How is Food Transported in Plants -Class 10

Question – How is Food Transported in Plants?

Answer –

Transportation-

• Transportation is the process of Transporting essential nutrients, water and food to various parts of living organisms
• In Plants, the process of Transporting food to various parts of the Plant from the leaves is called Translocation.

Phloem-

• Phloem is a complex permanent tissue present in all vascular Plants that helps in the Transportation of synthesised food from the leaves to various storage organs.
• Phloem consists of various elements, including Phloem parenchyma, Phloem fibres, companion cells and sieve tubes.
• The Transportation of food in Plants through Phloem is bidirectional, occurring in both upward and downward directions.

Mechanism of Translocation-

• The process of Translocation is driven by a pressure gradient created by the loading of sucrose into the sieve tube elements in the leaves and the unloading of sucrose in the sink tissues, such as roots, stems and fruits.
• Sucrose is actively Transported from source tissues, such as leaves, to sink tissues, such as developing fruits or growing roots.
• The pressure gradient created by this Transport process causes Phloem sap to flow from source tissues to sink tissues.

Types of Translocation-

• There are two types of Translocation- source-to-sink Translocation and sink-to-source Translocation.
• In source-to-sink Translocation, sucrose is Transported from source tissues, such as leaves, to sink tissues, such as developing fruits or growing roots.
• In sink-to-source Translocation, sucrose is Transported from sink tissues back to source tissues, such as leaves, where it can be used for energy or stored for future use.
• The type of Translocation that occurs depends on the metabolic needs of the Plant at a given time.

Factors Affecting Food Transportation in Plants-

• Environmental factors, such as temperature, light and water availability, can affect the rate of Translocation in Plants.
• Hormonal factors, such as the level of Plant growth hormones like auxins and gibberellins, can also affect Translocation.
• Diseases and pests can also affect food Transportation in Plants.
• ATP is essential for the process of Translocation to occur.

How is Food Transported in Plants – Detailed Explanation 

Food is Transported in Plants through a process called Translocation, which involves the movement of food from the leaves to other parts of the Plant. Food Transportation is an important  function of the Plant Transport system. Through this process, Plants are able to distribute the food they produce during Photosynthesis to all parts of their body. This allows them to grow, repair damaged tissues and carry out other essential functions.

To understand this complete process of food Transportation it’s important to understand  the process of food Transportation in Plants with the anatomy of Plants and the different types of Plant tissues that are involved in this process. It is also important to understand the process of Photosynthesis, which is responsible for food production in Plants. From there, we will explore the Phloem, the specialised tissue responsible for food Transportation in Plants. We will also explain the components of Phloem sap, the mechanism of Translocation and the different types of Translocation. We will also discuss the factors that can affect food Transportation in Plants and their implications for Plant growth and survival.

Plant Anatomy

Structure of a Typical Plant

A Typical Plant has several basic parts, including the roots, stem, leaves and flowers. The roots are responsible for anchoring the Plant in the soil and absorbing water and minerals from the soil. The stem supports the Plant and serves as a conduit for Transporting water and nutrients from the roots to the leaves. The leaves are where Photosynthesis occurs and they are responsible for producing food for the Plant. Flowers are responsible for reproduction in Plants.

Types of Plant tissues

There are three main types of Plant tissues: dermal, ground and vascular. Dermal tissues are found on the outer surface of the Plant and serve as a protective barrier. Ground tissues are located in the interior of the Plant and are responsible for functions such as Photosynthesis and storage of food and water. Vascular tissues, which are the most important for food Transportation, are responsible for the movement of water, minerals and nutrients throughout the Plant.

Vascular System of Plants

The Vascular System in Plants is a complex network of specialised tissues that Transport water, minerals and food throughout the Plant. This system is crucial to the survival and growth of the Plant, as it allows for the distribution of essential substances to all parts of the Plant.

The Vascular System is composed of two main types of specialised tissues- 

Xylem 

Phloem. 

Xylem is responsible for Transporting water and minerals from the roots to the rest of the Plant, while Phloem is responsible for Transporting food, primarily in the form of sucrose, from the leaves to the rest of the Plant.

