Structural Organisation in Animals and Plants

Introduction

Morphology deals with the study of the external forms of plants. Plants and animals are living machines; to understand how they function, we look at their external design (morphology) and internal wiring (anatomy).

1. The Root

Meaning: The root is the underground, non-green, positively geotropic part of the plant that absorbs water and minerals from the soil.

Definitions:

• According to Esau (1977), the root is the descending axis of the plant body that typically grows downward into the soil, anchoring the plant and absorbing water and dissolved nutrients.
• Botany textbooks define the root system as the subterranean vegetative organ system of vascular plants lacking nodes, internodes, and leaves.

Key Points:

• Radicle elongation forms the primary root.
• Tap root system in dicots (e.g., mustard); fibrous root system in monocots (e.g., wheat); adventitious roots arise from parts other than the radicle (e.g., banyan).
• Regions of root tip: Root cap, meristematic activity, elongation, and maturation.
• Modifications: Fusiform (radish), Napiform (turnip), Conical (carrot), Prop roots, Stilt roots, Pneumatophores.

Examples & Real-Life Use

• Carrots and radishes storing food; Rhizophora pneumatophores taking in oxygen.
• Vetiver grass utilized in civil engineering to stabilize slopes and prevent soil erosion.

2. The Stem

Meaning: The stem is the ascending, aerial, green or woody axis of the plant that develops from the plumule, bearing leaves, flowers, and fruits.

Key Points:

• Characterized by nodes and internodes.
• Modifications: Tubers (potato), Rhizome (ginger), Thorns (bougainvillea), Tendrils (cucumber), Phylloclade (Opuntia).

3. The Leaf

Meaning: The leaf is a lateral, flattened, green structure borne on the stem at a node, specialized for photosynthesis and transpiration.

Key Points:

• Venation: Reticulate (dicots) and Parallel (monocots).
• Types: Simple and Compound (pinnate, palmate). Phyllotaxy: Alternate, Opposite, Whorled.

4. Inflorescence & Flower

Meaning: Inflorescence is the arrangement of flowers on the floral axis. The flower is a modified shoot meant for sexual reproduction in angiosperms.

Key Points:

• Racemose (unlimited growth, acropetal) vs Cymose (limited growth, basipetal).
• Flower Whorls: Calyx, Corolla, Androecium, Gynoecium. Symmetry: Actinomorphic and Zygomorphic. Ovary position: Hypogynous, Perigynous, Epigynous.

5. Fruit, Seed & Plant Families

Meaning: A fruit is a mature ovary, and a seed is a fertilized ovule. Plant families group plants by shared morphological traits.

Comparison Table: Plant Families

1. Tissues

Meaning: A tissue is a group of cells having a common origin and usually performing a common function.

Key Points:

• Meristematic (actively dividing: apical and lateral meristems) vs Permanent (simple: parenchyma, collenchyma, sclerenchyma; complex: xylem, phloem).

2. Anatomy of Dicot and Monocot Organs

Comparison Table: Dicot vs Monocot Internal Anatomy

3. Secondary Growth

Meaning: Increase in the girth or width of plant stems and roots due to lateral meristems (vascular cambium and cork cambium).

Key Points:

• Vascular cambium produces secondary xylem (wood) and secondary phloem.
• Cork cambium (phellogen) produces cork (phellem) and secondary cortex (phelloderm), forming the periderm.
• Heartwood (dead, non-conductive) vs Sapwood (living, conductive). Annual rings are used in dendrochronology.

1. Animal Tissues

Comparison Table: Animal Tissues

2. Cockroach (Periplaneta americana) Systems

Key Points:

• Morphology: Head, Thorax, Abdomen. Chitinous exoskeleton, tergites, sternites, pleurites. Anal styles in males, anal cerci in both sexes.
• Digestive System: Foregut (Crop, Gizzard with chitinous teeth), Hepatic caeca, Midgut, Malpighian tubules, Hindgut.
• Circulatory System: Open type, haemocoel, tubular heart with ostia.
• Respiration: Tracheal tubes communicating via 10 pairs of spiracles.
• Excretion: Malpighian tubules excreting uric acid (uricotelic).

Problem 1

In a leaf epidermal peel analysis, counting under a microscope reveals 40 epidermal cells and 10 stomata in a given microscopic field. Calculate the stomatal index (\(SI\)) of the leaf surface.

Formula:

SI = [ S / (E + S) ] × 100

Where \(S = 10\) (stomata) and \(E = 40\) (epidermal cells).

Step-by-Step Solution:

1. SI = [ 10 / (40 + 10) ] × 100
2. SI = [ 10 / 50 ] × 100
3. SI = 0.2 × 100
4. SI = 20%
        

Answer: The stomatal index of the leaf sample is 20%.

• Confocal Laser Scanning Microscopy (CLSM): Captures high-resolution 3D optical slices of plant and animal tissues.
• Scanning Electron Microscopy (SEM): Studies ultra-fine external surface structures at nanoscale magnification.
• CT Scanning in Botany: Non-destructive internal imaging of tree trunks and wood density.
• Laser Microdissection (LMD): Isolates specific plant cell types for transcriptomic analysis.

Scenario: Legume crops (Fabaceae) survived dry spells in central India due to deep tap roots and secondary growth, but faced pest infestations by nocturnal insects (*Periplaneta*-like pests).

