RBSE Solutions Class 11 Biology Chapter 15 Internal Structure of Root, Stem and Leaf

RBSE Class 11 Biology Chapter 15 Multiple Choice Objective Questions

Question 1. Casparian strips are found in:
(a) Cuticle
(b) General cortex
(c) Endodermis
(d) Pith
Answer: (c) Endodermis
In simple words: Casparian strips are special bands found in the endodermis layer of plant roots. They help control what water and minerals can enter the central part of the root.

🎯 Exam Tip: Remember that Casparian strips are unique to the endodermis, acting as a barrier for apoplastic water flow.

Question 2. In T.S. of dicot stem we observe:
(a) Scattered Vascular bundle
(b) Vascular bundle present in ring
(c) radial vascular bundle
(d) losed vascular bundle
Answer: (b) Vascular bundle present in ring
In simple words: When you cut across a dicot stem, you will see the bundles that carry water and food arranged in a clear circle or ring. This arrangement is a key feature of dicot stems.

🎯 Exam Tip: Knowing the arrangement of vascular bundles (scattered vs. ring) is crucial for distinguishing between monocot and dicot stems in cross-section.

Question 4. Vascular bundle in root are:
(a) Conjoint
(b) Collatoral
(c) Open
(d) Radial
Answer: (d) Radial
In simple words: In plant roots, the water-carrying xylem and food-carrying phloem tissues are arranged in separate patches, forming a star-like shape, which is called a radial arrangement. This helps the root absorb water and nutrients efficiently.

🎯 Exam Tip: Radial vascular bundles are a distinguishing feature of roots, different from the conjoint bundles found in stems and leaves.

Question 5. Mesophyll is
(a) Chlorenchymatous
(b) Sclerenchymatous
(c) Meristematic
(d) made from bulliform cells
Answer: (a) Chlorenchymatous
In simple words: Mesophyll is the tissue inside a leaf, and it is made of cells that contain chlorophyll. These cells are specialized for photosynthesis, which is why they are called chlorenchymatous.

🎯 Exam Tip: The term "chlorenchymatous" highlights the presence of chloroplasts, indicating the primary function of photosynthesis in mesophyll tissue.

RBSE Class 11 Biology Chapter 15 Very Short Answer Questions

Question 1. Which type of vascular bundles are found in root?
Answer: Radial vascular bundles are found in roots. In this arrangement, the xylem and phloem are located on different radii, appearing as separate patches. This pattern is essential for efficient water and nutrient transport from the soil to the plant.
In simple words: Roots have vascular bundles arranged radially. This means the xylem and phloem are in separate lines, like spokes on a wheel.

🎯 Exam Tip: Always remember that radial vascular bundles are a defining characteristic of roots, distinguishing them from stems and leaves.

Question 2. What are conjunctive tissue?
Answer: Conjunctive tissue refers to the parenchymatous cells found between the patches of xylem and phloem in roots. These cells help to connect and support the vascular tissues. They play a role in storing food and water.
In simple words: Conjunctive tissue is made of simple cells that fill the spaces between the water and food pipes in a root. It helps connect and support these pipes.

🎯 Exam Tip: Focus on the location ("between xylem and phloem") and composition ("parenchymatous cells") when defining conjunctive tissue.

Question 4. How many type of Stele are formed on basis of number of xylem?
Answer: There are three main types of stele formed based on the number of xylem strands:
1. Protostele: This type has a solid core of xylem and does not have a central pith or any gaps for leaves.
2. Siphonostele: This stele has a hollow cylinder of xylem and contains a central pith, along with gaps where leaves emerge.
3. Eustele: In this arrangement, the xylem and phloem are organized into separate vascular bundles, with pith present between them and no leaf gaps. The arrangement of vascular tissues helps in understanding plant evolution.
In simple words: Stele types depend on how the xylem is arranged. Protostele has solid xylem, siphonostele has a hollow xylem cylinder with pith, and eustele has xylem and phloem in separate bundles with pith.

🎯 Exam Tip: Clearly define each stele type by describing its core structure, presence/absence of pith, and leaf gaps.

