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    Living Thing Biology Essay (4268 words)

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    Living things make up the world as we know it.

    Living things are involved in ourlife constantly, seeing that we are alive. There are five characteristics thatare common to all living things. Living things are made up of one or more cells. Each cell is made up of living matter and is separated by a barrier thatencloses the cell from its surroundings. However, there are many different kindsof cells that make up living things. A single cell can be one organism.

    Theseorganisms are known as unicellular. Most of the organisms that we know best suchas people, trees, and dogs are all made up of more than one cell. Organisms madeof more than one cell are said to be multicellular. Another characteristic thatliving things share is that they reproduce. They reproduce, or make neworganisms of the same sort. In order for a species to survive, it is a necessityfor them to reproduce because all organisms die eventually.

    There are two waysliving things reproduce, sexually and asexually. Sexual reproduction needs twocells from two different organisms to merge and form the first cell of a neworganism. Asexual reproduction is when only one organism can reproduce withoutthe assistance of another. The third characteristic of living things, is thatall living things need to grow and develop. When an organism is growing, most gothrough a cycle called development.

    The single cell that starts the cell dividesover and over again to make all the cells that the organism has when inadulthood. As the cycle continues the organism ages. Aging is when the organismbecomes less efficient in the process of life. The organism will not be able toreproduce, and death comes as finally too.

    The fourth characteristic of a livingthing is the ability to obtain and use energy. Living things obtain energy fromtheir environment or their surroundings. All living things require energy tolive and build their cells. This process is anabolism.

    Anabolism is the processin a living thing that involves putting together complex substances from simplersubstances. Plants get their energy from the sunlight through a process calledphotosynthesis. Animals get their energy from food that is eaten. The food isthen broken down through digestion, resulting in a release of energy calledcatabolism.

    Living things practice anabolism and catabolism through the wholetime they are living. The balance of anabolism and catabolism is calledmetabolism. The fifth and final characteristic that all living things share isthat all living things respond to their environment. Response to theirenvironment can be sudden, through behavior, or gradual, in metabolic process orgrowth. Stimulus is anything in the environment that causes a living thing toreact.

    Stimuli include light, temperature, odor, gravity, sound, water, andpressure. Plants generally act to stimuli slower than animals. The process inwhich living things respond to stimuli in ways to keep conditions in their bodysuitable for life is homeostasis. These five characteristics of living thingsare just the basics to knowing what makes up living things.

    Atomic Structure ofLiving Things The basic unit of matter is the atom. Atoms are extremely small,in fact, if you placed 100 million atoms in a row one after the other, it wouldbe one centimeter long. Even though the atom is small it consists of evensmaller particles, called subatomic particles. Scientists believe that there isat least 200 subatomic particles.

    The three main subatomic particles are theneutron, proton, and electron. In the middle of the atom there is a nucleus. Thenucleus makes up 99. 9 percent of the atoms weight even though it is a hundredtimes smaller than the atom itself.

    The nucleus contains two different kind ofsubatomic particles, the neutron and the proton. The proton has a positivecharge and the neutron is a electrically neutral subatomic particle. Both arealmost equal in mass, 1 amu (atomic mass unit). Another subatomic particle inthe atom is the electron. It is negatively charged and it’s mass is about 2000times smaller than that of a neutron or electron.

    Usually the number or electronin an atom is the same as the number of protons. So, usually the atoms have nota positive nor negative charge, but they are neutral. Electron are not in thenucleus like the protons and neutrons are. They travel at very high speedsthroughout the atom in energy levels. The energy levels are like orbits thatsurround the nucleus. The number of protons that are in the nucleus of an atomis called the atomic number.

    The atomic number identifies the atom because notwo atoms have the same number of protons in there nucleus. For example,hydrogen has the atomic number of 1, that means all atoms that have one protonin its nucleus is hydrogen. The atomic mass number is the number of neutrons andprotons in the nucleus. To find the number on neutrons in an atom, you mustround the atomic mass number to the nearest whole number and then subtract theatomic number. Remember the atomic number is the same as the number of protonsin the atom.

    To find out the number or electrons an atom contains, you just needto know the atomic number because there is the same number of protons as thereis electrons in atoms. For example, in sodium, the atomic number is 11, and theatomic mass number is 22. 98977. This means that sodium contains 11 protons, 11electron, and 12 neutrons. (See Figure 1) Substances known as elements are madeup of solely on type of atom.

