Science Assessment Task Preparation PDF

Chemistry CHEMICAL REACTIONS - RATE OF REACTIONS - TESTS FOR PRESENCE OF GASES CHEMICAL REACTIONS Combustion reactions A chemical reaction in which a fuel undergoes oxidation by reacting with an oxidising agent, resulting in the release of energy. It is an exothermic reaction, meaning that heat is r...

Chemistry CHEMICAL REACTIONS - RATE OF REACTIONS - TESTS FOR PRESENCE OF GASES CHEMICAL REACTIONS Combustion reactions A chemical reaction in which a fuel undergoes oxidation by reacting with an oxidising agent, resulting in the release of energy. It is an exothermic reaction, meaning that heat is released. Products: Heat Light Example equation: CH4 + O2 → CO2 + H2O Real life example: The burning of any kind of wood or coal to heat your home Cars and buses burning petrol or diesel to run. ------------------------------------------------------------------------------------------------------------------------------------------- Neutralisation reactions A chemical reaction in which acid and a base react with an equivalent quantity of each other (effectively cancelling each other out) to form salt and water as products. Products: Salt (sodium) Water Example equation: NaOH + HCl → H2O and NaCl (acid + base = salt + water) Real life example: Hair becomes rough after shampoo, but it becomes shiny after using a conditioner. This happens because shampoo is basic in nature and the conditioner is acidic. So, the conditioner neutralises its effect. Antacids for neutralising the acid content in your stomach that is responsible for acid reflux. They work by counteracting the acid as antacids are bases (alkalis), meaning they are the opposite of acids. ------------------------------------------------------------------------------------------------------------------------------- Precipitation reactions Precipitation reactions occur when cations and anions in aqueous solution (soluble salt + salt) combine to form an insoluble ionic solid (insoluble salt) called a precipitate. In other words, when 2 solutions containing salts combine to form a precipitate. Essentially, they switch partners with each other (as an analogy) AB + CD ---> AD + CB (in order to produce a solid) Products: Insoluble salt Example equation: Fe2+(aq) + 2 OH−(aq) → Fe(OH)2(s) Al3+(aq) + PO43−(aq) → AlPO4(s) Real life example: A kidney stone is nothing more than a precipitate - often of calcium ions (from cheese) and oxalates. It is often suggested that a good way to avoid kidney stones is to drink a lot of water. This helps because the solubility of the precipitate increases with the amount of water - thus avoiding the formation of the kidney stone. ------------------------------------------------------------------------------------------------------------------------------- Decomposition reactions A decomposition reaction is a reaction in which a compound breaks down into two or more simpler substances. Think of it as revealing a substance’s ingredients. There are multiple types of decomposition: Thermal Heat Electricity Light Products: All substances produced (broken down) Example equation: 2H2O → 2H2 + O2 Real life example: Digestion of food is a decomposition reaction. Through this reaction, nutrients are released from the food eaten. ------------------------------------------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------------------- Calculate mass changes The mass of a substance in a chemical reaction can be calculated by determining the mass of the reactants and the mass of the products and comparing the two. If the mass of the reactants is equal to the mass of the products, the reaction is said to be mass conserving. ------------------------------------------------------------------------------------------------------------------------------- Word equations (balancing) Word equations are a quick and simple way (not T-T) of summarising chemical reactions Reactants always go first in word equations, and the names of the reactants are separated using + symbols. After the reactants, there is an arrow, →, to show that the chemical reaction has taken place. The products are written after the arrow, separated by + symbols. Words like powder, solution or gas, are not included in word equations.  In a word equation, always write the names of the chemicals - not their symbols or formulas. Never mix words and formulas in the same equation. ------------------------------------------------------------------------------------------------------------------------------- RATE OF REACTIONS Collision theory Collision theory states that for a chemical reaction to occur, the reacting particles must collide with one another with sufficient energy and a correct orientation. The rate of the reaction depends on the frequency of collisions. Different factors can affect the rate of reaction by impacting the frequency and/or proportion of collisions that have the energy to react. WAYS TO IMPROVE THE CHANCE OF THE COLLISION THEORY Concentration Most reaction rates increase as concentrations increase. With an increase in the concentration of any reacting substance, the chances for collisions between molecules are increased because there are more molecules per unit of volume Key take-away: The denser the concentration, the more collisions are likely to occur ------------------------------------------------------------------------------------------------------------------------------- Temperature With an increase in temperature, there is an increase in energy that can be converted into activation energy in a collision, and that will increase the reaction rate. A decrease in temperature would have the opposite effect. Key take-away: Increase in temperature = increase in energy (kinetic) ------------------------------------------------------------------------------------------------------------------------------- Surface area Increasing the surface area of a reactant increases the frequency of collisions and increases the reaction rate. Several smaller particles have more surface area than one large particle. Key take-away: Increase the surface area of a reactant = more particles exposed, therefore rate of reaction is increased ------------------------------------------------------------------------------------------------------------------------------- Pressure If the pressure of gaseous reactants is increased, there are more reactant particles for a given volume. There will be more collisions and so the reaction rate is increased. The higher the pressure of reactants, the faster the rate of a reaction will be. Key take-away: Forcing the gas particles closer together ------------------------------------------------------------------------------------------------------------------------------ Use a catalyst The use of a catalyst lowers the overall activation energy of the reaction. With a lower activation energy barrier, a greater percentage of reactant molecules are able to have effective collisions, and the reaction rate increases. Key take-away: An alternative route that requires less energy for a reaction to occur ------------------------------------------------------------------------------------------------------------------------------- In order to slow reactions down, just do the opposite (obviously) ------------------------------------------------------------------------------------------------------------------------------- TEST FOR PRESENCE OF GASES Oxygen gas (glowing splints) Light a small splint, blow out the flame but leave the embers, and then place the glowing splint into the unknown gas. In carbon dioxide, the splint goes out completely. In oxygen, the splint reignites. (fire cannot exist without oxygen.) ------------------------------------------------------------------------------------------------------------------------------- Hydrogen gas (pop test) You can safely test for small quantities of hydrogen gas (eg collected in a test tube) by holding a burning splint near to the top of the test tube. The positive result is a squeaky pop sound as the hydrogen reacts with oxygen in the air in a small explosion ------------------------------------------------------------------------------------------------------------------------------- Carbon Dioxide (limewater) Carbon dioxide reacts with limewater (a solution of calcium hydroxide, Ca(OH)2), to form a white precipitate. (appears milky) of calcium carbonate, CaCO3. ------------------------------------------------------------------------------------------------------------------------------- Biology DNA (deoxyribonucleic acid) DNA is a sequence of bases that contains all the genetic information of an organism, constructed in the structure of a double helix (a twisted ladder). It is composed of subunits called nucleotides which are composed of Sugar Phosphate group Nitrogenous base (ADENINE, THYMINE, CYTOSINE, GUANINE) ------------------------------------------------------------------------------------------------------------------------------- Genes A gene is the basic physical and functional unit of heredity. Genes are made up of DNA and each chromosome contains many genes ------------------------------------------------------------------------------------------------------------------------------- Chromosomes Chromosomes are thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein and a single molecule of deoxyribonucleic acid (DNA). Passed from parents to offspring, DNA contains the specific instructions that make each type of living creature unique. ------------------------------------------------------------------------------------------------------------------------------- The structure of DNA A DNA molecule consists of two long polynucleotide chains composed of four types of nucleotide subunits. Each of these chains is known as a DNA chain/strand. Hydrogen bonds between the base portions of the nucleotides hold the two chains together. Nucleotides are composed of a five-carbon sugar to which are attached one or more phosphate groups and a nitrogen-containing base. In the case of the nucleotides in DNA, the sugar is deoxyribose attached to a single phosphate group, and the base may be either adenine (A), cytosine (C), guanine (G), or thymine (T). The nucleotides are covalently linked together in a chain through the sugars and phosphates, which thus form a “backbone” of alternating sugar-phosphate-sugar-phosphate. ------------------------------------------------------------------------------------------------------------------------------- DNA replication DNA replication is the process by which the genome's DNA is copied in cells. Before a cell divides, it must first copy (or replicate) its entire genome so that each resulting daughter cell ends up with its own complete genome. ------------------------------------------------------------------------------------------------------------------------------- GENE MUTATIONS Substitution A substitution is a mutation that exchanges one base for another (i.e., a change in a single “chemical letter” such as switching an A to a G). Such a substitution could: change a codon to one that encodes a different amino acid and cause a small change in the protein produced. Key-takeaway: One base is replaced with another that can cause a change in the protein produced. ------------------------------------------------------------------------------------------------------------------------------- Insertion An insertion is a type of mutation that involves the addition of one or more nucleotides into a segment of DNA. An insertion can involve the addition of any number of nucleotides, from a single nucleotide to an entire piece of a chromosome. Key-takeaway: Insertions are mutations in which extra base pairs are inserted into a new place in the DNA. ------------------------------------------------------------------------------------------------------------------------------- Deletion A deletion changes the DNA sequence by removing at least one nucleotide in a gene. Small deletions remove one or a few nucleotides within a gene, while larger deletions can remove an entire gene or several neighboring genes. The deleted DNA may alter the function of the affected protein or proteins. Key-takeaway: Deletions are mutations in which a section of DNA is lost, or deleted. ------------------------------------------------------------------------------------------------------------------------------- Chromosomes mutations Duplication Duplication refers to a type of mutation in which one or more copies of a DNA segment (which can be as small as a few bases or as large as a major chromosomal region) is produced. Duplications occur in all organisms. ------------------------------------------------------------------------------------------------------------------------------- Deletion Chromosomal deletion syndromes result from deletion of parts of chromosomes. Depending on the location, size, and whom the deletion is inherited from, there are a few known different variations of chromosome deletions. ------------------------------------------------------------------------------------------------------------------------------- Inversion An inversion in a chromosome occurs when a segment breaks off and reattaches within the same chromosome, but in reverse orientation. DNA may or may not be lost in the