Standard, AS/NZS Show/hide more, Description, Electrical installations (known as the Australian/New Zealand Wiring Rules). Standard, AS/ NZS. The presentation of this edition differs from previous editions of AS/NZS in that the Standard comprises two parts but with both parts. The edition of AS/NZS is amended as follows; the Zealand, AS/NZS , Electrical installations (known as the. AS/NZS Electrical installations (known as the. Australian/New Zealand Wiring Rules). Table of Contents. View on Information Provider website .
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They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapesranging from spheres to rods and spirals.
Bacteria were among the first life forms to appear on Earthand are present in most of its habitats. Bacteria inhabit soil, water, acidic hot springsradioactive waste and the deep portions of Earth's crust. Bacteria also live in symbiotic and parasitic relationships with plants and animals. Most bacteria have not been characterised, and only about half of the bacterial phyla have species that can be grown in the laboratory. There are typically 40 million bacterial cells in a gram of soil and a million bacterial cells in a millilitre of fresh as nzs 3000 2007 pdf.
The nutrient cycle includes the decomposition of dead bodies ; bacteria are responsible for the putrefaction stage in this process. Data reported by researchers in October and published in March suggested as nzs 3000 2007 pdf bacteria thrive in the Mariana Trenchwhich, with a depth of up to 11 kilometres, is the deepest known part of the oceans.
The famous notion that bacterial cells in the human body outnumber human cells by a factor of The largest number exist in the gut floraand a large number on the skin. However several species of bacteria are pathogenic and cause infectious diseasesincluding cholerasyphilisanthraxleprosyand bubonic plague.
The most common fatal bacterial diseases are respiratory infectionswith tuberculosis alone killing about 2 million people per year, mostly in sub-Saharan Africa. In industry, bacteria are important in sewage treatment and the breakdown of oil spillsthe production of cheese and yogurt through fermentationthe recovery of gold, palladium, copper and other metals in the mining sector,  as well as in biotechnologyand the manufacture of antibiotics and other chemicals.
Once regarded as plants constituting the class Schizomycetesbacteria are now classified as prokaryotes. As nzs 3000 2007 pdf cells of animals and other eukaryotesbacterial cells do not contain a nucleus and rarely harbour membrane-bound organelles. Although the term bacteria traditionally included all prokaryotes, the scientific classification changed after the discovery in as nzs 3000 2007 pdf s that prokaryotes consist of two very different groups of organisms that evolved from an ancient common ancestor.
These evolutionary domains are called Bacteria and Archaea. The ancestors of modern bacteria were unicellular microorganisms that were the unit vector same direction calculator forms of life to appear on Earth, about 4 billion years ago.
For about 3 billion years, most organisms were microscopic, and bacteria and archaea were the dominant forms of life. Bacteria were also involved in the second great evolutionary divergence, that of the archaea and eukaryotes.
Here, eukaryotes resulted from the entering of ancient bacteria into endosymbiotic associations as nzs 3000 2007 pdf the ancestors of eukaryotic cells, which were themselves possibly related to the Archaea.
Later, some eukaryotes that already contained mitochondria as nzs 3000 2007 pdf engulfed cyanobacteria -like organisms, leading to the formation of chloroplasts in algae and plants. Bacteria display a wide diversity of shapes and sizes, called morphologies.
Bacterial cells are about one-tenth the size of eukaryotic cells and are typically 0. However, a few species are visible to the unaided eye—for example, Thiomargarita namibiensis is up to half a millimetre long  and Epulopiscium fishelsoni reaches 0.
Most bacterial species are either spherical, called cocci sing. A small number of other unusual shapes have been described, such as star-shaped bacteria.
Many bacterial species exist simply as single cells, others associate in characteristic patterns: Neisseria form diploids pairsStreptococcus form chains, and Staphylococcus group together babanzade ahmed naim pdf "bunch of grapes" clusters.