    Scientists have discovered 109 elements, 90 werefound in nature, and 19 were artificially made in laboratories by scientists. Each element is represented by a chemical symbol. Each symbol is made up of oneor two letters, usually taken from the name of the element. The symbol of oxygenis O, the symbol for phosphorus is P, and the symbol for Nitrogen is N. Mostchemical elements are solid, like gold, iron, bronze, and silver to name a few.

    They are on the left 3/4 of the periodic table. Some elements are gases, likeoxygen and carbon. They are on the right 1/4 of the periodic table. Only a fewelements are liquids, mercury and bromine are the most common.

    The noble gasesare located all the way to the right on the periodic table. The atomic number ofan element is always the same, this means that an element will always have thesame number of protons. However, the number of neutrons in the nucleus maydiffer from one atom to the next. For example, the typical hydrogen atomcontains one proton and no neutrons inside the nucleus. Another form of hydrogenis called deuterium. It contains one proton and one neutron in the nucleus.

    Thethird form of hydrogen is sometimes referred to as tritium. Tritium has onproton and two neutrons in the nucleus of the atom. Even though the atomic massnumber may change the atomic number of hydrogen will be 1, and it will stillhave one proton and one electron. An isotope is an atom with the same number ofprotons and electrons but a different number of neutrons from the same element. Isotopes are represented by putting a number in front of the atomic symbol ofthat atom. The number represents the atomic mass.

    Regular hydrogen is written1H, deuterium is 2H, and tritium is 3H. Compounds and Molecules When elementscombine to form substances of consisting of two or more atoms, chemicalcompounds are produced. A chemical compound deals with the combination of two ormore atoms in definite proportions. Most materials in living things happen to becompounds, so they are very important to us. Chemical compounds are representedjust as elements are with chemical symbols.

    A chemical formula is made up of thechemical symbols that make the chemical compound. For example, water containstwo hydrogen atoms and one oxygen atom. The chemical formula would be H2O. Tablesalt is made from one sodium atom and one chlorine atom, so the chemical formulais NaCl. Chemical compounds are formed by the interaction of atoms. Chemicalbonding is the process in which atoms interact and combine.

    An important factorin chemical bonding is the number of electrons in an atom’s outermost energylevel. Each energy level can only hold a certain number of electrons. Theinnermost energy level, or first energy level can hold only two electrons. Thesecond energy level can hold eight electrons. The third holds eighteenelectrons, the fourth and fifth energy levels hold up to thirty-two electrons. The sixth energy level can bear eighteen electron, the seventh energy level canhold eight electrons.

    The eighth and outermost energy level can accommodate fora mere two electrons. In order for there to be electrons in outer energy levels,the inner energy levels must be full. There can’t be 1 electron on the firstenergy level and five on the second. It would have to be two on the first energylevel and four electrons on the second. When the electrons of an atom fill theoutermost energy level they are said to be stable, or unreactive. These atomswill not bond with other atoms to form chemical bonds.

    In order for an atom tobecome stable, it will either have to lose or gain electrons to make it’soutermost energy level complete. There is one other way an atom can be stable. It will be stable if it’s outermost energy level contains eight electrons. Onetype of bond to make atoms stable is called an ionic bond. An ionic bond is abond that involves the transfer of electrons. The name comes from the word ion.

    Ion means charged particles. Ions are produced when ionic bonds occur. Forexample, sodium has only one electron on its outermost energy level and chlorinehas seven on its outermost energy level. These two atoms want to bond in orderto become stable. That means it wants to get rid of it to become stable. Theloss of the one electron makes a sodium ion (Na+), which is positively charged.

    It’s positively charged because it lost one of it’s negatively chargedelectrons. Thus, the electrons and protons don’t balance, because now there isone more proton than electron, so the ion has a positive charge. The addition ofone electron makes a negatively charged chlorine ion (Cl-). The two ions areoppositely charged and now have an intense attraction to each other. Theattraction is caused by the transfer of electrons that holds the ions togetherin an ionic bond.

    (See Figure 2) A different type of bond is called a covalentbond. A covalent bond is formed when atoms share electrons in order to becomestable. The shared electrons are located in the outermost energy levels of bothatoms. This forms a strong bond that is in many living things. Covalent bondscan be in the form of single bonds, double, or triple.

