Science Exam Notes PDF

**Biology** **Genes** - A gene is the basic physical and functional unit of heredity. - A gene is a segment of DNA, arranged along the chromosome, that carries the instructions for making a protein and therefore determines a trait. - However, there are some genes that do not code f...

**Biology** **Genes** - A gene is the basic physical and functional unit of heredity. - A gene is a segment of DNA, arranged along the chromosome, that carries the instructions for making a protein and therefore determines a trait. - However, there are some genes that do not code for proteins. - The difference between one gene and the next is the: - *Order of bases along the DNA strand* - *Number of bases in that section of DNA* - The order of the bases along the DNA strand is the genetic code. Each gene codes for a specific protein. These proteins create structures and perform the actions needed for your cells to survive, grow and function. - A gene occupies a specific location on a chromosome which is called the gene locus or gene loci **Function of a gene product** - Proteins have 2 main functions: - **Structural**: proteins help make up all structures in living things - *Keratin -- nails, hair, skin, horns, scales, feathers* - *Actin & Myosin -- muscle proteins* - *Collagen -- bones, teeth, tendons, ligaments* - **Functional**: other proteins help us keep our bodies functioning properly and to digest our food - *Enzymes -- lower the energy of activation to digest our food and to assist in cellular metabolism* - *Regulatory -- growth hormone and insulin* **Inheritance** - Inheritance is the process by which genetic information is passed on from parent to child. - The simplest form of inheritance was uncovered from the work of an Austrian monk called Gregor Mendel in 1865. - From year of experiments using the common pea plant, Gregor Mendel was able to describe the way in which genetic characteristics are passed down from generation to generation. **Principles of inheritance** 1. *The inheritance of each trait is determined by 'factors' (now known as genes) that are passed onto descendants* 2. *Individuals inherit one 'factor' from each parent for each trait* 3. *A trait may not show up in an individual but can still be passed onto the next generation* - Humans have 46 chromosomes, 23 pairs 22 pairs of chromosomes are autosomes (not sex cells) - Chromosome number 23 is the sex chromosome - For a female it is XX and for a male it is XY. - X chromosome is larger (and carries more genes) than the Y chromosome. - Number 23 (the sex chromosome) contain genes with information for sexual characteristics *[BUT]* it also contains information for non-sexual characteristics **Punnet squares** - A Punnett square is a graphical representation of all the possible genotypes of an offspring arising from a particular genetic cross or breeding event. - A Punnett square represents the probability of specific genotypes occurring in the offspring. You cannot assume that the offspring will appear in exactly this order and in this exact ratio. **Chromosomes** - A karyotype is a pictorial representation of an individual's complete - Homologous chromosomes are paired and organized from largest - They are also allocated a number - Of the 46 chromosomes in the human body's somatic cells, there - Matching occurs based on their relative size, position of centromere and stained banding patterns (gene location). These are called AUTOSOMES. - Two chromosomes specify sex *(chromosome number 23)* - XX for female and XY for male. - The rest are arranged in pairs, numbered 1 through 22, from largest to smallest. - This arrangement helps scientists quickly identify chromosomal alterations that may result in a genetic disorder. **Cell division** - Cells need to divide for several reasons. - To **divide**, **cells** must **replicate** their **DNA.** - The **purpose** of **DNA replication** is to **produce two identical copies** of the **DNA molecule.** - DNA is packaged tightly into chromosomes for storage in the cell nucleus. - Each **cell contains pairs** of **chromosomes** -- **one inherited from each parent.** - **Homologous chromosomes** are a **pair of matching chromosomes** (one inherited from each parent) that are **similar in length, gene position and centromere location.