Photosynthesis

Despite looking relatively plain to the human eye, the leaf is very complex and holds the cells that perform photosynthesis.  A good example to compare the leaf to is a layer cake.  Starting with the icing, the top layer of the leaf is the upper epidermis and cuticle.  The function of this layer is to protect the plant and prevent water loss. It does this through the waxy compound cutin, which prevents water from escaping.  

 

The next layer of the cake is the first layer of cake batter.  In the leaf, it is called the palisade mesophyll.  The palisade layer is made up of long, slender cells called palisade parenchyma in which the vast majority of photosynthesis will take place.

 

Underneath the palisade layer is a very light layer of icing, filled with air pockets.  It is called the spongy mesophyll , and it includes vascular bundles, which are the leaf's veins that carry food and water in and out of the cell.  Bundle sheath cells surround the vascular bundles and offer stability and protection to the veins.  In addition, it houses spongy parenchyma.  The reason for this name is because the cells are very spread out to allow for air pockets, which holds the CO2 necessary for the plant to perform photosynthesis. The CO2 then has the room to move up to the palisade mesophyll for the palisade parenchyma to use during photosynthesis.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

The bottom layer of cake is called the lower epidermis.  It includes the stomata and guard cells.  The stomata are tiny openings that are "guarded" by the guard cells, which can open and close the stomata.  Think of the guard cells as guards controlling a gate to control the passage of people on a road.  The function of the stomata is to allow air to flow into the leaf and into the spongy mesophyll.