Senior Science Essentials - Semester 1 Exam

DNA

A double-stranded molecule that carries the genetic instructions for the development, functioning, and reproduction of all known organisms.

Nucleotide

The monomer unit of DNA consisting of a deoxyribose sugar a phosphate group and one of four nitrogen bases (adenine, thymine, guanine or cytosine).

Complementary base pairing

The specific bonding between nitrogen bases in DNA: adenine (A) pairs with thymine (T) and guanine (G) pairs with cytosine (C) held together by hydrogen bonds.

RNA

A single-stranded molecule involved in protein synthesis. It contains ribose sugar and uses uracil (U) instead of thymine unlike DNA.

Nitrogen bases

The four bases in DNA (adenine, thymine, guanine, and cytosine) whose sequence encodes genetic information. RNA replaces thymine with uracil.

Mutation

A change in the nucleotide sequence of DNA that can alter silence or create new genetic information.

Substitution

A type of point mutation where one nucleotide base is replaced by a different base potentially altering a single amino acid in the resulting protein.

Insertion

A mutation where one or more extra nucleotide bases are inserted into a DNA sequence causing a frameshift that alters all subsequent codons.

Frameshift

A mutation caused by insertion or deletion of bases (not in multiples of three) that shifts the reading frame usually drastically altering the protein produced.

Silent

A mutation that changes a DNA base but does not alter the amino acid sequence of the protein due to redundancy in the genetic code so it has no noticeable effect.

Genotype

The complete genetic makeup of an organism — the specific alleles it carries for one or more genes.

Phenotype

The observable physical or biochemical characteristics of an organism produced by the interaction of its genotype and the environment.

Dominant

An allele that is expressed in the phenotype whenever it is present even if only one copy is inherited (heterozygous). Represented by a capital letter.

Recessive

An allele that is only expressed in the phenotype when two copies are inherited (homozygous recessive). Represented by a lowercase letter.

Homozygous

Having two identical alleles for a particular gene (e.g. AA or aa). Can be homozygous dominant or homozygous recessive.

Heterozygous

Having two different alleles for a particular gene (e.g. Aa). The dominant allele is typically expressed in the phenotype.

Punnett square

A diagram used to predict the probability of offspring inheriting particular genotypes and phenotypes from a monohybrid or dihybrid cross.

Monohybrid cross

A genetic cross between two organisms that considers the inheritance of a single trait (one gene).

Pedigree chart

A diagram that shows the occurrence and inheritance of a genetic trait across multiple generations of a family using standardised symbols.

Carrier

An individual who is heterozygous for a recessive allele — they carry one copy of the allele but do not show the associated phenotype themselves.

Sex-linked inheritance

The inheritance of traits controlled by genes located on sex chromosomes (usually the X chromosome). Males (XY) are more likely to express X-linked recessive disorders.

X-linked recessive disorder

A disorder caused by a recessive allele on the X chromosome. Males only need one copy to be affected while females need two copies making males more commonly affected.

Atomic number

The number of protons in the nucleus of an atom. It defines which element the atom belongs to and determines its position in the periodic table.

Mass number

The total number of protons and neutrons (nucleons) in the nucleus of an atom.

Proton

A positively charged subatomic particle found in the nucleus of an atom. The number of protons equals the atomic number.

Neutron

A neutral (uncharged) subatomic particle found in the nucleus. Neutrons contribute to the mass number but not the charge of an atom.

Electron

A negatively charged subatomic particle that orbits the nucleus in shells. Atoms are electrically neutral when the number of electrons equals the number of protons.

Ion

An atom or group of atoms that has gained or lost electrons resulting in a net positive (cation) or negative (anion) charge.

Groups

The vertical columns of the periodic table. Elements in the same group have the same number of outer shell electrons and therefore similar chemical properties.

Periods

The horizontal rows of the periodic table. Each period represents an additional electron shell being filled as atomic number increases.

Electron configuration

The arrangement of electrons in an atom's shells (energy levels). It determines an element's chemical reactivity and position in the periodic table.

