The Structure and the Function of Leaf

1. The Structure of Leaf

      In general, leaf morphology is thin, flat, and green because it consists of green pigment (chlorophyll). There are two types of leaf, complete leaf and incomplete one. Complete leaf has sheath (stipulae), leaf stalk (petiole) and blade (lamina). Incomplete leaf does not have one or two of the components. Most of the plants have incomplete leaves, for example mango and jackfruit. Complete leaves can be found in banana and grasses.
      Each leaf has vein, and based on the size of the vein, leaves can be distinguished into three types, namely main vein, veinlets, and small vein. Look at the picture!
The venation of dicotyledon is pinnate-veined or palmate-veined. The arrangement of the veins in monocotyledon is paralel-veined or curve-veined.
There are four types of tissue on leaf organ, namely epidermis, palisade layer, spongy layer, and vascular tissue (xylem and phloem)

a. Epidermis

Epidermis tissue is the outermost layer of the tipper and lower layers. The cells are thin and cover up the tissue inside and some of them change into pore (stomata). Stomata as the means of gas exchange serve to control tissue liquid loss and to regulate the intake of CO2 which is requiredin photisyntesis. Gas exchange control occurs through the opening and the closing of the stomata. On land plants, stomata are mostly found on the flower surface of the leaves. On floatingleaves of aquatic plants, such as waterlily (Nymphaea sp.), stomata are found on the upper layer of the leaves. submersed plants, such as Hydrilla sp., do not have stomata.

b. Palisade Layer

      Palisade consists of one or few layers of cells elongating vertically and containing a lot of chloroplasts. Chloroplast is a plant cell component in which there are chlorophyll and other photosyntesis components.

c. Spongy Layer

      Spongy layer is an irregular cell layer which has many air spaces and lies beneath the palisade layer. It also consists of chloroplasts, so that it also becomes the place for photosynthesis.

d. Vascular Tissue

      Vascular tissue on leaf forms complex net-like branch system, which is called vein. The vein is located between palisade layer and spongy layer. A cross section of vein shows vascular bundles including xylem and phloem.

2. The Function of Leaf

      Leaf is an important organ on plant. The main functions of leaves are for photosynthesis and gas exchange. Leaves absorb light energy and CO2 whereas water (H2O) is absorbed by root. Respiration and photosynthesis waste are released through leaves as well. the large leaf blade is necessary to capture the energy of sunlight and CO2. The characteristics mentioned above are suitable to its functions.
      Leaves also undergo modification, such as attracting leaf, vine leaf, narrow and thickened leaf, and even spine.
      The function of clinging leaf on bean is to find something to hold on. On cactus, the leaves are even reduced into spine. However, not all spines derive from leaves. On acacia (Acacia pedaliriafolia), the leaves are reduced, but the leaves stalks axpand into leaf-like formation and have chlorophyll. So, acacia leaves that we usually see are leaf stalk that changes into leaf-like formation, called phyllode.