LEAVES ( daun ). The primary functions of leaves:. Photosyntesis Transpiration. Leaf Function:
Leaves are the powerhouse of plants. In most plants, leaves are the major site of food production for the plant. Structures within a leaf convert the energy in sunlight into chemical energy that the plant can use as food. Chlorophyll is the molecule in leaves that uses the energy in sunlight to turn water (H2O) and carbon dioxide gas (CO2) into sugar and oxygen gas (O2). This process is called photosynthesis.
Is composed of two principal parts:
Is divided into two parts:
Simple: not divided into leaflets; leaf composed of one blade
Compound: consists of two or more leaflets
Pinnately Compound: feather-like; leaflets along each side of a common axis.
Bipinnately Compound: primary and secondary divisions are pinnate.
Palmately Compound: 3 or more leaflets radiating from a common point.
Trifoliate: three leaflets
Opposite: leaves are directly across from each other on the stem.
Alternate: leaves are arranged singly at different heights and on different sides of the stem.
Elliptic: broadest in the middle and narrower at each end.
Lanceolate: longer than wide, broadest below the middle and tapering to the apex.
Obovate: inversely ovate, broadest above the middle
Ovate: egg-shaped, broadest below the middle
Broad Ovate: wide, egg-shaped
Leaves come in many sizes and shapes; they are often used to help identify plants. Some leaves are flat and wide; others are spiky and thin. Plant spines (like cactus spines) are actually modified leaves.
Form – Simple or Compound
The surface is smooth, not hairy.
Short, soft hairs cover the surface.
Covered with wool-like hair.
Covered with short, prickly hairs.
Covered with a bluish-white waxy substance.
Surface is wrinkly.
Glands filled with oil or resin cover the surface.
In the leaves of most trees, three distinct tissue layers can be discerned in their leaves. These are:
chloroplasts are found and photosynthesis takes place
3. The leaf veins which transport water and inorganic
compounds into the leaf, and organic compounds
produced by photosynthesis away from the leaf, to
other parts of the plant.
Cross section of a leaf, showing the anatomical features important to the study of photosynthesis: stoma, guard cell, mesophyll cells, and vein
Phloem cells conduct food from leaves to rest of the plant. They are alive at maturity and tend to stain green (with the stain fast green). Phloem cells are usually located outside the xylem. The two most common cells in the phloem are the companion cells and sieve cells. Companion cells retain their nucleus and control the adjacent sieve cells. Dissolved food, as sucrose, flows through the sieve cells.
1. Plastids: A green leaf is green because of the presence of a group of pigments known as chlorophylls. Minute structures called plastids contain the chlorophyll within the leaf.
2. Carotenoid pigments (yellow and orange) are also found in plastids. The carotenoids occure, along with the chlorophyll pigments, in tiny structures - called plastids - within the cells of leaves. Sometimes they are in such abundance iin the leaf that they give a plant a yellow-green color, Carotenoids are in many living things, giving
3. Anthocyanin pigments (reds and purples) occur in the sap of cells. The anthocyanins temporarily color the edges of some of the very young leaves as they unfold from the buds in early spring. They also give the familiar color to such common fruits as cranberries, red apples, blueberries, cherries, strawberries, and plums.
trichomes on the lower surface of a Coleus
Stomata open when the internal pressure of the guard cells rises as a result of water absorption. The pressure increases from 1.5 to 3.0 mega Pascal.
Since the walls of the guard cells are relatively flexible at the side of the stoma, the guard cells expand vertically and the stoma subsequentely opens.
Pea Leaf Stoma, Vicea sp.
- to bring about the fall of the leaf or other plant
- to protect the region of the stem from which
the leaf has fallen against insect damage or
rot caused by bacteria or fungi