Q: Q11. Define the following terms: (a) stele (b) vascular bundle (c) conjoint (d) radial (e) open (f) closed

Here are the definitions for the given terms:\n\n**(a) Stele:**\nThe stele is the central core of the stem and root of a vascular plant, consisting of the vascular tissue (xylem and phloem) along with the pericycle and pith (if present). It represents the primary vascular cylinder and is surrounded by the endodermis.\n\n**(b) Vascular Bundle:**\nA vascular bundle is a strand of conducting tissues (xylem and phloem) found in vascular plants. Xylem is responsible for water and mineral transport, while phloem transports food (sugars). These bundles are typically surrounded by a bundle sheath and are organized in various patterns within the plant body.\n\n**(c) Conjoint:**\nConjoint vascular bundles are those in which the xylem and phloem are situated on the same radius. They are typically found in stems and leaves. In these bundles, phloem is usually located towards the periphery and xylem towards the center.\n\n**(d) Radial:**\nRadial vascular bundles are characterized by the arrangement where xylem and phloem are arranged alternately on different radii. This type of vascular bundle arrangement is characteristic of roots, where xylem forms distinct patches alternating with phloem patches.\n\n**(e) Open:**\nAn open vascular bundle is a type of vascular bundle where a strip of cambium (a meristematic tissue) is present between the xylem and phloem. The presence of cambium allows for secondary growth, leading to an increase in the girth of the plant organ (e.g., dicot stems).\n\n**(f) Closed:**\nA closed vascular bundle is a type of vascular bundle in which cambium is absent between the xylem and phloem. Due to the lack of cambium, these bundles do not undergo secondary growth, and thus, the plant organ (e.g., monocot stems and leaves) does not increase in girth.

Question 1

Q1. State the location and function of different types of meristems.

Accepted Answer

Meristems are regions in plants where active cell division occurs, leading to growth. These cells are undifferentiated and retain the ability to divide throughout the plant's life. Based on their location, meristems are primarily classified into three types:

### 1. Apical Meristem

*   **Location:** Present at the tips of roots and shoots (apices). The shoot apical meristem is responsible for the growth of the stem and leaves, while the root apical meristem is responsible for the growth of the root.
*   **Function:** Responsible for primary growth of the plant, i.e., increase in length of the plant body. They produce new cells that differentiate into various primary tissues (epidermis, cortex, vascular tissues).

### 2. Intercalary Meristem

*   **Location:** Found at the base of leaves or internodes, especially in grasses and other monocots. They are part of the primary meristem that becomes separated from the apical meristem during growth.
*   **Function:** Responsible for the elongation of organs like leaves and internodes. They help in regenerating parts removed by grazing herbivores. Like apical meristems, they contribute to primary growth.

### 3. Lateral Meristem

*   **Location:** Occur along the lateral sides of the stem and root, parallel to the longitudinal axis of the plant. They are typically found in dicotyledonous plants and gymnosperms.
*   **Function:** Responsible for secondary growth, which is the increase in girth or diameter of the plant organs (stem and root). There are two main types of lateral meristems:
    *   **Vascular Cambium:** Located between the xylem and phloem, it produces secondary xylem (wood) towards the inside and secondary phloem towards the outside.
    *   **Cork Cambium (Phellogen):** Located in the cortex region, it produces cork (phellem) towards the outside and secondary cortex (phelloderm) towards the inside, forming the periderm (bark).

In summary, apical and intercalary meristems contribute to primary growth (increase in length), while lateral meristems contribute to secondary growth (increase in girth).

Question 2

Q2. Cacti have a thick cuticle, sunken stomata, and are succulent. Correlate these features with the habitat of the plant.

Accepted Answer

Cacti are plants that thrive in arid or desert environments, which are characterized by extreme water scarcity, high temperatures, and intense sunlight. These plants are known as xerophytes, and their anatomical features are specialized adaptations to minimize water loss and store water.

Here's how the mentioned features correlate with their desert habitat:

1.  **Thick Cuticle:** The cuticle is a waxy, protective layer covering the epidermis of leaves and stems. In cacti, this layer is exceptionally thick. Its primary function is to reduce transpiration (loss of water vapor from plant surfaces) by acting as a barrier to water evaporation. A thick cuticle significantly decreases the rate at which water escapes from the plant's surface, which is crucial in a dry environment.

