Cell membrane. Controls the movement of substances into and out of the cell. Plant and animal cells. Jelly-like substance, where chemical reactions happen.
It is a far more complex structure, however, and serves a variety of functions, from protecting the cell to regulating the life cycle of the plant organism. Chloroplasts - The most important characteristic of plants is their ability to photosynthesize, in effect, to make their own food by converting light energy into chemical energy.
This process is carried out in specialized organelles called chloroplasts. Endoplasmic Reticulum - The endoplasmic reticulum is a network of sacs that manufactures, processes, and transports chemical compounds for use inside and outside of the cell.
It is connected to the double-layered nuclear envelope, providing a pipeline between the nucleus and the cytoplasm. In plants, the endoplasmic reticulum also connects between cells via the plasmodesmata. Golgi Apparatus - The Golgi apparatus is the distribution and shipping department for the cell's chemical products.
It modifies proteins and fats built in the endoplasmic reticulum and prepares them for export as outside of the cell. Microfilaments - Microfilaments are solid rods made of globular proteins called actin.
These filaments are primarily structural in function and are an important component of the cytoskeleton. Microtubules - These straight, hollow cylinders are found throughout the cytoplasm of all eukaryotic cells prokaryotes don't have them and carry out a variety of functions, ranging from transport to structural support.
Mitochondria - Mitochondria are oblong shaped organelles found in the cytoplasm of all eukaryotic cells. In plant cells, they break down carbohydrate and sugar molecules to provide energy, particularly when light isn't available for the chloroplasts to produce energy. Nucleus - The nucleus is a highly specialized organelle that serves as the information processing and administrative center of the cell.
This organelle has two major functions: it stores the cell's hereditary material, or DNA, and it coordinates the cell's activities, which include growth, intermediary metabolism, protein synthesis, and reproduction cell division. Peroxisomes - Microbodies are a diverse group of organelles that are found in the cytoplasm, roughly spherical and bound by a single membrane. There are several types of microbodies but peroxisomes are the most common.
Plasmodesmata - Plasmodesmata are small tubes that connect plant cells to each other, providing living bridges between cells. Plasma Membrane - All living cells have a plasma membrane that encloses their contents. In prokaryotes and plants, the membrane is the inner layer of protection surrounded by a rigid cell wall. See also: Cytoplasm.
The organelles, which are compartments in which certain metabolic activities are localized, are bounded by membranes similar to the plasma membrane. The molecular components phospholipids and proteins of the membranes are subject to rapid turnover. The membranes act as sites for the synthesis or breakdown of materials and frequently, as in mitochondria, are structurally highly specialized for these activities. Therefore, far from being simply selective barriers to the movement of materials, the membranes of the plant cell are dynamic structures that play key roles in metabolism.
Conspicuous among the components of the cytoplasmic matrix are millions of particles, approximately 20 nanometers nm in diameter, known as ribosomes. Each ribosome is composed of a small subunit and a large subunit that are formed separately in the nucleolus from rRNA and proteins and brought together in the cytoplasm.
The ribosomes are the sites of protein synthesis and function in translating the sequence of nucleotides in mRNA into the sequence of amino acids that make up the protein encoded by the mRNA. Translation of the genetic code in the ribosomes also requires tRNA.
Smaller ribosomes are also present in the mitochondria and plastids, where they translate RNA encoded by the DNA that resides in these organelles. In all types of cells, some of the ribosomes in the cytoplasm appear to be free, whereas others are attached to the surface of the membranes of the endoplasmic reticulum or to the outer membrane of the nuclear envelope.
See also: Ribosomes. The endoplasmic reticulum is an architecturally regular structure only in a few types of plant cells. It is a protean highly variable structure, and the manners in which its profiles are associated differ with the stage of development and metabolic activity. In certain stages, numbers of profiles are seen to be stacked, frequently parallel to the surface of the cell.
