Movement of water through apoplast stops at the level of ________ and crosses membrane to undergo symplast till xylem cells

The correct option is All of the above.

To understand why, let us examine the pathways of water movement in plant tissues:
1. Apoplast Pathway: In this pathway, water moves exclusively through the non-living parts of the plant, such as the cell walls and intercellular spaces, without crossing any cell membranes.
2. Symplast Pathway: In this pathway, water enters the cytoplasm of the cells through the plasma membrane and moves from cell to cell through cytoplasmic connections called plasmodesmata.

As water travels through the apoplast, it moves freely until it reaches the innermost boundary of the cortex. Here, it encounters a water-impermeable barrier made of a waxy substance called suberin, known as the Casparian strip. Because suberin is hydrophobic, the apoplastic movement of water is blocked, forcing water to cross the selectively permeable plasma membrane to enter the symplast pathway in order to reach the xylem.

The options provided describe this boundary layer in different ways:
- Endodermis: This is the specialized innermost layer of the cortex in roots where the Casparian strip is located.
- Inner layer of cortex: Anatomically, the endodermis is the innermost layer of the cortex.
- Starch sheath: In dicot stems, the innermost layer of the cortex is homologous to the endodermis and is rich in starch grains, commonly referred to as the starch sheath.

Since "endodermis", "inner layer of cortex", and "starch sheath" all represent this innermost cortical barrier layer that forces water from the apoplast into the symplast, all of the options are correct. Therefore, the correct choice is All of the above.