Plant Anatomy: roots, stems and leaves
The plant body has a hierarchy of organs, tissues and cells Plants, like animals, have organs composed of different tissues, which are composed of cells. Tissue is group of cells with a common function and structure Organ consists of several types of tissues that carry out a particular function
Plant cells Plant cells have: cell membranes - Most cells have Chloroplasts: the sites of photosynthesis - Most cells have primary cell wall: is composed of cellulose, provides flexible support - Some cells have secondary walls: is composed of cellulose and lignin Major types of cells: provides greater support but its rigid Parenchyma Collenchyma Sclerenchyma Water conducting cells of xylem Sugar conducting cells of phloem
Parenchyma cells perform most of the metabolic functions of a plant They are in charge of photosynthesis, cellular respiration, and food storage. They remain alive when mature and usually have only primary cell walls, which are thin and flexible. Most parenchyma cells can divide and differentiate into other types of plant cells under certain conditions, such as during the repair of an injury.
Collenchyma cells provide flexible support Support for still growing parts like young stems the string of a celery stalk Resemble parenchyma cells in lacking secondary walls, but they have unevenly thickened primary walls. These living cells elongate as stems and leaves grow
Sclerenchyma cells provide support for non-growing regions They have thick secondary cell walls, usually strengthened with lignin, which is the main chemical component of wood. Mature sclerenchyma cells cannot elongate, and they occur in regions of the plant that have stopped growing in length. When mature, most sclerenchyma cells are dead, their cell walls form a rigid skeleton that supports the plant. Hemp fibers Give nutshells its hardness
Water conducting cells of xylem FUNCTION: Water transport Support They have rigid, lignin- containing secondary cell walls. The tubes are hollow because the cells are dead when mature, with only their cell walls remaining. Water passes through pits in the walls and through openings in the end walls of vessel elements. There are two kinds of cells Tracheids are long, thin cells with tapered ends. Vessel elements are wider, shorter, and less tapered.
Sugar conducting cells of phloem Food-conducting cells called sieve-tube members, are also arranged end to end, forming tubes as part of phloem Unlike water-conducting cells sieve-tube members remain alive at maturity, though they lose most organelles, The reduction in cell contents allows for nutrients to pass more easily through the cell. The end walls between sieve-tube members, called sieve plates, have pores that allow fluid to flow from cell to cell along the sieve tube. Each sieve-tube member has at least one companion cell, Helps sieve cells by producing and transporting proteins
These cells are grouped into tissues
The three types of tissues: dermal, vascular and ground Each tissue is continuous throughout the plant From root to stem to leaf But, Are there differences in the tissue arrangement between stems and roots? Are there differences in the tissue arrangement between monocots And dicots?
Dermal tissue covers the outside of the plant Non woody plants: One single layer called epidermis Woody plants: several layers form the cork Main function is protection Specializations of dermal tissue: In stems and leaves: there are trichomes (catch water, reduce airflow, produce substances) Leaves have special cells: guard cells Regulate the size of the stomata Roots: epidermis forms root hairs Function?
Vascular tissue transports materials and supports Xylem: Transports water and dissolved minerals Phloem: Transports organic nutrients (sugars) The arrangement of the vascular tissue varies depending on the organ And between monocots and dicots. Root: Stems: leaves:
Ground tissue fills the area between epidermis and vascular tissue Ground tissue in leaves is called the mesophyll Function? Ground tissue in stem Called pith or cortex Function? Ground tissue in roots also called cortex Function?
The three basic plant organs: roots, stems and leaves The solution to the separation of resources on land, was the development of the 3 basic organs The are organized into: Shoot system: Which organs? Function: Root system Which organs? Function:
Monocots and Dicots vary in the structure of these organs
Roots Function: Anchors plant in the soil, absorbs and transports minerals and water, stores food. Monocot roots consists of a mat of generally thin roots spread out shallowly in the soil. Dicots have one main vertical taproot with many small secondary lateral roots growing outward.
Dicot roots have phloem between arms of xylem in the center Monocots have xylem and phloem in a ring with pith in the center Endodermis is unique to roots and surrounds the vascular tissue
Stems Function: Support the leaves and flowers. Green stems also perform photosynthesis. In the case of a tree, the stems are: the trunk and all the branches, including the smallest twigs. A stem has nodes, the points at which leaves are attached, internodes, the portions of the stem between nodes. The buds are undeveloped shoots.
Stem s internal structure
Leaves Function: photosynthesis It is has a large surface area to maximize light harvesting They are thin so that light will penetrate through to the bottom cells Composed of the blade and the petiole Monocots have parallel venation Dicots have branched venation
Internal structure of a leaf Upper and Lower Epidermis: protective function lower epidermis generally contains more stomata Epidermal cells lack chloroplasts Palisade Mesophyll : tightly packed cells on the upper surface Contain three to five times as many chloroplasts as those of the spongy parenchyma. Chloroplasts remain usually near the cell wall, since this adjustment guarantees optimal use of light Spongy Mesophyll : loosely arranged cells Creates air spaces to facilitate gas exchange
Most of the primary plant body is made up of the tissue system. a. shoot b. dermal c. root d. vascular e. ground Which cell type forms a protective coat on some seeds? a. collenchyma cell b. vessel member c. fiber d. sclereid e. tracheid In the dermal tissue, are associated with stoma. a. epidermal cells b. guard cells c. pigment cells d. trichomes e. collenchyma cells