Semester 2 MYP Science Exam Checklist

Examination Overview and Administrative Details

• Assessment Title: Semester 2 MYP Science Exam
• Scheduled Timeline: Week 7
• Instructor Notice: Issued by Miss Mariam Nasser to guide revision across seven core units of study

Space and the Universe

• Redshift Fundamentals:

  • Definition: Redshift is the physical phenomenon where electromagnetic radiation emitted by an astronomical object is shifted toward longer, redder wavelengths (lower frequencies) of the electromagnetic spectrum as observed from Earth.
  • The Doppler Analogy: Similar to the Doppler effect observed in sound waves—where an ambulance siren drops in pitch as it moves away—light waves emitted by an object moving away from an observer are stretched out, shifting visible absorption lines toward the red end of the spectrum ($\lambda_{\text{observed}} > \lambda_{\text{emitted}}$).
  • Cosmological Redshift vs. Doppler Redshift: Unlike localized Doppler shifts caused by an object's motion through space, cosmological redshift occurs because the fabric of spacetime itself is expanding during the transit time of the photons, physically stretching the light waves.

• Evidence for Universal Expansion:

  • Hubble's Observations: In the late 1920s, Edwin Hubble discovered that the light from nearly all distant galaxies exhibits redshift.
  • Hubble's Law: The velocity ($v$) at which a distant galaxy recedes from an observer is directly proportional to its distance ($d$) from that observer:
    $v = H_0 \times d$
        where $H_0$ represents the Hubble constant. This proves that galaxies farther away are moving away faster than nearby ones.
  • Cosmological Implications: This uniform stretching indicates that space itself is expanding in all directions, providing empirical foundation for the Big Bang Theory, which posits that the universe expanded from an extremely hot, dense singularity.

• Light Travel Time from the Sun to Earth:

  • Physical Distance: The mean distance from the Sun to Earth (one Astronomical Unit, or $1\,\text{AU}$) is approximately $1.496 \times 10^8\,\text{km}$ ($1.496 \times 10^{11}\,\text{m}$).
  • Speed of Light ($c$): In a vacuum, light propagates at a constant speed of approximately $3.00 \times 10^8\,\text{m/s}$ ($300{,}000\,\text{km/s}$).
  • Calculation of Travel Time ($t$):
    $t = \frac{d}{c} = \frac{1.496 \times 10^{11}\,\text{m}}{3.00 \times 10^8\,\text{m/s}} \approx 498.7\,\text{seconds}$
  • Expressed in Minutes: Dividing $498.7\,\text{seconds}$ by $60\,\text{seconds/minute}$ yields approximately $8.31\,\text{minutes}$, or roughly $8\,\text{minutes and } 20\,\text{seconds}$.

Climate Change and the Environment

• Biodiversity:

  • Definition: Biodiversity (biological diversity) refers to the totality of variety and variability among all living organisms across different levels of biological organization, including genetic diversity within species, species diversity within an ecosystem, and ecological diversity across biomes.
  • Ecological Importance: High biodiversity stabilizes ecosystems by providing resilience against environmental disturbances, maintaining vital ecological services such as nutrient cycling, water purification, pollination, and pest regulation.

• Greenhouse Gases (GHGs):

  • Key Chemical Species:
  • Carbon Dioxide ($CO_2$): Emitted via the combustion of carbonaceous fuels, deforestation, and industrial processes; long atmospheric residence time.
  • Methane ($CH_4$): Emitted from enteric fermentation in ruminants, anaerobic rice cultivation, coal mines, and landfills; possesses a high Global Warming Potential (GWP).
  • Nitrous Oxide ($N_2O$): Generated primarily through synthetic agricultural nitrogen fertilizers and industrial activities.
  • Water Vapor ($H_2O$): The most abundant natural greenhouse gas; acts as an amplifying feedback loop rather than a direct anthropogenic radiative forcing driver.
  • Fluorinated Gases (CFCs, HFCs, $SF_6$): Synthetic industrial compounds with long atmospheric lifetimes and exceptionally high radiative efficiencies.