** - **Homologous chromosomes carry** the **same sequence of genes** **but not necessarily** the **same alleles** of those genes. - An allele is an alternate form of a gene - These inherited alleles result in the differences we see in organisms of the same species **Mitosis** - **Mitosis** is the **division of the nucleus** of the cell during cell division - DNA replication occurs in a stage of mitosis. - Mitosis **forms [diploid (2n)] daughter cells.** - Each daughter cells contains an **exact copy of the chromosomes from the parent cell.** **Meiosis** - **Meiosis** is another type of cell division that uses DNA replication - There are **two stages cell division** in meiosis - **Sexually reproducing organisms** utilise meiosis to **produce** **cells** with **half** the **number chromosomes as** the **original** cell - These are know as **sex cells or gametes** - Meiosis is where a diploid cell gives rise to **[haploid (n)]** cells - gametes. - During **sexual reproduction** two haploid cells, one from each parent, **meet**. - **Fertilisation** is where two **haploid gametes fuse **together to **form** a **diploid zygote**. - This zygote then develops into an organism through many rounds of mitosis. - Meiosis occurs in both paternal (male) and maternal (female) cells to form haploid gametes - The union of the gametes or fertilisation results in offspring containing chromosomes and genes - half from each parent **Physics** **Motion** - Motion occurs when an object changes its position relative to other objects - This can be modelled by using words, diagrams, graphs, numbers and equations **Scaler** **Vector** ---------------------------------------------------------------------- ------------ A number (size/magnitude) Are quantities that can be completely described by their size. Examples: *mass, temperature, time, distance, speed, energy, volume* **Distance** **Displacement** ------------------------------------------------------------ -------------------------------------------------------------------------------------------------------------------------- A measure of length It is the object's total change in position from a starting point to a finishing point, regardless the of the path taken An object travels is the total length of the path it takes It is a straight line between 2 points in a given direction How much ground an object has covered It is a vector quantity It is a scalar quantity Symbol - **S** Symbol -- **S** Unit -- **m** (metres), **km** (kilometres) Unit -- **m** (metres), **km** (kilometres) **Speed** **Velocity** ---------------------------------------------------- ---------------------------------------------------------------- Is the rate at which distance changes over time Refers to the rate at which an object changes its position How fast an object is moving Is how fast something is moving and the direction it is moving An object has no movement at all, has a zero speed It is a vector quantity It's a scaler quanitiy Symbol - **V** Symbol - **V** Units -- **m/s, km/h** Unit -- **m/s , km/h** **Speed Velocity**  **Instantaneous speed** Speed given at any instant time **Average speed** It's the overall measurement of how fast something something is moving **Acceleration** - It is a vector quantity - How an object's velocity is changing -- how quickly the speed changes - The rate at which an object changes its velocity over time - *[Acceleration]* -- speeding up; positive - *[Deceleration]* -- to lose (decrease) velocity at a particular rate; slowing down; negative - Symbol -- ***a*** - Units -- m/s^2^ *(ms^-2^) **[or]*** km/hr^2^ *(kmhr^-2^)* **Graphing motion** Graphs are mathematical models. They are a very useful means of describing relationships. Graphs are especially useful when\ describing the motion of objects. **Graphing motion**    When the horizontal line is actually on the time axis this indicates that the speed is zero. In other words, the object has stopped/stationary/not moving. Area under graph = 6 + 8 = 14 m Thus, the object has travelled a distance of 14 m **Newtons laws (weight/mass, vector diagrams)** **Forces** A force is a 'push' or 'pull' upon an object resulting from the object's interaction with each other. Whenever there is an interaction between two objects, there is a force upon each of the objects. When the interaction stops, the two objects no longer experience the force. Forces ONLY exist as a result of an interaction **Newtons 1^st^ law** object at rest will remain at rest unless it is acted upon by an outside unbalanced force A object that is in motion will remain in motion at the same speed and in the same direction unless it is acted upon by an outside unbalanced force. ***Inertia:*** the tendency of an object to resist changes in its motion Newton\'s first law is also known as the law on **Inertia.