In what root tissue are Casparian strips located?
A Oxylem only
B Oxylem and phloem
C phloem only
D epidermis
E cortex
The correct answer and explanation is:
The correct answer is:
E. cortex
Explanation:
Casparian strips are specialized structures located within the root endodermis, which is a single layer of cells that forms the innermost boundary of the cortex tissue in roots.
The root tissues from outside to inside are:
- Epidermis (outermost protective layer)
- Cortex (mostly parenchyma cells for storage and transport)
- Endodermis (a layer of cells within the cortex)
- Pericycle
- Vascular tissues (xylem and phloem)
The Casparian strip is a band of suberin (a waxy, hydrophobic substance) embedded in the cell walls of the endodermal cells. This strip acts like a selective barrier, preventing passive flow of substances through the spaces between endodermal cells. Instead, water and dissolved nutrients must cross the plasma membranes of the endodermal cells themselves to enter the vascular cylinder (where xylem and phloem are).
This control mechanism is crucial because it regulates which minerals and water can enter the plant’s vascular system and prevents harmful substances from freely passing into the xylem.
- It does not occur in xylem or phloem themselves; these are vascular tissues located inside the endodermis.
- It is not in the epidermis, which is the outermost layer.
- The Casparian strip is specifically a feature of the endodermis, which is a part of the cortex region of the root (the innermost boundary layer of the cortex).
Thus, the Casparian strip is located in the endodermis, which is considered part of the cortex tissue in the root anatomy.
Summary:
- Casparian strips are found in the endodermis, a specialized cell layer inside the cortex.
- They act as a barrier controlling water and nutrient movement into the vascular tissues.
- Therefore, the correct tissue classification is E. cortex.