Biology · Plant Growth and Development · NEET
NCERT defines growth as an irreversible increase in size, and this size can be shown by several measurable parameters: size, area, length, height, volume, and cell number. It also involves an increase in protoplasmic material (dry weight). So the parameters are the different physical quantities you can measure to prove growth happened.
You pick the parameter that fits the shape of the growth. A pollen tube or root growing in one direction is measured by length. A dividing pool of cells (like in tissue culture) is measured by cell number. A flat leaf spreading out is measured by surface area. A fruit or fleaf gaining mass is measured by fresh weight or dry weight.
Both can be used, but dry weight is the more reliable measure of true growth because it shows the increase in actual protoplasmic material and does not change with the plant's water content. Fresh weight can rise just from water uptake, which is not permanent growth, so dry weight is preferred for measuring real growth.
Measuring growth gives you a size at one time. Growth rate is the increased growth per unit time, so it needs two measurements over a time gap. NCERT expresses it mathematically: for arithmetic growth L(t) = L0 + rt, and for geometric growth W1 = W0 e^(rt), where r is the growth rate.
Because a permanent, irreversible increase in size must come from making new living material (cytoplasm, cell walls, organelles), not from temporary swelling with water. That is why dry weight, which reflects protoplasmic material, is a trusted parameter. A wilted and re-watered plant changes fresh weight without any real growth.
Length of the stem at time 0 is 20 cm. The arithmetic growth rate is 30 cm per day. What is the length of the stem at the end of the 7th day?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
NCERT lists size, area, length, height, volume, and cell number, along with increase in protoplasmic material (measured as dry weight). You select the parameter that suits the organ or structure being measured.
Length. A pollen tube grows in one direction, so its growth is measured by the increase in its length over time.
Dry weight is more reliable because it reflects the actual protoplasmic material made by the plant and is not affected by temporary water content, unlike fresh weight.
In a mass of dividing cells, such as in tissue culture, growth is measured by counting the increase in the number of cells over time rather than by length or area.
Growth rate is the increased growth per unit time. It can be expressed mathematically, for example L(t) = L0 + rt for arithmetic growth, where r is the growth rate per unit time.