** The inertia that a body has depends on its mass. Inertia is the property of objects that makes them resist changes in their motion. e.g. it takes a much larger force to change the motion of a heavy train than it does to change the motion of a small car. **Newtons 2^nd^ law** The mass of an object affects the way that it moves when acted upon by one or more forces.   So the acceleration of an object depends on the size of the force acting on the object and inversely on the mass of the object. Therefore the more force you apply to the object the more rapidly it accelerates. Also the greater the mass of the object, the harder it is for it to pick up speed or accelerate. Whenever you apply a force to an object and the object moves in the direction of the force, **work** is done. The amount of work done on an object by a constant force is the product of the size of the force and the distance the object moves in the direction of the force.  A= [\$\\frac{F}{M}\$]{.math.inline} **F**= The total force (N) **M**= The mass of the object **A**= acceleration **Mass** **Weight** ------------------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------------------------------------------- Mass is the amount of matter contained in a body. Weight is the force by which the earth attracts a body toward its centre Mass of the body is the constant quantity and does not change with the change of position or location Weight of the body is the variable quantity and changes with the change in position and location due to the acceleration of the gravity acting on it. **Newton\'s third law** Newton\'s third law states that for every action there is an equal an opposite reaction. All forces work in pairs. When an object applies a force to a second object, the second object applies an equal and opposite force. e.g. If you push on a wall (force) (an action) and the wall applies an equal but opposite force to the one you are applying (a reaction**).** **Chemistry** **ATOMS AND ELEMENTS** **·     ** Atoms are the particles that make up all the substances in the universe; they are the building blocks of all matter. ·      The nucleus is the solid centre of an atom. Most of the mass of an atom is concentrated in the nucleus. ·      A proton is a positively charged particle in the nucleus of an atom. ·      A neutron is a neutral (no charge) charged particle in the nucleus of an atom. ·      An electron is a negatively charged particle found around the nucleus of an atom -- they spin around the nucleus in regions called electron shells. ·      A substance is an element if it consists only of atoms of the same name.   - The mass number describes the total number of protons and neutrons in an atom. - The number of protons in a nucleus is called the atomic number of an atom. - Atoms containing the same number of protons, but different numbers of neutrons are called isotopes of an element. ** ** **PERIOD TABLE** - The periodic table of the chemical elements is a tabular method of displaying the chemical elements**.** - It was devised by the Russian chemist Dmitri Mendeleev in 1869. - The elements are arranged in increasing order of atomic number (Z) as you go left to right across the table. - Remember that each element has its unique atomic number. - The elements in the periodic table are divided into three major groups -- metals, non-metals and metalloids - There are 92 naturally occurring elements. - Elements after uranium are made artificially by bombarding other elements with particles. - The vertical rows are called groups (numbered 1 to 18 or the older way in Roman numerals I to VIII)-- the elements have similar properties and have the same number of electrons in their outer shell - The outer shell electrons are called valence electrons - The horizontal rows are called periods (numbered 1 to 7) -- the elements have the same number of shells occupied by their electrons **VALENCE SHELLS AND IONS** **       ** The electron configuration of atoms determines how stable they are.        This in turn determines how chemically reactive an element is.        