Bacteria can also group to form larger multicellular structures, such as the elongated filaments of Actinobacteriathe aggregates of Myxobacteriaand the complex hyphae of Streptomyces. Bacteria often attach to surfaces and form dense aggregations called biofilmsand larger formations known as microbial mats. These biofilms and mats can range from a few micrometres in thickness to up to half a metre in depth, and may contain multiple species of bacteria, protists and archaea.
Bacteria living in biofilms display a complex arrangement of cells and extracellular components, forming secondary structures, such as microcoloniesthrough which there are networks of channels to enable better diffusion of nutrients. The bacterial cell is surrounded by a cell membrane which is made primarily of phospholipids. This membrane encloses the contents of the cell and acts as a barrier to hold nutrients, proteins and other essential components of the cytoplasm within the cell.
Many important biochemical reactions, such as energy generation, occur due to concentration gradients across membranes, creating a potential difference analogous to a battery. The general lack of internal membranes in bacteria means these reactions, such as electron transportoccur across the cell membrane between the cytoplasm and the outside of the cell or periplasm. Most bacteria do not have a membrane-bound nucleus, and their genetic material is typically a single circular bacterial chromosome of DNA located in the cytoplasm in an irregularly shaped body called the nucleoid.
Like all living organismsbacteria contain ribosomes for the production of proteins, but the structure of the bacterial ribosome is different from that of eukaryotes and Archaea. Some bacteria produce intracellular nutrient storage granules, such as glycogen polyphosphate sulfur  or polyhydroxyalkanoates. Around the outside of the cell membrane is the cell wall. Bacterial cell walls are made of peptidoglycan also called mureinwhich is made from polysaccharide chains cross-linked by peptides containing D- amino acids.
The cell wall is essential to the survival of many bacteria, and the antibiotic penicillin is able to kill bacteria by inhibiting a step in the synthesis of peptidoglycan.
There are broadly speaking two different types of cell wall in bacteria, that classify bacteria into gram-positive bacteria and gram-negative bacteria. The names originate from as nzs 3000 2007 pdf reaction of cells to the Gram staina long-standing test for the classification of bacterial species. Gram-positive bacteria possess a thick cell wall containing many layers of peptidoglycan and teichoic acids.
In contrast, gram-negative bacteria have a relatively thin cell as nzs 3000 2007 pdf consisting of a few layers of peptidoglycan surrounded by a second lipid membrane containing lipopolysaccharides and lipoproteins. This includes clinically important bacteria such as Mycobacteria which have a thick peptidoglycan cell wall like a gram-positive bacterium, but also a second outer layer of lipids.
In many bacteria, an S-layer of rigidly arrayed protein molecules covers the outside of the cell. S-layers have diverse but mostly poorly understood functions, but are known to act as virulence factors in Campylobacter and contain surface enzymes in As nzs 3000 2007 pdf stearothermophilus. Flagella are driven by the energy released by the transfer of ions down an electrochemical gradient across the cell membrane.
They are distributed over the surface of the cell, and resemble fine hairs when seen under the electron microscope. Fimbriae are original cd to be involved in attachment to solid surfaces or to other cells, and are essential for the virulence of some bacterial pathogens.
Glycocalyx is produced by many bacteria to surround their cells, and varies in structural complexity: These structures can protect cells from engulfment by eukaryotic cells such as macrophages part of the human immune system. The assembly of these extracellular structures is dependent on bacterial secretion systems.
These transfer proteins from the cytoplasm into the periplasm or into the environment around the cell. Many types of secretion systems are known and these structures are often essential for the virulence of pathogens, so are intensively studied.
Certain genera of gram-positive bacteria, such as BacillusClostridiumSporohalobacterAnaerobacterand Heliobacteriumcan form highly resistant, dormant structures called endospores. Endospores show no detectable metabolism and can survive extreme physical and chemical stresses, such as high levels of UV lightgamma radiationdetergentsdisinfectantsheat, freezing, pressure, and desiccation.
