🧩 Subjective Questions and Answers (Chapter Review)

This section contains subjective questions and answers covering all topics from the chapter, based on the NCERT exercises and key concepts in plant anatomy.

Q1. Draw illustrations to bring out the anatomical difference between (a) Monocot root and Dicot root (b) Monocot stem and Dicot stem.

Answer:

(a) Difference between Dicot Root and Monocot Root:

Feature Dicot Root Monocot Root
Vascular Bundles Diarch to Tetrarch (Usually 2 to 4 patches of xylem and phloem). Polyarch (Usually more than 6 patches of xylem).
Pith Small or completely absent. Large and well-developed.
Cambium Develops later during secondary growth. Absent (No secondary growth).

👉 Summary points to remember:

  • Both are radial, but dicot root = few xylem bundles + small/absent pith, monocot root = many xylem bundles + large pith.

(b) Difference between Dicot Stem and Monocot Stem:

Feature Dicot Stem Monocot Stem
Arrangement Vascular bundles are arranged in a ring (Eustele). Vascular bundles are scattered throughout the ground tissue (Atactostele).
Type of Bundle Open (Cambium is present between xylem and phloem). Closed (Cambium is absent).
Ground Tissue Differentiated into cortex, endodermis, pericycle, and pith. Undifferentiated; a continuous mass of parenchyma.

👉 Key memory line:

  • Roots: “radial in both, but few vs many xylem bundles.”
  • Stems: “dicot = ring + cambium; monocot = scattered + no cambium.

Q2. How would you ascertain whether a transverse section is a monocot stem or a dicot stem?

Answer:

To identify the stem type under a microscope, look for these two distinct features:

  1. Arrangement of Vascular Bundles:

    • Dicot Stem: The bundles are arranged in a neat, circular ring. This is a classic feature of dicots.
    • Monocot Stem: The bundles are scattered all over the tissue, like stars in the sky. They are usually smaller near the edge and larger in the center.

  2. Presence of Cambium:

    • Dicot Stem: The bundles are 'Open', meaning you will see a strip of cambium (meristematic tissue) between the xylem and phloem.
    • Monocot Stem: The bundles are 'Closed', meaning there is no cambium present.

👉 So, to decide quickly:

  • Ring + open bundles + differentiated ground tissue = Dicot stem.
  • Scattered + closed bundles + undifferentiated ground tissue = Monocot stem.

Q3. A T.S. shows conjoint, scattered vascular bundles surrounded by a sclerenchymatous bundle sheath, and phloem parenchyma is absent. What is it?

Answer:

This description matches a monocot stem. Here is why:

  • Conjoint vascular bundles: Xylem and phloem are together in the same bundle → typical of stems (not roots).
  • Scattered vascular bundles: Not arranged in a ring → characteristic of monocot stems.
  • Sclerenchymatous bundle sheath: Each bundle is surrounded by a ring of sclerenchyma → typical of monocot stems like maize.
  • Phloem parenchyma absent: In monocot stems, phloem parenchyma is generally absent.

👉 Therefore, the T.S. belongs to a monocot stem (for example, maize stem).

Q4. What is the stomatal apparatus?

Answer:

The stomatal apparatus is the complete structure that controls the opening and closing of a stoma. It consists of three main parts:

  1. Stomatal Aperture (Pore): The tiny opening through which gases (CO₂, O₂) and water vapour move in and out.
  2. Guard Cells: A pair of specialised kidney-shaped (in dicots) or dumbbell-shaped (in grasses) cells on either side of the pore. They swell to open the pore and shrink to close it.
  3. Subsidiary Cells: Specialized epidermal cells surrounding the guard cells that provide support and help in the mechanism of opening and closing.

👉 So, stomatal apparatus = stomatal pore + guard cells + subsidiary cells. It is responsible for regulating transpiration and gas exchange.

Q5. Name the three basic tissue systems in flowering plants.

Answer:

According to plant anatomy, the body of a flowering plant is organised into three main tissue systems:

  1. Epidermal Tissue System: The outermost protective covering. It includes the epidermis, stomata (for breathing), and trichomes (hairs).
  2. Ground Tissue System: The main bulk of the plant. It fills the space between the epidermis and vascular tissue. It includes parenchyma, collenchyma, and sclerenchyma (cortex, pith, mesophyll).
  3. Vascular Tissue System: The transport system. It consists of xylem (for water) and phloem (for food).

👉 Easy memory: E – G – V

  • Epidermal → outer
  • Ground → middle/bulk
  • Vascular → conducting system

Q6.How is the study of plant anatomy useful to us?