Question 5. How are vascular bundles are arranged in monocot stem.
Answer: In monocot stems, the vascular bundles are numerous and appear scattered throughout the parenchymatous ground tissue. They are usually smaller in size near the periphery of the stem and larger towards the center. Each vascular bundle is conjoint, meaning xylem and phloem are on the same radius, collateral (phloem outside xylem), endarch (protoxylem towards the center), and closed (lacking cambium). This scattered arrangement is a key characteristic.
In simple words: Monocot stems have many vascular bundles spread out everywhere, not in a ring. They are smaller on the edges and bigger in the middle, and they do not have cambium.

🎯 Exam Tip: The "scattered" arrangement and "closed" nature (absence of cambium) are crucial points for monocot stem vascular bundles.

Question 6. How the vascular bundles are arranged in Dicot stem?
Answer: In a dicotyledonous stem, the vascular bundles are arranged in a ring, located between the cortex and the pith. Each bundle is conjoint, meaning xylem and phloem are on the same radius. They are typically collateral, with phloem positioned outside the xylem (e.g., Helianthus). Some may be bicollateral, having phloem on both sides of the xylem (e.g., Cucurbita). Rarely, they can be concentric (e.g., Begonia, Rumex), with phloem in the center surrounded by xylem. Dicot stem vascular bundles are open, as cambium is present between the xylem and phloem. This cambium allows for secondary growth, which makes dicot stems grow thicker.
In simple words: Dicot stems have vascular bundles in a clear ring. They are open, meaning they have a cambium layer that helps the stem grow wider.

🎯 Exam Tip: Emphasize the "ring" arrangement and "open" nature (presence of cambium) as key features for dicot stem vascular bundles.

Question 7. Where the bast or hard bast is found?
Answer: Hard bast, or thick-walled patches, usually occurs above the primary phloem in dicot stems. These strong, fibrous tissues provide mechanical support to the plant. Thin-walled patches are also found above the primary medullary rays. The thick-walled sclerenchymatous fibres are also called primary extraxylary fibres.
In simple words: Hard bast is found as thick, strong patches just above the main food-carrying tubes (phloem) in a dicot stem. It helps make the stem strong.

🎯 Exam Tip: Relate hard bast's location (above primary phloem) to its function of providing structural support in stems.

Question 9. What are lysogenous cavity?
Answer: Lysigenous cavities are intercellular spaces formed by the complete dissolution of cells. The word 'lysis' means loosening or breaking down. These cavities function as storage areas for water, gases, and essential oils. They are commonly observed in water plants and many monocotyledonous plants. For example, secretory cavities found in Eucalyptus, Citrus, and Gossypium are good examples of lysigenous cavities. This process is a common way for plants to create specialized storage structures.
In simple words: Lysigenous cavities are spaces in plants formed when cells break down completely. These spaces store water, gases, or oils and are common in water plants.

🎯 Exam Tip: Define lysigenous cavities by their formation (dissolution of cells) and function (storage of substances) and provide an example.

Question 10. Dorsiventral leaves are devoid or very less number of stomata. What are the benefits of this to plant.
Answer: Dorsiventral leaves have very few or no stomata on their upper epidermis. This arrangement helps the plant prevent excessive water loss when exposed to direct sunlight. By having most stomata on the lower, shaded surface, the plant can regulate transpiration more effectively. This adaptation is crucial for survival in environments where water conservation is important.
In simple words: Dorsiventral leaves have fewer pores (stomata) on their top side. This helps the plant save water by stopping too much water from leaving when the sun shines on the leaf.

🎯 Exam Tip: Connect the reduced number of upper stomata in dorsiventral leaves directly to the benefit of minimizing water loss, especially in sunny conditions.

