Sciences générales : systèmes vivants, matériaux, ondes et preuves
GAC Sciences Sujet 2 23:58 Narration en anglais · Sous-titres anglais + 中文 incrustés
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Imagine a pond beside a school. You see plants, water and a label describing a treatment. What can you establish from those observations? Plants do not prove that water is safe to drink, and a lower concentration after treatment does not prove that a chemical has been destroyed. General Science connects biology, chemistry, Earth resources and physics while keeping conclusions tied to evidence. We will work through the original handout's examples, then use separate additional notes to plan a collaborative investigation and a traceable report.
The original GAC zero two three handout covers seven science areas. The public outcomes also include collaborating on an investigation and writing a report using Internet research. Knowing a calculation does not demonstrate that a practical investigation has been conducted. Keep fictional practice records, published background and observations your team actually makes clearly separated. The centre's current brief determines the permitted method, required depth and assessment criteria. This lesson supports those tasks; it does not supply an official assessment paper or guarantee a mark.
Biology studies living systems, including their structures, functions and changes. A cell is the basic structural and functional unit of organisms. Prokaryotic cells have DNA without a membrane-bound nucleus. Eukaryotic cells typically contain a nucleus and other membrane-bound structures, although specialised exceptions matter. A poor image that fails to reveal a structure does not establish that the structure is absent. State what the observation shows, distinguish it from your interpretation, and consider whether another method or a better image would address the uncertainty.
The handout gives Hooke's Micrographia, published in sixteen sixty-five, as a selected historical development. He used the word cell for tiny spaces observed in cork. This is not the whole history of cell theory. Homeostasis is regulation of internal conditions within suitable limits as external conditions vary. It does not require an internal value to remain perfectly constant. Similarly, an image can show a structure at one time without establishing its growth rate. A question about change requires observations over a suitable period.
The original diagram separates three decisions: recording structures, checking image scale and limiting interpretation. In the supplied example the printed cell measures thirty millimetres while its stated actual length is zero point zero five millimetres. Before calculating, check that both lengths use the same unit. The resulting magnification is a ratio, not a length. Neither the cell's shape nor its magnification establishes how quickly it grew. A permitted growth study needs a specified measure, comparable organisms, controlled conditions and an observation period.
Divide the image length of thirty millimetres by the stated actual length of zero point zero five millimetres. The result is six hundred. Millimetres cancel because magnification is a ratio of two lengths. Report a magnification of six hundred times, rather than six hundred millimetres. If the lengths initially use different units, convert one before division. The supplied actual length is part of the case; the picture by itself does not give that number or establish a growth rate.
Classification organises organisms using evidence about relationships. The traditional hierarchy runs through kingdom, phylum, class, order, family, genus and species. Broader groups can include several groups at the next level. Visible traits help identification, while inherited traits and molecular information can support relationships. A leaf key might separate needle-like from broad leaves, then smooth from toothed margins. That order helps identify the prepared cards. It does not establish that those plants evolved in the same order as the branches of the key.
The original diagram shows a family containing different genera and species. In the supplied example lion and tiger belong to Panthera, with the species names Panthera leo and Panthera tigris. The domestic cat is Felis catus, in a different genus within Felidae. Binomial nomenclature uses both the genus and specific epithet. Capitalise the genus and keep the epithet in lower case; italicise both in print. In handwriting, follow the task's underlining convention. The epithet alone is not the complete species name.
An ecosystem includes living organisms and nonliving conditions. Producers make organic material using an energy source. Consumers obtain organic material from other organisms. Decomposers break down dead material and waste, helping return nutrients to available forms. Food-chain arrows point from food towards the organism consuming it. The categories describe roles in a system, not a guarantee that every organism has only one simple relationship. Keep the stated ecosystem boundary in mind when describing inputs, transfers and losses.
The algae diagram uses ten thousand joules, then one thousand and then one hundred. These are illustrative values supplied for that chain. They are not a law that every ecosystem always transfers ten percent. Energy transfers through the system, with dissipation through respiration and other pathways. It does not disappear from existence or endlessly cycle back to producers. Matter can cycle through living and nonliving parts, while a local ecosystem can also gain or lose matter across its boundary. Use the actual values for the case being analysed.
The separate meadow example starts with five thousand joules at the grass level, then six hundred at grasshoppers and sixty at frogs. Divide each next level by the preceding one and multiply by one hundred percent. The first transfer is twelve percent and the second ten percent. Not all material is eaten or assimilated, and energy is used and dissipated. These results do not make ten percent universal. The period's energy budget also contains no population time series, so it cannot predict an exact frog decline next week.
Biodiversity concerns the variety of life. Species richness and distributions of abundance are possible measures, depending on the question. Counting individuals of one species does not measure how many species are present. Comparing two sites also needs suitable sampling, times and identification rules. Diversity may affect how an ecosystem responds to a disturbance, but it does not guarantee resistance to every disturbance. State which aspect of diversity the evidence measures and avoid replacing a specific result with a claim about all ecosystem health.
