Structural Organisation in Animals and Plants

All living organisms, whether simple or complex, comprise cells — life's basic structural and functional units. However, in multicellular organisms like plants and animals, these cells are organized into specific structural levels that allow them to perform complex biological functions efficiently. In plants, tissues are mainly classified into meristematic and permanent tissues, each serving unique roles like growth, support, transport, and photosynthesis. The structure of plant organs like roots, stems, and leaves reflects their functions in absorption, transport, and food production. In animals, particularly invertebrates and vertebrates, tissues are classified into four major types: epithelial, connective, muscular, and nervous tissues. These tissues combine in various ways to form organs like the heart, lungs, and stomach, which are then part of larger systems such as the circulatory, respiratory, and digestive systems..

1.0Morphology of Flowering Plants

• Angiosperms show a large diversity in external structure or morphology. 
• They are all characterized by roots, stems, leaves, flowers and fruits. 

Root System

Roots anchor the plant and absorb water and minerals.

Types:

• Tap root system - In most dicotyledonous plants, radicals directly elongate into the primary root, which grows inside the soil. Primary root bears lateral roots such as secondary and tertiary roots. The primary root and its branches constitute the top root system. e.g. Mustard plant
• Fibrous root system - Fibrous root system In monocot Primary root is short-lived & replaced by many roots originating from the base of the stem. E.g. Wheat plant
• Adventitious roots - Roots arise from plant parts other than the radicle. eg. Grass, Monstera, Banyan

Stem

• The ascending part of the axis bears branches, leaves, flowers and fruits. It develops from the plumule 
• Stem bears nodes and internodes. 
• The stem region where leaves are born is called a node, while internodes are the portions between two nodes.

Main Functions of Stem

• Spreading out branches bearing leaves, flowers and fruits. 
• It conducts water, minerals and photosynthesizes. 
• Some stems perform the function of storage of food, support, protection and vegetative propagation

Leaf 

• It develops at the node and bears a bud in its axil.  
• Originates from shoot apical meristem and are arranged in an acropetal order.  
• A typical leaf has three main parts: Leaf base, petiole and lamina.  
• Pulvinus: Swollen leaf base. (In some leguminous plants.)  
• Sheathing leaf base: In monocotyledonous plants.
• The petiole helps hold the blade to light. 
• Petioles allow leaf blades to flutter in the wind, cooling leaf lamina and bringing fresh air to the leaf surface.

Phyllotaxy - Arrangement of leaves on stem or branch 

• Alternate: One leaf at each node, e.g. china rose, mustard, sunflower 
• Opposite: Two leaves at each node, e.g. Calotropis, Guava 
• Whorled: More than two leaves at each node, e.g. Alstonia

The inflorescence: The arrangement of flowers on the floral axis is called inflorescence.

Flower

• A flower is a modified shoot wherein the shoot's apical meristem changes to a floral meristem.  Internodes do not elongate, and the axis gets condensed.  
• Apex produced different floral appendages laterally at successive nodes instead of leaves.  
• When a shoot tip transforms into a flower, it is always solitary.

The Fruits

• Characteristic features of the flowering plants.  
• A mature or ripened ovary, after fertilization, develops into a fruit.  
• Fruit = Seeds + Pericarp (May be dry or fleshy) 
• When pericarp is fleshy, it is differentiated into epicarp, mesocarp and endocarp.

2.0Anatomy of Flowering Plants

• The study of the internal structure of plants is called anatomy. 
• The internal structure of plant organs also shows variations. 
• Monocots and dicots are also seen to be anatomically different. 
• Internal structure also shows adaptation to diverse environments.

Epidermal Tissue System

Epidermis: Outermost protective covering of primary plant body, Usually single-layered; Parenchymatous Cells have a central vacuole 

Cuticle: Waxy layer outside epidermis Prevents water loss from transpiration Absent in roots 

Stomata: Present in leaves, usually Regulates gaseous exchange and transpiration. Guard cells regulate the opening and closing of stomata.

Ground Tissue System

• All tissues except the epidermis and vascular bundle from ground tissue.
• A major part of plant organs consists of Simple permanent tissues (such as parenchyma, collenchyma, and sclerenchyma).
• Ground tissue system of leaf: Mesophyll.

Vascular Tissue System

• Conducting tissue 
• Xylem and phloem 
• Water, mineral and food conduction

Anatomy of Dicotyledonous Root

• The dicotyledonous root is a crucial part of a dicot plant that anchors it to the soil and helps absorb water and minerals. Unlike monocots, dicots typically have roots with a taproot system. 
• The internal structure of a dicot root shows a well-organized arrangement of tissues, which includes the epidermis, cortex, endodermis, pericycle, vascular bundles, and pith. 
• These tissues are arranged in a radial pattern and play specific roles in support, transport, and storage. 
• The study of dicot root anatomy helps us understand how these plants maintain stability and efficiently transport nutrients and water throughout the plant body.

Monocotyledonous Root

• The anatomy of the monocot root is similar to the dicot root in many respects. 
• It has an epidermis, cortex, endodermis, pericycle, vascular bundles and pith. 
• Compared to the dicot root, which has fewer xylem bundles, there are usually more than six (polyarch) xylem bundles in the monocot root. 
• The pith is large and well-developed. Monocotyledonous roots do not undergo any secondary growth.

Dicotyledonous Stem

• The stem of a dicotyledonous plant plays a vital role in supporting leaves, flowers, and fruits, as well as transporting water, minerals, and food throughout the plant. 
• In dicots, the stem typically shows a circular arrangement of vascular bundles in a ring, a key feature distinguishing them from monocots. 
• The anatomy includes distinct tissues such as the epidermis, cortex, endodermis, pericycle, vascular bundles (xylem and phloem), and pith. 
• One of the significant characteristics of a dicot stem is its ability to undergo secondary growth due to the presence of vascular cambium, leading to the formation of wood and an increase in stem thickness over time.

Monocotyledonous Stem

• The monocot stem has a sclerenchymatous hypodermis, a large number of scattered vascular bundles, each surrounded by a sclerenchymatous bundle sheath, and a large, conspicuous parenchymatous ground tissue. 
• Vascular bundles are conjoint and closed. 
• Peripheral vascular bundles are generally smaller than the centrally located ones. 
• The phloem parenchyma is absent, and water-containing cavities are present within the vascular bundles.

3.0Structural Organisation in Animals 

• These tissues are organised in specific proportions and patterns to form an organ like the stomach, lung, heart and kidney. 
• When two or more organs perform a common function by  their physical and/or chemical interaction, they together form an organ system, e.g., the digestive  system, respiratory system, etc.
• In a tissue, cells may be dissimilar in structure and function but they are always similar in origin.

Types of Tissues

A group of similar cells along with intercellular substances perform a specific function called tissue.

Frogs

Frogs can live both on land and in freshwater and belong to class Amphibia of phylum Chordata. The most common species of frog found in India is Rana tigrina.