RBSE Class 11 Biology Chapter 15 Short Answer Questions

Question 1. What are the anatomical features of structure of root?
Answer: The anatomical features of a typical root structure include:
1. Epiblema: This is the outermost layer of the root, also known as the piliferous layer or rhizodermis. It bears numerous short-lived, unicellular root hairs and lacks a cuticle and stomata.
2. Cortex: Composed of parenchymatous cells, the cortex provides storage and some transport functions within the root.
3. Endodermis: This layer is very distinct and features Casparian strips, which regulate water and solute movement into the vascular cylinder.
4. Pericycle: Also very distinct, the pericycle is a layer located just inside the endodermis and is responsible for the formation of lateral roots.
5. Vascular bundles: These are radially arranged, meaning the xylem and phloem are positioned on different radii, forming distinct patches. This arrangement optimizes water and nutrient absorption.
6. Xylem: It is exarch, with the protoxylem (smaller vessels) located towards the periphery and the metaxylem (larger vessels) towards the center.
7. Phloem: Consists of sieve tubes, companion cells, and phloem parenchyma (though phloem parenchyma is absent in monocotyledonous plants).
8. Conjunctive tissue: Parenchyma cells found between the patches of xylem and phloem are called conjunctive tissue. This helps in lateral transport.
In simple words: A root has an outer skin (epiblema with root hairs), a middle storage part (cortex), and an inner layer (endodermis) that controls what goes in. Inside, there's a ring called pericycle where side roots grow, and water and food pipes (vascular bundles) are arranged like spokes, with water pipes (xylem) having smaller parts on the outside.

🎯 Exam Tip: When describing root anatomy, ensure you cover all major tissue layers and their distinguishing features, like the radial vascular bundles and exarch xylem.

Question 3. Draw a well labelled diagram of T.S. of monocot root?
Answer: (Diagram: A well-labeled diagram of T.S. of monocot root would show a central pith, radial vascular bundles with hexarch to polyarch xylem, and a distinct endodermis with Casparian strips.)
Internal Structure of Orchid Root: Most orchids are epiphytes, meaning they grow on other plants, and have hanging aerial roots. Their anatomy is somewhat different from other monocotyledonous roots:
1. Velamen:
• It is the outermost tissue of the root.
• The cells of this tissue are large, closely packed, and have fibrous thickenings.
• These are dead cells that fill with air in dry seasons and absorb water during rains.
• Velamen is a multilayered epiblema.
• The outermost layer of velamen is called the limiting layer and is cuticularized. This specialized tissue helps orchids absorb moisture from the air.
2. Exodermis:
• It is the outermost layer of the cortex.
• The lateral walls of the exodermal cells are thickened.
4. Pericycle:
• It is a single-layered tissue located on the inner side of the endodermis.
• Consists of thin-walled cells.
5. Conjunctive tissue:
• This is the parenchymatous tissue surrounding and located between the vascular bundles.
6. Vascular bundles:
• Vascular bundles are radial, meaning xylem and phloem are present as alternate patches and are arranged in a ring.
• Xylem is exarch, with protoxylem away from the center and metaxylem towards the center.
• This condition of xylem is called exarch.
• The vascular bundles in gram root are tetraarch.
In simple words: A monocot root diagram would show its layers from outside to inside. Orchid roots have a special outer layer called velamen that absorbs water from the air. Their inner parts also have a pericycle, conjunctive tissue, and water/food pipes arranged radially.

🎯 Exam Tip: For diagrams, ensure all key parts are correctly identified and labeled. When describing specific root types like Orchid roots, highlight unique adaptations like the velamen.

Question 4. Draw a well labelled diagram of T.S. of dicot stem?
Answer: (Diagram: A well-labeled diagram of T.S. of dicot stem would show the epidermis, hypodermis, cortex, endodermis, pericycle, vascular bundles arranged in a ring with cambium, medullary rays, and a central pith. Refer to diagrams of "Transverse section of young stem of Sunflower (Helianthus annuus)" on page 8 or "Detailed structure of a portion of T.S. of sunflower stem" on page 8 and "Transverse section of young stem of sunflower" on page 19.)
In simple words: Draw a picture of a dicot stem cut across, showing all its layers from the outside skin (epidermis) to the center (pith), including the ring of water and food pipes.

🎯 Exam Tip: For diagrams, ensure clarity, accuracy, and proper labeling of all tissue layers and vascular structures, especially the cambium in dicot stems.

Question 6. What is mesophyll tissue and how it is differentiated in leaf of Dicot plants?
Answer: Mesophyll tissue is the bulk of tissue located between the upper and lower epidermis of a leaf, excluding the vascular bundles. It is composed of parenchymatous cells that contain many chloroplasts and are separated by numerous intercellular spaces. In dicot leaves, the mesophyll is typically differentiated into two distinct types:
1. Palisade parenchyma: These cells are elongated, columnar, and tightly packed, usually located below the upper epidermis. They are rich in chloroplasts and are the primary site of photosynthesis.
2. Spongy parenchyma: Found below the palisade layer, these cells are irregularly shaped and loosely arranged with large air spaces between them. These air spaces facilitate gas exchange within the leaf. This differentiation allows for efficient light absorption and gas exchange for photosynthesis.
In simple words: Mesophyll is the inner part of a leaf. In dicots, it has two types: long, tightly packed palisade cells at the top for making food, and round, loosely packed spongy cells below with air gaps for breathing.

