Which of the following is responsible for the red colour of beetroot?
- (a)Lycopene
- (b)Betanin
- (c)Curcumin
- (d)Beta carotene
Answer
Why
Correct — B. The red-violet of beetroot comes from betanin, a betacyanin belonging to the betalain family of pigments. Betalains are nitrogen-containing pigments confined to plants of the order Caryophyllales, and beet is their commonest source.
One consequence makes this checkable: a plant carrying betalains carries no anthocyanins — the two never occur together. The red of beet is chemically unlike the red of a rose petal. Option (b).
Why the others are wrong
- (a)Lycopene — Lycopene is the carotenoid that reddens tomato and watermelon. It is a hydrocarbon carotene, unrelated to the nitrogen-bearing pigment in beet.
- (c)Curcumin — Curcumin is the yellow polyphenol of turmeric, used as a colouring agent and as a natural acid-base indicator. Wrong colour and wrong plant.
- (d)Beta carotene — Beta-carotene gives carrot its orange and is the provitamin A the body converts to retinol. The shared syllable beta next to betanin is exactly what makes this option tempting.
Concept
Plant colours fall into four families worth holding as a single table.
Chlorophylls are green. Carotenoids, meaning carotenes and xanthophylls, cover yellow through orange to red, as in carrot and tomato.
Anthocyanins are water-soluble flavonoids running red to purple to blue, and they shift with pH. Betalains are the nitrogen-containing red and yellow pigments of beet and its relatives.
Learn the pairs in both directions, plant to pigment and pigment to plant.
Three of the four options are pigments a student meets in the same chapter, which is why recall alone is unreliable here. The nitrogen-containing family is the distinguishing idea.
Key facts
- Betanin is the betacyanin pigment responsible for the red colour of beetroot.
- Betalains contain nitrogen and occur only in plants of the order Caryophyllales.
- Betalains and anthocyanins are never found together in the same plant.
- Lycopene colours tomato, beta-carotene colours carrot, and curcumin colours turmeric.
Study next
Common traps
- Choosing lycopene because it is the pigment most strongly associated with the word red.
- Reading beta-carotene as the beet pigment because of the shared beta.
- Assuming every red plant colour must be an anthocyanin.
A pigment is matched to its source in the sea at 18 Sep 2024, 09:00, GA Q11, which asks which marine carotenoid is abundant in brown seaweed, macroalgae and diatoms (fucoxanthin).
Related PYQs
No directly related past PYQ was found.