• The Greenhouse Effect:

  • Mechanistic Steps:
  • High-energy solar radiation (shortwave ultraviolet and visible light) penetrates the Earth's atmosphere unimpeded.
  • Approximately half of this solar energy is absorbed by the Earth's surface, warming terrestrial and oceanic environments.
  • The warm surface re-emits this thermal energy back toward the atmosphere as lower-energy, longwave infrared radiation.
  • Greenhouse gas molecules in the troposphere absorb specific wavelengths of this outgoing infrared radiation through vibrational and rotational excitation.
  • These molecules isotropically re-radiate thermal energy in all directions, directing a significant fraction back downward toward the surface, maintaining a planetary mean temperature suitable for liquid water.
  • Natural vs. Enhanced Greenhouse Effect:
  • The natural greenhouse effect keeps Earth roughly $33\,^{\circ}\text{C}$ warmer than it would otherwise be ($\approx -18\,^{\circ}\text{C}$ without greenhouse gases versus $\approx +15\,^{\circ}\text{C}$ with them).
  • The enhanced (anthropogenic) greenhouse effect occurs when excessive industrial and agricultural emissions increase GHG concentrations, trapping excess thermal energy and disrupting global climate equilibria.

• Anthropogenic Drivers of Climate Change:

  • Motor Vehicles and Transportation: Internal combustion engines burn refined petroleum products (gasoline and diesel), releasing massive volumes of carbon dioxide ($CO_2$), carbon monoxide ($CO$), unburnt hydrocarbons, and nitrogen oxides ($NO_x$).
  • Agricultural Activities:
  • Intensive ruminant livestock farming (cattle and sheep) produces substantial enteric methane ($CH_4$) via microbial fermentation in the rumen.
  • Flooded paddy fields for rice cultivation foster anaerobic conditions where methanogenic bacteria release $CH_4$.
  • Widespread application of synthetic nitrogen-based fertilizers results in microbial nitrification and denitrification, releasing nitrous oxide ($N_2O$).
  • Deforestation:
  • Forest clear-cutting and slash-and-burn operations eliminate primary terrestrial carbon sinks that actively sequester atmospheric carbon via photosynthesis.
  • Burning and biological decay of cleared biomass immediately oxidizes stored organic carbon back into gaseous $CO_2$.

• Impact of Bushfires on Climate Change:

  • Direct Carbon Release: High-intensity bushfires oxidize enormous masses of vegetative biomass, releasing gigatons of stored carbon as $CO_2$ into the atmosphere.
  • Aerosol and Particulate Forcing: Fires generate black carbon (soot) aerosols, which alter planetary albedo; when deposited onto snow and ice sheets, these particulates accelerate thermal absorption and melting.
  • Destruction of Carbon Sinks: Scorched soils and devastated tree canopies lose their photosynthesizing biomass, converting productive carbon sinks into net carbon sources for years or decades.
  • Positive Feedback Mechanism: Warmer, drier regional conditions exacerbate fire seasons, leading to more frequent and intense bushfires, which release more GHGs, thereby driving further global warming.

• El Niño and its Impacts on Australia:

  • Definition: El Niño constitutes the warm phase of the El Niño-Southern Oscillation (ENSO), a coupled atmospheric-oceanic climatic phenomenon occurring across the tropical Pacific Ocean.
  • Mechanism: Prevailing easterly trade winds weaken or reverse direction. Warm equatorial surface water shifts eastward toward the west coast of South America, preventing upwelling and leaving the western Pacific (surrounding northern and eastern Australia) with cooler-than-normal sea surface temperatures.
  • Australian Impacts:
  • Suppressed atmospheric convection and reduced cloud formation over the Australian continent.
  • Substantially reduced rainfall, causing severe prolonged droughts across eastern and northern Australia.
  • Elevated ambient temperatures and more frequent, prolonged heatwaves.
  • Markedly increased risk, frequency, and severity of extreme bushfire conditions.
  • Depressed agricultural output, livestock stress, and water storage depletion.

