PLANTS Plants are made of Cells Root Stem Flower Fertilization

PLANTS ARE MADE OF CELLS Plant cells are eukaryotic cells, with distinct organelles, surrounded by membranes. Plant cells are different from other eukaryotic cells in having a cell wall, chloroplasts, and lots of vacuoles. Plant are composed of cells, organized into tissues.

ROOTS ABSORB WATER FROM THE SOIL BY ROOT HAIRS The most important part of a root is its tip, where the actively dividing cells in the meristem tissues are found. Just above the very end of the root, called the root cap, root hairs extend from the cells of the epidermis. These root hairs increase the surface area in contact with the soil and increase the plant's ability to draw water and minerals. The root hairs are seldom seen because when a plant is pulled up they are broken off.

STEMS SUPPORT THE PLANT AND TRANSPORT FOOD AND WATER BY THE PHLOEM AND XYLEM A crucial part of complex plants is the stem. (The simplest plants have none.) Stems give the plant support. The xylem and phloem within the stem distribute the water and sap throughout the plant. Leaves, flowers, and branches develop from buds on the stem.

PHOTOSYNTHESIS OCCURS IN THE LEAVES

HOW A LEAF MAKES FOOD Between the veins of the leaf is a spongy mass of cells filled with green material that gives the leaf its color. The green cells are called chloroplasts. The coloring matter is chlorophyll. Food is made by action of the chlorophyll in the plant. On the lower surface of the leaf, and sometimes on the upper surface, are many pores known as stomata (singular, stoma). Each stoma is a tiny opening between two bean- shaped guard cells. In most plants these pores are open all day and are closed all night. There are great numbers of pores in a single leaf. An oak leaf may have 1,400 in 1 square millimeter of area. A square millimeter is no larger than the tip end of a lead pencil. As sunlight shines on the leaf, carbon dioxide, in the form of gas from the air, enters the stomata. Inside the tissues of the leaf the carbon dioxide mixes with the water carried into the leaves from the roots. Then the green coloring matter, with the energy from sunlight, produces a chemical change. The carbon dioxide and the water are broken down into their separate parts (molecules), and the molecules are put together again in a new order to form sugars and starches (carbohydrates). These sugars and starches are the food materials of the plant. Furthermore, the chemical process, basic to all life, is called photosynthesis. The word comes from Greek words meaning "light" and "putting together"

KINDS OF LEAVES Simple Leaf Compound Leaf Palmately Compound Leaf

PARTS OF A FLOWER PARTS OF A FLOWER

FERTILIZATION When ripe pollen from an anther of the same kind of flower catches on the stigma, each pollen grain sends out a tiny threadlike tube. The tube grows down through the style and pierces one of the ovules in the ovary. This process is called fertilization. Each ovule must receive the contents of the pollen tube before it can develop into a seed. It usually takes the tube from two to five days to reach the ovule, but the time may vary from a few hours to six months.

A seed cannot grow until pollen is transferred from the stamen to the pistil. This transfer is called pollination. Since flowers cannot go after pollen, they depend upon some carrier to bring it to them. Flowers are pollinated by flies, moths, wasps, bees, and sometimes by hummingbirds. The flowers attract these helpers by their color, fragrance, and nectar. Some flowers open in the evening and invite night-flying insects to their banquet table. Such flowers are usually white or pale yellow, the colors that show best at dusk. To reach the nectar, insects must crawl over the pistils and anthers into the heart of the flower. Their bodies become covered with pollen dust. As they move from flower to flower, they transfer the pollen of one to the stigma of another. Flowers that require the help of insects are called entomophilous, meaning "insect-loving." Some flowers can be pollinated only by a single kind of insect. POLLEN TRANSFER

REVIEW AND WRAP UP Sketch and name the visible flower parts. Describe what the insect is doing and why. What must happen to make seeds? How does the flower get energy to make seeds?