Isotopes

Atoms of the same element that have the same number of protons but different numbers of neutrons giving them different mass numbers but similar chemical properties.

Ionic

A type of chemical bond formed by the electrostatic attraction between oppositely charged ions created when one atom transfers electrons to another.

Covalent

A type of chemical bond formed when two atoms share one or more pairs of electrons typically between non-metal atoms.

Metallic

A type of bonding in metals where positively charged metal ions are surrounded by a sea of delocalised (free-moving) electrons.

Delocalised electrons

Electrons not associated with a single atom or bond that are free to move throughout a structure (as in metals) which explains high electrical and thermal conductivity.

Electrical conductivity

The ability of a material to allow the flow of electric current. Metals conduct electricity due to delocalised electrons; ionic compounds conduct when dissolved or molten.

Complete combustion

Combustion that occurs with sufficient oxygen producing carbon dioxide and water as the only products.

Incomplete combustion

Combustion that occurs with insufficient oxygen producing carbon monoxide soot (carbon) and water in addition to or instead of carbon dioxide.

Conservation of mass

The principle that the total mass of reactants equals the total mass of products in a chemical reaction — atoms are rearranged not created or destroyed.

Balancing chemical equations

The process of adjusting coefficients in a chemical equation so that the number of each type of atom is equal on both sides reflecting conservation of mass.

Activation energy

The minimum amount of energy required to start a chemical reaction and break the bonds in reactants.

Exothermic

A reaction that releases energy (usually heat) to the surroundings. The products have less energy than the reactants.

Endothermic

A reaction that absorbs energy from the surroundings. The products have more energy than the reactants. Example: photosynthesis.

Energy profile diagram

A graph showing the energy of reactants and products during a chemical reaction indicating the activation energy and whether energy is released or absorbed.

Carbon cycle

The continuous movement of carbon atoms between the atmosphere, biosphere, hydrosphere, and geosphere through processes like photosynthesis, respiration and combustion.

Photosynthesis

The process by which plants absorb carbon dioxide from the atmosphere and convert it into glucose and oxygen using sunlight — removing carbon from the atmosphere.

Cellular respiration

The process by which organisms break down glucose using oxygen to release energy returning carbon dioxide to the atmosphere.

Natural greenhouse effect

The natural process by which greenhouse gases in the atmosphere trap heat from the sun keeping Earth warm enough to support life.

Enhanced greenhouse effect

The increase in the natural greenhouse effect caused by human activities raising concentrations of greenhouse gases leading to additional warming of Earth's surface.

Greenhouse gases

Gases in the atmosphere (e.g. carbon dioxide, methane, water vapour, nitrous oxide) that absorb and re-emit infrared radiation trapping heat and warming Earth.

Fossil fuel combustion

The burning of coal oil and natural gas which releases stored carbon as carbon dioxide into the atmosphere increasing greenhouse gas concentrations.

Deforestation

The clearing of forests which reduces the number of trees available to absorb CO2 through photosynthesis and often releases stored carbon when trees are burned or decompose.

Atmosphere

The layer of gases surrounding Earth including nitrogen, oxygen, carbon dioxide and other trace gases. It regulates climate protects from radiation and is part of the carbon and water cycles.

Biosphere

All living organisms on Earth and the environments they inhabit. The biosphere interacts with the atmosphere hydrosphere and geosphere through processes like respiration and photosynthesis.

Hydrosphere

All the water on above and below Earth's surface — including oceans lakes rivers glaciers and groundwater.

Geosphere

The solid rocky part of Earth including the crust mantle and core. It stores carbon in fossil fuels and rocks and interacts with other Earth systems.

Temperature anomaly

The difference between an observed temperature and a long-term baseline average used in climate graphs to show whether temperatures are above or below the historical norm.

Long term climate trend

A persistent directional change in climate data over decades or centuries distinct from short-term fluctuations or natural variation.

Short term fluctuation

A temporary variation in climate data (e.g. year-to-year changes due to weather patterns or volcanic eruptions) that does not indicate a long-term trend.