RBSE Solutions Class 11 Biology Chapter 13 Plant Tissue Internal Morphology and Anatomy

RBSE Class 11 Biology Chapter 13 Multiple Choice Objective Questions

Question 1. Which characteristic is not found in meristematic cells -
(a) Unclear nucleus
(b) Dense protoplasm
(c) Divisonal cells
(d) Nondivisonal cells
Answer: (a) Unclear nucleus
In simple words: Meristematic cells are special cells in plants that keep dividing. They usually have a clear nucleus. So, having an unclear nucleus is not a trait of these cells.

🎯 Exam Tip: Remember that meristematic cells are actively dividing and typically have a prominent, clear nucleus, dense cytoplasm, and are small in size.

Question 2. Protoderm forms which part of plant tissue?
(a) Vascular tissue
(b) Epidermis
(c) Cortex
(d) Lacuniferous vessels
Answer: (b) Epidermis
In simple words: Protoderm is like the first layer of cells that develops in a young plant. From this layer, the outer skin of the plant, called the epidermis, is formed. The epidermis protects the plant.

🎯 Exam Tip: Protoderm is one of the primary meristems that differentiates into the epidermal tissue system, which is the outermost protective layer of plants.

Question 3. Glandular hairs are -
(a) Internal secretory cells
(b) External secretory or external excretory cells
(c) Hydrathodes
(d) Gum glands
Answer: (b) External secretory or external excretory cells
In simple words: Glandular hairs are tiny structures on the outside of plants. They are special because they release substances, either secreting useful things or getting rid of waste from the plant. These cells help the plant interact with its environment.

🎯 Exam Tip: Glandular hairs are epidermal outgrowths involved in secretion or excretion, distinguishing them from internal secretory structures.

Question 4. Root cap is formed by -
(a) Periblem
(b) Pleorome
(c) Tunica
(d) Calyptrogen
Answer: (d) Calyptrogen
In simple words: The root cap is a protective layer at the tip of the root. This cap is specifically made by a group of cells known as calyptrogen. It helps the root push through the soil.

🎯 Exam Tip: The calyptrogen is a distinct meristematic region responsible for forming the root cap, especially in monocotyledons, protecting the delicate root apical meristem.

Question 5. Sclerenchymatous dies slowly and slowly why?
(a) Deposition of cellulose
(b) Deposition of pectin
(c) Deposition of lignin
(d) Deposition of silica
Answer: (c) Deposition of lignin
In simple words: Sclerenchyma cells, which provide strength to plants, slowly die because a hard substance called lignin builds up in their cell walls. Lignin makes the walls very thick and strong, stopping nutrients and water from reaching the cell, causing it to die.

🎯 Exam Tip: Lignin deposition is a key characteristic of sclerenchyma, providing mechanical support but leading to the death of the cell as it blocks transport.

Question 6. Gymnosperm and Pteridophytes do not contain -
(a) Seive tubes / plates
(b) Wood fibres
(c) Wood parenchyma
(d) Companion cells
Answer: (d) Companion cells
In simple words: Gymnosperms and Pteridophytes are older types of plants. Unlike more advanced plants, they do not have special cells called companion cells. These cells usually help sieve tubes transport food.

🎯 Exam Tip: Companion cells are a characteristic feature of angiosperm phloem; their absence in gymnosperms and pteridophytes is an important evolutionary distinction in vascular tissue.

Question 7. When we break aak tree, liquid comes out is -
(a) Latex
(b) Gum
(c) Tannin
(d) Resin
Answer: (a) Latex
In simple words: The 'aak' tree (Calotropis) releases a white, milky liquid when its stem or leaves are broken. This liquid is known as latex, which is a common plant sap. It helps protect the plant from pests.

🎯 Exam Tip: Latex is a milky fluid produced by many plants, often for defense, and is notably found in plants like Calotropis (aak).

Question 8. Glandular hairs are -
(a) Beetle leaf
(b) Insectivorous leaf
(c) Excretory gland
(d) Hydathodes
Answer: (c) Excretory gland
In simple words: Glandular hairs are small plant outgrowths that act like tiny organs for the plant. Their main job is to release substances, often waste products, making them a type of excretory gland. This helps the plant get rid of unneeded materials.

🎯 Exam Tip: Glandular hairs are epidermal structures with a secretory function, often involved in releasing excess substances, thus acting as excretory glands.

Question 9. Glandular hairs are -
(a) Internal secretory cells
(b) External secretory or external excretory cells
(c) Hydrathodes
(d) Gum glands
Answer: (b) External secretory or external excretory cells
In simple words: Glandular hairs are tiny structures on the outside of plants. They are special because they release substances, either secreting useful things or getting rid of waste from the plant. These cells help the plant interact with its environment.

🎯 Exam Tip: Glandular hairs are epidermal outgrowths involved in secretion or excretion, distinguishing them from internal secretory structures.