Chemical stability specifically relates to the number of valence electrons in atoms; in other words, the number of electrons in the valence shell (outer shell).        The most stable electron configurations are those where atoms have full valence shells -- Group 18 Noble Gases        Atoms that do not have full valence shells can gain or lose electrons to acquire full valence shells and become more stable. ** ** **NOBEL GASES** **       ** The only elements with full valence shells are the noble gases.        These all have eight valence electrons, except helium which has two.        Noble gases are very unreactive and rarely form compounds. ** ** ** ** **IONS**        In atomic form, other elements on the periodic table do not have full valence shells.        However, most of these can attain full valence shells by gaining or losing electrons.        When an atom loses or gains electrons, the number of electrons no longer equals the number of protons.        It is therefore no longer electrically neutral -- it is now charged.        Ion forms where the gain or loss of electrons forms a charged atom, therefore an ion is a charged atom or group of atoms **HOW POSITIVE IONS FORM** **       ** When an atom loses electrons, it forms a positive ion.        Positive ions are called cations This is because there are now more positively charged protons than negatively charged electrons **EXAMPLE OF HOW POSITIVE IONS FORM**        The sodium atom's configuration is 2.8.1        The 2nd shell has eight electrons.        It will lose one electron in the valence shell        Sodium is now charged as it has one less electron.        It forms sodium ion        The loss of the electron results in one /more proton- and sodium ion is positively charged. **       **Sodium ion is written as Na1+ or Na+ ** ** **HOW NEGATIVE IONS FORM** **       ** When an atom gains electrons, it forms a negative ion.        Negative ions are called anions        This is because there are now more negatively charged electrons than positively charged protons. ** ** **EXAMPLES OF HOW NEGATIVE IONS FROM**        The fluorine atom's configuration is 2.7        The valence shell has seven electrons.        To attain a full valence shell and achieve chemical stability it will gain an electron        Fluorine has one more electron.        The gain of an electron results in one more electron and becomes more negatively charged.        It forms a Fluoride ion.\*       Fluoride ion is written as F1- or F- ** ** **VALENCY** The charge of an ion is referred to as its valency. Valency is the capacity of an atom to lose, gain or share its electrons. Negative ions (gain of electrons)        If an atom gains one electron, it will have one more electron than protons -- the resulting ion will have a charge of --1.        If an atom gains two electrons, the resulting ion will have a charge of --2, gains 3 electrons charge is --3. Positive ions (loss of electrons)        If an atom loses one electron, it will have one more proton than electrons; the resulting ion will have a charge of +1.        If an atom loses two electrons, the resulting ion will have a charge of +2, if it loses three electrons, it will have a charge of +3.   **USING THE PERIODIC TABLE TO DETERMINE THE CHARGE OF AN ION**        Group 1 elements lose one electron and form a +1 charge e.g. Li+        Group 2 elements form ions with a +2 charge e.g. Mg2+        Group 13 elements lose 3 electrons and are more positively charged e.g. Aluminium ion -- Al3+        Group 15 elements gain three electrons and form a --3 charge e.g. Nitrogen ion N3-        Group 16 elements form ions with a --2 charge e.g. O2-        Group 17 elements gain 1 electron and are more negatively charged e.g. Cl- ** ** **NAMING IONS MONATOMIC AND POLYATOMIC** **NAMING IONS**        Metal elements form into positively charged metal ions. When a metal ion forms- the naming of a metal ion is the same.         E.g. Sodium when it becomes an ion Na+ is a sodium ion.        Non-metal elements form negatively charged ions. When a non-metal ion forms- the naming of the ion is changed.        The suffix -- end of the element is replaced with an - idea        A fluorine atom can form a Fluoride ion or chlorine -- Chloride ion. Oxygen -- Oxide ion. Nitrogen -- Nitride ion.   ** ** ** ** **MONOATOMIC IONS VS POLYATOMIC IONS** Monatomic ions        As the prefix -- 'mon' refers to one.        