9th Grade Science Units
Biology units
Neuroscience
What is the brain and what is it made of?
How do scientists study the brain?
What is the structure of the brain? What functions are thought to be performed by different parts of the brain?
How is the structure of a neuron adapted to its function?
How does a reflex action work?
How can scientists use non-invasive techniques to study the brain?(CAT, PET, MRI and fMRI, EEG)
Saving species
Species
A species is a population of related organisms. A species can be defined in a number of ways including: a group of organisms which can interbreed to produce fertile offspring.
Individuals within a species show genetic variation.
All living organisms are classified by kingdom, phylum, class, order, genus, and species.
The scientific name for each organism is Genus species. (e.g. Panthera tigris)
Population
A population is all the individuals of the same species in a particular geographical area.
A community is all of the populations of living organisms in one area. The community forms the biotic environment.
Air, water and soil make up the abiotic environment.
An ecosystem is all the living organisms and non-living factors in a particular part of the environment.
Ecosystems
A food web shows the feeding relationships between organisms in a community.
Producers, consumers and decomposers are related through a food web.
Producers transform energy from the sun into chemical energy in food by photosynthesis.
Energy is passed through a food web as organisms feed on each other.
There is less energy available at each trophic level in a food web.
A pyramid of number shows the size of the population of each species within a particular ecosystem.
Biomass is the mass of living biological organisms in an ecosystem.
A pyramid of biomass shows the biomass of each species within a particular ecosystem.
Factors affecting populations
Birth rate, death rate and migration affect the population size.
A population with little environmental resistance will grow quickly.
Populations can be affected by biotic factors including food, predation, competition and parasites.
Abiotic factors affecting populations include temperature, oxygen, light and toxins.
The carrying capacity is the maximum population of a particular species which can be supported by n ecosystem.
Measuring Populations
Population size is usually measured by taking a sample of the ecosystem.
Plants and sessile animals can be sampled using quadrats and transects.
Motile animals can be sampled using traps and population size estimated by mark-recapture.
Endangered Species
A species is endangered when it is at risk of extinction.
Preserving endangered species
Breeding programmes may help to preserve species which are extinct in the wild or to support wild populations.
Wildlife corridors can connect areas of habitat too small to support viable populations.
Ecological studies can uncover keystone species within a particular community.
Heart and circulation
Describe and explain the role blood plays as a transport system in the body – transporting oxygen, carbon dioxide, heat, food, chemical messengers (hormones) and waste products like urea — as well as a repair and defense system.
Sketch, label and describe the structure and function of the heart.
Sketch, label and describe the function of the main four constituents of blood: red blood cells, white blood cells, platelets and plasma.
Draw and label the structure and function of blood vessels: arteries, veins and capillaries.
Understand the notion of blood pressure and the main causes of low or high blood pressure.
Discuss how scientists investigate causal links between heart disease and various risk factors (smoking, diet etc.)
Discuss scientific solutions to heart problems.
Genetics and inheritance
Inheritance is the transmission of genetic information from generation to generation.
Cells
Cell theory says that all living things are made of cells, that a cell is the smallest unit of structure and function, and that all existing cells come from previously existing cells.
Cells have internal parts, each with a specific function.
Chromosomes and Genes
A chromosome is a strand of DNA, made up of a chain of genes.
Humans have 46 chromosomes in most somatic cells. Different genes are switched on or off within different cells depending on the location and function of the cell.
Human chromosomes exist in homologous pairs. Each pair contains a chromosome from each parent.
A gene is a length of DNA. It is the unit of heredity. A gene can be copied and passed on to the next generation.
An allele is one of two or more alternative forms of a gene.
Sex chromosomes determine the sex of a person and inherited sexual characteristics. A person with two X chromosomes is female and with one X and one Y is male.
Mitosis and Meiosis
Mitosis is cell division that produces genetically identical cells. The number of chromosomes is maintained by the exact duplication of chromosomes. Mitosis is involved in growth, repair of damaged tissues, replacement of worn out cells and asexual reproduction.
A diploid nucleus is a nucleus containing two sets of chromosomes, in somatic cells.
Meiosis produces gametes (sperm and egg cells). The chromosome number is halved from diploid to haploid. A haploid nucleus contains a single set of unpaired chromosomes.
Crossing over and independent assortment which occur during meiosis result in genetic variation, so the cells produced are not all genetically identical.
