Science subject selection notes (1).pdf

Chapter 6 6.1 Earth's Spheres: The Biosphere: - includes all parts of the Earth's surface and atmosphere where living things exist. - It is the sum of all Earth's ecosystems The biosphere is where other spheres of the planet interact: - The land (lithosphere) interacts with the water (hydr...

Chapter 6 6.1 Earth's Spheres: The Biosphere: - includes all parts of the Earth's surface and atmosphere where living things exist. - It is the sum of all Earth's ecosystems The biosphere is where other spheres of the planet interact: - The land (lithosphere) interacts with the water (hydrosphere). - The land interacts with the air (atmosphere). - Living things interact with the land, water and air. Cryosphere: regions where water has frozen into snow or ice Earthquakes: - Depending on severity it may cause parts of the lithosphere to move apart, move together, rise or subside (drop). - This movement may cause large cracks to appear or land to increase in height. - May cause landslides and mudslides that tear down forests and vegetation in their path which destroys ecosystems resulting in habitat loss Liquefaction: when saturated, sandy soils lose their structure and behave as a liquid. Volcanic Eruptions: Short term: - Volcanic eruptions that send ash clouds up into the atmosphere can produce very heavy rain and lightning - Rain occurs because the ash particles allow water vapour to condense around them and form rain droplets - cause of the lightning is the collision of ash and air particles that become positively or negatively charged and are then forced apart. - When the difference in charge and the voltage it creates becomes high enough, a flow of electric charge occurs which is seen as lightning Long term: - The clouds of ash in the atmosphere reduce the amount of sunlight reaching the surface of Earth which has a cooling effect later on. - Can cause mountains and islands to disappear and can also create them Effect on Biosphere: - Lava burns animals and plants - The new land formed by the lava is too hot for any living thing to survive and it takes years before the lava is cool enough for seeds and spores to start germinating. - Toxic gases and ash produced by volcanoes suffocate animals and can smother plants, making their survival unlikely Tropical Cyclones: - caused by intense low pressure atmospheric systems that develop in the warm tropics when the sea surface temperature is above 26.5C - Evaporation above the warm water causes clouds to form, and the low air pressure causes the clouds to spiral upwards forming very large, very high clouds. These spirals can be very destructive - Tropical cyclones produce very heavy rain and wind speeds of 63 km/h to more than 200km/h. - Heavy rain associated with tropical cyclones continues after the cyclone has moved inland and decayed. → the rain causes rivers to flood - Storm surges: the wind and low pressure increase the tide level of the sea by 2-5 metres. When this surge crosses the coast at the same time as a high tide, low-lying coastal areas may be flooded by salt water. Tsunamis: - A series of great destructive sea waves 1. Convection currents in the mantle move the plates towards each other​ 2. An earthquake rocks the ocean floor as plates on a destructive boundary collide.​ 3. Water is displaced and pushed up. Sea water is sucked back from the shore.​ 4. Wave height increases as it gets closer to the shore. ​ 5. A tsunami hits land at great speed and damages an area badly.​ Nitrogen Cycle (most likely need to label): - Important natural cycle for living things as nitrogen is an important element in protein - Air is 78% nitrogen but living things cant use nitrogen in the form of gas. - Plants use nitrogen compounds from the soil and animals obtain it from eating plants or other animals - Decomposers and nitrogen-fixing bacteria convert nitrogen into ammonia and then nitrates that plants can use. - Denitrifying- bacteria convert nitrates back into gaseous nitrogen (N2) which is then released back into the atmosphere Carbon Cycle (may need to label): - found in all living things, their dead bodies and wastes. part of the carbohydrates, fats, proteins, vitamins and DNA found in cells, tissues and organs. - Found in atmosphere as carbon dioxide (CO2) - Animals and other organisms obtain carbon from food Carbon in Photosynthesis: (know both equations) - Plants combine carbon dioxide with water to form glucose Respiration: (know both equations) - Respiration releases carbon back into the atmosphere and hydrosphere as carbon dioxide, where it becomes available for photosynthesis. - there is not an endless supply of carbon it is recycled through the soil, through living things and the atmosphere in the carbon cycle  ➔ Organisms release carbon into the soil in wastes such as faeces, urine and fallen leaves. These wastes are used as food by decomposer organisms. ➔ As the decomposer organisms respire, carbon is released as carbon dioxide back into the atmosphere, water and soil. Fossils: - the preserved remains of once-living organisms. - Fossil fuels such as coal and oil contain the carbon of plants and animals that died and were preserved millions of years ago. - Burning fossil fuels releases carbon that has been unavailable to the carbon cycle for millions of years ➔ When plenty of oxygen is available, carbon released in the atmosphere from burning fossil fuels and wood is in the form of carbon dioxide. ➔ If oxygen is limited, then the carbon is released as carbon particles (soot) and carbon monoxide gas (CO) instead 6.2 natural Influences on climate: Weather: - the state of the atmosphere in terms of temperature, wind, cloud cover and precipitation. - created through interactions of hydrosphere, lithosphere and atmosphere Climate: the long term averages of weather conditions Greenhouse Gases : - it absorbs infrared radiation from the Sun in the form of heat, which is circulated in the atmosphere, keeping the Earth warmer - Trap heat in atmosphere - They are natural but we have enhanced its effect Carbon Dioxide: - Accounts for the greatest portion of warming - Human activities have increased carbon dioxide through combustion of fossil fuels Methane: - Comes from human activities such as coal mining, natural gas production, waste decomposition in landfills and digestive processes in livestock agriculture. - Natural sources: wetlands and termite mounds Nitrous oxide: - Emitted during agricultural and industrial activities, combustion of solid waste and fossil fuels Hydrofluorocarbons (CFC’s): - Released as a result of commercial, industrial and household uses Ocean currents : Main causes: Wind, temperature, variations in salinity, rotations of earth on its own axis, gravitational pull of sun and moon Surface currents: - Caused by wind - Wind pushes the surface of water along until it reaches land, then it flows Deep currents: - Begin at the poles where extremely cold water is found - They flow through the ocean, carrying very cold water along the bottom Gulf Stream : - Part of global conveyor belt - Makes western europe much warmer in winter than any region at that altitude - Carries warm caribbean sea carrying heat across the north atlantic drift and the norwegian currents into labrador and green land seas - Very cold arctic winds then cool the water of the gulf stream, increasing its density → dense water sinks creating deep currents Global Warming : - Interglacial: period between glaciations- periods of global warming where average world temperature increases - During interglacials, ice caps melt which causes the sea level to rise and coastal lands to flood. - Evidence: sediments and fossils in coastal rocks. Evidence for climate change : Glaciers: - When glaciers move, they grind against the rocks on the side and floor of the valley through which they flow  - The rocks on the side of the valley get deeply scored by broken rocks - When the glacier retreats, the scoring of the rocks becomes visible Ice cores: - On some glaciers and ice sheets, sufficient snow falls each year to form recognisable annual layers. - Scientist analyse the chemical and physical properties of cores such as temperature and composition of air which shows links between temperature and variations in global sea level Pollen Analysis: - Pollen decays very slowly and becomes fossilised which indicates the species growing in the area when the sediments that created the fossils were laid down. - Changes in the types of pollen found indicate changes in vegetation and climate. Sea Level change: - The worldwide distribution of sedimentary rocks and the types of fossils found in them are indicators of changes in sea level in the past. 6.3 Human influence on climate: The enhanced greenhouse effect: - The increase in the natural green house effect caused by human activity - Major cause of the enhanced greenhouse effect is an increase in carbon dioxide, methane and nitrous oxide concentrations in the atmosphere Carbon dioxide in the atmosphere: - 95% of carbon dioxide is naturally produced however balanced by natural carbon sinks that remove it from the atmosphere. - Largest source of carbon dioxide is natural decay of organic material in forests and grasslands. - Carbon dioxide has increased after the industrial revolution due to extracting and burning coal and gas as a primary energy source Methane: - Produced when vegetation breaks down in the absence of oxygen e.g in rice paddies, rubbish tips and when cattle burp/fart. - Traps 20 times the heat of C02 Nitrous Oxide (N20): - Produced from burning forests, cars exhausts and artificial fertilisers - Traps 300 times more heat than CO2 Loss of ice: - ice is melting meaning more heat will be added to the atmosphere Shrinking Antarctica: - Antarctica is losing ice at an increasing rate Ozone: - Occurs naturally in the atmosphere, mostly in the stratosphere. - Absorbs ultraviolet (UV) radiation emitted by the sun- too much exposure to UV radiation can cause skin cancer and eye disease 6.4 Changing environments: The Great Barrier Reef: - Water temperature is rising resulting in bleached coral (loses colour). Reducing carbon dioxide: - Reduce amount entering the atmosphere from fossil fuels - Increase amount of plants and trees - Reduce deforestation Chapter 8 8.1 describing motion (know how to work out all): Displacement: - Straight line distance between finishing and starting points - Also specifies direction (vector quantity) Distance : - Scalar unit and has magnitude only - Distance in a certain time = Speed x time Speed: - How fast something moved - Unit m/s - Can be converted from m/s to km/h or vice versa Average speed: - how fast something moved overall - Work it out using the speed formula and doesn’t include stops. Instantaneous speed: - The speed at a particular instant - Measured by speedometer Velocity: - Measure of how fast something moved and its direction Acceleration: - The rate at which something changes speed - V is final velocity, u is initial velocity - Unit is m/s^2 Acceleration due to gravity: - Air resistance: the friction between air and a falling body - Terminal velocity: the final velocity of a falling object - A falling object accelerates towards earth due to the force of gravity- it speed up as it falls - Acceleration due to gravity is 9.8 m/s^2 - Air resistance eventually reduces the acceleration to zero 8.2 Newtons laws of motion: First Law: - An object at rest stays at rest unless acted upon by a force - An object in motion will continue to move at the same speed and direction unless an unbalanced force acts upon it. - A force is needed to get something moving or change the speed or direction of something that is already moving - Inertia: the tendency to resist any change in motion Second Law: - An object will accelerate in the direction of an unbalanced force acting upon it. - The size of this acceleration depends upon the mass of the object and the size of the force acting. - F= m x a a= f/m m= f/a - F is force, m is mass, a is acceleration Third Law: - For every action force there is an equal and opposite reaction force - Forces always occur in pairs - E.g 8.3 Energy changes: Kinetic energy: - The energy of a moving object - The amount of kinetic energy an object has depends on its mass - Measured in joules, J - M is mass, v is velocity - Kinetic energy= ½ mass x velocity squared = ½mv^2 Potential energy: - Energy that an object has because of its position or structure - Aka stored energy - Potential energy= mass x acceleration due to gravity (9.8) x height = mgh Law of conservation of energy: - States that energy may be transferred from one object to another, but is never created or destroyed - When energy is transferred there is always the same amount of energy Energy efficiency: - Although energy is always conserved in an energy transfer, a little energy is usually 'lost' because it changes into non-useful forms such as heat and sound. - Efficiency: measure of how much useful energy is produced Chapter 4: Chemicals reacting 4.1 Atoms and Elements: Current model of the Atom: Atoms: - Smallest building blocks of matter - In a neutral atom number of protons=number of electrons Nucleus: - Centre of the atom - Contains protons and neutrons - Positively charged because of protons - Dense as it contains most of the mass of the atom in a tiny place Neutrons: - Neutral charge/no charge - Found in nucleus Protons: - Positively charged - Found in nucleus Electrons: - Spin around in the space surrounding the nucleus - Negatively charged and therefore are attracted to the positive nucleus - Are able to be lost or gained in chemical reactions Elements: - A substance made up of one type of atom - Atoms have the same number of protons and electrons Atomic number: - Shows the number of protons - Atomic number is always the smaller number Mass number: - Amount of protons and neutrons - To find the amount of neutrons do mass-atomic number Isotopes: - Belong to the same element, with same number of protons and atomic number - have different numbers of neutrons, giving them different mass numbers. 