Question 10. Aerenchyma is found in -
(a) Hydrophytes
(b) Xerophytes
(c) Halophytes (plants growing in salt)
(d) In all plants
Answer: (a) Hydrophytes
In simple words: Aerenchyma is a special type of plant tissue with large air spaces. It's mostly found in water plants (hydrophytes). These air spaces help the plants float and also store air for breathing in water.

🎯 Exam Tip: Aerenchyma is a classic adaptation in hydrophytes, providing buoyancy and facilitating gas exchange in aquatic environments.

RBSE Class 11 Biology Chapter 13 Very Short Answer Questions

Question 1. Which plant parts are observed under plant anatomy?
Answer: Under plant anatomy, the main parts observed are the root, stem, and leaf. These parts are studied to understand their internal structure and arrangement of tissues. Plant anatomy focuses on the organization of cells into tissues and organs.
In simple words: When studying plant anatomy, scientists look at the root, stem, and leaves to see what they are made of inside.

🎯 Exam Tip: For basic plant anatomy, focus on the three primary organs: root (absorption, anchorage), stem (support, transport), and leaf (photosynthesis).

Question 2. Meristematic tissue are divided into how many types on basis of plane of division?
Answer: Meristematic tissues are divided into different types based on how their cells divide. Here are some examples:
(i) Mass meristem-
• The cells in this tissue divide in all directions, growing in bulk.
• These tissues form unspecialized cells, like those found in an embryosac. This allows for rapid growth and expansion in all dimensions.
(ii) Plate meristem-
• This meristem divides by anticlinal division, meaning the new cell walls are perpendicular to the surface. This helps form the long axis and the inner sap (vital fluid) of the stem and root.
In simple words: Meristematic tissue cells divide in different ways. Some divide in all directions to form a lump (mass meristem), while others divide in a flat way to make length and width (plate meristem).

🎯 Exam Tip: When classifying meristems by division plane, remember "mass" implies growth in all directions (volume), while "plate" implies growth in two dimensions (surface area), and "rib" implies growth in one dimension (length).

Question 3. Apical meristem is found in which part or organs of plants?
Answer: Apical meristem is located at the tips of the main and side shoots, as well as the tips of the roots. These meristems are responsible for the primary growth of the plant, helping it grow taller and roots grow deeper. This tissue is essential for increasing the length of the plant body.
In simple words: Apical meristem is found at the very ends of a plant's growing parts, like the top of stems and the tips of roots.

🎯 Exam Tip: Apical meristems are always at the 'apices' (tips) of roots and shoots, driving primary growth, which is the increase in length.

Question 4. Corpus is situated at what place of plants?
Answer: The corpus is found in the central part of the shoot apex. It forms the inner core beneath the tunica layer. This region helps in creating the bulk of the stem, contributing to its overall structure and growth. It's a key part of how the stem builds its body.
In simple words: The corpus is in the middle part of the very tip of a plant's stem.

🎯 Exam Tip: The Tunica-Corpus theory distinguishes the outer tunica (surface growth) from the inner corpus (volume growth) in the shoot apex.

Question 5. What is calyptrogen?
Answer: Calyptrogen is a specific layer of initial cells from which the root cap develops. This protective cap covers the tip of the root, helping it to push through the soil without damage. It's like a shield for the growing root. In monocotyledons, it is a distinct meristematic layer.
In simple words: Calyptrogen is a special group of cells that creates the root cap, which protects the root tip.

🎯 Exam Tip: Calyptrogen is particularly prominent in monocot roots, where it forms a distinct meristem responsible solely for the root cap.

Question 6. Where is Korper and Kappe found?
Answer: The terms Korper and Kappe are related to the root apex structure. They are found at the very tip of the plant's root. These terms describe a theory about how cells divide and organize in the root tip to facilitate growth and protection.
In simple words: Korper and Kappe are found at the growing tip of the plant's root.

🎯 Exam Tip: The Korper-Kappe concept is a German term referring to the body-cap arrangement in root apex organization, describing the planes of cell division.

Question 7. At the loss of divisional property of meristematic cells which cells are formed?
Answer: When meristematic cells lose their ability to divide, they change and become permanent tissues. These permanent tissues then perform specific functions like support, protection, or transport in the plant. This process is called differentiation. This transformation allows plants to develop specialized structures.
In simple words: When meristematic cells stop dividing, they turn into permanent tissues.

🎯 Exam Tip: Differentiation is the process where meristematic cells mature into specialized permanent tissues, each with a unique structure and function.

Question 8. What is the role of Chlorenchyma tissue?
Answer: Chlorenchyma tissue is a type of parenchyma cell that contains chloroplasts. Its main role is to perform photosynthesis, the process by which plants make their own food using sunlight. This tissue is typically found in the leaves and green stems of plants. Chlorenchyma cells are crucial for energy production in plants.
In simple words: Chlorenchyma tissue helps plants make their food using sunlight, a process called photosynthesis.

