Nutrition In Animals Class 7 Chapter Notes

Key Points: Must Remember

• Nutrition is the process of taking food by an organism and its utilization by the body.
• Animals are heterotrophic, meaning they obtain food directly or indirectly from plants.
• The main steps of nutrition in animals are: Ingestion, Digestion, Absorption, Assimilation, and Egestion.
• The human digestive system consists of the alimentary canal (mouth to anus) and associated glands (salivary glands, liver, pancreas).
• Digestion is the breakdown of complex food substances into simpler, soluble molecules.
• The small intestine is the site of complete digestion and absorption, facilitated by villi.
• Ruminants (e.g., cows, buffaloes) have a specialized stomach with four chambers, including the rumen, for digesting cellulose.
• Amoeba ingests food using pseudopodia (false feet) and digests it in a food vacuole.
• Different animals have diverse feeding mechanisms adapted to their food source and environment.

Key Definitions

Nutrition

The process of taking food into the body and its utilisation for growth, repair, and obtaining energy.

Digestion

The complex process of breaking down large, insoluble food molecules into smaller, water-soluble molecules that can be absorbed by the body.

Ingestion

The process of taking food into the body.

Absorption

The process by which digested food passes into the blood vessels in the wall of the intestine.

Assimilation

The process by which absorbed food is transported to different parts of the body and utilised for energy, growth, and repair.

Egestion

The process of eliminating undigested food materials from the body.

Villi

Thousands of small, finger-like outgrowths lining the inner wall of the small intestine, increasing the surface area for absorption of digested food.

Rumen

The largest first chamber of a ruminant's stomach where cellulose-rich food is partially digested (cud formation).

Pseudopodia

Temporary finger-like projections of the cytoplasm of Amoeba, used for movement and engulfing food.

The Human Digestive System: A Detailed Look

The human digestive system is a complex and efficient system designed to process the food we eat, extract nutrients, and expel waste. It consists of the alimentary canal (a long tube extending from mouth to anus) and associated digestive glands.

1. Mouth (Buccal Cavity): Food is ingested here. Teeth chew the food, breaking it into smaller pieces (mechanical digestion). The tongue helps mix food with saliva, which contains salivary amylase (ptyalin) to begin chemical digestion of starch. The chewed food becomes a bolus.

1. Oesophagus (Food Pipe): The bolus passes from the mouth through the pharynx into the oesophagus. Muscular contractions, called peristalsis, push the food down to the stomach. No digestion occurs here.

1. Stomach: A J-shaped muscular bag. The stomach secretes gastric juice, which contains:

• Hydrochloric acid (HCl): Kills bacteria and provides an acidic medium for enzyme action.
• Pepsin: An enzyme that begins the digestion of proteins.

Food stays in the stomach for several hours, churning and mixing with digestive juices.

1. Small Intestine: This is the longest part of the alimentary canal (about 7.5 meters). It's the primary site for complete digestion of carbohydrates, proteins, and fats, and also the main site for absorption. It receives secretions from two important glands:

• Liver: Secretes bile, stored in the gallbladder. Bile emulsifies fats (breaks large fat globules into smaller ones), aiding fat digestion.
• Pancreas: Secretes pancreatic juice, containing enzymes like pancreatic amylase (for carbohydrates), trypsin (for proteins), and lipase (for fats).

The small intestine's own walls also secrete intestinal juice, which completes the digestion. The inner lining of the small intestine has thousands of tiny, finger-like projections called villi, which significantly increase the surface area for efficient absorption of digested nutrients into the bloodstream.

1. Large Intestine: Wider and shorter than the small intestine (about 1.5 meters). Its main function is to absorb water and some salts from undigested food material.

1. Rectum and Anus: The remaining undigested, semi-solid waste is stored in the rectum and then expelled from the body through the anus by the process of egestion.

Steps of Nutrition in Animals

1. Ingestion — The process of taking food into the body. Different animals have different methods of ingestion (e.g., sucking, swallowing, chewing, filtering).
2. Digestion — The breakdown of complex, insoluble food substances into simple, soluble substances that the body can absorb. This involves both mechanical (chewing, churning) and chemical (enzyme action) processes.
3. Absorption — The process by which the digested food molecules pass from the digestive tract into the bloodstream or lymph, primarily occurring in the small intestine.
4. Assimilation — The utilisation of absorbed food by the body for energy production, growth, and repair of tissues. The body converts absorbed nutrients into its own components.
5. Egestion — The removal of undigested and unabsorbed food materials (faeces) from the body through the anus.

Diverse Feeding and Digestion Examples

• Amoeba: This single-celled organism uses pseudopodia (false feet) to engulf food particles, forming a food vacuole. Digestive enzymes within the vacuole break down the food. Digested food is absorbed into the cytoplasm, and undigested waste is expelled.
• Ruminants (e.g., Cows, Buffaloes): These herbivorous animals ingest grass rapidly and store it in a part of their stomach called the rumen. In the rumen, bacteria and protozoa partially digest cellulose (a tough plant carbohydrate), forming cud. The cud is later brought back to the mouth and re-chewed (rumination), then swallowed again into other stomach chambers for further digestion.
• Starfish: Feeds on hard-shelled animals like clams. It pushes its stomach out through its mouth, wraps it around the prey, and digests the soft body parts outside its own body before pulling the stomach back in.

Exam Tip: Diagrams and Functions

For 'Nutrition In Animals', diagram-based questions are very common. Practice drawing and labelling the human digestive system (alimentary canal and associated glands) and understanding the function of each organ and its secretions. Pay special attention to the role of villi in the small intestine, the differences in digestion between monogastric animals (like humans) and ruminants, and the simple yet efficient process in Amoeba. Knowing the precise function of enzymes (e.g., salivary amylase, pepsin, trypsin, lipase) and digestive juices (HCl, bile) is crucial for scoring well. Avoid confusing absorption with assimilation!

Practice Questions with Solutions

• Q: List the five main steps of nutrition in animals. A: The five main steps are Ingestion, Digestion, Absorption, Assimilation, and Egestion.
• Q: What is the primary function of villi in the small intestine? A: Villi increase the surface area for efficient absorption of digested food into the bloodstream.
• Q: Name two digestive glands associated with the human digestive system and their main secretions. A: The liver secretes bile, and the pancreas secretes pancreatic juice (containing amylase, trypsin, lipase). Salivary glands secrete saliva.
• Q: How do ruminants digest cellulose, which humans cannot? A: Ruminants possess a special four-chambered stomach, particularly the rumen, where cellulose-digesting bacteria and protozoa are present, which break down cellulose.

Frequently Asked Questions