Class 11 Biology Chapter 6 Anatomy of Flowering Plants

Key Concept: Real-world Application, Comparative Anatomy

c) Having more stomata on the abaxial than adaxial surface

[Solution Description] Monocot plants typically have stomata on both surfaces of their leaves (isobilateral), while dicot plants tend to have more stomata on the abaxial surface (dorsiventral). In arid environments where water conservation is crucial, having more stomata on the lower surface can reduce transpiration loss due to less direct exposure to sunlight and wind. Thus, for a monocot plant, evolving to have mainly abaxial stomata or adjusting leaf orientation to minimize upper stomatal exposure could help in such an environment.

Key Concept: Ground Tissue

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description] The assertion that monocot stems have a large parenchymatous ground tissue is true as it covers the fundamental structure of monocot stems. The reason provided, which indicates that this ground tissue aids in the storage and transport of nutrients, is also true and serves as a correct explanation for the assertion.

Key Concept: Location Recognition

a) Along the veins

[Solution Description] Bulliform cells are typically located along the veins of grass leaves. This strategic positioning helps in efficiently managing the opening and closing of the leaf surface to conserve water.

Key Concept: Epidermal Components

a) Guard cells

[Solution Description] Stomata are specialized epidermal cells that control gas exchange in plants. They open and close to regulate the passage of gases like oxygen, carbon dioxide, and water vapor.

Key Concept: Stomatal Apparatus

d) Trichomes

[Solution Description] The stomatal apparatus comprises guard cells, the stomatal pore, and usually involves subsidiary cells. Trichomes are separate epidermal structures not involved in forming the stomatal apparatus.

Key Concept: Functional Analysis

b) To prevent secondary growth

[Solution Description] Monocots possess closed vascular bundles because they lack cambium, which prevents secondary growth. This is an adaptation that suits their lifecycle, which typically does not require thickening of tissues through secondary growth.

Key Concept: Function Understanding

c) Cause leaves to curl to reduce water loss

[Solution Description] Bulliform cells in monocot leaves help conserve water by causing the leaves to curl. This curling reduces the surface area exposed to sunlight and air, thus minimizing water loss through evaporation.

Key Concept: Component Location

c) Between xylem and phloem

[Solution Description] In dicot vascular bundles, the cambium is situated between the xylem and phloem, allowing for secondary growth.

Key Concept: Evolutionary Adaptation, Advanced Comparative Analysis

a) Increased thickness of cell walls for enhanced rigidity

[Solution Description]

Collenchyma provides flexible support, making it ideal for adapting to dynamic forces like wind. In windy areas, having thicker, more robust collenchyma allows plants to bend without breaking, enhancing survival against strong winds.

Key Concept: Basic Structure

d) Pericycle

[Solution Description] Monocotyledonous roots include several key structures such as epidermis, cortex, endodermis, pericycle, vascular bundles, and a pith. We need to identify one that matches these features.

Key Concept: Detailed Functionality

c) Secrete substances

[Solution Description]

Trichomes are known for their role in reducing transpiration by creating a barrier to water loss. However, some trichomes have secretory functions. They can secrete substances such as essential oils or resins which may protect the plant from herbivores and pathogens.

Key Concept: Basic Structure

c) Absorption of water and minerals

[Solution Description] The epiblema is the outermost layer of the dicotyledonous root and its primary role is to facilitate water and mineral absorption from the soil through root hairs which are extensions of the epiblema.

Key Concept: Structural Adaptations

b) Thick cuticle

[Solution Description] A thick cuticle serves as a barrier against water loss by minimizing evaporation from the leaf surface.

Key Concept: Comparative Analysis

c) Collenchyma walls contain cellulose and pectin

[Solution Description]

Collenchyma cells have cell walls that are thickened with cellulose and pectin, making them flexible and supportive. In contrast, sclerenchyma cells have lignified walls that make them rigid and hard. This key difference reflects the different roles in plant structure: collenchyma provides flexibility and support, while sclerenchyma offers rigidity and strength.

Key Concept: Basic Structure

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

The mesophyll tissue in leaves is indeed situated between the upper (adaxial) and lower (abaxial) epidermis layers. This location allows it to play an essential role in photosynthesis due to the presence of chloroplasts within its parenchyma cells. Both statements are true, and the reason directly explains why the mesophyll is significant in this context because it highlights the function of the mesophyll related to its position within the leaf structure.

Key Concept: Environmental Interaction

c) By increasing the root’s surface contact with the surrounding soil

[Solution Description] The primary role of root hairs is to increase the surface area of roots, enabling more effective interaction with the soil. This facilitates better absorption of nutrients and water, enhancing the plant’s adaptation and survival in varying environmental conditions.

Key Concept: Palisade vs Spongy Parenchyma

b) It has large intercellular spaces

[Solution Description] Spongy parenchyma consists of oval or round cells that are loosely arranged with large spaces and air cavities between them. This structure facilitates efficient gas exchange within the leaf.

Key Concept: Vascular System Differences

c) Uniform-sized vascular bundles

[Solution Description] Monocot leaves typically have many small and uniform-sized vascular bundles scattered throughout the leaf. This is in contrast to dicots, which often have fewer, larger, and variably sized vascular bundles.

Key Concept: Secondary Growth

c) It increases thickness for structural support.

[Solution Description] Secondary growth allows dicotyledonous plants to increase in girth or thickness, which provides structural support and enables them to grow taller and withstand various environmental stresses. This growth is primarily facilitated by the activity of vascular cambium, producing secondary xylem (wood) and secondary phloem.

Key Concept: Stomatal Mechanism

a) Movement of water in guard cells

[Solution Description] The stomatal opening and closing are regulated by changes in the turgor pressure within the guard cells. When water enters the guard cells, they swell, causing the stoma to open. Conversely, when water exits, the guard cells become flaccid, leading to closure.