In sexual reproduction, a zygote is the result of fertilization when the male and female gametes (sperm and egg cell) fuse.
DNA and Proteins
A gene is a part of a chromosome with instructions coded as four different nucleotide bases (A, T, G and C).
These bases form pairs (A with T, G with C)
Replication (copying) of DNA occurs during mitosis.
Cells make proteins according to the coded instructions in the DNA. The types of protein that is made determines the particular phenotypic traits.
(Optional extra detail: When cells make proteins, the DNA first forms mRNA from the chromosomes in the cell nucleus.
Proteins are made from mRNA in the ribosomes of cells.)
Monohybrid inheritance
The Genotype is the genetic makeup of an organism in terms of the alleles present (e.g. Bb or cc).
The Phenotype is the physical and behavioural traits of an organism due to the way the genotype is expressed within a particular environment. Phenotype depends on genotype and environment.
Homozygous is having two identical alleles of a particular gene (e.g. BB or bb). Two identical homozygous individuals that breed together will be pure-breeding.
Heterozygous is having two different alleles of a particular gene (e.g. Bb or Cc).
A dominant allele is always expressed (represented by a capital letter such as B or C).
A recessive allele is only expressed when there is no dominant allele of the gene present (represented by a lower case letter such as b or c)
A monohybrid cross of dominant and recessive alleles gives phenotypes in the ratios 1:1 and 3:1.
Chemistry units
Ions and electrolysis
Atoms
Atoms are built from protons, neutrons and electrons.
The atomic number of an element is the number of protons in its nucleus.
The mass number of an element is the number of protons + the number of neutrons.
The electrons in an atom are arranged in shells which hold 2, 8, 8, 18 electrons. The position of elements in the periodic table reflects the arrangement of electrons.
Atoms with a full outer shell (the noble gases) are chemically stable and unreactive.
A neutral atom has equal numbers of protons and electrons. When the numbers of protons and electrons are not equal, the atom has a positive or negative electric charge and is known as an ion.
Ionic bonding:
Atoms can be held together by bonds.
In forming bonds, atoms can achieve a stable electron arrangement.
Ionic compounds are usually formed when metals combine with non-metals.
The elements which most readily form ions are found in groups 1 and 2 and 6 and 7 in the period table. It’s possible to predict the charge on an ion using the periodic table.
Positive ions (cations) are formed by metal atoms losing electrons. Negative ions (anions) are formed by non-metal atoms gaining electrons.
Some transition metal ions have variable valencies, for example Fe+, Fe+2, Fe+3; Cu+, Cu+2
Compound ions are groups of atoms that form an ion. The most common compound ions are NO3– (Nitrate), SO4-2 (Sulphate), OH– (Hydroxide) and NH4+ (Ammonia).
Ionic bonding is the electrostatic force of attraction between oppositely charged ions.
Ionic compounds consist of giant lattices of positive and negative ions.
Aqueous solutions
Most ionic compounds are soluble in water.
When an ionic compound dissolves, the water separates the positive and negative ions. The separated positive and negative ions are free to move in the solution.
In a precipitation reaction, two ions in solution combine to form an insoluble ionic compound. This insoluble compound appears as a suspension of a solid.
Reduction and oxidation
A “redox” reaction involves transfer of electrons from one atom to another.
One atom is oxidised – it loses electrons.
The other is reduced – it gains electrons.
OILRIG: Oxidation Is Loss; Reduction Is Gain
Electrolytic decomposition is one example of redox reactions.
We can write ionic equations to show how electrons are lost and gained.
E.g. Cu2++ 2e– à Cu
Conductors and insulators
Electricity is a flow of electric charge.
A conductor is a substance which allows electricity to flow through it.
A substance which is not a conductor is an insulator (or non-conductor).
Common conductors:
Metals and graphite conduct electricity because of their free electrons.
Ionic substances conduct if they are molten (liquid) or aqueous (dissolved in water) because the ions are free to move. Molten and aqueous ionic solutions are called electrolytes.
Electrolysis – electrolytic decomposition
Electrolysis is the process of decomposing (breaking apart) a compound by passing an electric current through it.
Electrolysis is carried out by immersing two electrodes in an electrolyte. The electrodes are connected to a battery. The battery provides energy to “pump” electrons through the circuit.
The positive electrode is called the anode. Ions are oxidised at the anode.
The negative electrode is called the cathode. Ions are reduced at the cathode.
