Biology · Plant Growth and Development · NEET
Growth is slow at the start (lag phase) because few cells are dividing. Then both daughter cells keep dividing, so growth speeds up fast (log phase). Later, food and space run out, so growth slows and becomes flat (stationary phase). Slow-fast-flat gives the S shape.
1) Lag phase — slow initial growth. 2) Log (exponential/log) phase — rapid growth at an exponential rate, both progeny cells keep dividing. 3) Stationary phase — growth slows and levels off because nutrient supply is limited. NCERT calls this a typical sigmoid or S-curve.
They are linked but not identical. Geometric growth means both daughter cells keep dividing, giving exponential increase. When you plot this real growth over time in nature (with limited nutrients), it does not rise forever — it flattens, producing the full S-shaped sigmoid curve. So the sigmoid curve is the real-world form of geometric growth.
Growth (rate) is maximum during the log or exponential phase. Here both progeny cells from mitosis keep dividing, so the increase is the fastest. This is a very common NEET question.
Because nutrient supply becomes limited. With less food and space, cells cannot keep dividing at the same speed, so the rate falls to almost zero and the curve becomes flat.
NCERT says a sigmoid curve is characteristic of a living organism growing in a natural environment. It is typical for all cells, tissues and organs of a plant, so it applies very widely.
The process of growth is maximum during
Try the real previous-year questions from this chapter — each with the answer and a full solution.
It is the S-shaped curve got by plotting plant growth against time, showing a lag phase, a log (exponential) phase and a stationary phase.
The log or exponential phase shows the highest growth rate.
Limited nutrient supply, which slows down and finally stops the increase in growth.
No. NCERT says it is characteristic of any living organism growing in a natural environment, and it is typical for all cells, tissues and organs of a plant.
W1 = W0 e^rt, where W1 is final size, W0 is initial size, r is growth rate, t is time and e is the base of natural logarithms.
