Transport in Plants: Overview, Topics, Mechanism, Books, Tips

Transportation in plants is the process by which water, minerals, and other substances are transported with the help of the xylem and phloem. This process is essential for the growth, development, and survival of plants. Plants have specialized tissues like xylem and phloem to carry out the long-distance transport of water, minerals, and food. The flowering plants—angiosperms have a highly coordinated transport system that supports their structure and functions efficiently.

This Story also Contains

1. Types of Transport Systems in Plants
2. Methods of Transportation in Plants
3. Transportation of Water in Plants
4. The Vascular Tissue System
5. Water Movement through Xylem
6. Stomata And Transpiration
7. Root Absorption in Plants
8. Mechanisms of Water Absorption
9. Recommended Video on Transport in Plants

The transport in plants involves various transport mechanisms, like diffusion, facilitated diffusion, active transport, and osmosis. This article includes the absorption of water by the roots, transpiration, and movement of water within the xylem. Translocation is also explained by how food and nutrients move through the phloem. The topic is a must in entrance exams like NEET, AIIMS, where biology is one of the major subjects.

Types of Transport Systems in Plants

Plants use a highly organized transport system to move water, minerals, and nutrients internally. It involves transport across cell membrane in plants that occurs at three levels:

• Cell-to-Cell Movement: The substances are moved from one cell to another through:

1. Diffusion

2. Facilitated diffusion

3. Active transport

4. Plasmodesmata (cytoplasmic connections)

• Long-Distance Translocation: Ascent of sap is the upward transport of water and minerals through xylem via mass flow or bulk flow. Phloem conducts the bidirectional transport of organic nutrients, also by bulk flow, based on the pressure flow hypothesis.

• Uptake and Release: Single cells absorb water and discharge solutes. Excretion or secretion of substances into surrounding tissues or the environment and carried out by osmosis, active transport, or endocytosis/exocytosis.

Also read:

• Plant Water Relations

• Symport Antiport Uniport

• Water Potential and Its Components

Methods of Transportation in Plants

Plants perform their transport procedures through three major types of transportation. Plants transport various substances at the cellular level, mainly through cell membranes, involving passive and active processes.

1. Diffusion

Diffusion in plants is the most common transport mechanism. This is because it does not involve the use of energy; molecules are simply transferred from a region of high concentration to a region of low concentration. The factors that affect this passive process include the concentration gradient, temperature, and pressure.

Importance

It plays a very significant or crucial role in the flow of gases, oxygen, carbon dioxide, and small solutes within the plant tissues.

2. Facilitated Diffusion

Movement of molecules across the cell membrane through particular transport proteins.

Source-to-Sink Model- It quantifies nutrient flow from source to sink—for instance, roots, and fruits—where they are either utilized or stored.

Mass Flow Hypothesis- This is used to explain the phloem sap flow due to the pressure difference between source and sink areas. This result follows because of the osmotic pressure and active transport mechanisms.

Key Proteins Involved:

• Porins: Form pores in cell organelles like mitochondria and plastids that allow specific molecules to pass through.

• Aquaporins: Specialized channels allowing the movement of water molecules.

3. Active Transport

The process by which molecules move against their concentration gradient, thus requiring energy, which is typically derived from ATP.

Significance

It primarily occurs during the absorption of indispensable minerals and nutrients from the soil, generally done to ensure there is ion balance within the plant cell.

Importance of Active Transport:

• This process is important in mineral and nutrient uptake, where they are available in a lower concentration outside the plant.

• It is also a factor contributing to the maintenance of different cellular functions and general health conditions of a plant.

Transportation of Water in Plants

Transportation of water in plants is quite essential for their growth and development. Every cell works along with the vascular system, xylem, and phloem for transporting water and nutrients across the plant. This process is somewhat similar to human circulatory systems carrying blood.

