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Rualo, Glenn,. Gerard, Potura,.
Typology: Lecture notes
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Don Mariano Marcos Memorial State University South La Union Campus COLLEGE OF ARTS AND SCIENCES Agoo, La Union
Module II
This module presents the morphological and anatomical features of plants. It is hoped that you will learn to appreciate plants for how wonderful they are. After studying this module, you should be able to:
What can you say about the picture? Yes, it has a density, it has height, width and its is full of structures both inside and outside the cell. What do you think are those structures? Plant cells are a eukaryotic cell that comprises a nucleus and organelles that are enclosed by a plasma membrane. It has both primary and secondary cell walls that include (1) cellulose, (2) hemicellulose, (3) pectin, and (4) plastids that has the power to perform photosynthesis and store starch. This structure also has a large vacuole that regulates turgor pressure, and the unique method of cell division with the formation of a cell plate (phragmoplast) that separates new daughter cells. Flagella or centrioles are absent in plant cells, except in the gametes. Now let us look again for the picture of a plant cell. This is a typical plant cell, where all the parts are placed accordingly. A typical plant cell with all parts labeled. Source: Wikipedia Can you still recall the parts of a cell? Plant cells have cell walls found outside the cell membrane. The cell walls are composed of cellulose, hemicelluloses, and pectin. In many cases, lignin or suberin is secreted by the protoplast in which they are referred to as secondary wall layers inside the primary cell
wall. Cutin, on the other hand, is secreted exterior to the primary cell wall going to the outer layers of the secondary cell wall on the epidermal cells of leaves, stems, and other parts of the shoot to form the plant cuticle. Cell walls provide shape to form the tissue and organs of the plant and are important in intercellular communication and plant-microbe interactions. All plant cells have a thin wall known as the primary cell wall. In specific unusually strong cells, the protoplast creates a secondary cell wall between the primary wall and the plasma membrane. The secondary walls are much thicker than the primary walls and are permeated with the compound lignin, which makes the wall even sturdier than hemicelluloses alone. The lignin can resist any fungal, bacterial, and chemical attack. The primary and secondary cell walls are both permanent, which means that once they are deposited, they are rarely degraded or depolymerized. The cellulose microfibrils are bound together by polysaccharides known as hemicelluloses, that are made in dictyosomes and transported to the wall by dictyosome vesicles. The hemicelluloses are deposited among the cellulose microfibrils and bind chemically to the cellulose, creating a solid structure that resembles reinforced concrete. In multicellular plants, one cell wall is glued to the walls of its adjacent cells by an adhesive layer called the middle lamella, composed of the third class of polysaccharides, pectic substances. The majority of the types of plant cells enclose a large central vacuole, always filled with water and is surrounded by a membrane known as tonoplast that maintains turgor pressure and controls the
There is a specialized cell-to-cell communication pathway in the cell. This is known as plasmodesmata (plasmodesma, sing.), which occur in the form of pores in the primary cell wall where plasmalemma and endoplasmic reticulum of adjacent cells. Plant cells contain plastids that often contain pigments that are used in photosynthesis. Some pigments can change the color of the cell. Chloroplasts contain chlorophyll, a green pigment that transforms solar energy into chemical energy, which the plant utilizes to make its own food from carbon dioxide and water. Other plastics are amyloplasts, specialized for starch storage, elaioplasts (a type of leucoplast), for storage of fat, and chromoplasts that are specialized for storage and synthesis of pigments. Other parts (organelles) are mitochondria, ribosomes, endoplasmic reticulum, dictyosomes (Golgi bodies), microbodies (peroxisomes and glyoxysomes), cytosol, microtubules, microfilaments
The cell organelles of a typical plant cell. Types of Plant Cells Plant cells specialize/differentiate from unspecialized/unspecialized meristematic cells to mold the major classes of cells and tissues of leaves, roots, stems, flowers, as well as the reproductive structures. Let us use the following diagram again:
meristem derivatives that initially resemble parenchyma. Plastids do not develop; the secretory apparatus like endoplasmic reticulum (ER) and Golgi (dictyosome) proliferate to secrete additional primary wall. The cell wall is usually thick at the corners ( comprised of more than three cells that come in contact), and thin where only two cells come in contact. Hemicellulose and pectin and are the dominant constituents of the collenchyma cell walls of dicots. Collenchyma cells are typically elongated and may divide transversely (crosswise) to give a septate appearance. The role of collenchyma is to support the plant in axes still growing in length and to confer tensile strength and flexibility on tissues. The primary cell wall lacks lignin and would make it sturdy and rigid, thus providing plastic support (capable of holding a petiole or a young stem into the air, however in cells that can be stretched as the cells surrounding them elongate). Stretchable support (lacks elastic snap-back) is an excellent way to describe what collenchyma does. In celery, parts of the strings are collenchyma. Collenchyma cells
Stone cells Vascular Tissue Cells
Dermal Tissue Cells The plant epidermis is composed of parenchyma cells that cover the external surfaces of plant parts: leaves, stems, and roots. Numerous cell types may be present in the epidermis. Prominent among these are the stomatal guard cells that regulate by controlling the rate of gas exchange between the atmosphere and the plant. The structure has a glandular and clothing hairs or trichomes, and root hairs. Guard cells are the only cells that possess chloroplasts in the shoot epidermis of most plants. The epidermal cells of aerial organs ascend from the superficial layer of cells known as the tunica or also known as layer (L1 and L2) that covers the plant shoot apex, whereas the cortex and vascular tissues arise from the innermost layer of the shoot apex known as the corpus (L3 layer). The epidermis of all aerial organs, except roots, is covered with a cuticle comprised of polymer cutan or polyester cutin (or both), with an epicuticular waxes - a superficial layer. Epidermal cells of primary shoots are assumed to be the only plant cells that has biochemical capacity to synthesize cutin.