Xylem

Xylem tissue is made up of long, hollow cells called tracheids and vessel elements that are arranged end-to-end to form a continuous tube. These cells are dead at maturity and have thick, lignin-rich cell walls that provide structural support to the Plant. As water is absorbed by the roots, it is Transported through the Xylem vessels by a process called Transpiration. Transpiration is the loss of water vapour from the leaves through small pores called stomata. As water evaporates from the leaves, it creates a negative pressure gradient that pulls water up through the Xylem vessels from the roots to the leaves.

Also Check -What are the Differences between the Transport of Materials in Xylem and Phloem?

Phloem

• The Phloem is a specialised tissue in Plants that is responsible for Transporting food, primarily in the form of sucrose, from the leaves to the rest of the Plant. 
• The Phloem tissue is composed of living cells called sieve tube elements and companion cells, which work together to form a continuous tube that spans the entire length of the Plant.
• Sieve tube elements are elongated cells that are arranged end-to-end to form the Phloem tube. These cells are characterised by their lack of a nucleus and other organelles, which allows for an unobstructed flow of sap through the tube. Companion cells, on the other hand, are small, nucleated cells that are closely associated with the sieve tube elements. They play a vital role in supporting the function of the sieve tube elements, providing them with energy and other essential substances.

Role of Phloem in Transportation of Food in Plants

• The Phloem plays a critical role in the distribution of food throughout the Plant. During Photosynthesis, the leaves produce glucose that is then converted into sucrose for Transport through the Phloem. The sucrose is loaded into the sieve tube elements in the leaves, creating a high concentration of sugar in these cells. This creates a pressure gradient, with high pressure in the source tissues (i.e., the leaves) and low pressure in the sink tissues (i.e., the roots, stems and fruits).
• Together, the xylem and phloem tissues form a continuous system of conduits that connect all parts of the plant. This allows for the efficient transport of water, minerals, and food, which is essential for the growth and survival of the plant. 

Also Check – Functions of the Xylem and Phloem

Components of Phloem sap

• Phloem sap is the fluid that is Transported through the Phloem tissue from the leaves to the rest of the Plant. It is a watery solution that contains primarily sucrose, which is the main form of sugar used by Plants for energy. The concentration of sucrose in Phloem sap can vary depending on the needs of the Plant, but it is typically around 10-30%.
• In addition to sucrose, Phloem sap also contains other important nutrients such as amino acids and hormones. Amino acids are the building blocks of proteins that are essential for Plant growth and development. Some hormones, such as auxins and cytokinins, are important for regulating various physiological processes in Plants.
• The composition of Phloem sap can also vary depending on the type of Plant and environmental conditions. For example-  some Plants may produce Phloem sap that contains higher levels of amino acids to help them cope with stress, while others may produce Phloem sap that contains more sucrose to support growth and development.

Also Check – 15 Difference between Xylem and Phloem

Mechanism of Translocation

Translocation in Plants involves the active Transport of sucrose into the sieve tube elements in the source tissue, the creation of a pressure gradient that drives the flow of Phloem sap and the active unloading of sucrose from the sieve tube elements in the sink tissue. This process ensures that the Plant is able to Transport the nutrients and energy it needs to grow and survive.

Steps of Translocation are as follows 

1. Loading of sucrose- During Photosynthesis, sucrose is produced in the leaves and stored in the companion cells located near the sieve tube elements. The sucrose is actively Transported into the sieve tube elements through special Transport proteins in the cell membrane.The Food made in leaves is loaded into the sieve tubes of Phloem tissue by using energy from ATP. Water now enters into sieve tubes containing Food by the process of osmosis due to which the pressure in the Phloem tissue rises. 
2. Creation of a pressure gradient– The loading of sucrose into the sieve tube elements creates a high concentration of solutes, including sucrose, in the Phloem sap in the source tissue (usually the leaves). This high concentration of solutes creates a pressure gradient that drives the flow of Phloem sap towards the sink tissue (such as developing fruits or growing roots).
3. Transport through Sieve tube elements- The Phloem sap flows through the sieve tube elements in the Phloem tissue. The sieve tube elements are connected end-to-end to form a continuous tube that extends throughout the Plant.
4. Unloading of Sucrose- The Phloem sap reaches the sink tissue where the sucrose is actively unloaded from the sieve tube elements and Transported into the surrounding cells, such as the growing root cells or developing fruit cells.
5. Maintenance of the Pressure Gradient- As sucrose is unloaded from the sieve tube elements in the sink tissue, the concentration of solutes in the Phloem sap decreases and the pressure gradient that was created by the loading of sucrose is maintained. This pressure gradient continues to drive the flow of Phloem sap from the source tissue to the sink tissue.

