T.S. of monocot root, Practice Problems and FAQs

Do you know what the tallest monocot in the world is? It is the Ceroxylon quindiuense (Quindío wax palm). Since it is the tallest, it might need a highly supportive root to anchor it to the soil, right? 

                                      Fig: Quindío wax palm

The tap root system has a structure that can support giant dicot trees. But when it comes to monocots, they have a fibrous root system. Are fibrous root systems capable of supporting tall monocot trees? Yes, they are. Although fibrous roots are not as thick and do not penetrate as deep as the primary root of a tap root system, they form an extensively branched network in the soil to support the tall monocot plants.

So now we know that morphologically, tap roots differ a lot from the fibrous roots found in monocots. Do they differ with respect to their anatomies too? In this article, we will discuss the anatomy of a monocot root to get an answer to this question.

Table of contents:

• Monocotyledonous root
• Epidermal tissue system
• Ground tissue system
• Vascular tissue system
• Stele
• Diagram representing T.S of monocot root
• Comparison between Dicot and Monocot roots
• Practice Problems
• FAQs 

Monocotyledonous roots

The plants in which the seeds contain one seed leaf or cotyledon are called monocotyledonous plants. They mainly include the plants belonging to the grass family. The anatomy of monocot plants differs from dicot plants. Monocots have a fibrous root system. It consists of several roots of similar size and length developed from the base of the stem of the plant. 

                     Fig: Fibrous root system

There is no distinction between the internal structure of young and old monocot roots as the secondary growth is absent. The transverse section of a monocot root shows different layers of tissues belonging to three different tissue systems - epidermal tissue system, ground tissue system and vascular tissue system.

                                Fig: Cross section of monocot root

Epidermal tissue system

The outermost layer or covering of the plant body is formed of the epidermal tissue system. It is derived from the protoderm. The major function of the epidermal layers is the protection of roots. Epidermal tissue system in monocot roots consists of epiblema and root hairs.

Epiblema, also known as the piliferous layer, is made up of a single layer of compact, tubular parenchymatous cells with no intercellular spaces. It lacks cuticle and stomata on the outer surface. Root hairs are the unicellular projections from the epiblema. They aid in water and mineral absorption. Root hairs are absent in the older parts. 

Ground tissue system

All tissues, except the epidermis and vascular bundles, are part of the ground tissue system. The ground tissues are large and parenchymatous. This system is responsible for the transport of water and salts from the root hairs to the centre of the roots. Different layers of the ground tissue system of a monocot root are cortex, endodermis, pericycle, conjunctive tissue and pith.

Cortex

Cortex lies inside the epiblema. It is not well differentiated. Large parenchymatous cells make up the structure. Intercellular spaces are present. Outer few layers of the cortex become thick walled and suberised to form exodermis in older roots. Exodermis protects the older roots after decaying of epiblema. Cortical cells help in the storage of food and transport water from the root hairs to inner tissues. 

                                                   Fig: Cortex

Endodermis

Endodermis lies inner to the cortex. It is made up of a single layer of barrel shaped cells which are thick-walled with no intercellular spaces. Young endodermal cells have casparian strips which are suberin depositions on the radial and tangential walls. Suberin is a water-proof waxy material and hence the cells with casparian strips form a water-proof jacket around the vascular bundles. Some endodermal cells lying opposite to the protoxylem lack casparian strips and are called passage cells. They help in the transportation of water and minerals from the cortex to the inner tissues.

                                             Fig: Endodermis

Pericycle

Pericycle lies inner to the endodermis. It is single layered and made up of parenchymatous cells. It produces lateral roots.

                                                 Fig: Pericycle

Conjunctive tissue

It is a mass of parenchymatous cells that lie in between the xylem and phloem bundles.

                                               Fig: Conjunctive tissue

Pith

A large, well-developed pith is present in the centre. It consists of thin walled parenchymatous cells having intercellular spaces. Food is stored in the form of starch in their bodies.

                             Fig: Pith of monocot root

Vascular tissue system

The vascular tissue system includes the vascular bundles. In a monocot root the xylem and phloem appear in radial arrangement, i.e, the xylem and the phloem bundles lie in separate bundles along different radii.

                                       Fig: Vascular bundles

Vascular bundles of a monocot root are different from that of a dicot root. Vascular bundles are polyarch which means they possess more than six separate bundles of xylem and phloem. No vascular cambium is formed in the monocot vascular bundles. Hence there is no secondary growth. They show the exarch condition, that is, protoxylem lies towards the pericycle and metaxylem towards the centre. Between the xylem and phloem bundles lies conjunctive tissue.

Stele

The tissues present inside the endodermis are called stele. It possesses pericycle, pith and vascular bundles.

