Biological Sciences
Cells
Cells are the basic structural and functional units of all living organisms. They are enclosed by a membrane and contain genetic material, organelles, and other cellular structures. Cells carry out essential processes such as metabolism, growth, and reproduction, and they can specialize to perform specific functions within multicellular organisms.
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6 Key excerpts on "Cells"
eBook - ePub- Laurie Ann Callihan(Author)
- 2013(Publication Date)
- Research & Education Association(Publisher)
CHAPTER 3 Cellular and Molecular Biology CHAPTER 3 CELLULAR AND MOLECULAR BIOLOGY CELL STRUCTURE AND FUNCTIONThe cell is the smallest and most basic unit of structure for all living things (organisms). A single organism can be unicellular (consisting of just one cell) or multicellular (consisting of many Cells). A multicellular organism may have many different types of Cells that differ in structure to serve different functions. Individual Cells may contain organelles that assist them with specialized functions. For example, muscle Cells tend to contain more mitochondria (organelles that make energy available to the Cells) since muscle requires the use of extra energy.Scientists first began to describe Cells after the invention of the light microscope in the mid-1600s. Antonie van Leeuwenhoek first observed tiny organisms (he called them “animalcules”) with the use of microscopes. We now know these tiny organisms were one-celled bacteria. Robert Hooke was the first to use the term “Cells” when he observed cell walls of dead cork under a light microscope.In the mid-nineteenth century, two German scientists (Matthias Schleiden and Theodor Schwann) developed the cell theory . It consists of the following tenets:1. All living things are made up of one or more Cells.2. Cells are the basic units of life.3. All Cells come from pre-existing Cells.These tenets of the cell theory developed by scientists over 150 years ago are still held today.The light microscope is useful in examining most Cells and some cell organelles (such as the nucleus). However, many cell organelles are very small and require the magnification and resolution power of an electron microscope.There are two main types of Cells: prokaryotic and eukaryotic. Prokaryotes
- Gabrielle I. Edwards, Cynthia Pfirrmann(Authors)
- 2021(Publication Date)
- Barrons Educational Services(Publisher)
3THE CELL: BASIC UNIT OF LIFE
WHAT YOU WILL LEARN
In this chapter, you will review the structure and function of Cells and the essential roles that Cells play in the life of an organism. SECTIONS IN THIS CHAPTER•The Cell as a Basic Unit•Parts of a Cell•Comparison of Plant and Animal Cells•Organization of Cells and Tissues•Cell Reproduction•Review Exercises•Connecting to Life/Job Skills•Chronology of Famous Names in BiologyThe Cell as a Basic Unit
CELL CONCEPT
The body of a living organism is built of units called Cells. All living things are similar in that they are composed of one or more Cells. The body of a unicellular organism is composed of one cell. Most plants and animals are multicellular, having a body made of numerous Cells.During the years 1838 and 1839, the cell theory was pioneered by two eminent scientists of the day. Matthias Schleiden, a botanist, and Theodor Schwann, a zoologist, combined some of their fundamental ideas about the structure of plants and animals into what has developed into a basic concept of biological thought. The work of Rudolf Virchow completed the cell theory when, in 1858, he established that new Cells could arise only from other living Cells. The cell theory states that (1) that Cells are the basic units of life; (2) that all plants and animals are made of Cells; and (3) that all Cells arise from preexisting Cells.UNIT OF STRUCTURE
Microscopic examination of plant and animal parts indicates that the bodies of living organisms are composed of Cells. Cells provide structure and form to the body. They appear in a variety of shapes: round, concave, rectangular, elongate, tapered, spherical, and others. Cell shape seems to be related to specialized function (Figure 3.1 ).Cells not only vary in shape, they also differ in size. Most plant and animal Cells are quite small, ranging in size between 5 and 50 micrometers in diameter (Figure 3.2 ). Cells are measured in units that are compatible with modern microscopes. (See Table 3.1
eBook - ePubCancer
Basic Science and Clinical Aspects
- Craig A. Almeida, Sheila A. Barry(Authors)
- 2011(Publication Date)
- Wiley-Blackwell(Publisher)
Cells: the fundamental unit of lifeThe uniformity of Earth’s life, more astonishing than its diversity, is accountable by the high probability that we derived, originally, from some single cell, fertilized in a bolt of lightning as the Earth cooled.Lewis Thomas, physician, researcher, educator, and essayistCHAPTER CONTENTS- Seven hierarchal levels of organization
- Four types of macromolecular polymers
- Cell structure and function
- Relationship between structure and function is important
- Expand your knowledge
- Additional readings
