Category: Biology Second Paper

1. Cuticle is absent at root.
2. Its rhizome is unicellular.
3. It has no hypodermis.
4. The cortex is not organized into different layers.
5. The endothelium is composed of single cells and the cells contain Caspian ribbons.
6. The pericycle is composed of single cells.
7. Vascular bundles are anterior.
8. Protoxylem towards the periphery and metaxylem towards the center i.e. exarch.
9. Its xylem or phloem bundles number 2-6.
10. Marrow is very small.

A thin cross-section of the root of a dicotyledonous plant shows two zones. Extracellular region and Intracellular region.
1. Extra-steel region
The region outside the steel is called extra-steel region. Its various parts are-
(i) Epiblema or Root: The outermost layer of the root is called epiblema or root. The cortex is single-layered. Its wall is thin. It has unicellular rhizomes. It absorbs water and mineral salts.
(ii) Cortex : Cortex is multilayered and composed of parenchyma cells. Cells are round or ovoid with intercellular spaces. It is parenchyma like cells and the wall is very thin.
(iii) Endodermis: It is composed of single layered and tubular cells. The cells are densely packed and without gaps. Casparian ribbons are present in the walls of the cells. It has few passage cells. This layer stores food, protects the stele region, and allows water and solutes to enter through the passage cells.
2. Intrastellar region
The region from pericycle to medulla is called stellie or intrastellar zone. Its various parts are-
(i) Pericycle or pericycle: Below the endothelium there is a layer of pericycle. It is composed of parenchyma cells and the cell wall is very thin.
(ii) Vascular bundles: Xylem or phloem bundles are four in number. They are arranged radially and circularly. Protoxylem towards the periphery and metaxylem towards the center i.e. exarch. It transports water and food.
(iii) Medulla: The part surrounded by vascular bundles situated in the center of the root is called Medulla. It is composed of parenchyma cells. The cells are spherical, thin-walled, and capsuled.
(iv) Medullary Rays: The portion from medulla to pericycle through vascular bundles is called medullary rays. It is composed of narrow and elongated parenchyma cells. It stores food.

1. Cuticle is absent at root.
2. Its rhizome is unicellular.
3. It does not have a hypodermis.
4. In this the cortex is not organized into different layers.
5. Pericycle is monolayer.
6. Its vascular bundles are anterior and alternately arranged.
7. Protoxylem towards the periphery and metaxylem towards the center i.e. exarch.
8. Its xylem or phloem bundles are more than 6 in number.
9. The marrow is quite large and conspicuous.

A thin cross-section of the root of a monocot shows two regions.
1. Extrastellar and intrastellar zones.
(i) Epiblema : Epiblema is single layered. It consists of unicellular rhizomes. It is composed of parenchyma cells. It absorbs water and mineral salts and protects the interior.
(ii) Cortex: Cortex is multilayered and composed of parenchyma cells. Cells are spherical and have intercellular spaces (may sometimes contain arenchyma or vacuoles). It stores food.
(iii) Endodermis: It is composed of single layered and tubular cells. The cells are densely packed and without gaps. The lateral and outer walls of the cells are thick. There are thin-walled passage cells or passage cells. It controls water penetration.
2. Intrastellar region
The region from the pericycle to the pith in the center of the root is called the stilt or intrastilt zone. Its various parts are-
(i) Pericycle: Under the endodermis there is a single layered pericycle. It is composed of parenchyma cells. The cells are very densely packed.
(ii) Vascular bundle: The number of xylem or phloem bundles is more than six. It is arranged radially and cyclically. Protoxylem towards the periphery and metaxylem towards the center i.e. exarch. It transports water, minerals and food.
(iii) Pith : The part surrounded by vascular bundles located in the center of the root is called pith. It is composed of parenchyma cells. The cells are round, thin-walled, and saccate. The raw root has a large pith. It stores food.
(iv) Medullary ray: The part from medulla to pericycle through the vascular bundle is called medullary ray. It is composed of narrow, long and thin-walled parenchyma cells. It separates the xylem and phloem and maintains the connection between the pith and the pericycle.