Motion and Speed

• Unit Conversions ($\text{km/h}$ to $\text{m/s}$):

  • Derivation:
    $1\,\text{km} = 1000\,\text{m}$
    $1\,\text{hour} = 3600\,\text{seconds}$
    $1\,\text{km/h} = \frac{1000\,\text{m}}{3600\,\text{s}} = \frac{1}{3.6}\,\text{m/s}$
  • Conversion Rules:
  • To convert speed from kilometers per hour ($\text{km/h}$) to meters per second ($\text{m/s}$), divide by $3.6$:
    $\text{Speed in m/s} = \frac{\text{Speed in km/h}}{3.6}$
  • To convert from $\text{m/s}$ to $\text{km/h}$, multiply by $3.6$:
    $\text{Speed in km/h} = \text{Speed in m/s} \times 3.6$
  • Worked Example:
        Convert a car traveling at $90\,\text{km/h}$ into $\text{m/s}$:
    $v = \frac{90}{3.6} = 25\,\text{m/s}$

• Calculations of Speed, Distance, and Time:

  • Average Speed ($s$): The total distance traveled divided by the total time taken to traverse that distance:
    $s = \frac{d}{t}$
  • Distance ($d$):
    $d = s \times t$
  • Time ($t$):
    $t = \frac{d}{s}$
  • Standard SI Units: Distance in meters ($\text{m}$), time in seconds ($\text{s}$), speed in meters per second ($\text{m/s}$).

• Acceleration Calculations:

  • Definition: The rate of change of velocity with respect to time.
  • Formula:
    $a = \frac{v - u}{t}$
  • $a = \text{acceleration } (\text{m/s}^2)$
  • $v = \text{final velocity } (\text{m/s})$
  • $u = \text{initial velocity } (\text{m/s})$
  • $t = \text{time interval } (\text{s})$
  • Deceleration (Negative Acceleration): When final velocity $v$ is less than initial velocity $u$, $a$ yields a negative sign, indicating that the object is slowing down.

• Distinction Between Scalar and Vector Quantities:

  • Distance vs. Displacement:
  • Distance ($d$): A scalar quantity measuring the total path length traversed between two points, having magnitude only ($\text{e.g., } 500\,\text{m}$). It cannot be negative.
  • Displacement ($\mathbf{s}$ or $\Delta \mathbf{x}$): A vector quantity defined as the straight-line distance and direction from an initial position to a final position ($\text{e.g., } 300\,\text{m [North]}$).
  • Illustrative Scenario: If an athlete runs one complete lap around a $400\,\text{m}$ circular track, their total distance traveled is $400\,\text{m}$, while their net displacement is $0\,\text{m}$.
  • Speed vs. Velocity:
  • Speed ($s$): A scalar quantity describing how fast an object moves regardless of direction ($\text{magnitude only}$).
  • Velocity ($\mathbf{v}$): A vector quantity specifying both the rate of change of displacement and the direction of travel ($\mathbf{v} = \frac{\Delta \mathbf{x}}{t}$). A change in velocity can occur through changing speed, changing direction, or both.

• Graphical Interpretation of Motion:

  • Distance-Time Graphs:
  • Slope / Gradient ($\frac{\Delta y}{\Delta x} = \frac{\Delta d}{\Delta t}$): Represents the speed of the object.
  • Horizontal Line: Gradient is zero; object is stationary.
  • Constant Positive Gradient: Straight diagonal line; object is traveling at a constant speed.
  • Curved Line: Gradient is changing; indicates changing speed (acceleration if curving upward, deceleration if flattening).
  • Speed-Time (and Velocity-Time) Graphs:
  • Slope / Gradient ($\frac{\Delta v}{\Delta t}$): Directly represents acceleration ($a$).
    • Horizontal line ($\text{slope} = 0$): Zero acceleration; constant speed.
    • Positive slope: Uniform acceleration.
    • Negative slope: Uniform deceleration.
  • Area Under the Curve: Directly represents the total distance (or displacement) traveled over the specified time interval ($\text{Area} = \text{distance}$).
    • Geometric decomposition: Calculated by splitting irregular regions into geometric rectangles ($\text{base} \times \text{height}$) and triangles ($\frac{1}{2} \times \text{base} \times \text{height}$).