2.  **Sunken Stomata:** Stomata are pores on the plant surface through which gas exchange occurs, but they are also the primary sites of water loss through transpiration. In cacti, stomata are located in pits or depressions below the epidermal surface (sunken stomata). This arrangement creates a localized humid microenvironment within the pit, reducing the water potential gradient between the inside of the leaf and the outside air. Consequently, the rate of water diffusion out of the stomata is significantly slowed down, conserving water.

3.  **Succulence:** Cacti are succulent plants, meaning they have fleshy stems or leaves that are adapted for water storage. Their stems are typically thick and contain large parenchyma cells with big vacuoles that can store significant amounts of water. This stored water acts as a reserve, allowing the plant to survive long periods without rainfall. The succulent nature also often results in a reduced surface area to volume ratio, further minimizing water loss.

All these features collectively enable cacti to efficiently conserve water, survive prolonged droughts, and thrive in their challenging desert habitat.

Question 3

Q3. Define a tissue.

Accepted Answer

In biology, a **tissue** is defined as a group of cells that are similar in origin, structure, and function, working together to perform a specific task within an organism.

Key characteristics of a tissue:
*   **Common Origin:** All cells within a tissue typically arise from the same embryonic or meristematic source.
*   **Similar Structure:** The cells often have a similar morphology and arrangement, though some tissues may contain different cell types working in coordination.
*   **Coordinated Function:** The cells cooperate to carry out a particular physiological process, contributing to the overall functioning of the organ or organism.

For example, in plants, xylem is a complex tissue composed of different cell types (tracheids, vessels, xylem parenchyma, xylem fibers) that collectively function in water and mineral transport. In animals, muscle tissue is composed of muscle cells that contract to produce movement.

Question 4

Q4. Differentiate between:
    (a) Monocot root and Dicot root
    (b) Monocot stem and Dicot stem

Accepted Answer

### (a) Differentiation between Monocot Root and Dicot Root

### (b) Differentiation between Monocot Stem and Dicot Stem

These anatomical differences are crucial for identifying monocots and dicots based on their internal structure.

Question 5

Q5. Write a note on the anatomical adaptations in xerophytes.

Accepted Answer

Xerophytes are plants adapted to survive in arid or semi-arid environments where water is scarce, such as deserts, rocky terrains, or saline soils. Their anatomical features are primarily geared towards minimizing water loss (transpiration) and maximizing water absorption and storage.

Here are the key anatomical adaptations found in xerophytes:

### 1. Epidermal Adaptations
*   **Thick Cuticle:** A prominent, waxy layer covering the epidermis of leaves and stems. This significantly reduces water evaporation from the plant surface.
*   **Sunken Stomata:** Stomata are located in pits or depressions, often lined with hairs, which create a humid microenvironment, reducing the water potential gradient and thus slowing down transpiration. Examples include *Nerium*.
*   **Hairy Leaves (Trichomes):** Presence of dense hairs on the leaf surface. These trichomes trap a layer of moist air, reducing air movement over the stomata and reflecting sunlight, thereby lowering leaf temperature and transpiration.
*   **Multiple Epidermis:** Some xerophytes have several layers of epidermal cells (e.g., *Nerium* leaf), providing extra protection and reducing water loss.

### 2. Mesophyll Adaptations
*   **Compact Mesophyll:** The mesophyll cells (palisade and spongy parenchyma) are often tightly packed, reducing intercellular air spaces. This decreases the internal surface area for evaporation and limits water loss from the mesophyll cells.
*   **Well-developed Palisade Tissue:** The palisade parenchyma is often multi-layered and well-developed, containing numerous chloroplasts for efficient photosynthesis, even under intense light.

### 3. Vascular Tissue Adaptations
*   **Well-developed Vascular Tissue:** Xerophytes typically have a well-developed vascular system (xylem and phloem) to efficiently transport the limited absorbed water to all parts of the plant and to distribute photosynthetic products. This ensures rapid water conduction when available.

### 4. Mechanical Tissue Adaptations
*   **Well-developed Sclerenchyma:** Presence of abundant sclerenchymatous tissues (fibers and sclereids) provides mechanical support and rigidity to the plant, helping to prevent wilting under water stress.

