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๐ฌ Think about it
If you trim the tip of a plant's shoot, does it keep getting taller? Where exactly does the growing happen — everywhere, or only at the tips? Let us test this with onion roots.
In this Activity, we will grow onion roots in two jars and cut the root tips in one jar, to see whether roots grow from their tips.
Materials needed
Two glass jars (or coupling jars), water, and two onion bulbs.
Procedure
1. Take two glass jars or coupling jars and fill them with water.
2. Take two onion bulbs and place one in each jar, as shown in Fig. 3.1.
3. Observe the growth of roots in both bulbs for a few days.
4. Measure the length of roots on days 1, 2 and 3.
5. On day 3, cut the root tips of the onion bulb in Jar B by about 1 cm. After this, observe the growth of roots in both jars, measure their lengths for four more days (day 4 onwards), and record your observations in Table 3.1.
2. Take two onion bulbs and place one in each jar, as shown in Fig. 3.1.
3. Observe the growth of roots in both bulbs for a few days.
4. Measure the length of roots on days 1, 2 and 3.
5. On day 3, cut the root tips of the onion bulb in Jar B by about 1 cm. After this, observe the growth of roots in both jars, measure their lengths for four more days (day 4 onwards), and record your observations in Table 3.1.
Table 3.1 — Experimental data
| Experimental Jars | Day 1 | Day 2 | Day 3 | Day 4 | Day 5 | Day 6 | Day 7 |
|---|---|---|---|---|---|---|---|
| A | 0.5 | 1.5 | 3.0 | 3.8 | 4.5 | 5.2 | 5.8 |
| B | 0.5 | 1.5 | 3.0 | 3.0 | 3.0 | 3.0 | 3.0 |
Observation
Roots in Jar A continue to grow in length. Roots in Jar B stop growing after the tips are cut.
Explanation
This shows that roots grow only from their tips. The tips have cells that divide continuously. You may recall observing mitosis in onion root tips in Chapter 2. So shoot tips and root tips both have actively dividing cells, called apical meristems, that help plants grow in length.
โ Summary
- Grow roots in two jars.
- Cut tips in Jar B.
- Jar A keeps growing.
- So tips do the growing.
What is the apical meristem?
- It is the growth tissue at the tips of roots and shoots.
- Its cells divide continuously.
- It helps the plant grow in length.
Important Points
- Roots and shoots grow from their tips.
- The apical meristem sits at the root and shoot tips.
- It makes the plant grow in length.
๐ฌ Meet a Scientist
- B. G. L. Swamy was a renowned Indian botanist.
- He is known for his work on plant morphology and anatomy.
- His Kannada book Hasuru Honnu blends science, satire and culture.
- It won the Kendra Sahitya Akademi Award in 1978.
โ Test Yourself
-
Where is the apical meristem found?
View Answer
At the tips of roots and shoots. -
What does the apical meristem do?
View Answer
It makes the plant grow in length. -
In Activity 3.1, why did Jar B stop growing?
View Answer
Its root tips, which contain the dividing cells, were cut off. -
What does Activity 3.1 prove about roots?
View Answer
Roots grow only from their tips.
Important Definitions
- Meristematic tissue — a tissue of actively dividing cells that makes a plant grow.
- Apical meristem — the meristem at root and shoot tips that increases length.
