Anatomy of Flowering Plants — NCERT Solutions

Given: We need to highlight anatomical differences through illustrations and descriptions.

(a) Monocot Root vs. Dicot Root

Illustration description (T.S. Monocot Root):
From outside inward — Epidermis (with root hairs) → Cortex (multilayered parenchyma) → Endodermis (with Casparian strips) → Pericycle (single layer) → Many alternating xylem and phloem bundles arranged in a ring → Large central pith.

Illustration description (T.S. Dicot Root):
From outside inward — Epidermis → Cortex → Endodermis → Pericycle → 2–6 xylem bundles (exarch) alternating with phloem bundles → Small or no pith.

(b) Monocot Stem vs. Dicot Stem

Illustration description (T.S. Monocot Stem — e.g., maize):
Epidermis → Sclerenchymatous hypodermis → Undifferentiated ground tissue with vascular bundles scattered (more numerous and smaller towards periphery, larger towards centre) → Each vascular bundle oval-shaped, surrounded by sclerenchymatous bundle sheath, with phloem (including water-containing cavity) and xylem (Y-shaped metaxylem).

Illustration description (T.S. Dicot Stem — e.g., sunflower):
Epidermis (with trichomes) → Collenchymatous hypodermis → Cortex (parenchyma) → Endodermis (starch sheath) → Pericycle (sclerenchyma + parenchyma) → Ring of vascular bundles (each with xylem below, cambium in middle, phloem above) → Large central pith.

Conclusion: The key differences lie in the arrangement of vascular bundles (scattered vs. ringed), type of hypodermis, presence/absence of cambium, and differentiation of ground tissue.

Given: A transverse section (T.S.) of a young stem is observed under the microscope.

Concept: Monocot and dicot stems differ in several anatomical features visible in T.S.

Observations and Reasoning:

To ascertain whether the stem is monocot or dicot, observe the following features:

1. Hypodermis:

• If hypodermis is sclerenchymatous → Monocot stem
• If hypodermis is collenchymatous → Dicot stem

2. Arrangement of Vascular Bundles:

• If vascular bundles are scattered throughout the ground tissue → Monocot stem
• If vascular bundles are arranged in a ring (eustele) → Dicot stem

3. Ground Tissue:

• If ground tissue is not differentiated into cortex and pith → Monocot stem
• If ground tissue is differentiated into cortex, endodermis, pericycle and pith → Dicot stem

4. Bundle Sheath:

• If each vascular bundle is surrounded by a sclerenchymatous bundle sheath → Monocot stem
• If bundle sheath is absent or parenchymatous → Dicot stem

5. Cambium:

• If cambium is absent (closed vascular bundle) → Monocot stem
• If cambium is present between xylem and phloem (open vascular bundle) → Dicot stem

6. Pith:

• Absent or indistinct → Monocot stem
• Large and distinct → Dicot stem

Conclusion: By examining the above features — especially the arrangement of vascular bundles (scattered vs. in a ring) and the presence or absence of cambium — one can confidently identify the stem as monocot or dicot.

Given:

• Vascular bundles are conjoint, scattered, and surrounded by sclerenchymatous bundle sheath.
• Phloem parenchyma is absent.

Concept: These are characteristic anatomical features used to identify plant organs.

Identification:
The plant material is a Monocotyledonous stem (e.g., stem of maize/*Zea mays*).

Reasons:

1. Conjoint vascular bundles — xylem and phloem are present together in the same bundle, which is a feature of stems.

2. Scattered arrangement of vascular bundles throughout the ground tissue is the hallmark of monocot stems (atactostele).

3. Sclerenchymatous bundle sheath surrounding each vascular bundle is characteristic of monocot stems.

4. Absence of phloem parenchyma is a distinguishing feature of monocot stems; in dicot stems, phloem parenchyma is present.

Conclusion: The given plant material is a monocotyledonous stem.

Stomatal Apparatus:
The stomatal apparatus refers to the stomata along with the surrounding subsidiary (accessory) cells. It includes the guard cells, the stomatal pore between them, and the subsidiary cells (epidermal cells surrounding the guard cells).

Structure of Stomata:

Each stoma is composed of the following parts:

1. Stomatal Pore:

• A small opening (pore) present in the epidermis of leaves, young stems and other green parts.
• It allows gaseous exchange ($\text{CO}_2$, $\text{O}_2$, water vapour) between the plant and the atmosphere.

2. Guard Cells:

• Each stoma is surrounded by two guard cells.
• In dicots, guard cells are bean-shaped (kidney-shaped).
• In monocots (grasses), guard cells are dumbbell-shaped.
• Guard cells contain chloroplasts and can perform photosynthesis.
• The inner walls (facing the pore) of guard cells are thick and inelastic, while the outer walls are thin and elastic.
• This differential thickening causes the pore to open and close:
• When guard cells are turgid (absorb water) → outer walls bulge outward → inner walls curve → pore opens.
• When guard cells are flaccid (lose water) → walls straighten → pore closes.

3. Subsidiary (Accessory) Cells:

• Specialised epidermal cells surrounding the guard cells.
• They assist in the movement of guard cells.

4. Substomatal Chamber (Air cavity):

• A large intercellular space below the stomatal pore.
• Facilitates gaseous exchange with the mesophyll cells.

Labelled Diagram Description:

$$\boxed{\text{Stomatal Apparatus (T.S.)}}$$

The diagram should show:

• Epidermal cells on either side
• Two bean-shaped guard cells enclosing the stomatal pore
• Thick inner wall and thin outer wall of guard cells
• Chloroplasts inside guard cells
• Subsidiary cells flanking the guard cells
• Substomatal chamber below the pore

(Note: Draw a neat labelled diagram showing the above components in transverse section and surface view.)

Function: Stomata regulate transpiration and gaseous exchange. They open during the day (when guard cells are turgid due to photosynthesis-driven $\text{K}^+$ ion accumulation) and close at night.