Anatomy of Flowering PlantsClass 11 Biology NCERT Solutions
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Q1Exercises
Draw illustrations to bring out the anatomical difference between
(a)
Monocot root and Dicot root
(b)
Monocot stem and Dicot stem
Solution
While illustrations should be drawn based on Figures 6.3 and 6.4 from the textbook, the key anatomical differences are tabulated below.
(a) Differences between Monocot Root and Dicot Root
| Feature | Dicot Root | Monocot Root |
|---|---|---|
| Xylem Bundles | Usually two to four (diarch to tetrarch). | Usually more than six (polyarch). |
| Pith | Small or inconspicuous. | Large and well-developed. |
| Secondary Growth | Occurs due to the formation of a cambium ring. | Absent. |
| Cambium | Develops between xylem and phloem at a later stage. | Absent. |
| Cortex | Relatively narrow. | Wide. |
(b) Differences between Monocot Stem and Dicot Stem
| Feature | Dicot Stem | Monocot Stem |
|---|---|---|
| Vascular Bundles (Arrangement) | Arranged in a distinct ring. | Scattered throughout the ground tissue. |
| Vascular Bundles (Type) | Conjoint, collateral, and open (cambium is present). | Conjoint, collateral, and closed (cambium is absent). |
| Ground Tissue | Differentiated into cortex, endodermis, pericycle, medullary rays, and pith. | Undifferentiated parenchymatous ground tissue. |
| Hypodermis | Collenchymatous. | Sclerenchymatous. |
| Bundle Sheath | Absent. Pericycle is present as sclerenchymatous patches (bundle cap). | Each vascular bundle is surrounded by a sclerenchymatous bundle sheath. |
| Phloem Parenchyma | Present. | Absent. |
| Secondary Growth | Present. | Absent. |
| Pith | Present and well-developed. | Absent. |
Q2Exercises
Cut a transverse section of young stem of a plant from your school garden and observe it under the microscope. How would you ascertain whether it is a monocot stem or a dicot stem? Give reasons.
Solution
To ascertain whether the young stem is a monocot or a dicot, I would observe the following anatomical features in its transverse section under a microscope:
-
Arrangement of Vascular Bundles:
- Dicot Stem: The vascular bundles are arranged in a characteristic ring.
- Monocot Stem: The vascular bundles are scattered throughout the ground tissue.
-
Type of Vascular Bundles:
- Dicot Stem: The vascular bundles are 'open', meaning a strip of cambium is present between the xylem and phloem. This allows for secondary growth.
- Monocot Stem: The vascular bundles are 'closed', meaning cambium is absent between the xylem and phloem.
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Ground Tissue Differentiation:
- Dicot Stem: The ground tissue is clearly differentiated into an outer cortex, endodermis, pericycle, medullary rays, and a central pith.
- Monocot Stem: There is no such differentiation; it consists of a large, uniform parenchymatous ground tissue.
-
Hypodermis:
- Dicot Stem: The hypodermis (the layer just below the epidermis) is made of collenchyma cells, which provide flexible support.
- Monocot Stem: The hypodermis is made of sclerenchyma cells, which provide rigid support.
Based on the presence of vascular bundles in a ring and differentiated ground tissue, I would identify it as a dicot stem. Conversely, if the vascular bundles are scattered and the ground tissue is undifferentiated, it would be a monocot stem.
Q3Exercises
The transverse section of a plant material shows the following anatomical features - (a) the vascular bundles are conjoint, scattered and surrounded by a sclerenchymatous bundle sheaths. (b) phloem parenchyma is absent. What will you identify it as?
Solution
Based on the given anatomical features, the plant material is identified as a Monocotyledonous Stem.
Reasons:
- Scattered Vascular Bundles: The arrangement of vascular bundles in a scattered manner throughout the ground tissue is a characteristic feature of monocot stems. Dicot stems have vascular bundles arranged in a ring.
- Sclerenchymatous Bundle Sheath: Each vascular bundle being surrounded by a sclerenchymatous bundle sheath is a distinctive feature of monocot stems.
- Absence of Phloem Parenchyma: Phloem parenchyma is characteristically absent in the vascular bundles of monocot stems.
All these features collectively confirm the identity of the plant material as a monocot stem.
Q4Exercises
What is stomatal apparatus? Explain the structure of stomata with a labelled diagram.
Solution
Stomatal Apparatus:
The stomatal apparatus consists of the stomatal aperture (pore), the two guard cells that surround it, and the surrounding subsidiary cells.
Structure of Stomata:
Stomata are tiny pores present in the epidermis of leaves, and sometimes on young stems. They are essential for regulating transpiration and gaseous exchange.
-
Stomatal Pore: This is the actual opening through which gas exchange and water vapour release occur.
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Guard Cells: Each stomatal pore is enclosed by two specialized cells called guard cells.
- Shape: In dicots, the guard cells are typically bean-shaped. In grasses (monocots), they are dumb-bell shaped.