Anatomical Findings: Root nodules fixed nitrogen; deep xylem vessels drew groundwater. Pest insects resisted liquid pesticides due to water-conserving chitinous exoskeletons, tracheal breathing tubes bypassing skin absorption, and uric acid excretion via Malpighian tubules.

Solution: Intercropping drought-resistant legumes with drip irrigation, paired with chitin-synthesis inhibitor baits targeting nocturnal insect molting processes.

1. Which of the following plant parts is characterized by the presence of nodes and internodes?
   A) Root
   B) Stem
   C) Root hair
   D) Pneumatophore
   Answer: B | Stems have nodes and internodes.
2. A plant having parallel venation in its leaves is most likely to possess:
   A) Tap root system
   B) Reticulate venation
   C) Fibrous root system and trimerous flowers
   D) Pentamerous flowers
   Answer: C | Monocots show parallel venation, fibrous roots, and trimerous flowers.
3. In a dicot stem, the vascular bundles are described as:
   A) Radial and closed
   B) Conjoint, collateral, and open
   C) Scattered and closed
   D) Concentric
   Answer: B | Dicot stems feature conjoint, collateral, and open vascular bundles.
4. Which plant family is known for its papilionaceous corolla and diadelphous stamens?
   A) Solanaceae
   B) Liliaceae
   C) Fabaceae
   D) Brassicaceae
   Answer: C | Fabaceae features a papilionaceous corolla and 9+1 diadelphous stamens.
5. The cork cambium (phellogen) cuts off cells on its outer side to form:
   A) Secondary xylem
   B) Secondary phloem
   C) Cork (phellem)
   D) Phelloderm
   Answer: C | Cork cambium produces cork externally.
6. Which animal tissue is specialized for lining body cavities and forming protective layers?
   A) Connective tissue
   B) Epithelial tissue
   C) Muscular tissue
   D) Neural tissue
   Answer: B | Epithelial tissue forms continuous protective linings.
7. In a cockroach, excretory wastes are eliminated primarily through:
   A) Malpighian tubules
   B) Green glands
   C) Nephridia
   D) Lungs
   Answer: A | Malpighian tubules absorb and excrete uric acid.
8. The respiratory system of a cockroach consists of:
   A) Lungs
   B) Gills
   C) Tracheal tubes opening via spiracles
   D) Book lungs
   Answer: C | Insects respire via tracheal tubes opening through spiracles.
9. What is the function of gizzard (proventriculus) in a cockroach?
   A) Storage
   B) Grinding food particles
   C) Secretion of enzymes
   D) Water absorption
   Answer: B | The gizzard mechanically grinds food.
10. Which represents a false fruit where the thalamus contributes to fruit formation?
    A) Mango
    B) Pea
    C) Apple
    D) Tomato
    Answer: C | Apple develops from the swollen thalamus.

1. Q: Distinguish between tap root system and fibrous root system with examples.
   Answer: A tap root system develops from the radicle with lateral branches (e.g., mustard). A fibrous root system originates from the stem base with a cluster of slender roots (e.g., wheat).
2. Q: What is venation? Differentiate between reticulate and parallel venation.
   Answer: Venation is the arrangement of veins in a leaf blade. Reticulate forms a net-like web (dicots); parallel features veins running parallel (monocots).
3. Q: Define inflorescence. Differentiate between racemose and cymose inflorescence.
   Answer: Inflorescence is flower arrangement on the axis. Racemose has unlimited main axis growth with acropetal succession; cymose terminates in a flower with basipetal succession.
4. Q: Explain 'Placentation' and name three types.
   Answer: Placentation is ovule arrangement in the ovary. Three types are Marginal (e.g., pea), Axile (e.g., tomato), and Basal (e.g., sunflower).
5. Q: Why are vascular bundles in dicot stems 'open' while monocot stems are 'closed'?
   Answer: Dicot bundles possess vascular cambium between xylem and phloem (open for secondary growth); monocot bundles lack cambium (closed).
6. Q: Differentiate between heartwood and sapwood.
   Answer: Heartwood is dark, central, non-conductive secondary xylem providing mechanical support. Sapwood is light, peripheral, active secondary xylem conducting water.
7. Q: What are the four primary animal tissues? State one function each.
   Answer: Epithelial (lining/protection), Connective (binding/support), Muscular (contraction/movement), Neural (impulse transmission).
8. Q: Describe the structure of a cockroach's heart.
   Answer: The heart is a muscular, tubular organ running along the dorsal side, divided into funnel-shaped chambers with valved openings called ostia.
9. Q: How does respiration take place in a cockroach?
   Answer: Respiration occurs via branching tracheal tubes that communicate with the atmosphere through 10 pairs of spiracles.
10. Q: Explain the formation of ootheca in female cockroaches.
    Answer: Fertilized eggs are encased in a capsule-like ootheca (containing 14-16 eggs) secreted by collateral gland secretions during reproduction.

• Solanaceae Family: Potato, Tomato, Brinjal, Chilli, Ashwagandha.
• Cockroach Alimentary Canal: Mouth → Pharynx → Esophagus → Crop → Gizzard → Ileum → Colon → Rectum.
• Four Animal Tissues: Epithelial, Connective, Muscular, Neural.

Mnemonics:
- Solanaceae: “Potato Tomato Brinjal Chillies Are Super”
- Animal Tissues: “Every Cute Mouse Naps”