Chapter 2 Nutrition in Animals

a) ingestion, digestion, absorption, assimilation, egestion

These are the basic steps of holozoic nutrition.

1. Ingestion: Ingestion involves the consumption of food by an organism. Animals are variously adapted for ingestion of food of specific types, that intakes through the mouth into the gastrointestinal tract (GI); by eating or drinking processes. In single-celled organisms ingestion takes place by absorbing a substance through the cell membrane or through the surface of the skin.

2. Digestion: Digestion involves the breakdown of large complex organic food molecules (carbohydrates, proteins, lipids, nucleic acid etc.) into the simpler, smaller or soluble molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substance are absorbed by the small intestine into the blood stream.

3. Absorption: Absorption involves passing of digested food components through the wall of small intestine into the blood of lymph. These absorbed food molecules circulated to different cells of the body where they are being absorbed.  

4. Assimilation: Assimilation involves the movement of digested food molecules into the different cells of the body where they are used. For example: glucose is used in respiration to provide energy to do the processes; and amino acids are used to build new proteins.

5. Egestion: Egestion involves the removal or elimination of undigested food materials from the alimentary canal as faeces.

On reaching the end of the small intestine the digested food products with the minerals and vitamins that are useful to the body, this should have been removed from the watery contents. These materials are then passed on to the large intestine for the forward processes.

(b) liver

Liver is the largest gland which is located in the upper right side of the abdominal cavity. The liver consists of two lobes: the right and the left lobe. The liver is an essential organ weighing body 1.6 kg that has many functions in the body, including making proteins and blood clotting, making of triglycerides and cholesterol, synthesis of glycogen and bile production.

(c) pepsinogen, prorennin etc.

Contraction and the expansion of muscles of the wall of the stomach brings about churning movement which helps in the mixing of food with the gastric juices which is a mixture of HCL, pepsinogen, prorennin, lipase and mucus etc.

(d) villi

Villi are small finger-like numerous microscopic projections found inside the inner walls of the small intestine. Villi absorb nutrients from the food we eat and then shuttle those nutrients into your bloodstream so that they can travel where they’re needed.

(e) food vacuole

A vacuole is a membrane-bound organelle and are kind of vesicle. Vacuoles are closed sacs, made of membranes with inorganic or organic molecules inside such as enzymes. They have irregular shape or size like the cell can change them as needed. They are present in eukaryotic cells and do many things.

a) False

Carbohydrate digestion begins in the buccal cavity with the mechanical action of chewing and this contains several enzymes salivary analyse and lysozyme. Then digestion of carbohydrates continues in the stomach then in the small intestine which contains pancreatic (helps in starch hydrolization) and intestinal juice.

b) True

Enzymes in the saliva begins to digest complex food materials that is partly digested by salivary amylase. With the help of the tongue, the bolus is moved into the oesophagus by swallowing the food’ smaller pieces. Saliva contains mucus that moistens the food and also cleans the tongue. It also contains immunoglobulins and lysozymes that contains antibacterial action.

c) True

The gall bladder stores and secretes the bile juice in the duodenum and is stored in it until the food material reaches the stomach. Gall bladder contains natural mechanism to contract at the same time when the food material reaches the stomach.

d) True

The ruminants brings back swallowed grass to their mouth and chew this for some time. Grass contains cellulose and is a carbohydrate which can only be digested by ruminants because they have rumen. When they eat grass, it sent to the rumen where enzymes are present that acts on it and moisten it. Then it is sent back to the mouth from where ruminants chew it for sometimes.

 

(a) (iii) Small Intestine

The digestion of fats starts in the stomach and completes or ends in the small intestine. Small intestine secretes bile, pancreatic juice and intestinal juice. They all contains fat digesting enzymes.

(b) (iv) Large Intestine
The large intestine consists of 75% water, fats and proteinaceous substance. Water from the undigested food is absorbed as the waste material. It takes several hours for food to travel and enters into the large intestine via the digestive tract.

Column I                                  Column II
Food components               Product(s) of digestion
Carbohydrates                    Sugar
Proteins                              Amino acids
Fats                                    Fatty acids and glycerol

1) Carbohydrate: Carbohydrates are the sugars, starches and fibres found in fruits, grains, vegetables and milk products as well; they are of three types: polysaccharides, disaccharides and oligosaccharides. Though often maligned in trendy diet, carbohydrates are one of the basic food groups that are important to a healthy diet like curd etc. and these all needs to be digested.