1. When xylem and phloem form separate bundles, it is called aorial vascular bundle. If the number of auricular vascular bundles is less than five, dicotyledonous plants will have roots.
2. When xylem and phloem form separate bundles, it is called aorial vascular bundle. If the number of auricular vascular bundles is more than six, the plant will be rooted in monocots.

1. If there is no cambium tissue between xylem and phloem, it is called a closed collateral vascular bundle. Closed collateral vascular bundles are present in the stem of monocots.
2. Cambium tissue between xylem and phloem is called free lateral vascular bundle. Free collateral vascular bundles are present in stems of dicots and gymnosperms.
3. Xylem in the middle and phloem on either side are called bilateral vascular bundles. Equilateral vascular bundles are found in stems of plants like gourd, pumpkin, cucumber etc.
4. If the xylem is in the center and the phloem surrounds it, it is hydrocentric or amphicribal. Hydrocentric vascular bundles are found in stems of plants like Lycopodium, Selaginella, Pteris etc.
5. If phloem is in the center and xylem surrounds it, it is called leptocentric or amphivesal. Leptocentric vascular bundles are found in stems of plants like Dracaena, Yucca etc.

1. If there is no cambium tissue between the xylem and phloem, it is called a closed collateral vascular bundle. Closed collateral vascular bundles are the identifying feature of monocots.
2. Cambium tissue between xylem and phloem is called free lateral vascular bundle. Free lateral vascular bundles are identifying features of dicots and gymnosperms.
3. If xylem is in the middle and phloem is located on either side, it is called bilateral vascular bundle. Equilateral vascular bundles are found in plants like gourd, pumpkin, cucumber etc.
4. If xylem and phloem form separate bundles, it is called aorial vascular bundle. If the number of auricular vascular bundles is less than five then the plant is dicotyledonous. If the number of auricular vascular bundles is more than six then the plant is monocotyledonous.
5. If the xylem is in the center and the phloem surrounds it, it is hydrocentric or amphicribal. Hydrocentric vascular bundles are found in plants like Lycopodium, Selaginella, Pteris etc.
6. If phloem is in the center and xylem surrounds it, it is called leptocentric or amphivesal. Leptocentric vascular bundles are found in plants like Dracaena, Yucca etc.

1. Transport of water and mineral salts: Xylem tissue transports water and mineral salts from the soil to the plant body. This tissue transports water and mineral salts to all parts of the plant. As a result, water and mineral salt requirements are met in various organs.
2. Food transport: Phloem tissue transports food from the leaves to the plant body. This tissue carries food to all parts of the plant. As a result, various organs store food and food needs are met.
3. Photosynthesis: Photosynthesis takes place in the green leaves and young green stems of plants. Xylem provides the water needed for photosynthesis. Phloem transports the food produced in the leaves. So the role of xylem and phloem in photosynthesis is undeniable.
4. Transpiration: In the process of transpiration, water evaporates through the stomata. As a result water flow is created in the plant body. Xylem controls water flow.
5. Imbibition: Imbibition is the process of absorption of water by plants. Xylem plays an important role in absorbing water in the process of imbibition.
6. Osmosis: In the process of osmosis, water moves from an area of higher concentration to an area of lower concentration. Xylem contributes to this process.
7. Stiffness: Xylem and phloem give strength to the plant. As a result the plant can survive any adversity.
8. Providing mechanical energy: Xylem and phloem provide mechanical energy to the plant. Mechanical energy helps plants perform various functions.
9. Wood structure: The word xylem means wood. Xylem forms the wood in the plant body.
10. Fiber structure: The word phloem means bark. Phloem forms fibers in the plant body.

A vascular bundle with phloem in the center and xylem surrounding it is called leptocentric or amphivascular. Such as Dracaena, Yucca etc.
Function of Central Vascular Bundle: Xylem transports water and mineral salts. Phloem transports food. It gives strength to the plant. Provides mechanical energy to plants.

A vascular bundle in which xylem is in the center and phloem surrounds it is called hadrocentric or amphicribal. Like- Lycopodium, Selaginella, Pteris, Psilotum etc.