Grade 7 Science and Technology cheat sheet

Independent variable: the factor the investigator deliberately changes; dependent variable: the factor measured as a result; controlled variables are held constant to make the comparison fair.

Hypothesis: a testable, falsifiable prediction stated before data collection; it must be able to be shown wrong by evidence.

Valid experiment design changes one independent variable at a time and includes a control group that receives no treatment or a standard treatment.

Reliability improves with repeated trials and larger samples; a single measurement cannot establish a pattern.

Accuracy is closeness to the true value; precision is closeness of repeated measurements to each other. A systematic error shifts all readings the same way; random error scatters them.

Mean = sum of values divided by number of values; median = middle value when ordered; mode = most frequent value. The median resists distortion by outliers.

A conclusion must be supported by the data collected and must state whether the hypothesis was supported or rejected; correlation alone does not prove causation.

Metric prefixes: kilo (10^3), centi (10^-2), milli (10^-3), micro (10^-6). Convert by moving the decimal point, and always report units with numbers.

Scientific models and theories are revised when new evidence conflicts with them; peer review and replication are the checks on claims.

Particle model: all matter is made of particles in constant motion; solids vibrate in fixed positions, liquids slide past each other, gases move freely and far apart.

Physical change alters form or state without forming a new substance (melting, dissolving, cutting); chemical change produces new substances with different properties.

Signs of a chemical reaction: new colour, gas bubbles, precipitate, temperature change, light, or a new odour not present before.

Density = mass / volume, usually in g/cm^3; density is a property of the material and does not change with sample size.

Pure substances have fixed melting and boiling points; mixtures can be separated by filtration (insoluble solid), evaporation, distillation (different boiling points), or magnetism.

Atoms combine into molecules; elements contain one kind of atom, compounds contain two or more elements chemically bonded in fixed ratios.

Conservation of mass: in a closed system, total mass before a reaction equals total mass after, because atoms are rearranged, not created or destroyed.

Acids have pH below 7 and turn blue litmus red; bases have pH above 7 and turn red litmus blue; pH 7 is neutral.

Properties used to choose materials include strength, hardness, conductivity, flexibility, melting point, and resistance to corrosion or water.

Speed = distance / time; velocity includes direction; acceleration = change in velocity / time, in m/s^2.

Newton's first law: an object stays at rest or in uniform motion unless a net force acts on it; this is inertia.

Newton's second law: net force = mass x acceleration (F = ma). Doubling force doubles acceleration; doubling mass halves it for the same force.

Newton's third law: every action force has an equal and opposite reaction force acting on a different object.

Friction opposes relative motion, converts kinetic energy to heat, and depends on surface type and pressing force.

Gravity on Earth accelerates falling objects at about 9.8 m/s^2 downward, ignoring air resistance; weight = mass x gravitational field strength.

Work = force x distance moved in the direction of the force, in joules; power = work / time, in watts.

Kinetic energy = 1/2 mv^2; gravitational potential energy = mgh. Energy is conserved but transforms and spreads as heat.

Simple machines (lever, pulley, inclined plane, wheel and axle) trade force for distance; no machine creates energy.

Cell theory: all living things are made of cells, the cell is the basic unit of life, and new cells arise from existing cells.

Plant cells have a cell wall, chloroplasts, and a large central vacuole; animal cells lack these but both have a nucleus, cytoplasm, and cell membrane.

Mitochondria release energy from glucose by respiration; ribosomes build proteins; the nucleus holds DNA and directs activity.

Levels of organisation: cell, tissue, organ, organ system, organism.

Digestive system breaks food into absorbable nutrients; small intestine absorbs most nutrients, and villi increase surface area.

Circulatory system: heart pumps blood through arteries away from the heart and veins toward it; capillaries exchange gases and nutrients with cells.

Respiratory system exchanges oxygen and carbon dioxide in the alveoli; gas moves by diffusion from high to low concentration.

Health depends on nutrition, exercise, sleep, hygiene, and avoiding harmful substances; vaccines train the immune system using weakened or inactive antigens.

Communicable diseases spread by pathogens through air, water, food, contact, or vectors; hygiene and clean water reduce transmission.

Producers capture energy by photosynthesis; consumers eat other organisms; decomposers break down dead matter and recycle nutrients.

Food chains show one path of energy flow; food webs show many interconnected paths. Arrows point in the direction of energy transfer.

Only about 10% of energy passes to the next trophic level; the rest is lost as heat and in waste, so food chains rarely exceed four or five links.

Population size is limited by food, water, shelter, disease, and predators; carrying capacity is the maximum a habitat can sustain.

Symbiosis: mutualism benefits both species, commensalism benefits one with no effect on the other, parasitism benefits one and harms the other.

Biodiversity includes genetic, species, and ecosystem variety; it increases ecosystem resilience to change and disease.

Habitat loss, pollution, invasive species, overharvesting, and climate change are leading causes of biodiversity decline.

Carbon cycle: photosynthesis removes carbon dioxide; respiration, combustion, and decomposition release it. Nitrogen is fixed by bacteria and lightning.

Sustainable practices include reducing waste, recycling, renewable energy, and protecting habitats and corridors.

Earth's rotation on its axis (about 24 hours) causes day and night; its revolution around the Sun (about 365.25 days) with a tilted axis causes seasons.

Moon phases result from the changing angle between Earth, Moon, and Sun; a full cycle takes about 29.5 days.

Solar eclipse: Moon between Earth and Sun. Lunar eclipse: Earth between Sun and Moon.

Gravity keeps planets in orbit; inner planets are small and rocky, outer planets are large and gas- or ice-rich.

Rock types: igneous forms from cooled magma or lava, sedimentary from compacted deposits, metamorphic from heat and pressure on existing rock.

Plate tectonics: moving plates cause earthquakes, volcanoes, mountain building, and sea-floor spreading at boundaries.

Water cycle steps: evaporation, transpiration, condensation, precipitation, runoff, and collection; the Sun supplies the energy.

Weather is short-term atmospheric condition; climate is the long-term average pattern of an area.

Fossils and rock layers give relative ages; sedimentary layers are usually oldest at the bottom unless overturned.

Design cycle: identify the problem and constraints, research, generate ideas, select, build a prototype, test, evaluate, and redesign.

Criteria are the goals a design must meet; constraints are limits such as budget, materials, time, safety, and size.

A prototype is an early working model used to test ideas cheaply before full production.

Fair testing in design: change one variable, keep others constant, and measure performance with a consistent method.

Trade-offs are unavoidable: improving one property (strength, weight, cost) often worsens another.

Iteration improves designs; failure data are useful evidence, not a reason to stop.

Technical drawing conventions: top, front, and side views; scale; dimensions with units; labels for materials.

Appropriate technology fits the user, local materials, cost, and maintenance skills; automation can raise output but needs energy and repair support.

Science seeks explanations through evidence and testing; technology applies scientific knowledge to solve practical problems; engineering designs the solutions.

A scientific claim becomes accepted through replication, peer review, and consistency with existing evidence, not by authority alone.

Risk assessment compares the likelihood and severity of harm against the benefit of a technology.

Renewable resources (solar, wind, hydro, biomass) replenish quickly; non-renewable resources (coal, oil, minerals) are finite.

Life-cycle thinking considers extraction, manufacture, use, disposal, and recycling when judging environmental impact.

Ethical issues in science include informed consent, privacy of data, animal welfare, and fair access to benefits.

Bias can enter through sample selection, funding influence, or how results are reported; independent replication reduces it.

Technology transfer and access affect equity; solutions must suit local culture, economy, and infrastructure to be adopted.