Problem 80 - Objective Biology for NEET

Question

Which of the following is incorrect about symplastic pathway? (a) Movement of water is relatively slower. (b) Movement is down the concentration gradient. (c) It may be aided by cytoplasmic streaming. (d) Most of the water flow in root occurs by this pathway.

Step-by-Step Solution

Answer

The incorrect statement about symplastic pathway is (d) Most of the water flow in root occurs by this pathway.

Step 1: Understand symplastic pathway

In the symplastic pathway, water movement occurs through the cytoplasm of cells, which are connected by plasmodesmata (tiny threads connecting living cells). The water goes from one cell to the next through these connections.

Step 2: Analyze each statement

(a) Movement of water is relatively slower: This is true because the symplastic pathway involves movement through the cytoplasm, which is slower compared to direct cell-to-cell movement. (b) Movement is down the concentration gradient: This is true, as water naturally moves from areas of higher concentration to lower concentration. (c) It may be aided by cytoplasmic streaming: This is also correct, as cytoplasmic streaming can facilitate fluid movement in the symplastic pathway. (d) Most of the water flow in root occurs by this pathway: This is false, as the majority of water transport in roots happens via the apoplastic pathway, not the symplastic pathway.

Step 3: Choose the incorrect statement

Given the analysis in the previous step, the incorrect statement about symplastic pathway is option d.

Key Concepts

Water Movement in Plants

Plants have evolved sophisticated systems to transport water from the soil, where it is absorbed by roots, to the leaves, where it is used for photosynthesis and transpired into the atmosphere. There are two main pathways for water movement within plants: the apoplastic and symplastic pathways.

Understanding these pathways is crucial, as water is essential for plant life. It is not only a constituent of cells and tissues but also a medium for transporting nutrients and a participant in many metabolic processes. In plants, the regulation of water movement is a finely tuned mechanism important for maintaining homeostasis and ensuring survival.

Plasmodesmata

Plasmodesmata are microscopic channels that traverse the cell walls of plant cells, facilitating communication and transport between them. Think of them as tiny tunnels enabling cells to share water, nutrients, and chemical signals. Each plasmodesmata is lined with the cell membrane and filled with cytoplasm, creating a continuous network known as the symplast.

Critical Role in Plant Physiology: The presence of plasmodesmata indicates a shared life; plant cells use these pathways to synchronize their biological processes, much like office workers use internal mail to circulate information and work together effectively.

Cytoplasmic Streaming

Cytoplasmic streaming, also known as cyclosis, is the directed flow of the cytoplasm within cells. This movement distributes nutrients, organelles, and genetic material within the cell. In plant cells, it also aids in the symplastic movement of water and solutes.

Imagine a bustling city, where cytoplasmic streaming is like the transit system, continuously moving materials to where they are needed most. This dynamic process is thought to enhance material exchange by preventing stagnation and ensuring that cellular contents are evenly distributed.

Apoplastic vs Symplastic Pathways

The apoplastic and symplastic pathways represent two different routes through which water and solutes travel within a plant. The apoplastic pathway involves movement through the cell walls and intercellular spaces, bypassing the cell membrane. It allows for rapid transport, like a highway for water molecules.

On the other hand, the symplastic pathway is the route through the cytoplasm of cells interconnected by plasmodesmata. It's a more controlled, regulated path, akin to a series of small roads with many checkpoints. As water moves cell to cell, it must pass through the semi-permeable cell membranes, which can regulate its flow. This pathway is slower but facilitates selective transport of solutes and maintains cellular compartmentalization.

Both pathways are pivotal for plant physiology, serving complementary roles in the transport and distribution of water and nutrients.