Learning Objectives
- Understand the process of digestion in humans
- Learn about the human digestive system
- Know about digestion in grass-eating animals
- Understand feeding and digestion in amoeba
Key Concepts
Human Digestive System
The alimentary canal is a long tube extending from mouth to anus. Food passes through: Mouth → Oesophagus → Stomach → Small intestine → Large intestine → Anus
Steps of Digestion
1. Ingestion: Taking food into the mouth.
2. Digestion: Breaking down complex food into simpler substances. Includes mechanical (chewing) and chemical (enzymes) digestion.
3. Absorption: Digested food passes through intestinal wall into blood.
4. Assimilation: Absorbed nutrients are used by body cells.
5. Egestion: Removal of undigested waste from the body.
Digestion in Different Organs
Mouth: Teeth break food mechanically. Salivary glands secrete saliva containing amylase enzyme that breaks down starch into sugar.
Oesophagus: Food pipe that pushes food to stomach by peristaltic movements.
Stomach: Churns food. Gastric glands secrete hydrochloric acid, pepsin, and mucus. Pepsin digests proteins.
Small intestine: Longest part. Receives bile from liver and pancreatic juice from pancreas. Complete digestion occurs here. Villi absorb nutrients.
Large intestine: Absorbs water and some salts. Remaining material forms faeces.
Digestion in Grass-Eating Animals (Ruminants)
Ruminants like cows have a four-chambered stomach: Rumen, Reticulum, Omasum, and Abomasum. They swallow food quickly, store in rumen, then bring it back to mouth for re-chewing (cud-chewing). Cellulose is digested by bacteria in rumen.
Feeding and Digestion in Amoeba
Amoeba uses pseudopodia (false feet) to engulf food. A food vacuole forms around the food particle. Digestive juices break down food inside the vacuole. Absorbed nutrients are used, undigested matter is expelled.
Summary
Animals get food from plants or other animals (heterotrophs). The human digestive system processes food through ingestion, digestion, absorption, assimilation, and egestion. Ruminants have specialized stomachs for cellulose digestion. Single-celled organisms like amoeba use pseudopodia for feeding.
Important Terms
- Alimentary canal: Tube from mouth to anus
- Peristalsis: Wave-like muscle contractions that push food
- Villi: Finger-like projections in small intestine for absorption
- Ruminant: Cud-chewing animal with four-chambered stomach
- Pseudopodia: False feet used by amoeba for movement and feeding
Quick Revision
- 5 steps: Ingestion → Digestion → Absorption → Assimilation → Egestion
- Saliva breaks starch, Pepsin breaks protein, Bile breaks fats
- Small intestine: complete digestion + absorption (villi)
- Ruminants: 4-chambered stomach, cud-chewing
- Amoeba: pseudopodia → food vacuole → digestion