Final answer:
Casparian strips are composed of proteins and lipids and are crucial for controlling water and solute movement into the plant's vascular system. They consist of suberin, a hydrophobic substance, that ensures selective permeability through the endodermal cells surrounding the vascular tissue in plant roots.
Step-by-step explanation:
Casparian strips are bands that play a crucial role in the regulation of water and solute movement in plants. They are found in the endodermis, which is a layer of cells surrounding the vascular tissue in roots. The function of Casparian strips is to create a barrier that forces water and dissolved substances to enter the vascular system of the plant through the symplast, thus ensuring selective permeability. The correct answer to the question about the composition of Casparian strips is Option 4: Proteins and Lipids.
The Casparian strip is made up of suberin, a fatty substance that is hydrophobic, meaning it prevents passive flow of water and solutes through the endodermal cell walls. Instead, it ensures that the water must pass through the cell membranes, where the plant can control the uptake of minerals and other substances. This is essential for the plant's ability to prevent the backflow of nutrients and maintain a directed flow of water from the soil into the root xylem.