Unit 2: Structural Organisation in Animals and Plants

 Plant Morphology and Modifications

Plant Morphology

Plant morphology, or phytomorphology, is the study of the external form and structure of plants. It is distinct from plant anatomy, which focuses on internal structures at the microscopic level. Morphology plays a crucial role in identifying, classifying, and understanding plants based on their physical traits.

Key Areas of Plant Morphology

1.      Comparative Morphology:

o    Examines structures across different species to identify similarities and differences.

o    Homologous structures (e.g., cactus spines and leaves) share developmental pathways despite differing appearances.

o    Links morphology with plant evolution and paleobotany.

2.      Vegetative and Reproductive Structures:

o    Vegetative Structures: Includes the shoot system (stems and leaves) and root system.

o    Reproductive Structures: Specific to plant groups, such as flowers in angiosperms, sori in ferns, and seed cones in gymnosperms. These are key for taxonomy.

3.      Scale of Study:

o    Ranges from ultrastructure (cellular level) to growth habits (overall plant architecture).

o    Includes cytology and branching patterns.

4.      Developmental Patterns:

o    Plants produce new tissues throughout their life due to embryonic tissues.

o    Development is influenced by environmental factors and life stage, overlapping with physiology and ecology.

Importance in Identification

Morphological traits are used for plant identification through diagnostic characters:

·         Quantitative Characters: Measurable traits (e.g., petal width).

·         Qualitative Characters: Observable features (e.g., leaf shape or flower color).

Plant Modifications

Plants adapt their roots, stems, and leaves to perform additional functions beyond their primary roles.

Root Modifications

Roots are modified for storage, respiration, support, and other functions:

1.      Tap Root Modifications:

o    Conical Roots: Cone-shaped; broad at the base (e.g., carrot).

o    Fusiform Roots: Swollen in the middle; tapering ends (e.g., radish).

o    Napiform Roots: Swollen at one end; tapering sharply at the other (e.g., beetroot).

2.      Adventitious Root Modifications:

o    Tuberous Roots: Swollen roots for storage (e.g., sweet potato).

o    Fasciculated Roots: Tufts of swollen roots (e.g., dahlia).

o    Nodulose Roots: Swollen at specific points for energy storage.

Stem Modifications

Stems are modified for storage, protection, climbing, or vegetative propagation:

1.      Storage Stems:

o    Tubers store food and have buds (e.g., potato).

2.      Protective Stems:

o    Thorns protect against herbivores (e.g., bougainvillea).

3.      Climbing Stems:

o    Tendrils help in climbing (e.g., grapevine).

4.      Propagative Stems:

o    Stolons or runners spread horizontally to form new plants (e.g., strawberry).

Leaf Modifications

Leaves adapt for photosynthesis, transpiration control, support, or defense:

1.      Storage Leaves:

o    Succulent leaves store water (e.g., aloe vera).

2.      Support Leaves:

o    Tendrils aid climbing (e.g., pea plant).

3.      Defensive Leaves:

o    Spines reduce water loss and deter predators (e.g., cactus).

4.      Reproductive Leaves:

o    Some leaves produce plantlets for propagation (e.g., bryophyllum).

Significance of Morphological Data

Morphological data is vital for taxonomy as it helps in identifying species, resolving ambiguities in classification, and supporting phylogenetic hypotheses when molecular evidence is inconclusive. It also aids in breeding programs by selecting desirable traits such as disease resistance or drought tolerance.

By studying morphology and modifications, researchers gain insights into plant adaptation strategies that ensure survival and reproduction across diverse environments.

Plant Tissues

Meristematic Tissue

• Apical Meristem: Root and shoot tips for primary growth.
• Lateral Meristem: Vascular cambium (secondary growth).

Permanent Tissue

1. Simple Tissues:
• Parenchyma: Storage, photosynthesis.
• Collenchyma: Mechanical support.
• Sclerenchyma: Rigidity (dead cells).
2. Complex Tissues:
• Xylem: Water transport (tracheids, vessels).
• Phloem: Food transport (sieve tubes).

Anatomy of Flowering Plants

Root Anatomy

• Epidermis: Absorbs water.
• Cortex: Stores starch.
• Endodermis: Regulates water flow.
• Vascular Bundle: Xylem and phloem arranged radially.

Stem Anatomy

• Epidermis: Protective layer.
• Vascular Bundles: Arranged in rings (dicots) or scattered (monocots).

Leaf Anatomy

• Epidermis: Cuticle reduces water loss.
• Mesophyll: Palisade (photosynthesis) and spongy (gas exchange).

Key Plant Families

Family	Characteristics	Examples
Malvaceae	Hibiscus-like flowers, fibrous bark, cyclopropenoid fatty acids.	Cotton, okra.
Cruciferae	Four-petaled flowers (cruciform), siliqua/silicula fruits5.	Mustard, cabbage.
Leguminosae	Compound leaves, root nodules with nitrogen-fixing bacteria, fruit = legume.	Pea, beans.
Compositae	Composite inflorescence (capitulum), seeds with pappus.	Sunflower, marigold.
Graminae (Poaceae)	Hollow stems (culm), spikelet inflorescence, grains as fruit.	Wheat, rice.

Animal Tissues

1. Epithelial Tissue:
• Simple: Single layer (e.g., alveoli).
• Stratified: Multiple layers (e.g., skin).
2. Connective Tissue:
• Bone: Rigidity.
• Blood: Transport.
3. Muscular Tissue:
• Skeletal: Voluntary movement.
• Smooth: Involuntary (e.g., stomach).
4. Nervous Tissue: Neurons transmit impulses.

Morphology and Anatomy of Frog (Brief)

Digestive System

• Alimentary Canal: Mouth → esophagus → stomach → intestine → cloaca.
• Liver and Pancreas: Secretion of bile and enzymes.

Circulatory System

• Heart: 3-chambered (2 atria, 1 ventricle).
• Blood: Transports nutrients, O₂, and CO₂.

Respiratory System

• Lungs: Main respiratory organ.
• Skin: Cutaneous respiration (moist skin).

Nervous System

• Brain: Forebrain, midbrain, hindbrain.
• Spinal Cord: Transmits signals.

Reproductive System

• Male: Testes produce sperm.
• Female: Ovaries release eggs; external fertilization.

Practical Applications

• Plant Anatomy: Study root/stem cross-sections under a microscope.
• Inflorescence Types: Compare racemose (mustard) vs. cymose (Hibiscus).
• Frog Dissection: Observe organ systems (digestive, circulatory).

This unit integrates structural adaptations with functional roles, emphasizing how form and function are interconnected in living organisms.