Vitamins
NCERT Class 12 Chemistry Chapter 10 Section 10.4
Quick answer
Vitamins are organic compounds needed in small amounts in the diet, whose deficiency causes specific diseases. Vitamins A, D, E and K are fat-soluble and are stored in the liver and fat tissue, while the B group and vitamin C are water-soluble, are excreted in urine and must be taken regularly, except vitamin B, which can be stored. Lack of vitamin A causes night blindness, B beri beri, C scurvy, D rickets and K a longer blood clotting time.
With your textbook
NCERT Chemistry Part II (Class 12), Chapter 10 “Biomolecules”, Section 10.4 “Vitamins”, pages 295–297.
Open the official NCERT chapter (PDF, 3.1 MB, ncert.nic.in) (opens in a new tab)
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What are vitamins?
Vitamins
Vitamins are organic compounds needed in small amounts in the diet for specific biological functions, for normal growth and for health. NCERT introduces them by their deficiency diseases:
It has been observed that certain organic compounds are required in small amounts in our diet but their deficiency causes specific diseases. These compounds are called vitamins.
NCERT Chemistry Part II (Class 12), Section 10.4, page 295
- Most vitamins cannot be made in our body, but plants can make almost all of them, so vitamins are counted as essential food factors. Bacteria in the gut make some of the vitamins we need (NCERT page 295). NCERT’s Summary calls vitamins accessory food factors required in the diet (page 301), so an exam may use either name.
- Vitamins belong to many chemical classes, so they are hard to define by structure (NCERT page 295).
- They are named by letters, A, B, C, D and so on, and some by sub-groups, such as B1, B2, B6 and B12. Too much of a vitamin is also harmful, and vitamin pills should not be taken without a doctor’s advice (NCERT page 296).
- The name comes from “vitamine”, vital + amine, because the first ones found had amino groups. Most turned out to have none, so the “e” was dropped (NCERT page 296).
In plain words: a vitamin is a small helper molecule that the body needs a little of but cannot make enough of. Without it, a particular disease appears.
Classification of vitamins
Vitamins are classified by whether they dissolve in water or in fat (NCERT page 296), an example of like dissolving like:
| Group | Vitamins | Stored? |
|---|---|---|
| fat soluble | A, D, E, K | yes: liver, fat tissue |
| water soluble | B group, C | no (except B12) |
Fat soluble and water soluble vitamins
- Fat-soluble vitamins, A, D, E and K, dissolve in fats and oils but not in water. They are stored in the liver and in adipose (fat-storing) tissue (NCERT page 296).
- Water-soluble vitamins, the B group and vitamin C, dissolve in water. They are readily excreted in urine and cannot be stored in the body, except vitamin B12, so they must be supplied regularly in the diet (NCERT page 296).
Vitamin deficiency diseases
NCERT Table 10.3 (pages 296–297) lists nine vitamins, their sources and the diseases their deficiency causes:
| Vitamin | Sources | Deficiency disease |
|---|---|---|
| A | fish liver oil, carrots, butter, milk | xerophthalmia (hardening of the cornea), night blindness |
| B1 (thiamine) | yeast, milk, green vegetables, cereals | beri beri (loss of appetite, retarded growth) |
| B2 (riboflavin) | milk, egg white, liver, kidney | cheilosis (fissuring at the corners of the mouth and lips), digestive disorders, burning sensation of the skin |
| B6 (pyridoxine) | yeast, milk, egg yolk, cereals, grams | convulsions |
| B12 | meat, fish, egg, curd | pernicious anaemia |
| C (ascorbic acid) | citrus fruits, amla, green leafy vegetables | scurvy (bleeding gums) |
| D | exposure to sunlight, fish, egg yolk | rickets (bone deformities in children), osteomalacia (soft bones and joint pain in adults) |
| E | vegetable oils such as wheat germ oil and sunflower oil | increased fragility of RBCs, muscular weakness |
| K | green leafy vegetables | increased blood clotting time |
- Note on pernicious anaemia (beyond the NCERT text): NCERT describes it as “RBC deficient in haemoglobin”. In this anaemia too few red blood cells are made, and they are larger than normal, while each still carries a normal concentration of haemoglobin (Wikipedia, “Pernicious anemia”). So read NCERT’s phrase as blood short of red cells, and so of haemoglobin. In an exam, name pernicious anaemia for vitamin B12. Vitamin B12 is cyanocobalamin (NCERT Unit 5 spells it cyanocobalamine), a coordination compound of cobalt that NCERT calls the anti-pernicious anaemia factor (Unit 5, page 137).
