6 Most FAQ’s of Histology and Anatomy of Flowering Plants Chapter in Inter 1st Year Botany (TS/AP)

8 Marks

LAQ-1 : Describe the internal structure of dorsiventral leaf with the help of labelled diagram

Introduction

The dorsiventral leaf, commonly found in dicot plants, exhibits a distinct internal structure that allows for efficient photosynthesis and gas exchange. A detailed description of its internal structure is essential for understanding how these leaves function.

Internal Structure of Dorsiventral Leaf

1. Upper Epidermis:
   • The upper layer of the leaf, known as the upper epidermis, is typically a single layer of cells.
   • These cells are flattened and contain few or no chloroplasts.
   • The primary function of the upper epidermis is to provide protection and reduce water loss.
2. Palisade Mesophyll:
   • Beneath the upper epidermis lies the palisade mesophyll, consisting of elongated cells rich in chloroplasts.
   • This layer is the primary site of photosynthesis due to its high chloroplast content and its arrangement allows for maximum light absorption.
3. Spongy Mesophyll:
   • Below the palisade mesophyll is the spongy mesophyll, characterized by loosely arranged cells with large intercellular spaces.
   • These spaces facilitate gas exchange (CO2 and O2) and water vapor movement within the leaf.
4. Vascular Bundles (Veins):
   • Vascular bundles, or veins, are distributed throughout the leaf and are embedded in the mesophyll layer.
   • They consist of xylem (which transports water and minerals) and phloem (which transports organic nutrients).
5. Lower Epidermis:
   • The lower surface of the leaf is covered by the lower epidermis, which also consists of a single layer of cells.
   • It contains openings called stomata, which are surrounded by guard cells.
   • Stomata are crucial for gas exchange and transpiration.
6. Guard Cells:
   • Guard cells are specialized cells that control the opening and closing of the stomata.
   • They help regulate the exchange of gases and the loss of water vapor from the leaf.

Summary

The dorsiventral leaf of dicot plants displays a specialized internal structure adapted for photosynthesis and gas exchange. Key components include the upper epidermis, palisade mesophyll, spongy mesophyll, vascular bundles, lower epidermis, and guard cells. Each part plays a significant role in the overall function of the leaf, contributing to the plant’s ability to photosynthesize, respire, and transpire efficiently.

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LAQ-2 : Describe the internal structure of an isobilateral leaf with the help of labelled diagram.

Introduction

An isobilateral leaf is a type of leaf where both surfaces (upper and lower) are similar in appearance and function. This leaf structure is typically found in plants that grow in dry or windy environments, such as grasses. Understanding the internal structure of an isobilateral leaf is crucial for comprehending how these plants adapt to their environments.

Internal Structure of Isobilateral Leaf

1. Epidermis:
   • The leaf is covered on both sides by a protective layer known as the epidermis.
   • This layer is usually one cell thick and is coated with a waxy substance called the cuticle to reduce water loss.
2. Stomata:
   • Stomata are present on both surfaces of the leaf, facilitating gas exchange.
   • They are regulated by guard cells that control their opening and closing.
3. Mesophyll:
   • Unlike dorsiventral leaves, isobilateral leaves do not have distinct palisade and spongy mesophyll layers.
   • The mesophyll is more or less uniform and is filled with chloroplasts for photosynthesis.
4. Vascular Bundles (Veins):
   • The leaf contains vascular bundles, which are responsible for the transport of water, minerals, and food.
   • These bundles are surrounded by a layer of cells called the bundle sheath.
5. Bulliform Cells:
   • Often, isobilateral leaves have specialized large, empty cells known as bulliform cells.
   • These cells help in the rolling and unrolling of the leaf in response to changes in humidity, reducing water loss.

