Q1.
How do the complex food components get broken down into simpler forms and used by the body in various animals? Is this process the same in all animals or does it vary?
Answer
The complex components of food — carbohydrate, protein and fat — are broken down inside a long tube called the alimentary canal. It begins at the mouth and ends at the anus. As food is pushed along this tube, digestive juices secreted at different parts break it down into simpler forms. These simpler forms are then absorbed into the blood and carried to every part of the body.
| Part of the canal | Juice / secretion it receives | What it does to the food |
|---|---|---|
| Mouth | Saliva | Teeth crush and chew (mechanical digestion); saliva starts changing starch into sugar |
| Stomach | Digestive juice, acid and mucus | Proteins are broken into simpler components; acid kills harmful bacteria; mucus protects the stomach lining |
| Small intestine | Bile from the liver, pancreatic juice from the pancreas, and juice from its own wall | Fat, protein and the remaining carbohydrate are broken into the simplest forms, and the nutrients are absorbed into the blood |
| Large intestine | — | Absorbs water and some salts, leaving semi-solid stool |
No, the process is not exactly the same in all animals. The plan is similar, but the canal is built differently to suit the food an animal eats.
- Cows and buffaloes (ruminants) swallow grass after chewing it only partly, and later bring it back to the mouth for thorough chewing — this is rumination.
- Birds have no teeth at all. They grind food in a muscular chamber called the gizzard, often with the help of grit they swallow.
Why it happens: the body cannot use a big molecule of starch or protein as it is. It has to be cut into small, soluble pieces that can pass through the wall of the intestine into the blood. Digestive juices are the tools that do this cutting.