- What the vitamins do (reasoned from NCERT Table 10.3): each vitamin keeps healthy what its lack damages. Vitamin A is needed for the eyes (night vision and the cornea), D for the bones of children and adults, C for the gums, E for red blood cells and muscles, and K for blood clotting, which is why NCERT’s Exercise 10.19 (page 302) asks for the vitamin “responsible for the coagulation of blood”. In the B group, B1 is needed for appetite and growth, B2 for the lips, mouth and skin and for digestion, B6 to prevent convulsions and B12 for making red blood cells. Many vitamins are also parts of coenzymes, the helpers that some enzymes need: NAD and NADP contain the vitamin niacin (NCERT Class 11 Biology, Chapter 9, page 118; see co-factors).
Solved examples
Example 1: Sort the vitamins
Sort vitamins A, B1, C, D, K and B12 into fat-soluble and water-soluble, and say which of them the body can store.
Answer: Fat-soluble: A, D and K, stored in the liver and fat tissue. Water-soluble: B1, C and B12; of these only B12 can be stored (NCERT page 296).
Example 2: Match the disease
A child has bone deformities, and an adult has bleeding gums. Which vitamins are lacking, and name one source of each.
Answer: Bone deformities in a child are rickets, from a lack of vitamin D: sunlight exposure, fish or egg yolk. Bleeding gums are scurvy, from a lack of vitamin C: citrus fruits, amla or green leafy vegetables (NCERT Table 10.3, pages 296–297).
Common mistakes to avoid
Common mistake
Calling vitamin B12 an ordinary water-soluble vitamin
It is water-soluble, but unlike the rest of the B group and vitamin C, it can be stored in the body.
Common mistake
Thinking more vitamins are always better
Too much of a vitamin is also harmful; vitamin pills need a doctor’s advice (NCERT page 296).
Quick revision summary
- Vitamins: organic compounds needed in small amounts in the diet; their deficiency causes specific diseases. The name came from “vital amine”.
- Fat-soluble: A, D, E, K (stored). Water-soluble: B group and C (not stored, except B12).
- Deficiency: A, xerophthalmia and night blindness; B1, beri beri; B2, cheilosis; B6, convulsions; B12, pernicious anaemia; C, scurvy; D, rickets and osteomalacia; E, fragile RBCs and muscular weakness; K, longer clotting time.
- Functions, read from the deficiencies: A the eyes, D the bones, C the gums, E red blood cells and muscles, K blood clotting, B12 red blood cells; many vitamins are parts of coenzymes (niacin in NAD and NADP).
Formula sheet
- Fat-soluble (stored): A, D, E, K
- Water-soluble (not stored, except B): B group, C
- Vitamin C is ascorbic acid; vitamin B thiamine, B riboflavin, B pyridoxine, B cyanocobalamin (a cobalt complex)
Practice questions
Try each question first, then open the answer to check your working.
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Q1. Why cannot vitamin C be stored in our body? (NCERT Intext Question 10.6, page 301.)
Show answerHide answer
Vitamin C is water-soluble, so it is readily excreted in urine and cannot be stored; it must be taken regularly in the diet (NCERT page 296).
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Q2. Which vitamin’s deficiency increases the blood clotting time, and where is it found? (Compare NCERT Exercise 10.19, page 302.)
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Vitamin K, found in green leafy vegetables (NCERT Table 10.3, page 297).