Exhaustive Guide to Year 9 Science: Biology, Chemistry, and Physics

Environmental and Inherited Variation

• Environmental Factors: An organism's surroundings are its environment, which contains environmental factors that can change the organism. These are divided into:

  • Abiotic factors (physical environmental factors): Examples include temperature, amount of light, water, and mineral salts.

  • Biotic factors: Activities of other organisms, such as competition, predation, and infectious diseases.

• Variation: The differences between the characteristics of organisms.

• Environmental Variation: Variation caused by an organism's surroundings. In humans, examples include scars (caused by physical factors) and hairstyles (caused by social factors like fashion).

• Inherited Variation: Variation in characteristics passed from parents to offspring. Examples include eye colour, dimpled chins, and blood groups.

• Types of Variation Data:

  • Continuous Variation: Variation that can have any value between two points (e.g., human height). This usually results in a normal distribution, shown as a 'bell shape' on a bar chart or graph.

  • Discontinuous Variation: Variation that can only have a value from a limited set of possible values (e.g., blood groups A, B, AB, or O). This is plotted on a bar chart with gaps between the bars.

• Classification: The process of sorting organisms into groups. The smallest group is the species. Members of the same species can reproduce with each other, and their offspring are also fertile.

Genetic Information and DNA

• DNA (Deoxyribonucleic Acid): The substance found in cells that stores genetic information.

• Discovery of DNA Structure:

  • James Watson and Francis Crick: Built a cardboard model of DNA in 1953 after discovering its secondary structure.

  • Rosalind Franklin and Maurice Wilkins: Used X-rays to take photos of DNA (such as Photo B, a blurry X-shape). Watson realized this pattern meant the molecule was a spiral.

• Chromosomes: Structures found in the nuclei of cells. Each contains one long DNA molecule. Humans typically have 23 pairs (46 total).

• Genes: Sections of a DNA molecule that control inherited characteristics. Specific traits like ABO blood groups are controlled by one gene, while most characteristics (like height) are controlled by many genes.

• Sex Determination: Determined by the 23rd pair of chromosomes. Females have two X chromosomes ($XX$); males have one X and one smaller Y chromosome ($XY$).

• Reproduction: Gametes (sperm and egg) contain only 23 chromosomes. During fertilisation, they fuse to form a zygote with 46 chromosomes.

Natural Selection and Evolution

• Natural Selection: A process where individuals with certain inherited variations are more likely to survive and reproduce.

  • Example: Peppered Moths: In Manchester during the 1800s, soot from factories turned trees black. Black moths were harder for predators to spot than pale moths, leading to an increase in the black moth population.

  • Example: Tilapia in the Salton Sea: As the sea became 25% saltier than the ocean, fish with genetic variations allowing them to tolerate high salt survived and reproduced.

• Evolution: A change over time in the characteristics of organisms. Charles Darwin and Alfred Russel Wallace developed the hypothesis that natural selection causes evolution.

• Extinction: When an organism no longer exists. Causes include habitat destruction, climate change, competition, and disease.

  • Thylacines: Last one died in 1936 in Tasmania.

  • Preserving Biodiversity: Methods include nature reserves, breeding programmes, and gene banks (storing seeds or gametes at low temperatures).

Plant Biology and Photosynthesis

• Photosynthesis: The process by which plants make their own food.

  • Reactants: Carbon dioxide and water.

  • Products: Glucose and oxygen.

  • Equation: $6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$

  • Chlorophyll: Contained in chloroplasts; traps energy transferred by light.

  • Limiting Factors: Variables that slow the rate of photosynthesis, such as shortage of light, water, or carbon dioxide.

• Aerobic Respiration: The process used by plant cells to release energy from glucose (the opposite of photosynthesis).

  • Equation: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O$

  • ATP: Molecules that store energy for a cell until needed.

• Plant Adaptations:

  • Roots: Branched and spread out to absorb water and mineral salts (nitrogen for proteins, magnesium for chlorophyll, potassium for water absorption). Root hair cells provide a large surface area.

  • Xylem: Hollow tubes made of dead cells that carry water and minerals.

  • Phloem: Chains of living cells that carry sugar solutions.

  • Stomata: Small holes in leaves for gas exchange, controlled by guard cells.

Farming and Food Production

• Boosters for Yield:

  • Fertilisers: Contain nitrates, phosphates, and potassium.

  • Pesticides: Include insecticides (kill insects), fungicides (kill fungi), and herbicides (kill weeds).

  • Selective Breeding: Choosing plants with specific characteristics to breed over many generations to create new varieties.

• Environmental Problems:

  • Eutrophication: Fertilisers wash into water, causing algae to grow rapidly. Bacteria then decompose dead material, using up oxygen and killing fish.

  • Biomagnification: Toxins (like mercury) increase in concentration as they move up the food chain.

• Sustainable Development: Developing human needs without destroying habitats.

• Organic Farming: Using natural fertilisers (manure), crop rotation, and biological control (e.g., hoverfly larvae to eat aphids) instead of artificial chemicals.

