Anatomy of Flowering Plants - Exercises

Subject: Biology
Chapter: 6 - Anatomy of Flowering Plants

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Exercises

1. Draw illustrations to bring out the anatomical difference between: (a) Monocot root and Dicot root:

• Dicot Root: Fewer xylem bundles (2-4), inconspicuous pith, presence of secondary growth.
• Monocot Root: Many xylem bundles (polyarch, > 6), large well-developed pith, no secondary growth. (b) Monocot stem and Dicot stem:
• Dicot Stem: Vascular bundles arranged in a ring, conjoint, open, with medullary rays and central pith.
• Monocot Stem: Vascular bundles scattered, conjoint, closed, each surrounded by a sclerenchymatous bundle sheath.

2. Cut a transverse section of young stem of a plant from your school garden and observe it under the microscope. How would you ascertain whether it is a monocot stem or a dicot stem? Give reasons. Answer: By observing the arrangement of vascular bundles:

• Dicot Stem: Vascular bundles are arranged in a ring. They are conjoint, open (with cambium), and endarch. There is a distinct cortex, pericycle, and pith.
• Monocot Stem: Vascular bundles are scattered throughout the ground tissue. They are conjoint, closed (no cambium), and often smaller at the periphery. There is no distinct cortex or pith; the ground tissue is mostly undifferentiated parenchyma.

3. The transverse section of a plant material shows the following anatomical features - (a) the vascular bundles are conjoint, scattered and surrounded by a sclerenchymatous bundle sheaths. (b) phloem parenchyma is absent. What will you identify it as? Answer: It is identified as a Monocotyledonous Stem.

4. What is stomatal apparatus? Explain the structure of stomata with a labelled diagram. Answer: Stomatal apparatus consists of the stomatal aperture (pore), two guard cells, and the surrounding subsidiary cells.

• Structure: Stomata are small pores in the leaf epidermis. Each is enclosed by two bean-shaped guard cells (in dicots) or dumb-bell shaped guard cells (in grasses). The inner walls of guard cells are thick, while the outer walls are thin. They contain chloroplasts and regulate the opening and closing of the pore, controlling transpiration and gas exchange.

5. Name the three basic tissue systems in the flowering plants. Give the tissue names under each system. Answer:

1. Epidermal Tissue System: Epidermal cells, stomata, and epidermal appendages (trichomes and hairs).
2. Ground (Fundamental) Tissue System: Simple tissues like parenchyma, collenchyma, and sclerenchyma.
3. Vascular (Conducting) Tissue System: Complex tissues like xylem and phloem.

6. How is the study of plant anatomy useful to us? Answer: Plant anatomy study is useful for:

• Understanding the internal organization and functional specialization of plants.
• Identifying plants and plant materials, which is crucial in forensic science and pharmacognosy.
• Studying adaptations of plants to different environmental conditions.
• Differentiating between monocots and dicots, which has practical implications in agriculture and horticulture.
• Understanding evolutionary relationships between different plant groups.

7. Describe the internal structure of a dorsiventral leaf with the help of labelled diagrams. Answer: A dorsiventral (dicot) leaf has three main parts:

1. Epidermis: Covers both upper (adaxial) and lower (abaxial) surfaces, often with a waxy cuticle. The lower surface usually has more stomata.
2. Mesophyll: The tissue between the upper and lower epidermis, made of parenchymatous cells containing chloroplasts. It is differentiated into:
   • Palisade Parenchyma: Adaxially placed, elongated cells arranged vertically and parallel to each other.
   • Spongy Parenchyma: Below the palisade cells, oval or round, loosely arranged with large air cavities.
3. Vascular System: Includes vascular bundles found in veins and the midrib. These are surrounded by a layer of thick-walled bundle sheath cells. Xylem is typically located towards the upper surface, while phloem is towards the lower surface.