Answer: The study of plant anatomy (internal structure) is useful in many ways:

A. Taxonomy (Classification and Identification):

  • Anatomical features like type of vascular bundle, arrangement of tissues, presence/absence of secondary growth help to distinguish between monocots and dicots, or between different families.

B. Physiology (Understanding plant functions):

  • Knowing the structure of xylem helps us understand water transport.
  • Studying stomata and mesophyll explains transpiration and photosynthesis.
  • Structure of phloem is related to translocation of food.

C. Agriculture and Forestry:

  • Knowledge of wood anatomy (heartwood vs sapwood, vessel size) is important for timber selection and quality.
  • Anatomical features help in understanding drought resistance, disease resistance and can guide breeding for better crops.

D. Economic Uses:

  • Many plant products like fibres, wood, cork are used commercially, and their quality depends on their anatomical structure.

👉 In simple words, plant anatomy connects structure with function and practical use, making it very important in botany and applied plant sciences.

Q7. Describe the internal structure of a dorsiventral leaf.

Answer:

A dorsiventral leaf is a typical dicot leaf (e.g., sunflower) with distinct upper and lower surfaces.

It shows three main regions in T.S.:

  • Epidermis: It has an upper and lower epidermis. Crucially, the stomata are mostly on the lower surface to prevent water loss from direct sunlight.
  • Mesophyll (The middle tissue): It is differentiated into two types:
    • Palisade Parenchyma: Tall, tightly packed cells near the upper surface. They have many chloroplasts to catch sunlight.
    • Spongy Parenchyma: Loose, round cells with big air gaps near the lower surface. These gaps help gases (CO₂ and O₂) move around.
  • Vascular System: The veins contain vascular bundles. They are reticulate (net-like). The xylem is always facing the upper surface, and phloem faces the lower surface.

👉 Because the upper and lower sides are structurally different, the leaf is called dorsiventral.

Q8. What is heartwood? What is sapwood?

Answer:

In an old tree trunk, the secondary xylem can be divided into two zones:

  1. Heartwood (Duramen):

    • Location: The central, dark-coloured core of the trunk.
    • Nature: It is dead and non-functional (does not conduct water).
    • Function: It is filled with tannins, resins, and gums which make it hard and resistant to insects. Its main job is mechanical support.

  2. Sapwood (Alburnum):

    • Location: The outer, lighter-coloured region surrounding the heartwood.
    • Nature: It contains living parenchyma cells.
    • Function: It is physiologically active and responsible for the conduction of water and minerals from roots to leaves.

👉 Simple memory:

  • Sapwood = "Service wood" (still conducting).
  • Heartwood = "Hard wood" (for strength and durability).

Q9. What are the functions of the vascular cambium?

Answer:

The vascular cambium is a lateral meristem present between xylem and phloem in dicot stems and roots.

Its main functions are:

A. Secondary growth (increase in thickness):

  • Vascular cambium divides continuously and adds new cells.
  • On the inner side, it forms secondary xylem (wood).
  • On the outer side, it forms secondary phloem (bast).
  • This leads to increase in girth of stems and roots.

B. Formation of medullary rays:

  • At some regions, cambium produces parenchyma cells in radial rows.
  • These form secondary medullary rays, which help in radial transport of water and food.

👉 Thus, vascular cambium is responsible for thickening of stems/roots and formation of wood and bast in dicot plants.

Q10. What is the periderm? How does it form?

Answer:

When secondary growth increases the girth of the stem/root, the outer epidermis and cortex cannot stretch and eventually rupture. They are replaced by a new protective tissue called the periderm.

Periderm is a collective term for:

A. Phellem (Cork):

  • Formed outwards from cork cambium.
  • Cells are dead, with suberised walls, and form a protective, waterproof layer.

B. Phellogen (Cork cambium):

  • A lateral meristem that arises usually in the outer cortex.
  • Divides and forms cork outwards and secondary cortex inwards.

C. Phelloderm (Secondary cortex):

  • Formed inwards from cork cambium.
  • Made of living parenchyma cells.

Formation process:

  • A layer of cortical cells becomes meristematic → forms cork cambium (phellogen).
  • Phellogen cuts off phellem (cork) towards outside and phelloderm (secondary cortex) towards inside.
  • Together, phellem + phellogen + phelloderm = periderm.

👉 Periderm completely replaces the old epidermis and acts as a new protective covering in woody plants.

Q11. Describe the process of secondary growth in a dicot stem.