4.2 Periodic Table: Divisions: - Lists elements according to their atomic number - The horizontal rows known as periods are numbered 1-7 → - The vertical columns known as groups numbered 1-18 Properties: - Elements with similar physical and chemical properties are placed in the same group - Special blocks:transitional, lanthanides and actinides Dmitri mendelev: - Russian scientist who constructed a table of rows and columns and places each element in a box 4.3-The Alkali metals and the Alkaline earth metals: Group 1- The Alkali metals: - Soft, reactive metals - react vigorously with water - more reactive as you go down the group Properties: - form +1 ion. - too reactive to be found naturally in their pure forms. - Ductile, malleable, - low melting and boiling points - very soft and can be cut easily with a knife. - low densities  - react quickly with water, producing hydroxides and hydrogen gas - their hydroxides and oxides dissolve in water to form alkaline solutions Group 2- The Alkaline Earth metals: - Are metals and less reactive than group 1 - From +2 ions Properties: - shiny - Silvery white - Low density - Low melting and boiling points Chemical Properties: React with hydrogen to create metallic hydrides React with oxygen to create metal oxides All except beryllium react with water to form metal hydroxides and hydrogen gas Matter: - Matter is anything that has mass and takes takes up space - Matter can change form through physical and chemical changes, but through any of these changes, matter is conserved Law of conservation of Matter: - Matter cannot be created or destroyed - the total mass would remain constant in a reaction Group 14- Metalloids: - Metal and non-metal properties - Substances that have carbon are known as organic and have organic molecules Allotropes: - Allotropes are the different forms of an element- pure carbon exists in several different forms - The most common is amorphous carbon (charcoal), diamond, graphite and buckyball - The molecular structure of all 4 allotropes are different Group 17- Halogens: - All are electronegative therefore forming a -1 charge - Not found in nature in their pure form but are found in many salts - Become bigger and less reactive as you move down the group - All form molecules that are made up of 2 atoms (F2 , Cl2 ) - Have coloured and poisonous vapours Group 18- Inert/Noble gases: - Colourless and occur naturally in the atmosphere - Can be separated from liquid air by the process of fractional distillation - Very stable – valence shells are filled - React under rare or extreme circumstances - Become denser as you move down the group Group 3-12 Transition Metals - Include some of most colourful and valuable metals such as iron, zinc, copper, gold and silver - Form coloured compounds - Good conductors or heat and electricity - Can be hammered or bent into shape easily - Less reactive than alkali metals - High melting points- but mercury is liquid at room temperature Chapter 5: Chemical Reactions 5.1 Energy in Chemical Reactions Chemical Equations: - Describes what happens in a chemical reaction - Reactants → Products Word Equations: - Represents a chemical reaction using the name of the substances involved Balanced Chemical Equations: - A chemical reaction doesn’t create or destroy atoms, it rearranges them. - The number of atoms of each element has to be equal on both the reactant and product side Exothermic: exo means out - Chemical reactions that release energy in the form of heat or light - E.g Flames, explosions, fireworks Endothermic: endo means in - Chemical reactions that absorb energy- usually feel cold - E.g Chemical ice packs The activity series: - Whether or not a metal corrodes or combusts depends on how easily the metal reacts with oxygen is known as Metals reactivity. - Activity series is the order of these metals according to their reactivity Biofuels: - Biofuels are a type of fuel that promises to be a renewable source - Manufactured by fermenting the sugars in crops such as sugarcane, potato and corn (maize) which uses yeast to convert the sugars into ethanol - biofuels are unlikely to ever be the only source of fuels as it would require huge areas of land to grow the raw materials required to supply all of our fuel needs. - Contributes to inflation of food as the crops and farmlands once used for food are now used for biofuels which means less food available 5.2 Classifying Chemical Reactions Decomposition: - When a single reactant breaks apart to form several products --> reactant decomposes. XY → X+Y Thermal decomposition: - when substances decompose when heated - Metal carbonates and metal hydrogen carbonates undergo thermal decomposition. Precipitation: - Precipitate: When Two clear liquids are mixed they react to form an insoluble solid Solubility: the ability to dissolve - Soluble things dissolve, and insoluble things don’t dissolve. - The purpose of the Solubility Table is to tell whether a substance will dissolve or not. - If a substance dissolves in water, it forms an aqueous solution, written with (aq). - If a solid substance does not dissolve, it remains solid, written with (s). Cations and Anions: - Cations: atoms that lose electrons and have positive charge - Anions: (a negative ion) atoms that gain electrons and have negative charge - When ionic compounds dissolve, the cations and anions break away from the crystal lattice and spread evenly throughout the solvent. Example: When sodium chloride, 𝑵𝒂𝑪𝒍 dissolves in water, the sodium cations 𝑵𝒂 +,and chloride anions 𝑪𝒍 −, are dispersed throughout the liquid. - If valence electrons are 5 or more, atom gains electrons → negative charge → anion.  - If valence electron are 3 or less → lose electrons → positive charge → cation - Atoms gain or lose electrons in the valence (last) shell to become stable Ions: Role of Electrons: - Chemical reactions occur when atoms bump into each other and trade or share valence electrons. - In this process they form bonds and join to form compounds. Ionic compounds: - substances made up of a crystal lattice of positive ions (cations) and negative ions (anions). - No overall charge-always neutral, charge of cation balances the charge of anion. Naming Ionic compounds: - Name of cation first then anion → cation anion Electron configuration: - Electrons are attracted to the nucleus - Electrons are filled closest to the nucleus first and when filled this way the atom is in ground state (lowest energy state) Excited electron: When electrons jump to a higher energy level - Some outer shell electrons jump from one shell to another which requires energy - As these excited electrons return to their ground state they release energy in the form of light - Different elements release different amounts of energy and so different colours of light as each element has a different amount of protons and holds its electrons more tightly than others. Polyatomic Ions: - Ions with more than one atom- the chemical symbol is put inside a bracket when more than one is needed for a balanced equation - To balance: drop and swap charges Ca +2 + OH -1 Drop → Ca2 + OH 1 Swap → Ca1 + OH 2 Acid: - Any substance that releases hydrogen ions when dissolved in water - pH less than 7 and corrosive - Turns blue litmus paper red, red stays red  - Tastes sour - Reacts with metals to produce hydrogen gas - Reacts with carbonates to release carbon dioxide gas - Conducts electricity in solution Strong acid: hydrogen breaks away very easily Name of acid Chemical Formula Uses Hydrochloric acid HCl -helps digest food in stomach -brick cleaners -cleaning metals Sulfuric acid H2SO4 -used in car batteries -manufacturing fertilisers Nitric acid HNO3 Used to etch artwork into etching plates Weak acid: holds on to hydrogen and very little breaks away Name of acid Common name Uses Acetic acid vinegar Flavour and preserving food ascorbic acid Vitamin c supplement and antioxidant Acetylsalicylic acid Aspirin Pain reliever Base: - Any substance that producers hydroxide ions in when dissolved in water - Base + water = alkaline - pH more than 7 - Turns red litmus paper blue, blue paper remains blue - Corrosive and tastes bitter - Slippery feel much like soap - Neutralise or destroy the properties of acids - Conduct electricity in solution Strong base: attack living tissue and cause serious harms Name of base Chemical Formula Uses Sodium hydroxide (aka NaOH -making soaps caustic soda) -oven cleaner -unblocking drains Potassium hydroxide KOH -used in a similar way to NaOH Calcium hydroxide Ca(OH)2 reduces soil acidity weak base: many household cleaners contain bases as they are excellent at dissolving oil and grease Name of base Common name Uses Ammonium hydroxide ammonia Cleaning products Sodium hydrogen Baking soda cooking carbonate Bicarbonate of soda Sodium carbonate Washing soda Washing powders Reactions with acids: - Acids are common reactants used in industry and can be used to classify chemical reactions: 1. Neutralisation reactions: - When an acid and a base are mixed together they can neutralise each other - This is because hydrogen ions from the acid combine with hydroxide ions from the base to form water. Water is neutral - The ions that acids and bases leave behind form a salt in the solution Acid + base → salt + water Salt refers to the ionic compounds that are produced through a chemical reaction with an acid 2. Acids and metals: - Acids react with metals to produce salt and hydrogen gas acid + metal → salt + hydrogen 3. Acid carbonate: - Acids react with carbonate to produce salt, water and carbon dioxide gas acid + carbonate salt → water + carbon dioxide Fast and slow chemical reactions: Factors affecting rate of reactions: The rate of a chemical reaction can be increased or decreased: 1.Temperature: - Increasing temperature will increase the rate of a chemical reaction because: 1. the speed of particles in liquids and gases increases which makes the particles collide more frequently so more chemical reactions occur in a shorter amount of time. 2. It gives particles more energy so when particles collide they hit harder 2. Concentration: the amount of a particular substance present in a particular volume of liquid or gas - Increasing the concentration of reactants will increase the rate of reaction because more particles are more likely to collide and react when there are more of them. - Collisions between particles are necessary for the reactants to rearrange to form the products - The rate of some reactions can be slowed down using the concentration of reactants 3.Surface area of reactants: - Cutting up or crushing solid reactants into smaller pieces creates a larger surface area in contact between the reactants - This means more particles are reacting at the same time so the reaction is faster. 