Forces and Newton's Laws

• Classification of Forces:

  • Gravity ($F_g$ or $W$): The non-contact attractive force exerted by a planetary mass upon an object, pulling it toward the center of mass:
    $W = mg$
        where $g \approx 9.8\,\text{m/s}^2$ on Earth.
  • Frictional Force ($F_f$): A contact resistance force operating parallel to the contact interface that opposes the relative motion or tendency of motion between two surfaces.
  • Normal Force ($F_N$): A contact support force exerted perpendicularly by a surface upon an object resting on or pressing against it, balancing the perpendicular component of external loads.
  • Additional Forces: Tension ($F_T$) in cables/ropes, applied force ($F_{\text{app}}$), and fluid drag/air resistance ($F_d$).

• Free-Body Diagrams (Force Diagrams):

  • Constructed by modeling the object of interest as a point or box isolated from its environment.
  • All external forces acting on the object are represented as vector arrows originating from the center of mass.
  • Arrows point in the direction of the respective force, with their relative lengths drawn to scale representing magnitude.
  • Every vector must be explicitly labeled (e.g., $F_N$, $F_g$, $F_f$, $F_{\text{app}}$).

• Net Force ($F_{\text{net}}$ or $\Sigma F$):

  • The vector sum of all concurrent forces acting on a single body.
  • Collinear Calculations: Forces operating in opposite directions along a single axis are subtracted; forces operating in the same direction are added.
  • Equilibrium ($F_{\text{net}} = 0\,\text{N}$): Forces are balanced; the object remains in a state of rest or constant linear velocity.
  • Non-equilibrium ($F_{\text{net}} \neq 0\,\text{N}$): Forces are unbalanced; causes the object to accelerate in the direction of the resultant vector.

• Newton's Second Law of Motion:

  • Principle: The acceleration of an object is directly proportional to the magnitude of the net force acting upon it, in the same direction as the net force, and inversely proportional to the mass of the object.
  • Mathematical Formula:
    $F_{\text{net}} = ma$
  • $F_{\text{net}} = \text{net force in Newtons } (\text{N})$
  • $m = \text{mass in kilograms } (\text{kg})$
  • $a = \text{acceleration in meters per second squared } (\text{m/s}^2)$
  • Algebraic Manipulations:
    $a = \frac{F_{\text{net}}}{m}$
    $m = \frac{F_{\text{net}}}{a}$

• Newton's First Law of Motion (Law of Inertia):

  • Statement: An object at rest remains at rest, and an object in uniform motion continues moving at a constant velocity in a straight line, unless acted upon by a non-zero net external force.
  • Inertia: The inherent physical resistance of any physical object to any change in its velocity; mass serves as the quantitative measure of inertia.
  • Seatbelt Mechanism:
  • When a vehicle moving at high speed undergoes sudden, violent braking or a collision, the vehicle rapidly decelerates due to an external resistive force.
  • By Newton's First Law, the unfastened occupants possess inertia and continue moving forward at the vehicle's initial velocity.
  • A seatbelt applies the necessary external restraint force across the pelvis and ribcage over an extended time interval, safely decelerating the occupant to prevent impact with the dashboard, windshield, or ejection from the cabin.

