SS2 WEEK 5 BIOLOGY_ TRANSPORT SYSTEM IN HIGHER PLANT

Mechanism of Transport in Higher Plants

Transport in higher plants involves a series of complex processes that ensure the movement of water, minerals, and nutrients across different parts of the plant. This transportation is vital for plant growth, metabolic activities, and overall functioning. It primarily occurs through two mechanisms: absorption and transport of water and minerals, and transpiration and translocation. Below, we discuss each of these processes in detail.

A) Absorption and Transport of Water and Mineral Salts

1. Absorption of Water and Mineral Salts: Water and mineral salts are absorbed primarily through the root system. The process begins when water from the soil is absorbed by the roots, moving through specialized root cells.

• Root Hair Cells: The outermost layer of roots consists of tiny extensions called root hairs, which greatly increase the surface area for absorption. These cells have a semi-permeable membrane that allows water and dissolved minerals to enter through osmosis.
• Osmosis: Water moves from an area of lower solute concentration (soil) to an area of higher solute concentration (root cells) via osmosis. This movement of water creates a flow of nutrients, such as minerals, into the root.
• Active Transport of Minerals: Minerals such as potassium, calcium, and magnesium are absorbed through active transport, which requires energy in the form of ATP. This allows plants to absorb minerals against the concentration gradient, ensuring that essential nutrients are available for growth.

2. Transport of Water and Mineral Salts: Once absorbed, water and minerals must be transported to various parts of the plant. This is achieved through the plant’s vascular tissue, specifically the xylem.

• Xylem Vessels: Water and dissolved minerals move upward through the xylem, a specialized tissue that forms continuous tubes extending from the roots to the leaves. The movement occurs through a combination of physical forces:
  • Root Pressure: Water entering the root creates a pressure that pushes water upward, particularly in smaller plants.
  • Capillary Action: Water rises in the xylem vessels due to adhesive forces between water molecules and the vessel walls, and cohesive forces between water molecules themselves.
  • Transpirational Pull: This is the primary force for water movement in tall plants. As water evaporates from the stomata in the leaves (transpiration), it creates a negative pressure that pulls more water upward through the xylem.

B) Transpiration and Translocation

1. Transpiration: Transpiration is the process of water loss from plants, primarily through the stomata in the leaves, although some water also escapes through lenticels in the stems and bark.

• Role in Water Transport: Transpiration plays a crucial role in maintaining the flow of water and minerals through the plant. As water evaporates from the leaves, it generates a negative pressure that pulls water up through the plant’s vascular system, from the roots to the leaves.
• Types of Transpiration:
  • Stomatal Transpiration: The major form, where water vapor escapes through tiny pores called stomata.
  • Cuticular Transpiration: Water evaporates through the cuticle, a waxy layer on the surface of the leaf.
  • Lenticular Transpiration: Water loss through openings in the stems.
• Significance: Transpiration helps in cooling the plant, maintaining turgor pressure in cells, and facilitating nutrient transport. It also helps in the uptake of minerals by creating a continuous flow of water through the plant’s vascular system.

2. Translocation: Translocation refers to the movement of organic compounds, primarily sugars and other products of photosynthesis, throughout the plant.

• Phloem Vessels: Unlike the xylem, which is responsible for transporting water, the phloem is responsible for the transport of sugars, amino acids, and other organic compounds. These substances are synthesized in the leaves (especially in the mesophyll cells) and are moved to areas where they are needed (e.g., growing tissues or storage organs like roots and fruits).

  • Source to Sink Movement: In the process of translocation, substances move from a source (such as a leaf, where photosynthesis occurs) to a sink (such as growing regions or storage organs). The movement occurs through pressure flow mechanism: sugars are actively transported into the phloem, creating a concentration gradient that causes water to flow into the phloem, thus generating pressure. This pressure pushes the sugary solution toward the sinks.

• Role of Active Transport: Translocation in the phloem requires both active and passive transport. The active transport of sugars into phloem cells creates a pressure difference that drives the movement of the sap through the plant.

• Significance: Translocation ensures that all parts of the plant receive essential nutrients and energy, allowing for growth and the development of reproductive structures.

• EVALUATION

1. List the materials and media of transportation in higher plants

2. Mention the vascular tissues in higher plants

ASSESSMENT:

3. Describe the mechanism of transport in higher plants

4. Demonstrate experimentally the flow of materials in higher plants.