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

What is Transport in Plants?

Transport in plants is the process of moving water, minerals and other substances in plants. They are transported with the help of the xylem transport and phloem transport. This process is essential for the plant's growth and development, and the survival of plants. Plants have specialised 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. The mechanisms of transport in plants include diffusion in plants, osmosis in plants, and active transport in plants. These are key topics in NEET biology notes and NEET exam preparation biology.

Also Read:

• MCQs on Factors Affecting Diffusion

• Root Pressure Theory

• Difference between Ascent of Sap and Phloem Translocation

Types of Transport Systems in Plants

Transport in plants uses a highly organised transport system to move water, minerals, and nutrients internally. Short‑distance transport in plants occurs cell to cell by diffusion in plants, osmosis in plants, and active transport in plants. Long‑distance transport in plants happens through xylem transport and phloem transport. 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 in plants

2. Facilitated diffusion

3. Active transport in plants

4. Plasmodesmata connections(cytoplasmic connections)

Long-Distance Transport (Mass Flow or Bulk Flow)

Long-distance transport in plants is also called mass flow or bulk flow. The ascent of sap is the upward transport of water and minerals through xylem transport. Phloem transport conducts the bidirectional transport of organic nutrients, also by bulk flow. This process is explained by the pressure flow hypothesis and translocation in phloem..

Uptake and Release Mechanisms

Single cells absorb water and release solutes. Uptake and excretion occur by osmosis in plants, active transport in plants, and endocytosis/exocytosis. These mechanisms of transport in plants regulate ion balance, nutrient supply, and water movement.

Short-Distance Transport in Plants: Cell‑to‑Cell Transport

Short-distance transport in plants occurs at the cellular level. Transport in plants at this level includes diffusion in plants, osmosis in plants, facilitated diffusion, and active transport in plants. These mechanisms of transport in plants are essential for the local movement of water, minerals, and solutes.

Diffusion in Plants

Diffusion in plants is the most common transport mechanism. This is because it does not involve the use of energy. Molecules move 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. It plays a very significant or crucial role in the flow of gases, oxygen, carbon dioxide, and small solutes within the plant tissues. This makes diffusion in plants vital for short‑distance transport in plants and a repeated topic in NEET biology notes.

Facilitated Diffusion in Plants

Facilitated diffusion refers to the movement of molecules across the cell membrane through particular transport proteins. It supports the source-to-Sink Model, which explains nutrient flow from source to sink- for example, roots and fruits, where they are either utilised or stored. The Mass Flow Hypothesis 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 in plants.

Key Proteins Involved:

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

• Aquaporins are specialized channels allowing the movement of water molecules.

Active Transport in Plants

Active transport is the process by which molecules move against their concentration gradient. They require energy, which is typically derived from ATP. It primarily occurs during the absorption of indispensable minerals and nutrients from the soil, generally done to ensure there is an ion balance within the plant cell. Active transport in plants maintains ion balance and supports cellular functions. It is a major mechanism in short‑distance transport in plants and is highlighted in NEET exam preparation for biology.

Long - Distance Transport in Plants: Vascular Tissue System

The vascular tissue system includes xylem transport and phloem transport, which are the channels for moving substances in plants. The xylem transport carries the water and minerals from the roots to the leaves. The phloem transport carries the sugars and nutrients produced in the leaves to the rest of the plant. Together, the vascular tissue system forms a spider's web, moving from the roots up through the trunk into the leaves.

Structure and Function of 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.

• 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

Structure and Function of 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, fibres, 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

Difference Between Xylem Transport vs Phloem Transport

Xylem transport and phloem transport are the two main parts of the vascular tissue system in plants. Xylem transport manages water movement in xylem and mineral transport in plants, while phloem transport ensures food transport in phloem through the source‑sink relationship. The difference between xylem and phloem table includes:

Transport of Water in Plants

Transport of water in plants occurs through different mechanisms. It involves xylem transport, transpiration pull, cohesion‑tension theory, capillary action, and root absorption in plants. These processes explain how water movement in xylem supports growth and survival. The transport of water in plants takes place through various mechanisms, such as:

• Cohesion-Tension Theory in Xylem Transport: 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.

• Capillary Action in Plants: The rise of water up through the narrow xylem vessels is occasioned by the combined effects of cohesion and adhesion.

• Transpiration Pull: In transpiration, the water evaporates through the stomata of the leaf. This creates negative pressure that pulls more water up from the roots through the xylem.

Root Absorption in Plants

Water is essential for all physiological activities in plants. Water absorption in plants 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.

Transport in Plants NEET MCQs (With Answers & Explanations)

Important topics for NEET exam are:

• Types of Transport System

• Vascular Tissue system

Practice Questions for NEET

Q1. Diffusion is the result of concentration gradient which refers to

1. Change of concentration with respect to time

2. Change of concentration with respect to space

3. Change of concentration with respect to temperature

4. Change of concentration with respect to gravity

Correct answer: 2) Change of concentration with respect to space

Explanation:

Movement of all substances from the area of their higher free energy to the area of their lower free energy along the concentration gradient. Neutral solutes move across the membranes by diffusion. The net direction of diffusion of particles depends on their concentration in a particular region or space.

Hence, the correct answer is option 2) Change of concentration with respect to space.

Q2. Why does an increase in temperature increase the rate of diffusion?

1. The increased thermal energy of the medium reduces the kinetic energy of particles

2. The decreased thermal energy of the medium increases the kinetic energy of particles

3. The increased thermal energy of the medium does not change the kinetic energy of particles

4. The increased thermal energy of the medium increases the kinetic energy of particles

Correct answer: 4) The increased thermal energy of the medium increases the kinetic energy of particles

Explanation:

Higher the thermal energy in a medium: this raises the kinetic energy of its particles resulting in faster diffusion. The more heat there is, the more violent motion the particles perform the more collisions they experience, and the better the diffusion becomes as particles spread out and mix with others. Such a process plays a very significant role in biological and chemical systems, for example, in the transport of molecules, gases, and ions that determine the rate of chemical reactions and dynamics of systems.

Hence, the correct answer is option 4) The increased thermal energy of the medium increases the kinetic energy of particles.

Q3. Which of the following has the maximum diffusion pressure?

1. Cell sap

2. Rainwater

3. Ice caps

4. All of these

Correct answer: 2) Rainwater

Explanation:

Pure water has a maximum diffusion pressure of 1236 atm, meaning it has the highest tendency to diffuse and move freely. When solutes are added, the diffusion pressure decreases, leading to a reduction in water potential. This works on the principle that during osmosis, the water moves from a region of higher diffusion pressure (pure water) to a region of lower diffusion pressure (solution).

Hence, the correct answer is option 2) Rainwater.

Also Read:

• Imbibition, Difference Between Imbibition And Diffusion

• Excretion In Plants And Transpiration

• Reverse Osmosis

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