Biology · Plant Growth and Development · NEET
A meristem is a group of cells at certain locations in the plant that can keep dividing. NCERT says the cells of such meristems have the capacity to divide and self-perpetuate. This means some new cells stay as meristem to divide again, while the rest lose the ability to divide and become the plant body. Because the meristem stays active, plants can grow all through their life.
Growth at the cellular level is mainly an increase in the amount of protoplasm. Meristem cells divide by mitosis to add new cells. New cells first join the plant body, then enlarge and mature. So growth is a two-part story: the meristem makes new cells, and those cells then increase in size. One maize root apical meristem can make more than 17,500 new cells per hour.
Apical meristems are at the tips: the root apical meristem and the shoot apical meristem. They cause primary growth, meaning elongation along the axis (length). Lateral meristems (vascular cambium and cork cambium) appear later in dicots and gymnosperms and cause secondary growth, meaning increase in girth (thickness).
Self-perpetuate means the meristem keeps a copy of itself. When a meristematic cell divides, one daughter can stay as an active dividing cell (initial) and keeps the meristem going, while the other daughter is added to the plant body and later stops dividing. This is why the meristem is never used up and growth continues.
When new cells are always being added to the plant body by the activity of the meristem, this is called the open form of growth. It is the direct reason plant growth is indeterminate (unlimited). If the meristem stopped dividing, this open growth would stop.
Meristematic (dividing) cells are rich in protoplasm, have large conspicuous nuclei, and have thin, primary, cellulosic walls with abundant plasmodesmatal connections. Mature cells have large vacuoles, thicker walls, and have usually lost the capacity to divide. This is why the meristematic phase, not the mature region, is where cell division happens.
Which of the following statements is not correct?
Which one of the following is not a characteristic of plant cells in the phase of elongation?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Because only meristem cells can keep dividing to make new cells. Most mature plant cells lose the ability to divide, so without the meristem the plant could not add new cells and grow.
The apical meristems (root apical and shoot apical) cause primary growth, which is elongation along the axis, so they increase length.
Lateral meristems, that is vascular cambium and cork cambium, cause secondary growth, which increases the girth (thickness) of the plant in dicots and gymnosperms.
First, the meristem divides to form a new cell. Second, that cell enlarges and matures. So growth = cell division followed by cell enlargement.
NCERT states that one single maize root apical meristem can give rise to more than 17,500 new cells per hour, showing how fast cell division drives growth.
