DNA and Genetics (Winston) Quizgecko PDF
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Summary
These notes cover various biological topics, including DNA, genetics, and evolution. The content delves into aspects like the structure of DNA and the processes of DNA replication and the life cycle of stars, as well as the formation and evolution of the universe.
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DNA and Genetics (Winston) 2 DNA and the molecule (not in test)...
DNA and Genetics (Winston) 2 DNA and the molecule (not in test) 2 Making new cells 3 Characteristics and inheritance 7 Gene technology 10 Geological Time (Winston) 12 Fossils 12 Dating techniques 16 Geological time scale 18 Natural Selection and Evolution 20 Changes over Generations (Neel) 20 Natural selection 21 Species and evolution 22 Human evolution 24 Motion and Energy (Winston) 25 The Universe (Aarush) 26 Stars 26 Colour and magnitude 29 Cosmology 32 DNA and Genetics (Winston) DNA and the molecule (not in test) Deoxyribonucleic acid (DNA)determines the characteristicsof living things, such as humans DNA ismade up of smaller moleculescallednucleotides.Nucleotide molecules arecomposed of three parts, which are ○ Phosphate group ○ Deoxyribose sugar ○ One of 4 nitrogen-rich bases These are adenine (A), thymine (T), guanine (G) and cytosine (C) Theycan only pair up in one way, which is known as complementary base pairing These pairs areA-T(adenine and thymine) andG-C(guanine and cytosine) Nucleotides are organised in a way thatshapes DNAas a double helix. This shape issimilar to atwisted, rope ladder ○ The sides are ‘uprights’, composed ofalternatingphosphate and sugar groups ○ The bases pair up to form ‘rungs’ andconnect withthe sugar groups ○ Chromosomesare long, thin, threadlike structuresand aremade up of DNA and protein ○ They arefound in the nuclei of all cellsin the humanbody with a nucleus ○ Each cell in the human bodycarries 46 chromosomes,arranged as 23 pairs Exceptions are red blood cells and gametes(spermand egg cells, which only carry 23 chromosomes, one of each pair) Genesaresections of the DNA, whichvary in length and the order of basesalong the DNA strand ○ Each chromosome can have over 1000 genes Structural (eg. keratin, found in human skin, hair and nails) Enzymes (eg. amylase, which helps to digest starch) Regulatory (eg. growth hormones, stimulate growth and cell reproduction) Making new cells DNA replicationoccurs when strands of thedoublehelix separate, exposing the bases ○ In a nucleus, there areindividual nucleotidesthataren’t part of a DNA chain ○ These individualnucleotidesthenpair up with theexposed bases according to the rules of complementary base pairing ○ Afterwards,2 identical DNA strands are formed ○ ○ Chromosomes after replicationbecome adouble structuremade up of 2 chromatids joined together Chromatids are each a double helix of DNA Interphaseis the time in whichcell growth and DNAreplicationoccur, preparing for cell division Two types of cell division are mitosis and meiosis ○ Mitosisinvolves thegrowth and repair of the body It produces 2 daughter cells that are identical to the parent cell ○ Meiosisproduces gametes(eggs and sperm) They have half the number of chromosomes as the parent cell Mitosis begins with prophasewhen the DNA coils upand separate chromosomes become visible ○ Metaphaseis when the membrane surrounding the nucleusthen breaks away, andchromosomes line up across the equator (middle) Anetwork of fibres appears, extending from the polesof the cell and to each chromosome ○ Anaphaseis whenchromatids then separateto become independent chromosomes and arepulled to oppositepoles ○ Telophaseis when thenuclear membrane encloses the chromosomesat each pole, and the chromosomes thenuncoil ○ Cytokinesisthenseparates the cytoplasmand is thelast step of mitosis ○ Your body cells have46 chromosomes, half of whichare from your father and the other half from your mother ○ The number of chromosomes in your body cells is known as the diploid number of 2N, which means 2 sets Gametes are sex cellsand are the: ○ Eggs produced in the ovaries of females ○ Sperm produced in the testes of males ○ They havehalf the diploid numberso when you receiveeach from your parents, the diploid number is kept constant ○ Azygote is a diploid cellresultingfrom a fertilisedegg cell Of the 46 chromosomes in your cells,2 are sex chromosomesand determine whether you are male or female ○ Femaleshave a pair of X chromosomes(XX) ○ Maleshave one X and Y chromosome(XY) Theother 44 chromosomesare known asautosomes ○ Autosomes aregrouped into 22 pairs, known ashomologous chromosomes ○ Properties of Homologous chromosomesinclude: Same length Have the centromere (the point where 2 chromosomes join) in the same place Have genes for certain characteristics in the