Class 7 Science Notes Chapter 2 (Chapter 2) – Examplar Problems Book

Alright class, let's get started with Chapter 2: Nutrition in Animals from your Science Exemplar book. Understanding how different organisms obtain and utilize food is fundamental, and concepts from this chapter often appear in various government examinations. So, let's focus and make detailed notes.

Chapter 2: Nutrition in Animals - Detailed Notes for Exam Preparation

1. Heterotrophic Nutrition in Animals

• Animals cannot synthesize their own food like plants (autotrophs). They depend directly or indirectly on plants for food. This mode of nutrition is called heterotrophic nutrition.
• Animal nutrition involves understanding the nutrient requirements, the mode of intake (ingestion), and its utilisation by the body (digestion, absorption, assimilation, egestion).

2. The Process of Nutrition: The Five Steps
Every complex animal follows these essential steps to process food:

• (i) Ingestion: The act of taking food into the body. The method varies greatly depending on the animal (e.g., swallowing, chewing, sucking, scraping, capturing).
• (ii) Digestion: The process of breaking down complex, insoluble food substances (like carbohydrates, proteins, fats) into simpler, soluble forms that the body can absorb. This involves:
  • Physical Digestion: Mechanical breakdown (e.g., chewing by teeth, churning by stomach muscles).
  • Chemical Digestion: Breakdown by chemical agents called enzymes present in digestive juices.
• (iii) Absorption: The process where the digested, soluble food molecules pass through the walls of the intestine (mainly the small intestine) into the bloodstream or lymph.
• (iv) Assimilation: The process where the absorbed food is transported by the blood to different body cells and tissues and is used for energy, growth, building new tissues, and repairing old ones.
• (v) Egestion: The process of eliminating undigested and unabsorbed waste material (faeces) from the body through the anus.

3. Diverse Methods of Ingestion in Animals

• Humans: Use hands to put food into the mouth, followed by chewing.
• Amoeba: Engulfs food particles using pseudopodia.
• Paramecium: Uses cilia to sweep food particles into its oral groove.
• Hydra: Uses tentacles to capture prey and push it into the mouth.
• Spider: Weaves a web to trap insects.
• Frog: Uses its long, sticky tongue to catch insects.
• Butterfly: Uses its feeding tube (proboscis) to suck nectar.
• Mosquito/Lice: Have piercing mouthparts for sucking blood.
• Eagle: Captures prey with talons and tears flesh with its beak.
• Starfish: Feeds on animals covered by hard shells. It pops open the shell, pushes its stomach out through its mouth into the shell, eats the soft animal inside, and then retracts its stomach.

4. Human Digestive System
It comprises the Alimentary Canal and Associated Digestive Glands.

• (A) Alimentary Canal (Digestive Tract): A long, continuous, muscular tube running from the mouth to the anus.

  • 1. Buccal Cavity (Mouth):
    • Ingestion takes place here.
    • Teeth: Perform mechanical digestion (mastication/chewing). Types: Incisors (cutting), Canines (tearing), Premolars & Molars (grinding).
    • Tongue: Muscular organ. Functions: Mixes food with saliva, helps in swallowing (deglutition), bears taste buds (sweet, sour, salty, bitter).
    • Salivary Glands: Produce saliva. Saliva moistens food, helps form a bolus for swallowing, and contains the enzyme salivary amylase (ptyalin) which begins the digestion of starch into simpler sugars (maltose).
  • 2. Pharynx: Common passage for food and air. Epiglottis prevents food from entering the windpipe during swallowing.
  • 3. Oesophagus (Food Pipe): Connects the pharynx to the stomach. Food moves down by rhythmic contractions and relaxations of its muscular walls – this movement is called peristalsis. No digestion occurs here.
  • 4. Stomach:
    • A thick-walled, J-shaped muscular bag. Stores food for some time (up to 3-4 hours).
    • Churns food, mixing it with gastric juices (physical digestion).
    • Inner lining secretes:
      • Mucus: Protects the stomach lining from the action of acid and enzymes.
      • Hydrochloric Acid (HCl): Kills ingested bacteria and provides an acidic medium (pH 1.5-3.5) required for the enzyme pepsin to function.
      • Pepsin: An enzyme that begins the digestion of proteins into smaller peptides.
  • 5. Small Intestine:
    • Longest part of the alimentary canal (about 6-7.5 meters long), highly coiled.
    • Receives secretions from the liver (bile) and pancreas (pancreatic juice). Its own walls also secrete intestinal juice.
    • Site of complete digestion of carbohydrates (into glucose), proteins (into amino acids), and fats (into fatty acids and glycerol).
    • Absorption: The inner lining has millions of tiny, finger-like projections called villi (singular: villus). Villi vastly increase the surface area for efficient absorption of digested food into the network of blood capillaries within them.
  • 6. Large Intestine:
    • Wider and shorter than the small intestine (about 1.5 meters long).
    • Main function is to absorb water and some essential salts from the remaining undigested food material.
    • Forms and stores faeces.
  • 7. Rectum: Lower part of the large intestine where faeces are stored temporarily.
  • 8. Anus: The opening at the end of the alimentary canal through which faeces are eliminated (egestion).

