Question

Casparian strips are the bands of thickenings present on walls of endodermis. (a) radial (b) tangential (c) central (d) both \((a)\) and \((b)\)

Short answer

The correct answer is (d) both (a) and (b).

Step-by-step solution

Understanding Casparian Strips

Casparian strips are bands of cell wall material called suberin found in the endodermis, which is the innermost layer of cells in the root cortex of plants. They are responsible for the control of water and nutrient uptake.

Identifying the Orientation of Casparian Strips

The Casparian strips are located on the radial and tangential walls of the endodermal cells, forming a continuous band around each cell, which acts as a barrier to passive flow of substances into the vascular system of the plant root.

Choosing the Correct Option

Since the Casparian strips are found on both radial and tangential walls of endodermal cells, the correct option is the one that includes both of these orientations.

Key concepts

Endodermis

The endodermis is an essential cylindrical layer of cells in the plant root, which acts as a selective barrier, regulating the flow of water and nutrients from the soil into the plant's vascular system. This regulatory role is vital to the plant's survival, as it ensures that only necessary substances enter the plant while harmful substances are kept at bay.

Structurally, the endodermis is situated between the cortex and the vascular bundles, serving as a checkpoint for soluble materials. Its most distinctive feature is the presence of Casparian strips, which are deposits of suberin found on the endodermal cell walls. Suberin is a waxy substance that makes the cell walls impermeable to water and dissolved substances, thus forcing them to pass through the cell's plasma membrane. This selectivity allows the plant to maintain an internal balance of nutrients and prevent the loss of water and minerals back into the soil.

Plant Root Structure

The structure of plant roots is a marvel of nature designed for efficient water and nutrient uptake. A typical root system comprises the root apex, root hairs, the cortex, endodermis, and vascular tissue. The root hairs increase the root's surface area, significantly enhancing its ability to absorb water and nutrients from the soil.

As we progress inward, the cortex provides storage for starch and other nutrients. Next, the endodermis serves as a gatekeeper, thanks to the Casparian strips that enforce selective entry. Finally, the central vascular tissue, including the xylem and phloem, transports water, nutrients, and food throughout the plant. Understanding this elegant structure highlights the sophisticated mechanisms plants use to survive and thrive in various environments.

Water and Nutrient Uptake

Water and nutrient uptake in plants is a finely tuned process involving both passive and active mechanisms. Roots absorb water through osmosis, which is the passive movement of water from an area of higher concentration to one of lower concentration. Meanwhile, nutrients are often taken up actively against their concentration gradient, requiring energy in the form of ATP.

This uptake is not indiscriminate; it is carefully regulated by the endodermis and the strategically placed Casparian strips, which prevent the passive flow of solutes into the xylem. This system ensures that plants efficiently acquire the essential elements needed for growth and development while defending against excess salts or toxins. Comprehending these processes can be crucial in fields such as agriculture and environmental science, where maintaining plant health is vital.