    The bond between twohydrogen atoms and oxygen atom (H2O), forms a single bond. A single pair ofelectron is shared between the two hydrogen atoms and the oxygen atoms. (SeeFigure 2) On the other hand, the compound that forms carbon dioxide (CO2), formsa double bond. The carbon atom shares two pairs of electrons, four total withthe two oxygen atoms. In covalent bonds the combination of atoms that are causedfrom sharing form molecules. A molecule is the smallest particle of a covalentlybonded compound.

    Besides water and carbon dioxide that were already mentioned,sugar (C6H12O6) and ammonia (NH3) are compounds. Organic compounds are compoundsthat contain carbon. Carbon is a unique element because of its ability to formcovalent bonds that are exceptionally strong and stable. The carbon atom has twoelectrons in the first energy level and four in the second energy level.

    Thereare four open positions in carbon’s outermost energy level, allowing it to formfour single covalent bonds. Carbon can easily bond with hydrogen, oxygen,nitrogen, phosphorus, and sulfur atoms. Carbon also has the extraordinaryability to form long chains with other carbon atoms. The bonds between carboncan be single, double, or triple covalent bonds. No other element has this rareability.

    (See Figure 2) Cell Structures Cells from a living thing come in manydifferent sizes and shapes. Even though cells differ in size and shape, certainparts of the cells are the same. The cells of animals, plants, and otherorganisms have three major but basic structures in common: the cell membrane,the nucleus, and the cytoplasm. The cell membrane acts as the cell’s outer walland protects it from it’s surroundings.

    It also moderates what goes in, and whatcomes out of the cell. The cell membrane is made up of several different typesof molecules. The most important of these is lipids. Most of the cell membraneis made up of a double layer of lipids. The cell membrane is also made up ofproteins and carbohydrates.

    In plants the cell membrane is surrounded by thecell wall of the plant. The cell wall helps protect and support the plant. Thecell wall lets water, oxygen, and carbon dioxide pass through easily. The cellwall is made up of three layers which are extremely porous.

    In the majority ofcells there is a dark structure we know as the nucleus. Not all cells havenuclei though. Bacteria and other small unicellular organisms don’t have anucleus. These are said to be prokaryotes, or cells without nuclei.

    Cells thatdo have a nucleus are called eukaryotes. The nucleus is very important to thecell, it is the information center and contains DNA. DNA stores geneticinformation that is passed to one generation to the next. The DNA in a cell isattached to special proteins. These proteins are called chromosomes.

    Chromosomescontain genetic information that is passed through generations. The nucleus of acell tend to be about two to five micrometers in diameter. Surrounding thenucleus there are two membranes called the nuclear envelope. The nuclearenvelope contains dozens of small pores, through which molecules move in and outof the nucleus. In most nuclei, there is a small region called the nucleolus.

    Itis made up of RNA and proteins. In the nucleolus, ribosomes are made. Ribosomesare important because they help out with the productions or proteins in a cell. The space inside of a cell can be divided into two parts, the nucleus and thecytoplasm.

    The cytoplasm is the area between the nucleus and the cell membrane. The cytoplasm contains other important structures in the cell. Structures insidethe cell are called organelles. An organelle is a tiny structure in the cellthat preforms a special function within the cell.

    The mitochondria is greatlyimportant to the cell. In animals, the mitochondria changes the stored chemicalenergy from food into more useful energy for the cell. In plants, an organellecalled the chloroplast changes energy from sunlight to energy that can be usedby the cell. The mitochondria is found in both the cells of plants and animals,where as the chloroplast is only found in plants. Ribosomes are the structuresin which proteins are produced.

    They are made out of protein and RNA. Someribosomes in a cell are attached to membranes, while some are free in thecytoplasm. Ribosomes are one of the smallest organelles in a cell. Many cellsare filled with a network of channels we call the endoplasmic reticulum. Theendoplasmic reticulum transports through the inside of the cell. There happensto be two different types of endoplasmic reticulums.

    The smooth endoplasmicreticulum has channels that are smooth. In some cells special enzymes andchemicals are stored within the smooth endoplasmic reticulum. The other type ofendoplasmic reticulum is called the rough endoplasmic reticulum. It is calledrough because it has ribosomes that are attached to the surface making it lookrough. Many proteins that are released are transported from the cell in therough endoplasmic reticulum. The newly formed proteins are often first movedinto special compartments known as the Golgi apparatus.

    In the Golgi apparatusthe proteins are modified and then releases it. The Golgi apparatus’ function isto modify, collect, package, and finally distribute molecules made in onelocation to another location. When foreign materials that are too big to move inthe cell get into the cell, the cell membrane forms a pocket around it. Then thelysosomes come in and digest, then break down the particle. Lysosomes are smallstructures that contain chemicals and enzymes that help break down and digestforeign particles in the cell.