The rock cycle connects several formation and change processes. Cooling and solidification form igneous rock. Deposited sediment can become sedimentary rock through compaction and cementation. Heat and pressure can alter rock into metamorphic rock without melting it. Weathering and erosion produce sediment, while melting followed by cooling offers another route. Every rock does not have to pass through one compulsory circular sequence. A photograph alone may not establish a rock's type, formation history or exact age; those questions can require additional evidence.
A renewable resource can be replenished on a relevant timescale. A non-renewable resource is not replenished fast enough on human-use timescales. Renewable does not mean unlimited: demand can exceed replacement, and ecosystem needs still matter. The water cycle includes evaporation, condensation, precipitation, runoff, infiltration and groundwater movement or storage. A pond is open to inputs and losses. To evaluate its use, define the boundary and period, identify the flows included, and state which important processes have been omitted from the simplified calculation.
The original pond diagram represents inputs, storage and losses. In the supplied period, thirty cubic metres enter, eighteen leave through the outlet and seven are lost by evaporation. With other changes excluded, storage increases by five cubic metres. A proposed extra extraction of twelve cubic metres changes the result to a decrease of seven. This calculation does not establish initial storage, long-term sustainability or permission to extract. Reeds do not prove drinking-water safety, and a simplified period's budget cannot answer every environmental question.
Start with input minus outlet loss minus evaporation. Thirty minus eighteen minus seven gives plus five cubic metres. Include the proposed extraction as another loss: subtract twelve to obtain minus seven. The sign tells you the direction of change under the stated assumptions. It does not tell you how much water was initially stored or what happens in a different season. A decision needs the relevant additional information, environmental requirements and actual permission. Keep the numerical result separate from a recommendation that the evidence cannot yet justify.
An atom has a nucleus and electrons. Atomic number is its proton count, while mass number counts protons and neutrons. Most nuclei contain both, but hydrogen one has one proton and no neutron. Isotopes of the same element share proton number and differ in neutron number. The original diagram separates element identity, isotope identity and ionic charge. Changing the number of electrons can change charge without changing the element. Avoid subtracting electrons from mass number when you are calculating neutrons.
Sodium twenty-three has eleven protons and mass number twenty-three. Subtract the proton count from the mass number to obtain twelve neutrons. A neutral atom has eleven electrons. Losing one electron gives a positive ion with ten electrons and the same eleven protons. Sodium twenty-four has thirteen neutrons and remains sodium. Neutral chlorine has seventeen electrons; gaining one gives a negative ion with eighteen. Opposite ionic charges explain attraction. In all these comparisons, track protons, neutrons and electrons separately.
The periodic table orders elements by atomic number. In the introductory main-group model, outer electron arrangements help explain similarities within groups. Group members are not identical, and the simplified rule needs care beyond its stated scope. Ionic bonds are attractions between oppositely charged ions. Electron transfer can explain how those ions form; it is not itself the attraction. Covalent bonds involve shared electron pairs. These models help explain structures and behaviour. They are not instructions for handling reactive substances or performing an unapproved experiment.
Combustion of carbon-containing fuels can release carbon dioxide. The greenhouse effect involves absorption and emission of thermal infrared by gases including carbon dioxide. Acid rain involves atmospheric reactions of sulfur dioxide and nitrogen oxides forming acidic compounds. The mechanisms differ, so their evidence and responses must also be distinguished. Pollution depends on the substance or agent, its amount, its pathway and its effects. A report should connect the stated chemical process with evidence rather than using one environmental label as an explanation for every problem.
The treatment diagram keeps two outputs in view: the remaining liquid and filter waste. Moving a substance from water onto a filter is not necessarily destroying it. Chemistry can help monitor or treat pollution, but evaluating an application includes its energy demand, residual material and appropriate waste handling. In the supplied fictional case, volume remains ten litres while concentration falls from twelve to three milligrams per litre. Follow the substance accounting under those assumptions. Students analyse the case; it is not a direction to discharge chemicals.
Mass equals concentration multiplied by volume when the units are compatible. Three milligrams per litre multiplied by ten litres gives thirty milligrams remaining in solution. The initial mass was one hundred and twenty milligrams, leaving ninety retained on the filter under the case assumptions. The concentration reduction is seventy-five percent. Nevertheless, the final three milligrams per litre exceeds the task's fictional target of two. A large percentage reduction and meeting a target are different claims. This target is not a real drinking-water standard.
A wave transfers energy through a travelling disturbance without carrying each medium particle along with it. For a transverse wave, oscillation is perpendicular to propagation. For a longitudinal wave, it is parallel. The direction a line happens to be drawn on the page does not decide the wave type. A point on a string can oscillate vertically while the disturbance travels horizontally. Describe particle motion and propagation separately. This distinction also prevents the mistaken idea that the marked point travels all the way with the wave.
The original schematic is a snapshot against position, not a time graph. Its wavelength spans successive points in the same phase, such as adjacent crests. Amplitude is the maximum displacement from equilibrium. Crest-to-trough height is twice the amplitude, so it is not another name for wavelength. The propagation arrow and displacement axis describe different directions. A snapshot can show spatial spacing; frequency counts complete oscillations per second and needs the relevant temporal information. Identify the graph's horizontal quantity before reading a distance or time from it.
