Science yearly outcomes

Law of conservation of mass

stating that matter is neither created or destroyed during a chemical reaction, so the total mass of reactants equals the total mass of products.

System (chemical reaction)

The specific reactants and products directly involved in a chemical reaction.

Surroundings (chemical reaction)

All matter outside the reacting species, such as the reaction flask, solvent, air, and measuring apparatus.

Ionic compound

A substance composed of positively charged cations and negatively charged anions bound by electrostatic forces, typically formed when electrons transfer from a metal to a non-metal.

Covalent compound

A substance composed of non-metal atoms that share pairs of valence electrons.

Ethanoate ion formula

$$CH_3COO^-$$

Ammonium ion formula

$$NH_4^+$$

Carbonate ion formula

$$CO_3^{2-}$$

Hydroxide ion formula

$$OH^-$$

Hydrogen carbonate ion formula

$$HCO_3^-$$

Nitrate ion formula

$$NO_3^-$$

Nitrite ion formula

$$NO_2^-$$

Phosphate ion formula

$$PO_4^{3-}$$

Sulfate ion formula

SO-2 4

Naming conventions for ionic compounds

1. State the cation name first as written on the periodic table. 2. For transition metals, specify the ionic charge using Roman numerals in parentheses. 3. State the anion second, changing the monatomic element ending to -ide (polyatomic ions retain their specific names).

Ammonia chemical formula

$$NH_3$$

Carbon dioxide chemical formula

$$CO_2$$

Ethanol chemical formula

$$C_2H_5OH$$

Glucose chemical formula

$$C_6H_12O_6$$

Methane chemical formula

$$CH_4$$

Water chemical formula

H2O

Naming conventions for covalent compounds

1. Name the element located furthest to the left on the periodic table first. 2. Use a numerical prefix (di-, tri-, etc.) on the first element only if there are two or more atoms. 3. Change the ending of the second element to -ide and always include a numerical prefix (mono-, di-, tri-, etc.) to indicate the atom count.

Genetic material

The molecular instructions within living organisms responsible for directing inherited traits, cellular development, and biological processes.

DNA (deoxyribonucleic acid)

The nucleic acid polymer that stores and transmits hereditary information in most living organisms.

Double helix (DNA structure)

A polymer composed of two polynucleotide strands winding around a central axis, joined by complementary base pairs.

Components of a nucleotide and the four DNA bases

Consists of a phosphate group, a deoxyribose sugar, and one of four nitrogenous bases: adenine ($A$), thymine ($T$), cytosine ($C$), and guanine ($G$).

Bonding between complementary DNA strands

Hydrogen bonds join complementary nitrogenous base pairs: adenine pairs with thymine ($A-T$), and cytosine pairs with guanine ($C-G$).

Chromosome

A long, tightly coiled DNA molecule packaged with proteins that carries numerous individual genes.

Location of DNA in eukaryotic cells

Enclosed primarily within chromosomes located in the cell nucleus.

Gene

A specific segment of DNA located on a chromosome that codes for a particular protein, characteristic, or biological function.

Genome

The entire complement of genetic material and DNA sequences present within an organism.

Structural features allowing DNA to store and transmit hereditary information

Linear nucleotide base sequences store encoded instructions, complementary base pairing enables accurate replication, and organised gene segments serve as templates for protein synthesis across generations.

Scientific contributions of Franklin, Wilkins, Watson, and Crick

Franklin and Wilkins captured critical X-ray diffraction images of DNA fibres, which Watson and Crick interpreted to formulate the double-helix model.

Two biological mechanisms of inheritance

Sexual reproduction (fusion of gametes) and asexual reproduction (mitotic cell division or budding).

Genetic variation in sexual vs. asexual reproduction

Sexual reproduction combines genetic material from two distinct parents to produce diverse offspring, whereas asexual reproduction produces clones with identical genetic sequences.