    Lysosomes are made in the Golgi apparatus, andplants don’t have lysosomes. Vacuoles are sac-like structures in a cell thatstore water, salts, proteins, and carbohydrates. Plants also have a structurebesides the vacuole called the plastid. The plastid also stores food as well aspigments for the plant. The cytoskeleton in a cell is the frame work that holdsthe cell together and gives it their shape. The cytoskeleton is made fromfilaments and fibers.

    One of the main parts in a cytoskeleton is a componentcalled microtubules. They are made out of hollow tubules made from proteins. They help move organelles throughout the cell. (See Figure 3) The Cell As aLiving Thing Living things are made up of cells and they grow in size. In mostinstances, a living thing grows because it produces more and more cells. Cellsin an adult human are no bigger that cells in a human baby, there is just moreof them.

    In a cell, water, oxygen, and food enter the cell through the cellmembrane, and waste products exit the cell. The time it takes to exchange thesematerials depends on the surface area of the cell. How quickly food and oxygenis used, and how quickly waste products are produced depends on the volume ofthe cell. As a cell gets bigger, the volume increases faster than the rate ofits surface area.

    This can be a problem for the cell. If the diameter of a cellincreases 5 times, the surface area would increase 25 times, and the volumewould increase 125 times. The bigger the cell is the harder time it has gettingthe nutrients and oxygen it needs in order to support it’s massive volume. Cellgrowth is controlled in multicellular organisms.

    Cells in parts of the body likethe heart and liver rarely divide. These cells are unlike skin cells that dividerapidly through a person’s lifetime. Controls on cell growth can be turned onand off like a light switch. If a bone or skin is broken, cells divide in orderit repair the damage that needs to be fixed. Uncontrolled cell growth can bevery harmful to multicellular organisms. Cancer is a disorder when cells havelost the ability to control their growth.

    Cancer cells keep growing and growinguntil the supply of nutrients shuts off. Cancer is a very serious disease thatshows the importance of controls on cell growth. Eukaryote cells divide in orderto slow down cell growth. Cell division is the process in which a cell dividesto form two daughter cells.

    The first stage of cell division is called mitosis. Mitosis is the process when the nucleus of a cell is divided into two nuclei,and both have the same number and type of chromosomes as the parent cell. Mitosis can be split into four parts. Interpahse occurs before mitosis canbegin. It is the period in between cell division and is the longest part of thecell cycle.

    The cell cycle is the process when a cell grows, prepares fordivision, divides, and begins a new cell cycle. Interphase itself is dividedinto three phases: G1, S, and G2. G1, called growth 1, or gap 1, is the stage inwhich a cell grows. The S stage is called the DNA synthesis stage. During thisstage of interphase the DNA is replicated in DNA replication.

    Proteins are alsosynthesized in the S phase. G2, or growth 2, takes place when the S stage isfinished. During G2 the synthesis or organelles and other materials happensfurthermore preparing the cell for division. While interphase is taking placethe nucleus is busy in synthesizing messenger RNA to direct all the steps. Thefirst phase in mitosis is called prophase. Prophase takes the longest time inmitosis, consuming 50-60% of the time it takes mitosis to occur.

    In prophase thechromosomes in a cell condense and coil up, making them more visible. Thecentrioles separate and go to opposite sides of the cell. Centrioles are smallstructures in the cytoplasm that contain tubulin, a microtubule protein. Plantcells don’t contain centrioles.

    The condensed chromosomes become attached tofibers in the spindle. The spindle is a mesh-like structure that helps move thechromosomes apart. At the end of prophase the chromosomes condense tighter, thenucleolus disappears, and the nuclear envelope begins to break down. Metaphaseis the second phase of mitosis, and is the shortest as well.

    During this phasethe chromosomes line up across the center of the cell. Anaphase is the nextphase in mitosis. It begins when the sister chromatids split. Chromatids are theidentical parts that form the chromosome. The chromatids become individualchromosomes and continue to split until they reach the opposite poles.

    Anaphaseends when the new chromosomes stop moving. Telophase is the fourth and finalstage of mitosis. The chromosomes begin o uncoil into a tangle of chromatin. Chromatin is the material that makes up chromosomes and itself is made fromprotein and DNA.

