Acceleration is any change in speed or direction. It is measured in metres per second per second (m/s/s).
air resistance
A force that resists an object's motion through air
Air resistance is a contact force caused by collisions between the object and air molecules.
applied force
A type of force exerted by a person, animal or machine
When a person kicks a ball, an applied force acts between their foot and the ball.
balanced force
A force with an equal and opposite force acting on the same object
Balanced forces cancel out and do not cause an object to accelerate.
collision force
A contact force that acts on an object when it hits another object
The collision forces on both objects are equal and opposite, and exist only so long as the objects are touching.
contact force
Any force that can only occur when two objects are touching
Contact forces include friction, air resistance and applied forces.
first law of motion
An object has a constant velocity unless acted on by a net force
An object will keep moving at the same speed in the same direction unless acted on by a net force (law of inertia).
force
A push or pull
A force (F) causes an object to accelerate unless it's balanced by an equal and opposite force.
free body diagram
A representation of all the forces acting on an object
The object is represented as a box. The forces acting on it are drawn as arrows radiating from the box.
friction
A force that resists an object's motion
Friction is a contact force. It is larger on rough or sticky surfaces.
gravity
The attractive force between any two objects that have mass
The force of gravity depends on the sizes of the masses and the distance between them.
inertia
The natural tendency of an object to maintain a constant velocity
Any object will stay at rest, or keep moving at the same velocity, unless acted on by a net force.
mass
The amount of matter in an object
Mass (m) is measured in the standard unit of kilograms (kg). An object's mass does not depend on gravity.
net force
The overall force on an object
The net force is calculated by cancelling out any balanced forces and adding or subtracting the remaining forces.
newton
The standard unit of force
The newton (N) is named after Isaac Newton. 1 N is the force needed to give a mass of 1 kg an acceleration of 1 m/s/s.
non-contact force
Any force that can occur even when two objects are not touching
Non-contact forces include gravity, magnetism and electrostatic forces.
reaction force
The force that is paired with another force by the third law of motion
The paired forces are of the same size and type, but acting on different objects in opposite directions.
second law of motion
Net force equals mass times acceleration
An object's acceleration is directly proportional to the net force acting on it, and inversely proportional to its mass.
speed
The rate of change of an object's position
Speed is calculated by measuring the distance travelled during a certain time.
support force
An upward force exerted on an object by a solid surface
The upward support force balances gravity and prevents the object from falling.
tension
A force that pulls inward when a solid object is stretched
Tension is a contact force that can prevent a stretched rope from breaking.
third law of motion
Every force has an equal and opposite reaction force
Forces always come in pairs of the same size and type, but acting on different objects in opposite directions.
thrust
A force that acts on an object when it shoots out a jet of liquid or gas
Thrust is a reaction force that moves objects such as rockets and jet skis by jet propulsion.
unbalanced force
A force without an equal and opposite force acting on the same object
Unbalanced forces result in a net force that causes an object to accelerate.
velocity
The speed of an object in a certain direction
Velocity is different from speed because it must have a specific direction. A stationary object has zero velocity.
water resistance
A force that resists an object's motion through water
Water resistance is a contact force caused by collisions between the object and water molecules.
weight
The force of gravity on an object
Weight depends on mass and gravitational field strength. A 1 kg mass weighs 9.8 N on Earth but only 1.6 N on the Moon.
abiotic factor
A non-living thing in an ecosystem
Abiotic factors include sunlight, water, sand and rocks.
biodiversity
The variety of living things in a particular area
High biodiversity makes an ecosystem more resilient because there are many species that can play the same role.
biotic factor
A living thing in an ecosystem
Biotic factors include corals, sea jellies, whales and seabirds.
carbon cycle
The continual movement of carbon through ecosystems
The carbon cycle involves processes such as photosynthesis, respiration and decomposition.
cellular respiration
The reaction in living cells that releases energy for life processes
Cellular respiration converts sugar and oxygen into water and carbon dioxide, releasing usable energy.
chemical energy
The energy stored in molecules
Chemical energy is stored in food and released for use by cells through cellular respiration.
commensal
Benefiting one species while the other species is not affected
The emperor shrimp rides on the nudibranch and picks up food. This does not appear to affect the nudibranch.
consumer
An organism that gets its food by eating other organisms
Animals are examples of consumers because they must eat other living things for energy.
contaminant
A harmful substance in the environment or in living things
Car exhaust and petrol can be sources of contaminants such as sulfur, heavy metals and carbon monoxide.
decomposer
An organism that breaks down dead matter by releasing chemicals
Nudibranchs and sea cucumbers decompose waste and dead matter on the sea floor.
ecology
The scientific study of ecosystems, a branch of biology
Ecologists investigate the relationships between organisms in an ecosystem and their dependence on non-living things.
ecosystem
A collection of organisms interacting with each other and their environment
A coral reef ecosystem includes a wide variety of living things and their non-living environment.
energy
The ability to move, grow and function
Producers get energy from sunlight, while consumers get energy by eating other organisms.