When our bodies work properly we have the tendency to take their complex structure and functions for granted. It is important to realize that the more we know about healthy body function, the better the position we will be in to fix what is wrong when we are ill. This and the following two chapters will provide a basic understanding of the way Cells function normally and how an attack on the body by rogue Cells that divide uncontrollably and function abnormally can result in cancer. This chapter will take a stepwise approach to gradually build a working knowledge of subcellular components in order to understand how they work together as a single entity – the cell. The whole is more than the sum of its parts, and all components of the cell must work together seamlessly to carry out the processes that give rise to what we know as life.SEVEN HIERARCHAL LEVELS OF ORGANIZATIONUsing the stepwise approach to understand how a living organism as complex as a human is put together first requires some knowledge of the seven levels of biological organization (Figure 2.1 ), and there is no better place to start than at the beginning, at the level of the atom.Atoms are the building blocks of all moleculesEverything around us is composed of atoms – the building blocks of matter (Figure 2.1a ). An atom is composed of negatively charged particles called electrons that spin in orbitals around a central nucleus possessing positively charged protons and uncharged neutrons. A chemical or covalent bond can be created between two atoms when their orbitals overlap, allowing their electrons to be shared. A molecule is formed by such bonding of two or more atoms, and when molecules bond with other molecules they can serve as building blocks for the formation of macromolecules such as proteins, carbohydrates, fats, and DNA (Figure 2.1b ). A cell is a collection of atoms, molecules, macromolecules, and macromolecular structures (Figure 2.1c
eBook - ePub- R. Michael Akers, D. Michael Denbow(Authors)
- 2013(Publication Date)
- Wiley-Blackwell(Publisher)
2 The cell: The common physiological denominatorContentsCells: a Common Denominator Water: the Universal SolventCellular OrganellesFluid Mosaic Model Microscopy Techniques Organelles of the Cytoplasm Nuclear StructureCell Growth and DifferentiationStages of the Cell Cycle Stages of Mitosis Regulators of Cell DivisionMacromolecules and Cellular PhysiologyProteins Carbohydrates Lipids Nucleic AcidsCellular BiochemistryChemical Bonds Chemical Reactions Significance of EnzymesExtracellular Environment and Cell FunctionChapter SummaryOsmosis Transport MechanismsCells: A common denominator
All of the physiological systems, for example, digestive, respiratory, or cardiovascular, depend on the actions and activities of Cells. Groups of Cells and their products coalesce to create the four basic tissue types (epithelial, neural, muscular, and connective tissues). Attributes of these tissues will be discussed in detail in Chapter 4 . Combinations of these tissues produce organs. Functionally related organs are arranged into physiological systems. To illustrate, the digestive system includes the mouth and oral cavity, esophagus, stomach, small intestine and large intestine, and related accessory organs (liver, pancreas, gall bladder). This tube-within-a-tube organization allows for acquisition of food, physical mastication, chemical digestion, and ultimately, absorption of nutrients across the lining of the gastrointestinal (GI) tract into the bloodstream. The mature GI tract has elements of each of the four major tissue types.The internal lining, the mucosa (an example of epithelial tissue), is composed of a layer of specialized epithelial Cells called enterocytes. The enterocytes rest upon a thin layer of extracellular proteins, the basement membrane. The mucosal layer also includes other specialized connective tissue elements, including the structurally important proteins collagen and elastin, as well as protein-carbohydrate hybrid molecules called proteoglycans. The mucosa also has a population of scattered smooth muscle Cells, the muscularis mucosa, and a distinctive connective tissue called the lamina propria. The submucosa appears between the enterocytes and the next major tissue layer, the muscularis. This region provides a passageway for capillaries and lymphatic vessels. Exocrine glands, which produce secretions destined for the lumen of the GI tract, also reside in this location. Closer to the outer circumference of the tract, there are two closely aligned, dense layers of smooth muscle Cells called the muscularis externa. The innermost layer of smooth muscle Cells are arranged around the circumference of the GI tract, while the outer layer is oriented along the longitudinal axis of the GI tract. The coordinated contraction and relaxation of these two smooth muscle cell layers provide for mixing and movement of gut contents. A thin layer of epithelial Cells called the serosa covers the outside of the GI tract that is adjacent to the internal body cavity. The serosa is continuous with the mesentery, which provides a means for entrance of veins, arteries, and nerve fibers into the muscularis externa and submucosa and for general support via attachment to ligaments.