The supplied string wave has frequency five hertz and wavelength zero point four metres. Multiply frequency by wavelength to obtain a speed of two metres per second. Period is the time per complete oscillation, so take one divided by frequency to obtain zero point two seconds. These are different quantities with different units. The supplied amplitude of zero point zero three metres gives a crest-to-trough height of zero point zero six metres. Neither is the wavelength, and the case does not establish how amplitude changes frequency.
The electromagnetic spectrum runs through radio, microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays. Electromagnetic waves do not require a material medium. They share the same speed in a vacuum while differing in frequency and wavelength. Mechanical waves do not all have that speed and depend on the relevant medium. When comparing spectrum regions, identify whether the task asks about wavelength, frequency or a specific application. Do not infer the nature of a wave solely from the orientation of a sketch.
The additional notes compare two reports about the same pond. One records where and when observations were made; the other combines undated photographs with general website claims. Which report lets a reader check its conclusion? A collaborative investigation requires a shared question, method and evidence record, rather than simply dividing the final writing into equal sections. The new notes develop public investigation and reporting outcomes alongside the original handout. The centre brief still governs the actual task, required methods and assessment criteria.
An example question asks how the proportion of ground covered by a selected plant differs between two accessible, teacher-approved areas. This can be addressed by a specified coverage rule. It is not automatically a study of growth rate, which needs change over time, or a demonstration of the cause of any difference. Define the areas and observation period before collecting records. Obtain agreement on a safe, permitted method and respect access restrictions. A report about a proposed investigation must identify it as proposed, rather than implying that observations have already occurred.
A sampling method specifies how observations are selected. Use the same frame size and counting rule at both areas. Select positions by the agreed method rather than choosing only attractive examples. Random selection within an accessible area can reduce deliberate selection, but cannot represent excluded places. Repeated photographs of one patch do not turn that location into ten independent patches. Match the sampling unit to the question. Explain where the sample came from and what wider claims it cannot support.
Agree who records location and time, who estimates coverage and who checks the entries. Rotate or check roles if different observers could systematically use different rules. A common recording sheet needs labels, units, the selection method and deviations. Keep each original record and identify its observer. When members disagree, check the rule and evidence; do not replace an inconvenient result with the group average. A coordination reflection should identify actual contributions and a concrete problem, rather than assuming equal paragraph lengths demonstrate equal participation.
The supplied coverage table is fictional practice, not a completed field investigation. Both areas use the same frame size and coverage rule. Area A has twenty, thirty and forty percent, with a mean of thirty. Area B has forty, fifty and sixty percent, with a mean of fifty. Each row represents a different selected position. Calculate the means from the three records rather than assuming a result. Label supplied data explicitly in a report so a reader can distinguish the exercise from observations the team actually collected.
Subtracting thirty percent coverage from fifty percent gives twenty percentage points. This is not a twenty-percent relative increase. Relative to Area A's mean, divide the difference of twenty by thirty and multiply by one hundred percent, giving approximately sixty-six point seven percent. Each area's readings span twenty percentage points. State the intended comparison and its unit. A reported percent change needs its reference value, whereas a difference between two percentages can be expressed directly in percentage points.
A suitable conclusion says that mean coverage was greater in B in the supplied samples, with variation within both areas. Three samples do not establish every season or every part of the pond. The table includes no light, soil, water or time-series measurements, so it cannot show that pollution caused the difference or that the plant grew faster. Coverage also does not measure species richness. Identify the additional question and measurements needed instead of inventing a cause. A limitation should constrain the conclusion, not merely appear as a closing sentence.
A physical feature concerns conditions such as layout, slope, shade or water movement. A chemical feature concerns substances and quantities, such as a dated concentration measured by a stated method. A biological feature concerns organisms, distributions and relationships. The categories connect, but one is not proof of another. An organism photograph may support an identification within its limits, not drinking-water safety. For a local environment report, include a labelled location description and dated records. State whether each observation was made by the team or taken from another source.
A secondary source reports information collected or interpreted by someone else. Check who produced it, when, for what purpose, using what method and how it relates to your question. Prefer an original measurement record or research report when available. A search-result preview does not replace reading the source. Two websites repeating one report are not two independent observations. A borrowed chemical measurement without a date, unit or method may not suit your comparison. State missing information rather than inventing it.
Keep a source log with author or organisation, title, date, address, the claim used and its limits. A citation links a claim to its source, while the reference list gives locating details. Explain ideas in your own words and cite them. Cite borrowed images and respect their permitted use. Organise the report around question and background, method and responsibilities, results, discussion and conclusion, and references. Distinguish observations from explanations and your own records from published background. Include checked calculations and a specific limitation with a matching improvement.
Pause and answer the checks in the additional notes. Extra photographs of one patch do not broaden the set of sampled locations. The mean coverage difference is twenty percentage points. Pollution was not measured, so these data cannot establish it as the cause. A borrowed chemical measurement needs its source, date, unit, method and limitations. Two sites repeating one report establish only that underlying report, not a new observation. When the team disputes an entry, check the shared rule and evidence, retaining the original record and correction trail.