food chain
One pathway of energy transfer between organisms
The arrows in a food chain show the transfer of energy from one type of organism to another.
food web
Connected pathways of energy transfer between organisms
A food web is built by connecting all the food chains in a particular ecosystem.
matter
Any substance that takes up space and has mass
Matter is cycled through ecosystems by processes such as photosynthesis, respiration, feeding and decomposition.
mutualistic
Benefiting both species
When cleaner fish eat algae from turtles, the cleaner fish get food and the turtles have their bodies cleaned.
parasitic
Benefiting one species while the other species is harmed
Lampreys use their curved teeth to latch on to fish and then suck the blood of their victims.
photosynthesis
The reaction in producers that transforms light energy into chemical energy
Photosynthesis produces sugar molecules that store chemical energy to support life processes.
producer
An organism that makes its own food by harnessing sunlight energy
Producers store the Sun's energy via photosynthesis, providing food for consumers.
resilience
The ability to recover after a change
Resilient ecosystems can recover after disruptive changes, such as bushfires, droughts or oil spills.
species
A group of similar organisms that can breed with each other
The Emperor penguin is one of at least 16 species of penguin on Earth.
symbiosis
A long-term relationship between species where at least one benefits
Symbiotic relationships may be mutualistic, parasitic or commensal. Clownfish and sea anemones have a mutualistic relationship.
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acquired trait
A feature that is gained during an individual's lifetime
Acquired traits, such as scars and learned skills, cannot result in the evolution of a population.
adaptation
A genetic trait that helps an organism survive in its environment
Better adapted organisms have a greater chance of reproducing and passing their genes to the next generation.
antibiotic
A medicine that kills bacteria or prevents their growth
Antibiotics are used to treat diseases caused by bacteria. They have saved countless lives since their discovery.
antibiotic-resistant
Able to survive in the presence of antibiotics
Some bacteria have evolved antibiotic resistance and are known as superbugs.
behavioural adaptation
A behaviour or action that helps an organism survive
Behavioural adaptations include migrating, burrowing and building dams or nests.
common ancestor
A species that two or more other species have evolved from
The common ancestor of humans and sharks lived about 470 million years ago.
competition
The struggle between organisms for resources, such as food or mates
Competition means that many organisms will not survive long enough to reproduce.
DNA
A molecule that contains genetic information
DNA is stored in the nucleus of a plant or animal cell. It is passed on to offspring during reproduction.
ecosystem
A collection of organisms interacting with each other and their environment
A coral reef ecosystem includes a wide variety of living things and their non-living environment.
evolution
A change in the genetic traits in a population over many generations
Evolution occurs over generations through repeated genetic variation, natural selection and reproduction.
evolutionary tree
A diagram that shows how species are related
An evolutionary tree shows how related species evolved from common ancestors.
extinction
The dying out or complete disappearance of a species
A species is said to be extinct when the last individual of that species has died.
gene
A unit of genetic information
A gene is a section of a DNA molecule that provides instructions for building a specific protein.
genetic diversity
The amount of genetic variation in a population
Genetic variation is needed for evolution because it makes some individuals better adapted to the environment than others.
genetic trait
A feature that can be passed down by genes to the next generation
Genetic traits, such as neck length and fur colour, can result in the evolution of a population.
inheritance
The passing down of traits via genes from one generation to the next
The inheritance of traits via sexual reproduction explains family resemblances.
mutation
A small random change in an organism's DNA
Mutations can be passed on to offspring through reproduction, increasing the genetic variation in a population.
natural selection
The survival of organisms that are better adapted to their environment
Over generations, natural selection causes a population to evolve in response to its environment.
population
A group of organisms of the same species living in the same place
Different populations of the same species can be found in different regions around the world.
selection pressure
A challenge that affects an organism's ability to survive and reproduce
Selection pressures include hunting by predators, access to resources, diseases and weather conditions.
speciation
The formation of a new species
Speciation occurs when a population splits into two isolated populations that evolve under different selection pressures.
species
A group of similar organisms that can breed to produce fertile offspring
The ability to reproduce allows a species to continue to exist and evolve.
structural adaptation
A physical feature of the body that helps an organism survive
Structural adaptations include scales, fur, feathers, long tails and bright colours.
trait
A feature of an organism
Traits include physical features, such as tail length and eye colour, and behaviours, such as nest building.
variation
A difference in traits between individuals of the same species
Variations in genetic traits arise because of mutations. Some traits provide an advantage for survival or reproduction.
adenine
The base that combines with thymine to form a base pair
Adenine is one of the four letters that make up the genetic code in humans and other living things.
allele
A version of a gene
An organism gets two alleles of each gene – one from its mother and one from its father.
amino acid
A small molecule that joins with others to form proteins
Amino acids are the building blocks of proteins, which are the building blocks of cells.
anaphase
A stage of cell division in which the chromosomes separate
Anaphase is when the chromosomes separate and are pulled away from each other to opposite sides of the cell.