Summary

The isobilateral leaf is adapted for efficiency in harsh environments with features such as a uniform mesophyll layer, stomata on both surfaces, and bulliform cells for controlling leaf movement. The epidermis with its waxy cuticle and the well-developed vascular bundles also play key roles in the leaf’s adaptation to its environment. Understanding the structure of isobilateral leaves provides insight into how plants survive in extreme conditions.

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LAQ-3 : Describe the T.S of a Dicot stem.

Introduction

The Transverse Section (T.S.) of a Dicot stem provides insight into the internal structure and arrangement of different tissues in dicotyledonous plants. It is characterized by a distinct arrangement of cells and tissues that are crucial for the plant’s growth and functionality.

Structure of T.S. of Dicot Stem

1. Epidermis:
   • The outermost layer is the epidermis, which is usually a single layer of cells.
   • It is covered with a protective layer called the cuticle to minimize water loss.
   • The epidermis may contain trichomes (hair-like structures) and stomata for gas exchange.
2. Cortex:
   • Beneath the epidermis lies the cortex, which is typically divided into three regions: the hypodermis, general cortex, and endodermis.
   • The hypodermis is often made of collenchyma cells providing mechanical strength.
   • The general cortex consists of loosely packed parenchyma cells.
   • The endodermis is the innermost layer of the cortex, often distinguished by the Casparian strip.
3. Pericycle:
   • The pericycle lies just inside the endodermis and gives rise to lateral roots and vascular cambium during secondary growth.
4. Vascular Bundles:
   • The vascular bundles are arranged in a ring and consist of xylem and phloem.
   • Xylem conducts water and minerals and is oriented towards the center of the stem.
   • Phloem transports organic nutrients and is located peripheral to the xylem.
   • A layer of cambium may be present between the xylem and phloem in mature stems, contributing to secondary growth.
5. Pith:
   • The central part of the stem is occupied by the pith, composed of large, thin-walled parenchyma cells.
   • The pith stores nutrients and helps in the transport of water and solutes.

Summary

The Transverse Section of a Dicot stem exhibits a well-organized structure consisting of the epidermis, cortex, pericycle, vascular bundles, and pith. Each layer has specific functions, from protection and storage to transport and support, contributing to the overall health and growth of the plant. Understanding this structure is fundamental for studying plant anatomy and physiology.

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LAQ-4 : Describe the T.S of a Monocot stem.

Introduction

The Transverse Section (T.S.) of a Monocot stem reveals the unique internal structure of monocotyledonous plants, differing significantly from dicotyledons. This structure is specialized to support the plant’s growth and physiological processes.

Structure of T.S. of Monocot Stem

1. Epidermis:
   • The outermost layer is the epidermis, typically a single layer of cells.
   • It is covered by a cuticle and often has epidermal hairs.
   • The epidermis serves as a protective layer and helps in reducing water loss.
2. Hypodermis:
   • Beneath the epidermis lies the hypodermis, which is usually composed of sclerenchymatous fibers.
   • This layer provides mechanical strength to the stem.
3. Ground Tissue:
   • Unlike dicots, monocots do not have a distinct cortex and pith.
   • The ground tissue is a mass of parenchyma cells filling the space between the epidermis and the vascular bundles.
   • It serves various functions including storage, support, and photosynthesis.
4. Vascular Bundles:
   • Vascular bundles in monocots are scattered throughout the ground tissue.
   • Each vascular bundle is surrounded by a sheath of sclerenchyma fibers, known as the bundle sheath.
   • Xylem and phloem are present within each bundle, often with phloem surrounding the xylem.
   • The arrangement of vascular bundles is not in a ring as in dicots but is scattered, a characteristic feature of monocots.
5. No Secondary Growth:
   • Monocot stems typically lack secondary growth due to the absence of vascular cambium.
   • The size of the stem is mainly increased by elongation of cells rather than the addition of new cells.

Summary

The Transverse Section of a Monocot stem is characterized by its epidermis with cuticle, hypodermis, homogeneous ground tissue, and scattered vascular bundles with a bundle sheath. The absence of distinct cortex and pith, along with the lack of secondary growth, differentiates it from dicot stems. These features are crucial for the support, storage, and transport functions in monocot plants.

