Describe the cell layers in the mesophyll.?

Answer 1

The first cell layer in the mesophyll (from the top epidermis to the lower epidermis) are the pallisade parenchyma cells. These cells are columnar (elongated) and generally exist in two cell layers. These cells perform a large majority of the photosynthetic activity of the plant. Then the next layer is the spongy parenchyma and this is generally the layer in which the vascular tissue (xylem and phloem) will be found. The spongy parenchyma are more or less spherical, although their shapes are a bit irregular. These cells wil generally be around four or five layers thick. The spongy parenchyma will extend to the lower epidermis. The lower two or three layers of the spongy parenchyma cells will be quite hollow (contain only a few cells), which provides area for CO2 influx to the leaf and H2O efflux from the leaf as these hollow areas are contiguous with the stomatal openings on the lower epidermis.

Answer 2

Mesophyll Layer

Answer 3

Most of the interior of the leaf between the upper and lower layers of epidermis is a parenchyma (ground tissue) or chlorenchyma tissue called the mesophyll (Greek for "middle leaf"). This assimilation tissue is the primary location of photosynthesis in the plant. The products of photosynthesis are called "assimilates".

In ferns and most flowering plants the mesophyll is divided into two layers:

An upper palisade layer of tightly packed, vertically elongated cells, one to two cells thick, directly beneath the adaxial epidermis. Its cells contain many more chloroplasts than the spongy layer. These long cylindrical cells are regularly arranged in one to five rows. Cylindrical cells, with the chloroplasts close to the walls of the cell, can take optimal advantage of light. The slight separation of the cells provides maximum absorption of carbon dioxide. This separation must be minimal to afford capillary action for water distribution. In order to adapt to their different environment (such as sun or shade), plants had to adapt this structure to obtain optimal result. Sun leaves have a multi-layered palisade layer, while shade leaves or older leaves closer to the soil, are single-layered.
Beneath the palisade layer is the spongy layer. The cells of the spongy layer are more rounded and not so tightly packed. There are large intercellular air spaces. These cells contain less chloroplasts than those of the palisade layer.
The pores or stomata of the epidermis open into substomatal chambers, connecting to air spaces between the spongy layer cells.

These two different layers of the mesophyll are absent in many aquatic and marsh plants. Even an epidermis and a mesophyll may be lacking. Instead for their gaseous exchanges they use a homogeneous aerenchyma (thin-walled cells separated by large gas-filled spaces). Their stomata are situated at the upper surface.

Leaves are normally green in color, which comes from chlorophyll found in plastids in the chlorenchyma cells. Plants that lack chlorophyll cannot photosynthesize.


Fallen autumn leavesLeaves in temperate, boreal, and seasonally dry zones may be seasonally deciduous (falling off or dying for the inclement season). This mechanism to shed leaves is called abscission. After the leaf is shed, a leaf scar develops on the twig. In cold autumns they sometimes change color, and turn yellow, bright orange or red as various accessory pigments (carotenoids and anthocyanins) are revealed when the tree responds to cold and reduced sunlight by curtailing chlorophyll production.