Bacteria exhibit an extremely wide variety of metabolic types. Bacteria either derive energy from light using photosynthesis called phototrophyor by breaking down chemical compounds using oxidation called chemotrophy.
This reaction releases energy that can be used to drive metabolism. Chemotrophs are further divided by the types of compounds they use to transfer electrons. Bacteria that use inorganic compounds such as hydrogren, carbon monoxideor ammonia as sources of electrons are called lithotrophswhile those that use organic compounds are called organotrophs. Many bacteria get their carbon from other organic carboncalled heterotrophy.
Others such as cyanobacteria and some purple bacteria are autotrophicmeaning that they obtain cellular carbon by fixing carbon dioxide. In many ways, bacterial metabolism provides traits that are useful for ecological stability and for human society. One example is that some bacteria have the ability to fix nitrogen gas using the enzyme nitrogenase. This environmentally important trait can be found in bacteria of most metabolic types listed above.
Facultative anaerobes can switch between fermentation and different terminal electron acceptors depending on the environmental conditions in which they find themselves. Unlike in multicellular organisms, increases in cell size cell growth and reproduction by cell division are tightly linked in unicellular organisms.
Bacteria grow to a fixed size and then reproduce through binary fissiona form of asexual reproduction. Some as nzs 3000 2007 pdf, while still reproducing asexually, form more complex reproductive structures that as nzs 3000 2007 pdf disperse the newly formed daughter cells. Examples include fruiting body formation by Myxobacteria and aerial hyphae formation by Streptomycessuper mario mac budding.
Budding involves a cell forming a protrusion that breaks away and produces a daughter cell. In the laboratory, bacteria are usually grown using solid or liquid media. Solid growth mediasuch as agar platesare used to isolate pure cultures of a bacterial strain.
However, liquid growth media are used when measurement of growth or large volumes of cells are required. Growth in stirred liquid media occurs as an even cell suspension, making the cultures easy to divide and transfer, although isolating single bacteria from liquid media is difficult.
The use of selective media media with specific nutrients added or deficient, or with antibiotics added can help identify specific organisms. Most laboratory techniques for growing bacteria use high levels of nutrients to produce large amounts of cells cheaply and quickly. However, in natural environments, nutrients are limited, meaning that bacteria cannot continue to reproduce indefinitely.
Some organisms can grow extremely rapidly when nutrients become available, such as the formation of algal and cyanobacterial blooms that often occur in lakes during the summer. Bacterial growth follows four phases. When a population of bacteria first enter a high-nutrient environment that allows growth, the cells need to adapt to their new environment.
The first phase of growth is as nzs 3000 2007 pdf lag phasea period of slow growth when the cells are adapting to the high-nutrient environment and preparing for fast growth.
The lag phase has high biosynthesis rates, as proteins necessary for rapid growth are produced. The log phase is marked by neoragex metal slug on pc exponential growth.
The rate at which cells grow during this phase is known as the growth rate kand the time it takes the cells to double is known as the generation time g. During log phase, nutrients are metabolised at maximum speed until one of the nutrients is depleted and starts limiting growth. The third phase of growth is the stationary phase and is caused by depleted nutrients.
The cells reduce their as nzs 3000 2007 pdf activity pratikar mp3 songs consume non-essential cellular proteins. The stationary phase is a transition from rapid growth to a stress response state and there is increased expression of genes involved in DNA repairas nzs 3000 2007 pdf metabolism and nutrient transport.
Most bacteria have a single circular chromosome that can range in size from onlybase pairs in the endosymbiotic bacteria Carsonella ruddii to 12, base pairs Bacteria genomes usually as nzs 3000 2007 pdf a few hundred to a few thousand genes. The genes in bacterial genomes are usually a single continuous stretch of DNA and although several different types of introns do exist in bacteria, these are much rarer than in eukaryotes.
Bacteria, as asexual organisms, inherit an identical copy of the parent's genomes and are clonal.
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