same location One chromosome from each homologous pair ends up in each gamete Thenumber of chromosomes in gametesis known as thehaploid number or N Female sex chromosomes are a homologous pair ○ Male sex chromosomes are not but still act as a pair in meiosis Meiosisis the process of cell division and isbasicallymitosis but done twice and begun with homologous pairs ○ Thestages of meiosis are numberedto signify whetherthey're in the first or second stages of division Eg. Prophase I(in the first stage of division) ○ WhenmetaphaseIoccurs in meiosis, rather than liningup individually,chromosomes line up in their homologouspairs ○ Crossing overis when homologous pairstransfer geneticinformation during prophaseI, allowing differences in offspring Asexual reproductionoccurs when plants or animals reproduce without the union of gametes Characteristics and inheritance Genetics: Study of inherited characteristics, calledtraits Allelesrefer to variations in homologous pairs ○ Eg. Homologous pair containing flower colour, being red and white Pure breedingoccurs when all individuals carry thesame genetic information When cross-breeding, thedominant alleleis the onewhose traits are outwardly expressed Therecessive alleleis the one whose traits remainhidden ○ Eg. When cross-breeding red and white flowering pea plants, the next generation of plants are red This shows the red allele is the dominant allele, and the white allele is recessive However, therecessive allele is still passed on Thedominant alleleis expressed with acapital letter,while therecessive alleleis represented with alowercase letter ○ The combination of 2 dominant or 1 dominant and 1 recessive allele will produce a generation with the traits of the dominant allele ○ The combination of 2 recessive alleles will produce a generation displaying characteristics of the recessive allele When an individual has2 of the same alleles, theyarehomozygous, the individual being described as a homozygote When the individual has2 different alleles, theyareheterozygous, described as heterozygotes Punnett squarescan be used to display the possibletypes of offspring from a cross of alleles, showing their probability as well ○ A heterozygote will produce gametes of 2 types, half carrying the recessive allele and half carrying the dominant allele (total 4) ○ Phenotypeis the observablephysical characteristicsof the genotype ○ Eg. Height, hair colour, eye colour Genotypeis thegenetic informationof a phenotype ○ Eg. Dominant and recessive genes, Tt An individual’s sexis determined by whether a male’ssperm carries an X or a Y chromosome when fertilising a female’s eggs Sex-linked genesare traits found on sex chromosomes ○ Most sex-linked genes are carried on the X chromosome, such as color blindness ○ Eg.Females who are heterozygous for colour blindnessare carriers for colour blindness and are represented as XNXn The Y chromosome does not carry the colour blindness gene, so the possible genotypes of a male offspring are XNY and XnY , The recessive allele is expressed in XnY and the dominant allele is expressed in XNY ○ Chromosomal abnormalityis when during meiosis, chromatidsfail to split, giving the offspring born anextra chromosome or partof a chromosome ○ Eg. Down syndrome, Klinefelter syndrome Mutationsoccur when a mistake occurs during DNA replication ○ It mayoccur spontaneously or as the result of damageto the DNAstrand, such as from radiation or certain chemicalssuch as nicotine ○ The mutation may be passed on to the next generation if it occurs in the eggs or sperm Types of mutationsare as follows: Silent mutations: Changes to genetic code thatdonot affect an individual Missense mutations: A mutation thatchanges the proteinproduced, potentially causing diseases such as sickle cell anemia Nonsense mutations: Causes cells tostop reading genetic information to the end, resulting in the incomplete production ofprotein that doesn’t function Frameshift mutations: Caused by theinsertion or deletionof a single base, results in the rest of thegenetic code beingjumbledand unable to be read to produce protein Gene technology Gene modificationin plants occurs whennew genesare inserted into their genetic code, creating a new strain of plantswhen these new genes are copied to all daughter cells during mitosis ○ This gives plants new, desirable traits, such as resistance to insects ○ Eg. GM Canola is resistant to herbicides ○ GM Golden rice has more Vitamin A than regular rice Gene splicingis the process of cutting open plasmidswith enzymes, and then inserting desirable genes ○ Plasmids are separate rings of DNA in bacteria ○ Recombinant DNA technologyis the combination of DNAfrom different genes ○ Eg. Splicing human genes to manufacture insulin Agenomeis the genetic information carried by a haploidset of gametes The