Morphology of the Roots
Session 5: Morphology of the Roots
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 |25 minutes |Presentation |Characteristics of Plant |
| | | |Roots |
|3 |30 minutes |Presentation |Anatomy of Monocotyledonous |
| | | |Roots |
|4 |30 minutes |Presentation |Anatomy of Dicotyledonous |
| | | |Roots |
|5 |20 minutes |Presentation |Difference between Monocot |
| | |Small group |and Dicot Roots |
| | |Discussion | |
|6 |05 minutes |Presentation |Key Points |
|7 |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: Characteristics of Plant Roots (25 minutes)
the soil
minerals
o Tap roots
o Fibrous roots
o Adventitious roots
[pic]
o The following are the functions of the roots
which the plant is growing)
STEP 3: Anatomy of the Monocotyledonous Roots (30 minutes)
o Epiblema or rhizodermis
o Cortex and
o Stele
Fig 5.1: Internal Structure of the Monocotyledonous Root
[pic]
o Outermost layer of the root
o Single row of parenchyma cells, no intercellular space
o Stomata and cuticle are absent
o Root hairs are always unicellular
o The key function of rhizodermis is protection of the inner
tissues of the root
o The cortex is made of only one type of tissue (parenchyma)
o Has many layers of parenchyma cells with lot of intercellular spaces
o Cortical cells are generally oval or rounded in shape; chloroplasts are
absent
o The cells are living and possess leucoplasts
o The inner most layer of the cortex is endodermis and is composed of
single layer of barrel shaped parenchymatous cells
o The function of cortical cells is storage
o Endodermis (innermost layer of cortex) forms a complete ring around the
stele (tissues inside endodermis)
o There is a band-like structure made of (thickened with) suberin present
in the radial and transverse walls of the endodermal cells
o The band is called Casparian strips
o The endodermal cells opposite to the protoxylem elements, are thin-
walled without Casparian strips
o These cells are called passage cells and their function is to transport
water and dissolved salts from the cortex to the xylem
o Water cannot pass through other endodermal cells due to Casparian
strips (blocking effect)
o The main function of Casparian strips in the endodermal cells is to
prevent the re-entry of water into the cortex once water enters the
xylem tissue
o Vascular tissues are in radial arrangement with many protoxylem
groups
o This arrangement of xylem is called polyarch and the xylem is in
exarch condition
o The tissue present between the xylem and the phloem, is called
conjunctive tissue
o The central portion
o It consists of thin walled parenchyma cells with intercellular
spaces
o These cells are filled with abundant starch grains
STEP 4: Anatomy of the Dicotyledonous Roots (30 minutes)
o Structure of a Dicotyledonous Root
[pic]
o Outermost layer aka rhizodermis (epidermis in stems) made of a single
layer of parenchyma cells which are arranged compactly without
intercellular spaces, with no stomata or cuticle
o Root hair is always single celled
o Protects inner tissues of the root
o Consists of only parenchyma cells loosely arranged with intercellular
spaces to make gaseous exchange easier
o These cells may store food reserves
o The cells are oval or rounded in shape
o Sometimes are polygonal due to mutual pressure
o Cortical cells are devoid of chloroplasts but starch grains are stored
in them
o The cortical cells also possess leucoplasts
o Inner most layer of the cortex is endodermis
o Endodermis is made up of single layer of barrel shaped parenchymatous
cells
o Stele is completely surrounded by the endodermis
o The radial and the inner tangential walls of endodermal cells are
thickened with suberin
o Casparian strips
o Casparian strips are absent in the endodermal cells located opposite to
the protoxylem elements
o These thin-walled cells without Casparian strips are called passage
cells through which water and mineral salts are conducted from the
cortex to the xylem elements
o Water cannot pass through other endodermal cells due to the presence of
Casparian thickenings
o Include all the tissues present inside endodermis
o The stele includes pericycle and vascular tissues
inner to the endodermis
the xylem is in exarch condition
tetrarch
phloem parenchyma
roots they are circular
STEP 5: Difference between Monocot and Dicot Roots (20 minutes)
|Activity: Small Group Discussion (15 minutes) |
| |
|DIVIDE students into small manageable groups |
| |
|ASK students to discuss on the following question |
|What are the differences between monocot root and dicot root? |
| |
|ALLOW students to discuss for 15 minutes |
| |
|ALLOW few groups to present and the rest to add points not |
|mentioned |
| |
|CLARIFY and SUMMARIZE by using the contents below |
[pic]
STEP 6: Key Points (10 minutes)
of the soil
adventitious roots
tissues namely the epidermis, the cortex, the endodermis, the pericyle
and the vascular system
STEP 7: 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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