🎯 Exam Tip: Clearly distinguish between palisade and spongy parenchyma based on their shape, arrangement, and primary function in photosynthesis and gas exchange.

Question 7. Why the ventral surface is lighter green in Dorsiventral leaves?
Answer: The ventral (lower) surface of dorsiventral leaves is typically lighter green because it receives less direct sunlight compared to the dorsal (upper) surface. This reduced light exposure means the lower epidermis and the spongy parenchyma beneath it have fewer chloroplasts. Also, the palisade layer, which contains more chloroplasts, is usually located only on the upper side. This difference in chloroplast density and light exposure results in a lighter coloration on the ventral surface.
In simple words: The underside of a leaf is lighter green because it gets less sun. This means it has fewer green pigments (chloroplasts) there compared to the top side.

🎯 Exam Tip: The key reason for the lighter color on the ventral surface is the lower density of chloroplasts due to less direct sunlight exposure.

Question 8. What is Bundle sheath and what is difference of it in dicot and monocot?
Answer: A bundle sheath is a layer of cells that surrounds the vascular bundles in leaves. It provides support and helps in the transport of materials.
Differences in dicot and monocot leaves:
In Dicot Leaf: The bundle sheath is usually made up of parenchymatous cells or collenchymatous cells, found both above and below the vascular bundle, extending up to the epidermis.
In Monocot Leaf: The bundle sheath is primarily made of sclerenchymatous cells, especially above and below the vascular bundles, also extending up to the epidermis. These sclerenchymatous cells provide stronger mechanical support.
In simple words: A bundle sheath is a protective cover around the leaf's water and food pipes. In dicots, it's often made of softer cells, but in monocots, it's made of harder, stronger cells.

🎯 Exam Tip: Focus on the cell type (parenchymatous/collenchymatous vs. sclerenchymatous) to differentiate bundle sheaths in dicots and monocots.

Question 9. Differentiate between T.S. of Monocot and dicot stem?
Answer: The differentiation between the transverse section (T.S.) of a monocot and dicot stem is shown in the table below:

🎯 Exam Tip: Focus on the arrangement of vascular bundles, the presence or absence of pith, medullary rays, and the nature of hypodermis to effectively differentiate between monocot and dicot stems.

RBSE Class 11 Biology Chapter 15 Essay Type Questions

Question 1. Explain the internal structure of Dicot root with help of well labelled diagram and also differentiate between vascular bundle od Monocot and dicot root?
Answer: Internal Structure of Dicot Root:
The internal structure of a dicot root includes several distinct layers from the outside to the center:
1. Epiblema:
• Also known as the piliferous layer or rhizodermis, it is the outermost layer.
• It consists of thin-walled, living parenchymatous cells.
• The outer walls of the epiblema cells form unicellular tubular elongations called root hairs, which are crucial for water absorption from the soil.
2. Cortex:
• This layer is made up of several parenchymatous cells.
• The innermost layer of the cortex that surrounds the stele (central vascular cylinder) is called the endodermis.
• Endodermal cells have special thickenings called Casparian strips in their radial and tangential walls, regulating the passage of water and solutes.
• Endodermal cells located outside the protoxylem do not have Casparian strips and are called passage cells, allowing water movement.
3. Pericycle:
• This unilayered structure is found just inside the endodermis.
• It consists of thin-walled cells and is the site for the development of lateral roots.
4. Vascular bundles:
• These are always arranged in a radial pattern, meaning xylem and phloem are situated on different radii.
• The protoxylem (smaller xylem vessels) is always positioned away from the center, towards the periphery, while the metaxylem (larger xylem vessels) is towards the center. This condition of xylem is called exarch.
• The vascular bundles in a gram root are typically tetraarch (four xylem bundles).
5. Conjunctive tissue:
• Parenchymatous cells located between the xylem and phloem patches are called conjunctive tissue, which aids in transport and support.
6. Pith:
• Pith is found in the center but is typically small or poorly developed in dicot roots. This detailed arrangement ensures effective absorption and transport.

