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T.S. of Dicot Root, Practice problems and FAQs

T.S. of Dicot Root, Practice problems and FAQs

Roots are the structures that allow a plant to attach to the soil. It also helps to transport the nutrients and water absorbed from the soil to different parts of the plant. How are the roots doing all these functions? There must be a specific arrangement of tissues in the roots which enable them to absorb and distribute water and minerals so efficiently. Do you think this arrangement of tissues is the same in all parts of the plant? It definitely is not. The arrangement of tissues in roots will vary greatly from the arrangement of tissues in stems because the functions that they perform are very different. A study of the anatomy of the root helps us to understand their internal structure.

Roots are of two types, tap root and fibrous root. Tap roots are observed in dicot plants and fibrous roots are observed in monocot plants. Since the morphology of tap root and fibrous root are different, their anatomy will also be different. But how different is it? Let's discuss more about the anatomy of roots found in dicots.

Table of contents:

Dicotyledonous root

Have you ever observed the root of a dicot plant? Dicot plants have a taproot system. A taproot system is composed of a primary root from which lateral roots emerge. The internal structure can be studied by observing the transverse section of the root under the microscope. Root possesses the epidermal tissue system, ground tissue system and vascular tissue system. Let us discuss each of these.

Epidermal tissue system

The epidermal tissue system of dicot roots consist of the epiblema and root hair cells. Stomata are absent in the epidermis of roots as they remain under the ground and are hence not capable of exchanging gases with the atmosphere. The cuticle layer is absent in the roots to facilitate the entry of water into the cells.



                                      Fig: Epidermal tissue system

Epiblema 

Epiblema or the piliferous layer is the outermost uncutinised layer of the root which is protective in function. It is unilayered and possess compactly arranged parenchymatous cells. 

Unicellular root hairs 

Root hairs are the unicellular protuberances of epiblema. It is absorptive in function. It also helps in the attachment to the substratum.



                                                Fig: Root hairs

Ground tissue system

The ground tissue system includes all the tissues except epidermis and vascular bundles. 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 dicot root include cortex, endodermis, pericycle, pith, and conjunctive tissue.



                                     Fig: Ground tissue system

Cortex

Cortex possesses multilayered parenchymatous cells. Cells are thin walled with no chloroplasts. They have intercellular spaces. Leucoplast is present which helps in the storage of starch grains. 

Endodermis

Endodermis is the innermost layer of the cortex. It is single layered. Cells are barrel shaped. Casparian strips and passage cells are present. 

Casparian strips

Casparian strips are present on the tangential and radial walls of endodermis. It is made of waxy material called suberin. It is impermeable to water. It allows the plant to control the amount of water and minerals absorbed from the soil. Thus, the endodermis forms a water-tight jacket around the vascular cylinder. 



                                           Fig: Casparian strip

Passage cells

Passage cells are the endodermal cells without casparian strips or suberin deposition. They are also called transfusion cells. They allow the radial diffusion of water and minerals through the endodermis. These cells lie opposite to the protoxylem and allow the passage of water and minerals into the xylem from the cortex.



                                               Fig: Passage cell

Pericycle

The pericycle is present below the endodermis. It is few layered and possess thick walled parenchymatous cells. Initiation of lateral roots occurs here. Formation of vascular cambium is a major function of the pericycle.



                                          Fig: Lateral root initiation

Vascular cambium

Secondary growth occurs in dicot root due to the activation of the vascular cambium. It is a secondary meristematic tissue which arises from the cells of the pericycle that lie above the protoxylem and from the conjunctive tissue lying between the xylem and phloem bundles. Secondary meristems are formed in the roots after the tissues of the primary plant body have differentiated. The vascular cambium is responsible for increasing the diameter of roots resulting in the formation of woody tissues.



                         Fig: Formation of cambium from pericycle

Pith

Pith is small and inconspicuous in the roots. It is made up of parenchyma cells. It is located at the centre of the root and stores and transports nutrients. 



                                Fig: Pith

Conjunctive tissue

Conjunctive tissue is made up of parenchymatous or sclerenchymatous cells. It is present between the xylem and phloem bundles.



                               Fig: Conjunctive tissue

Vascular tissue system

The vascular tissue system includes separate xylem and phloem bundles. In dicot root 2 to 4 xylem and phloem bundles are seen. Hence it is diarch to tetrarch. The arrangement of vascular bundles is radial as the xylem and phloem are arranged in an alternate manner along different radii. Xylem is in exarch condition as the protoxylem is towards the periphery and metaxylem is towards the centre. 

Types of vascular bundles

Vascular bundles are of different types based on the number of xylem bundles. They are diarch, triarch, and tetrarch. Diarch possess two xylem bundles. Examples include tomatoes. Triarch possesses three xylem bundles. Examples include pea. Tetrarch possesses four xylem bundles. Examples include gram.



                       Fig: Vascular tissue system

Stele

All the tissues inside the endodermis are called stele. It includes xylem, phloem, pericycle and pith. It consists of ground tissue and vascular tissue systems.