Water contains hydrogen (H+) and hxdroxyl (OH–)ions. When it is electrolysed, hydrogen is evolved at the cathode and oxygen at the anode.
When the electrolyte is an aqueous solution, either hydrogen or the metal ion is produced at the cathode, depending on the reactivity of the metal. Oxygen or a non-metal is produced at the anode.
Some common applications of electrolysis include electroplating, refining metals, anodising aluminium, and producing chemicals (hydrogen gas, chlorine gas, sodium hydroxide) from brine (salt water).
Acids and bases
Common acids include sulfuric acid (H2SO4), hydrochloric acid (HCl), nitric acid (HNO3) and ethanoic acid (CH3COOH).
Common alkalis include sodium hydoxide (NaOH), potassium hydoxide (KOH), calcium hydoxide (Ca(OH)2) and ammonium hydoxide (NH4OH).
Acids contain hydrogen ions (H+) in solution.
Alkalis contain hydroxyl ions (OH–) in solution.
Bases are substances which neutralise acids.
Alkalis are bases which are soluble in water.
Metal oxides are bases; non-metal oxides are acidic.
The pH scale is a range of values used to represent the concentration of hydrogen ions in a solution. Neutral solutions have a pH of 7, acids have pH values less than 7 and alkalis have pH values greater than 7.
An indicator is a compound that changes colour in the presence of an acid or a alkali.
An exothermic neutralisation reaction occurs between an acid and a base, producing a metal salt and water.
A salt is a compound containing a metal ion and a negative ion from an acid.
Sulfates are produced in reactions with sulfuric acid; nitrates are produced in reactions with nitric acid; chlorides are produced in reactions with hydrochloric acid.
Acids react with metals to produce a metal salt and hydrogen.
Acids reacts with carbonates to produce a metal salt, water and carbon dioxide.
The concentration of a solution is given in mol/L. A more concentrated solution has more ions dissolved in each unit volume of water.
Titration is a technique for finding the concentration of a solution using a burette.
Rates of reaction
Describe the effect of concentration, particle size, catalysts (including enzymes) and temperature on the speeds of reactions.
Describe a practical method for investigating the speed of a reaction involving gas evolution.
Describe the application of the above factors to the danger of explosive combustion with fine powders (e.g. flour mills) and gases (e.g. mines).
Devise a suitable method for investigating the effect of a given variable on the speed of a reaction.
Interpret data obtained from experiments concerned with speed of reaction.
Describe and explain the effects of temperature and concentration in terms of collisions between reacting particles.
Polymer materials
Covalent bonding
Covalent bonds are strong bonds between non-metal atoms
By sharing electrons, atoms complete their outer shells and become stable
Atoms are held together by electrostatic attraction to shared electrons
We can represent covalent bonding with dot and cross diagrams showing outer shell electrons, Lewis diagrams, or structural formulas
Atoms can bond with single, double or triple covalent bonds, depending how many pairs of electrons are shared.
Hydrocarbons
Hydrocarbons are compounds built only of carbon and hydrogen atoms
Alkanes have only single bonds and the general formula CnH2n+2
Alkenes include at least one double bond and the general formula CnH2n
Organic molecules are named with reference to the longest chain, with additions made to indicate double bonds, methyl or ethyl groups, halides etc.
The number of carbon atoms in the longest chain of a molecule gives the names methane (1C), ethane (2Cs), propane (3Cs), butane (4Cs) etc.
Extra branches are named according to the number of C atoms (methyl, ethyl, propyl, etc.)
Numbers are used to denote the position of the branch, double bond or halide atom (e.g. but-2-ene or 3chloropentane)
Polymers
A polymer is a long chain molecule consisting of thousands of copies of a smaller molecule, or monomer, bonded together.
In addition polymerisation, monomers react to form polymers with no byproduct.
Polymerization of ethene, propene, chloroethene gives the products polyethene (polythene), polypropene and polychloroethene. Equations can be written to show these reactions.
In condensation polymerisation there is a byproduct. The polymerisation of glucose to form starch is an example.
Polymerised materials are typically strong, low density, low melting point, flexible, moldable, stretchy.
Physics units
Physics of road safety (forces and momentum)
Speed, Velocity and Acceleration
In physics, vectors are quantities which have a magnitude and a direction.
Speed is distance travelled/time taken. It is measured in m/s.
Velocity is speed in a particular direction. Velocity is a vector, so it has a direction. It is also measured in m/s.
