Question

Middle lamella in an angiosperm leaf is composed of
A. Lignin and hemicellulose
B. Cellulose and xylan
C. Cellulose, hemicellulose, and xylan
D. Calcium and magnesium pectate

Answer 1

Hint: The middle lamella in an angiosperm leaf is the layer between two adjacent plant cells, which cement both cells together. The middle lamella forms from the cell plate during cytokinesis from which the primary and secondary cell walls emerge.

Complete answer:
Plants cells require cementing molecules that hold adjacent cells together to maintain the structural integrity of the tissues. And unlike animal cells, the plant cells have both primary and secondary cell walls which also need to be considered.
-This cementing is done through a layer called the middle lamella or lamellae. This layer is named so as it is the middle layer between two adjacent plant cells. During cytokinesis, the cell wall degenerates to aid in the formation of the cell plate.
-The cell plate after cytokinesis forms the middle lamella and both the primary and secondary cell walls emerge from this layer. This layer in angiosperm leaves is composed of calcium and magnesium pectates.
-In some plants, the middle lamella is indistinguishable from the primary cell wall as the secondary cell wall appears so thick, in such cases the layer is known as compound middle lamella. During ripening, enzymes within the fruit degrade this layer and cause the cells to separate.
Therefore, the correct answer is option D.

Note: The main purpose of this layer is to fuse and hold in place the adjacent cells of the plant cell. This is of importance as it aids intracellular communication and maintains structural integrity. For example, in the case of unripe fruits, you can see the fruit being much harder and rigid than compared to ripe fruits. This is mainly due to the middle lamella layer which during ripening degenerates.