Nutrition in Animals Class 7 Notes Science Chapter 2

What is Animal Nutrition?

Animal nutrition is the study of how animals obtain and utilize nutrients from their food. 

• It involves understanding how animals consume food and how their bodies digest and absorb nutrients. 
• Food components, such as carbohydrates, are complex and need to be broken down into simpler substances through digestion. 

Different Ways of Taking Food

Each species or type of organism has their own way of taking in food.  Bees and humming birds suck plant-nectars, infant of humans and some animals feed on mother’s milk, Snakes such as python consume the animals upon which they prey. Aquatic animals filter small food particles floating close by and feed on them.

All organisms have their unique ways of consuming food, tailored to their physiology. These methods include:

• Chewing: This involves biting and grinding food using teeth within the mouth. Examples include humans and dogs.
• Scraping: Here, an organ like the jaw scrapes food off a surface. Examples are seen in snails and ants.
• Syphoning: Food is absorbed into the mouth. Butterflies use this method.
• Capturing and swallowing: This involves seizing food and then swallowing it whole. Lizards are an example.
• Sucking: Organisms pierce food and draw out liquid. Mosquitoes utilize this method.
• Sponging: Saliva combines with food to dissolve it in the mouth. Houseflies demonstrate this approach.

Note: A starfish feeds on animals that have hard shells made of calcium carbonate. It opens the shell and then extends its stomach out through its mouth to eat the soft animal inside. Afterward, the stomach retracts back into the body, where the food is slowly digested.

Star Fish

Digestion in Humans

The food travels through a continuous canal that starts at the mouth and ends at the anus.  The alimentary canal is a continuous passage starting from the buccal cavity and ending at the anus. Compartments of the alimentary canal include:

Human Digestive System

1. Buccal cavity
2. Food pipe or esophagus
3. Stomach
4. Small intestine
5. Large intestine terminating in the rectum
6. Anus
7. These parts collectively form the digestive tract.

Food components gradually get digested as they move through different compartments. The inner walls of the stomach and small intestine, along with associated glands like salivary glands, liver, and pancreas, secrete digestive juices. Digestive juices convert complex food substances into simpler ones. The digestive tract and associated glands constitute the digestive system.

The Mouth and Buccal Cavity

The process of ingesting food begins with the mouth, where food is taken in.

• Teeth: Teeth play a crucial role in masticating food into small pieces through mechanical breakdown. Each tooth is anchored in a distinct socket within the gums and serves different functions. Two sets of teeth are present in humans: milk teeth, which are shed during childhood, and permanent teeth, which replace them.

Arrangement of teeth 

• Saliva: Salivary glands are present in the mouth which are responsible for secreting saliva. Saliva aids in breaking down starch into sugars, facilitating digestion.
• Tongue: The tongue, a muscular organ in the buccal cavity, assists in speech, mixing food with saliva, swallowing, and tasting different flavors.
• Tooth Decay: Bacteria naturally present in the mouth are typically not harmful. If oral hygiene is neglected after eating, harmful bacteria can thrive by breaking down sugars from leftover food, releasing acids that gradually damage teeth. This process, known as tooth decay, can lead to severe toothache and, in extreme cases, tooth loss. 

The Foodpipe/Oesophagus

The food pipe, also known as the Oesophagus, is where swallowed food travels into the stomach. The food pipe is located along the neck and the chest.

Movement of food in Oesophagus

• Movement: Food is propelled downwards in the food pipe by the contractions of its walls.
• Function: This movement of pushing food downwards occurs throughout the entire digestive tract. At times, when the stomach rejects food, it can lead to vomiting.

The Stomach

The stomach is a thick-walled organ shaped like a flattened J and is the widest part of the alimentary canal.

• Journey of Food: Food enters the stomach from the esophagus and exits into the small intestine.
• Function: The inner lining of the stomach produces mucus, hydrochloric acid, and digestive juices. Mucus protects the stomach lining, while hydrochloric acid aids in killing bacteria and creating an acidic environment for digestion. Digestive juices in the stomach help break down proteins into simpler substances.

The Small Intestine

The small intestine is approximately 7.5 meters long and highly coiled. It receives secretions from the liver, pancreas, and its own walls.

