Tissues in Action · Lesson 2 of 11
Tissues for Growth in Plants
“Plants keep tiny construction crews exactly where the growing gets serious.”
• Identify the three forms of growth seen in plants. • Locate apical, lateral and intercalary meristems. • Interpret the onion-root investigation and its graph. • Relate meristematic-cell structure to continuous division. • Explain how differentiation produces permanent tissues.
A lawn grows again after it is cut, a root pushes deeper into soil, and a young stem becomes a thick tree trunk. These changes look different, but each begins with cells that continue to divide. Plants keep such cells in particular growth regions instead of distributing them equally throughout the body.
Meristematic Tissue
Meristematic tissue is a special type of plant tissue made up of cells that divide continuously. These cells keep producing new cells, which allows the plant to grow throughout its life.
Unlike many mature plant cells, meristematic cells do not become permanently specialised very early. Instead, they remain active and continue to divide whenever the plant needs new growth. The new cells produced by them may later increase in size, change their shape, and develop into different kinds of permanent tissues.
Meristematic tissue is found mainly in regions where growth takes place. For example, it is present near the tips of roots and shoots, where it helps the plant increase in length. It is also present in certain regions along stems and roots, where it helps them increase in thickness.
The cells of meristematic tissue are usually small and closely packed together. They have thin cell walls, dense cytoplasm, and a prominent nucleus. Vacuoles are either very small or absent because these cells are mainly focused on active cell division rather than storage.
In simple terms, meristematic tissue acts like the plant's growth-producing tissue. It continuously forms new cells, and these new cells later become part of roots, stems, leaves, flowers, and other plant structures.
Meristematic tissue consists of actively dividing cells that add new cells to the plant body.
Apical Meristem - How Do Plants Grow in Length?
Apical meristems occur at the growing tips of roots and shoots. Their cells divide repeatedly. Some new cells remain in the meristem, while others enlarge and become specialised. The continued addition of cells makes a root extend deeper into soil and a shoot rise higher or form new leaves.
Activity: Let us Design Experiments
Two onion bulbs are placed over water in separate jars. Their root lengths are measured for three days. After the third measurement, about one centimetre is cut from the root tips in one jar, while the roots in the other jar remain untouched. Measurements continue under the same conditions.
Problem
What conclusion is supported if both sets of roots grow for three days, but only the uncut roots continue growing afterwards?
- 1.Before cutting, both sets have intact root tips and increase in length.
- 2.The treatment changes only one important condition: the presence of the root tips.
- 3.After removal of the tips, growth in that jar stops while the control roots continue.
- 4.The observation supports the conclusion that the main growth region lies at the root tip.
- 5.It does not show that every cell in the entire root divides equally.
Lateral Meristem - How Do Plants Grow in Girth?
A stem becomes thicker because a lateral meristem forms a ring of dividing cells around it. The cells produce new tissue towards the inside and outside in a concentric pattern. Repeated activity increases the diameter or girth of the stem.
On a cut tree trunk, this growth can appear as annual rings. A wider ring indicates more favourable growth during that period, whereas a narrower ring suggests less favourable conditions. Counting rings can help estimate age, while differences in ring width provide clues about the conditions under which the tree grew.
Intercalary Meristem - How Do Plants Grow After Being Cut?
A node is a point on a stem from which a leaf or branch arises. The part between two nodes is an internode. Intercalary meristems occur at the base of an internode or just above a node. Because these cells remain capable of division, grass can grow again after grazing or mowing, and new branches can arise from nodes when a young stem tip is cut.
| Meristem | Location | Growth produced | Familiar observation |
|---|---|---|---|
| Apical | Root and shoot tips | Increase in length | Roots extend into soil. |
| Lateral | A ring along the stem circumference | Increase in girth | A trunk becomes thicker. |
| Intercalary | Base of an internode or just above a node | Regrowth and extension from nodes | Grass regrows after mowing. |
Meristematic cells are small and tightly packed, with thin cell walls and little or no intercellular space. They contain dense cytoplasm, many organelles and a large, prominent nucleus. Vacuoles are generally absent because these cells are actively dividing rather than mainly storing materials. These features keep the living contents concentrated and support repeated cell division.
Differentiation is the process by which cells formed by a meristem change in structure and function and become specialised permanent tissues.
Every new cell does not remain meristematic. Some retain the ability to divide, maintaining the growth region. Others lose that ability and specialise for support, storage, protection or transport. Plant growth therefore depends on both processes: division supplies new cells, and differentiation prepares those cells for particular jobs.
Quiz
Which description best matches Meristematic Tissue?
Which description best matches Differentiation?
Which term matches this description: Meristematic tissue consists of actively dividing cells that add new cells to the plant body.
Which term matches this description: Differentiation is the process by which cells formed by a meristem change in structure and function and become specialised permanent tissues.
Which statement is a key takeaway from this lesson?
Practice Problems
- Predict what will happen to an onion root if its tip is removed, and justify the prediction.
- Name the meristem responsible for an increase in stem diameter.
- Explain why grass can regrow even after its upper portion is removed.
- Compare a node with an internode.
- Why are large storage vacuoles generally absent from meristematic cells?
- Describe the connection between mitosis, meristematic tissue and plant growth.
Key Takeaways
• Apical meristems increase length. • Lateral meristems increase girth. • Intercalary meristems support regrowth from nodes or internode bases. • Meristematic cells are adapted for rapid division. • Differentiation converts some newly formed cells into specialised permanent tissues.