- Cell Walls: The outer walls of the guard cells (away from the pore) are thin and flexible, while the inner walls (towards the pore) are highly thickened and inelastic. This differential thickening facilitates the opening and closing of the pore.
- Chloroplasts: Guard cells are the only epidermal cells that contain chloroplasts and can perform photosynthesis.
-
Subsidiary Cells: These are specialized epidermal cells that are located adjacent to the guard cells. They are distinct in shape and size from other epidermal cells and support the function of the guard cells.
The opening and closing of the stomatal pore are regulated by the turgidity of the guard cells.
(A labelled diagram of a stomatal apparatus, as shown in Figure 6.1 of the textbook, should be drawn, clearly labelling the stomatal pore, guard cells, chloroplasts, and subsidiary cells.)
Q5Exercises
Name the three basic tissue systems in the flowering plants. Give the tissue names under each system.
Solution
On the basis of their structure and location in the plant body, there are three basic tissue systems in flowering plants. These are:
-
The Epidermal Tissue System: This system forms the outermost covering of the plant body.
- Tissues/Components: It comprises epidermal cells, stomata, and epidermal appendages (which include root hairs and trichomes).
-
The Ground or Fundamental Tissue System: This system constitutes all tissues of the plant body except for the epidermis and vascular bundles.
- Tissues/Components: It consists of simple tissues such as parenchyma, collenchyma, and sclerenchyma. These tissues form the cortex, pericycle, pith, and medullary rays.
-
The Vascular or Conducting Tissue System: This system is responsible for the transport of water, minerals, and food materials.
- Tissues/Components: It consists of complex tissues, the xylem and the phloem, which are organized into vascular bundles.
Q6Exercises
How is the study of plant anatomy useful to us?
Solution
The study of plant anatomy, which is the study of the internal structure of plants, is useful in several ways:
-
Understanding Plant Function: Anatomy helps us understand how different tissues and organs are structured to perform specific functions like photosynthesis, transport, storage, and support. For example, the structure of xylem relates to its function of water conduction.
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Taxonomic Classification: Anatomical features are crucial for distinguishing between different plant groups. For instance, the arrangement of vascular bundles helps differentiate between monocots and dicots.
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Understanding Adaptations: It reveals how plants adapt their internal structures to survive in diverse environments. For example, the presence of a thick cuticle in xerophytes to prevent water loss or the presence of aerenchyma in aquatic plants for buoyancy.
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Crop Improvement: Knowledge of plant anatomy helps plant breeders understand the structural basis of traits like drought resistance, pest resistance, and mechanical strength, which aids in developing improved crop varieties.
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Economic Applications: In fields like forestry, anatomy is used for wood identification. In pharmacognosy, it is used to identify and check the purity of medicinal plants by studying their internal cellular structure.
Q7Exercises
Describe the internal structure of a dorsiventral leaf with the help of labelled diagrams.
Solution
A dorsiventral leaf is typical of dicotyledonous plants. A vertical section through the lamina reveals three main parts: the epidermis, the mesophyll, and the vascular system.
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Epidermis:
- It forms the outermost protective layer on both surfaces of the leaf.
- Adaxial Epidermis: This is the upper surface of the leaf. It is a single layer of cells covered by a conspicuous, waxy cuticle to prevent water loss. Stomata are generally absent or few in number.
- Abaxial Epidermis: This is the lower surface of the leaf. It is also covered by a cuticle but generally bears a larger number of stomata compared to the adaxial epidermis. The stomata facilitate gaseous exchange and transpiration.
-
Mesophyll:
- This is the ground tissue located between the adaxial and abaxial epidermis. It is made of parenchymatous cells containing chloroplasts and is the primary site of photosynthesis.
- It is differentiated into two distinct regions:
- Palisade Parenchyma: Located just below the adaxial epidermis, it consists of one or more layers of elongated, compactly arranged cells. These cells are rich in chloroplasts and are oriented vertically, which maximizes light absorption.
- Spongy Parenchyma: Situated below the palisade layer and extending to the abaxial epidermis, it consists of oval or irregularly shaped cells that are loosely arranged. There are numerous large intercellular spaces and air cavities which facilitate the diffusion of gases to and from the stomata.
-
Vascular System:
- The vascular system is composed of vascular bundles, which are seen in the veins and the midrib.
- Arrangement: The vascular bundles are of varying sizes depending on the size of the veins, which is characteristic of the reticulate venation in dicot leaves.
- Structure: Each vascular bundle is conjoint and collateral, and is surrounded by a layer of thick-walled cells called the bundle sheath. The xylem is located towards the adaxial (upper) epidermis, and the phloem is located towards the abaxial (lower) epidermis.
(A labelled diagram of the T.S. of a dorsiventral leaf, as shown in Figure 6.5 (a) of the textbook, should be drawn, showing the cuticle, adaxial epidermis, palisade mesophyll, spongy mesophyll, air cavity, stomata, abaxial epidermis, bundle sheath, xylem, and phloem.)