Plant Tissues
Session 3: Plant Tissues
Total Session Time: 120 minutes
Prerequisites
Learning Tasks
By the end of this session students are expected to be able to:
Resources Needed:
SESSION OVERVIEW
|Step |Time |Activity/ |Content |
| | |Method | |
|1 |05 minutes |Presentation |Introduction, Learning Tasks |
|2 |30 minutes |Presentation |Plant Tissues and their |
| | |Brainstorming |Classification |
|3 |75 minutes |Presentation |Properties of the Plant Tissues |
|4 |05 minutes |Presentation |Key Points |
|5 |05 minutes |Presentation |Evaluation |
SESSION CONTENTS
STEP 1: Presentation of Session Title and Learning Tasks (5 minutes)
READ or ASK students to read the learning objectives and clarify
ASK students if they have any questions before continuing.
STEP 2: Plant Tissues and Their Classification (30 minutes)
|Activity: Brainstorming (5 minutes) |
| |
|Ask students to brainstorm on the following question: |
| |
|Define a plant tissue |
| |
|ALLOW few students to respond? |
| |
|WRITE their responses on the flip chart/ board |
| |
|CLARIFY and SUMMARISE by using the content below |
origin, form and function or as a group of dissimilar cells that perform
a common function. E.g. phloem elements conduct food
cell performs all the vital functions of life. It grows, prepares food,
undergoes metabolism, reproduces and completes its span of life
functions. Due such division of labour, the cells of the plant are
differentiated to form different tissues. The different tissues perform
different functions
o Meristematic tissue and
o Permanent tissue
Scheme below Shows Classification of Plant Tissues
Plant Tissue
Meristematic Permanent
(Mature cells incapable of division) (Cells are capable
of division)
Simple Complex
(Single type of cells) (More than
one type of cells)
Parenchyma Collenchyma Sclerenchyma Xylem
Phloem
Xylem vessel Sieve
tube
Tracheids Companion
Cells
cells that are in a continuous state of division
o Some cells produced by meristematic tissue stop dividing and acquire
certain changes (differentiation) to become permanent tissues of the
plant
types:
o Apical meristem
o Intercalary meristem
o Found in the nodal region, prominently in monocotyledons, e.g.
grasses.
o It is derived from the apical meristem
o Elongates the internodes
o Lateral meristem
o Found along the longitudinal axis of stem and root
o E.g. Vascular cambium and cork cambium (phellogen)
o Produces secondary permanent tissues
o Increase thickness of stem and root
o Are tissues that have temporarily or permanently lost the power to
divide
o The cells formed by the apical meristem are differentiated into
different types of permanent tissues
into two types: –
o Simple tissue
function
o Complex tissue
function together as a single unit
o Xylem is made up of four kinds of cells
o Phloem is composed of four types of cells:
angiosperms
STEP 3: Properties of Plant Tissues (75 minutes)
o May be round, oval, polygonal or rectangular in shape
o Are closely arranged without intercellular spaces
o Have dense cytoplasm with large nuclei.
o Have smaller vacuoles, scattered throughout the cytoplasm.
o Their cell walls are thin, elastic and made up of cellulose
o Generally present in all plant organs
o Form the ground tissue in a plant
o Is living tissue made of thin walled cells
o Is the precursor of all the other tissues
o The cell wall is made up of cellulose
o Parenchyma cells may be oval, spherical, rectangular, cylindrical or
stellate
o Parenchyma is of different types
o In green parts of the plants, the parenchymatous cells have
chloroplasts; they are called chlorenchyma. Its important function is
photosynthesis
o Is a living tissues generally occurring in the dicot stems in two or
more layers below the epidermis, these layers form the hypodermis
o It also occurs in petiole and pedicel
o The cell wall is unevenly thickened, thickening is confined to the
corners of the cells
o Collenchyma strengthen young organs
o Is a dead tissue; lacks protoplasts
o The cells are very thick i.e. have lignified secondary walls (woody)
o Sclereids
thickness
o Fibers
ends, with simple pits
protect from strong winds
E.g. cotton.
o Is a complex tissue mainly responsible for conduction of water and
mineral salts from roots to other parts of the plant
o Primary xylem is formed from procambium,
o Secondary xylem: from vascular cambium
o Tracheids
above the other and their roles are to conduct water and mineral
salts in in gymnosperms and pteridophytes and also to provide
mechanical support to these plants
o Vessels or Tracheae
vessels
perforation plate
angiosperms
mechanical support to the plant
[pic]
o The fibres of sclerenchyma associated with the xylem are known as xylem
fibres
o Give additional mechanical support to the plant body.
o Present both in primary and secondary xylem
o Xylem fibres are dead lignified cells
o The parenchyma cells associated with the xylem are known as xylem
parenchyma
o Is the only living tissue in the xylem
o Their functions are to store food reserves in the form of starch and
fat and assist in conduction of water
o Conducts food materials to various parts of the plant
o Primary phloem: formed from pro-cambium of apical meristem
o Secondary phloem: vascular cambium
o Sieve elements are the conducting elements of the phloem
o Their end walls are transverse or oblique
o End wall contains pores and look like a sieve, hence sieve plate
o Sieve elements are arranged one above the other and form vertical sieve
tubes
o In matured sieve tube, nucleus is absent
o Are thin-walled, elongated, specialized parenchyma cells, associated
with the sieve elements
o Have cytoplasm and a prominent nucleus.
o Present only in angiosperms and absent in gymnosperms and pteridophytes
o Assist sieve tubes in conduction of food materials
o Phloem Parenchyma
o Parenchyma cells associated with phloem
o Are living cells and store starch and fats
o Also contain resins and tannins in some plants
o Present in all pteridophytes, gymnosperms and dicots
o Usually absent in monocots
o Phloem fibres
o The fibers of sclerenchyma associated with phloem are called phloem
fibers or bast fibers
o They are narrow, vertically elongated cells with very thick walls and a
small lumen (the cell cavity)
o Are the only dead tissue in the phloem
o Strengthening and supporting cells
STEP 5: Key Points (5 minutes)
function
a common function. E.g. phloem elements conduct food
STEP 6: Evaluation (5 minutes)
References
Trease, G. E., Evans, W. C., & Evans, D. (2009). Trease and Evans
pharmacognosy. London: Saunders.
Joanne Barnes et al (2002), Herbal medicines 3rd Edition: Pharmaceutical
Press
Wallis, T. E. (2005). Textbook of pharmacognosy. New Delhi: CBS.
Robbers, J. E., Speedie, M. K., Tyler, V. E., & Tyler, V. E. (1996).
Pharmacognosy and pharmacobiotechnology. Baltimore: Williams &
Wilkins.
Heinrich, M., Kinghorn, A. D., Maizels, D., Gibbons, S., & Phillipson, J.
Churchill Livingstone/Elsevier.
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