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LAQ-5 : Describe the internal structure of a Dicot Root.

Introduction

The internal structure of a Dicot root plays a vital role in the plant’s ability to absorb water and nutrients, anchor itself in the soil, and store food. Understanding this structure is crucial for comprehending how dicot plants interact with their environment and meet their physiological needs.

Internal Structure of a Dicot Root

1. Epidermis:
   • The outermost layer of the dicot root is the epidermis.
   • It consists of a single layer of cells and is primarily involved in the absorption of water and minerals from the soil.
   • The epidermis often has root hairs which increase the surface area for absorption.
2. Cortex:
   • Beneath the epidermis lies the cortex, composed mainly of parenchyma cells.
   • These cells are loosely packed for easy passage of water and nutrients.
   • The cortex stores food and aids in the transportation of absorbed materials to the central vascular system.
3. Endodermis:
   • The innermost layer of the cortex is the endodermis.
   • It is characterized by the Casparian strip, a waterproof band that regulates the flow of substances into the vascular cylinder.
4. Pericycle:
   • Just inside the endodermis is the pericycle, a layer of cells from which lateral roots originate.
   • It plays a key role in the formation of branch roots.
5. Vascular Cylinder:
   • At the center of the root is the vascular cylinder or stele, consisting of xylem and phloem.
   • Xylem vessels are typically star-shaped and are responsible for the upward transport of water and minerals.
   • Phloem tissues are located between the xylem arms and are involved in the transport of food.
6. Pith:
   • In some dicot roots, a central pith may be present, though it is often absent or reduced.
   • When present, the pith is composed of parenchyma cells and serves as a storage area for nutrients.

Summary

The internal structure of a Dicot root consists of several layers, each with specific functions. These include the epidermis with root hairs, cortex, endodermis with the Casparian strip, pericycle, vascular cylinder with xylem and phloem, and sometimes a pith. This complex structure enables the dicot root to efficiently absorb nutrients, anchor the plant, and transport water and minerals.

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LAQ-6 : Describe the internal structure of a Monocot Root.

Introduction

The internal structure of a Monocot root is distinctively different from that of a Dicot root, reflecting adaptations to their specific growth conditions. Understanding this structure is crucial for studying monocotyledonous plants and their interactions with the environment.

Internal Structure of a Monocot Root

1. Epidermis:
   • The outermost layer of the monocot root is the epidermis.
   • It is composed of a single layer of cells and includes root hairs for effective absorption of water and minerals.
2. Cortex:
   • Beneath the epidermis lies the cortex, primarily made up of parenchyma cells.
   • These cells are loosely arranged to facilitate the easy movement of water and nutrients.
   • The cortex also serves as a storage region for starch and other nutrients.
3. Endodermis:
   • The innermost layer of the cortex is the endodermis.
   • It is characterized by the presence of the Casparian strip, which controls the selective uptake of minerals and water.
4. Pericycle:
   • Just inside the endodermis is the pericycle, from which lateral roots arise.
   • This layer is important for root branching and can sometimes contribute to secondary growth.
5. Vascular Bundle:
   • The central part of the monocot root is occupied by a vascular bundle, consisting of xylem and phloem.
   • The xylem typically forms a ring around the phloem, differing from the star-shaped arrangement seen in dicots.
6. Pith:
   • In the center of the vascular bundle is a large pith, made up of parenchyma cells.
   • The pith serves as a storage area and helps in the transport of water and solutes.

Summary

The internal structure of a Monocot root includes the epidermis with root hairs, a cortex for nutrient storage, the endodermis with the Casparian strip, the pericycle for root branching, a centrally located vascular bundle with xylem and phloem, and a prominent pith for storage and transport. This structure facilitates efficient water and nutrient absorption, storage, and transport within monocot plants.