🎯 Exam Tip: Chlorenchyma is essentially photosynthetic parenchyma, identifiable by the presence of chlorophyll and its primary role in food synthesis.

Question 10. How many types of pits are there?
Answer: There are two main types of pits found in plant cell walls: simple pits and bordered pits. These pits are thin areas in the cell wall that allow for communication and transport between adjacent plant cells. They are like small windows in the cell walls.
In simple words: There are two kinds of pits in plant cell walls: simple pits and bordered pits.

🎯 Exam Tip: Pits are crucial for intercellular communication and water movement in vascular plants, with bordered pits characteristic of tracheids in xylem.

RBSE Class 11 Biology Chapter 13 Short Answer Questions

Question 1. What are the functions of protoderm?
Answer: The primary function of protoderm is to produce the epidermal tissue system of a plant. This system includes the epidermis, which is the outermost protective layer of leaves, stems, and roots. The epidermis protects the plant from water loss, injury, and infection. It also plays a role in gas exchange and absorption.
In simple words: Protoderm makes the plant's outer skin, called the epidermis, which protects the plant.

🎯 Exam Tip: Remember that protoderm is one of the three primary meristems (along with procambium and ground meristem) and is specifically responsible for forming the epidermis.

Question 2. What is the difference in direction of division of tunica and corpus?
Answer: In the shoot apex, the tunica and corpus layers divide in different directions. Tunica cells primarily divide by anticlinal division, where the new cell walls form perpendicular to the surface. This increases the surface area and maintains the layered structure. In contrast, corpus cells divide in all planes, leading to an increase in volume and contributing to the bulk of the plant body. This difference in division patterns allows for distinct growth forms.
In simple words: Tunica cells divide mostly sideways to make more layers, while corpus cells divide in all directions to make the plant thicker.

🎯 Exam Tip: Anticlinal divisions in tunica contribute to surface growth (length/girth), while periclinal and anticlinal divisions in corpus contribute to volume growth (bulk of the stem).

Question 3. What is the difference in base division of corpus and cap?
Answer: The question refers to the Tunica Corpus Theory, proposed by Schmidt in 1924, which describes the shoot apex. It explains two distinct zones:
(i) The outer tunica, which surrounds and envelops:
• Tunica consists of one or more outer layers of cells. These cells are smaller and divide by anticlinal divisions, meaning new cell walls are perpendicular to the surface. This prevents the number of layers from increasing but expands the surface. Cells from the tunica eventually form the epidermis.
(ii) The inner corpus, which forms the central core:
• The corpus occupies the central part, with larger cells. These cells divide in all planes, which helps increase the volume. The corpus forms the procambium and ground meristem. The procambium develops into primary xylem and primary phloem, while the ground meristem forms the cortex, endodermis, pericycle, and pith. The different division patterns are key to how a plant grows.
In simple words: The Tunica Corpus Theory explains how the plant stem tip grows. The outer layer (tunica) mostly grows outwards, while the inner part (corpus) grows in all directions to make the stem thicker.

🎯 Exam Tip: The Tunica Corpus Theory is fundamental for understanding shoot apical meristem organization, focusing on the plane of cell division (anticlinal vs. all planes) and derivative tissues.

RBSE Class 11 Biology Chapter 13 Essay Type Questions

Question 1. Explain different theories with diagram in relation to organisation of shoot apex and root apex?
Answer: The organization of shoot and root apices is crucial for plant growth, and several theories explain their structure and function.

Shoot Apex:
The shoot apex is the terminal meristem located at the tips of stems and branches. It is derived from the plumular tip of the embryo or the axil of a leaf. It is radially symmetrical, cone-shaped, and usually not protected by a cap. While not capped, it is protected by young leaves and bud scales. Cell division in the apical meristem continuously adds new cells. The apex shows alternating broad and narrow zones due to the formation of leaf primordia. The interval between successive leaf primordia is called plastochron. Various theories describe its organization:

Tunica Corpus Theory (for Shoot Apex):
This theory, proposed by Schmidt (1924), states that the shoot apex has two distinct zones:
(i) The outer tunica: This layer consists of one or more peripheral cell layers. Tunica cells are smaller and primarily undergo anticlinal divisions (perpendicular to the surface). This increases the surface area but keeps the number of layers constant. Cells from the tunica differentiate into the epidermis.
(ii) The inner corpus: This forms the central core, composed of comparatively larger cells that divide in all planes. The corpus gives rise to the procambium (which forms primary xylem, primary phloem, and intrafascicular cambium) and the ground meristem (which forms the cortex, endodermis, pericycle, and pith).