• Newton's Third Law of Motion (Action and Reaction):

  • Statement: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body ($F_{A \text{ on } B} = -F_{B \text{ on } A}$).
  • Action-Reaction Pairs: These forces always act on different objects, meaning they do not cancel each other out.
  • Balloon Rocket Mechanism:
  • An inflated, untied balloon contains air compressed by the elastic tension of its rubber walls.
  • When released, the elastic membrane contracts, exerting a powerful backward force on the internal air, exhausting it out of the nozzle (Action Force).
  • Simultaneously, the escaping column of air exerts an equal and opposite forward reaction force upon the inner structure of the balloon (Reaction Force / Thrust), propelling the balloon rocket forward along its trajectory.

Scientific Graphs and Data Interpretation

• Reading Data from Tables:

  • Independent Variable (IV): Typically listed in the left-hand column or the top row; this is the parameter intentionally manipulated by the experimenter.
  • Dependent Variable (DV): Positioned in subsequent columns; this is the observed parameter measured across repeated trials.
  • Derived Statistics: Extracting ranges, calculating mean values across trials, identifying anomalous trial data, and correlating changes between independent conditions.

• Graph Construction Conventions:

  • Axis Assignment: Independent variable plotted strictly along the horizontal x-axis; dependent variable plotted along the vertical y-axis.
  • Labeling: Every axis must have a descriptive label denoting the physical quantity accompanied by its appropriate standard units in parentheses or brackets (e.g., $\text{Time (s)}$, $\text{Temperature }(^{\circ}\text{C})$).
  • Linear Scaling: Grid divisions must remain uniform, consistent, and cleanly divisible ($\text{e.g., } 1, 2, 5, 10$); data must fill at least $50\,\%$ to $75\,\%$ of the provided grid area.
  • Plotting Points: Individual coordinate points must be precisely plotted with small, clean crosses ($\times$) or circled dots ($\odot$).
  • Lines and Curves of Best Fit: Drawn smoothly to show the general trend of data points. For linear data, a single straight line is drawn using a ruler, balancing the number of points distributed symmetrically above and below the line while ignoring clear outliers.
  • Document Title: Graphs require an explicit, descriptive title stating the relationship tested: "The Effect of [Independent Variable] on [Dependent Variable]".

• Identifying Trends and Explaining Graphs:

  • Linear Direct Proportionality: Straight line passing through the origin ($(0,0)$). As the independent variable increases, the dependent variable increases at a constant rate ($y = kx$).
  • Positive Non-linear Correlation: As $x$ increases, $y$ increases, but the rate of increase either accelerates (exponential) or decelerates (logarithmic/diminishing returns).
  • Inverse Relationships: As the independent variable increases, the dependent variable decreases ($y \propto \frac{1}{x}$).
  • Plateau Phase (Saturation): The curve levels off into a horizontal asymptote, demonstrating that the dependent variable has reached a physiological or physical maximum where another factor becomes limiting.

Energy and Sustainability

• Renewable vs. Non-Renewable Energy Resources:

  • Renewable Energy: Energy derived from natural sources that are replenished naturally on a human timescale at a rate equal to or faster than their consumption rate.
  • Solar Energy: Photovoltaic cells convert photons directly into electrical energy; solar thermal collectors capture infrared heat.
  • Wind Energy: Kinetic energy of atmospheric air masses turns aerodynamic turbines connected to mechanical generators.
  • Hydroelectric Energy: Gravitational potential energy of elevated reservoir water is converted into kinetic energy flowing through hydraulic turbines.
  • Geothermal Energy: Harnessing thermodynamic heat from radioactive decay and residual thermal energy within the Earth's crust to produce steam.
  • Biomass: Organic materials (wood, agricultural waste, algal biofuels) that store recent solar energy via photosynthesis.
  • Non-Renewable Energy: Finite terrestrial energy resources that exist in limited quantities and take millions of years of geological processing to form, depleting permanently with usage.
  • Coal: Carbon-dense sedimentary rock formed from ancient fossilized swamp vegetation.
  • Petroleum (Crude Oil): Liquid hydrocarbons derived from ancient marine planktonic sediments exposed to deep thermal cracking and pressure.
  • Natural Gas ($CH_4$): Volatile gaseous hydrocarbon mixtures found trapped within geological formations.
  • Nuclear Fuels (Uranium-235): Heavy radioactive fissile isotopes extracted from mined mineral ores.

