Class 7 Science Notes Chapter 2 (Nutrition in Animals) – Science Book

Okay, here are the detailed notes for NCERT Class 7 Science, Chapter 2: Nutrition in Animals, structured for government exam preparation.

Chapter 2: Nutrition in Animals

1. Introduction

• Animal Nutrition: Includes the nutrient requirement, mode of intake of food, and its utilisation in the body.
• Heterotrophic Nutrition: Animals cannot prepare their own food and depend directly or indirectly on plants.
• Components of Food: Carbohydrates, proteins, fats, vitamins, minerals, water, and roughage. Complex substances like carbohydrates need to be broken down into simpler substances.
• Digestion: The process of breakdown of complex components of food into simpler substances.

2. Different Ways of Taking Food

The mode of taking food into the body varies in different organisms. Examples:

• Bees and Hummingbirds: Suck nectar from plants.
• Infants (Human and many other animals): Feed on mother's milk.
• Snakes (like Python): Swallow the animals they prey upon.
• Aquatic Animals: Filter tiny food particles floating nearby.
• Starfish: Feeds on animals covered by hard shells of calcium carbonate. It pops out its stomach through its mouth to eat the soft animal inside the shell. The stomach then goes back into the body, and the food is slowly digested.
• Other methods: Scraping, chewing, siphoning, capturing and swallowing, sponging, etc.

3. Digestion in Humans

The human digestive system consists of the alimentary canal (digestive tract) and secretory glands.

A. Alimentary Canal (Digestive Tract): A continuous canal starting at the buccal cavity and ending at the anus.
* Buccal Cavity (Mouth):
* Ingestion: The process of taking food into the body.
* Teeth: Break down food mechanically (mastication/chewing). Types of teeth: Incisors (cutting), Canines (tearing), Premolars & Molars (chewing & grinding).
* Salivary Glands: Secrete saliva.
* Saliva: Contains an enzyme called salivary amylase (also known as ptyalin), which breaks down starch (a complex carbohydrate) into simpler sugars.
* Tongue: A muscular organ. Functions: mixing saliva with food, helping in swallowing, detecting tastes (taste buds).
* Oesophagus (Food Pipe):
* Connects the buccal cavity to the stomach.
* Food moves down by wave-like muscular contractions called peristalsis.
* No digestion occurs here.
* Stomach:
* Thick-walled, J-shaped bag. Widest part of the alimentary canal.
* Inner lining secretes:
* Mucus: Protects the stomach lining from acid.
* Hydrochloric Acid (HCl): Kills bacteria entering with food and makes the medium acidic, which helps digestive enzymes to act.
* Digestive Juices (Pepsin): Break down proteins into simpler substances.
* Small Intestine:
* Highly coiled, about 7.5 meters long.
* Receives secretions from the liver and the pancreas.
* Its own walls also secrete intestinal juice.
* Liver: Largest gland in the body. Secretes bile juice, stored in the gall bladder. Bile helps in the digestion of fats (emulsification - breaking large fat globules into smaller ones).
* Pancreas: Large cream-coloured gland located below the stomach. Secretes pancreatic juice. Pancreatic enzymes act on carbohydrates, fats, and proteins, breaking them down further.
* Intestinal Juice: Secreted by the walls of the small intestine. Completes the digestion process:
* Carbohydrates -> Simple sugars (like glucose)
* Fats -> Fatty acids and glycerol
* Proteins -> Amino acids
* Absorption: The digested food passes into the blood vessels in the wall of the small intestine.
* Villi (Singular: Villus): Finger-like outgrowths on the inner walls of the small intestine. They increase the surface area for efficient absorption of digested food. Each villus has a network of thin blood capillaries close to its surface.
* Large Intestine:
* Wider and shorter than the small intestine (about 1.5 meters long).
* Function: Absorbs water and some salts from the undigested food material.
* Rectum:
* The remaining undigested waste material passes into the rectum.
* Stores semi-solid faeces.
* Anus:
* Faecal matter is removed through the anus from time to time.
* Egestion: The process of removal of faecal matter.

B. Secretory Glands (Associated Glands):
* Salivary Glands: In the mouth (secrete saliva).
* Liver: Secretes bile (aids fat digestion).
* Pancreas: Secretes pancreatic juice (contains enzymes for digesting carbohydrates, fats, and proteins).

Summary of the Steps in Human Nutrition:

1. Ingestion: Taking food into the mouth.
2. Digestion: Breakdown of complex food into simpler, soluble forms (starts in mouth, continues in stomach and small intestine).
3. Absorption: Passage of digested food into blood vessels (mainly in the small intestine via villi).
4. Assimilation: Utilisation of absorbed substances by the body for energy, growth, and repair. Transported via blood vessels.
5. Egestion: Elimination of undigested waste material (faeces) from the body.