 2) Protein: Proteins are the macronutrient that are essential for building muscles. It is mostly found in animal products and is also present in other sources like nuts and pulses etc. Protein of the ingested food are broken down to the amino acids by the peptidase enzyme. It plays various roles in your body like repair and building of body tissues, allows metabolic reactions to take place and coordinates body functions.

3) Fats: Fats are nutrients that provides energy. Fats contains 9 calories in each gram. It help in the absorption of fat soluble vitamins A, D, E, and K; and their ingested foods are triglycerides. Fats are either saturated or unsaturated and they are digested by lipases enzyme.

Villi; the inner surface of the small intestine has numerous tiny, finger-like and are present as leaf shaped in the duodenum and tongue like in the jejunum and finger like as the ileum. The presence of villi provides the inner wall of the small intestine a very large surface area for the rapid absorption of food. Each villi has a network of thin and small blood vessels which is known as blood capillaries that are close to its surface. The surface of villi absorbs the digested food materials into blood flowing through them.

Bile: Bile is a fluid that is secretes and released by the liver (carried from the liver by the bile duct) and stored in the gall bladder. Bile helps in digestion of complex substance like fats etc. It is a greenish-yellow alkaline liquid and is secreted into the small intestine where it helps in the digestion of fats, lipids etc.  

Cellulose is a type of carbohydrate can be digested by ruminants but not by humans because ruminants have a large sac-like structure called rumen between the oesophagus and small intestine. The cellulose of the food is digested here by the action of certain bacteria which are not present in humans.

Glucose is a simple sugar which is readily absorbed by the body. Unlike other foods such as carbohydrate, glucose doesn’t have to be processed by the digestive system for energy. It is directly absorbed into the bloodstream and all cells of the body. Once inside, glucose undergoes oxidation, which leads to the release of ATP, a high-energy molecule that provides energy for the cell.

 

i) Small Intestine

The digestion of fats starts in the stomach and completes or ends in the small intestine. Small intestine secretes bile, pancreatic juice and intestinal juice. They all contains fat digesting enzymes.

ii) Buccal Cavity (Mouth)

The entire process of digestion starts in our mouth, with churning. When we chew food, it gets broken down complex large pieces into smaller pieces which are easier to digest. When mixed with saliva which secretes salivary amylase, chewing process allows to extract the greatest possible amount of nutrients from the food we eat.

iii) Stomach

Antibiotics are present to kill the bacteria or antigens/ pathogens in our body, such as amoxicillin, clarithromycin (Biaxin), metronidazole (Flagyl), tetracycline (Sumycin), or tinidazole (Tindamax). Drugs which reduce the amount of acid in our stomach by blocking the tiny pumps that produce it.

iv) Small Intestine

Digestion of food completes in small intestine. The partially digested food is absorbed by the duodenum of the small intestine with the digestive juices from the liver, pancreas and its own walls.

v) Large Intestine

The large intestine consists of 75% water, fats and proteinaceous substance. Water from the undigested food is absorbed as the waste material. It takes several hours for food to travel and enters into the large intestine via the digestive tract. It occurs when fluid is in excess amount that is absorbed by the colon. As part of the digestion process, or due to fluid intake, food is mixed with large quantity of water. The colon absorbs the water and leaves the remaining materials as a semisolid mixture.

Similarity: Amoeba and humans are heterotrophs. This means we need to derive energy from other organic sources of carbon.

• The digestive juices in amoeba are secreted into foods vacuole and in human beings the digestive juices are secreted in stomach and small intestine. Then the juices convert complex food into simpler soluble and absorbable substances.
• An amoeba is like a human being because they are both living things made of the same elements, similar macromolecules, and cells.

Difference: Amoeba captures the food with the help of pseudopodia and engulf it. In human beings food is taken by the mouth.

• Human beings have complex structure for the complete process of nutrition involving the following steps ingestion, digestion and egestion of food while Amoeba has a simple process in which it engulfs the food with the help of pseudopodia and traps it in food vacuoles. Though amoeba and humans share the same mode of nutrition, both process the nutrients and convert them into energy in different ways.

