Activity 3.1 — Onion Root Growth and Apical Meristem
Full explanation of NCERT Exploration Activity 3.1 for Class 9 (Chapter 3: Tissues in Action). This activity uses two onion bulbs to prove that root growth occurs only at the root tip, where the apical meristem — a zone of actively dividing cells — is located. Covers materials, step-by-step procedure, expected observations, Fig. 3.2 graph explanation, and connection to meristematic tissue theory. Aligned with CBSE syllabus 2026–27.
Q. What does Activity 3.1 in NCERT Exploration aim to prove?
Activity 3.1 is designed to answer a fundamental question about plant growth: where exactly does a root grow? Does the entire root elongate uniformly, or is growth restricted to a specific region? By comparing two onion bulbs — one with an intact root tip and one with the tip removed — this activity provides direct experimental evidence that:
Objective
To demonstrate that root growth occurs only at the root tip, and that the root tip contains a region of actively dividing cells called the apical meristem. Removing the root tip stops further growth because the meristematic tissue responsible for cell division and elongation has been removed.
2. Materials Needed
Two glass jars (or coupling jars) of similar size, filled with water
Two onion bulbs of similar size and similar stage of root development (preferably with roots already a few millimetres long)
A sharp blade or scissors (for cutting the root tip of one onion)
A ruler (for measuring root length each day)
A notebook for recording daily observations over 5–7 days
3. Step-by-Step Procedure
Q. How is Activity 3.1 performed?
Set up both jars — fill two identical glass jars with water and balance one onion bulb on top of each jar so that the base of the onion (from which the roots emerge) just touches the water surface. Label one jar Jar A and the other Jar B.
Cut the root tips of Jar B — once the roots on the Jar B onion have grown a few millimetres long, carefully cut off the tips (approximately 2–3 mm) from all roots using a sharp blade. Leave the Jar A onion completely undisturbed.
Place both jars in the same conditions — keep both jars in a bright, warm location receiving the same amount of light, temperature, and water. This ensures that any difference in growth is due only to the presence or absence of the root tip.
Measure daily — each day, carefully measure the length of the roots on both onion bulbs using a ruler. Record the measurements in a table (Day 1, Day 2, Day 3, etc.).
Observe and record — continue observing for 5–7 days, noting the appearance, length, and any changes in the roots of both jars. Record your findings in the data table.
4. Expected Observations
Q. What do you expect to observe in Jar A and Jar B?
Observation
Jar A (Root Tips Intact)
Jar B (Root Tips Cut Off)
Root growth
Roots continue to grow longer each day throughout the experiment
Root length stops increasing after tips are removed; no further elongation
Appearance of roots
Healthy, white, actively elongating roots with visible root hair zone
Cut ends may become slightly brownish or blunt; no new growth from the cut surface
New roots
Existing roots grow and new roots may also emerge from the base of the bulb
No regrowth from cut tips; new roots may eventually emerge from higher up on the bulb base but this is slow
5. What the Graph Shows — Fig. 3.2 (NCERT Exploration)
Q. What does the graph in Fig. 3.2 of NCERT Exploration show?
Fig. 3.2 (NCERT Exploration): Root length (cm) plotted against number of days for Jar A (root tips intact) and Jar B (root tips removed on Day 3). Jar A shows continuous growth; Jar B shows growth arrest after Day 3.
The graph in Fig. 3.2 plots root length (cm) on the Y-axis against number of days on the X-axis, with two lines — one for Jar A and one for Jar B:
Jar A (solid line) — the root length increases steadily and continuously throughout the observation period. The line slopes upward from Day 1 to Day 7, showing that the intact apical meristem continues to divide and produce new cells, driving root elongation.
Jar B (dashed line) — root length increases normally until the tips are removed (around Day 3). After this point, the line becomes flat (horizontal) — root length no longer increases. This shows that without the root tip, cell division stops and growth is arrested.
Key Reading of the Graph
The divergence point in the graph — where the Jar A line continues upward and the Jar B line goes flat — is the most important feature. This is the point at which the root tips were removed from Jar B. The graph makes it visually clear that root growth depends entirely on the presence of the apical meristem at the root tip.
6. Conclusion
Q. What conclusion do you draw from Activity 3.1?
Conclusion
Root growth occurs exclusively at the root tip. The root tip contains a region of actively dividing cells called the apical meristem. When this region is present (Jar A), the root continues to elongate as new cells are produced by mitosis. When the root tip is removed (Jar B), the source of new cells is eliminated and growth stops permanently. This proves that:
(i) Meristematic tissue (specifically apical meristem) is the only region of a root that is capable of cell division.
(ii) The rest of the root is made of permanent tissue — cells that have differentiated and lost the ability to divide.
(iii) Growth in length in roots (and similarly in shoots) is entirely dependent on the activity of apical meristems.
7. Connection to Theory — Apical Meristem
Q. How does this activity connect to the theory of meristematic tissue?
Activity 3.1 provides direct experimental proof for one of the key concepts in meristematic tissue theory:
Apical meristems are found at the tips of roots and shoots. They are made of small, compactly arranged, thin-walled cells with a large nucleus and dense cytoplasm — all characteristics of actively dividing meristematic cells.
Apical meristems are responsible for primary growth — the increase in the length of roots and shoots. Every new cell added to the elongating root originates from a division in the apical meristem at the root tip.
This is why gardeners pinch off shoot tips to encourage bushier growth — removing the shoot apical meristem stops further elongation and stimulates the development of lateral (side) branches.
The contrast with permanent tissue is also clear from this activity: the cells above the root tip that have already differentiated into permanent tissue do not contribute to further elongation — only the meristematic region at the tip does.
8. Quick Revision — 4 Key Points
Activity 3.1 uses two onion bulbs in water — Jar A (tips intact) and Jar B (tips cut off) — to prove that root growth depends entirely on the presence of the root tip.
Observation: Jar A roots grow continuously; Jar B roots stop growing after the tips are removed around Day 3.
Fig. 3.2 graph: Jar A line slopes upward continuously; Jar B line goes flat after Day 3 — the divergence point is where the tips were removed.
Conclusion: The root tip contains the apical meristem — a zone of actively dividing meristematic cells (dividing by mitosis) responsible for all root growth in length. Without it, growth stops permanently.