base
Part of a DNA molecule that comes in four types: A, C, G and T
Bases join together in pairs to form the 'rungs' of the DNA molecule.
base pair
Two bases joined together
Base pairs form in only two combinations: A-T or G-C. These are the letters that make up the genetic code.
cell cycle
The repeated process of cell growth and division
During most of the cell cycle, a cell grows and performs its function. This ends when the cell divides by mitosis.
cell division
The splitting of a cell to form new cells
Cell division allows organisms to grow, repair damage and reproduce. There are two types: mitosis and meiosis.
chromosome
A DNA molecule that condenses during cell division
Most human cells contain 46 chromosomes but sex cells only contain 23 chromosomes.
crossing over
The swapping of genes between chromosomes in a homologous pair
Crossing over only occurs in meiosis, during prophase I. It increases the genetic variety of the sex cells produced.
cytosine
The base that combines with guanine to form a base pair
Cytosine is one of the four letters that make up the genetic code in humans and other living things.
daughter cell
Any new cell formed by cell division
Each daughter cell has its own nucleus and set of DNA.
DNA
A molecule that contains genetic information
DNA, or deoxyribonucleic acid, is a very large molecule that contains instructions for building proteins.
dominant allele
A version of a gene that is expressed even when only one copy is present
A dominant allele is represented by an uppercase letter. Yy or YY will result in the appearance of the Y trait.
dominant trait
A feature that appears when at least one allele is present
Dominant traits include freckles, dimples and the ability to roll your tongue.
fertilization
The joining of an egg and a sperm to form a new organism
Fertilization combines DNA from the mother and father so the child gets half of its chromosomes from each parent.
gene
A unit of genetic information
A gene is a section of a DNA molecule that provides instructions for building a specific protein.
generation
Members of a family that are born and live at about the same time
Traits are passed down from one generation to the next by the transfer of DNA from parents to children.
genotype
A pair of alleles that influence the appearance of a particular trait
A genotype is represented by two letters. An organism's genotype determines which traits it acquires – its phenotype.
guanine
The base that combines with cytosine to form a base pair
Guanine is one of the four letters that make up the genetic code in humans and other living things.
heterozygous
A genotype in which the two alleles are different
A heterozygous genotype consists of one dominant allele and one recessive allele – Yy.
homologous pair
Two chromosomes that contain versions of the same genes
One chromosome in a homologous pair is inherited from the mother and the other from the father.
homozygous
A genotype in which the two alleles are the same
A homozygous genotype consists of either two dominant alleles – YY – or two recessive alleles – yy.
inheritance
The passing down of traits via genes from one generation to the next
The inheritance of traits via sexual reproduction explains family resemblances.
interphase
The stage of the cell cycle in which a cell grows and copies its DNA
Interphase covers most of a cell's life span, while it is growing and performing its normal function in the body.
meiosis
A type of cell division that produces sex cells for reproduction
Meiosis produces egg and sperm cells. One cell divides into four sex cells by two cycles of cell division.
metaphase
A stage of cell division in which the chromosomes line up
Metaphase is when the chromosomes line up in the middle of the cell.
mitosis
A type of cell division that produces cells for growth and repair Base pairs form in only two combinations: A-T or G-C. These are the letters that make up the genetic code.
mutation
A permanent change in the sequence of bases that make up a gene
Some mutations are harmless while others cause disease. Mutations can be inherited by offspring.
parent cell
Any cell that divides to form new cells
A parent cell needs to copy its DNA before dividing so that it can be passed down to its daughter cells.
pedigree
A family tree that shows how a trait is passed down through generations
In a pedigree, filled symbols show the presence of a trait and open symbols show its absence.
phenotype
The collection of traits observable in an organism
A phenotype includes traits such as tall, purple flowers and yellow seeds. It is determined by the organism's genotype.
prophase
A stage of cell division in which the chromosomes condense
Prophase is when the cell prepares to divide. The chromosomes condense and the nucleus starts to break down.
protein
A large molecule made up of amino acids
Proteins form structures and perform functions in an organism. DNA contains instructions for building proteins.
recessive allele
A version of a gene that is only expressed when two copies are present
A recessive allele is represented by a lowercase letter. Only yy will result in the appearance of the y trait.
recessive trait
A feature that only appears when two alleles are present
Recessive traits include cleft chins, attached earlobes and hitchhiker's thumbs.
sex chromosome
A chromosome that helps determine an organism's gender
Sex chromosomes come in two types: X or Y. Most females have two X chromosomes while most males have an X and a Y.
simple inheritance
When the appearance of a trait is controlled by a single gene
Many traits are influenced by lots of genes but some, like albinism, are controlled by single genes.
telophase
A stage of cell division in which two nuclei form
Telophase is when two new nuclei form, each with its own set of DNA.
thymine
The base that combines with adenine to form a base pair
Thymine is one of the four letters that make up the genetic code in humans and other living things.
trait
A feature of an organism
Traits include height, hair colour, skin colour and freckles.
Note
Studied by 23 people