Autotrophic Nutrition

Nutrition is the biological process through which organisms obtain and utilize food. Based on how organisms acquire food, nutrition is classified into two major types: autotrophic and heterotrophic.

• Autotrophic nutrition refers to the ability of an organism to produce its own food using raw materials like carbon dioxide and water, usually with the help of sunlight or chemical reactions.
• Organisms that follow this method are called autotrophs.
  Examples: Green plants, algae, some bacteria.
• Types of autotrophs:
  1. Photoautotrophs – Use sunlight (e.g., green plants)
  2. Chemoautotrophs – Use chemicals instead of light (e.g., sulfur bacteria)

Photoautotrophic Nutrition

This is the light-based self-feeding process most commonly seen in green plants and algae. Here:

• Sunlight is used as the energy source
• Carbon dioxide (from air) and water (from soil) are converted into glucose and oxygen through photosynthesis

Examples: Algae, mosses, and higher green plants.

Heterotrophic Nutrition

Unlike autotrophs, heterotrophs cannot produce their own food. They rely on plants or other animals to meet their energy needs.

Types of heterotrophic nutrition:

1. Holozoic – Intake of solid complex food (e.g., humans, cows, lions)
2. Saprophytic – Feeds on decayed organic matter by absorbing nutrients (e.g., fungi, some bacteria)
3. Parasitic – Lives on or inside another organism and derives nutrition (e.g., worms, Plasmodium)

Autotrophic vs Heterotrophic Nutrition

Feeding Methods in Animals

Animals adopt various ways to consume food, such as:

• Scraping (snails)
• Chewing (cows)
• Sucking (mosquitoes)
• Swallowing (snakes)
• Capturing (frogs)
• Lapping (dogs)

Each mode is adapted to the animal’s mouthparts and feeding habits.

Stomach – Food Mixing Chamber

The stomach is a J-shaped muscular organ located on the left side of the abdomen. It performs:

• Temporary storage of food
• Mixing of food with digestive juices
• Formation of chyme, which is semi-liquid food that moves to the small intestine

Accessory Digestive Organs

These organs aid digestion but food does not pass through them.

1. Liver:
   • Largest internal organ
   • Produces bile, which emulsifies fats
2. Gall Bladder:
   • Stores and releases bile when needed during digestion
3. Pancreas:
   • Produces enzymes that break down carbohydrates, proteins, and fats
   • Also regulates sugar via insulin

Large Intestine

• Absorbs water and remaining minerals from digested food
• Forms semi-solid waste (faeces)
• Stores faeces temporarily in the rectum
• Eliminates waste via the anus

Small Intestine

Divided into three parts:

1. Duodenum
2. Jejunum
3. Ileum

Functions:

• Main site for digestion and absorption
• Receives bile and pancreatic juices
• Lined with villi and microvilli for nutrient absorption

Anus – Exit Point

The anus is the terminal opening of the digestive system, responsible for the removal of solid waste from the body through the process of defecation.

Overview: Human Digestive System

The system breaks down food into nutrients and absorbs them.
Main parts:

• Mouth (buccal cavity)
• Oesophagus
• Stomach
• Small intestine
• Large intestine
• Anus
  Also includes accessory glands like the liver and pancreas.

Buccal (Oral) Cavity

Starting point of digestion.

Contains:

• Teeth – for grinding and chewing
• Tongue – moves and mixes food
• Salivary glands – secrete saliva, which contains enzymes that begin carbohydrate digestion

🪄 Food Pipe (Oesophagus)

• A muscular tube connecting mouth to stomach
• Moves food using rhythmic contractions called peristalsis

What is a Dental Formula?

A dental formula represents the number and types of teeth on half of the upper and lower jaw.