Histogen Theory (for Shoot Apex):
This theory, proposed by Hanstein (1870), states that the shoot apical meristem has three distinct meristematic zones or layers:
1. Dermatogen (external layer): This forms the outer covering, which is the epidermis, in all plant organs.
2. Periblem (middle layer): This gives rise to the cortex and endodermis.
3. Plerome (the central core): This forms the pith and the primary vascular tissue.
Haberlandt (1914) later named protoderm for dermatogen, ground meristem for periblem, and procambium for plerome. These layers are crucial for the development of different plant parts.

Root Apex:
The root apex is the tip of a growing root, consisting of a group of initial cells protected by a root cap. It is embryonic, forming from the radicle of the embryo. In adventitious roots, it is produced from derivatives of the root apex. Cell division in the apical meristem adds new cells to both the root body and the root cap. The root apex is generally short and uniform.

Histogen Theory (for Root Apex):
Hanstein's theory also applies to the root apex, which consists of three meristematic zones or layers:
1. Plerome: Forms the pith, vascular strands, and pericycle.
2. Periblem: Forms the endodermis and cortex.
3. Dermatocalyptrogen: This layer gives rise to the protoderm and the root cap. This is a special layer found in monocotyledons.

Quiescent Centre:
In addition to actively dividing cells, a zone of inactive cells is present in the central part of the root apex called the quiescent centre, identified by Clowes (1961). This cap-like or hemispherical region is found between the root cap and the active meristematic region. It contains hundreds of cells with lower concentrations of DNA, RNA, and protein, as well as fewer mitochondria and endoplasmic reticulum. The quiescent centre acts as a reserve of cells, becoming active when the initial cells are damaged or during the formation of secondary roots. Normally, its cells remain inactive. This ensures a backup supply of cells for root growth and repair.

In simple words: Different theories like Tunica Corpus and Histogen explain how the growing tips of plant stems and roots are organized. They describe different cell layers and how they divide to help the plant grow longer and thicker, with some special areas for protection and cell storage.

🎯 Exam Tip: When explaining theories, always state the name of the theory and its proposer, describe the main layers/zones, and explain their respective roles in growth, using clear diagrams to illustrate the concepts.

Question 1. Explain different theories with diagram in relation to organisation of shoot apex and root apex?
Answer:
Shoot Apex:
The terminal meristem is found at the very top of the stem and its branches. It forms from the tiny plumular tip of the embryo or from the side of a leaf. It sits just above the newest young leaf and looks like a cone, usually rounded. Its shape and size can change between different plants or even different branches on the same plant. It doesn't have a protective cap.
Young leaves and bud scales protect it. The cells in this tip keep dividing to add new cells to the stem below it. Growth here isn't smooth because new leaves, nodes, and spaces between nodes keep forming.
The apex has wide and narrow parts because new leaves form at regular times. A new leaf forms on the side of the apex, making it wider there. After the leaf forms, the apex becomes narrow again.
The time between two new leaves forming is called plastochron. Many theories try to explain how the shoot apex is built and organized. Some of these theories include:

Histogen Theory:
Hanstein proposed this theory in 1870. It says the shoot apical meristem has three distinct layers of cells, or histogens:
1. Dermatogen (external layer): This forms the outer covering, like the epidermis, for all plant organs.
2. Periblem (middle layer): This layer grows to form the cortex and endodermis.
3. Plerome (the central core): This part forms the pith and the primary vascular tissue.
Later, Haberlandt (1914) renamed dermatogen as protoderm, periblem as ground meristem, and plerome as procambium. This theory explains how different parts of the plant's skin, inner layers, and core are formed.

Tunica Corpus Theory:
Schmidt proposed this theory in 1924. It states that the shoot apex has two distinct zones:
(i) The outer tunica, which surrounds and covers the apex. It has one or more outer layers of smaller cells that divide only sideways (anticlinally). This means new cell walls form perpendicular to the surface, so the number of layers does not increase. Cells from the tunica become the epidermis.
(ii) The inner corpus, which forms the central core. This central part has larger cells that divide in all directions. These cells form the procambium (which gives rise to primary xylem, primary phloem, and interfascicular cambium) and the ground meristem (which forms the ground tissue like cortex, endodermis, pericycle, and pith).

Root Apex:
The root apical meristem, or root apex, is a group of initial cells found at the very end of a growing root tip. A root cap protects this region. It starts from the radicle part of the embryo. In roots that grow from other parts of the plant (adventitious roots), it comes from parts of the root apex.
The root apex is shorter than the shoot apex and looks fairly uniform because it does not have side branches. It also lacks leaves, branches, nodes, and internodes. When cells in the apical meristem divide, they add new cells to both the root body and the root cap.

Histogen Theory (Hanstein, 1870) for the root apex in most dicotyledons says it has three meristematic zones or layers:
1. Plerome forms the pith, vascular strands, and pericycle.
2. Periblem forms the endodermis and cortex.
3. Dermatocalyptrogen gives rise to the protoderm and the root cap. This structure helps organize the different tissue systems in a growing root.

