Lesson 4 Botany 2nd Quarter Reviewer PDF

**LESSON 4: TISSUES** **TISSUES** The plant, being a complex organism, needs the cooperation and correlation of its cells for its development and growth. For example, water is absorbed by the roots from the soil; but this water evaporates from the aerial (above ground) portions of the plant. To pr...

**LESSON 4: TISSUES** **TISSUES** The plant, being a complex organism, needs the cooperation and correlation of its cells for its development and growth. For example, water is absorbed by the roots from the soil; but this water evaporates from the aerial (above ground) portions of the plant. To prevent desiccation, the plant must be able to transport water from roots to leaves much more rapidly than the diffusion or osmosis from cell to cell. Fortunately, in vascular plants, there developed conducting tissues which enable such rapid movement of water. A tissue is defined as a group of structurally similar cells performing essentially the same function. The process involved in tissue formation are: 1. **Cell Multiplication** 2. **Histological Differentiation** 4.1 **Types of Tissues** Based on **structure** and **function**, tissues are grouped into **two** **principal** **types**: 1. **Meristematic tissue.** It consists of cells which possess the ability to repeatedly form other cells like themselves. When fully differentiation and mature, it becomes a permanent tissue. Meristematic tissues are responsible for the continued growth of plants throughout their lives. They are found near the tips of roots, the buds, at the tips of stems, between the bark and wood of trees; elsewhere in the bodies of plants where extensive growth occurs. The cells of this tissue are immature; cubical or box-shaped, have thin walls and dense protoplasm; vacuoles are very small or none at all. There is no differentiation among the cells, one cell being the same size and shape as any other. 2. **Permanent tissue.** In this tissue, the cells are stable and no longer dividing. Although they have been derived from Meristematic tissues, they have become modified both in structure and function. Each type of permanent tissue is specifically modified and made possible an efficient division of labor. Permanent tissues are divided into: **a.) Simple permanent tissues** **b.) Complex permanent tissues** **Simple permanent tissues are tissues that are made up only of one kind with specialized functions.** Examples are: 1. **Epidermis** -- this tissue is one cell in thickness and forms the surface of leaves, flower, young stems and roots. In most cases, it is covered with a waxy water-proof material called cutin. The continuous layer of cutin is terraced cuticle. Its function is to conserve moisture and to protect the inner tissues from the entrance of micronism and from mechanical injury. 2. **Parenchyma** -- the cells of tissues are more or less spherical; their cells thin and vacuoles large. This tissue is found throughout the plant body; it functions mainly for storage of food materials. If **chloroplasts develop**, the cells become capable of **photosynthesis activity.** **Parenchyma cells** are capable of **becoming Meristematic** under certain conditions such as **wounding** or **injury**. This is very important for recovery from adverse conditions. 3. **Collenchyma** -- the cells of this tissue are somewhat elongated and the walls are irregularly thickened usually at the corners where they meet. Collenchyma tissue forms the strengthening and supporting tissue found in young stems near the epidermis. 4. **Sclerenchyma** -- the cells of this tissue have extremely thick walls and are dead at maturity. The young and developing, they are alive, but the thick walls become impregnated with such material as lining, and the protoplast subsequently dies. The gritty texture of chicos and pears is due to the presence of stone cells -- a sclerenchyma type of cells. Elongated sclerenchyma cells are termed fibers. Strength, mechanical support and protection are the main functions of the sclerenchyma tissue. 5. **Cork** -- this tissue composed of cells that have very thick walls, which are impregnated with suberin, a waxy material. These cells are dead at maturity and form a water-proof layer of tissues that cover the outermost parts of stems and roots of woody plants. Water conservation and protection are the function of the cork. The cork from oak (Quercus suber) is removed and used commercially for stronger, life preservers and insulators. **COMPLEX PERMANENT TISSUE** These tissues consist of a number of different kinds of cells. They **xylem** and the **phloem** which **form** **the vascular or conducting tissues** are examples. They server principally for **conduction of materials** in the **plant for manufactured food.** **Xylem tissue** is composed of: **- Tracheids** **- Xylem parenchyma** **- Xylem fibers** **Phloem tissue** is composed of: **- Sieve tube** **- Companion cells** **- Phloem parenchyma** **4.2 Diagram of Simple Permanent Tissue** **Simple Permanent Tissues** **1. **Epidermis **2.** Parenchyma **3.** Sclerenchyma **4.** Collenchyma **5.** Cork **Complex Permanent Tissues** **1. **Xylem **2.** Phloem. **- EPIDERMIS (cut-away view) -** showing a cutin layer **- COLLENCHYMA AND STONE CELLS (cut-away views) --** showing lumen and wall **- PARENCHYMA --** a cross-section view of cells **- FIBERS (longitudinal section) --** showing lumen and wall **- CORK TISSUE --** a longitudinal view of cells Note : Please refer to our module for visual representation of the figures, thank you! : )) **4.3 Diagram of Complex Permanent Tissues** **- PHLOEM TISSUES (longitudinal cut-away view) showing:** sieve pore, sieve plate, sieve tube, phloem parenchyma, phloem fiber, companion cell. **- XYLEM ELEMENTS showing:** tracheid (thin long section), pitted vessel element, (annular), (spiral), (netted) segments of vessels. **Note : Please refer to our module for visual representation of the figures, thank you! : ))**