Column I                                  Column II
(a) Salivary gland                     (iii) Saliva secretion
(b) Stomach                             (iv) Acid release
(c) Liver                                    (i) Bile juice secretion
(d) Rectum                               (ii) Storage of undigested food
(e) Small intestine                    (v) Digestion is completed
(f ) Large intestine                    (vi) Absorption of water

1. Salivary glands: The salivary glands present in mammals are exocrine glands which produces saliva that contains salivary amylase enzyme through a system of ducts. Humans contain three paired major salivary glands (parotid, submandibular, and sublingual), a pair of seromucous tubarial glands and as well as various minor salivary glands.

2. Stomach: Stomach is a muscular organ located on the left side of the upper abdomen and it stomach receives food from the oesophagus through the buccal cavity. As food reaches the end of the oesophagus, it enters to the stomach which secretes acid and various enzymes that helps in the digestion of food.

3. Liver: The liver is the largest gland that only found in vertebrates which detoxifies various metabolites, synthesizes proteins and produces biochemical substances which are necessary for digestion and growth. In humans, it is located in the right upper part of the abdomen.

4. Rectum: The rectum is a chamber that starts at the end of the large intestine, immediately continues the sigmoid colon, and ends at the anus. The rectum is empty because stool is stored higher in the descending colon.

5. Small Intestine: The small intestine is an organ in gastrointestinal tract where most of the end of absorption of nutrients and minerals from food takes place. It is present between the stomach and large intestine, and it receives bile and pancreatic juice through the pancreatic duct for the digestion of complex substances.

6. Large Intestine: The large intestine is shorter than the small intestine and is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed in the large intestine and the remaining waste material is stored as faeces before the elimination or by defecation.

7. Anus: The anus is the opening where the gastrointestinal tract ends and exits from the body. The anus starts at the bottom part of the rectum and is the last portion of the colon i.e. large intestine. The anorectal line helps in the separation of the anus from the rectum.

Part Name	Work
Salivary glands	Saliva secretion
Stomach	Acid release
Liver	Bile juice secretion
Rectum	Storage of undigested food
Small Intestine	Digestion is completed
Large Intestine	Absorption of water
Anus	Release of faeces

1. Salivary glands: The salivary glands in mammals are exocrine glands that produce saliva through a system of ducts. Humans have three paired major salivary glands (parotid, submandibular, and sublingual), a pair of seromucous tubarial glands (discovered in 2020) as well hundreds of minor salivary glands.
2. Stomach: Stomach is a muscular organ located on the left side of the upper abdomen. The stomach receives food from the oesophagus. As food reaches the end of the oesophagus, it enters the stomach through a muscular valve called the lower oesophagus sphincter. The stomach secretes acid and enzymes that digest food.
3. Liver: The liver is an organ only found in vertebrates which detoxifies various metabolites, synthesizes proteins and produces biochemical necessary for digestion and growth. In humans, it is located in the right upper quadrant of the abdomen.
4. Rectum: The rectum is a chamber that begins at the end of the large intestine, immediately following the sigmoid colon, and ends at the anus. Ordinarily, the rectum is empty because stool is stored higher in the descending colon.
5. Small Intestine: The small intestine or small bowel is an organ in gastrointestinal tract where most of the end absorption of nutrients and minerals from food takes place. It lies between the stomach and large intestine, and receives bile and pancreatic juice through the pancreatic duct to aid in digestion.
6. Large Intestine: The large intestine, also known as the large bowel, is the last part of the gastrointestinal tract and of the digestive system in vertebrates. Water is absorbed here and the remaining waste material is stored as faeces before being removed by defecation.
7. Anus: The anus is the opening where the gastrointestinal tract ends and exits the body. The anus starts at the bottom of the rectum, the last portion of the colon (large intestine). The anorectal line separates the anus from the rectum. Tough tissue called fascia surrounds the anus and attaches it to nearby structures.

No we cannot survive only raw, leafy vegetables\grass, because we cannot get all required nutrients, such as carbohydrates, proteins, lipids, vitamins and minerals, from them so we have to consume other things also like curd for carbohydrates etc. Moreover raw vegetables may not be digested easily as compared to cooked vegetables and sometimes eating raw vegetables makes stomach upset.