not as good SCIENCE REVISION

Scientific method

A repeatable, evidence-based framework used to investigate phenomena and answer questions systematically. It proceeds through seven structured stages: observing and questioning, researching existing knowledge, formulating a testable hypothesis, conducting a controlled experiment, recording quantitative and qualitative results, drawing evidence-based conclusions, and evaluating or communicating findings.

Independent variable

The single condition or factor deliberately altered or manipulated by the experimenter to test its effect on a system (e.g., varying water temperature to examine sugar dissolving rate). It is plotted on the horizontal x-axis of a standard graph.

Dependent variable

The factor that is measured, counted, or observed to assess the effect of changing the independent variable (e.g., recording the time required for sugar to dissolve completely). It responds to experimental changes and is plotted on the vertical y-axis of a standard graph.

Controlled variables

All extraneous conditions and factors deliberately kept constant throughout every trial of an experiment (e.g., maintaining identical liquid volume, stirring rate, and container type). Controlling them ensures a fair test and maintains experimental validity.

Accuracy

The closeness of an experimental measurement to the true or accepted reference value. It is improved by using properly calibrated equipment (such as a digital analytical balance instead of kitchen scales) and reading instrument scales directly at eye level to eliminate parallax error.

Precision vs. accuracy

Two distinct qualities of experimental data: precision describes how closely grouped repeated measurements are to one another, reflecting consistency, whereas accuracy describes how close a value is to the true standard. Data can be highly precise yet inaccurate if equipment has an uncorrected systematic bias.

Validity

The extent to which an investigation truly tests the specific hypothesis it was designed to evaluate. It is maintained by testing only one independent variable at a time while strictly controlling all other potential variables.

Reliability

The consistency and reproducibility of experimental results across repeated trials. It is evaluated by checking if findings remain consistent and is improved by conducting multiple trials, increasing sample size, and calculating an average to reduce the impact of random errors.

Random error

An unpredictable, chance variation that causes individual measurements to differ unpredictably from the true value, such as slight variations in human reaction time when using a stopwatch. Its impact is reduced by performing repeat trials and calculating an average.

Systematic error

A consistent, repeatable flaw that biases measurements by the exact same amount or direction each time (e.g., a balance scale reading $5\,\text{g}$ too high due to improper zeroing). It cannot be fixed by repeating trials or averaging, and requires recalibrating equipment or modifying the method.

Hypothesis

A testable, falsifiable scientific prediction proposing an expected cause-and-effect relationship, typically structured as 'If [independent variable changes], then [dependent variable result], because [scientific reasoning]'. It is never considered proven, only supported or refuted by empirical evidence.

Line graph

A graphical representation used when both the independent and dependent variables consist of continuous numerical data. Data points are plotted on evenly scaled axes and fitted with a smooth curve or straight line of best fit to illustrate relationships, rates of change, and continuous trends.

Heat

Thermal energy that naturally transfers from an object of higher temperature to an object of lower temperature through conduction, convection, or radiation until thermal equilibrium is achieved. It differs from temperature, which measures the average kinetic energy of the constituent particles.

Transverse vs. longitudinal waves

Two fundamental wave types classified by particle motion relative to energy propagation: in transverse waves (e.g., light and water ripples), particles oscillate perpendicular (at right angles) to the direction of wave travel; in longitudinal waves (e.g., sound), particles oscillate parallel to the direction of energy propagation, creating alternating compressions and rarefactions.

Wave speed formula

The mathematical equation $v = f \times \lambda$, where $v$ represents wave speed in meters per second ($\text{m/s}$), $f$ represents wave frequency in hertz ($\text{Hz}$), and $\lambda$ represents wavelength in meters ($\text{m}$). It can be rearranged to calculate frequency ($f = \frac{v}{\lambda}$) or wavelength ($\lambda = \frac{v}{f}$).

Gene

A distinct segment of DNA along a chromosome that contains the specific sequence of nucleotide bases coding for the synthesis of a single protein or polypeptide chain. Humans carry approximately $20{,}000$ genes that determine structural and biochemical traits.

Natural selection

The primary evolutionary mechanism proposed by Charles Darwin by which populations adapt to their environment over generations. It follows five successive stages: genetic variation within a population, overproduction leading to competition, differential survival of individuals with advantageous adaptations, higher reproductive success among survivors, and inheritance of beneficial alleles by offspring.

Mutation

A permanent alteration in the nucleotide sequence of an organism's DNA, arising from replication errors or exposure to environmental mutagens (such as ultraviolet radiation, X-rays, or toxic chemicals). Mutations serve as the original source of new alleles and can have neutral, harmful, or beneficial effects.

Karyotype

An organised photographic arrangement of an individual's complete set of chromosomes isolated during cell division and paired from largest to smallest. It displays $22$ pairs of autosomes and $1$ pair of sex chromosomes ($\text{XX}$ or $\text{XY}$), allowing scientists to verify biological sex and diagnose numerical chromosomal abnormalities such as Down syndrome (trisomy $21$).

Punnett square

A grid diagram used in genetics to predict the probable genotypic and phenotypic ratios of offspring resulting from a cross. Alleles contributed by parental gametes are listed along the borders, and the grid boxes are filled to display all potential allelic combinations produced during fertilisation.