This refers to only ONE element that forms an ion.        Single metal or non-metal elements form ions (as previously discussed). ** ** ** **  **Polyatomic ions**        As the prefix -- 'poly' refers to more atoms that are        This refers to a group of atoms that together form a charge ion.        A polyatomic ion forms from non-metal elements grouped or metal elements grouped to form a charge (Hg22+) ** ** ** ** **METAL CATIONS AND NON-METAL ANIONS COMBINE TO FORM IONIC COMPOUNDS** Metals form cations when they lose electrons to achieve a full, stable valency shell. Non-metals form anions when they gain electrons to achieve a full, stable valency shell. Polyatomic ions Polyatomic ions form when two or more atoms combine to form a charged ion Positive cations Positive cations are attracted to negative anions and form ionic compounds. Difference between an atom and an ion An atom is a natural particle, consisting of a nucleus. an ion is a charge formed when an atom gains or loses elections Cations and anions \-              The name given to a metal when it forms an ion is a cation which is positively charges \-              The name given to a non-metal when it forms an ion is an anion, which negatively charges **IONIC COMPOUNDS** **-             ** Atoms combine to form compounds, helped together by chemical bonds, in different arrangements based on the types of atoms and how they bond. \-              Atoms form chemical bonds (and therefore compounds) to achieve full valency shells. \-              Ironic compounds are formed when a metal cation (positive) transfers its valency electron/s to a non-metal anion (negative). \-              Ionic compounds are arranged in an alternating pattern of cations and anions. e.g. Na (sodium metal)         + Cl (non-metal chlorine) \-              NaCl= sodium chloride (salt) 1 sodium + 1 chlorine \-              Ionic compounds are hard, brittle crystals that are hard to melt. When dissolved into their constituent ions, which conduct electricity in solution ** ** **WHY DO CHEMICAL BONDS FORM** \-              Everything you can see right now is made up of atoms. But the atoms in your computer or your right hand aren\'t just sitting there by themselves. They\'re joined together by attractive forces called chemical bonds to form larger structures: molecules or lattices. \-              Molecules are fairly small groups of bonded atoms such as oxygen (O2) or water (H2O). Lattices are continuous arrangements of bonded atoms in regular patterns, found in metals like iron (Fe) and crystals like quartz (SiO2).   \-              There\'s one group of elements in the periodic table that tend to exist as single atoms. These are the noble gases in Group 18, the far-right column of the periodic table, such as helium, neon and argon. \-              These elements are stable and unreactive. They\'re unlikely to interact with other atoms in chemical reactions. Watch the video to find out more.   **ATOMS FORM CHEMICAL BONDS TO OBTAIN FULL VALENCE SHELLS** **-             ** By bonding together in chemical reactions, atoms can reach a more stable state. \-              There are three basic types of chemical bonds. The type of bond depends on whether the elements involved are metals, non-metals or a mix of both.   **IONIC BONDS** **-             ** The first type of chemical bond we\'ll look at is the ionic bond that forms between a metal and a non-metal. Ionic bonds form when one or more electrons are transferred from one atom to another. \-              Remember that ions are charged particles formed when atoms either loss or gain electrons: \-              cations \[pronounced CAT-eye-onz\] are positively charged ions, formed by the loss of electrons \-              anions \[AN-eye-onz\] are negatively charged ions, formed by the gain of electrons \-              So, the transfer of electrons from one atom to another results in two ions with opposite charges. The attraction between these opposite charges is what makes ionic bonds ** ** **METALLIC BONDING** **·     ** Metallic bonds form between metal and metal atoms (same or different) ·      Metals form ions by losing electrons (hence positively charged). Those lost electrons "swim" around the metal atoms, which are strongly together ·      This structure accounts for the properties of metals- they are malleable as the mobile structure makes them flexible, they conduct electricity due to the floating electrons (can carry a charge from place to place), and they have high melting and boiling points due to the strong bonds **Earth and space science** **The Earth Cycles** 1. **Four Spheres That Matter Can Cycle Through:** - **Atmosphere**: The layer of gases surrounding the Earth. - **Hydrosphere**: All of Earth\'s water, including oceans, lakes, rivers, and groundwater. - **Lithosphere (or Geosphere)**: Earth\'s solid outer layer, including rocks, soil, and sediments. - **Biosphere**: All living organisms, including plants, animals, and microorganisms. 