Meristematic Tissues Meristems are places in plants where cell division is
occurring.
During cell division, one cell becomes two cells. Each new cell can also divide.
Meristematic Tissues In this class we will discuss three kinds of meristems:
Apical Meristems
Intercalary Meristems
Lateral Meristems
Apical Meristems In plants belonging to
the DICOT class, apical meristems are located in BOTH the shoot tips and root tips. A shoot is simply a young, leaf-bearing stem.
In plants belonging to the MONOCOT class, apical meristems are located ONLY in the root tips.
Microscopic View of an Apical Meristem
Apical Meristems•Primary growth of shoots and roots occurs as the cells of the apical meristem divide and elongate.
Intercalary Meristems In addition to the apical meristems located in their
root tips, plants in the MONOCOT class have special meristems called intercalary meristems.
Intercalary meristems are located on monocots where the leaf bases connect to the stem of the plant.
Intercalary Meristems
Monocots, like grasses, have intercalary meristems which allow the leaves to grow back after mowing.
Lateral Meristems In addition to the
apical meristemslocated in the shoot and root tips, plants in the DICOT class have lateral meristems.
Lateral meristemscause SECONDARY GROWTH.
Secondary growth causes stems and roots to grow larger in diameter.
Lateral Meristems cause an increase in stem diameter
Lateral Meristems
Think of a lateral meristem as being a cylinder, several cell layers thick, of actively dividing cells.
Permanent TissuesPermanent tissues are of two types;
Simple permanent tissue
Complex permanent tissue
Simple permanent tissue Parenchyma
store food and water
Collenchyma provide support for plant organs
Sclerenchyma supporting function
secondary walls impregnated with lignin fibers and sclerids
may be nonliving at maturity
Parenchyma - are the general purpose ceIIs of plants - cells are
rounded in shape & have uniformly thin walls
found in all parts of the plants.
- living at maturity, have large vacuoles
- location Ieaf, stem (pith), roots, fruits
collenchyma cells are elongated (up to 2mm long) with unevenly
thickened walls ( thin on the sides but thick at the angles where 2 or more cells meet)
differentiate from parenchyma cells & are alive at maturity
sclerenchyma - sclerenchyma cells which are non-living and lack
protoplasts at maturityTypes:1. scIereids or stone cells2. fibers
Complex Permanent Tissues
Vascular Tissues- specialized for long-distance transport of water
and dissolved substances.
- contain transfer ceIIs, fibers in addition to parenchyma and conducting ceIIs
- location, the veins in Ieaves
types
1. Xylem
2. phloem
Xylem Xylem tissue conducts
water and dissolved mineral nutrients.
It is composed of columns of vessel cells (tracheids in gymnosperms), stacked one upon another, and fibers.
Vessel cell walls are pitted and allow water passage between the xylem and surrounding tissues. Mature xylem cells are dead.
Xylem Phloem
Xylary elements – the conducting cells in xylem
- 2 kinds of xylary elements:
tracheids – the only water conducting cells in most woody, non flowering plants.
vessel elements – occur in several groups of plants, including angiosperm.
- both are elongated, dead at maturity, lignified secondary cell walls
Phloem Phloem tissue conducts the
food produced by the leaves in a downwards direction to stems and roots (from source to sink).
Phloem is composed of sieve tubes, companion cells, and fibers.
The end walls of the sieve tubes are called sieve plates.
Xylem Phloem
Sieve tube elements – main conducting ceIIsof phloem
- elongated and non-nucleated
- uniformly thin walled with the end walls
perforated to from the sieve plate.
- sieve tube element are attached end to end to form the sieve tube.
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