process. ------------------------------------------------------------------------------------------------------------------------------- Translocation A genetic change in which a piece of one chromosome breaks off and attaches to another chromosome. Sometimes pieces from two different chromosomes will trade places with each other. ------------------------------------------------------------------------------------------------------------------------------- Cell division Mitosis Mitosis, a process of cell duplication, or reproduction, during which one cell gives rise to two genetically identical daughter cells. Strictly applied, the term mitosis is used to describe the duplication and distribution of chromosomes, the structures that carry the genetic information. ------------------------------------------------------------------------------------------------------------------------------- Meiosis Meiosis is a type of cell division in sexually reproducing organisms that reduces the number of chromosomes in gametes (the sex cells, or egg and sperm). In humans, body (or somatic) cells are diploid, containing two sets of chromosomes (one from each parent). ------------------------------------------------------------------------------------------------------------------------------- Inheritance Pedigrees A pedigree, as related to genetics, is a chart that diagrams the inheritance of a trait or health condition through generations of a family. The pedigree particularly shows the relationships among family members and, when the information is available, indicates which individuals have a trait(s) of interest. ------------------------------------------------------------------------------------------------------------------------------- Punnet square The Punnett square is a square diagram that is used to predict the genotypes of a particular cross or breeding experiment. The diagram is used by biologists to determine the probability of an offspring having a particular genotype. ------------------------------------------------------------------------------------------------------------------------------- Alleles An allele is one of two or more versions of DNA sequence (a single base or a segment of bases) at a given genomic location. An individual inherits two alleles, one from each parent, for any given genomic location where such variation exists. If the two alleles are the same, the individual is homozygous for that allele. ------------------------------------------------------------------------------------------------------------------------------- ------------------------------------------------------------------------------------------------------------------------------- Heterozygous A term that describes having two different versions of the same gene (one inherited from the mother and one inherited from the father). In a heterozygous genotype, each gene may have a different mutation (change) or one of the genes may be mutated and the other one is normal. ------------------------------------------------------------------------------------------------------------------------------- Homozygous Homozygous, as related to genetics, refers to having inherited the same versions (alleles) of a genomic marker from each biological parent. ------------------------------------------------------------------------------------------------------------------------------- Dominant/recessive An allele of a gene is said to be dominant when it effectively overrules the other (recessive) allele. Eye colour and blood groups are both examples of dominant/recessive gene relationships. ------------------------------------------------------------------------------------------------------------------------------- Biotechnologies Biotechnology Biotechnologies harness cellular and biomolecular processes to improve our health, wellbeing, economy and environment. ------------------------------------------------------------------------------------------------------------------------------- Evolution The theories of evolution Darwin and a scientific contemporary of his, Alfred Russel Wallace, proposed that evolution occurs because of a phenomenon called natural selection. In the theory of natural selection, organisms produce more offspring than are able to survive in their environment. ------------------------------------------------------------------------------------------------------------------------------- Natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Individuals in a population are naturally variable, meaning that they are all different in some ways. This variation means that some individuals have traits better suited to the environment than others. ------------------------------------------------------------------------------------------------------------------------------- Types of evolution Divergent evolution: Convergent evolution: Parallel evolution: Coevolution: ------------------------------------------------------------------------------------------------------------------------------- Evidence for evolution Anatomy: Molecular biology: Biogeography: Fossils: Direct observation: ------------------------------------------------------------------------------------------------------------------------------- Adaptions Evolutionary adaptation, or simply adaptation, is the adjustment of organisms to their environment in order to improve their chances at survival in that environment. ------------------------------------------------------------------------------------------------------------------------------- Superposition Law of superposition, a major principle of stratigraphy stating that within a sequence of layers of sedimentary rock, the oldest layer is at the base and that the layers are progressively younger with ascending order in the sequence. Artifacts found in the same soil level are believed to be of the same time period. They were deposited at that level at the same point in time. The law of superposition is one of the principles of geology scientists use to determine the relative ages of rock strata, or layers. ------------------------------------------------------------------------------------------------------------------------------- Physics Properties of Waves Waves are disturbances that travel, transferring energy without moving matter. They have key characteristics like period, wavelength, and frequency. The speed of a wave can be affected by its type and the medium it travels through. ------------------------------------------------------------------------------------------------------------------------------- Wave equations -------------------------------------------------------------------------------------------------------------------------------