Acceleration is the change in velocity per unit time. It is measured in m/s/s. An object is accelerating if either its speed or its direction is changing.
Forces and Newton’s Laws
Forces are pushes and pulls. They are interactions between two objects. If I push the table, the table pushes me.
Forces are measured in Newtons. Forces are vectors – they have direction.
Forces cause changes in motion or changes in shape (stretching, compressing, twisting etc.)
Newton’s 1st law (law of inertia): If no unbalanced force acts on an object, the object will continue in the same state of motion, that is, it will either remain at rest, or continue moving in a straight line at constant speed.
Newton’s 2nd law: The unbalanced force on an object is equal to the mass times the acceleration.
Newton’s 2nd law with momentum: Impulse (force X time) = change in momentum.
Newton’s 3rd law: If A pushes B, B pushes back on A with the same force.
Momentum, impulse and collisions
Momentum of an object = mass x velocity. Momentum is a vector and has units of kg m/s or Ns.
Two useful things to do with momentum
Force and motion: An impulse (force x time) changes an object’s momentum. F x t = m Δv. For the same change in momentum, if you increase time, you decrease force. Many car safety features work by increasing stopping time to decrease the forces experienced by humans in cars.
Conservation of momentum: If two objects collide, the total momentum of the objects before the collision is equal to the total momentum of the objects after the collision.
Waves and sound
Waves
A wave transfers energy (but not matter) through a medium.
Mechanical waves can be transferred through water, strings and springs.
The frequency of a wave is the number of oscillations a particular point per second, measured in Hertz.
The wavelength of a wave is measured from one point on a wave to an equivalent point on the next wave.
In a transverse wave, the vibrations are at right angles to the direction of motion of the wave.
In a longitudinal (compressional) wave, the vibrations are in the same direction as the motion of the wave.
The wavespeed is the speed at which a wavefront travels through the medium. The wavespeed of a wave through a particular medium is a constant.
Wave properties include:
reflection from a surface
refraction due to a change of speed
diffraction through gaps and around corners
interference producing areas of higher and lower intensity
The wave equation v = f λ relates wavespeed, frequency and wavelength.
Sound
Sound is produced by a vibrating source.
Sound waves are longitudinal (compressional) waves, with compressions which are areas of high pressure and rarefactions which are areas of low pressure.
The range of human hearing is between approximately 20Hz and 20kHz, and usually decreases with age.
A medium is required in order to transmit sound waves.
The loudness of a sound wave is related to its amplitude.
The pitch of a sound waves is related to its frequency.
A reflection of sound is an echo.
The speed of sound in air is approximately 340m/s. Sound travels faster in liquids and solids.
Standing waves are produced by the superposition of waves travelling down strings, air columns, rods, etc.
The length of the medium is related to the wavelength of the wave.
A node is the point on the standing wave where there is no vibration. An antinode is the point of maximum vibration.
Standing waves can vibrate in different ways (modes), and these produce harmonics, which are related in frequency and wavelength to the fundamental frequency.
Radioactivity
Atomic Structure
An atom consists of protons and neutrons in the nucleus and electrons arranged in shells.
The atomic number of an atom is the number of protons in the nucleus.
The mass number of an atom is the number of neutrons and protons in the nucleus.
One atomic mass unit (amu) is approximately the mass of a neutron or proton.
Isotopes of an element are atoms with the same number of protons but different numbers of neutrons.
Radioactive decay
Unstable isotopes can undergo radioactive decay, emitting energy and matter.
Radioactive decay is a random process: it is impossible to predict when a particular atom will decay.
An alpha particle consists of 2 neutrons and 2 protons, and has a +2 charge and a mass of 4 amu.
A beta particle consists of a fast moving electron and has a charge of -1.
Gamma rays, which are high energy electromagnetic waves, may be emitted during radioactive decay.
Alpha, beta and gamma radiation are ionizing radiation- they create ions as they pass through matter.
Decay equations show the parent and daughter nuclei and other decay products.
Half Life
The activity of a sample of radioactive material is measured in Becquerels where 1 Bq = 1 decay/s
The half life of an isotope is the time for the activity of a sample of a radioactive isotope to fall by ½.
The half life of an isotope is the time for the number of undecayed nuclei in a sample of a radioactive isotope to fall by ½.
Uses of Radioactivity
Radioisotopes are used in medicine for diagnosis and therapy.
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