Human Genome Project was an international project with the objectives of: ○ Identifying all 20,000-25,000 genes in the human genomes ○ Determining the sequence of the 3 billion base pairs that make up human chromosomes When the function of a gene is known, scientists can test for the gene ○ Gene testingallows individuals to make lifestylechoices that help themreduce their chances of developing diseases ○ Gene testing detects a particular problem gene, butcannot detect its severity, should it affect an individual ○ Genetic disordersin fetuses which are tested forusing gene testing include: Down syndrome Turner syndrome Fragile X syndrome Other uses of genetic testing include: ○ Identifying suspects in criminal investigations ○ Identifying the biological parents of children ○ Analysis of DNA to check for compatibility when donating bone marrow or organs Drawbacks of genetic testinginclude the knowledgeof potential diseases affecting a person’s ability to get life insurance coverage, or whether other family members are to get tested (kinda stupid ngl) Gene therapyis when the defective gene is replacedwith a functional gene ○ In 2008, a gene was discovered that can be turned off, reversing the growth of blood vessels in tumours, potentially treating cancer Geological Time (Winston) Fossils Fossils: Thepreserved evidence of organismsthatonce existed on Earth, in rocks and soil ○ Fossils may be the whole body of an organism, parts of it or traces of its activity ○ E.g. Burrows, tracks, faeces Palaeontology: The study of past life, particularlyfossils Palaeontologists: Scientists who reconstruct pastenvironments using fossils and geology Thefossil recordis alist of all the species foundas fossils, including their location and relative age ○ It acts as a timeline of Earth’s development since its formation 4.5 billion years ago Not all organisms are equally represented in the fossil record, asbeing fossilised requires very specific conditions.Theseconditions include: ○ Avoiding being eaten by scavengers ○ Decaying very slowly ○ Soft parts decaying faster than hard parts For an organism’s remainsto be fossilised, itmustbequickly covered by sediments ○ Thistypically takes placeat the bottom of awaterbody ○ Sediments in water bodies will collect at the bottom, covering up the remains and gradually build up ○ As sediments build up, they will naturally cement and dry, forming sedimentary rock ○ Fossils are only found in sedimentary rock, as the pressure and heat from igneous or metamorphic rocks would destroy the fossils Another process by which fossils can form on landis windblown sediments covering the remains, eventually cementing and forming sedimentary rock ○ Erosion and movements of soil may expose rock layers, revealing fossils Themain classifications of fossilsareoriginal,replacement, carbon film and indirect fossils Original fossilsform when part of anorganism ispreserved, mostly retaining its chemical compositionfrom when it wasliving ○ These aremostly sea creatures that had shells and vertebrates ○ E.g. Complete skeleton, bones, teeth, shells ○ This is becausebone is composed of minerals(eg.calcium carbonate) that isresistant to decayand difficultfor scavengers to eat ○ After death, the proteins in bones that allow their flexibility die, leaving the minerals as being brittle bones Replacement fossilsoccur when a part of theorganism’sremains is chemically changedinto another mineral ○ This process is very lengthy, with most replacement fossils dating over 60 million years ago ○ For instance, when the calcium carbonate found in bones and shells isreplaced by the mineral silica,also called silicondioxide ○ When wood is being replaced, it is referred to as being petrified Carbon film fossilsoccur when theremains partiallydecay, leaving a thin film of carbon, which takes on the shape andfiner details of the organism ○ Common carbon film fossilsincludeplants, formingcoal, though leaving no identifiable traces of the plants as part of the coal Indirect fossilsare the preserved remains ofimprintsof the body, tracks and dung(known as coprolites) ○ A mould is typically animprint of the exterior ofan organism left in rock, known as anexterior mould ○ It iswithout the original body, or anegative image ○ E.g. Arthropods (crabs, lobsters, prawns, which have shells) ○ Thiscommonly occurs in the ocean, as calcium carbonate(found in bones and shells) is dissolved faster and at higher pressures ○ When themould forms from the inside of the organismand the original body decays or breaks, it’s known as aninternalmould ○ E.g. Inside of a sea snail’s shell ○ A castis when anorganism in rock decomposes and is filledwith soil, which turns to rock, ○ This forms a3-dimensional model and a positive image Environments in which soft part can be preservedincludepermafrost, amber, tar, peat