(Diagram: A well-labeled diagram of T.S. of Dicot Root (Gram) would show these layers: Epiblema with root hairs, Cortex, Endodermis with Casparian strips, Pericycle, radial arrangement of Xylem and Phloem (exarch xylem), Conjunctive tissue, and a small or absent Pith. Refer to the diagram "T.S. of Dicot Root (Gram) (A sector enlarged)" on page 14 of the source document.)

Differentiation between vascular bundles of Monocot and Dicot root:
• Dicot Root: Vascular bundles are typically diarch to hexarch (2 to 6 xylem bundles). Cambium develops during secondary growth, allowing the root to increase in girth. Pith is usually absent or poorly developed.
• Monocot Root: Vascular bundles are hexarch to polyarch (more than 6 xylem bundles). Cambium is typically absent, so there is no secondary growth. Pith is usually large and well-developed.
In simple words: A dicot root has an outer skin (epiblema with root hairs), a thick middle layer (cortex), and a central part with water and food pipes (vascular bundles) arranged like spokes, with smaller water pipes on the outside. Dicot roots usually have fewer water pipe bundles and little to no pith, while monocot roots have many water pipe bundles and a large pith.

🎯 Exam Tip: For explaining dicot root structure, clearly list and describe each layer. For differentiation, compare the number of xylem bundles, presence/absence of cambium, and pith development in dicot and monocot roots.

Question 2. Explain the T.S. of monocot stem with help of well labelled diagram and also differentiate between cortex of Dicot and monocot stem?
Answer:

Internal Structure of Monocot Stem (e.g., Zea mays)
A typical monocotyledonous stem shows the following internal structures from the outside towards the center:

1. Epidermis: This is the outermost protective layer, made of a single row of living parenchymatous cells. The outer cell walls are very thick (highly cutinized). A few stomata might be present, but multicellular hairs are usually not found. This tough outer layer protects the delicate tissues inside from harm and water loss.

2. Hypodermis: Below the epidermis are a few layers (2-4) of sclerenchymatous cells. These cells have thickened, woody walls (lignified) and provide mechanical support to the stem. There are no spaces between these cells. Sometimes, this hypodermis might even be absent, like in wheat or asparagus.

3. Ground Tissue: In monocot stems, there is no distinct cortex, endodermis, pericycle, or pith. Instead, the entire central mass from the hypodermis to the center is called the ground tissue. It is made of parenchymatous cells. The cells closer to the outside are smaller, polygonal, and tightly packed, while those towards the center are larger, oval, rounded, and loosely arranged. These cells store starch grains, which provide energy to the plant.

4. Vascular System: The vascular bundles are numerous and scattered throughout the parenchymatous ground tissue (except in some plants like runners and grasses). These bundles are smaller near the edges of the stem and larger towards the center. Each vascular bundle is conjoint (xylem and phloem together), collateral (phloem outside xylem), endarch (protoxylem towards center), and closed (no cambium for secondary growth). The xylem often forms a Y-shape, with metaxylem facing outwards and protoxylem inwards. Sometimes, a water-filled cavity, called a lysigenous cavity, forms at the end of the protoxylem vessels due to cell breakdown. The phloem is located on the outer side and contains sieve-tubes and companion cells, but usually no phloem parenchyma. The phloem can be divided into an outer crushed protophloem and an inner functional metaphloem. These bundles act like tiny transport tubes, carrying water and food throughout the plant.

Internal Structure of Dicot Stem (e.g., Sunflower stem)
A typical dicotyledonous stem shows the following internal structure from the outside towards the center:

2. Cortex: The epidermis is followed by a distinct zone called the cortex, which can be several layers thick. It may be entirely made of parenchymatous cells (like in Ranunculus) or divided into two parts: hypodermis and general cortex. The hypodermis in young stems is typically collenchymatous (3-5 layers thick). It lacks intercellular spaces, and its cells have thickened corners due to extra cellulose and pectic substances. These cells often contain chloroplasts. The rest of the cortex consists of loosely arranged parenchymatous cells, which are spherical or oval and have some intercellular spaces. This region helps in support and storage.