### 5. Water Storage Tissues (Succulence)
*   **Succulent Organs:** Many xerophytes, like cacti and aloes, have fleshy stems or leaves that are specialized for storing large quantities of water in large parenchyma cells with mucilage. This stored water acts as a reserve during prolonged dry periods.

### 6. Reduced Leaf Surface Area
*   **Reduced Leaves/Spines:** Leaves are often reduced in size, modified into spines (e.g., cacti), or even absent. This significantly reduces the surface area available for transpiration. Stems often take over the photosynthetic function.

These anatomical features, in conjunction with physiological adaptations (like CAM photosynthesis) and morphological adaptations (like deep root systems), enable xerophytes to survive and flourish in harsh, water-limited environments.

Question 6

Q6. Give the anatomical differences between:
(a) Monocot root and Dicot root
(b) Monocot stem and Dicot stem

Accepted Answer

The anatomical differences between monocot and dicot roots, and monocot and dicot stems are significant and are key to understanding their physiological functions and adaptations.

**(a) Anatomical Differences between Monocot Root and Dicot Root**

| Feature             | Dicot Root                               | Monocot Root                               |
|---------------------|------------------------------------------|--------------------------------------------|
| **Shape**           | Generally cylindrical                    | Generally cylindrical                      |
| **Cortex**          | Relatively narrow                        | Relatively broad                           |
| **Endodermis**      | Prominent, barrel-shaped cells, Casparian strips present. Passage cells may be present. | Prominent, barrel-shaped cells, Casparian strips present. Passage cells are common. |
| **Pericycle**       | Gives rise to lateral roots and vascular cambium (during secondary growth). | Gives rise to lateral roots only.          |\ | **Vascular Bundles**| Typically 2-6 (diarch to hexarch) xylem bundles, arranged radially. | Usually more than 6 (polyarch) xylem bundles, arranged radially. |\ | **Cambium**         | Present, forms a complete ring during secondary growth. | Absent, no secondary growth.               |\ | **Pith**            | Small or absent                          | Large and well-developed                   |\ | **Secondary Growth**| Present                                  | Absent                                     |\

**(b) Anatomical Differences between Monocot Stem and Dicot Stem**

| Feature             | Dicot Stem                               | Monocot Stem                               |
|---------------------|------------------------------------------|--------------------------------------------|\ | **Epidermis**       | Single layered, covered with cuticle, stomata present. | Single layered, covered with cuticle, stomata present. |\ | **Hypodermis**      | Collenchymatous                          | Sclerenchymatous                           |\ | **Ground Tissue**   | Differentiated into cortex, endodermis, pericycle, and pith. | Undifferentiated, a continuous mass of parenchymatous cells. |\ | **Vascular Bundles**| Arranged in a ring, conjoint, collateral, and open (with cambium). | Scattered, conjoint, collateral, and closed (without cambium). |\ | **Bundle Sheath**   | Generally absent                         | Present, sclerenchymatous                  |\ | **Vascular Bundle Size** | Uniform in size                          | Peripheral bundles are smaller, central ones are larger. |\ | **Pith**            | Large and well-developed                 | Absent, ground tissue is continuous.       |\ | **Medullary Rays**  | Present, parenchymatous                  | Absent                                     |\ | **Secondary Growth**| Present                                  | Absent                                     |

These anatomical distinctions are crucial for understanding the evolutionary adaptations and functional specializations of monocotyledonous and dicotyledonous plants.

Question 7

Q7. Write short notes on:
(a) Periderm
(b) Lenticels

Accepted Answer

**(a) Periderm**

Periderm is a protective tissue that replaces the epidermis in older stems and roots of dicotyledonous plants and gymnosperms, as they undergo secondary growth. It is formed by the activity of the cork cambium (phellogen).

**Components of Periderm:**
1.  **Phellogen (Cork Cambium):** A secondary lateral meristem that arises typically in the cortex region. It is a few layers thick, narrow, thin-walled, and rectangular cells.
2.  **Phellem (Cork):** Cells cut off by the phellogen towards the outside. These cells are dead, compactly arranged, and suberized (impregnated with suberin), making them impermeable to water and gases. Cork provides protection against mechanical injury, desiccation, and pathogen invasion.
3.  **Phelloderm (Secondary Cortex):** Cells cut off by the phellogen towards the inside. These cells are parenchymatous and living, and may store food.