In monocotyledons, this theory suggests that the root cap comes from a separate layer of initial cells called calyptrogen, while the protoderm comes from dermatogen. Periblem forms the cortex.

Quiescent Centre:
In addition to active dividing cells, the central part of the root apex has a zone of inactive cells called the quiescent centre (discovered by Clowes in 1961). This region is like a cap or hemisphere of inactive cells found between the root cap and the active meristematic zone of the root apex. It contains hundreds of cells with lower levels of DNA, RNA, and protein, as well as fewer mitochondria, less endoplasmic reticulum, and small dictyosomes. These cells are mostly resting.
The quiescent centre acts as a reserve of cells. It becomes active if the initial cells get damaged or when secondary roots start to form. However, normally, the cells of the quiescent centre do not divide and stay inactive. This inactive region ensures that new cells are always available if the main dividing cells are harmed.
In simple words: Plants have special growing tips called apexes in their shoots and roots. Different theories, like Histogen and Tunica Corpus, explain how these tips are organized into layers or zones that create all the plant's tissues. The root also has a quiet "quiescent centre" of cells ready to grow if needed.

🎯 Exam Tip: When explaining theories, clearly state the name of the theory and the scientist who proposed it. Mention the key layers or zones and what tissues each forms, and remember to specify if it applies to shoot or root apex.

Question 2. What are simple tissues? Describe salient features and functions of meristematic tissue?
Answer:
Simple tissues are made of only one type of cell. They often cover surfaces of both internal and external organs of the body. These cells are tightly packed together. For example, in animals, simple tissue is called epithelium, and in plants, it's called epidermis. Muscle tissue is an example of simple tissue in animals.
Meristematic tissues are crucial plant tissues with special characteristics and roles.

Salient features of meristematic tissues:
1. Meristematic cells are small, round, or polygonal, and their cell walls are thin.
2. In early embryonic stages, all cells are meristematic, but later, this activity is restricted to specific areas called meristems (which means "divisible").
3. Meristematic tissues are found in the growing parts of plants, and these tissues allow plants to grow.

Based on origin and method of development, meristems are of three types:
1. Promeristem (Primordial Meristem):
• This group of cells comes from the embryo, so it is also called embryonic meristem.
• These cells represent the earliest stages of meristematic cells.
• They are found in small regions at the tips of shoots and roots.
• Promeristem gives rise to the primary meristem.
2. Primary Meristem:
• These meristematic cells originate from the promeristem.
• They are always actively dividing and produce primary permanent tissues.
• They are located below the promeristem at the tips of shoots and roots, at the apex of leaves, and in parts between nodes.
• Examples include protoderm (forms epidermal tissue), procambium (forms primary vascular elements), and ground meristem (forms cortex and pith).
3. Secondary Meristem:
• These meristems develop from primary permanent tissues.
• They do not have their own promeristem.
• They develop later in the plant's life and give rise to secondary permanent tissues.
• Examples include the cambium of roots, vascular cambium (in dicots when secondary growth is needed), and cork cambium (for periderm formation and wound healing). This allows plants to grow thicker and repair themselves.

Characteristics of different meristematic tissues:

In simple words: Simple tissues are made of one type of cell. Meristematic tissues are special plant tissues that constantly divide to help the plant grow. They have thin walls, no large vacuoles, and create new primary tissues like the epidermis or vascular bundles. They are responsible for the plant's overall growth and development.

🎯 Exam Tip: When defining simple tissues, clearly state their composition (one cell type) and give common examples. For meristematic tissue, focus on their role in growth and their ability to divide continuously. Use the table format for clarity when comparing different types of meristems.

Question 4. Comment on structure, type and functions (a) Collenchyma (b) Sclerenchyma
Answer:
The question asks for comment on Collenchyma and Sclerenchyma. However, some background on Parenchyma is also given in the source, which is another simple tissue, so it is included for completeness.

(i) Parenchyma:
Parenchyma (from Greek words meaning "beside" and "to pour") is the simplest and least specialized tissue. It is mainly involved in the plant's everyday activities. It is considered the most primitive tissue in terms of evolution and development. This tissue mostly consists of living cells with thin walls and spaces between them. The cell wall is made of cellulose or calcium pectate. These cells have a clear nucleus and cytoplasm with vacuoles.
The spaces between cells can form either by cells splitting apart (schizogenously) or by cells dissolving (lysigenously). Sometimes, there are no intercellular spaces. Each parenchyma cell can be spherical, oval, cylindrical, rectangular, star-shaped, or long and spindle-like. Their shape varies in different plants and different parts of the same plant.
Parenchyma is found throughout almost all parts of a plant, making up the basic vegetative tissue. It is present in the epidermis, cortex, pith, pericycle, mesophyll of leaves, fruit pulp, endosperm of seeds, and in meristematic tissues. Parenchymatous cells are also found in xylem and phloem.

