Which part of the leaf consists of open spaces that allow for gas movement?

The spongy mesophyll is the correct answer because it contains a network of air spaces that facilitate the exchange of gases, such as oxygen and carbon dioxide, between the leaf and the atmosphere. This layer is located below the palisade mesophyll and is composed of loosely arranged cells, which creates these air pockets. The presence of these spaces is crucial for photosynthesis and respiration, as it allows for the diffusion of gases necessary for these processes.

In contrast, the palisade mesophyll is tightly packed with cells and is primarily responsible for photosynthesis due to its high chlorophyll content, but it does not have the open spaces found in the spongy mesophyll to facilitate gas movement. The epidermis serves as a protective layer and is involved in minimizing water loss, but it does not contain spaces for gas exchange. Vascular bundles, which include xylem and phloem, transport water, nutrients, and sugars, but they do not play a role in gas movement within the leaf.