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

4 Marks

SAQ-1 : State the location and function of different types of meristems.

Introduction

Meristems are regions in plants where active cell division occurs, leading to growth. There are different types of meristems located in various parts of a plant, each with specific functions. Understanding the location and function of these meristems is crucial for studying plant growth and development.

Types of Meristems and Their Functions

1. Apical Meristems:
   • Location: Apical meristems are found at the tips of roots and shoots.
   • Function: They are responsible for primary growth, which leads to an increase in the length of the plant. This growth enables the plant to access new resources – light in shoots and nutrients in roots.
2. Lateral Meristems:
   • Location: Lateral meristems are located along the sides of roots and stems.
   • Function: These meristems are responsible for secondary growth, contributing to an increase in the girth or thickness of the plant. Lateral meristems include the vascular cambium (producing new vascular tissues) and the cork cambium (producing cork cells for protection and water retention).
3. Intercalary Meristems:
   • Location: Intercalary meristems are typically found at the base of leaves or internodes (the space between two nodes) in grasses and other monocots.
   • Function: They contribute to the regrowth of grasses after being grazed or mowed. Intercalary meristems aid in the plant’s ability to continue growing even after losing a part of its shoot system.
4. Root Apical Meristem:
   • Location: Specifically located at the tip of the root.
   • Function: The root apical meristem is essential for the growth of new cells in the root, enabling the root to penetrate deeper into the soil for water and nutrient absorption.

Summary

Meristems play a pivotal role in plant growth and development. Apical meristems are involved in primary growth, lateral meristems in secondary growth, and intercalary meristems in the regrowth of certain plants. Additionally, the root apical meristem is crucial for root growth. Each type of meristem contributes significantly to the plant’s ability to grow, adapt, and survive in its environment.

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SAQ-2 : What is periderm? How does periderm formation take place in the dicot stems?

Introduction

Periderm is a protective tissue that forms in plants, particularly in dicot stems, as part of secondary growth. It replaces the epidermis in mature stems and roots to provide protection and prevent water loss. Understanding the formation of periderm is key to comprehending how plants adapt to their environment as they grow.

Periderm Formation in Dicot Stems

1. Initiation of Periderm:
   • Location: Periderm formation begins in the cork cambium (phellogen), which is a layer of meristematic cells.
   • Function: The cork cambium develops from the parenchyma cells of the epidermis or the outer cortical layer in response to internal and external factors like injury, aging, or environmental conditions.
2. Development of Cork Cambium:
   • Activity: The cork cambium actively divides to produce cork cells (phellem) outwardly and phelloderm cells inwardly.
   • Cork Cells (Phellem): These cells become suberized (impregnated with suberin) and die, forming a tough and waterproof layer.
   • Phelloderm: It is a layer of living parenchyma cells produced inwardly by the cork cambium, contributing to the thickness of the periderm.
3. Replacement of Epidermis:
   • As the cork cambium produces more cells, the outer tissues including the original epidermis are eventually sloughed off.
   • The periderm, consisting of the cork cambium, cork cells, and phelloderm, takes over the protective role of the epidermis.
4. Role in Secondary Growth:
   • The formation of periderm is a part of secondary growth in dicot stems, which involves the increase in girth of the stem.
   • This growth is particularly important for woody plants, where the periderm forms the outer bark.

Summary

Periderm is a crucial protective tissue in dicot stems, formed during secondary growth. It originates from the cork cambium, which produces cork cells and phelloderm. The periderm replaces the epidermis in mature stems, providing protection and reducing water loss. Its formation is essential for the longevity and survival of woody plants, helping them to adapt to various environmental stresses.

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SAQ-3 : A transverse section of the trunk of a tree shows concentric rings which are known as annual rings. How are these rings formed? What is the significance of these rings:

Introduction

Annual rings in the trunk of a tree, visible in a transverse section, are key indicators of the tree’s age and the environmental conditions it has experienced. These rings are formed as a result of periodic growth patterns and hold significant importance in dendrochronology, the study of tree rings.

Formation of Annual Rings

1. Growth Patterns:
   • Seasonal Variation: Annual rings are formed due to seasonal variations in growth. In temperate regions, a tree grows rapidly in the spring and summer (resulting in wider, lighter-colored rings) and slows down in the autumn and winter (leading to narrower, darker rings).
   • Spring Wood and Summer Wood: The wider rings formed during the growth season are known as spring wood or earlywood, while the narrower rings formed later are referred to as summer wood or latewood.
2. Vascular Cambium Activity:
   • The rings are a result of the changes in the activity of the vascular cambium, a layer of meristematic cells.
   • During the growing season, the cambium is active and produces a large number of xylem cells, which are larger and have thinner walls. In contrast, during the dormant season, it produces fewer, smaller xylem cells with thicker walls.

