Transport In Plants - Session 1

Imagine a world without plants. No lush green forests, no colourful flowers, and no delicious fruits. Plants provide oxygen, food, and shelter for countless organisms. But have you ever wondered how plants manage to transport water, nutrients, and other essential substances from their roots to the tips of their leaves? It is a fascinating process that occurs within the intricate system of plant tissues.

We begin our exploration with the outermost layer of plant tissue, known as the epidermis. Like our skin, the epidermis acts as a protective barrier. It shields the plant from physical damage and reduces water loss. Epidermis consists of tightly packed cells. These cells often have a waxy coating called the cuticle. Cuticle helps to minimize the evaporation of water.

Epidermis also contains specialized structures called stomata. Stomata are microscopic pores found in the epidermis of leaves and stems. These tiny openings allow for gas exchange between the plant and its environment. They facilitate the uptake of carbon dioxide and the release of oxygen.

Each stomata consists of two specialized cells called guard cells. These guard cells regulate the opening and closing of the stomatal pore. Stomatal pore opens when guard cells are filled with water and become turgid. This enables the plant to take up carbon dioxide from environment and release oxygen. When the guard cells undergo loss of water and become flaccid, the stomatal pore closes. This prevents excessive water loss.

Inside the leaves, we find a special tissue called the mesophyll. These cells are responsible for the green color of plants. The mesophyll cells contain chloroplasts. Chloroplasts capture sunlight and converts it into energy. This energy is used to produce sugars, which are essential for the growth and survival of plant.

The mesophyll is divided into two distinct layers. These layers are palisade mesophyll and the spongy mesophyll. The palisade mesophyll consists of vertically elongated cells arranged parallel to the leaf surface. These cells contain numerous chloroplasts and are responsible for the majority of photosynthesis. The spongy mesophyll is located beneath the palisade mesophyll. It consists of loosely arranged cells with air spaces between them. They allow for gas exchange and facilitate the diffusion of gases in and out of the leaf.

Vascular bundles are complex networks of specialized tissues. They are responsible for the transport of water, nutrients, sugars, and other substances throughout the plant. They are found in stems, leaves, and roots. Vascular bundles consist of two main types. These are xylem and phloem.

Xylem is responsible for the upward transport of water and minerals from the roots to the aerial parts of the plant. It is composed of several cell types, including vessel elements and tracheids. Vessel elements are wide, cylindrical cells joined end to end to form long tubes called vessels. Tracheids are elongated cells with tapered ends and overlapping secondary cell walls. These cells are dead at maturity. They provide structural support to the plant. The xylem also contains substances such as lignin. Lignin strengthens the cell walls and helps prevent collapse.

Phloem is responsible for the transport of organic compounds, mainly sugars, throughout the plant. It moves these nutrients both upwards and downwards. The main cell types in the phloem are sieve elements, which include sieve tube elements and companion cells. Sieve tube elements are elongated, living cells that form tubes. Sap flows through these tubes. Sap is a sugary fluid. Companion cells are intimately associated with sieve tube elements. Companion cells provide metabolic support to keep the sieve tube elements functioning.

The cortex is a region between the epidermis and the vascular cylinder in the root. It consists of parenchyma cells and plays several important roles. The cortex stores nutrients and water. It provides mechanical support to the root. It also helps in the movement of water and solutes towards the vascular tissues. In some plants, the cortex also performs functions such as root hair development and secretion of substances involved in nutrient uptake.

The endodermis is a single layer of cells that surrounds the vascular cylinder in the root. It acts as a selective barrier. It controlls the movement of water and solutes into the vascular tissues. The endodermal cells are unique because they possess a band like structure called the Casparian strip. This strip is composed of suberin. Suberin is a waxy substance that blocks the passage of water and solutes between cells. The endodermis also plays a role in nutrient uptake and can selectively transport ions into the vascular tissues.

Adjacent to the endodermis lies the pericycle. Pericycle is a layer of cells that surrounds the vascular cylinder. The pericycle is responsible for lateral root development. Pericycle contains actively dividing cells that can give rise to new roots. It increases the capacity of plant for water and nutrient absorption.

Root hairs are tiny projections that look like fingers. They extend from the surface of young roots. They greatly enlarge the surface area of the root. Root hairs facilitate the absorption of water and nutrients from the soil. Root hairs are thin walled, elongated cells that grow from the epidermal cells of the root. Their large surface area allows for efficient water and mineral uptake.

Parenchyma cells are versatile and the most common type of plant cells. They are involved in various functions depending on their location within the plant. Parenchyma cells can be found in the epidermis, cortex, mesophyll, and other plant tissues. They often have thin cell walls and contain large vacuoles. Parenchyma cells can perform functions such as photosynthesis, storage of nutrients and water, secretion, and support.

Sclerenchyma cells are long, thick walled cells that provide mechanical strength and support to plant tissues. They are characterized by their heavily lignified secondary cell walls. This cell wall makes them rigid and resistant to bending or stretching. Sclerenchyma fibers are commonly found in stems, leaves, and other parts of the plant. Their primary function is to provide structural support, especially in mature and woody plants.