Human Health and Immune System

• Pathogens: Microorganisms that cause disease (bacteria, viruses, fungi, protoctists).

• Immune Response:

  • Phagocytes: Ingest and digest microorganisms.

  • Lymphocytes: Produce specific antibodies (proteins that stick to pathogens) and memory cells.

• Vaccines: Contain parts of a pathogen's surface to trigger antibody production and memory cell formation, leading to immunity without causing the disease.

• Pandemic: An infectious disease that spreads across several countries in a short time (e.g., Ebola, SARS, Bird Flu).

• Surface Area to Volume (SA:V) Ratio: Crucial for exchange. Unicellular organisms have large ratios. Large organisms need transport systems.

  • $SA:V \text{ ratio} = \frac{\text{Surface Area}}{\text{Volume}}$

Chemistry: Materials and Reactions

• Ceramics: Hard, brittle, unreactive, and heat-resistant materials (e.g., china, glass, bricks). They have a lattice structure with many strong bonds.

• Polymers: Long chains of repeating monomer groups.

  • Vulcanisation: Heating rubber with sulfur to create cross-links, making it harder and heat-resistant.

  • Addition Polymerisation: Small monomers add together to form chains (e.g., ethene to poly(ethene)). This reaction is often exothermic.

• Composites: Combinations of two or more materials (e.g., reinforced concrete, carbon fiber, GRP).

• Thermal Decomposition: Breaking down a compound using heat (e.g., $CaCO_3(s) \rightarrow CaO(s) + CO_2(g)$). This is an endothermic reaction.

• Pollutants: Combustion of fossil fuels releases $CO_2$ (greenhouse effect), $CO$ (incomplete combustion), and $SO_2$ (acid rain).

Reactivity and Metal Extraction

• Reactivity Series: Metals ranked by how vigorously they react with water, acids, and oxygen (Potassium is high; Gold is low).

• Displacement Reactions: A more reactive metal takes the place of a less reactive one in a compound (e.g., $Aluminium + Iron\,Oxide \rightarrow Aluminium\,Oxide + Iron$).

• Redox Reactions: Simultaneous oxidation (gain of oxygen) and reduction (loss of oxygen).

• Extraction Methods:

  • Heating with Carbon: For metals less reactive than carbon (e.g., Iron in a blast furnace: $Fe_2O_3 + 3C \rightarrow 2Fe + 3CO$).

  • Electrolysis: For highly reactive metals (e.g., Aluminium from bauxite).

Physics: Forces, Motion, and Energy

• Resultant Force: The difference between forwards and backwards forces. Unbalanced forces cause acceleration ($F = ma$).

• Terminal Velocity: The constant maximum speed reached when drag/air resistance balances the weight of a falling object.

• Energy Stores: Chemical, Kinetic, Gravitational Potential (GPE), Elastic Potential, Internal (Thermal), Nuclear.

• Energy Transfer: Heating, Electricity, Light, Sound.

• Efficiency: $\frac{\text{Useful Energy Transferred}}{\text{Total Energy Transferred}} \times 100$

• Speed: $\text{Speed} = \frac{\text{Distance}}{\text{Time}}$

• Moments: The turning effect of a force.

  • $\text{Moment (N m)} = \text{Force (N)} \times \text{Perpendicular distance from pivot (m)}$

• Work Done: $\text{Work (J)} = \text{Force (N)} \times \text{Distance moved (m)}$

Force Fields and Electricity

• Magnetic Fields: Space where non-contact magnetic forces act. Opposite poles ($N-S$) attract; like poles ($N-N$) repel.

• Gravitational Fields: Space where mass attracts mass. On Earth, $g \approx 10\,N/kg$.

  • $\text{Weight (N)} = \text{Mass (kg)} \times g\,(N/kg)$

• Electric Fields: Space around charged objects. Static electricity is caused by the transfer of electrons through rubbing.

• Circuits:

  • Series: Current is the same everywhere; voltage is split.

  • Parallel: Current splits at junctions; voltage is the same across branches.

• Resistance: Measures how difficult it is for current to flow.

  • \text{Voltage (V)} = \text{Current (A)} \times \text{Resistance (\Omega)}

• Electromagnets: A coil of wire with a current. Strength is increased by more coils, higher current, or a magnetic core.

Science Skills and Statistics

• Averages:

  • Mean: Total sum divided by the number of values.

  • Mode: Most common value.

  • Median: Middle value in an ordered set.

• Standard Form: $A \times 10^n$ (where $1 \le A < 10$).

• Probability: The chance of something happening, shown as a decimal ($0$ to $1$) or percentage ($0\%$ to $100\%$).

• Quartiles: Lower quartile ($LQ$) is 1/4 into the data; Upper quartile ($UQ$) is 3/4.

  • $\text{Interquartile Range} = UQ - LQ$

• Significant Figures: Rounding based on the first non-zero digit.

• Peer Review: Evaluation of scientific papers by other experts to check for mistakes or invalid conclusions.