Significance of Annual Rings

1. Determining Age: By counting the number of annual rings, the age of the tree can be determined, which is a crucial aspect in forestry, ecology, and historical studies.
2. Environmental Indicators: The width and density of the rings can indicate environmental conditions, such as climate and weather patterns, during the tree’s growth. For instance, wider rings usually signify favorable growing conditions, like adequate rainfall and optimal temperatures, while narrower rings can indicate drought or other stress factors.
3. Historical Climate Data: These rings serve as valuable records for reconstructing past climate conditions, aiding scientists in understanding historical climate changes.
4. Health and Growth Patterns: The study of annual rings can provide insights into the health and growth patterns of trees, useful in forest management and conservation efforts.

Summary

Annual rings in trees are formed due to the seasonal variation in growth, marked by alternating patterns of spring wood and summer wood. The study of these rings, known as dendrochronology, allows for the determination of the tree’s age, assessment of past environmental conditions, and understanding of climate change over time. These rings serve as crucial data points for ecological and historical studies.

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SAQ-4 : What is the difference between lenticels and stomata?

Introduction

Lenticels and stomata are specialized structures in plants that facilitate gas exchange. While both play essential roles in the exchange of gases, they have distinct locations and functions. Understanding these differences is crucial for students preparing for their Class 12 Board Exam.

Differences between Lenticels and Stomata

1. Lenticels:
   • Location: Lenticels are found on the surface of old stems and old aerial roots of plants.
   • Structure: Lenticels consist of closely arranged parenchymatous cells.
   • Function: The primary function of lenticels is to allow the exchange of gases between the external atmosphere and the internal tissues of woody organs, such as stems and roots.
   • Opening and Closing: Lenticels do not have any specialized opening and closing mechanisms.
   • Photosynthesis: Lenticels do not participate in photosynthesis; they are not involved in the synthesis of food.
2. Stomata:
   • Location: Stomata are mainly found on the leaves and young stems of plants.
   • Structure: Each stoma (singular of stomata) consists of two guard cells that contain chloroplasts.
   • Function: Stomata serve as openings that facilitate both transpiration (the loss of water vapor from leaves) and respiration in plants.
   • Opening and Closing: Stomata have specialized guard cells that regulate their opening and closing based on factors like light, humidity, and CO2 levels.
   • Photosynthesis: Unlike lenticels, the guard cells of stomata can conduct photosynthesis, contributing to the production of food in plants.

Summary

Lenticels are found on the surface of old stems and aerial roots and are involved in gas exchange between the atmosphere and internal tissues. They lack specialized opening and closing mechanisms and do not participate in photosynthesis. On the other hand, stomata are present on leaves and young stems, with each stoma guarded by two specialized cells that control their opening and closing. Stomata play a crucial role in transpiration, respiration, and photosynthesis in plants. Understanding the differences between lenticels and stomata is essential for a comprehensive understanding of plant physiology.

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SAQ-5 : Cork cambium forms tissues that form the cork. Do you agree with this statement? Explain.

Introduction

The statement that cork cambium forms tissues that form the cork is accurate. Understanding the role of cork cambium, also known as phellogen, is essential in botany, particularly in the study of secondary growth in plants.

Role and Function of Cork Cambium

1. Formation of Cork Cambium:
   • Origin: Cork cambium originates from the parenchyma cells located just beneath the epidermis or from the outer cortical cells.
   • Location: It is found in the bark of woody plants, particularly dicots.
2. Activity of Cork Cambium:
   • Cell Division: Cork cambium is a meristematic tissue that actively divides to produce cork cells (phellem) outwardly and occasionally phelloderm cells inwardly.
   • Suberization: The newly formed cork cells undergo suberization, a process where their walls are impregnated with suberin, making them waterproof and resistant to microbial attack.
3. Function of Cork:
   • Protection: The cork layer formed by the cork cambium serves as a protective barrier against physical damage and pathogen entry.
   • Prevention of Water Loss: Due to its suberized cell walls, cork is effective in reducing water loss from the plant.
   • Insulation: Cork provides insulation against extreme temperatures and reduces the impact of environmental stressors on the plant.

Summary

Cork cambium is crucial for the formation of cork in woody plants. Through its meristematic activity, it produces cork cells that are suberized and form an essential protective layer. This layer not only protects the plant from external damage and water loss but also provides insulation. The role of cork cambium in forming cork is a key aspect of secondary growth in plants and is fundamental to their survival and longevity.