Meristems in Plants: Types, Differentiation, Dedifferentiation & NEET Questions
Meristems are regions of actively dividing plant cells responsible for plant growth. They contain cells that are capable of repeated cell division and subsequently differentiate into permanent tissues.
This article covers important NCERT-based concepts of meristems, including primary and secondary meristems, apical and lateral meristems, differentiation, dedifferentiation and important NEET questions.
1. What is a Meristem?
A meristem is a group of actively dividing, undifferentiated plant cells that continuously produce new cells and contribute to plant growth.
Meristematic cells generally have:
- Dense cytoplasm
- Prominent nucleus
- Thin primary cell walls
- Little or no intercellular space
- Ability to undergo repeated cell division
2. Classification of Meristems Based on Position
Apical Meristem
Apical meristems are present at the tips of roots and shoots. They are mainly responsible for primary growth, which results in an increase in the length of the plant.
Intercalary Meristem
Intercalary meristems occur between mature tissues, commonly at the bases of internodes or leaves in grasses and other monocots.
They contribute to the elongation and regeneration of plant parts.
Lateral Meristem
Lateral meristems are located along the sides of stems and roots and are responsible for secondary growth, resulting in an increase in girth.
Examples include:
- Vascular cambium
- Cork cambium (phellogen)
3. Primary and Secondary Meristems
Primary Meristem
Primary meristems originate from the apical meristems and contribute mainly to the primary growth of plants.
Examples include meristematic regions that give rise to primary tissues such as:
- Primary xylem
- Primary phloem
- Dermal tissues
- Ground tissues
Secondary Meristem
Secondary meristems arise later in the life of a plant and are generally associated with secondary growth.
Examples include:
- Vascular cambium
- Cork cambium or phellogen
4. Differentiation of Meristematic Cells
Differentiation is the process by which cells derived from meristematic tissue become structurally and functionally specialised.
For example, meristematic cells can differentiate into specialised permanent tissues such as:
- Xylem
- Phloem
- Parenchyma
- Collenchyma
- Sclerenchyma
Thus, differentiation results in the development of cells with specific structures and functions.
5. Dedifferentiation
Dedifferentiation is the process by which living mature or differentiated plant cells regain the capacity to divide.
Examples include:
- Formation of interfascicular cambium from mature parenchymatous cells.
- Formation of cork cambium from certain mature tissues.
Therefore, a differentiated cell can sometimes regain meristematic activity under suitable conditions.
6. Redifferentiation
Redifferentiation is the process by which cells produced by a secondary meristem again become specialised permanent cells.
The sequence can therefore be remembered as:
Meristematic cell → Differentiation → Permanent tissue
and in some cases:
Permanent cell → Dedifferentiation → Secondary meristem → Redifferentiation → Permanent tissue
7. Vascular Cambium and Secondary Growth
The vascular cambium is a lateral meristem involved in the formation of secondary vascular tissues.
- It produces secondary xylem towards the inner side.
- It produces secondary phloem towards the outer side.
Therefore, secondary xylem and secondary phloem in a dicot stem are produced by the vascular cambium.
8. Interfascicular Cambium
In a young dicot stem, vascular bundles are arranged in a ring. The cambium present within the vascular bundles is called intrafascicular cambium.
The parenchymatous cells between vascular bundles can become meristematic and form interfascicular cambium by dedifferentiation.
The intrafascicular and interfascicular cambia together form a continuous cambium ring.
9. Important NEET Questions
Question 1
Secondary xylem and phloem in a dicot stem are produced by:
- Apical meristem
- Vascular cambium
- Axillary meristem
- Phellogen
Answer: 2. Vascular cambium
Question 2
Which one of the following is NOT a meristem?
- Intercalary meristem
- Intrafascicular cambium
- Interfascicular cambium
- Phelloderm
Answer: Phelloderm
10. Quick NEET Revision Table
| Term | Key Point |
|---|---|
| Apical meristem | Present at root and shoot tips; primary growth |
| Intercalary meristem | Present between mature tissues; common in grasses |
| Lateral meristem | Increases girth; secondary growth |
| Vascular cambium | Produces secondary xylem and secondary phloem |
| Phellogen | Cork cambium; produces periderm |
| Differentiation | Meristematic cells become specialised permanent cells |
| Dedifferentiation | Mature cells regain the ability to divide |
| Redifferentiation | Cells produced by meristem become specialised again |
| Intrafascicular cambium | Cambium present within vascular bundles |
| Interfascicular cambium | Develops between vascular bundles |
11. One-Minute Memory Trick
Apical = Length
Lateral = Girth
Vascular cambium = Secondary xylem + Secondary phloem
Phellogen = Cork cambium
Dedifferentiation = Mature cell becomes dividing again
Redifferentiation = Dividing cells become specialised again
Conclusion
Understanding meristems, differentiation, dedifferentiation, redifferentiation and cambium is essential for NEET Biology and NCERT Class 11 Plant Anatomy. These concepts explain how plants increase in length and girth and how mature plant cells can regain meristematic activity.
Related Topics: Anatomy of Flowering Plants, Plant Tissues, Secondary Growth, Vascular Cambium, Cork Cambium, Xylem and Phloem.