grade 11 first term SUPPORTING TISSUES IN PLANTS.pdf

supportinf tissue in plants s

1. Date: 11th Nov; 2024
Topic: SUPPORTING TISSUES IN
PLANTS

2. LEARNING OBJECTIVES: Learners
should be able to:

1.Name and describe plant supporting tissues under the
sub-heading; location, structure and function.
2.Determine the need for support and movement in
organisms, identify supporting tissues in plants
(collenchyma, sclerenchyma, xylem and phloemfibres).
3.Describe the distribution of supporting tissues in roots,
stems and leaf.

3. There are several types of plant tissues that confer rigidity, flexibility
and resilience.
TYPES OF PLANT SUPPORTING TISSUE
Turgid parenchyma (unspecialized plant cells).
Collenchyma
Sclerenchyma
Xylem

4. PARENCHYMA: Parenchyma cells are living plant cells with thin
cellulose cell walls. They have large vacuole filled with cell sap.
Parenchyma is found in roots, leaves and stem.
When parenchyma cells are filled with water, they become turgid and
tightly packed. This provides support and maintains the shape and firmness
of plant organs that are rich in parenchyma cell e.g herbaceous plant

5. COLLENCHYMA: Collenchyma cells are also living cells. Unlike
parenchyma cells, parts of their cell walls, mainly the corners, are thickened
with cellulose. The collenchyma cells are flexible and thus allow the
bending and twisting of plants without breaking. The flexibility also allows
for cell growth and elongation of the immature parts of the plant body

6. SCLERENCHYMA : Sclerenchyma tissue is made up of mostly dead cells
with cell walls that are filled with cellulose and lignin. This confers strength
and resilience to the plants. Their thick and rigid cell walls are able to
prevent the cells form expanding if too much water is taken in. They are
mostly found in the mature parts of plants. There are two kinds of
sclerenchyma cells, fibres and sclereids. Sclerenchyma fibres are narrow,
polygonal, elongated cells with tapering end walls. Sclereids or stone cells
are heavily lignified cells which are roughly spherical and slightly
elongated.

8. XYLEM: This is found mainly in the vascular tissues of
stems, roots and leaves. Xylem is the water conducting
tissue and has a strengthening function. Four types of cells
make up the xylem tissue: the tracheids, vessels, fibres and
parenchyma. The first three are lignified and so provide
mechanical support.

9. STRUCTURES OF PLANTS

The entire plant body be it internal or external parts provide the
necessary support for plant.
Epidermis: This is the outer covering of leaves and stems. It prevents
the evaporation of water from the leaves.
Cortex: This is found between the epidermis and vascular bundles of
a dicotyledonous plant.
Vascular bundles: This is found in the inner part of the stem.
It consists of xylem, phloem and cambium.

10. STRUCTURES OF PLANTS

Xylem: This is responsible for conducting water and mineral salts from the soil to the
leaves.
Phloem: This is responsible for the conduction of manufactured food. Phloem tissues
are made up of four cells; sieve tubes, phloem parenchyma, companion cells and
phloem fibres. Sieve tubes conduct mainly food, phloem parenchyma provides
strength and support to the plant, phloem fibres are concerned with the strengthening
of the organs which they are found, companion cells assist in the conduction of food
substances.

11. STRUCTURES OF PLANTS

Cambium: Cambium found between the phloem and xylem are constantly
dividing cells, which increases the size of the cells. This increase in size is called
secondary thickening and it is responsible for the increase in size of trunks of
many trees.
Pith: This is the central part of the stem. It is large and made of parenchyma and
extends between the vascular tissue.
Piliferous layer: This is the outer covering of the root.

15. FUNCTIONS OF SUPPORTING TISSUES IN
PLANTS

1.It gives strength to the plant
2.It provides the plant with rigid shape
3.It gives protection to the plant
4.It makes the plant flexible
5.Some supporting tissues especially xylem and phloem tissues are
known to conduct water and manufactured food respectively.

16. HOW SUPPORT IS PROVIDED FOR
HERBACEOUS AND WOODY PLANTS

Herbaceous plant
1. By turgidity, water is preserved
2. Thickening of walls of collenchyma cell (at the corners)
3. Due to the presence of water, vacuoles inside parenchyma
cells/living Cells

17. HOW SUPPORT IS PROVIDED FOR
HERBACEOUS AND WOODY PLANTS
Woody plant
1. Sclerenchyma in the cortex
2. The xylem strengthened by deposits of lignin in their walls.
3. Secondary growth/thickening provides extensive wood/secondary
xylem and bark.

18. REVISION QUESTIONS

1. Make a drawing, 10-12 cm long of a transverse section of a dicotyledonous
stem. (WASSCE JUNE, PRACTICAL, 2013)
2. State one function each of the following structures found in plants i)
epidermis ii) phloem iii) sclerenchyma (WASSCE June, 2014)
3. How is support provided for, in each of the following? i) herbaceous plants
ii) woody plants. (WASSCE June, 2005).
4. Mention one function each of the following structures in plants: i. phloem ii.
Leaf iii. Xylem iv. Flower (SSCE JULY, NECO 2021)