NCERT Solutions for Class 9th Science Chapter 3 .2.1 Apical meristem — Activity 3.1: Let us design experiments
Book page 293 Updated on2026-09-08
Q1.
What trend do you observe in the data you recorded in Table 3.1? Are your observations similar to those presented in the graphical representation (Fig. 3.2)? What do you infer?
Answer
The roots in Jar A keep getting longer day after day; the roots in Jar B grow at the same rate until their tips are cut, and then they stop completely.
These are the readings printed in Fig. 3.2 of the book (length of root in cm from the base of the bulb):
Day
1
2
3
4
5
6
7
Jar A (uncut)
0.25
0.8
1.8
2.9
3.8
4.9
5.8
Jar B (tip cut)
0.25
0.7
1.6
2.6 → 1.6
1.6
1.6
1.6
Growth of onion roots, redrawn from the readings in Fig. 3.2. The dashed drop is the 1 cm of root tip removed.
Now work out the rates:
Growth rate = (change in length) ÷ (time taken)
Jar A, day 1 → day 7 = (5.8 cm − 0.25 cm) ÷ 6 days = 5.55 cm ÷ 6 days ≈ 0.93 cm day⁻¹
Jar B, before cutting (day 1 → day 4) = (2.6 cm − 0.25 cm) ÷ 3 days = 2.35 cm ÷ 3 days ≈ 0.78 cm day⁻¹
Length removed by the cut = 2.6 cm − 1.6 cm = 1.0 cm (matches the 1 cm cut in step 5)
Jar B, after cutting (day 4 → day 7) = (1.6 cm − 1.6 cm) ÷ 3 days = 0 cm day⁻¹
Inference: a root grows only from its tip. Remove the tip and the whole root stops elongating, even though the rest of the root is alive and healthy.
Why it happens: the tip holds the root apical meristem — small cells with thin walls, dense cytoplasm, a large nucleus and no vacuole, which divide continuously. You saw these very cells in mitosis in an onion root tip in Chapter 2. Cutting the tip removes the only dividing cells; the cells left behind have already differentiated into permanent tissue and cannot divide. The shoot tip has the same kind of meristem, which is why a plant also grows in height from its tip.
Check it yourself: Jar A is the control. Everything — same water, same light, same bulbs — is kept identical, and only the tip is cut in Jar B. That is what lets you say the tip, and nothing else, caused the difference.