Answer:

Secondary growth in a dicot stem (e.g., sunflower) mainly involves the activity of vascular cambium and cork cambium.

Step 1: Formation of cambial ring

  • Initially, each vascular bundle has intrafascicular cambium between primary xylem and primary phloem.
  • The parenchyma cells of medullary rays (between vascular bundles) become meristematic and form interfascicular cambium.
  • Intrafascicular + Interfascicular cambium join to form a continuous cambial ring.

Step 2: Activity of vascular cambium

  • The cambial ring becomes active and starts dividing.
  • On the inner side, it forms secondary xylem.
  • On the outer side, it forms secondary phloem.
  • More secondary xylem is produced than phloem → stem becomes thicker.
  • Primary phloem is gradually crushed, while primary xylem remains near the centre.
  • At some regions, cambium forms secondary medullary rays for radial conduction.

Step 3: Activity of cork cambium (phellogen)

  • As the stem girth increases, epidermis and outer cortex are stretched and ruptured.
  • A new cork cambium arises in the cortex.
  • Cork cambium forms cork (phellem) towards the outside and secondary cortex (phelloderm) towards the inside.
  • These together form the periderm, which acts as new protective tissue.

👉 Result: The dicot stem becomes woody due to massive deposition of secondary xylem and develops bark on the outside.

Q12. Differentiate between spring wood and autumn wood.

Answer:

Both spring wood and autumn wood are types of secondary xylem, produced in different seasons.

A. Spring wood (Early wood):

  • Formed in spring / early growing season.
  • Cambium is highly active.
  • Produces larger, thin-walled xylem vessels with wider cavities.
  • Wood is lighter in colour and less dense.

B. Autumn wood (Late wood):

  • Formed in autumn / later part of the growing season.
  • Cambium activity is reduced.
  • Produces smaller, thick-walled xylem vessels with narrow cavities.
  • Wood is darker and denser.

👉 One year’s spring wood + autumn wood = one annual ring. This ring can be seen in a cross-section of a tree trunk and is used to estimate the age of the tree.

Q13: Differentiate between collenchyma and sclerenchyma.

Answer:

Both are mechanical tissues, but they differ in many aspects.

Collenchyma:

  • Nature of cells: Living cells.
  • Cell wall: Unevenly thickened at the corners with cellulose, hemicellulose and pectin.
  • Intercellular spaces: Usually absent or very small.
  • Location: Found in young stems, petioles, below epidermis; rarely in leaves.
  • Function: Provides flexible support to growing parts of the plant. Allows bending without breaking.

Sclerenchyma:

  • Nature of cells: Usually dead at maturity.
  • Cell wall: Uniformly thickened and lignified.
  • Types:
  • Fibres: Long, narrow, pointed cells.
  • Sclereids: Short, irregular cells with very thick walls.
  • Location: Present in hard parts like seed coats, nutshells, vascular bundles, etc.
  • Function: Provides rigid, mechanical strength to mature parts.

👉 Memory help:

  • Collenchyma = soft, flexible support for young parts.
  • Sclerenchyma = hard, rigid support for mature parts.

Q14. What are bulliform cells?

Answer:

Bulliform cells are special epidermal cells found in many monocot leaves, especially grasses.

Location: Found in the upper epidermis of monocot leaves (especially grasses).

Structure: They are large, empty, and colourless cells.

Function: They act like water sensors.

  • When water is plenty: They absorb water, become turgid, and the leaf opens up flat.
  • When water is scarce (Stress): They lose water, become flaccid, and make the leaf curl inwards. This hides the surface from the sun to stop water loss.

👉 So, bulliform cells act as water-sensitive motor cells that help the plant conserve water.

Q15: What are lenticels?

Answer:

Lenticels are small, raised, lens-shaped openings in the bark of woody stems.

  • Origin:

  • They are formed by the activity of cork cambium (phellogen).

  • Instead of forming tightly packed cork cells, the cambium at certain points produces loosely arranged parenchyma cells with many intercellular spaces.

  • These cells push outwards, rupture the epidermis, and form a lenticel.

  • Structure:

  • Made up of loosely arranged complementary cells.

  • Appear as small spots or raised areas on the surface of bark.

  • Function:

  • Lenticels provide aeration to the internal tissues.

  • They allow exchange of gases (O₂, CO₂, water vapour) between the atmosphere and the living cells inside the stem, especially when stomata are absent or covered by bark.

👉 In short, lenticels are like tiny breathing pores in woody stems.