Basic External Features of Plants and Animals

Study Notes

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.

Description

Explore the fundamental external characteristics that differentiate plants and animals in this engaging quiz. Learn about the primary classifications based on these traits and discover the diversity of life forms on Earth. Test your knowledge on this essential aspect of biology with a variety of intriguing questions.