SPECIALIZED PLANT CELLS Corn plant Corn plant cells

Plants have specialized cells: 1. Because the surface area to volume problem limits the growth of cells to very small sizes, 2. Because large organisms need ways to transport materials around inside them and to support themselves, 3. Because specialized cells enable an organism to adapt to different environments and give the organisms unique capabilities.

KINDS OF PLANT TISSUE Plant cells specialize into three basic kinds of tissues: 1. Epidermis - The epidermis is protective covering tissue. For stems and leaves, it helps to retain moisture and protect from parasites.\ 2. Vascular tissue - consists of tubelike xylem and phloem. These tissues transport water, dissolved minerals, and food throughout the plant. 3. Ground tissue - is unspecialized tissue that supports vascular tissues and protects them from physical injury and stores food and water. Specific makeup and function of ground tissue varies in each organ of the plant. In the following pictures, try to identify the sorts of cells you are seeing.

ROOT CELLS A root (top) is composed of distinct tissues and cells. Each cell of the endodermis (bottom) has a waxy ring that prevents water from flowing around the cell. Water and solutes (arrows) must pass through the cell.

Roots grow in length and width. The length- wise growth occurs at the tip or meristem. These cells in the meristem divide and then elongate up to ten times their original length. Either during or after elongating, the root cells specialize and form the epidermis cortex and vascular cylinder. The meristem is fragile and is protected by an outer layer of cells called the root cap, which are scraped away as the root pushes through the soil. In the meristem, cell divisions produce new xylem and phloem, which increase the root’s diameter. This is called secondary growth. As it gets old, it develops a tough outer tissue called bark, which replaces the epidermis and much of the cortex.

STEMS and their CELLS Corn Plant Stem 1. Ground Tissue 2. Sclerenchyma 3. Sieve tube cell in phloem 4. Storage vessel in xylem 5. Phloem 6. Xylem

Wheat Stem (Monocot) §1. Vascular Bundles §2. Epidermis §3. Ground Tissue Cavity §4. Ground Tissue §5. Xylem §6. Phloem

Clover Stem (Dicot) §1.Epidermis §2.Cortex §3. Pith §4. Air Space §5. Vascular § Bundles l Phloem l Xylem

Leaves and their Cells

Stomata (Plural of Stoma) Stomata occur primarily on the underside of leaves. Carbon dioxide enters the leaf through the stomata and oxygen and water leave. They have guard cells on each side to control entry.

Mesophyll On one side of this picture, you can see the culumnar cells that are close- ly packed to expose as many chloro- plasts as possible to the sun. On the left side of the picture, you can see the spongy layer of loosely packed, irregular cells, surrounded by air spaces. Gasses and water vapor accumulate in these spaces.

Pollen Grains §Each pollen grain is made of two cells of unequal size inside a hard shell. The large cell is a tube cell, and the smaller is the generative cell. §Top: rose pollen §Middle::ragweed §Bottom: cotton