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π¬ Think about it
If you trim the tip of a plant's shoot, does it keep getting taller?
Where exactly does the growing happen β everywhere, or only at the tips?
Let's see.
How do plants increase in length?
![3.2.1 Apical meristem β How do p - Tissues in Action - [Teachoo] - Concepts](https://cdn.teachoo.com/13071ba2-7f42-4c1e-a584-53170a3a5167/3.2.1-apical-meristem-how-do-plants-grow-in-length-image-11.webp)
Apical Meristem
at shoot
Apical Meristem
at root
- Plants increase in length from two places β the apex of the stem (the shoot tip) and the end of the roots (the root tip).
- At these places, we have apical meristem tissues .
What are apical meristem tissues?
Apical Meristem
Apical
at the apex β the tipsΒ
of shoots and the end of roots
Meristem
tissue whose cells
divide continuously
β
The meristem present at root and shoot tips whose cells divide continuously so the plant grows in length.
Shoot tip β
apical meristem
Small, dividing
cells
Growth in length
Root tip β
apical meristem
Small, dividing
cells
= Growth in length
- The apical meristem is the growth tissue at the tips of roots and shoots .
- Its cells divide continuously .
- It makes the plant grow in length .
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.
Onion bulb
Water in the jar
White roots
growing into water
Jar A and Jar B
(identical at start)
Jar B
Jar A
Observation
Roots in Jar A continue to grow in length. Roots in Jar B stop growing after the tips are cut.
Graph
Table 3.1 β Experimental data
Sample readings are shown below β record your own measurements in your notebook.
| 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 | 2.0 | 2.0 | 2.0 | 2.0 |
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.
Jar A - roots
keep growing
Jar B roots
stop growing
Jar B-
root tips cut
(about 1 cm)
Growth happens
at the tips
β Summary
In this activity, we learnt that:
- Roots were grown in two jars, and the tips were cut in Jar B.
- Jar A kept growing in length, while the cut roots in Jar B slowed down.
- So a plant grows in length only at its tips.
What are the different growth zones of a plant, and what are they called?
Growth Zones of a Plant
Growth zones
β
Tips of the shoots
apical meristem
Tips of the
roots
apical meristem
β
They help the plant grow in length.
- Plants have growth zones at the tips of their roots and shoots .
- These zones are called the apical meristems .
- They help 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.
β 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
- Apical meristem β the meristem at the root tips and shoot tips that increases the length of the plant.
- Growth zone β a region of a plant where cells actively divide; in a plant these are the apical meristems at the root and shoot tips.