and dry air Permafrostis land that is permanently frozen andprevents fungi and bacteria from decaying matter, due to not being ableto grow in freezing temperatures Amberrefers tosolid plant sap or gum, which catchessmall vertebrates and insects,perfectly entombing and preserving themwhen hardened Taroccurs whenoil naturally seeps out of the ground,catching and preserving organisms that get stuck in sticky tar pits Peatrefers to thepartly decomposed remains of plants,such as moss, and is commonly found in swampy areas and bogs ○ The layers of peat can be very deep,oxygen and bacteriabeing often absent in the lowest layers, preserving soft tissueand dissolving hard minerals in bones, making them soft ○ E.g. Tollund man, found in Europe Dry airdehydrates soft tissue,mummifying it andforming a mould in sediments ○ Bacteria and fungi require moisture to survive, so dry air prevents the growth of bacteria and fungi ○ This can occur inhot deserts, as well ascold, frozenplaces, where there is ice but no liquid water Thefossil record is incomplete, assome organismsare more likely to be fossilised, such as marine organisms with skeletonsor shells ○ Marine organisms with soft bodies, such as jellyfish and worms, are unlikely to form fossils, as they have delicate bodies that decay quickly and are easily damaged ○ Land organisms are also unlikely to fossilise, unless they die near water bodies, or where sediments would blow over them Dating techniques Relative datingis a method of comparing the agesof fossils and rocks to see which is older,relying on 2 basic facts ○ Sedimentary rock forms in layers (calledstrata) Stratumrefers to a single layer of sedimentary rock ○ Fossils are the same age as the rocks in which they are found When sediments settle, newer sediment always settles on top and older layers are found at lower strata ○ However, sometimesthe lowest stratum is not alwaysthe oldest, due to thestrata folding over each otherfrom themovements of the Earth’s crust Most species have existed on Earth for a relatively short time, meaning each fossil species is only found in a narrow band of strata, in any one location ○ This meansall rocks containing a particular speciesshould be the same age, even if they’re of different kinds of rock ○ This is an example of relative dating and allows palaeontologists to determine how old one fossil is relative to another, though not its actual age Index fossilsare fossils that can beused to comparethe ages of strata in different locations ○ For a species to be an index fossil, it must fulfilthe following conditions: ○ Found fairly widespread ○ Lived in a fairly narrow time period ○ Abundant and easily identifiable Stratigraphyrefers to theuse of index fossils tocompare the ages of rock layersin different locations ○ ○ 2reliable index fossilsaretrilobites and ammonites Another method of relative dating isfluorine dating,whichcompares the amounts of fluorine in different bones, found in thesame rock ○ Bones slowly absorb fluorine from the water in rocks ○ A famous instance of fluorine dating is when it was used to prove the Piltdown Man skull was a forgery in 1953 Absolute dating methodsare methods thatgive theactual age of rocks and fossils, such as radioactive dating and inspectingtree rings Radioactive datinguses thenatural rate of decay of radioactive isotopes (atoms with different numbers of protons) to estimate a fossil’s age ○ Radioactive elements decay at a known rate, releasing radiation ○ Half-liferefers to thetime it takes for half ofa radioactive sample to decay ○ Half-life is determined from a graph called a decay curve E.g. Carbon-14’s half-life: 5730 years E.g. Potassium-40’s half-life: 1251 million years Tree ring datinginvolves counting the growth ringsin the woody trunks of trees ○ Trees grow by adding layers on the outside each year ○ This methodcan only be used by comparing wood withtrees from the same climatic region, as climate affectsgrowth Geological time scale Geological time scalerefers to thesequence of allpast life and geologyfound throughout the world, tracking the historyof life on Earth ○ It was constructed through relative and absolute dating Initially, index fossils were used to construct a continuous sequence of rock strata into the past, using relative dating ○ Theparticular period covered by each set of indexfossils was referred to as ageological period, and each periodwas given a name Later, absolute dating allowed palaeontologists to find the exact ages of index fossils and add dates to the geological periods ○ Geological periods were further organised into setsbased on major events, such as dramatic changes in climates ○ Thesesetswere calledeons, eras and periods The geological time scale suggests thatthere wasa period of Earth’s history where no life