• Fossil Fuel Combustion and Climate Dynamics:

  • Chemical Combustion Reaction:
    $\text{Hydrocarbon} + O_2 \rightarrow CO_2 + H_2O + \text{Thermal Energy}$
  • Disruption of the Carbon Cycle: Hydrocarbons represent geological carbon sinks isolated deep underground for hundreds of millions of years. Rapid commercial extraction and combustion release this sequestered carbon back into the atmospheric-oceanic biosphere over a timescale of decades.
  • Atmospheric Burden: This rapid release drives up global atmospheric $CO_2$ concentrations, strengthening thermal absorption in the troposphere, driving oceanic acidification, and shifting long-term meteorological patterns.

• Waste Reduction and Environmental Conservation:

  • The Waste Hierarchy:
  • Reduce: Minimizing total resource consumption and upstream manufacturing waste; eliminating single-use packaging.
  • Reuse: Extending product lifespans by repairing, refurbishing, and repurposing existing manufactured goods.
  • Recycle: Processing waste materials (aluminum, paper, glass, specific thermoplastics) into secondary raw materials, reducing the energy needed for primary extraction.
  • Mitigation Strategies:
  • Accelerating the transition to low-emission renewable energy grids.
  • Implementing energy-efficient technologies (LED lighting, high-grade architectural insulation, heat pumps).
  • Reforestation and afforestation programs to restore active biological carbon sinks.
  • Adopting regenerative agricultural practices and reducing municipal food waste to curtail anaerobic landfill emissions of methane ($CH_4$).

Populations and Ecosystems

• Predator-Prey Dynamics:

  • Definition: A biological interaction where one organism (the predator) hunts, kills, and consumes another organism (the prey) for sustenance.
  • Cyclical Population Fluctuations (Lotka-Volterra Mechanics):
  • An abundance of prey provides ample food resources, leading to higher reproductive rates and survival in the predator population.
  • As the predator population increases, higher predation pressure drives the prey population down.
  • The depleted prey population can no longer support the elevated predator population, leading to predator starvation, reduced fecundity, and a declining predator population.
  • With reduced predation pressure, surviving prey reproduce and rebuild their numbers, initiating a repeating cycle.
  • Lag Phase Characteristic: Peaks and troughs in the predator population curve consistently lag behind the corresponding peaks and troughs of the prey curve.

• Interpreting Population Growth Curves:

  • Exponential Growth Phase ($J$-curve): Occurs when resources (nutrients, space, water) are non-limiting; population expands rapidly without significant mortality constraints.
  • Logistic Growth Phase ($S$-curve): Environmental resistance takes effect as the population nears maximum capacity.
  • Carrying Capacity ($K$): The maximum population density of a given species that a specific environment can sustainably support over time without environmental degradation.
  • Oscillations Around $K$: Stable populations naturally fluctuate above and below the carrying capacity due to minor variations in resource availability.

• Factors Driving Population Changes:

  • Biotic (Density-Dependent) Factors:
  • Predation: Changes in the abundance or efficiency of higher trophic level consumers.
  • Competition: Intraspecific (within species) and interspecific (between species) competition for finite resources such as territory, food, mates, and sunlight.
  • Pathogens and Parasitism: High population densities accelerate the transmission of infectious microbial diseases and parasites, increasing mortality.
  • Food Supply: Fluctuations in primary producer biomass or prey abundance.
  • Abiotic (Density-Independent) Factors:
  • Climatic and Meteorological Extremes: Prolonged droughts, severe cold snaps, heatwaves, and seasonal fluctuations.
  • Natural Catastrophes: Bushfires, flash floods, volcanic eruptions, and severe storms that cause mortality independent of population density.
  • Anthropogenic Disturbance: Habitat fragmentation, clearing of native vegetation, industrial chemical pollution, and shifts in regional microclimates caused by global warming.