    All of this takes place where the two new daughter cells aretaking shape. Two nuclear envelopes begin to reappear around the chromatin. Thespindle begin to break apart and the nucleolus forms around the nucleus of thedaughter cells. Mitosis is over but there is still one more step. Cytokenesisfollows quickly after mitosis is finished. In cytokenesis the cytoplasm of theparent cell splits into two to form the daughter cells.

    In animals, the cellmembrane moves together and pinches the cells, giving making the daughter cellshave their own nucleus and organelles. In plants the cell plate appears andforms a barrier between the two daughter cells. The cell plate then forms into acell membrane, then the cell wall develops. (See Figure 4) Tissues and Organs Inmulticellular organisms, cells are organized in specialized groups, known astissues. A tissue is a group of similar cells that preform similar functions.

    Different tissues form many different tasks. For example, a kind of tissue ismade up of cells that produce digestive enzymes in the pancreas, and the cellsin an eye respond to light. Most multicellular organisms have four main types oftissues: muscle, epithelial, nerve, and connective. Some tasks in the body aretoo complicated to be preformed by only one type of tissue. So, organs preformthese duties. An organ is a group of tissues that work together to preform aspecific function.

    Many types of tissues may be used to form one organ. Forexample, a muscle in an organism is classified as an organ because not onlymuscle tissue makes up the muscle. There is nerve tissue, connective tissue, aswell as a special tissue that connects the muscle with certain parts of thebody. All the tissues in an organ work together to preform one common function.

    Sometimes not just one organ can complete one task, so an organ system isneeded. An organ system is a group of organs that work together to preform onefunction. There are many organ systems in our body. We have a muscular system,skeletal system, nervous system, and circulatory system.

    Multicellular OrganismsA multicellular organism is a living thing that is made up of more than onecell. These organisms can contain hundreds, thousands, even billions of cells ormore. We see multicellular organisms everyday: people, plants, and house pets. To describe a multicellular organism, we have to put them into levels oforganization. The levels of organization in multicellular organisms includecells, tissues, organs, and organ systems.

    The first level is cells, the secondis tissues, next is the organs, and finally the fourth level is the organsystem. Multicellular organisms start off with one basic unit, the atom, andbuild up to make bigger things. Atoms combine to form compounds which then formorganelles. Organelles then come together to make a cell. Cells then formtissues, which could then make organs. After organs are formed, then organs canbe in an organ system.

    Eagle The eagle is sometimes referred to as the”king of flight” because of the power it shows while in flight. Theeagle has been a symbol or strength and courage since ancient times. In 1782,Congress chose the American bald eagle to be the symbol of our nation. Thenational seal was the bird with its wings spread outward. It holds an olivebranch in one claw and arrows in the other.

    The eagle appears in many placestoday in the United States. Only two species of eagles are found in NorthAmerica today: the American bald eagle, and the golden eagle. The bald eagle ismore common than the golden eagle. This extraordinary bird has white tailfeathers and white plumes on its head and neck.

    The bald eagle lives in openareas, or forests, near water. The bald eagle is usually 35-40 inches in length,and have a wingspan of 7. 5 feet. The female bald eagle is more ferocious thanthe male, and is a couple inches larger. A bald eagle migrates only if the waterit feeds in freezes in the winter months. It returns every year to the same nestand the same mate.

    The nests are built in trees or on cliffs, and sometimes onthe ground. The eagle adds to it every year, making it bigger and bigger as timegoes on. The nests can weigh up to one thousand pounds. The nests are made fromsticks, weeds, and dirt.

    Bald eagles eat carrion, waterfowl, and especiallyfish. The golden eagle was more common than the bald eagle when settlers firstcame here, but this is not the case today. It’s found in the western portion ofNorth America, from Alaska, south to Mexico. The golden eagle is about the samesize as a bald eagle. It’s feathers are much darker than that of its famouscounterpart.

    There are feathers on the head and the neck of the bird that shinelike gold when they’re in the sun. The toes and claws of the golden eagle arefeathered, where as the bald eagle has no feathers on its legs. With theirclaws, golden eagles eat squirrels, prairie dogs, and rabbits. The golden eagleis very brave and can attack large animals such as deer, but can’t carry themaway.

    They build nests in trees and rocky cliffs with sticks. The golden eaglehas been known to defend its nest up to 75 square miles. As you can see, the twotypes of eagles in North America are similar and different in many ways. Both ofthe eagles are very powerful birds. One thing is for sure, the eagle is a verybeautiful bird that is extremely interesting.

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