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SECOND TERM: E-LEARNING NOTES

SUBJECT: BIOLOGY

CLASS:   SS 1

WEEK 1

Revision of work done in first term

WEEK 2

TOPIC:  TISSUE AND SUPPORTING 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

  1. Parenchyma
  2. Collenchyma,
  • Sclerenchyma,
  1. Xylem
  2. PARENCHYMA
  • Tissues made up of living unspecialized plant cells that are roughly spherical in shape
  • They are composed of mainly cellulose and a large vacuole containing cell sap
  • It gives rigidity to plants as a result of tightly packed cells.
  • Other tissues are derived from parenchyma.
  • They possess thin wall and are found in the cortex of stems, leaf mesophylls, and flesh of fruits.
  1. COLLENCHYMA
  • Consist of living cells that are thickened at the corners.
  • Collenchyma cells are found beneath the epidermis in stems and petioles and around the veins in dicot leaves.
  • Usually, polygonal elongated cells with tapering ends
  • It enables flexibility and resilience
  • Does not support secondary growth in plant
  • SCLERENCHYMA
  • This is made up of cells impregnated with lignin that gives the plant hardness, rigidity and mechanical support.
  • They are made up of dead cells (fibres and sclereids/stone cells)
  • Fibres are made up of narrow polygonal elongated cells
  • It has thick secondary walls.
  1. XYLEM OR WOOD TISSUE
  • It is the tissue that conducts water and mineral from the soil to the plant and vessels.
  • Xylem is made up of (a) fibres (b) vessels (c) tracheids and (d) parenchyma.
  • Has strengthening function that undergo secondary growth.

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.

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