existed, due to a lackof fossils ○ This may have been due to the difficulty of fossilising tiny, delicate creatures, but the previous prospect is more likely ○ Regardless, palaeontologists concludedthe very firstlife forms were single-celled organisms, such as bacteria The oldest fossils suggest life began in the ocean ○ The most ancient fossils recorded were of a type of bacteria called cyanobacteria, forming structures called stromatolites Vertebrates are animals with bonny, inner skeletons ○ The earliest known vertebrate ancestors are primitive fish, dating around 525 million years ago in the Cambrian era Land plants first appeared about 416 million years ago in the fossil record, in the Silurian period ○ This is significant, as it allowed life to move from water to land ○ Animals such as insects and vertebrates soon followed the first land plants, as indicated by the fossil record The first land vertebrates in the fossil record were amphibians and were the first to be called tetrapods (meaning four having legs) ○ Amphibians were followed by reptiles, and then dinosaurs appeared ○ Reptiles were the dominant animal group from 250-65 million years ago, during the Triassic, Jurassic and Cretaceous periods of the Mesozoic era Bird-like animals first appeared about 200 million years ago, in the Jurassic period ○ True birds date from about 110 million years ago ○ Birds share many features with a small group of dinosaurs called theropods, which most scientists believe birds evolved from The earliest mammal-like fossils date 190 million years ago, from the Triassic period Humans belong to an order of mammals, called primates, including monkeys, apes and gibbons ○ The earliest members of the human sub-tribe date around 4 million years ago, in Africa ○ The oldest known fossils of our species (Homo sapiens) date from over 130,000 years ago in Africa ○ ○ Really not that important so I'm not highlighting much Natural Selection and Evolution Changes over Generations (Neel) Species can change over many generations, this creates variety. The Devonian period was 419-358 million years ago. The apparent change in a species over time is called evolution. ○ Evolutionis defined as thegenetic change in thecharacteristicsof a species over many generations, resulting in a new species. ○ Agenerationis the time between the birth of an individualand the time the individual produces their offspring Palaeontologists can trace a line through a species family tree and find out how it originated. Some groups seem very similar when organisms are classified based on their structure (e.g. cats and lions). Species with similar structures share many identical genesor genes with similar effects. ○ Genes control the structure and functions of an organism. ○ Organisms that share genes must be related. ○ Due to Hox genes present in all life, scientists believe that all life was at one point related. Characteristics that have thesame basic structuresare called homologous characteristics ○ Homologous structuresdon't always share the samefunctions ○ Just because some structures look similar they might not be homologous as they can have different genes. This is called analogous structures Artificial selection or selective breedingis thehuman intervention of natural breeding, such as for the colour of an animal. Artificial selection only happens across generations. ○ One way to do artificial selection is bycross-breeding,by combining one parent with another parent that both have desirable traits. ○ Another way is inbreeding/line breeding. Natural selection Natural selection was a theory first proposed by Charles Darwin Natural selectionis a process in whichenvironmentalfactors influence which mutation survivesand produces more offspringthan others ○ Environmental factors that act on populations are calledselective agents ○ Biotic selective agentsrefer toother living things,such as competitors and predators ○ Abiotic selective agentsrefer tophysical factors,such as temperature, water and available nutrients Animals that are less suited to surviving their environment are referred to as beingpoorly adapted or less fit Most selective agents act by killing but not all ○ Female birds tend to favour brighter, male birds as their mates, resulting in more offspring with those characteristics being produced ○ Darwin called this change of characteristics in aspecies sexual adaptation ○ This demonstrates how natural selection causes populations to become better suited to their environment after a few generations For natural selection to occur,variationin the populationsmust occur ○ Variation is caused by a difference in genes, which are inherited and passed down, producing different characteristics ○ These variations in characteristics include colour, Resistanceis an animal's ability to survive its