These questions ask you to follow food through the digestive tract and match each organ to a process. Build the route first, then decide whether the event is mechanical breakdown, chemical breakdown, movement, absorption, storage or elimination.
Follow the material and name the process
In the mouth, teeth make smaller physical pieces while saliva moistens food and begins starch digestion. Waves of muscle contraction called peristalsis move swallowed material down the oesophagus. The stomach stores and churns food and begins substantial protein digestion with acid and enzymes. Most chemical digestion is completed in the small intestine, and most digested nutrients cross there into transport systems. Villi and microvilli increase the available surface for that transfer.
| Stage or organ | Working role |
|---|---|
| Mechanical and chemical digestion | Mechanical action changes piece size; chemical action changes large food molecules into smaller molecules. Neither term means absorption. |
| Liver, gallbladder and pancreas | The liver produces bile, the gallbladder stores and concentrates it, and the pancreas sends digestive enzymes and bicarbonate into the small intestine. Bile disperses fat droplets; bicarbonate reduces acidity. |
| Small intestine | Most chemical digestion and nutrient absorption occur here, helped by a large folded surface. |
| Large intestine and rectum | The large intestine recovers much remaining water and compacts undigested material; the rectum stores faeces before elimination. |
| Material leaving the body | Egestion removes undigested material from the tract. Excretion removes metabolic wastes made by cells, so it is a different process. |
For any unfamiliar description, ask three questions in order: Where is the material now? Is it being physically moved, chemically changed or transferred across a surface? What enters and leaves that stage? This prevents nearby organs from inheriting one another's jobs.
Where the mistakes come from
| Tempting wrong route | How to reject it |
|---|---|
| Treating mechanical digestion, chemical digestion and absorption as the same event | Check what changes. Piece size, molecule size and movement across a lining are three different outcomes. |
| Giving teeth an absorptive or chemical role, or making saliva responsible for most fat digestion | Teeth provide physical force. Saliva moistens food and starts starch digestion; neither performs the later intestinal absorption step. |
| Making the stomach produce bile or perform mechanical work only | The stomach both churns and uses acid and enzymes. Bile production belongs to the liver. |
| Moving most digestion and nutrient uptake to the stomach, large intestine or rectum | Place the main digestion-and-absorption stage in the small intestine. Later regions mainly recover water, compact material and store faeces. |
| Confusing the organ that produces bile with the organ that stores it | Separate manufacture from handling: the liver makes bile, while the gallbladder concentrates and releases it. |
| Making pancreatic bicarbonate increase acidity or replacing its release with bile | The pancreas supplies enzymes plus bicarbonate to the small intestine. Bicarbonate reduces the acidity of arriving contents. |
Try it
A swallowed food ball moves through the esophagus, or food pipe, even when gravity is not helping. What drives it toward the stomach?
- Teeth inside the esophagus
- Air flowing down the trachea
- Peristaltic muscle contractions
- Gravity as the only possible force
Villi and microvilli are projections along the small intestine. How do they support nutrient uptake?
- They reduce the area exposed to digested food.
- They act as valves that control swallowing.
- They increase the area available for absorption.
- They grind food into smaller physical pieces.
Spot the false statement about digestive-system egestion and bodily excretion.
- Egestion deals with undigested material in the digestive tract.
- Excretion deals with metabolic wastes produced by cells.
- Egestion and excretion describe the identical process.
- The two processes remove materials with different origins.