Lesson Objectives
By the end of the lesson, students should be able to:
1. Define the alimentary canal and identify its components.
2. Explain the digestive system and processes in invertebrates.
3. Describe the digestive system and processes in vertebrates.
4. Compare the digestive systems of invertebrates and vertebrates.
What happens to the food we eat?
Do animals digest food the same way humans do?
Definition of Key Terms:
1. Alimentary Canal: A long, continuous tube that starts from the mouth and ends at the anus, where digestion and absorption occur.
2. Digestive System: The organs and structures involved in breaking down food into nutrients the body can absorb.
Invertebrates: Animals without a backbone (e.g., earthworms, insects).
Vertebrates: Animals with a backbone (e.g., fish, birds, mammals).
a. Alimentary Canal in Humans
Components of the Alimentary Canal:
1. Mouth: Ingestion and mechanical digestion (chewing).
2. Esophagus: Passageway for food using peristalsis.
3. Stomach: Chemical digestion using enzymes and acids.
4. Small Intestine: Main site for digestion and nutrient absorption.
5. Large Intestine: Absorption of water and formation of feces.
6. Anus: Egestion (elimination of undigested food).
Digestive Process in Humans:
Ingestion → Digestion → Absorption → Assimilation → Egestion.
Digestive System in Invertebrates eg Earthworms:
1. Straight Alimentary Canal:
2. Mouth: Food intake.
3. Pharynx: Pushes food to the esophagus.
4. Crop: Temporary food storage.
5. Gizzard: Grinds food.
6. Intestine: Digestion and absorption.
7. Anus: Egestion.
Insects (e.g., Grasshopper):
1. Mouthparts: Specialized for chewing or sucking.
2. Foregut: Food storage and initial digestion.
3. Midgut: Digestion and absorption.
4. Hindgut: Water absorption and waste elimination.
C. Digestive System in Vertebrates eg Fish:
Simple digestive tract with no differentiation between small and large intestines.
Mouth → Esophagus → Stomach → Intestine → Anus.
Birds:
Special Structures: Crop (storage) and gizzard (grinding).
Beak → Esophagus → Crop → Proventriculus (stomach) → Gizzard → Intestine → Cloaca.
Mammals (e.g., Humans):
Highly developed digestive system with specialized organs for enzymatic digestion.
Includes accessory organs like the liver and pancreas.
Feature | Invertebrates | Vertebrates |
Complexity | Less complex (e.g., earthworm) | Highly specialized (e.g., mammals) |
Accessory Organs | Rarely present | Present (e.g., liver, pancreas) |
Specialized Regions | Fewer | More differentiated (e.g., stomach) |
Example | Earthworm, Grasshopper | Fish, Birds, Humans |
Evaluation
1. What is the function of the alimentary canal?
2. How does digestion differ between invertebrates and vertebrates?
3. Mention two invertebrates and describe their digestive systems.
Summarize key points from the lesson:
Alimentary canal components and their roles.
Differences in digestion between invertebrates and vertebrates.
Assignment:
Compare digestive system of man and fish
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