LESSON NOTE

SUBJECT: BIOLOGY

TOPIC: TISSUE AND SURPPORTING SYSTEMS IN PLANTS.


LESSON OBJECTIVES: By the end of the lesson, the learners should be able to:

1. Different types of supporting tissues

2. 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:
Parenchyma
Collenchyma,
Sclerenchyma,
Xylem,

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.

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 enable 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.

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.

Picture of a woody stem, dicot and monocot stem.

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/TEST
1. List four plant tissues and discuss any one of your choice.
2. Mention three cells of the xylem tissue
State three functions supporting tissues in plants.
3. One of these is not a plant tissue (a) Bark (b) Collenchyma (c) Parenchyma (d ) phloem (e) sclerenchyma.
4. The first cells formed from the meristem are called (a) Xylem (b) Cortex (c) Epidermis (d) Collenchyma (e) Parenchyma.
5. One of these forms the protective skin of the stem (a) Wood (b) Epidermis (c) Phloem (d) Cortex (e) Cambium layer.

6. Write short note to explain the following:
Phloem
Epidermis.
Endodermis
pith
Piliferous layer.
Cortex.
Cambium
Mechanism of support.


ASSIGNMENT
Sketch an annotated diagram of the cross section of the stem.


SUGGESTED PRACTICAL
Cut a stem of a shrub, and identify all the parts with the aid of a microscope.