Key Concept: Function of Cuticle

c) By forming a protective barrier

[Solution Description] The cuticle acts as a barrier against environmental stress by minimizing water loss and providing a shield against external factors like UV radiation and pathogens.

Key Concept: Function Identification

a) Photosynthesis

[Solution Description] The primary function of the mesophyll, which contains chloroplasts, is to perform photosynthesis by capturing light energy and converting it into chemical energy.

Key Concept: Role in Cortex

c) They help in storage and conduction activities.

[Solution Description] Parenchyma cells located between xylem and phloem serve as conjunctive tissue, providing structural support and facilitating the transport of nutrients and water within the plant.

Key Concept: Location Identification

b) Hypodermis

[Solution Description]

Sclerenchyma is commonly located in the hypodermis of monocot stems and serves as bundle sheaths around vascular bundles, providing structural support.

Key Concept: Environmental Adaptation, Vascular System Efficiency

b) Both Assertion and Reason are true, but Reason is NOT the correct explanation of Assertion.

[Solution Description]

The assertion states that having stomata on both sides of the leaf aids in gas exchange, particularly under windy conditions which could cause more uniform gas exchange across the leaf surface compared to having them only on one side. This is true as it helps in balancing transpiration rates irrespective of wind direction.

The reason, regarding parallel venation optimizing nutrient and water transport, is also true; parallel venation ensures an even distribution of resources due to the homogeneity of vein sizes and spacing.

However, although both statements are true, the reason does not explain why stomata on both surfaces would specifically aid gas exchange under windy conditions. Instead, parallel venation is more related to nutrient distribution rather than directly impacting stomatal function.

Key Concept: Mesophyll Structure

c) Isobilateral leaves have undifferentiated mesophyll

[Solution Description] The mesophyll in an isobilateral leaf is not differentiated into palisade and spongy parenchyma, while in a dorsiventral leaf, it is differentiated.

Key Concept: Functional Adaptation, Complex Tissue Interaction

b) By curling the leaf surface inward to minimize water loss.

[Solution Description] Bulliform cells are large, thin-walled cells found on the upper epidermis of monocot leaves. During periods of water stress or drought, these cells lose turgor pressure and cause the leaf to fold or roll inward to reduce surface area exposed to sunlight, minimizing water loss through transpiration. This folding mechanism helps conserve water within the plant tissues by reducing evaporation.

Key Concept: Function of Stomata

c) Transpiration and gaseous exchange

[Solution Description] The stomatal apparatus, consisting of guard cells and subsidiary cells, primarily regulates transpiration and gaseous exchange in plants.

Key Concept: Vascular Bundle Types

b) Closed

[Solution Description] Monocotyledonous stems have closed vascular bundles. These lack cambium and do not allow secondary growth, which distinguishes them from the open vascular bundles of dicotyledonous plants.

Key Concept: Comparative Anatomy, Vascular Bundle Arrangement Analysis, Secondary Growth Potential

c) Dicot stems have vascular bundles arranged in a ring, allowing potential for secondary growth.

[Solution Description] In dicot stems, the vascular bundles are typically arranged in a ring formation, which allows them to have an open type of vascular bundle with cambium present. The presence of cambium facilitates secondary growth as it contributes to the increase in girth through the formation of secondary xylem and phloem.

Key Concept: Comparative Anatomy

c) Stomata are present on both surfaces in isobilateral leaves.

[Solution Description] In dorsiventral leaves, stomata are generally present only on the abaxial surface (underside), whereas in isobilateral leaves, stomata are present on both surfaces. This characteristic allows for more uniform gas exchange in isobilateral leaves.

Key Concept: Structural Differences

c) Open with cambium

[Solution Description] Dicot vascular bundles are characterized by being open, which means they have cambium. This allows for secondary growth in dicots. The arrangement of these bundles is typically in the form of a ring within the stem.

Key Concept: Function Analysis

c) Transport of water and minerals

[Solution Description] Xylem is primarily responsible for the transport of water and minerals from the roots to other parts of the plant. This transportation occurs through specialized cells known as tracheids and vessels that facilitate the movement of water due to capillary action and transpiration pull.

Key Concept: Pattern Recognition

b) Parallel

[Solution Description] In dry, arid environments, plants often have leaves with parallel venation commonly found in grasses. These structures facilitate efficient water transport and help minimize water loss due to their straightforward vein arrangement, which benefits quick uptake and reduces transpiration.

Key Concept: Comparative Analysis

c) Closed vascular bundles

[Solution Description] Monocot stems are characterized by having closed vascular bundles without cambium, whereas dicot stems have open vascular bundles with cambium present between xylem and phloem.

Key Concept: Tissue Types

d) Cortex

[Solution Description] The three main tissue systems in higher plants are the epidermal, ground, and vascular systems. There is no “Cortex” tissue system as a main classification.

Key Concept: Secondary Growth, Vascular Cambium Activity

a) Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.

[Solution Description]

Annual rings are formed due to variations in the activity of the vascular cambium during different seasons. In temperate regions, these variations are influenced by factors like temperature and moisture, leading to distinct bands representing periods of growth and dormancy. Thus, the assertion that secondary growth leads to annual rings is true, and the reason correctly explains this phenomena, as it highlights the environmental influence on cambial activity.

Key Concept: Function Identification

b) Water absorption

[Solution Description] Root hairs increase the surface area of roots, aiding in efficient absorption of water and minerals from the soil.

Key Concept: Stomatal Apparatus

a) Guard cells

[Solution Description] The guard cells are responsible for controlling the opening and closing of the stomatal pore through changes in their turgidity. When they swell due to water uptake, the stomatal pore opens; when they lose water, the pore closes.