Mitosis

A type of eukaryotic nuclear division that yields two genetically identical diploid ($2n$) somatic daughter cells for bodily growth and tissue repair.

Four main stages of mitosis

1. Prophase: chromatin condenses into distinct chromosomes. 2. Metaphase: chromosomes align along the equatorial plate. 3. Anaphase: sister chromatids separate toward opposite poles. 4. Telophase: nuclear envelopes re-form around daughter nuclei.

Meiosis

A two-stage reduction division producing four genetically unique haploid ($n$) gametes containing half the somatic chromosome complement.

Sequential stages of meiosis

Consists of two successive nuclear divisions: Meiosis I (prophase I, metaphase I, anaphase I, telophase I) and Meiosis II (prophase II, metaphase II, anaphase II, telophase II).

Comparison of mitosis and meiosis

Mitosis involves one division to produce two identical diploid somatic cells; meiosis involves two divisions to produce four genetically varied haploid gametes.

Mutation

A permanent alteration in the nucleotide sequence of an organism's DNA.

Examples of beneficial, harmful, and neutral mutations

Beneficial: mutations providing malaria resistance (e.g., sickle-cell trait). Harmful: mutations causing genetic disorders (e.g., cystic fibrosis). Neutral: silent base changes or variations in eye pigmentation.

Meiotic processes generating genetic variation

Crossing over (reciprocal exchange of genetic segments between non-sister homologous chromatids during prophase I) and independent assortment (random alignment and segregation of maternal and paternal chromosomes during metaphase I and anaphase I).

Primary drivers of variation in a population

Spontaneous DNA mutations generating new alleles, coupled with sexual reproduction mechanisms including crossing over, independent assortment, and random fertilisation.

Interaction between genes and the environment on phenotype

Most biological traits develop through polygenic interactions between multiple gene loci influenced by external environmental factors such as diet, climate, and lifestyle.

Genotype vs. Phenotype

Genotype refers to an organism's underlying genetic constitution or specific combination of alleles; phenotype refers to observable physical, physiological, and biochemical traits.

Allele

An alternative variant form of a specific gene residing at the same locus on homologous chromosomes.

Dominant vs. Recessive alleles

A dominant allele is expressed in both heterozygous and homozygous genotypes, whereas a recessive allele is phenotypically expressed only in homozygous genotypes.

Punnett square

A grid-based calculation model used to predict the expected genotypes, phenotypes, and probability ratios of offspring from a genetic cross.

Gregor Mendel's key discovery in genetics

Demonstrated through controlled pea plant breeding that inheritance occurs via discrete particulate factors (genes/alleles) that segregate and assort independently rather than blending.

Pedigree diagram

A standardized family tree diagram tracing the phenotypic expression and inheritance pattern of a particular trait across multiple generations.

Fossil

The preserved remains, impressions, casts, or trace evidence of an ancient organism preserved in sedimentary rock.

Evidence provided by the fossil record

Reveals extinct organisms, evolutionary transitions, mass extinctions, and shifts in global biodiversity over geological time scales.

Key evidence supporting biological evolution

Transitional fossils, comparative anatomy (homologous and vestigial structures), comparative embryology, and molecular homology in DNA and amino acid sequences.

Natural selection

where organisms with traits best suited to their environment are more likely to survive and reproduce

Key steps of natural selection

1. Overproduction and heritable variation in a population. 2. Environmental selection pressures. 3. Differential survival and reproduction of advantageous phenotypes. 4. Gradual accumulation of favourable alleles over generations.

Lamarckism vs. Darwinian evolution

Lamarck proposed that organisms have phenotypic adaptations through use and disuse during their lifetimes and pass them to offspring and Darwin demonstrated that natural selection acts on pre-existing, inherited genetic variations.

Speciation through reproductive isolation

Barriers halt gene flow between separated populations, allowing divergent mutations and selective pressures to accumulate until populations can no longer interbreed to produce viable, fertile offspring.