Together, phellogen, phellem, and phelloderm constitute the periderm. Its primary function is to provide protection to the inner tissues from water loss, mechanical damage, and microbial attacks.

**(b) Lenticels**

Lenticels are lens-shaped, raised openings on the surface of the periderm, typically found on the bark of woody stems and some fruits. They are formed due to the activity of the cork cambium (phellogen) at specific regions.

**Formation and Structure:**
At certain points, the phellogen cuts off parenchymatous cells instead of cork cells, towards the outer side. These parenchymatous cells are loosely arranged and form a mass called **complementary cells**. The epidermis ruptures due to the pressure exerted by these cells, forming a lens-shaped opening known as a lenticel. The complementary cells have numerous intercellular spaces.

**Function:**
The primary function of lenticels is to facilitate gaseous exchange between the internal living tissues of the stem (or root) and the outer atmosphere. Since the cork layer (phellem) is impermeable to gases, lenticels provide the necessary pores for respiration and transpiration, compensating for the stomata which are lost with the shedding of the epidermis.

Question 8

Q8. Differentiate between the following:
(a) Stele and vascular bundle
(b) Open vascular bundles and closed vascular bundles
(c) Albuminous cells and sieve tube members
(d) Apical

Accepted Answer

Here are the differentiations between the given pairs:

**(a) Stele and Vascular Bundle**

| Feature             | Stele                                    | Vascular Bundle                          |\ |---------------------|------------------------------------------|------------------------------------------|\ | **Definition**      | The central vascular cylinder of a plant stem or root, consisting of pericycle, vascular tissues (xylem and phloem), and pith (if present). | A strand of conducting tissues (xylem and phloem) within the plant. |\ | **Composition**     | Includes pericycle, vascular bundles, and pith. | Composed of xylem and phloem, and sometimes cambium. |\ | **Scope**           | A broader anatomical region, encompassing multiple vascular bundles and associated tissues. | A component part of the stele (or ground tissue in monocots). |\ | **Location**        | Occupies the central part of the stem or root, internal to the endodermis. | Located within the stele (in dicots) or scattered in the ground tissue (in monocots). |\ | **Function**        | Overall transport and structural support for the central axis. | Specific transport of water, minerals (xylem), and food (phloem). |\

**(b) Open Vascular Bundles and Closed Vascular Bundles**

| Feature             | Open Vascular Bundles                    | Closed Vascular Bundles                  |\ |---------------------|------------------------------------------|------------------------------------------|\ | **Cambium**         | Possess a strip of vascular cambium between xylem and phloem. | Lack vascular cambium between xylem and phloem. |\ | **Secondary Growth**| Capable of secondary growth (increase in girth) due to the activity of cambium. | Incapable of secondary growth.           |\ | **Occurrence**      | Characteristic of dicot stems and gymnosperms. | Characteristic of monocot stems.         |\ | **Example**         | Sunflower stem, Pea stem                 | Maize stem, Wheat stem                   |\

**(c) Albuminous Cells and Sieve Tube Members**

| Feature             | Albuminous Cells                         | Sieve Tube Members                       |\ |---------------------|------------------------------------------|------------------------------------------|\ | **Association**     | Associated with sieve cells (in gymnosperms and some lower vascular plants). | Associated with companion cells (in angiosperms). |\ | **Nucleus**         | Possess a nucleus.                       | Enucleated (lack a nucleus at maturity). |\ | **Cytoplasm**       | Dense cytoplasm.                         | Parietal cytoplasm.                      |\ | **Function**        | Help in loading and unloading of sugars into and from the sieve cells. | Primary conducting elements for food (sugars) transport in phloem. |\ | **Occurrence**      | Found in gymnosperms and some pteridophytes. | Found exclusively in angiosperms.        |\