Functions of Parenchyma:
Parenchymatous tissue performs several functions in different plant organs:
1. Storage of reserve food materials.
2. Storage of water in succulent plants (e.g., Opuntia, Euphorbia).
3. Provides buoyancy and helps in gas exchange in water plants (Aerenchyma).
4. Gives rigidity to the plant body due to cell turgidity, helping maintain the plant's shape.
5. They can give rise to secondary meristem, like cork cambium and vascular cambium, which helps in secondary growth and healing.
6. They perform all vital activities of plants.
7. Sometimes they develop chloroplasts and are then called chlorenchyma, which perform photosynthesis.

(a) Collenchyma:
Collenchyma (from Greek words meaning "glue" and "infusion") is a primary body tissue. Its cells are living and contain protoplasm. The cell walls have localized thickenings due to about 45% pectin, 35% hemicellulose, and 20% cellulose. These cells are never lignified but may have simple pits. The cellulose and pectic substances in the cell wall give them a high capacity to absorb water. The tissue is flexible, can stretch, and provides tensile strength to the plant part. It originates from elongated cells that look like procambium.
Its cells are generally elongated with slanted end walls, which can sometimes be rounded. They are mainly found in the layer below the epidermis (hypodermis) of dicotyledonous stems (like cucurbita, helianthus) and leaves. They are usually absent in monocots and roots, but can appear in root cortex if the root is exposed to light.

Functions of Collenchyma:
1. It is the main supporting tissue in young dicotyledonous stems.
2. It can expand and provides tensile strength to the plant body.
3. It is present at the edges of some leaves and helps them resist tearing by wind.
4. Some cells have chloroplasts and perform photosynthesis.

(b) Sclerenchyma (Sclereids):
Sclerenchyma (from Greek "sclerous" meaning "hard"; "enchyma" meaning "infusion") is made of thick-walled dead cells. These cells vary in shape, size, and origin. They have hard and very thick secondary walls due to uniform deposition of lignin. Sometimes, they may not be lignified. In the beginning, these cells are living and have protoplasm, but they die when impermeable secondary walls are deposited.
Sclerenchymatous cells, which are short and have very thick lignified walls with long, tube-like simple pits, are called sclereids. They develop from ordinary parenchyma cells as secondary wall layers are deposited. They can be simple or branched. Sclereids vary greatly in their shape and size; they can be spherical, oval, cylindrical, T-shaped, dumbbell-shaped, or even star-shaped. They are usually shorter than fibres.
In simple words: Collenchyma is a living tissue that provides flexible support and strength, especially in young stems and leaves, allowing them to bend without breaking. Sclerenchyma is a hard, dead tissue with thick, tough walls (due to lignin) that provides strong, rigid support and protection to various plant parts, like the hard shell of a nut.

🎯 Exam Tip: When describing plant tissues, always include whether the cells are living or dead, the nature of their cell walls (thin, thick, lignified, pectic), their location in the plant, and at least two specific functions. For Collenchyma, remember flexible support; for Sclerenchyma, remember rigid, hard support.

Question 5. What are different types of vascular tissues? Write different components of it and explain any one in detail?
Answer:
Vascular tissues are complex tissues responsible for transporting water, minerals, and food throughout a plant. The two main types of vascular tissues are xylem and phloem. These tissues are vital for a plant's survival, much like veins and arteries are for animals, distributing essential resources to every part of the organism.

Xylem:
The term xylem (from Greek "xylos" meaning "wood") was introduced by Nageli in 1858. It is the primary conducting tissue in vascular plants, responsible for transporting water and inorganic solutes from roots to the leaves. Xylem is made up of several different cell types:

(i) Tracheids:
Tracheids are long, tube-like, dead cells that lack protoplasm and have tapering ends. In cross-section, they can appear elongated, rectangular, somewhat rounded, angular, or polygonal, though sometimes they look completely round. Their walls are hard and lignified, but not very thick, and they enclose a wide, empty space (lumen). Tracheids are long but not as long as fibres, typically reaching up to 1 mm in length, though in some plants they can be 12 cm or longer.
Tracheids in primary xylem develop from procambium, while those in secondary xylem develop from vascular cambium. Initially, these cells have living protoplasm, but as lignin and other thickening materials are deposited in their walls, they die at maturity.

Wall thickenings in Tracheids:
Tracheids have various types of wall thickenings, including annular (ring-like), spiral (helical), scalariform (ladder-like), reticulate (network), and pitted. Protoxylem tracheids usually have annular and spiral thickenings. Metaxylem and secondary xylem tracheids have scalariform, reticulate, and pitted thickenings. The pits are either simple or bordered, and their size and number vary significantly among different tracheids.

