the-human-digestive-system MCQs for UPSC Prelims

30 practice questions on the-human-digestive-system from the Life Processes in Animals section of the UPSC Prelims syllabus. 30 come with a written explanation. Try the sample set below - the answer stays hidden until you ask for it.

11 Easy 13 Medium 6 Hard

Sample questions

Q1
easy
Why should food be chewed well before it is swallowed?
  1. A it changes the food into water
  2. B it stops the stomach from making any juice
  3. C it is broken into small pieces and mixed with saliva, so digestion becomes easier
  4. D it makes salty food taste less salty
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Correct answer: C - it is broken into small pieces and mixed with saliva, so digestion becomes easier

Chewing breaks food into small bits and mixes saliva into them, so the digestive juices can act on a far larger surface and the work goes faster. Chewing does not change how salty a food is, the stomach makes its juice in any case, and food is never turned into water.
Q2
medium
If a piece of chapati is chewed slowly for about a minute, it begins to taste slightly sweet. This happens because
  1. A the teeth give out a sweet juice while grinding
  2. B the tongue adds a little sugar to the food
  3. C chewing for long makes every kind of food taste sweet
  4. D saliva has started changing the starch in it into sugar
Show answer and explanation

Correct answer: D - saliva has started changing the starch in it into sugar

Chapati is rich in starch, and saliva acting on it changes some of that starch into sugar, which the tongue can taste. The tongue only senses taste and adds nothing, teeth give out no juice, and a piece of lemon chewed for a minute would never taste sweet.
Q3
easy
The stomach is best described as
  1. A a thick-walled bag-like part of the food canal that churns food
  2. B a solid organ in which blood is stored
  3. C a long narrow coiled tube in which food is absorbed
  4. D a short tube that carries food up to the mouth
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Correct answer: A - a thick-walled bag-like part of the food canal that churns food

The stomach is a wide bag-shaped part with thick muscular walls that squeeze and churn the food inside it. The long coiled tube is the small intestine, the short tube that carries food is the food pipe, and the stomach is hollow and stores no blood.
Q4
easy
Saliva in the mouth helps digestion mainly by
  1. A adding water so that the stomach need not work at all
  2. B wetting the food and starting to change starch into sugar
  3. C killing every germ present in the food
  4. D making the food acidic before it is swallowed
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Correct answer: B - wetting the food and starting to change starch into sugar

Saliva moistens food so that it can be swallowed easily, and it begins changing the starch in the food into sugar. The stomach still has a great deal of work left, saliva does not sterilise food, and the acidic juice is made in the stomach and not in the mouth.
Q5
hard
Food normally stays in the stomach for a few hours. What is the most likely result if it were pushed out of the stomach almost at once?
  1. A it would harden back into a dry solid lump
  2. B it would be absorbed faster into the blood from the food pipe
  3. C it would reach the small intestine only partly broken down
  4. D no digestion at all would take place anywhere in the body
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Correct answer: C - it would reach the small intestine only partly broken down

The stomach needs time to churn food and let its juices act, so food leaving too soon would arrive in the small intestine still coarse and poorly mixed. Nothing is absorbed from the food pipe, churned food does not harden again, and the small intestine would still carry on with the digestion it can manage.
Q6
medium
The small intestine is far longer than the large intestine, and yet it is called small. The reason is that
  1. A it holds less food than the mouth does
  2. B it is a much narrower tube than the large intestine
  3. C it was studied by doctors at a later date
  4. D food stays in it for a shorter time
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Correct answer: B - it is a much narrower tube than the large intestine

The two names describe the width of the tubes and not their length: the small intestine is narrow, while the large intestine is short but much wider. Food stays in the small intestine for hours and it handles far more food than the mouth, and the names have nothing to do with when they were studied.
Q7
easy
The main work of the large intestine is to
  1. A make the acidic juice of the canal
  2. B complete the digestion of food
  3. C churn food into a fine paste
  4. D take back water from the undigested matter
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Correct answer: D - take back water from the undigested matter

The large intestine absorbs much of the water from the leftover matter, so that a semi-solid waste is left to be thrown out. Digestion is completed earlier in the small intestine, churning happens in the stomach, and the acidic juice is made there too.
Q8
medium
Besides mixing food with its juices, the churning movement of the stomach helps by
  1. A pushing the food back up into the mouth
  2. B taking back most of the water from the food
  3. C turning the food directly into blood
  4. D breaking the food into a fine paste so the juices can act all over it
Show answer and explanation

Correct answer: D - breaking the food into a fine paste so the juices can act all over it

Churning grinds the lumps into a smooth paste and so gives the digestive juices a much larger surface to act upon. Food is not pushed back up in normal digestion, blood is formed long after absorption, and water is taken back in the large intestine.

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