It uses this order:
I (Incisors), C (Canines), P (Premolars), M (Molars)
Total teeth = 2 × (upper + lower)

Human Teeth at Different Ages

• Milk Teeth (up to age 6–8): 20 teeth
  Formula: 2 1 2 0 / 2 1 2 0
• Teenager (around age 17): 28 permanent teeth
  Formula: 2 1 2 2 / 2 1 2 2
• Adult (with wisdom teeth): 32 teeth
  Formula: 2 1 2 3 / 2 1 2 3

Types of Teeth and Their Functions

Milk vs Permanent Teeth

• Milk teeth: Appear during infancy and fall off by age 6–8
• Permanent teeth: Replace milk teeth and last a lifetime
  • Include incisors, canines, premolars, and molars

Parts of a Tooth

1. Enamel – Strong outer layer
2. Dentine – Beneath enamel; protective
3. Pulp – Contains nerves and blood vessels
4. Cementum – Anchors tooth to gums and jawbone

Canine Teeth

• Sharp, pointed
• Used for tearing flesh
• Located next to incisors
• 2 in each jaw

Incisors

• Flat and sharp-edged
• Ideal for biting and cutting
• 4 in each jaw

Teeth Based on Function

1. Incisors – Cutting
2. Canines – Tearing
3. Premolars – Grinding + tearing
4. Molars – Crushing and final grinding

Molars

• Strongest teeth, with a broad surface
• Crush and grind food completely
• 6 in each jaw

🍽️ Premolars

• Transitional teeth between canines and molars
• Used for initial grinding
• 4 in each jaw

Tooth Decay

Caused by:

• Bacteria feeding on sugar → produces acids
• These acids dissolve enamel
• Leads to cavities, pain, and infections

Prevention: Brushing regularly, avoiding excess sugar, dental checkups

What is Bile?

• Yellow-green liquid made in the liver
• Stored in the gall bladder
• Helps in breaking fats into smaller droplets (emulsification)
• Makes the intestine alkaline to activate digestive enzymes

Small Intestine – Structure and Function

3 parts:

1. Duodenum
2. Jejunum
3. Ileum

• Villi and microvilli increase absorption area
• Digestive enzymes break down nutrients
• Bile and pancreatic juices help digest fats, proteins, and carbs

Large Intestine – Structure & Role

Sections:

1. Caecum – Initial pouch with bacteria; appendix arises here
2. Colon – Absorbs water; forms stool
3. Rectum – Stores stool for elimination

Also:

• Secretes mucus for lubrication
• Bacteria in colon make vitamins B & K

Functions of Large Intestine

1. Absorbs water
2. Forms and stores faeces
3. Eliminates waste via rectal muscles and anus

Digestion in Ruminants

Ruminants like cows and buffaloes have a special stomach to digest cellulose-rich plant food.

They chew the food partially, store it in a chamber called the rumen, and later regurgitate and rechew it. This partially digested food is called cud.

Rumen and Cud Explained

• Rumen: Largest stomach chamber; has microbes to digest cellulose
• Cud: Regurgitated, partially digested food chewed again for better digestion

Digestive System of a Ruminant

Includes:

• Mouth, oesophagus
• Rumen – fermentation
• Reticulum – collects metals
• Omasum – absorbs water and minerals
• Abomasum – true stomach with enzymes
• Small & Large intestine, caecum

Reticulum

• Second chamber after the rumen
• Honeycomb structure
• Collects unwanted hard particles (nails, stones)

Rumen

• Largest chamber, left side
• Contains microbes that ferment and digest cellulose
• Absorbs fatty acids
• Has papillae to increase surface area

Compound Stomach in Ruminants

Made of 4 chambers:

1. Rumen
2. Reticulum
3. Omasum
4. Abomasum

Supports cellulose digestion through bacteria and protozoa.

Omasum

• Has folded walls like pages of a book
• Absorbs water and minerals from the digested material

Abomasum

• Also called the true stomach
• Secretes digestive enzymes and hydrochloric acid
• Begins chemical digestion

Small Intestine in Ruminants

• Same 3 parts: Duodenum, jejunum, ileum
• Main site for final digestion and absorption
• Villi and microvilli absorb nutrients

Caecum in Ruminants

• Connects small and large intestine
• Assists in further digestion of fibrous plant matter

Large Intestine in Ruminants

• Absorbs water from food
• Stores and compacts waste material
• Prepares for excretion