Plants have numerous systems and types of tissues in order to provide for their own nutrient needs, just like the similar structures in mammals. Essentially, every living organism needs to have the means to acquire, metabolize and use energy; energy storage also exists in most organisms, and is beneficial in that it eliminates the need to constantly take in nutrients just to stay alive. The leaves are one of the most important parts of a plant, as they are the means by which plants absorb most of the nutrients needed to carry out normal functions.
Mesophyll tissue consists of two layers-the palisade layer and the spongy layer. The palisade layer consists of one or more layers of palisade cells, which are situated with gaps between each that vary according to the needs of the plant. Spaces between the palisade cells must be wide enough to allow for the absorption of enough carbon dioxide (CO2) for the plant, but close enough together that water can still travel throughout the tissue via capillary action. The spongy layer consists of rounded, loosely-set cells with plenty of air space.
The mesophyll is rich in chloroplasts. In other words, this is the part of the leaf that's responsible for collecting sunlight and absorbing it into the plant. Mesophyll tissue also stores the plant's energy that results from photosynthesis, or the conversion of sunlight into usable nutrients.
When you think of the green surface of a leaf, you're thinking about the palisade layer in the mesophyll tissue. The mesophyll lies directly below the epidermal layer, which is completely transparent. Mesophyll tissue is generally some shade of green due to the chlorophyll content.
While there are some exceptions, the mesophyll tissue of a plant tends to be dark green and smooth in appearance if it's a plant that receives full sunlight. Species of plants that prefer partial sun, filtered light or shade are generally lighter in color due to the lower chlorophyll content of the mesophyll tissue, and the leaves may appear bumpy or corrugated. This texturing maximizes the surface area of the leaf, allowing for the most absorption for leaf size possible. Trees also commonly have textured leaves, as they require a lot more energy than plants that are primarily comprised of leaves.
While mesophyll tissue refers to the central layer in the leaves of plants, it can get a little confusing with the different uses of the word "mesophyll." In ecology, this term refers to the entire leaf rather than a certain tissue type.
Importance of mesophyll tissue
Without this central mesophyll tissue, plants would be unable to collect, metabolize and store essential nutrients. In addition, the layers of mesophyll offer some structural support to the leaf, helping it to keep its flat, spread-out shape. This shape is what enables plants to take maximum advantage of the sunlight that's available to them. Any exposed surface of mesophyll tissue is a passage by which nutrients can enter the plant.