2. **Processes That Transfer Carbon Between Spheres:** The **Carbon Cycle** refers to the movement of carbon between the Earth\'s spheres through various processes: - **Photosynthesis (Biosphere ↔ Atmosphere)**: Plants (in the biosphere) absorb carbon dioxide (CO₂) from the atmosphere and convert it into glucose (C₆H₁₂O₆) during photosynthesis, storing carbon in their tissues. - **Respiration (Biosphere ↔ Atmosphere)**: Organisms (both plants and animals) in the biosphere release CO₂ back into the atmosphere through respiration, as they break down glucose for energy. - **Decomposition (Biosphere ↔ Lithosphere)**: When organisms die, decomposers (like bacteria and fungi) break down organic material, releasing CO₂ into the atmosphere or storing it as organic matter in the soil. - **Combustion (Biosphere/Lithosphere ↔ Atmosphere)**: The burning of fossil fuels (from the lithosphere) or biomass releases stored carbon into the atmosphere as CO₂. - **Ocean-Atmosphere Exchange (Hydrosphere ↔ Atmosphere)**: Oceans absorb CO₂ from the atmosphere, and carbon dioxide can also be released back into the atmosphere through diffusion. - **Sedimentation and Burial (Hydrosphere/Lithosphere)**: Carbon in the form of dead marine organisms can be buried on the ocean floor, becoming part of the lithosphere as sediments. Over geological time, this can form fossil fuels. - **Volcanic Activity (Lithosphere ↔ Atmosphere)**: Volcanic eruptions release CO₂ stored in the lithosphere back into the atmosphere. 3. **Interpreting Carbon Cycle Diagrams:** In a carbon cycle diagram, various processes (e.g., photosynthesis, respiration, combustion) are shown connecting the Earth\'s spheres (atmosphere, hydrosphere, lithosphere, biosphere). To interpret these diagrams: - **Identify processes**: Look for arrows representing processes like photosynthesis, respiration, and decomposition. - **Identify spheres**: Trace the arrows to see how carbon moves between the atmosphere, hydrosphere, lithosphere, and biosphere. - **Carbon reservoirs**: Larger circles or boxes often represent carbon reservoirs (e.g., atmosphere, oceans, soil), with arrows showing the direction of carbon flow. **Greenhouse Effect and Global Warming** 1. **Electromagnetic Spectrum: Shorter to Longer Wavelengths** - **Ultraviolet (UV)**: Short-wavelength radiation with high energy, capable of causing sunburn and DNA damage. - **Visible Light**: The portion of the electromagnetic spectrum visible to the human eye, ranging from violet (shorter wavelength) to red (longer wavelength). - **Infrared (IR)**: Longer-wavelength radiation that we perceive as heat. 2. **Greenhouse Gases**: Greenhouse gases trap heat in the Earth\'s atmosphere, contributing to the greenhouse effect. Examples include: - **Carbon Dioxide (CO₂)**: Released from burning fossil fuels, deforestation, and respiration. - **Methane (CH₄)**: Emitted from livestock digestion, rice paddies, and landfills. - **Nitrous Oxide (N₂O)**: Produced by agricultural activities and industrial processes. - **Water Vapor (H₂O)**: The most abundant greenhouse gas, which amplifies the effects of other gases. - **Chlorofluorocarbons (CFCs)**: Synthetic compounds once used in refrigeration and aerosols. 3. **Short vs. Long-Wavelength Radiation**: - **Short-wavelength radiation** (UV and visible light) enters the Earth\'s atmosphere from the Sun. It is high energy and penetrates easily. - **Long-wavelength radiation** (infrared or heat) is emitted by the Earth after absorbing solar energy. Greenhouse gases absorb and re-radiate this infrared radiation, trapping heat in the atmosphere. 