Root, Stem, Leaf, Stomata

Key Concepts

• Root
• Stem
• Leaf
• Stomata

Introduction: 

Our body includes organs such as the stomach, heart, liver, kidney, etc., and organ systems like the digestive system, circulatory system, excretory system, etc. All these systems work together to perform various animal functions. The same way plants also consist of organs like root, stem, leaves, etc., that are made of cells and tissues. Plant tissues contain cells that consist of specific organelles.  All these cells, tissues, and organs carry out the essential activities of lives in plants. 

Explanation: 

Plant organs 

Plants consist of cells with organelles in which specific metabolic activities take place. Plants also contain similar cells working together to form a tissue. Different types of tissue work collectively to perform a unique function, they form an organ. Organs work together to form organ systems.  

The vascular plants have two systems: a shoot system and a root system. The organs of the shoot system contain the vegetative (non-reproductive) parts, like the leaves and the stems, and the reproductive parts, which include flowers and fruits. The root system includes the parts which are underground, such as roots, tubers, and rhizome. 

The shoot system generally grows above ground and absorbs the sunlight needed for photosynthesis. The root system supports the plants and absorbs water and minerals from the soil.  

Root System 

Root system is present below the soil. The main functions of a root system are – 

• Fixing the plant in soil to absorb water and minerals.  
• Transporting the water and mineral in upward direction. 
• Storing of photosynthetic products. 

Some plants have adventitious roots which grow above the ground shoot system, whereas some plants have modified roots for gaseous exchange and absorption of moisture from the soil. 

Root systems are mainly of two types – tap root system and fibrous root system. 

Taproot system:  

It is the main root that grows downward in the soil from which many lateral roots grow. It penetrates deep into the soil and anchors the plant very firmly. It is the main root system of the dicotyledonous plant. Examples of taproot system – Rose, neem, beans, gram, carrot, beetroot. 

Fibrous root system: 

They have a dense network of roots and are present close to the soil surface. It helps to prevent soil loss. They cannot help plants in anchoring. It is the main root system of monocotyledonous plants. Examples of taproot systems – grass, maize, rice, wheat. 

Adventitious root system: 

These roots develop from any part of the plant such as nodes (money plant), stem cutting (rose plant) except radical. According to the species, this root system can be thick, thin, or modified.  

Regions of root 

There are four regions of root.  

1. Root cap: This is a rapidly dividing region produced by meristematic zone. Its function is to protect the apical meristem. As the root grows down the soil, root cap wears out and is constantly renewed. The main function of root cap is to absorb water and minerals from the soil. Root cap is absent in some aquatic and parasitic plants. It is replaced by special cells called root pockets. 

2. Meristematic region: It is present above the root cap. The cells of this region are small, thin walled and consists of dense protoplasm. It helps in root elongation by dividing the cells and forming new cells for the developing root. 

3. Elongation region: It is present above the meristematic region. They are not capable of cell division. This region helps to increase the length and size of the root cell that has lost the capability of cell division. It helps in the absorption of water and minerals from the soil. 

Maturation region: It is present above the elongation region. It develops when the cells of elongation region mature into specialized tissues such as cortex, endodermis and root hairs. This region helps in the formation of specialized tissues that helps in conduction (xylem, phloem) and absorption of water and minerals from the soil.  

Shoot system 

The shoot system consists of stem, leaves, flowers, and fruits.  

Stem: The main function of the stem is to provide support to the plant by holding leaves, buds, fruits, and flowers. It helps in the transportation of water and minerals absorbed by the roots to various parts of a plant. It also helps in the transportation of sugar prepared by leaves by photosynthesis to other parts of a plant. Stems are mostly above the ground but stems of some plants such as potatoes, sweet potatoes also grow underground. 

There are different types of stems: Woody, herbacious, branched and unbranched. 

Woody stems are hard and woody, whereas herbaceous stems are green in colour and soft. Branched stems have division and side stems. Unbranched stems have a single stem. 

Nodes and internodes are part of the stem. The points of attachment for leaves and flower is called nodes. The stem which is present between two nodes is called an internode. The stalk that extends from the base of the leaf to the stem is called a petiole. The axillary bud is present between the petiole and the stem. The axillary bud is also called a lateral bud. The axillary bud gives rise to a flower or a new branch. The apical bud is present at the tip of the shoot system that contains the apical meristem. The various plant organs and stems grow from the ground tissue.  

Leaves 

The main source of food is leaves. Food is prepared by the process of photosynthesis. Leaves are mostly green in color due to the presence of green color pigment called chlorophyll which is present in the cells of the leaf. Some leaves have different color due to the presence of various color pigments. The leaves are attached to the plant stem by petiole which holds the leaves in the correct position. There are some plants where leaves are directly attached to the stem without a petiole. 

Leaf base is the part of the leaf that attaches to the petiole and the petiole attaches to the stem. Stipules are two leaf-like structures present at the leaf base.  Lamina or leaf blade is the green part of the leaf. It has a broad and flat surface. Leaf-blade consists of branched veins and venules.  It helps in the transportation of water and nutrients. It also gives strength to the leaf. The midrib is the vein that runs from the middle line of the leaf. 

Leaf venation is the design made by veins in leaf. Suppose, the design is like a network, then it is called a reticulate venation. If that design of veins looks like parallel to each other, it is called a parallel venation. The plants which has reticulate venation are rose, coriander, neem etc. The examples of parallel venation are grass, paddy, maize, sugarcane etc. 

Stomata 

Stomata (singular is stoma) are present in the epidermis (surface of the leaf). They are tiny microscopic pores or openings which help in the gaseous exchange of O₂, CO₂, and water in the process of photosynthesis. It is observed under microscope. Stomata help in the release of water vapor into the atmosphere. 

Stomata helps in reducing water loss by closing when the situation is hot and dry. It also helps in transpiration. A stoma is surrounded by two cells called as guard cells. The shape of these cells is crescent. These guard cells contract and enlarge to open and close the stomatal aperture. Stomata are open in daytime when photosynthesis occurs. In the process of photosynthesis, the stomata open up and takes in CO₂ from the air and releases O₂ and water vapor in the atmosphere. In the nighttime, stomata are closed because photosynthesis does not take place in the absence of light. So closed stomata help to prevent water loss from the leaf. 

Summary

• Plant tissues contain cells which consists of specific organelles.
• The vascular plants have two systems: a shoot system, and a root system.
• Root system is present below the soil. It is of two types – tap root system and fibrous root system.
• The shoot system consists of stem, leaves, flowers, and fruits.
• The main function of stem is to provide support to the plant and transportation of water and minerals absorbed by the roots to various parts of a plant.
• Leaves are the main source of food which is prepared by the process of photosynthesis.