Small & Large Intestine

• Liver: The liver, a reddish-brown gland in the upper right abdomen, is the largest gland in the body. It secretes bile juice stored in the gall bladder, crucial for fat digestion.
• Pancreas: The pancreas, a large cream-colored gland beneath the stomach, produces pancreatic juice that aids in breaking down carbohydrates, fats, and proteins into simpler forms.
• Function of Small Intestine: In the lower part of the small intestine, intestinal juice completes the digestion process, breaking down carbohydrates into glucose, fats into fatty acids and glycerol, and proteins into amino acids.

Absorption in the small intestine

After food is digested, it moves into the blood vessels lining the intestine through a process known as absorption.

Villi

• Digestion and Absorption: After digestion, food moves into the blood vessels lining the small intestine through a process called absorption.
• Role of Villi: The inner walls of the small intestine have finger-like projections called villi, which enhance the surface area for efficient absorption of digested food.
• Transport of Nutrients: Each villus contains a network of small blood vessels that absorb digested nutrients and transport them to various body organs for assimilation.
• Assimilation and Energy Production: Assimilation involves using absorbed substances, like proteins, to build complex molecules. Glucose is broken down into carbon dioxide and water in cells, releasing energy with the help of oxygen
• Further Processing: Undigested and unabsorbed food moves into the large intestine for additional processing

Large Intestine

The large Intestine absorbs water and certain salts from undigested food material.

• Structure and Length: The large intestine is wider and shorter than the small intestine, with an approximate length of 1.5 meters.
• Absorption: It absorbs water and certain salts from undigested food material.
• Formation of Feces: The remaining waste moves into the rectum, where it forms semi-solid feces.
• Egestion: Fecal matter is regularly eliminated through the anus in a process known as egestion.

Digestion in Grass-eating Animals

 Grass-eating animals, such as cows and buffaloes, chew continuously even when not actively eating. This helps them break down the fibrous material in grass.

• Storage in the Rumen: After being swallowed, grass is stored in the rumen, a specialized stomach compartment. In the rumen, food undergoes partial digestion and forms cud.
• Rumination Process: The cud, which is partially digested food, is regurgitated in small lumps and chewed again. This process, known as rumination, is characteristic of ruminant animals.
• Role of Bacteria in Digestion: Ruminants, including cattle and deer, benefit from bacteria in the rumen that help digest cellulose, a carbohydrate found abundantly in grass. These bacteria break down cellulose, which is otherwise indigestible for many animals, including humans.
• Cellulose Digestion in Non-Ruminants:Animals like horses and rabbits, which are not ruminants, possess a large structure called the caecum. The caecum contains specific bacteria that assist in the digestion of cellulose.

Diarrhea

• Sometimes, individuals may experience frequent passing of watery stool, a condition known as diarrhea.
• Diarrhea can be triggered by factors such as infection, food poisoning, or indigestion and is prevalent in India, especially among children.
• Severe cases of diarrhea can potentially lead to fatality due to the excessive loss of water and salts from the body.
• It is crucial not to overlook diarrhea; even before consulting a doctor, the patient should consume ample boiled and cooled water with a pinch of salt and sugar dissolved in it. This solution is referred to as Oral Rehydration Solution (ORS).

Feeding and Digestion in Amoeba

Amoeba is a tiny single-celled organism discovered in pond water. Characteristics of Amoeba include a cell membrane, a dense nucleus, and multiple small vacuoles within its cytoplasm.

• Amoeba is known for its ability to change shape and position frequently.
  
• For movement and food capture, Amoeba extends finger-like projections known as pseudopodia or false feet.
• Amoeba primarily feeds on microscopic organisms, engulfing them by extending pseudopodia around the food particle, forming a food vacuole.
• Upon trapping the food in a food vacuole, digestive juices are secreted into it, breaking down the food into simpler substances.
• The digested food is gradually absorbed to be utilized for growth, maintenance, and reproduction.
• Any undigested remains are expelled outside the cell through a vacuole.
• The digestion process in Amoeba involves breaking down food into simpler substances to extract energy, a fundamental process similar across all animals.