Fossil record insights on biodiversity dynamics

Documents catastrophic mass extinctions followed by evolutionary radiations, illustrating past losses and restructuring of biodiversity across geological eras.

Examples of modern genetic technologies

CRISPR-Cas9 gene editing, recombinant DNA production (genetically modified organisms), reproductive and therapeutic cloning, and whole-genome sequencing.

Practical applications of genetic technologies

Developing gene therapies, engineering pest- and drought-resistant crops, biosynthesizing pharmaceutical products, and preserving genetic diversity in endangered species.

Ethical and social considerations in genetic engineering

Balancing biomedical benefits against risks concerning biosafety, equitable access, informed consent, potential off-target genetic changes, and animal welfare.

Perspectives on gene editing and reproductive cloning

Supporters highlight the potential to eradicate debilitating monogenic diseases and boost agricultural yields, while critics raise concerns regarding ecological disruption, social inequality, and moral boundaries.

components of a scientific ethical argument

1. State a clear moral position. 2. Substantiate claims with peer-reviewed scientific evidence. 3. Analyze differing cultural and stakeholder viewpoints. 4. Weigh short- and long-term biological and societal consequences.

Mechanical wave

A disturbance that transfers energy through the physical oscillation of particles in a medium; examples include sound waves, seismic waves, and water waves.

Electromagnetic wave

A transverse disturbance of synchronized, oscillating electric and magnetic fields capable of transmitting energy through a vacuum without a material medium.

Anatomy of a transverse wave

1. Crest: peak positive displacement. 2. Trough: peak negative displacement. 3. Amplitude ($A$): maximum displacement from rest position. 4. Wavelength ($\lambda$): spatial distance between adjacent in-phase points. 5. Period ($T$): duration of one complete wave cycle.

Particle oscillation in transverse vs. longitudinal waves

In transverse waves, particles oscillate perpendicular to the direction of wave travel; in longitudinal waves, particles oscillate parallel to the direction of wave travel.

The wave equation

$v = f\lambda$, where $v$ represents wave speed ($\text{m}\,\text{s}^{-1}$), $f$ represents frequency ($\text{Hz}$), and $\lambda$ represents wavelength ($\text{m}$).

components of the electromagnetic spectrum

Radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

Relationship between wavelength and frequency in electromagnetic waves

Inversely proportional according to $c = f\lambda$; as wavelength increases, frequency and photon energy decrease proportionally.

Technological uses across the electromagnetic spectrum

Radio waves: long-range telecommunications; microwaves: wireless networks and radar; infrared: thermal imaging; visible light: fibre-optic communications; X-rays: diagnostic radiography; gamma rays: radiotherapy and instrument sterilisation.

Main anatomical structures of the human eye

Cornea (outer refracting surface), iris and pupil (light admission control), crystalline lens (fine focusing), retina (photoreceptive layer), optic nerve (neural signal transmission), and sclera (protective outer coat).

Four wave phenomena when light meets a boundary

Absorption, specular or diffuse reflection, refraction, and scattering.

Refraction

The change in direction of propagation of a wave caused by a change in speed when entering an optically different medium at an oblique angle.

Direction of light refraction relative to the normal

Light bends toward the normal when entering an optically denser medium (slowing down) and bends away from the normal when entering an optically less dense medium (speeding up).

Path of a light ray through a rectangular glass block

The ray bends toward the normal upon entering the glass from air, bends away from the normal upon exiting into air, and emerges parallel to the incident ray with a sideways lateral displacement.

Applications of reflection, refraction, and total internal reflection

Reflection: plane mirrors and retroreflectors; refraction: magnifying and optical camera lenses; total internal reflection: endoscopes and high-bandwidth fibre-optic cables.

The Big Bang Theory

The cosmological framework stating that the universe originated from an extremely hot, dense singularity approximately $13.8 \times 10^9\,\text{years}$ ago and has been expanding and cooling ever since.

