Which of the following layers is NOT a part of a leaf from top to bottom?

The root cortex is not a part of a leaf structure because it is found in the root system of a plant, serving a different function. The root cortex primarily facilitates the transportation of water and nutrients from the soil and provides storage. In contrast, the layers of a leaf, such as the lower epidermis, palisade mesophyll, and spongy mesophyll, are involved in photosynthesis and gas exchange. The upper layers of a leaf, including the palisade mesophyll, are packed with chloroplasts for maximum light absorption, while the spongy mesophyll aids in gas exchange due to its loosely arranged cells. The lower epidermis contains stomata that regulate the exchange of gases. Thus, the correct option highlights the distinction between root and leaf anatomy.