme is absent The pairs of food components in humans reaches the stomach totally undigested are fats and cellulose.
• So, the correct answer is 'Fat and cellulose'.

The correct answer is (d).

Digestion starts from the mouth and ends at large intestine. When the food enters mouth (ingestion), it is broken into small pieces by the teeth and acted upon by salivary amylase. Then it travels down the oesophagus to the stomach, where digestive enzymes from the pancreas, gall bladder, liver and duodenum further digest it. Assimilation of nutrients occurs at small intestine and absorption of water and other substances happen at the large intestine before it is egested or excreted. Thus, the correct answer is option D.

 A layer of mucus along the inner walls of the stomach is vital to protect the cell linings of that organ from the highly acidic environment within it.

Answer is option (D) 

Digestion is a  process where the food is broken down by the mechanical and chemical process. Digestion begins at the mouth where the only carbohydrate is digested due to the presence of salivary amylase. Food then moves to the stomach through oesophagus where the gastric juice is secreted by the stomach wall which contains pepsin for protein digestion HCl and mucus. It digestion the complex form of protein into the simple form. Maximum protein is digested in the stomach.

Digestion in the human body is a complex process where pH of the digestive tract plays a crucial role. pH level in the region of pharynx and mouth is controlled by the saliva and is maintained at about 6.8. However, in the stomach, the gastric acid lowers the pH to 1-3 making it highly acidic. This acidic condition activates the digestive enzyme pepsinogen and converts it into pepsin for protein digestion and kills the pathogenic bacteria. Therefore, the correct answer is option A.

Digestion starts from the mouth. The salivary gland in the mouth secretes saliva, with the help of tongue saliva mixes with the food when is chewed. The tongue is a muscle with glands, sensory cells, and fatty tissue that helps to moisten food with saliva.

Ruminants are mammals that are able to acquire nutrients from plant-based food by fermenting it in a specialized stomach prior to digestion, principally through bacterial actions. The process typically requires the fermented cud to be regurgitated and chewed again. The process of re chewing the cud to further break down plant matter and stimulate digestion is called rumination. Thus, option B is correct. Chyme is the semifluid mass of partly digested food that is expelled by the stomach into the duodenum and moves through the intestines during digestion. Bolus is a small rounded mass of a substance, especially of chewed food at the moment of swallowing. 

A. Sphincter of Oddi is the opening of the hepatopancreatic duct into duodenum.

Digestion starts in mouth and starch is the biomolecule whose digestion is first carried out by Ptyalin enzyme present in saliva.
No digestion occurs in oesophagus. It functions to transport semi solid bolus of food from mouth to stomach.
Intestine comes after stomach. Stomach is important for digestion of proteins.

Digestion of food starts in mouth. It is carried out in following two ways

• Mechanical digestion which is breaking of food into smaller chunks with the help of teeth and aided by muscular tongue.
• Chemical digestion due to ptyalin (salivary amylase) in saliva
• So, the correct answer is 'Mouth'

The alimentary canal begins with an anterior opening the mouth, and it opens out posteriorly through the anus. The mouth leads to the buccal cavity or oral cavity. The oral cavity has 32 teeth and a muscular tongue. The buccal cavity is lined with mucous membrane, whose secretions keep mouth moist.

The oral cavity leads into a short pharynx, which serves as a common passage for food and air. The oesophagus and the trachea (wind pipe) open into the pharynx. A cartilaginous flap, called as epiglottis, prevents the entry of food into the glottis opening of the wind pipe during swallowing.

The epiglottis is a flexible flap at the superior end of the larynx in the throat. It acts as a switch between the larynx and the esophagus to permit air to enter the airway to the lungs and food to pass into the gastrointestinal tract. The epiglottis also protects the body from choking on food that would normally obstruct the airway.

Amylase is a digestive enzyme that acts on starch in food, breaking it down into smaller carbohydrate molecules. It is produced at two sites. First, salivary glands in the mouth make salivary amylase, which begin the digestive process by breaking down starch when the food is chewed. The starch is converted to maltose, a smaller carbohydrate. When starchy foods like rice or potatoes begin to break down in the mouth, a slightly sweet taste is detected, as maltose is released. So, if we chew a piece of bread (made of polysaccharides) long enough, it will begin to taste sweet because amylase is breaking down starches to dissaccharides such as maltose. Thus, option C is correct.

Carbohydrate digestion begins in the mouth or buccal cavity. The salivary glands in the mouth secrete saliva, which helps to moisten the food. The food is then chewed while the salivary glands also release the enzyme salivary amylase, which begins the process of breaking down the polysaccharides in the carbohydrate food.

