Biology · Plant Growth and Development · NEET
| Definition | Total growth per unit time | Growth per unit time per unit initial size |
| Basis of comparison | Raw amount added | Expressed on a common basis (per unit starting parameter) |
| Also called | — | Efficiency index |
| Best use | Reporting how much a single part grew | Fairly comparing systems of different sizes |
| NCERT leaf example | Leaves A and B show equal absolute increase in area | Smaller leaf shows the higher relative growth rate |
No. Arithmetic and geometric growth describe the pattern of how a plant grows over time (linear line or J-shaped curve). Absolute and relative growth rate are two ways to compare the amount of growth between systems. Absolute growth rate simply reports the total growth per unit time, no matter what pattern produced it.
In the NCERT example, leaves A and B are of different sizes but add the same area in the same time, so their absolute growth rates are equal. But relative growth rate divides the growth by the starting size. The smaller leaf has a smaller starting size, so the same added area is a bigger fraction of what it started with. So the smaller leaf shows the higher relative growth rate.
Relative growth rate is also called the efficiency index. It measures the ability of the plant to produce new plant material per unit of existing material. A high relative growth rate means the plant makes new material efficiently compared to its own current size.
Relative growth rate = (absolute increase in size per unit time) divided by the initial size. Example: a leaf grows from 5 cm2 to 10 cm2 in 1 day. Absolute rate = 5 cm2/day. Relative rate = 5 divided by 5 = 1 per day. A leaf growing 50 to 55 cm2 in 1 day also has absolute rate 5 cm2/day, but relative rate = 5 divided by 50 = 0.1 per day.
Use relative growth rate. Because it is expressed per unit initial size, it gives a fair comparison between a large and a small system. Absolute growth rate alone can be misleading when the two starting sizes are very different.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Absolute growth rate is the measurement and comparison of total growth per unit time of a system, such as a leaf, root or whole plant.
Relative growth rate is the growth of a given system per unit time expressed on a common basis, for example per unit of the initial size or initial parameter.
Yes. NCERT states that relative growth rate is also the measure of the ability of the plant to produce new plant material, referred to as the efficiency index.
The smaller leaf. Both leaves show the same absolute increase in area, but the smaller starting size makes that increase a larger fraction, so the smaller leaf has the higher relative growth rate.
NEET regularly asks one-mark conceptual and numerical questions on growth rates from Plant Growth and Development. Knowing the exact definitions and the leaf comparison prevents easy mistakes.
