Rucete ✏ Campbell Biology In a Nutshell
Unit 7 ANIMAL FORM AND FUNCTION — Concept 41.2 Food Processing Involves Ingestion, Digestion, Absorption, and Elimination
1. The Four Stages of Food Processing
- Ingestion: Eating or taking food into the body.
- Digestion: Breaking food down mechanically and chemically into absorbable molecules.
- Absorption: Transporting nutrients into body tissues and cells.
- Elimination: Removing undigested material as feces.
2. Feeding Mechanisms
Animals use various feeding strategies adapted to their ecological roles:
- Filter feeders: Extract food particles from water (e.g., whales).
- Substrate feeders: Live in or on their food (e.g., caterpillars).
- Fluid feeders: Drink nutrient-rich fluids (e.g., mosquitoes).
- Bulk feeders: Eat large chunks of food (e.g., humans, snakes).
3. Gastrovascular Cavities vs. Alimentary Canals
- Gastrovascular cavity:
- Single opening for food and waste
- Found in simple animals like cnidarians
- Alimentary canal:
- Digestive tube with mouth and anus
- Allows one-way food flow and specialized compartments
4. Nutrient Absorption: When Does Food Enter the Body?
- Food is not "inside" the body until nutrients are absorbed into cells.
- The digestive tract is essentially a tunnel open to the outside world.
5. An Engine Analogy for Digestion
- Just as a car engine breaks down fuel to release energy, digestion breaks down food to power cells.
- Both systems:
- Break down fuel
- Use controlled, stepwise reactions
- Release usable energy
In a Nutshell
Food processing in animals follows a four-stage pathway: ingestion, digestion, absorption, and elimination. While the structure and method vary across species, all are designed to efficiently extract energy and nutrients from the environment to sustain life.