Cosmological red shift as evidence for cosmic expansion

The stretching of light from distant galaxies toward longer, redder wavelengths caused by the expansion of space, demonstrating that distant galaxies are moving away from our vantage point.

Emission spectrum vs. Continuous spectrum

An emission spectrum consists of discrete bright lines produced by excited gas atoms transitioning to lower energy states; a continuous spectrum displays an unbroken band of all wavelengths produced by a dense, glowing thermal source.

Compressions and rarefactions in longitudinal waves

Compressions are high-pressure, high-density zones where medium particles are pressed close together; rarefactions are low-pressure, low-density zones where particles are spread apart.

Oscilloscope representation of pitch and loudness

Pitch corresponds to wave frequency (number of cycles visible horizontally per division); loudness corresponds to wave amplitude (vertical peak-to-equilibrium height).

Acoustic factors affecting musical instrument pitch

The vibrational frequency from string tension and length

Doppler effect

The observed shift in frequency and wavelength of a wave caused by relative motion between the emitting wave source and an observer.

structures of the human auditory system

Outer ear (pinna, auditory canal), middle ear (tympanic membrane, auditory ossicles: malleus, incus, stapes), and inner ear (fluid-filled cochlea and auditory nerve).

Physiological pathway of human hearing

1. Pressure waves deflect the eardrum. 2. Ossicles mechanically amplify the vibrations. 3. Fluid movement inside the cochlea deflects hair cells. 4. Hair cells convert mechanical energy into electrical nerve impulses sent via the auditory nerve to the brain.

Traditional Aboriginal and Torres Strait Islander musical instruments

The didgeridoo (yidaki), a wind instrument made from hollowed eucalyptus producing resonant drone frequencies, and clapping sticks (bilma), used for percussive timing in traditional songlines.

Physical control of pitch in simple acoustic instruments

Altering vibrational frequency by shortening or lengthening the vibrating string or air column, increasing tension, or opening/closing tone holes.

Principles of medical ultrasound imaging

Transducers emit high-frequency acoustic pulses ($>20\,\text{kHz}$) into the body; partial reflections from acoustic impedance boundaries between soft tissues are detected and computationally reconstructed into real-time images.

Advantages of ultrasound compared with diagnostic X-rays

Operates without ionising radiation (making it safe for obstetric imaging), visualises soft-tissue boundaries clearly, and offers real-time physiological motion monitoring.

Ultrasound pulse-echo depth formula

$d = \frac{v \times t}{2}$, where $v$ is acoustic wave speed in tissue, $t$ is the two-way transit time, and division by $2$ accounts for the return path of the echo.

Scalar vs. Vector quantities

A scalar quantity is described completely by magnitude and units alone; a vector quantity requires both magnitude, units, and a specific directional orientation.

Kinematic quantities categorized as scalars vs. vectors

Scalars: distance, speed, time, mass. Vectors: displacement, velocity, acceleration, force.

Distance vs. Displacement

Distance is the total path length traversed by an object regardless of direction (scalar); displacement is the straight-line vector directed from the starting point to the final position.

Velocity

The vector rate of change of displacement with respect to time, mathematically defined as $v = \frac{\Delta s}{\Delta t}$.

Acceleration

The vector rate of change of velocity over an elapsed time interval, mathematically defined as $a = \frac{\Delta v}{\Delta t}$.

Displacement–time graph: physical meaning of the gradient

The slope of the tangent represents instantaneous or average velocity ($\text{gradient} = \frac{\Delta s}{\Delta t} = v$).

Velocity–time graph: physical meaning of the gradient

The slope represents instantaneous or average acceleration ($\text{gradient} = \frac{\Delta v}{\Delta t} = a$).

Velocity–time graph: physical meaning of the area under the curve

The definite integral or geometric area bounded by the curve and time axis represents total displacement ($\text{Area} = \Delta s$).