Arithmetic Growth in Plants: Meaning and Example

In arithmetic growth, after a cell divides by mitosis, only one of the two daughter cells continues to divide. The other daughter cell stops dividing and differentiates (matures). Because only one cell keeps dividing each time, new cells are added at a constant rate. NCERT gives the example of a root elongating at a constant rate.

The formula is Lt = L0 + rt, where Lt is the length at time t, L0 is the length at the start (time zero), r is the growth rate (elongation per unit time), and t is the time. You simply add the same amount (r) for each unit of time. This is why NEET questions on arithmetic growth are just addition, not multiplication.

Because the same fixed amount is added in every equal time interval, the length increases by an equal step each day. When you plot length on the y-axis against time on the x-axis, these equal steps produce a straight, sloping line. So arithmetic growth = linear curve. Geometric growth, in contrast, gives an S-shaped (sigmoid) curve.

Only ONE daughter cell continues to divide. After mitosis, one cell stays meristematic (keeps dividing) and the other differentiates and matures. This is the single most tested point that separates arithmetic growth from geometric growth, where BOTH daughter cells keep dividing.

Here r is the growth rate, meaning the elongation (increase in length) per unit time. For example, if a stem grows 30 cm per day, then r = 30 cm/day. You add this r to the starting length for every unit of time passed.

Growth in which only one daughter cell keeps dividing after each division, so length increases at a constant rate and gives a linear (straight-line) graph.

A root (or root tip) elongating at a constant rate is the NCERT example of arithmetic growth.

A straight line (linear curve). The S-curve (sigmoid) is for geometric growth.

Lt = L0 + rt, where L0 is starting length, r is growth rate per unit time, and t is time. Just add r for every time unit.