environment Bacteria can become resistant to antibiotics. (there were a lot of examples in this exercise including how horses evolved, how mice and butterflies evolved and were tested and how insects become resistant to pesticides) (why even mention it if u not even gonna include it properly!?) Species and evolution All life is related To determine if two animals were in the same species,they would be tested to see if theycould produce offspringtogether(this method was proven incorrect.) ○ Today we test their genes ○ Proteins are made by genes, so identical proteins = identical or at least very similar genes Speciationis the process by which aspecies splitsinto two or more different species, it is the reason for any new species to form Biodiversityis the number and range of species Speciation occurs due tovariation, isolation andselection ○ There has to bevariationin the population for naturalselection. ○ Isolationmust occur between the splitting species so they can't breed and share particular genes This may occur as the result ofgeographical or climatic barriers ○ Once isolated by barriers,natural selectionaffectsthe genotype, causing groups tono longer be able to interbreed Possible changes as a result include: Courtship behaviour Breeding seasons Sterility Chemical barriers Natural selection has been proven through fossils,as fossils get more and more complex the more recent they are ○ Additionally, the fossil record shows an increasing number of species Fossils have showntransformational formswhen onespecies is in the process of changing to become another ○ Transformation forms display characteristics of 2 different groups, making them hard to classify Comparative anatomycompares the structures of bothliving species and fossils All living cells share the same basic DNA structure and genetic code, supporting the theory of natural evolution ○ Organisms with similar anatomy show more genes in common, such as humans and monkeys sharing 96% of their genes The more proteins (cytochrome c) in DNA arranged and apparent in similar ways, the more related a species is Thedistribution of speciesis a map of where allspecies occurred Rare or unique speciesare usuallyfound on smallislands, as the result of isolation During the development of embryos the Gem-2 gene produces different structures in different species. (which is weird). This supports the theory that reptiles evolved from fish and both reptiles and fish have this gene. Human evolution Fun fact homosapians means wise man (W) Humans have been around for 200 000 years and fossils indicate that other human-like species also existed. Humans are classified as class mammalia, order primates, family hominidae and genus homo. Primates have grasping hands, nails instead of claws and forward facing eyes. Humans are in a level of classification called sub tribe, because we walk upright Australopithecus is a group of 6 species that we believe are our ancestors. ○ The Australopithecus afarensis is likely to be the ancestor of the genus homo Our species is believed to originate from Africa and 60 000 years ago a subgroup left Africa and colonised the whole world by 15 000 years ago DNA and y chromosome analysis we can track migration and prove this theory. When the skulls of human families are compared we see that through evolution, the face becomes more vertical, the jaw shortens, a chin develops, forehead becomes flatter and brain space and size increases. Motion and Energy (Winston) Scalar Quantity:A quantity such as time or distancethathas size but not direction Vector quantity:A quantity such as displacement orvelocity, thathas size and direction Motion: Movement Distance: The total length travelled Displacement: A straight line from the starting to ending point Acceleration:Rate of change of velocity Instantaneous speed: The speed of an object at a particular time Terminal speed: The final velocity that an object falls with no further acceleration possible due to air resistance Action-Reaction: Action in response to action Speedis a scalar quantity, meaninghow fast it travelsin m/s ○ Speed= Distance/Time Velocityis a valar quantity, meaninghow fast andin what direction something travels in a straight line The formula for acceleration(m/s² or ms-²) :a=v-u/t ○ Acceleration= final velocity-initial velocity/time The formula for displacement(m):s= ut+½at² ○ Displacement= initial velocity x time + ½ acceleration x time² Newton’s first law:An object at rest tends to stayat rest, andan object in motion tends to stay in motionwith the same speedand in the same direction ○ That is unless acted upon by an unbalanced force ○ This tendency is calledinertia Newton's second law:An object will accelerate inthe direction of an unbalanced force action upon it ○ The size of this acceleration depends on the mass