Functions of Tracheids:
1. Their main role is to conduct water and dissolved mineral elements from the roots to the leaves. They are structured specifically for this function.
2. They are placed one above the other and also parallel to the long axis of the plant. The end walls have perforations (bordered pits) that allow water to flow from one cell to another.
3. They also provide mechanical support to the plant due to their hard and firm secondary walls.

(ii) Vessels (or Tracheae):
Xylem vessels are long tubes formed by a series of drum-shaped cells placed one above the other. Their end walls are either perforated or completely dissolved. Thus, vessels are like connected tubes formed by the fusion of many cells (syncytes). Each cell in cross-section appears circular, oval, or sometimes polygonal, with a very wide internal space. They become dead and lose their protoplasm as lignified secondary walls are deposited.
Vessels of primary xylem develop from procambium, while those of secondary xylem develop from vascular cambium. They can also form from the dissolution of end walls or pit membranes. Although each cell is short, the fusion creates much longer tubes, reaching up to 10 cm in length, and sometimes even 2-6 meters (in Quercus) or 3-6 meters (in Eucalyptus).

Wall thickenings in Vessels:
The most common wall thickenings in vessels are scalariform, reticulate, and pitted. Protoxylem vessels have annular and spiral thickening, which later transform into scalariform and reticulate forms as more thickening materials are deposited. Metaxylem vessels generally have simple pits. Secondary xylem vessels also have scalariform, reticulate, and pitted thickenings. The pits can be simple or bordered.

(iii) Xylem fibres (or wood fibres):
Xylem fibres develop from the same meristematic tissue as other xylem cells. They have lignified secondary walls and a narrow cell space (lumen). They are usually longer than the tracheids of the same plant and are found in both primary and secondary xylem.

(iv) Xylem parenchyma:
These are living parenchyma cells found as a component of xylem in both primary and secondary xylem. The parenchyma in secondary xylem is of two types: wood parenchyma and ray parenchyma.
Wood parenchyma forms from fusiform cambial initials, while ray parenchyma forms from ray initials of the cambium. Both types have thin walls and living protoplasm. They help in conduction. The main function of xylem parenchyma is to store food reserves like starch or fat.

Phloem:
Phloem is the main tissue that transports food in vascular plants, specifically organic solutes. It is made of several different kinds of cells. The basic components of phloem in most vascular plants include sieve elements, which have thin or thick cellulose walls and viscous contents. The cytoplasm forms a thin lining around a large central vacuole. The nucleus, plastids, mitochondria, endoplasmic reticulum, and dictyosomes are absent. The vacuole contains albuminous substances, and leucoplasts have also been reported.

(i) Sieve Elements (Plate and Sieve areas):
Sieve elements have sieve plates and sieve areas. In a sieve cell, these areas with groups of pores are usually on the side walls. In a sieve-tube element, these areas are located on the end walls (cross-walls). The part of the cross-wall that has sieve areas is called a sieve plate. In most flowering plants, the sieve plate is a single structure found in the cross-wall or slanted end wall (e.g., Cucurbita, Nicotiana), and it's called a simple sieve plate. In some cases, there are many sieve areas in the end walls, which are called compound sieve plates. The nucleus disappears in mature sieve elements.

Function of Sieve elements:
Sieve elements transport organic solutes. This is possible because of their special anatomical features. Sieve tubes are syncytes (formed by fused cells) and allow soluble organic substances to diffuse freely. A sticky substance called callose also plays an important role. Usually, the pores in the sieve plates are surrounded by callose. Callose is soluble and disappears when the solute is dilute, allowing the solute to pass from one cell to another through the pores. Callose reappears and sometimes closes the pores when the solute is less dilute, stopping movement.
In simple words: Vascular tissues are like a plant's transport system. Xylem carries water and minerals from roots to leaves using tracheids (long, dead tubes) and vessels (wider, dead pipes). Phloem carries food (sugars) from leaves to other parts using sieve elements and companion cells. These two systems work together to keep the plant nourished and stable.

🎯 Exam Tip: When asked about vascular tissues, always differentiate between xylem and phloem, clearly stating what each transports and in which direction. For components, list and describe each cell type (e.g., tracheids, vessels, xylem parenchyma, xylem fibers for xylem) and their specific features and functions. Diagrams can significantly boost your score.