                                                          Fig: Division of stele



                                      Fig: Stele

Diagram showing T.S of dicot root



                                                      Fig: T.S. of dicot root

Practice Problems

Q 1. Which of the following does not have intercellular spaces?

a. Cortex of root
b. Endodermis of root
c. Spongy parenchyma of the leaf
d. All of these

Answer: The endodermis is the cortex's innermost layer. It has only one layer. The cells are shaped like a barrel and are tightly packed with no intercellular spaces between these cells. Most of the endodermal cells have a suberin deposition in their tangential and radial walls. These cells do not allow the passage of water. Some endodermal cells which lie opposite to the protoxylem lack the casparian strips and are known as passage cells. These allow the conduction of water from the cortex to the xylem.

Hence the correct option is b.

Q 2. Which of the following plants can be used to study the anatomy of a dicot root?

a. Onion
b. Grass
c. Maize
d. Sunflower

Answer: Onions, grasses, and maize are monocot plants. Sunflowers are a dicotyledonous plant. The transverse section of a sunflower root can be used to study the anatomy of a dicot plant.

Hence the correct option is d.

Q 3. From the centre to the periphery, arrange the following tissues as they can be seen in the transverse section of the dicot root.

a. Epiblema. Cortex, Endodermis, pericycle, pith.
b. Pith, pericycle, endodermis, cortex, epiblema.
c. Pith, endodermis, pericycle, cortex, epiblema.
d. Pith, cortex, pericycle, endodermis, epiblema.

Answer: The pith, which is made up of parenchyma cells, is the most central part of the roots. It is surrounded by the vascular bundles. The pericycle surrounds the vascular bundles. A few layers of thick-walled parenchyma cells make up the pericycle. The endodermis is located next to the pericycle. It is the cortex's deepest layer. It is made up of a single layer of barrel-shaped cells with casparian strips containing suberin deposits. The remaining portion of the cortex, which is made up of multiple layers of thin-walled parenchyma cells, is located next to the endodermis. Epiblema is the root's outermost layer. Epiblema cells protrude in the form of single-celled root hairs.

Hence the correct option is b.

Q 4. In monocot and dicot roots, how does the stele differ?

a. In the arrangement of xylem and phloem
b. In pith region
c. In the number of xylem bundles
d. Both b and c

Answer: The central region of the roots and stems is known as the stele. Stele is made up of pericycle, pith, and vascular tissues. The plant body's pith is made up of parenchyma cells that store and transfer nutrients. The pith of a dicot root is small and inconspicuous, whereas the pith of a monocot root is massive and fully developed. Dicot roots have two to four xylem and phloem bundles (diarch to tetrarch). More than six (polyarch) bundles of xylem and phloem can be found in a monocot root. In both dicot and monocot roots, the xylem and phloem are arranged in the same way. The xylem and phloem are alternately arranged along different radii. Radial is the term for this kind of arrangement. This is a unique anatomical trait of the root.

Hence the correct option is d.

FAQs

Q 1. What's the difference between a dicot root and a dicot stem?
Answer: The cortex of a dicot root is divided into two parts: the general cortex and the endodermis. The cortex of the dicot stem, on the other hand, is divided into three layers: hypodermis, general cortex, and endodermis. The pericycle of a dicot stem is multilayered and made up of sclerenchyma, parenchyma, or both. The pericycle of dicot roots is single layered. The vascular bundles in dicot roots are arranged radially whereas in the dicot stems they are conjoint.

Q 2. How does taproot development take place?
Answer: Taproots grow from a seed's radicle to generate the primary root. It splits into secondary roots, which then split into tertiary roots. These may branch out further to generate rootlets. A root system that extends horizontally in all directions as far as the tree's height or more is found in the top 50 cm of soil in a typical mature tree that is 30–50 m tall. The architecture of taproots is heavily influenced by soil qualities; for example, deep and rich soils encourage the establishment of vertical taproots in many oak species, whereas clay soils encourage the emergence of numerous taproots.

Q 3. What is the role of conjunctive tissue in the plant body?
Answer: A short strip of conjunctive tissue separates the xylem and phloem from one another. If this tissue is parenchymatous, the cells perform the job of storing food. When they get sclerified, they provide mechanical strength. During secondary growth the cells of conjunctive tissue can become meristematic and form strips of cambium.

Q 4. Why are lateral roots said to be endogenous?
Answer: Lateral roots are said to have an internal, or endogenous, origin since they begin in the pericycle and develop out through the cortex and epidermis, as opposed to the external, or exogenous origin of leaves and the apical meristem of stems.

Related Topics

T.S. of dicotyledonous stem, Practice problems and FAQs

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

Secondary growth in stem, Practice problems and FAQs 

Epidermal tissue system: Epidermis, Stomata, Epidermal appendages, Practice problems and FAQs

Tissue system: Ground tissue system, Practice problems and FAQs

Tissue system: Vascular tissue system, Practice problems and FAQs

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