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Why do we have more than cell making up our bodies? Why don’t we have just one huge cell? When a cell’s surface area to volume ratio is too small (the surface area and volume are too close in number), the efficiency of the cell’s functioning decreases. An efficient cell has the highest surface area to volume ratio possible! That’s from the previous section. So, if a cell gets too big, it’s surface area to volume ratio goes down, decreasing its efficiency. Each type of cell in a multicellular organism is an “expert” at what it does. This is also called specialization. (really is important!) Internal transport systems in multicelluar organisms allows individual cells to remain small and efficient. If one or a few cells of a multicellular organism die, then the organism can still go on living. This is not the case for single-celled organisms Shoot System 2:52 Everything that is above ground: • stem • leaves • fruits • tubers • buds • flowers 1:46 Root System Everything that is below ground. Meristems are sites of rapid cell division. These areas are found at the ends of growing roots and leaves. root apical meristem The epidermis is the very thin outer layer of cells that covers all parts of plants. It’s main function is to facilitate gas exchange. epidermis stem cross section leaf cross section Dermal cells secrete a waxy cuticle that helps protect the plant and prevent water loss. cuticle electron microscope view of the cuticle on a cactus plant cross section of the upper surface of a leaf The ground tissue is found just below the epidermis and makes up the majority of the plant. ground tissue The cells are loosely packed to allow gases to diffuse easily around the cells. In the stem of a plant, the ground tissue provides strength and support 3:17 stem cross section The cells that make up the ground tissue (or cortex) in the root of a plant are involved in food and water storage. 1:43 root cross section ground tissue In the leaf of a plant, the ground tissue is the site for photosynthesis. Xylem tissue are the non-living cells responsible for transporting water and dissolved minerals up the stem to the leaves for use in photosynthesis. Phloem tissue transports the products of photosynthesis (dissolved sugars) from the leaves to the rest of the plant. 3:29 root cross section leaf cross section vascular bundle xylem phloem xylem phloem Cells in a vascular bundle seen through the light microscope (200X) root hairs Root hairs on a developing bean plant Cells of the root showing root hairs as seen through the light microscope (100X) Root hairs increase the surface area of the root to maximize the rate of water absorption into the plant. Frozen hydrated root hairs seen with a scanning electron microscope (SEM) Stomata are tiny pores on the underside of leaves that facilitate gas exchange. stoma singular: stoma plural: stomata guard cells Guard cells are specialized cells that surround each stoma whose function is to regulated the size of the opening. stomata cuticle upper epidermis ground tissue vascular tissue xylem phloem stoma lower epidermis guard cells read pages 296 – 302 C3.1 Check and Reflect page 302 #’s 1 – 6 Line Master 8