of an object and the size of the force action upon it ○ In other words,F=ma ○ Force= mass x acceleration ○ Net force refers to the combined force acting upon an object Newton’s third law:For every action, there is anequal and opposite reaction Joules (J)is theunit of measuring energy ○ 1KJ= 1000J, 1MJ= 1,000,000 J Potential energy:Energy that is stored or conservedin an object or substance ○ Formula:PE= mgh ○ Potential Energy = mass x gravitational acceleration (9.8/ms²) x height Kinetic energy:The energy of motion ○ Formula:KE= ½mv² ○ Kinetic Energy = ½ mass x velocity² Law of Conservation of Energy:Energy can neither be created nor destroyed, only converted from one form to another T he Universe (Aarush) Stars 1 Light Year (l.y.)= Distance that light travels in one year (9.5x1012). 1 Parsec = 3.26 lightyears. Parsecs arebased on phenomenaknown as aparallax. Parallaxcausesdifferent views of the same object.i.e. Imagine you’re looking at an object, and you shut one eye, open it, shut the other, and you get slightly different views of the same scene. That is parallax. Stellar parallaxis theshift in position betweendistant stars from Earth. Stellar parallax is often quite unnoticeable, the difference being less than one-thousandth of 1 degree. It is often used tocalculatedistance to the nearest stars. Gravityis theforce of attraction between any twoobjects in the universe. Gravitydepends onthe masses of the two objects.The masseshave to be largeforgravityto becomesignificant.Examplesinclude stars, or planets. Nuclear fusionis theprocess of atoms fusing together. Nuclear fusion is present in stars, fusing atoms of hydrogen into heliumat their centredue to gravity’s immense force. Nuclear fusionproduces enormous amounts of heat andlight→ causes stars to glow. Thestructure of a staris determined by thebalancebetween two opposing forces: ○ Theinwards force of gravity ○ Theoutward force from heat from nuclear fusioninthe star. This pressure is also calledradiation pressure. Life cycle of a star: Stellar Nebula → Protostar → Main Sequence Star → Red Giant → Supergiant → Supernova → Neutron Star → Black Hole. Gravityis alsoresponsibleforcreating starsfromhuge clouds of interstellar dust and gasknown asnebulae. Gasesinclude hydrogen, with small amounts of helium and heavier elements such as carbon and iron. Protostar→T he slow pull of gravitational forcescausing clouds of gas to gather into larger clumps.Material far away fromthe formation would be drawn in and clumped to form the planets. ○ Formation of our sun As the protostar (gas cloud) collapsed, it flattened out and started to spin faster and faster into a protoplanetary disk Protoplanetary disk→Speed creating energy for thegas cloud therefore being able to stay in orbit creating a disk. Accretion→T he remaining material clumping to eventually form planets. As theprotoplanetary disk becomes larger,gravitydoes nuclear fusionand theprotostar emits heat and light→ sun is born. Galaxies→T he grouping of ‘close’ stars by gravityto form gigantic structures. Our sun is part of the Milky Way. ○ Can contain from 107 → 1014 number of stars. Black hole→A region of spacetime so strong thatnothing – including light or electromagnetic radiation – can escape from it. Binary Star system→W hen two stars orbit a commoncentre of mass between them. Black holes can be indicated by: ○ A binary star system →X-ray signals detected fromthe other star while getting its material stripped awayfrom it. ○ Gravitational lensing→An observer can see two ofthe same star – due tolight being manipulated by the black hole– around a black hole. Supermassive black holes→Black holes with massesequivalent to millions or billions of stars the size of our sun. Colour and magnitude Magnitude→ Thebrightness of a star. ○ Brighter starsare givenlowermagnitudes ○ Dimmer starsare givenhighermagnitudes ○ Thebrightest starsare givennegativemagnitudes Apparent magnitude→How bright it will appeartoan observer on Earth. Apparent magnitude ismeasured on a logarithmic scale.1 unit changes the brightness of a star by a factor of ≈2.5.1:2.5 Two factorsthatdeterminea star'sapparent magnitude: ○ T he amount of light the star emits ○ Distance between the star and Earth → Greater the distance the dimmer the star. Absolute magnitude→T he measurement of how brighta star would appear if it was a distance of 10 parsecs from Earth. Thecolourof a star is due to itstemperature andthe elements it contains. Stars emit light at a range ofdifferent wavelengths. Your eyes collect the visible lightfrom stars and perform acomplex averagingprocessto perceive the stars as a particular colour. Scientists use filtersto accuratelymeasurethelightcoming from a star. Cooler stars appear red→ emitted asinfrared andvisible redparts of the spectrum. Hot stars appear blue→ emitvisible violet and UVparts of the spectrum. Spectrometre→ Adeviceused toanalyse starlightand convert light into a spectrum to reveal its component colours. ○ Helps determine elements in a star→ they emit certaincolours ○ Fraunhofer lines → when light interacts with atoms in the outer layers of the star. Spectral class→Indicates elements present, coloursand temperature in a star. ¾ of the material in a star is hydrogen. Plasma→Electrons that have too much energy to staybound to the protons. One of the four states of matter. During nuclear fusion,one proton is converted toa neutronand two tiny particlesare released: ○ Positron→Small, positively charged particle. ALSOan antimatter for an electron. Does not exist for long. ○ Neutrino→T iny, neutral particle. When apositroncollideswith anelectron, theydestroyeach otherandcreate high-energy gamma rays. These gamma rays make their way out from the core, andshine into the heat, light and UV radiationthat we get on Earth. Thenucleus formedfrom Nuclear Fusion is anisotopeof hydrogen known asdeuterium. H-R diagram→A graph relating temperature, brightnessand colour→ acts as the life-cycle of a star. Main sequence→A line on a H-R diagram that moststars fall on. Main sequence star→A star in which gravity and radiation pressure are in equilibrium. T he heavier a star, the hotter and brighter it will be. More mass → greater gravitational force. Larger starsburn upquicker. Red Giant→A star that expands and cools. ○ Gravitycollapsesthe starinwards,outer layersstarttofuse. ○ Outer pressure exceeds inward pressure, causing expansion. ○ Heat from fusion at the centreproducesradiationpressure, causingouter layerstoexpand and cool. When ared giantruns out of helium fuel, thestarcollapses → loses its outer layers → becomes a cloud of gas known as a planetary nebula. Aplanetary nebuladispersesto reveal thehot, densespherethat remains of the red giant, known as awhite dwarf. White dwarfsareextremely dense,but havelow brightnesses. Nuclear fusion stopsin awhite dwarf, fadingto becomeablack dwarf→a cold dark ball of inert matter. Supergiants→stars with masses 10-70 times greaterthan our Sun, sometimes 30,000+ times brighter than our sun. ○ Supergiants haveshort lifespans. ○ When its helium fusion begins, thestar slowly coolsdown →maintains its brightness. When theseatoms finish fusingand thefuel of a supergiantruns out, a supernova occurs. ○ When the core of a star stops producing energy,gravity absorbs all materialin the outer layers and itcollapses inwards at incredible speeds. ○ After reaching the core, a massive explosion(supernova) occurs. ○ Much of thestar’s massisblown into space, and many neutrons form heavy elements such as gold and silver. Neutron stars→Gravitational forces that allow electronsand protons to combine and form neutrons. Has an enormous density. ○ Happens when the amount of material left behind by a supernova isbetween 1.4 – 3 times the mass of ourSun. If thesupernova remnants are >3 times the mass ofour Sun, immense gravitational forces cause the star to shrink into a singularity/black hole. Cosmology Galaxies can take many shapes including: ○ Spiral-A rotating disc with spiral ‘arms’ that curveout from a dense, central region. ○ Barred Spiral- A spiral galaxy, but a bar for a centremade up ofstars. ○ Elliptical- A galaxy with an even, elliptical shape. ○ Irregular- No particular shape. TheMilky Wayis estimated to containbetween 200-400billion stars and be about100,000 light years across. TheCanis Major dwarf galaxyis theclosest galaxyto the Milky Way. Distances to other galaxies can be measured using aCepheid variable. Cepheid Variable→A star picked to measure its variationin brightness over time used to measure distances. Measuring period of variation of Cepheid → Absolute magnitude can be determined. Relating absolute : apparent magnitude, the distance to the star and the galaxy that contains it can be calculated. Steady State Theory→T he theory that the universeis infinite in extent andhas always existed in roughly the same formasobserved today. Expressed byEnglish astrophysicist Sir Fred Hoyle(1915-2001). Big Bang Theory→T he theory that the universe wasall in one place, and all matter was squished into an infinitely small point (a singularity) and then exploded. Doppler Effect→Waves produced by a moving objectare either lengthened or shortened due to the motion of a source.E.g. Siren of an ambulance passing by, mosquito passing your ear, aircraft passing overhead. Blue shift→Light from stars moving towards us willbe compressed, making light/wavesbluerthan itshould Red-shift→W hen light from stars moves away fromus, making the light appear redder. Cosmic Microwave Background Radiation→T he afterglowof the Big Bang. T he Big bangwasestimatedto haveoccurredjust under14 billion years ago.
