1ST TERM

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TOPIC: TISSUE AND SURPPORTING SYSTEMS
CONTENT (a) Different types of supporting tissues (b) Functions of supporting tissues in plants.
Types of supporting tissues
Plants have various types of supporting tissues that make them up. Like animals, these tissues help them to stand some meters above the ground without falling. They have definite shape, strength, rigidity and to resists external force like wind and water.
Tissues that give support to plant are simple, having one type of cell. This includes, parenchyma, collenchymas, sclerenchyma, and complex tissue i.e. with two or more types of cells e.g., xylem, phloem, and epidermis.
PARENCHYMA
These are the first cells formed from the meristerm. Other tissues are derived from parenchyma. They possess thin wall and are found in the cortex of stems, leaf mesophylls, and flesh of fruits.

COLLENCHYMA
Collenchymas cells are found beneath the epidermis in stems and petioles and around the veins in dicot leaves. Collenchymas have flexible cell walls that allow elongation of plants. It gives rigidity, hardness, and support to the plant.
SCLERENCHYMA
This is made up of cells impregnated with lignin that gives the plant hardness, rigidity and mechanical support. It has thick secondary walls. Cells occurs in fibre cells and stone cells.
XYLEM OR WOOD
It is the tissue that conducts water and mineral from the soil to the plant and vessels. Xylem has other supporting tissues in form of fibres of fibre and wood parenchyma.
PHLEOM
This is the thin walled and lies externally in each vascular bundle. It has three types of cells; sieves, companion cells and phloem parenchyma.
CORTEX: It surrounds the vascular bundles. Cortex is a tissue of parenchyma cells.


Plant Tissues
Stems differ between gymnosperms (conifers and related plants) and angiosperms (flowering plants) and between the two divisions of angiosperms—monocotyledons and dicotyledons. Common to all of them, though, are basic tissue types: vascular tissue (xylem and phloem), which conducts water and nutrients to the cells of the plant; ground tissue, called pith at the center of the stem, which surrounds the vascular tissue; and dermal tissue, a protective layer.

EPIDERMIS
This is the outer most layers of cells of plants. It forms the protective skin of the stem, leaves, flowers and fruits. It is made up of single layer of cells. It secrets waxy substances known as cutin, that forms layer of cuticle which prevents excess water loss and mechanical damage to plants.



Nectarine Tree
The nectarine tree is a variety of peach tree that produces a smooth-skinned fruit called a nectarine. The color and seed of the fruit are very similar to that of the peach. Nectarine seeds have been known to grow trees that bear peaches and peach trees have been known to bear nectarines. Commercial farming of nectarines is extensive in California.

FUNCTION OF SUPPORTING TISSUES IN PLANT
1. It gives definite shape to the plant.
Epidermis, the outmost skin determines the structure of the plant and how it looks.
2. Strength: Collenchyma cells, sclerenchyma cells , xylem vessles and turgid parenchyma cells have been identified as tissues that strengthen the plants; walls are thickened to provide strength to plant.
3. Rigidity ;
Supporting tissues gives rigidity that plant needs to withstand blows from outside.
4. Resilience and Flexibility
By the help of supporting tissues, plant sway in the direction of the wind, breezes, and water without being moved.
EVALUATION
1. List four plant tissues and discuss any one of your choice.
2. Mention three cells of the phloem tissue
3. State three functions supporting tissues in plants.
GENERAL EVALUATION
1. One of these is not a plant tissue (a) Bark (b) Collenchyma (c) Parenchyma (d ) phloem (e) sclerenchyma.
2. The first cells formed from the meristem are called (a) Xylem (b) Cortex (c) Epidermis (d) Collenchyma (e) Parenchyma.
3. One of these forms the protective skin of the stem (a) Wood (b) Epidermis (c) Phloem (d) Cortex (e) Cambium layer.
ESSAY TEST
Write short note to explain the following:
a. Xylem or Wood.
b. Sclerenchyma.
c. Parenchyma.
d. Collenchyma.
WEEKEND ASSIGNMENT
1. Sketch an annotated diagram of the cross section of the stem.
2. Mention five other parts of plants apart from the supporting tissue.
PRE-READING ASSIGNMENT
Read MELROSE Biology for SS1, page71 and list all the supporting tissues of plants.
WEEKEND ACTIVITY
Cut a stem of a shrub, and identify all the parts as it is in e-note above.
REFERENCE TEXTS
MELROSE Biology for Senior Secondary School 1, by O. S. Obayori et-al.

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