The profiles may also surround the nucleus or seem to encompass any of several types of organelles. The endoplasmic reticulum may be smooth or rough; that is, the outer surfaces of the membranes may be studded with ribosomes. Although all plant cells have rough and smooth types of endoplasmic reticulum to synthesize the proteins and lipids necessary to construct many of the membranes of the cell, the rough endoplasmic reticulum is enriched in cells that are specialized for protein synthesis, including the cells of the aleurone layer of cereal seeds, and the smooth endoplasmic reticulum is enriched in cells specialized for lipid production, including oil gland cells and some stigmatic cells.
Transitional endoplasmic reticulum, which is intermediate in structure between the smooth and rough endoplasmic reticulum, is rich in cells of the tapetum and the cells of seeds that store lipids in the form of osmotically active lipid bodies. See also: Endoplasmic reticulum. The Golgi apparatus in many plant cells clearly functions in secretion, but the ubiquitous occurrence of the organelle suggests that it may have other roles in cellular activity. Although many aspects of its function are still obscure, it is apparent that certain materials are sequestered into its cisternae or saccules, synthesized there, or variously combined in the cisternae to form complex secretion products.
The secretory products are then separated from the cisternae as membrane-bound vesicles and transported to and through the plasma membrane or to the vacuolar compartment where they remain inside the cell. While the Golgi apparatus is important in the secretion of many proteins, including the fucose-rich mucilage secreted by root cap cells, the digestive enzymes secreted by insectivorous plants, and the wall-degrading enzymes released by the cells in the abscission zone, it is bypassed in the secretion of some proteins, including the prolamin proteins that make up some of the protein vacuoles in the seeds of cereals.
In the majority of plant cells, the Golgi apparatus is responsible for packaging and exporting the hemicelluloses, pectins, and hydroxyproline-rich glycoproteins of the wall that is built up around the cell. See also: Golgi apparatus. The vacuole Fig. In meristematic cells, vacuoles are generally small and are characterized by contents that stain darkly with certain procedures.
The contents of these vacuoles seem to be utilized in the process of development and then are replaced by water. At a certain stage in this process, the vacuoles fuse to form the large central vacuole, and most mature plant cells have large, centrally located vacuoles that make up the greatest part of the total volume of the cell. The cell sap is typically clear, making the vacuole look empty or vacuous. The increase in volume of this vacuole is important in the growth of the plant cell.
Moreover, the presence of water in the vacuole allows plants to have a large open dendritic form with a minimum investment of energy-intensive compounds in order to help the plants acquire light and the necessary nutrients that are dilute in the environment. In plant cells, vacuoles of different sorts are known to have different origins, with the endoplasmic reticulum, the Golgi apparatus, and the plasma membrane being involved. See also: Vacuole. Vacuoles participate in the homeostasis of the cytosol by acting as large reversible stores of water, protons and other ions, amino acids, and other metabolites.
The vacuoles in cells of many seeds function in the storage of proteins, and the vacuoles in the cells of many desert plants function in the storage of water as well as the storage of carbon in the form of organic acids. In addition, the colors of many flowers and fruits result from the presence of pigments dissolved in the vacuolar fluid. See also: Plant pigment. Another conspicuous feature of many types of plant cells is the presence of large numbers of lipid bodies or spherosomes.
They frequently are abundant in cells of embryos or in root or shoot apices and less numerous in more mature plant cells. These bodies are unique in having a structural boundary that is composed of a monolayer instead of a bilayer that is typical of most membranes.
The lipid bodies provide a carbon source for the production of biofuels. See also: Lipid. Mitochondria typically are ellipsoidal bodies bounded by a double-membrane system with the inner membrane projecting into the lumen to form cristae Fig. In general, there is less extensive development of the cristae in the mitochondria of plant cells than in those of animals. What Is the Origin of Chloroplasts? Figure 1: The origin of mitochondria and chloroplasts. Mitochondria and chloroplasts likely evolved from engulfed prokaryotes that once lived as independent organisms.
What Is the Function of Chloroplast Membranes? Figure 2: Structure of a chloroplast. What Is the Cell Wall? What Are Vacuoles? Plant cells have certain distinguishing features, including chloroplasts, cell walls, and intracellular vacuoles. Photosynthesis takes place in chloroplasts; cell walls allow plants to have strong, upright structures; and vacuoles help regulate how cells handle water and storage of other molecules.
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