Digestion of food is an important function of the animal body. In animals like lions, cows, humans, etc., the process involves use of various organs starting from the mouth and ending with the anus. The longest part of this canal is known as the ________.

Correct — A. The question is describing the alimentary canal — the tube that runs mouth, oesophagus, stomach, small intestine, large intestine, rectum, anus.

Of those sections the small intestine is by far the longest. It has to be: this is where digestion is completed and where the nutrients are absorbed, and absorption needs surface area, so the tube is long and tightly coiled.

Length follows function here, which is why option (a) is the keyed one.

Why the others are wrong

• (b)
  stomach — The stomach is a sac, not a length of tube — it widens to hold a meal and churn it with acid. Its capacity is large, but the distance food travels through it is short.
• (c)
  oesophagus — The oesophagus is only the food pipe from throat to stomach, about as long as your neck and chest together and a fraction of the coiled small intestine. It transports; it neither digests nor absorbs.
• (d)
  large intestine — The large intestine is wider but much shorter. It is named for its diameter, and its job is reclaiming water from undigested material, not the long work of digestion and absorption.

Digestion in humans, cows and lions alike happens along one continuous tube, with glands — salivary glands, liver, pancreas — emptying into it.

Each section is shaped by its job. The oesophagus only transports. The stomach stores and churns. The small intestine digests and absorbs. The large intestine takes back water.

Learn the order of the parts and one distinguishing job for each. A superlative — longest, widest — and a question about where a named process happens are both answered off the same two lists.

Key facts

• The human alimentary canal runs mouth, oesophagus, stomach, small intestine, large intestine, rectum, anus.
• The small intestine is the longest part of the alimentary canal.
• Most absorption of digested food happens in the small intestine, through finger-like villi on its inner wall.
• The large intestine is shorter but wider than the small intestine, and mainly absorbs water.

Common traps

• Reading 'longest' as 'largest' and picking the large intestine, which is named for width, not length.
• Assuming the stomach does most of the digesting — most of it is completed further down, in the small intestine.

No directly related past PYQ was found.