Question
Draw a neat labelled diagram of the human digestive system. Name each organ and briefly state its function.
(NCERT Class 7, Chapter 2 — Nutrition in Animals)
Solution — Step by Step
The digestive system is essentially a long tube from mouth to anus, with several specialised organs along the way. Here are the parts in order:
- Mouth (Buccal Cavity) — contains teeth for mechanical digestion and salivary glands that release saliva with the enzyme amylase
- Oesophagus (Food Pipe) — pushes food down to the stomach by wave-like contractions called peristalsis
- Stomach — a muscular bag where gastric juice (HCl + pepsin) breaks down proteins
- Small Intestine — the main site of digestion and absorption; about 6-7 metres long in adults
- Large Intestine — absorbs water and minerals from undigested food
- Rectum and Anus — stores and expels waste (faeces)
These organs are not part of the tube but secrete digestive juices into it:
- Salivary Glands (3 pairs) — produce saliva containing amylase
- Liver — the largest gland; produces bile that helps digest fats
- Pancreas — secretes pancreatic juice with enzymes for proteins, fats, and carbohydrates
- Gall Bladder — stores bile from the liver and releases it into the small intestine
When drawing, make sure to label these clearly:
- Mouth → Oesophagus → Stomach → Small intestine (duodenum, jejunum, ileum) → Large intestine (colon) → Rectum → Anus
- Show liver on the right side (as we look at the diagram) with the gall bladder below it
- Show the pancreas behind the stomach, near the duodenum
- Draw arrows to show the direction of food movement
Why This Works
The digestive system follows a logical sequence: ingestion → digestion → absorption → assimilation → egestion. Each organ is specialised for a particular step. The mouth starts mechanical breakdown, the stomach handles protein digestion in an acidic environment, and the small intestine completes digestion and absorbs nutrients into the blood.
The associated glands (liver, pancreas) act like chemical factories — they don’t store food, but they produce the chemicals needed to break it down. Bile from the liver emulsifies fats (breaks them into tiny droplets), while pancreatic juice contains a cocktail of enzymes for all three food types.
Alternative Method — Remember with a mnemonic
To remember the order: “My Excellent Stomach Seems Like Really Awesome” — Mouth, Esophagus, Stomach, Small intestine, Large intestine, Rectum, Anus. For the glands, just remember SLP — Salivary glands, Liver, Pancreas.
Common Mistake
Students often forget to label the gall bladder as separate from the liver, or they place the pancreas in the wrong position. The gall bladder sits just below the liver and stores bile — it does NOT produce bile. The pancreas sits behind the stomach, nestled in the curve of the duodenum. Getting these positions wrong in the diagram costs marks.