Apoplast - An Overview, Types

What is Apoplast?

The apoplast is the continuous system of cell walls and intercellular spaces in plant tissues that allows for the movement of water and solutes outside of the cell membranes. It forms a crucial pathway for water and nutrient transport in plants because it provides a low-resistance pathway for water movement from roots to leaves. It allows for rapid, long-distance water transport without crossing cell membranes, which is essential for maintaining plant hydration and supporting transpiration.

Components of Apoplast

The major components of apoplast include:

Pathways of Water Transport in Plants

Plants require water to survive just as animals and mammals need. Plants require water to complete their daily basis of biological processes. Water plays a very important role in processes such as seed germination and photosynthesis. Three major water means of transport are discussed below:

Apoplast Pathway

Apoplast is defined as the pathway in which the movement of water occurs through the cell wall and other intercellular spaces that are present in the cell. The apoplast, also known as the cell wall of the plant, is located on the outer side of the cell.

Symplast Pathway

Symplast is defined as the transfer of water from one cell to another cell with the help of some connections that are called plasmodesmata. The inner side of the plasma membrane consists of symplast.

Transmembrane Pathway

As the name suggests, transmembrane is defined as a combination of both the Apoplast and Symplast pathways and forms a transmembrane pathway. This is the pathway that helps in the movement of water across cells and cell walls.

Materials Transported via Apoplast

Materials required during the Apoplast Pathway are discussed below in the table:

Functions of Apoplast in Plants

The functions of apoplast in plants include:

• It enables the rapid movement of water and solute across the cell walls.

• It also maintains the turgor and hydration in the plant tissues.

• It facilitates the process of guttation and transpiration in plants.

• It provides mechanical support because of the presence of lignified xylem.

Difference Between Apoplast and Symplast Pathway

The differences between the apoplast and symplast pathway are:

Role of Xylem in Apoplast Transport

The basic transportation of water and ions through the apoplast path includes:

• Xylem vessels and tracheids act as continuous channels.

• The lignin depositions prevent collapse under tension.

• It also helps to maintain an uninterrupted water column during transpiration.

Apoplast NEET MCQs (With Answers & Explanations)

The key concepts to be covered under this topic for different exams are:

• Mechanism of Root pressure

• Factors affecting Root pressure

Practice Questions for NEET

Q1. The apoplast pathway involves movement of water through:

1. Cytoplasm

2. Vacuoles

3. Cell walls and intercellular spaces

4. Plasmodesmata

Correct answer: 3) Cell walls and intercellular spaces

Explanation:

The apoplast pathway refers to the movement of water through the cell walls and intercellular spaces without crossing the plasma membrane. It is a non-living continuum outside the protoplast. Since it does not involve the cytoplasm, vacuoles, or plasmodesmata (which are cytoplasmic connections used in the symplast pathway), the correct answer is cell walls and intercellular spaces. This makes apoplast transport rapid and passive.

Hence, the correct answer is option 3) Cell walls and intercellular spaces.

Q2. Which of the following is absent in apoplast transport?

1. Cell membrane crossing

2. Passive movement

3. Intercellular spaces

4. Diffusion

Correct answer: 1) Cell membrane crossing

Explanation:

In apoplast transport, water and solutes move outside the cell membranes through cell walls and intercellular spaces, so they do not cross the plasma membrane until they reach the endodermis (Casparian strip). Passive movement, intercellular spaces, and diffusion are all part of apoplast transport. Therefore, the correct answer is cell membrane crossing, which is absent until the symplast pathway takes over at the endodermis.

Hence, the correct answer is option 1) Cell membrane crossing.

Q3. Lignin in xylem vessels mainly provides:

1. Photosynthesis

2. Structural support and water transport

3. Respiration

4. Nutrient storage

Correct answer: 2) Structural support and water transport

Explanation:

Lignin is a complex organic polymer deposited in the cell walls of xylem vessels. It provides mechanical strength to withstand the negative pressure generated during transpiration pull. Additionally, lignin makes the walls impermeable to water leakage, creating an efficient, continuous channel for long-distance water transport. It does not play a role in photosynthesis, respiration, or direct nutrient storage, making structural support and water transport the correct answer.

Hence, the correct answer is option 2) Structural support and water transport.

Also Read:

• MCQs on Mechanism of Water Absorption

• Plant Water Relations

• Water Potential and Its Components