Epidermal cells: guard cells (left), and a dorsoventral section of a leaf showing the epidermal cells. Trichomes. Root hairs. Taken from the biology of plants, 7th^ edition. Copyright 2005 W.H. Freeman and Company Root hairs are protuberances of the epidermis. They exhibit an essential role in the absorption of water and dissolved minerals. They increase the absorptive area, thereby increasing the volume of water being absorbed by the plants through their roots. Enumerate the parts of a plant cell. Give also at least 5 types of plant cells.
leaves and flowers to differentiate. The roots and stems increase in length because the meristem adds tissue "behind" it, always propelling itself more to air (for stems) or ground (for roots). Often, the apical meristem of a single branch will become dominant, suppressing the growth of meristems on other branches, and leading to the development of a single trunk. In grasses, meristems at the base of leaf blades (intercalary meristem) permit for regrowth after mowing by lawnmowers or grazing by herbivores. Apical meristems are capable of differentiating into the three basic types of meristem tissue, which correspond to the three types of tissue: (1) protoderm that produces new epidermis, (2) ground meristem that provides ground tissue, and (3) procambium that produces new xylem and phloem. These three meristems are considered primary meristem, for they allow growth, whether in height or in length, which is called primary growth. Secondary meristems permit growth in diameter (secondary growth) in woody plants. Herbaceous plants do not possess this secondary growth. Secondary meristem has two types, which are both named cambium , meaning "exchange" or "change." First, the vascular cambium produces secondary xylem and phloem (xylem is located towards the center of the stem and phloem is located toward the outside of the stem or root), responsible for growing the diameter of the plant. This process made by the vascular cambium produces wood and constructs the sturdy trunks of trees. Cork cambium is positioned between the phloem and the epidermis. It replaces the epidermis of both the roots and stems with bark. One layer of this bark is the cork.
Woody plants develop in two ways. Primary growth enhances length or height, intermediated by apical meristem tissue at the tips of both the roots and shoots. Secondary growth enlarges the diameter of a stem or root; vascular cambium adds phloem (outward), and xylem (inward), and cork cambium replaces epidermis with bark. The Cell Cycle A diagram of the cell cycle in plants is located below.
chromosomal DNA and the associated proteins as well as collecting energy reserves to complete the task of replicating each chromosome in the nucleus. S Phase (Synthesis of DNA) The configuration of nuclear DNA rests as semi-condensed chromatin in this phase. In the S phase , DNA replication carries on through the mechanisms that end in the formation of sister chromatids
widen. The sister chromatids start to coil tightly with the help of condensin proteins and become visible under a light microscope. During metaphase or the "change phase," all chromosomes are aligned in the metaphase plate, or the equatorial plane, halfway between the two poles of the cell. The sister chromatids are still tightly fastened to each other by cohesin proteins. At this point, the chromosomes are extremely condensed. In the course of anaphase orthe "upward phase," cohesin proteins degrade, and the sister chromatids detach at the centromere. Each chromatid is now called a chromosome and is pulled rapidly toward the centrosome to which its microtubule is attached. The cell becomes visibly elongated (oval-shaped) as the polar microtubules overlap as they slide against each other at the metaphase plate. During telophase or the "distance phase," the chromosomes stretch the opposite poles and begin to unravel and de-condense, modifying into a chromatin configuration. The mitotic spindles are further depolymerized into tubulin monomers that are used to draw together cytoskeletal components for each daughter cell. Nuclear envelopes arrange around the chromosomes, and nucleosomes arise within the nuclear area. Cytokinesis or "cell motion," is the second stage of the mitotic phase during which cell division is completed through physical separation of the cytoplasmic components into two daughter cells. The division is only complete when cell components have been distributed and completely separated into the two daughter cells. Although the stages of mitosis are alike for most eukaryotes, the process of cytokinesis is not the same for eukaryotes that have cell walls (e.g., plant cells). In animal cells that do not have cell walls, cytokinesis follows the start of anaphase. Actin filaments or contractile rings form just inside the plasma membrane at the former metaphase plate. The actin
