Plant Growth And Development

Measurement of growth and growth rates is introduced in NCERT Class 11, Chapter 15 (Plant Growth and Development). The absolute growth rate is the total increase in a measured parameter divided by the time taken, giving the increase per unit time. In this case the plant grows from twenty centimetres to fifty centimetres, so the total increase in height is fifty minus twenty, which equals thirty centimetres. This growth occurs over three days, so the average absolute growth rate is thirty centimetres divided by three days, equal to ten centimetres per day. The option thirty centimetres per day mistakenly reports the total height gain rather than the daily rate. Seven centimetres per day does not match any correct division of the figures given. Fifteen centimetres per day would result only from dividing by two days, which is inconsistent with the stated three-day span. A numerical sanity check confirms the answer: ten centimetres per day multiplied by three days gives thirty centimetres of growth, which restores the observed final height of fifty centimetres from the initial twenty centimetres, demonstrating that the rate and the time span are mutually consistent with the measured data.