🦁 1. How Animals Get Nutrition
Unlike plants, animals cannot make their own food. They are heterotrophs — they
must eat (ingest) food from their surroundings and then digest it to get nutrients. The process of nutrition
in animals involves five steps:
Flowchart: 5 Steps of Nutrition in Animals
Step 1: INGESTION 🍽️
Taking food into the mouth
⬇
Step 2: DIGESTION ⚙️
Breaking large food molecules into small ones
⬇
Step 3: ABSORPTION 🔄
Small molecules absorbed into blood through intestine
wall
⬇
Step 4: ASSIMILATION 💪
Nutrients used by cells for energy, growth,
repair
⬇
Step 5: EGESTION 🚽
Undigested waste removed from body
😁 2. The Human Digestive System
The human digestive system is a long tube (about 9 metres!) called the alimentary
canal, along with associated glands (salivary glands, liver, pancreas) that help in digestion.
📸 AI Image Prompt
A detailed, labeled anatomical diagram of the human digestive system shown as a
full-body profile outline (from mouth to anus). Each organ is clearly labeled with an arrow and a brief
function note: Mouth (teeth chew food, saliva adds amylase), Oesophagus (food pipe — muscular tube,
peristalsis moves food down), Stomach (churns food, adds HCl and pepsin — kills bacteria, digests
protein), Small intestine with three parts labeled (Duodenum — receives bile from liver + enzymes from
pancreas; Jejunum — further digestion; Ileum — nutrient absorption through villi), Large intestine
(water absorption, waste formed), Rectum (stores waste), Anus (egestion). Also show: Liver (dark red —
produces bile), Gall bladder (stores bile), Pancreas (produces digestive enzymes). Color-coded organs,
clean white background, educational medical illustration style. A dotted arrow shows the food pathway
downward.
Fig. 2.1 — The Human Digestive System
Journey of Food — Organ by Organ
| Organ |
What Happens |
Key Enzyme / Substance |
| Mouth |
Teeth chew food (mastication). Saliva moistens food and begins digestion of starch |
Salivary amylase (breaks starch → simpler sugar) |
| Oesophagus (Food Pipe) |
Carries food from mouth to stomach via peristalsis (wave-like muscle contractions) |
No digestion; physical movement only |
| Stomach |
Churns food into a paste. HCl creates acidic environment to kill bacteria. Begins protein digestion
|
Pepsin (breaks proteins); HCl (kills germs) |
| Small Intestine |
Main site of digestion AND absorption. Bile (from liver) helps digest fats. Many enzymes break down
all nutrients into simplest forms |
Bile (emulsifies fats); Trypsin, Lipase, Intestinal juice |
| Villi (in Small Intestine) |
Tiny finger-like projections on inner wall that increase surface area for absorption → nutrients
enter blood |
No enzyme; absorption structure |
| Large Intestine |
Absorbs water from undigested food; remaining material becomes solid waste (faeces) |
No enzyme |
| Rectum & Anus |
Stores and expels waste (egestion/defecation) |
— |
Mouth → Oesophagus → Stomach → Small
intestine → Large intestine → Rectum → Anus
Mnemonic: "MO SS LRA"
🦷 3. Teeth — Tools for Ingestion
Types of teeth in humans (adults have 32 teeth):
| Type |
Number |
Shape |
Function |
| Incisors |
8 |
Chisel-shaped, sharp |
Cutting / biting food |
| Canines |
4 |
Pointed, sharp |
Tearing/piercing food (meat) |
| Premolars |
8 |
Flat with 2 cusps |
Crushing and grinding food |
| Molars |
12 |
Large, flat, multi-cusped |
Grinding and chewing food |
🦠 4. Digestion in Amoeba — A Single Cell Does It All!
Amoeba is a single-celled organism that ingests food through a fascinating process:
Amoeba senses food particle (e.g., algae, bacterium)
⬇
Extends pseudopodia (temporary finger-like projections)
around the food
⬇
Pseudopodia merge → form a food vacuole (digestion
chamber) inside the cell
⬇
Digestive enzymes released into vacuole → food digested into simple molecules
⬇
Digested nutrients absorbed into cytoplasm. Undigested waste expelled from
cell body
📝 5. Quick Revision
- 5 steps of animal nutrition: Ingestion → Digestion → Absorption → Assimilation →
Egestion
- Digestion begins in the mouth via salivary amylase (starch → sugar)
- Stomach: HCl kills bacteria; pepsin digests protein
- Small intestine = main site of digestion AND absorption. Bile emulsifies fats
- Villi = tiny projections in small intestine → increase absorption surface area
- Large intestine = absorbs water; forms solid faeces
- Teeth: Incisors (cut), Canines (tear), Premolars (crush), Molars (grind). Adults = 32 teeth
- Amoeba ingests food using pseudopodia → forms food
vacuole for intracellular digestion