A bolus is a mass of food that (with animals that can chew) has been chewed at the point of swallowing. Under normal circumstances, the bolus then travels down the oesophagus to the stomach for digestion. Bolus has the same colour as the food that has been chewed by the person and is different from chyme. The bolus is a rolled up ball-like structure formed when the animal is about to swallow. Its pH is alkaline because of the presence of saliva. Thus, option A is correct.

Digestion of food starts in the mouth in humans. In the mouth masticated food gets mixed with saliva secreted by salivary gland. Saliva is a mixture of water, electrolytes, ptyalin enzyme (salivary amylase). The digestion of starch is initiated in the mouth due to the action of salivary amylase. Enzymatic hydrolysis helps in the partial breakdown of starch into maltose, isomaltose.

The pharynx is an organ found in vertebrates and invertebrates. In humans, the pharynx is a part of the digestive system and also of the conducting zone of the respiratory system. The conducting zone includes nose, larynx, trachea, bronchi and bronchioles and their function is to filter, warm and moisten air and conduct it into the lungs.
Therefore, the correct answer is option A.

The food is ingested through the mouth. The mouth contains tongue, teeth and salivary glands. Teeth break the food into smaller particles. This process is called as mastication. The chewed food is mixed with saliva. Saliva is a watery fluid secreted by the salivary glands. Saliva contains a type of enzyme called the salivary amylase, which converts starch into sugar. The tongue is a muscular organ. Tongue helps to mix saliva in the food. It also helps to push the food down the food-pipe or oesophagus. Taste receptors are present in tongue and give us the sense of taste. 

The fist stage of digestion in human being takes place in the buccal cavity where the chewing and churning of food and mixing of saliva occurs. Saliva consists salivary amylase which acts on the starch molecule of food and converts it into the simple form. The semisolid food with saliva in buccal cavity is called as a bolus. Bolus is then transferred to the stomach with the help of peristaltic movement of the oesophagus. Thus, the correct answer is option C.

The alimentary canal is a long tube through which food is taken into the body and digested. In human beings, this passage is about 30 ft (9 m) long." The alimentary canal, or the digestive tract as it is most commonly known, is 9 meters from the oesophagus to the anus.

In humans, the alimentary canal begins with an anterior opening, called mouth and it opens out posteriorly through another opening, anus. Such an alimentary canal is called complete. In some animals like coelenterates only single opening is present, such an alimentary canal is called incomplete. 

The digestive functions of saliva include moistening food, and helping to create a food bolus, so it can be swallowed easily. Saliva contains the enzyme amylase that breaks some starches down into maltose and dextrin. The pancreas produces a juice containing several enzymes that break down carbohydrates, fats, and proteins in food. Hence, partial digestion occurs in the mouth.

Sodium-potassium pumps in the axonal membrane ionic gradients across the membrane by active transport of Na${+}$ outwards and K${+}$ inwards.

Amylase is an enzyme that catalyses the hydrolysis of starch into sugars. Amylase is present in the saliva of humans and some other mammals, where it begins the chemical process of digestion in mouth. Protein digestion begins in the stomach with the action of an enzyme called pepsin. Lipids are digested mainly in the small intestine by bile salts through the process of emulsification, which allows lipases to divide lipids into fatty acids and glycerol. The large intestine is the final section of the gastrointestinal tract that performs the vital task of absorbing water and vitamins while converting digested food into faeces. 

Carbohydrate digestion begins in the mouth or buccal cavity. The salivary glands in the mouth secrete saliva, which helps to moisten the food. The food is then chewed while the salivary glands also release the enzyme salivary amylase, which begins the process of breaking down the carbohydrate food.

There are two kinds of digestion: mechanical and chemical. In mechanical digestion, food particles are physically broken down into smaller pieces. It begins in the mouth where the food is chewed. 

An organ that helps with digestion but is not part of the digestive tract. The accessory digestive organs are the tongue, salivary glands, pancreas, liver, and gallbladder. Chemical digestion in the small intestine relies on the activities of three accessory digestive organs the liver, pancreas, and gallbladder. The digestive role of the liver is to produce bile and export it to the duodenum. The gallbladder primarily stores, concentrates, and releases bile. The pancreas produces pancreatic juice, which contains digestive enzymes and bicarbonate ions, and delivers it to the duodenum.

Adenoids, also called Pharyngeal tonsils, a mass of lymphatic tissue, similar to the tonsils, that is attached to the back wall of the nasal pharynx (i.e., the upper part of the throat opening into the nasal cavity proper). An individual fold of such nasopharyngeal lymphatic tissue is called an adenoid.