**(d) Apical Meristem and Intercalary Meristem**

| Feature             | Apical Meristem                          | Intercalary Meristem                     |\ |---------------------|------------------------------------------|------------------------------------------|\ | **Location**        | Present at the tips of roots and shoots. | Located between mature tissues, often at the base of internodes or leaf bases. |\ | **Growth Type**     | Responsible for primary growth, leading to increase in length of the plant. | Contributes to the elongation of organs like leaves and internodes, especially in grasses. |\ | **Persistence**     | Persists throughout the life of the plant at the apices. | Often temporary; may become permanent tissue or get consumed during growth. |\ | **Origin**          | Derived from the embryonic meristem.     | A portion of the apical meristem that gets separated during primary growth. |\ | **Example**         | Root apex, Shoot apex                    | Base of grass leaves, internodes of mint. |

Question 9

Q9. Cut a transverse section of young stem and observe it under a microscope. Name the various tissues present in the transverse section and arrange them in order of their occurrence f

Accepted Answer

When a transverse section (TS) of a young dicot stem is observed under a microscope, several distinct tissues can be identified, arranged concentrically from the periphery to the centre. These tissues collectively form the primary structure of the stem.

### Tissues Present in a Transverse Section of Young Dicot Stem:

1.  **Epidermis:** This is the outermost protective layer of the stem, composed of a single layer of parenchymatous cells. It is covered by a thin cuticle to prevent water loss. Stomata may be present, and sometimes epidermal outgrowths called trichomes are found.

2.  **Cortex:** Located just beneath the epidermis, the cortex is a multi-layered region composed of several types of tissues:
    *   **Hypodermis:** The layer immediately below the epidermis, typically consisting of 2-3 layers of collenchymatous cells in dicot stems. It provides mechanical support to the young stem.
    *   **General Cortex:** Located below the hypodermis, it consists of several layers of thin-walled parenchymatous cells with intercellular spaces. These cells store food substances.
    *   **Endodermis:** The innermost layer of the cortex, often referred to as the starch sheath because its cells contain abundant starch grains. It is a single layer of barrel-shaped cells.

3.  **Pericycle:** Situated just inner to the endodermis and above the phloem, the pericycle is composed of sclerenchymatous cells (forming a semi-lunar cap over vascular bundles) and parenchymatous cells. It provides mechanical support and may be involved in the formation of secondary meristems.

4.  **Vascular Bundles:** These are arranged in a ring, typically conjoint, collateral, and open (meaning cambium is present between xylem and phloem). Each vascular bundle consists of:
    *   **Phloem:** Located towards the periphery, responsible for the translocation of food. It consists of sieve tube elements, companion cells, phloem parenchyma, and phloem fibres.
    *   **Cambium:** A strip of meristematic tissue located between the phloem and xylem, responsible for secondary growth.
    *   **Xylem:** Located towards the centre, responsible for water and mineral transport. It consists of tracheids, vessels, xylem parenchyma, and xylem fibres. Protoxylem (smaller vessels) is towards the centre (pith), and metaxylem (larger vessels) is towards the periphery (pericycle), a condition known as endarch.

5.  **Medullary Rays (Pith Rays):** These are strips of parenchymatous cells located between the vascular bundles, extending from the pith to the cortex. They help in radial conduction of water and food.

6.  **Pith (Medulla):** The central-most region of the stem, composed of large, rounded parenchymatous cells with large intercellular spaces. It primarily functions in food storage.

### Order of Occurrence from Periphery to Centre:

1.  **Epidermis**
2.  **Cortex**
    *   Hypodermis (Collenchymatous)
    *   General Cortex (Parenchymatous)
    *   Endodermis (Starch Sheath)
3.  **Pericycle** (Sclerenchymatous and Parenchymatous)
4.  **Vascular Bundles** (arranged in a ring)
    *   Phloem
    *   Cambium
    *   Xylem (Metaxylem then Protoxylem)
5.  **Medullary Rays** (Parenchymatous, between vascular bundles)
6.  **Pith** (Parenchymatous)

Question 10

Q10. Cut a transverse section of a dorsiventral leaf and observe it under a microscope. Name the various tissues present in the transverse section and arrange them in order of their occ

Accepted Answer

When a transverse section (TS) of a dorsiventral (dicot) leaf is observed under a microscope, distinct tissues can be identified, arranged from the upper (adaxial) surface to the lower (abaxial) surface. The term 'dorsiventral' refers to the differentiation of the upper and lower surfaces, both structurally and functionally.