4. **The Natural Greenhouse Effect**: - **Process**: Sunlight (short-wavelength) passes through the Earth\'s atmosphere and is absorbed by the surface. The Earth\'s surface then re-emits this energy as infrared radiation (long-wavelength). Greenhouse gases absorb this heat and re-emit it in all directions, including back toward the Earth\'s surface, warming the planet. - **Importance**: The natural greenhouse effect is essential for life on Earth, keeping the planet warm enough to support ecosystems and human civilization. 5. **Enhanced Greenhouse Effect and Global Warming**: - **Cause**: Human activities, such as burning fossil fuels, deforestation, and industrial processes, increase concentrations of greenhouse gases (CO₂, CH₄, N₂O). This enhances the natural greenhouse effect by trapping more heat. - **Effect**: The enhanced greenhouse effect leads to **global warming**, an overall rise in Earth\'s average temperature. - **Consequences**: This results in rising sea levels, changes in weather patterns, and increased frequency of extreme weather events. 6. **Weather, Climate, Global Warming, and Climate Change**: - **Weather**: The day-to-day state of the atmosphere at a specific place and time, including temperature, humidity, and precipitation. - **Climate**: The long-term average of weather patterns in a particular region over decades. - **Global Warming**: The ongoing increase in Earth\'s average surface temperature due to the enhanced greenhouse effect. - **Climate Change**: Long-term changes in global or regional climate patterns, including shifts in temperature, precipitation, and storm activity. It encompasses both natural and human-induced changes, with global warming being a major driver. 7. **Importance of Maintaining Equilibrium of Carbon Dioxide Levels**: - Carbon dioxide levels regulate the Earth\'s temperature. Too much CO₂ leads to global warming, while too little can cause cooling and disrupt ecosystems. - **Maintaining balance** is crucial to avoid extreme temperature shifts, which could threaten food security, biodiversity, and human life. Balanced CO₂ levels help sustain stable ecosystems and climates, essential for the future of the Earth. 8. **Interpreting Graphical Models of Global Warming**: - Graphs typically show trends in temperature, CO₂ levels, and sea level rise. When interpreting these, look for upward or downward trends, the rate of change, and correlations between variables (e.g., rising CO₂ levels correlating with rising global temperatures). - **Predictions**: Models may predict future warming based on current trends in greenhouse gas emissions. Understanding the implications of these trends is essential for projecting future climate conditions. 9. **Impact of Global Warming on Life on Earth**: - **Biodiversity**: Global warming can lead to habitat loss (e.g., melting polar ice, coral bleaching), forcing species to migrate or face extinction. Ecosystems may become less resilient. - **Agriculture**: Changes in climate (e.g., more droughts, heatwaves, or shifting growing seasons) can reduce crop yields and disrupt food supply. - **Sea Level Rise**: Melting glaciers and thermal expansion of seawater cause sea levels to rise, leading to coastal erosion, flooding, and displacement of populations. - **Natural Disasters**: Global warming increases the frequency and intensity of extreme weather events such as hurricanes, floods, droughts, and wildfires. 1. **Characteristics of Stars**: - **Mass**: Determines the star\'s brightness, lifespan, and eventual fate. - **Temperature**: Stars range from cool (red) to hot (blue). Temperature also affects a star\'s brightness and color. - **Luminosity**: The total amount of energy a star emits per second. - **Size**: Stars can vary from smaller than Earth (white dwarfs) to supergiants, which are several hundred times larger than the Sun. - **Composition**: Stars are primarily made of hydrogen and helium, with heavier elements produced through nuclear fusion. - **Brightness**: Measured as **apparent magnitude** (brightness as seen from Earth) or **absolute magnitude** (intrinsic brightness at a standard distance). 2. **Nuclear Fusion**: - **Process**: Nuclear fusion is the process where hydrogen nuclei (protons) fuse together to form helium, releasing a tremendous amount of energy in the form of light and heat. - **Location**: This process occurs in the core of stars, where the pressure and temperature are high enough to overcome the repulsive forces between protons. - **Importance**: Fusion powers stars and is the source of their luminosity. 