Also Check – Translocation in Plants – Steps ,Phloem Structure , Importance and Factors Affecting Translocation

Types of Translocation

There are two types of Translocation in Plants that are responsible for the movement of food (primarily sucrose) from one part of the Plant to another – 

• Source-to-Sink Translocation 
• Sink-to-Source Translocation

Source-to-Sink Translocation

Source-to-Sink Translocation is the process by which sucrose is Transported from source tissues, such as leaves, to sink tissues, such as developing fruits or growing roots. This type of Translocation occurs when Photosynthesis produces more sugars than the Plant can use at the source tissues. The steps involved in source-to-sink Translocation are as follows-

1. Sucrose is loaded into the Phloem sieve tube elements at the source tissue, which creates a pressure gradient.
2. The pressure gradient causes Phloem sap to flow from the source tissue towards the sink tissue.
3. At the sink tissue, sucrose is unloaded from the Phloem and used for growth or storage.
4. The removal of sucrose from the Phloem sieve tube elements at the sink tissue reduces the pressure in the Phloem.
5. The reduced pressure allows the Phloem sap to flow back towards the source tissue.

Sink-to-Source Translocation

Sink-to-Source Translocation is the process by which sucrose is Transported from sink tissues back to source tissues, such as leaves. This type of Translocation occurs when the Plant requires more sugars for energy or storage than are being produced at the source tissues. The steps involved in sink-to-source Translocation are as follows-

1. Sucrose is loaded into the Phloem sieve tube elements at the sink tissue, which creates a pressure gradient.
2. The pressure gradient causes Phloem sap to flow from the sink tissue towards the source tissue.
3. At the source tissue, sucrose is unloaded from the Phloem and used for energy or storage.
4. The removal of sucrose from the Phloem sieve tube elements at the source tissue reduces the pressure in the Phloem.
5. The reduced pressure allows the Phloem sap to flow back towards the sink tissue.

Factors Affecting Food Transportation in Plants

Many factors can have a significant impact on the ability of Plants to produce and Transport food .  they are as follows 

• Temperature- The rate of Transpiration and Photosynthesis can be affected by temperature. High temperatures can cause an increase in Transpiration, which can lead to a decrease in the amount of water available for Transport. Additionally, high temperatures can cause enzymes involved in Photosynthesis to denature, which can lead to a decrease in food production.
• Water availability- Water is essential for the Transport of minerals and other nutrients in Plants. A lack of water can lead to a decrease in food production and Transport. Conversely, excess water can lead to waterlogging, which can inhibit the Transport of nutrients.
• Light intensity- Light is necessary for Photosynthesis, which is the process by which Plants produce food. An increase in light intensity can lead to an increase in Photosynthesis and food production. However, too much light can also lead to photoinhibition, which can cause damage to the Plant.
• Carbon dioxide concentration- Carbon dioxide is a necessary component of Photosynthesis. A decrease in carbon dioxide concentration can lead to a decrease in Photosynthesis and food production.
• Hormones- Hormones play a crucial role in the regulation of food Transport in Plants. For example, auxins can promote the Transport of food from the leaves to the rest of the Plant, while cytokinins can promote the Transport of food to developing fruits.
• Soil nutrients- The availability of soil nutrients, such as nitrogen, phosphorus and potassium, can affect food production and Transport in Plants. A lack of these nutrients can lead to a decrease in food production and Transport.

Also Check – What are the Components of Transport System in Highly Organised Plants

Frequently asked Questions on Transportation of Food in Plants