3. Endodermis: This is the innermost layer of the cortex. In most dicot stems, the endodermis is not very clear. It is a single layer of barrel-shaped cells that may contain starch grains and sometimes lack Casparian strips. Because of the starch grains, this layer is also known as the starch sheath.

4. Pericycle: The pericycle is found between the endodermis and the central vascular cylinder. It can be made of alternating bands of parenchymatous and sclerenchymatous cells. It might form a continuous ring of sclerenchymatous tissue (as in Cucurbita) or alternating patches of thick-walled and thin-walled cells (as in Helianthus). The thick-walled patches, usually above the primary phloem, are called hard bast. The thin-walled patches are found above the primary medullary rays. These sclerenchymatous fibers are also known as primary extraxylary fibers, providing strength to the stem.

5. Vascular System: The vascular system of a dicotyledonous stem consists of many vascular bundles arranged in a ring between the cortex and the central pith. Each vascular bundle is conjoint (xylem and phloem together), and both are on the same radius. They are usually collateral, meaning the phloem is towards the outside of the xylem (as in Helianthus). Sometimes, they can be bicollateral, with phloem on both sides of the xylem (as in Cucurbita). In a few cases, vascular bundles are concentric (e.g., Begonia), where the phloem is in the center surrounded by xylem (amphivasal type). These vascular bundles are "open," meaning cambium is present between the xylem and phloem, allowing for secondary growth. The phloem consists of sieve tubes, companion cells, phloem parenchyma, and phloem fibers. The xylem has vessels, tracheids, xylem fibers, and xylem parenchyma. The xylem is endarch, with protoxylem towards the pith and metaxylem towards the outside. The organized arrangement of vascular bundles in a ring allows for efficient transport and flexibility in growth.

Differentiation between Monocot and Dicot Stem

🎯 Exam Tip: When explaining internal structures, always describe the layers from outside to inside. For differentiation, use clear comparative points, ideally in a table format, to highlight the contrasting features.

Internal Structure of Leaf
Based on their internal structure, leaves are categorized into three main types:

• Bifacial or Dorsiventral leaves: These leaves have clearly different upper (dorsal) and lower (ventral) surfaces. The palisade tissue, which is responsible for most photosynthesis, is usually found below the upper epidermis.
• Unifacial leaves: In these leaves, there is no clear difference between the upper and lower surfaces. An example is the cylindrical leaves of Allium (onion or garlic).
• Isobilateral or Equifacial leaves: These leaves have similar upper and lower surfaces. The mesophyll tissue (the middle layer) is generally not divided into palisade and spongy parenchyma, or if it is, the palisade layer is present on both sides.

Differentiation of Leaf Internal Structures: Dorsiventral (Dicot) vs. Isobilateral (Monocot) Leaf

Question 4. Differentiate between internal structure of Dicot and monocot stem?
Answer: The internal structures of dicot and monocot stems show several key differences:

• Hypodermis: Dicot stems have a collenchymatous hypodermis (cells with thickened corners), providing flexibility, while monocot stems have a sclerenchymatous hypodermis (cells with hard, woody walls), providing rigidity.
• Cortex: Dicot stems have a well-defined cortex made of several layers of parenchymatous tissue. Monocot stems typically lack a distinct cortex, with the ground tissue directly following the hypodermis.
• Endodermis: Dicot stems usually have an endodermis, often called a starch sheath, separating the cortex from the vascular cylinder. Monocot stems do not have an endodermis.
• Vascular Bundles: In dicot stems, vascular bundles are arranged in a ring, are generally of the same size, and are open (meaning they have cambium for secondary growth). In monocot stems, vascular bundles are scattered throughout the ground tissue, vary in size (smaller at the periphery, larger towards the center), and are closed (lack cambium).
• Pith and Medullary Rays: Dicot stems possess a distinct central pith and medullary rays (parenchymatous cells between vascular bundles). Monocot stems typically lack both pith and medullary rays, having a continuous ground tissue.

🎯 Exam Tip: Remember that dicots have vascular bundles arranged in a ring and can grow wider, while monocots have scattered bundles and typically grow taller. These structural differences are closely related to their growth patterns.