3. **Absolute vs. Apparent Magnitude**: - **Apparent Magnitude**: The brightness of a star as seen from Earth, which can vary depending on the star's distance from Earth. - **Absolute Magnitude**: The intrinsic brightness of a star, measured as if the star were 10 parsecs away from Earth. - Stars with the same absolute magnitude can appear different in brightness depending on their distance from us (apparent magnitude). 4. **Light-Years to Parsecs Conversion**: - **Light-Year**: The distance light travels in one year (about 9.46 trillion kilometers). - **Parsec**: A unit of distance used by astronomers, equal to 3.26 light-years. - **Conversion**: To convert from light-years to parsecs, divide the number of light-years by 3.26. To convert parsecs to light-years, multiply by 3.26. 5. **Temperature and Color of Stars**: - **Blue Stars**: Hot stars, with temperatures above 10,000 K. - **Yellow Stars**: Medium-temperature stars like our Sun, with temperatures around 5,500-6,000 K. - **Red Stars**: Cooler stars, with temperatures below 3,500 K. - **Relationship**: The color of a star indicates its surface temperature, with blue being the hottest and red being the coolest. 6. **Hertzsprung-Russell Diagram**: - A graph plotting stars according to their luminosity (y-axis) and temperature (x-axis). - **Main Sequence**: Stars in the stable phase of hydrogen fusion are found along a diagonal band called the main sequence. - **Giants and Supergiants**: Cooler but very luminous stars are located above the main sequence. - **White Dwarfs**: Hot but dim stars are found below the main sequence. - The HR Diagram is useful for studying the life stages and properties of stars. 7. **What is a Galaxy?**: - A galaxy is a massive system of stars, stellar remnants, interstellar gas, dust, and dark matter, all bound together by gravity. - **Types of Galaxies**: Spiral (e.g., Milky Way), elliptical, and irregular. - Galaxies can contain billions to trillions of stars, along with star clusters, nebulae, and planetary systems. **The Life Cycle of Stars** 1. **Terminology**: - **Nebula**: A large cloud of gas and dust in space where stars are born. - **Protostar**: A contracting mass of gas in the early stage of star formation before nuclear fusion begins. - **Main Sequence**: The longest phase of a star's life, where it fuses hydrogen into helium in its core. - **Red Giant**: A late phase where a star expands and cools after exhausting hydrogen in its core. - **White Dwarf**: The remnants of a small to medium star after it has shed its outer layers, leaving a hot, dense core. - **Neutron Star**: A small, incredibly dense remnant of a supernova, consisting mostly of neutrons. - **Supernova**: A massive explosion marking the death of a large star, leading to the formation of either a neutron star or a black hole. 2. **Life Cycle of Stars**: A star's life depends on its mass. Here's a summary diagram: - **Nebula → Protostar → Main Sequence**: - Stars form from a nebula, enter the protostar phase, and become stable main-sequence stars. - For **low-mass stars** (like the Sun): - Main Sequence → Red Giant → Planetary Nebula → White Dwarf. - For **high-mass stars**: - Main Sequence → Red Supergiant → Supernova → Neutron Star or Black Hole. 3. **How Black Holes Are Formed**: - A black hole forms when a massive star undergoes a supernova and the remaining core is so dense that its gravity causes it to collapse into a point of infinite density (singularity). Not even light can escape from the gravitational pull of a black hole. **Big Bang Theory and a Changing Universe** 1. **Big Bang Theory Timeline**: - **13.8 billion years ago**: The universe began from a singularity, a point of infinite density and temperature, in an event called the **Big Bang**. - **First few seconds**: The universe rapidly expanded and cooled, forming the first subatomic particles (protons, neutrons, electrons). - **3 minutes after**: Nucleosynthesis occurred, where the first light elements (hydrogen and helium) formed. - **380,000 years after**: The universe became transparent as electrons combined with nuclei to form neutral atoms (recombination), and the first light, known as the **Cosmic Microwave Background Radiation**, was released. - **Millions of years later**: Gravity pulled gas together to form the first stars and galaxies. - **Present Day**: The universe continues to expand, with galaxies moving away from each other, as observed through redshift.