Study Structural Organisation in Animals and Plants for MH-CET 2014
Structural Organisation in Animals and Plants
i. Types Of Tissues In Flowering Plants
Plant cells form the basis for plant tissues (i.e., meristematic, simple,
or complex), which in turn form the basis for various organs (e.g.,
leaves, roots, reproductive organs, etc.). Tissue patterns in roots and
stems vary among woody dicots, herbaceous dicots, and monocots.
ii. Meristematic Tissues
The meristematic tissue is formed exclusively by undifferentiated or
embryonic cells. These cells, known as meristematic cells, are
responsible for bringing about growth of the plant body due to their
capacity to undergo continuous mitotic divisions. Meristems are
classified by their location in the plant as apical (located at root and
shoot tips), lateral (in the vascular and cork cambia), and intercalary
(at internodes, or stem regions between the places at which leaves
attach, and leaf bases, especially of certain monocotyledons - e.g.
1. Apical meristems - Apical meristems are responsible for
primary growth. It gives rise to 3 types of primary or transitional
meristems - protoderm (becomes epidermis), ground
meristem(becomes cortex and pith, or ground tissue), and
procambium (becomes vascular tissue). Primary growth occur
at the tips of shoots and roots.
2. Lateral meristems ==> Vascular and cork cambium
is responsible for secondary growth. Secondary growth is not
common to all plants, predominates in woody species. In the
dicot plants, there is a process of growth that begins after a
known period of primary growth. Such a growth is known as
secondary growth. It is the result of the activity of secondary
meristem. It results in the formation of secondary permanent
tissues such as secondary xylem, secondary phloem and
secondary cortex. As a result, secondary growth brings about
an increase in the girth of the plant body.
i. vascular cambium, increases girth of stem, replaces dead
phloem and xylem.
ii. cork cambium – phellogen add cork and parenchyma
cells to replace the damaged epidermis
3. Intercalary nodes Another type of meristem active in certain
plants, especially grasses, is the intercalary meristem. These
cells possess the ability to divide and produce new cells, as do
apical and lateral meristems. They differ, however, in being
situated between regions of mature tissue, such as at the base
of grass leaves, which are themselves located on mature stem
iii. Simple Tissues
∙ Parenchyma - found in roots, stems and leaves,
undifferentiated thin-walled, large vacuoles, often contain
secreted material (starch, oils, tannins, crystals).
∙ Aerenchyma - parenchyma tissue with extensive intercellular
air spaces (e.g. water lilies and spongy mesophyll of leaves).
∙ Chlorenchyma - parenchyma with numerous chloroplasts
(common in leaves).
∙ Collenchyma - thick-walled but flexible and strong, usually
right below the epidermis of a leaf or stem, used for support in
stems and leaves of non-woody or young plants.
∙ Sclerenchyma - thick walls impregnated with lignin, usually
dead at maturity, function is support.
∙ Sclerids - stone cells in pear, hard part of seeds and
nutshells (cells are long as they are wide).
∙ Fibers - much longer in length than they are wide, fibers
are used in rope, textiles, canvas, paper money (common
sources are hemp, cotton, and flax).
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