Some of the major processes in plant transport involve the uptake of water and minerals by roots, the flow of these substances through the xylem, the distribution of sugars and other organic compounds through the phloem, and stomata control transpiration in leaves by regulated opening. All these mechanisms are of importance to understanding perfecting plant care and increasing agricultural productivity.

The Vascular Tissue System

The xylem and phloem are the channels for moving substances in the plants. The xylem carries the water and minerals from the roots to the leaves, while the phloem carries the sugars and nutrients produced in the leaves to the rest of the plant. It thus forms like a spider's web, moving from the roots up through the trunk into the leaves.

1. Xylem

• The xylem is a long, hollow tube running from the roots up to the leaves. It includes tracheids, vessel elements, fibres, and parenchyma cells.

• Water in the soil is absorbed by root hairs and moved through cells by osmosis before entering the xylem. The process of water and mineral transport through this tissue in a plant is considered to be one of its most important features.

Transport of Water in the Xylem

• Water and minerals are carried upwards, from the roots to all parts of the plant, through the xylem.

• Meanwhile, sucrose and amino acids are carried throughout the leaves through the phloem.

Types of Xylem Cells

• Tracheids: Long, thin cells with tapered ends; found in all vascular plants

• Vessel Elements: Shorter, wider cells with perforated end walls; primarily in angiosperms

2. Phloem

The phloem serves to bring nutrients and sugars manufactured by the leaves to where they are needed most. The phloem is made up of living cells, which have small pores termed sieve plates for transport. It comprises sieve tubes, companion cells, fibers, and parenchyma cells. It conducts Organic nutrients, mainly sucrose, produced by photosynthesis from leaves to other parts of the plant.

Types of Phloem Cells

• Sieve Tubes: The long tubes formed by sieve tube elements joined end-to-end conduct nutrient transport

• Companion Cells: The cells that assist in conducting the process by providing pressure to the sieve tubes and giving them metabolic support

Water Movement through Xylem

The movement of water in plants through a mechanism involving the long-distance transport of water from roots to leaves is as follows:

1. Cohesion-Tension Theory

Water molecules exhibit cohesion, thereby sticking to one another, and adhesion, thereby sticking to xylem walls, forming a continuous column of water moving upwards due to tension created by transpiration.

2. Capillary Action

The rise of water up through the narrow xylem vessels is occasioned by the combined effects of cohesion and adhesion.

3. Transpiration Pull

Water evaporates through the stomata of the leaf; this creates negative pressure that pulls more water up from the roots through the xylem.

Stomata And Transpiration

Transpiration is the process of loss of water vapor from the aerial parts of plants, mainly through small pores on the leaf surface called stomata. The small leaf surface pores controlled by guard cells regulate gas exchange and the loss of water vapors.

• Factors Affecting Transpiration Rate

Light intensity, temperature, humidity, and wind. Generally, light intensity increases the temperature, which raises the rate of transpiration, and high humidity with low wind reduces it.

• Role in Water Regulation

It regulates the water balance of plants, cools the plant, and the suction force that it pulls helps in the upward flow of nutrients by pulling up water through the xylem.

Root Absorption in Plants

Root hairs are designed to increase the surface area for both water absorption and nutrient mineral intake from the soil. It helps to absorb the water and minerals through osmosis.

• Osmosis: Movement of water into root cells.

• Diffusion: Movement of solutes like mineral ions and gases across membranes.

Mechanisms of Water Absorption

Water is essential for all physiological activities in plants. Its absorption by roots and movement through the plant involve both passive and active mechanisms. Water absorption takes place through two basic mechanisms:

1. Active Absorption

Active absorption of water happens in the symplast with the help of the Diffusion Pressure Deficit. It is relatively slow, and both osmotic and non-osmotic forces play a part. The cells of the root generate the force required to absorb the water; this can be affected by temperature and humidity.

2. Passive Absorption

Passive absorption of water takes place through osmosis, and there is no energy involved. It occurs via the apoplast pathway (through cell walls). It is a dominant method under transpiring conditions.

Other Useful Resources:

Recommended Video on Transport in Plants