4. Digestion in Grass-Eating Animals (Ruminants)

• Ruminants: Animals like cows, buffaloes, deer, sheep that chew cud.
• They quickly swallow grass and store it in a part of the stomach called the rumen.
• Rumen: Food gets partially digested here (forming cud). Bacteria present in the rumen help in digesting cellulose (a carbohydrate present in grass that humans cannot digest).
• Rumination: Later, the cud returns to the mouth in small lumps, and the animal chews it thoroughly.
• Stomach Structure: Ruminants have a stomach with four chambers: Rumen, Reticulum, Omasum, and Abomasum. After chewing, the food moves through these chambers for complete digestion.
• Caecum: A large sac-like structure between the small intestine and large intestine where cellulose digestion (by bacteria) also occurs in some animals like rabbits, horses.

5. Feeding and Digestion in Amoeba

• Amoeba: A microscopic, single-celled organism found in pond water.
• Structure: Has a cell membrane, a round nucleus, and cytoplasm containing bubble-like vacuoles. Constantly changes its shape.
• Pseudopodia (False Feet): Finger-like projections used for movement and capturing food.
• Ingestion: When Amoeba senses food, it pushes out pseudopodia around the food particle and engulfs it, forming a food vacuole.
• Digestion: Digestive juices are secreted into the food vacuole, breaking down the food into simpler substances.
• Absorption: Digested food is absorbed directly into the cytoplasm.
• Assimilation: Absorbed substances are used for growth, maintenance, and multiplication.
• Egestion: Undigested residue is expelled outside by the vacuole moving near the cell surface.

Key Terms for Revision:

• Absorption: Process by which digested food passes into the blood.
• Amino Acids: Simple units that make up proteins.
• Amoeba: Single-celled organism with irregular shape.
• Assimilation: Process of using absorbed food for energy, growth, etc.
• Bile: Digestive juice secreted by the liver; helps digest fats.
• Buccal Cavity: The mouth cavity.
• Canine: Pointed teeth used for tearing food.
• Cellulose: A type of carbohydrate found in plants; digested by ruminants.
• Digestion: Breakdown of complex food into simpler substances.
• Egestion: Removal of undigested waste material.
• Fatty Acids & Glycerol: Simple units that make up fats.
• Food Vacuole: Membrane-bound sac in Amoeba where food is digested.
• Gall Bladder: Organ that stores bile.
• Glucose: A simple sugar; the simplest form of carbohydrate after digestion.
• Incisors: Front teeth used for cutting and biting.
• Ingestion: Taking food into the body.
• Liver: Largest gland; produces bile.
• Milk Teeth: First set of teeth during infancy (temporary).
• Molars: Back teeth used for grinding.
• Permanent Teeth: Second set of teeth that replace milk teeth.
• Oesophagus: Food pipe.
• Pancreas: Gland that secretes pancreatic juice.
• Peristalsis: Wave-like movement pushing food down the alimentary canal.
• Premolars: Teeth located in front of molars; used for chewing and grinding.
• Pseudopodia: "False feet" of Amoeba used for movement and capturing food.
• Rumen: First chamber of a ruminant's stomach where cellulose digestion begins.
• Ruminant: Cud-chewing animal.
• Rumination: Process of chewing the cud.
• Salivary Amylase: Enzyme in saliva that breaks down starch.
• Villi: Finger-like projections in the small intestine that increase surface area for absorption.
• Saliva: Liquid secreted by salivary glands.

Exam Focus Points:

• Know the five steps of nutrition (Ingestion, Digestion, Absorption, Assimilation, Egestion) and their definitions.
• Understand the sequence of organs in the human alimentary canal and the function of each part.
• Know the associated glands (Salivary, Liver, Pancreas) and the role of their secretions (Saliva, Bile, Pancreatic Juice).
• Understand the role of HCl, mucus, and enzymes (like salivary amylase, pepsin) in digestion.
• Know where different components (Carbohydrates, Proteins, Fats) are primarily digested and what they are broken down into.
• Understand the importance and function of villi in the small intestine.
• Know the key features of digestion in Ruminants (Rumen, Cud, Rumination, Cellulose digestion).
• Understand the process of feeding and digestion in Amoeba (Pseudopodia, Food Vacuole).
• Be familiar with the key terms and definitions.

These notes cover the essential information from the chapter relevant for objective and short-answer questions in government exams based on NCERT syllabus. Remember to visualize the processes, especially the human digestive system.