Basic External Features of Plants and Animals

Basic External Features of Plants and Animals

• Living beings on Earth are divided into two primary categories: plants and animals.
• External morphology refers to the study of external features, crucial for understanding the differences among organisms.
• Example: Angiospermic plants differ fundamentally from animals in shape and size.

Parts of Angiospermic Plants

• The root is the underground part anchoring the plant, while the shoot refers to the above-ground portion.

Definition and Types of Roots

• Roots develop from the radicle, which can be classified into two main types:
  • True Root: Develops directly from the radicle (e.g., taproot).
  • Adventitious Root: Forms from other plant parts (e.g., fibrous roots).

Taproot Structure

• Composed of the primary root that grows downward, typical in dicotyledons.
• Secondary roots branch from the primary root, producing a complex root system beneficial for stability and nutrient uptake.

Fibrous Root Structure

• Characterized by a cluster of roots emerging from the stem base, common in monocotyledons.
• Retains a weak or non-existent primary root structure, relying on new roots for anchorage.

Root Characteristics

• Grows downwards (positively geotrophic) and is colorless, lacking chlorophyll.
• Root hairs are found behind the root tip, aiding in water and nutrient absorption.
• Roots are negatively phototropic, growing away from light and positively hydrotrophic, growing towards water.

Regions of Taproot and Functions

• Five distinct regions in a young taproot:
  • Root cap region: Protects the root apex from soil interference.
  • Meristematic region: Site of active cell division, renewing root cap.
  • Region of elongation: Cells grow in length, increasing overall root length.
  • Root hair region: Contains one-celled root hairs for absorption.
  • Permanent region: Where lateral branches form.

Stem Functionality and Structure

• The stem is the central axis of the shoot system, supporting branches, leaves, flowers, and fruits.

Parts of the Stem

• Node: Point where leaves emerge.
• Internode: Area between nodes.
• Leaf: Flat extension of the stem responsible for photosynthesis and transpiration.

Buds

• A condensed shoot system containing immature leaves, with axillary buds linked to branching and apical buds aiding stem elongation.

Stem Characteristics

• Develops from the plumule, grows upward, and contains chlorophyll.
• Stems exhibit positive phototropism (grow towards light) and negative hydrotropism (grow away from water).

Types of Stems

• Herbs: Soft and tender, completing their life cycle in varying durations (ephemerals, annuals, biennials, perennials).
• Shrubs: Medium-sized with woody branches that arise near the base, often bushy in nature.
• Trees: Tall, woody structures with a trunk. They can be categorized based on branching (branched or unbranched) and leaf retention (evergreen or deciduous).

Functions of the Stem

• Mechanical: Supports the weight of the plant.
• Physiological:
  • Synthesizes food with chlorophyll.
  • Conducts water and nutrients throughout the plant.
  • Stores surplus food for future needs.