• (B) Associated Digestive Glands: Glands that secrete digestive juices poured into the alimentary canal.

  • 1. Salivary Glands: (In mouth) Secrete saliva (contains salivary amylase).
  • 2. Liver:
    • Largest gland in the body. Located in the upper right abdomen.
    • Secretes bile juice, which is stored in the gall bladder.
    • Bile is released into the small intestine. It contains bile salts but no enzymes.
    • Function of Bile: Emulsification of fats (breaking down large fat globules into smaller droplets, increasing the surface area for lipase action) and making the medium alkaline.
  • 3. Pancreas:
    • Located below the stomach. Acts as both an endocrine and exocrine gland.
    • Secretes pancreatic juice into the small intestine.
    • Pancreatic juice contains powerful enzymes acting in an alkaline medium:
      • Pancreatic Amylase: Digests remaining starch.
      • Trypsin: Digests proteins into peptides.
      • Lipase: Digests emulsified fats into fatty acids and glycerol.

5. Digestion in Ruminants (Grass-Eating Animals)

• Examples: Cows, buffaloes, sheep, deer.
• They have a complex stomach with four chambers: Rumen, Reticulum, Omasum, Abomasum.
• Process:
  1. Quickly swallow grass (rich in cellulose) and store it in the Rumen (largest chamber).
  2. Here, symbiotic bacteria and protozoa partially digest the cellulose. This partially digested food is called cud.
  3. Later, the cud is brought back from the rumen/reticulum to the mouth (Rumination or chewing the cud).
  4. The thoroughly chewed cud is swallowed again, bypasses the first two chambers, and enters the Omasum (water absorption) and then the Abomasum (the 'true stomach') where gastric juices act on it.
  5. Digestion is completed in the small intestine.
• Caecum: A large sac between the small and large intestine, also containing cellulose-digesting bacteria. (Humans have a very small, vestigial caecum called the appendix).

6. Nutrition in Amoeba

• Amoeba is a unicellular organism living in water.
• Ingestion: Senses food, extends temporary finger-like projections called pseudopodia ('false feet') around the food particle, and engulfs it, forming a food vacuole.
• Digestion: Lysosomes fuse with the food vacuole, releasing digestive enzymes into it. These enzymes break down the complex food into simpler substances inside the vacuole.
• Absorption: Digested food diffuses from the food vacuole into the surrounding cytoplasm.
• Assimilation: Absorbed nutrients are used for energy, growth, and repair.
• Egestion: The food vacuole with undigested waste moves to the cell surface and ruptures, throwing the waste out.

Multiple Choice Questions (MCQs)

Here are 10 MCQs based on the chapter to check your preparation level:

1. The breakdown of complex food components like starch into simpler sugars primarily begins in the:
   (a) Stomach
   (b) Oesophagus
   (c) Buccal Cavity
   (d) Small Intestine

2. Which enzyme present in pancreatic juice helps in digesting proteins?
   (a) Amylase
   (b) Lipase
   (c) Trypsin
   (d) Pepsin

3. Villi, responsible for increasing the surface area for absorption, are characteristic features of the:
   (a) Large Intestine
   (b) Stomach
   (c) Small Intestine
   (d) Oesophagus

4. Bile juice aids in the digestion of fats through a process called:
   (a) Assimilation
   (b) Emulsification
   (c) Egestion
   (d) Peristalsis

5. Ruminants can digest cellulose due to the presence of specific microorganisms located mainly in their:
   (a) Abomasum
   (b) Oesophagus
   (c) Rumen and Caecum
   (d) Gall Bladder

6. Amoeba uses which of the following for ingesting food particles?
   (a) Cilia
   (b) Flagella
   (c) Tentacles
   (d) Pseudopodia

7. Hydrochloric acid in the stomach serves primarily to:
   (a) Digest starch
   (b) Protect the stomach lining
   (c) Provide an acidic medium for pepsin and kill germs
   (d) Emulsify fats

8. The final products of protein digestion are:
   (a) Glucose
   (b) Fatty acids and glycerol
   (c) Amino acids
   (d) Simple sugars

9. Water absorption from undigested food primarily occurs in the:
   (a) Stomach
   (b) Small Intestine
   (c) Large Intestine
   (d) Rectum

10. The wave-like muscular contractions that move food down the oesophagus are called:
    (a) Rumination
    (b) Peristalsis
    (c) Egestion
    (d) Deglutition

Answer Key:

1. (c) Buccal Cavity
2. (c) Trypsin
3. (c) Small Intestine
4. (b) Emulsification
5. (c) Rumen and Caecum
6. (d) Pseudopodia
7. (c) Provide an acidic medium for pepsin and kill germs
8. (c) Amino acids
9. (c) Large Intestine
10. (b) Peristalsis

Study these notes thoroughly. Remember the sequence of organs, the specific enzymes and their functions, and the unique digestive processes in ruminants and Amoeba. Good luck with your preparation!