4.Agitation: - Stirring, agitation the reactants increases the rte of reaction - Agitation ensures that the reactants are kept in contact by removing build up of product around the reactants 5.Catalyst: - Catalysts are chemicals that speed up chemical reactions but aren’t consumed or used up during the reaction 1. They reduce the amount of energy that is required to convert the reactants into products 2. They make it easier for the reactant molecules to collide and form products 6.Enzymes: - Enzymes are biological catalysts.  - They are natural molecules that hold reactant molecules together until they are rearranged to form products. Nuclear decay: - Nuclear reactions involve the nucleus, radioactive decay and transmutation - Some isotopes are unstable and decay Alpha decay: - When an alpha decay occurs the radioactive nucleus changes into a different more stable nucleus, with 2 less protons and 2 less neutrons, and a helium nucleus is emitted - Mass number decreases by 4 → -2 protons, -2 neutrons - Atomic number decreases by 2 → -2 protons Beta decay: - When a beta minus (B-) decay occurs, a neutron in the radioactive nucleus is converted into a proton - Neutron changes to proton → mass number stays the same - Atomic number increases by 1 Gamma decay: - Gamma rays are high energy proton beams - no mass and no charge, do not strongly interact with matter. They can cover great distances through air without being stopped, it takes a few cm of lead to stop a gamma ray. - A gamma ray will travel in a straight line through magnetic and electric fields as it has no electric charge. Evolution and genetics 1.1 DNA the molecule: Genetics: the study of hereditary and the variation of inherited characteristics DNA: deoxyribonucleic acid - Found in the nucleus of cells - Determines the characteristics of an organism and contributes to its diversity - Double helix structure (looks like a twisted ladder) - Contains a genetic code unique to each individual - There are 2 types of nucleic acids: DNA and RNA - All organisms have DNA, but each species has its own unique DNA sequence that defines the species - The more closely related the species are, the more similar the DNA Double helix structure: - The two strands of the DNA molecule consist of complementary nucleotides that are held together by weak hydrogen bonds Watson-Crick model: - 1953 James Watson and Francis Crick completed a model explaining the structure of DNA - Watson, Crick, Franklin and Wilkins co-discovered the double helix structure Nucleotides: the continuously repeating blocks of DNA - Nucleotide molecules have 3 parts 1. Phosphate 2. Deoxyribose sugar 3. base When drawing a nucleotide make sure the pentagon is the biggest - The sugar and phosphate form the backbone of the DNA - Bases link the strands of DNA - There are 4 types of nitrogen bases in DNA: - Adenine (A) - Thymine (T) - Guanine (G) - Cytosine (C) Complementary base pairs: - Adenine (A) always pairs with Thymine (T) - Guanine (G) always pairs with Cytosine (C)  - Chargaff's rule: number of A=T and number of G=C bc they’re complementary Importance of DNA: 2 Vital properties: 1. It can replicate itself 2. It can carry information - the order of bases along a strand can be used as a code for making proteins - DNA sequences must be converted into messages that can be used to produce proteins DNA vs Gene vs Chromosome: - DNA strands are twisted around to form chromosomes - Chromosomes carry DNA and proteins - A gene is a section/length of DNA that has a specific code for a particular characteristic 1.2 Making new cells: DNA replication: the process of copying DNA - DNA can’t move out of the nucleus so a copy of it needs to be made to take the information to the ribosomes to make new proteins. - When a cell divides it must give a full set of chromosomes with their entire DNA to their daughter cells. Thus, before dividing a cell needs to make a 2nd copy of its DNA through replication Importance of replication: - allows the organism to retain its characteristics and pass it onto new cells, required for growth and repair. - ensures each new cell receives its own copy of DNA. Once the cells have made copies of their DNA, they are ready to divide. Steps of replication: 1. Strands of the double helix unwind and unzip which exposes the base 2. Free nucleotides pair up with their complementary base pair 3. Sugar and phosphate molecules bond with the neighboring nucleotides and form new strands of DNA. 1. Unwinds & Unzips 2.Free nucleotides pair up 3.sugar and phosphate make new with their complementary base DNA strands