Biology · Plant Growth and Development · NEET
Gibberellin. Sugarcane stores its sugar inside the STEM. Gibberellin makes the internodes (stem segments) longer, so a longer stem holds more sugar. NCERT says this can raise yield by up to 20 tonnes per acre. Auxin does NOT elongate the stem this way, so students who pick auxin lose the mark. Remember: sugar is in the stem, gibberellin lengthens the stem.
Two hormones together: auxin AND ethylene. Pineapple naturally takes a long time to flower. Farmers spray auxin and ethylene to force flowering throughout the year so fruit can be set on demand (this also helps synchronise fruit-set). This exact pair was asked in NEET 2019. Do not write only 'ethylene' or only 'auxin' — the standard answer is the combination.
Same hormone (gibberellin), different plant part. In SUGARCANE it elongates the STEM to increase sugar yield. In GRAPES it elongates the fruit STALK (the pedicel), so grape bunches spread out and berries grow bigger. In the NEET 2023 match-the-column question, 'increase in length of grape stalks' was matched to gibberellin. So: sugarcane = stem length; grape = stalk length; both by gibberellin.
In the brewing industry, GA3 (gibberellic acid) is used to speed up the MALTING process. Malting means letting cereal grains (like barley) sprout so their stored starch is broken into sugar for making beer. Gibberellin makes this sprouting/enzyme step faster. This 'malting' use is a common match-the-column item in NEET, so link GA3 → malting → brewing in your memory.
Ethylene is the fruit-ripening hormone. Commercially it is used to ripen fruits like tomatoes and apples quickly and evenly, to initiate flowering and synchronise fruit-set in pineapples, and it also promotes root growth and root hair formation. Because ethylene is a gas, ripening rooms use ethylene gas or ethylene-releasing chemicals. Do not confuse ripening (ethylene) with stem elongation (gibberellin).
Name the plant growth regulator which upon spraying on sugarcane crop increases the length of stem, thus increasing the yield of sugarcane crop.
It takes a very long time for pineapple plants to produce flowers. Which combination of hormones can be applied to artificially induce flowering in pineapple plants throughout the year to increase yield?
Match List-I with List-II. List-I: (A) Auxin (B) Gibberellin (C) Cytokinin (D) Ethylene. List-II: (I) Promotes female flower formation in cucumber (II) Overcoming apical dominance (III) Increase in the length of grape stalks (IV) Promotes flowering in pineapple.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Gibberellin. Sprayed on sugarcane it lengthens the stem, and since sugar is stored in the stem this raises yield by up to 20 tonnes per acre.
Auxin and ethylene together. They force year-round flowering and help synchronise fruit-set, which increases yield.
GA3 (gibberellic acid) speeds up the malting process — the sprouting of cereal grain that converts stored starch to sugar for beer production.
It increases yield by increasing stem length, not by making the plant sweeter. More stem length means more sugar-storing tissue, so total sugar goes up.
Ethylene. It is a gaseous PGR used to ripen fruits like tomatoes and apples quickly and evenly, and it also triggers pineapple flowering and fruit-set.