### Tissues Present in a Transverse Section of Dorsiventral Leaf:

1.  **Upper Epidermis (Adaxial Epidermis):** This is the outermost protective layer on the upper side of the leaf. It consists of a single layer of parenchymatous cells that are usually compactly arranged without intercellular spaces. The outer surface is covered by a thick cuticle. Stomata are generally absent or very few on the upper epidermis, which helps in reducing water loss.

2.  **Mesophyll:** Located between the upper and lower epidermis, the mesophyll constitutes the ground tissue of the leaf and is the primary site of photosynthesis. It is differentiated into two types of parenchyma:
    *   **Palisade Parenchyma:** Located just below the upper epidermis, it consists of elongated, vertically arranged, tightly packed cells. These cells contain a large number of chloroplasts and are the main site of photosynthesis.
    *   **Spongy Parenchyma:** Situated below the palisade parenchyma and extending to the lower epidermis, it consists of irregularly shaped cells with large air spaces between them. These air spaces facilitate the exchange of gases (CO2 and O2) within the leaf. Spongy parenchyma cells also contain chloroplasts, though fewer than palisade cells.

3.  **Vascular Bundles (Veins):** These are scattered within the spongy parenchyma, varying in size depending on the vein. The larger veins form the midrib and lateral veins, while smaller veins are embedded within the mesophyll. Each vascular bundle is typically surrounded by a bundle sheath of thick-walled parenchymatous cells. Within the bundle:
    *   **Xylem:** Located towards the upper epidermis (adaxial side), responsible for water and mineral transport.
    *   **Phloem:** Located towards the lower epidermis (abaxial side), responsible for food translocation.

4.  **Lower Epidermis (Abaxial Epidermis):** This is the outermost protective layer on the lower side of the leaf. Similar to the upper epidermis, it is a single layer of parenchymatous cells. However, the lower epidermis typically bears a much larger number of stomata than the upper epidermis. These stomata are flanked by guard cells and regulate gas exchange and transpiration. The cuticle on the lower epidermis is usually thinner than that on the upper epidermis.

### Order of Occurrence from Upper Surface to Lower Surface:

1.  **Upper Epidermis** (Adaxial Epidermis)
2.  **Mesophyll**
    *   Palisade Parenchyma
    *   Spongy Parenchyma (containing Vascular Bundles/Veins)
3.  **Lower Epidermis** (Abaxial Epidermis)

Question 11

Q11. Define the following terms: (a) stele (b) vascular bundle (c) conjoint (d) radial (e) open (f) closed

Accepted Answer

Here are the definitions for the given terms:

**(a) Stele:**
The stele is the central core of the stem and root of a vascular plant, consisting of the vascular tissue (xylem and phloem) along with the pericycle and pith (if present). It represents the primary vascular cylinder and is surrounded by the endodermis.

**(b) Vascular Bundle:**
A vascular bundle is a strand of conducting tissues (xylem and phloem) found in vascular plants. Xylem is responsible for water and mineral transport, while phloem transports food (sugars). These bundles are typically surrounded by a bundle sheath and are organized in various patterns within the plant body.

**(c) Conjoint:**
Conjoint vascular bundles are those in which the xylem and phloem are situated on the same radius. They are typically found in stems and leaves. In these bundles, phloem is usually located towards the periphery and xylem towards the center.

**(d) Radial:**
Radial vascular bundles are characterized by the arrangement where xylem and phloem are arranged alternately on different radii. This type of vascular bundle arrangement is characteristic of roots, where xylem forms distinct patches alternating with phloem patches.

**(e) Open:**
An open vascular bundle is a type of vascular bundle where a strip of cambium (a meristematic tissue) is present between the xylem and phloem. The presence of cambium allows for secondary growth, leading to an increase in the girth of the plant organ (e.g., dicot stems).

**(f) Closed:**
A closed vascular bundle is a type of vascular bundle in which cambium is absent between the xylem and phloem. Due to the lack of cambium, these bundles do not undergo secondary growth, and thus, the plant organ (e.g., monocot stems and leaves) does not increase in girth.

Chapter 6: Anatomy of Flowering Plants