eBook - ePub- Alexander Fridman, Gary Friedman(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
As mentioned above, life exhibits hierarchical organization. Atoms are organized into molecules, molecules into organelles, organelles into Cells and so on. It seems, however, that all living things are composed of one or more Cells as the most basic units of life, and the functions of a multicellular organism are a consequence of the types of Cells it contains and how these Cells are arranged and work together. Cells fall into two broad groups: prokaryotes and eukaryotes. Prokaryotic Cells are smaller (as a general rule) and lack much of the internal compartmentalization and complexity of eukaryotic Cells. No matter which type of cell we are considering, all known Cells have certain features in common such as a cell membrane, DNA and RNA, cytoplasm and ribosomes.The natural shapes of Cells vary. For example, neurons can grow parts called axons that are often many centimeters long. Skeletal muscle Cells can also be several centimeters long. Others such as parenchyma (a common type of plant cell) and erythrocytes (red blood Cells) are much more equi-dimensional. Cells often change their shape when they attach to firm substrates or other Cells. Some Cells are encased in a rigid wall which constrains their shape, while others have a flexible cell membrane (and no rigid cell wall). The size of Cells is also related to their functions. Eggs (or to use the Latin word, ova) are relatively large, often being the largest Cells an organism produces. The large size of many eggs is related to the process of development that occurs after the egg is fertilized, when the contents of the egg (now termed a zygote) are used in a rapid series of cellular divisions, each requiring tremendous amounts of energy. In general, Cells range in size from small bacteria (about 1 micrometer) to unfertilized eggs produced by birds and fish.3.3.1 Primary cell componentsJust as larger living organisms differ from each other in structure and function, so do many Cells. There are also many similarities between different types of Cells. Figure 3.16 illustrates the typical structure of a eukaryotic cell, while Figure 3.17 shows the anatomy of a typical prokaryotic (bacterial in this case) cell.Figure 3.16 Eukaryotic cell anatomy.3.3.1.1 The cell envelope: Membranes and wallsFigure 3.17 Anatomy of a bacterial cell.The cell membrane functions as a semi-permeable mechanically flexible barrier, allowing very few molecules across it while fencing the majority of organically produced chemicals inside the cell. Electron microscopy examinations of cell membranes have led to the development of the lipid bilayer model (also referred to as the fluid-mosaic model).
eBook - ePub- Daniel Greenberg(Author)
- 2014(Publication Date)
- Research & Education Association(Publisher)
6Life Science
6.1 CellsA. Cell Features
1. All living things are composed of Cells .2. All Cells come from preexisting Cells.3. All Cells carry out the basic processes of life:a. Take in food and metabolize it for energyb. Respond to the environmentc. Growd. Reproduce e. Get rid of waste4. All Cells exist in one of the three basic domains—bacteria, archaea, and eukaryotes. The archaea were classified relatively recently and for our purposes can be grouped with the bacteria as prokaryotes.Prokaryotes Eukaryotes Single-celled Single-celled and multicelled Bacteria, algae Plants, animals, fungi, and protists Extremely small Cells Large Cells (10 times as large as prokaryotes) No nucleus or organelles Nucleus and organelles Single, usually circular chromosome Multiple chromosomes Reproduces by fission (budding) Mitosis and meiosis(see section 6.4 )for reproduction and growthB. Cells in the Laboratory: Serial Dilution of Bacteria
1. Serial dilution is a process that is used to estimate bacterial populations. This can be useful for many environmental, health, and commercial purposes.2. In serial dilutions, a sample is repeatedly diluted. This series starts with bacteria of concentration c in the flask.3. 1 ml is taken out of the flask and put into the first test tube with 9 ml of water, representing a 0.1 or 10−1 dilution.4. The process is repeated three more times.5. 1 ml is taken from the fourth test tube and found to have 40 bacteria.6.1Problem 1: Which of the following is a characteristic of eukaryotic but not prokaryotic organisms?A) Forming tissues and organsC) Cell divisionB) Obtaining energy from foodD) LocomotionSTRATEGY
Refer to the characteristics of prokaryotes and eukaryotes.THINK
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