                                           Fig: Types of tissues in monocot root

Diagram representing T.S of monocot root

                                         Fig: Anatomy of monocot root

Comparison between Dicot and Monocot roots

Practice Problems

Q 1. Arrange the following organs in ascending order of number of vascular bundles.

1. Monocot Root
2. Monocot stem
3. Dicot root

a. III, I, II
b. II, I, III
c. I, III, II
d. I, II, III

Answer: In the dicot root, there are two to four vascular bundles (diarch to tetrarch condition). In the monocot root, there are more than six vascular bundles (polyarch condition). A vast number of vascular bundles are dispersed throughout the ground tissue of the monocot stem. The monocot stem has more vascular bundles than the monocot root, which in turn has more vascular bundles than the dicot root. 

Hence the correct option is a.

Q 2. Choose the correct statement about the monocot root from the following:

1. Root hairs are the unicellular projections from the epiblema. 
2. Outer few layers of cortex become thick walled and suberised to form exodermis. 
3. Young endodermal cells have casparian strips. 
4. A small pith is present in the centre of the monocot root.

a. A, B, C, D
b. A, B and D
c. A, B, C
d. All the above

Answer: The outermost layer or covering of the plant body is formed of the epidermal tissue system. In monocot roots it is composed of the epiblema and the root hairs. Root hairs are the unicellular projections from the epiblema. It aids in water and mineral absorption. 

Cortex lies inner to the epiblema. It is not well differentiated. Large parenchymatous cells make up the structure. Intercellular spaces are present. Outer few layers of the cortex become thick walled and suberised to form exodermis. Exodermis protects the older roots after decaying of epiblema. 

Endodermis lies inner to the cortex. It is made up of a single layer of barrel shaped cells. Young endodermal cells have casparian strips which are suberin depositions in the radial and tangential walls. The endodermal cells lying opposite to the protoxylem lack the casparian strips and are known as passage cells. They help in the transportation of water and minerals from the cortex to the inner tissues. 

In the centre, there is a large and well-developed pith. It consists of thin walled parenchymatous cells with intercellular spaces present. Food is stored in the form of starch in their bodies.

Hence the correct option is c.

Q 3. Explain the arrangement of vascular bundles in a monocot root.

Answer: In a monocot root the xylem and phloem appear in radial arrangement, i.e, the xylem and the phloem bundles lie in separate bundles along different radii. Vascular bundles are polyarch. Which means they possess more than six separate bundles of xylem and phloem. No vascular cambium is formed in the monocot vascular bundles. Hence there is no secondary growth. They show the exarch condition, that is, protoxylem lies towards the pericycle and metaxylem towards the centre. Between the xylem and phloem bundles lies conjunctive tissue.

Q 4. Why is the epiblema devoid of cuticle covering in roots?

Answer: The outermost layer or covering of the plant body is formed of the epidermal tissue system. It is derived from protoderm. The major function of the epidermal layers is the protection of roots. The epidermal tissue system in roots possesses epiblema and root hairs. Epiblema is made up of a layer of parenchymatous cells. It lacks cuticle on the outer surface because cuticle is a water-proof waxy covering which would hinder the roots ability to absorb water. Root hairs are the unicellular projections from the epiblema which aid in water and mineral absorption. 

FAQs

Q 1. Which floral families include monocot plants?
Answer: Monocots include the most economically important of all plant families, Poaceae (real grasses), and the largest of all plant families, Orchidaceae (orchids), with about 60,000 species. Liliaceae (lilies), Arecaceae (palms), and Iridaceae are other well-known monocot families (irises).

Q 2. How are vascular bundles arranged in monocot stems?
Answer: Vascular bundles in monocot stems are scattered throughout the ground tissue. The vascular bundles are conjoint and closed (without cambium). The xylem is arranged towards the centre of the bundle and phloem towards the periphery. The xylem arrangement is endarch.

Q 3. What is phytotomy?
Answer: Plant anatomy, also known as phytotomy, is the study of a plant's interior structure. Plant morphology, the description of a plant's physical form and external structure, was originally included, but plant anatomy has been deemed a separate science since the mid-twentieth century, relating primarily to internal plant structure. Plant anatomy is now frequently studied at the cellular level, and tissue sectioning and microscopy are frequently used.

Q 4. What are the differences between mycorrhizal and non-mycorrhizal plant roots?
Answer: In the absence of fungal symbionts, the root structure of non-mycorrhizal plants was more branching than that of mycorrhizal plants, presumably facilitating the uptake of water and mineral nutrients

YOUTUBE LINK: https://www.youtube.com/watch?v=GjfjE5B-P1w&t=1613s

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