Question 5. What are different types of vascular tissues? Write different components of it and explain any one in detail?
Answer: Plants have specialized vascular tissues, xylem and phloem, which are responsible for transporting water, minerals, and food throughout the plant. Xylem mainly transports water, while phloem transports food. Both tissues are made up of different types of cells.
**Components of Xylem:** Xylem tissue is made of tracheids, vessels, xylem fibres, and xylem parenchyma cells. These components work together to conduct water and provide structural support.
**Components of Phloem:** Phloem tissue is composed of sieve elements, companion cells, phloem parenchyma, and phloem fibres. These parts help in the efficient transport of sugars and other nutrients.
Let's explain **Phloem Parenchyma** and **Phloem Fibres** in detail:
(iii) **Phloem Parenchyma:** These are living, elongated cells found within the phloem tissue. They have rounded ends and their cell walls are made of cellulose. Phloem parenchyma cells are found in pteridophytes and most dicotyledonous angiosperms, but they are typically absent in monocots and some dicots (like Ranunculus). In active phloem, these cells remain alive, but they can become lignified (woody) if the sieve tubes stop functioning. The main roles of phloem parenchyma are to help in the movement of food and to store reserve food materials, such as starch.
(iv) **Phloem fibres:** These are also known as bast fibers and are mostly found in the secondary phloem. The fibres of primary phloem have walls thickened with both cellulose and lignin. Secondary phloem fibres are long, lignified cells with simple pits. Their ends can be pointed, needle-like, or blunt. These cells are non-living and provide essential mechanical support, giving strength and rigidity to the plant organ.
In simple words: Plants move water and food using vascular tissues like xylem and phloem. Phloem parenchyma cells store food and help move it, while phloem fibers are strong, non-living cells that give the plant stiffness and support.

🎯 Exam Tip: When describing components of vascular tissues, clearly state whether the cells are living or dead and their specific role, such as transport, storage, or structural support. Providing examples for each component can also earn more marks.

Question 6. What are different types of special tissues. Explain salient features and special tissues of each type?
Answer: Special tissues in plants perform unique functions, such as secreting substances like resins, gums, oils, and latex. These tissues are mainly divided into two types: Glandular tissue and Laticiferous tissue. Each type has distinct characteristics and roles.
**1. Glandular Tissue** Glandular tissues are responsible for producing and releasing various substances. They can be found externally or internally in the plant.
**External glands:** These glands typically appear as outgrowths on the epidermis (outer layer) of stems and leaves. Examples include glandular hairs, nectar-secreting glands, and enzyme-secreting glands.
(a) **Glandular hair:** These hairs are found in the epidermal layers of leaves and can be single-celled or multi-celled and are alive. For example, stinging hairs on the underside of *Urtica dioica* (Bichhu buti) are single-celled and break easily. They contain a poisonous albuminoid that causes irritation and blisters when injected into the skin.
(b) **Nectaries:** These glands secrete nectar, which attracts pollinators. They are found in flowers or on leaves. In plants like Rutaceae, they often appear as a disc below the ovary. In *Euphorbia pulcherrima*, nectaries are made of layers of elongated cells with thin walls and dense cytoplasm.
(c) **Digestive glands or Enzyme-secreting glands:** These glands are found in insectivorous plants. They secrete digestive enzymes that help break down proteins from insects the plant has captured.
**Internal glands:** These glands are located inside the plant tissues and come in several forms.
• **Oil glands:** In citrus fruits like oranges (*Citrus sinensis*), internal glands secrete volatile oils into a central storage area.
• **Resin glands:** In pine trees (*Pinus*), resin-secreting cells form one or two layers around a canal or duct found in the leaves and stem.
• **Water-secreting glands (Hydathodes or water stomata):** These glands release water as drops, a process called guttation. They are commonly found on the margins of leaves of herbaceous angiosperms that grow in humid conditions, such as *Colocasia*. Hydathodes have an aperture guarded by guard cells, with an air cavity and thin-walled, colorless epithem cells beneath, which are filled with water. Water-conducting tracheids connect directly to the epithem tissue.
**2. Laticiferous Tissue** Laticiferous tissues are long, branched, multi-nucleate tubes with thin walls. They contain a colorless, milky, or yellow fluid called latex, which stores various organic substances like starch, rubber, tannins, alkaloids, mucilage enzymes, and proteins. This tissue is distributed throughout the plant's ground tissue. There are two main types:
(1) **Latex cells:** These cells are distinct from latex vessels because they do not form through cell fusion and do not create a network with other latex cells. They can be branched or unbranched and do not connect to each other. Examples include plants like *Calotropis*, *Nerium*, *Thevetia*, and *Euphorbia*.
(2) **Latex vessels:** These are formed when many cells are arranged end-to-end, and their transverse walls dissolve, creating long, continuous tubes. They start unbranched but can become branched later on.
In simple words: Special plant tissues include glandular tissues and laticiferous tissues. Glandular tissues make and release things like oils, nectar, or digestive juices, found on the plant surface or inside. Laticiferous tissues carry a milky fluid called latex, found in special cells or tubes that are spread throughout the plant.

🎯 Exam Tip: When describing special tissues, always specify whether they are external or internal glands and provide clear examples. For laticiferous tissues, distinguishing between latex cells and latex vessels based on their formation and network structure is key.