DC CAPE 2.0 Science Grade 8 cheat sheet
DC CAPE 2.0 Science Grade 8 · Keep the key ideas within reach.
Matter and Its Interactions
Atoms are the smallest unit of an element that keeps that element's properties; molecules are two or more atoms bonded together.
In a chemical reaction, atoms are rearranged but never created or destroyed (conservation of mass), so total mass of reactants equals total mass of products.
Subscripts show how many atoms of an element are in a formula (H2O has 2 H, 1 O); coefficients show how many molecules (2H2O has 4 H, 2 O).
A balanced chemical equation has equal numbers of each type of atom on both sides of the arrow.
Physical changes alter form or state but not identity (ice melting); chemical changes produce new substances with new properties (rusting).
Evidence of a chemical change includes gas production, color change, precipitate formation, light or heat release, and odor change.
In a solid, particles are closely packed and vibrate in place; in a liquid they slide past each other; in a gas they move freely and far apart.
Adding thermal energy generally increases particle motion, which can raise temperature or cause a phase change such as melting or boiling.
Synthetic materials are designed by chemists to have specific properties; the properties of a material determine its best use.
Motion and Stability: Forces and Interactions
Speed = distance ÷ time; velocity is speed in a stated direction; acceleration is a change in velocity, including a change in direction.
Newton's first law: an object at rest or in uniform motion stays that way unless a net force acts on it (inertia).
Newton's second law: net force = mass × acceleration (F = ma); greater mass means less acceleration for the same force.
Newton's third law: every action force has an equal and opposite reaction force acting on a different object.
Forces are balanced when the net force is zero (no change in motion) and unbalanced when the net force is nonzero (motion changes).
Gravity is an attractive force between masses; on Earth it pulls objects downward with an acceleration of about 9.8 m/s².
Friction opposes motion between surfaces in contact and converts kinetic energy into thermal energy.
Weight is the gravitational force on an object (changes with location); mass is the amount of matter (stays the same).
Energy
Energy is the ability to cause change and is measured in joules; it cannot be created or destroyed, only transferred or transformed.
Kinetic energy depends on mass and speed (KE = ½mv²); doubling speed quadruples kinetic energy.
Potential energy is stored energy due to position or condition; gravitational PE increases with height and mass.
Energy forms include kinetic, potential, thermal, chemical, electrical, radiant (light), and sound.
In every energy transformation some energy spreads as thermal energy, so no system is 100% efficient.
Conduction transfers heat by direct contact, convection by moving fluids, and radiation by electromagnetic waves.
Heat flows spontaneously from warmer objects to cooler objects until thermal equilibrium is reached.
Total mechanical energy (potential plus kinetic) stays constant in a system with no friction; friction reduces it as thermal energy.
Waves and Their Applications in Technologies for Information Transfer
A wave transfers energy, not matter, from place to place; the medium (if any) vibrates and returns to its rest position.
Amplitude relates to a wave's energy; greater amplitude means more energy (brighter light, louder sound).
Wavelength is the distance between corresponding points on consecutive waves; frequency is the number of waves passing a point per second (hertz).
Wave speed = frequency × wavelength; in a given medium, changing frequency changes wavelength inversely.
Mechanical waves (sound, water) need a medium; electromagnetic waves (light, radio, X-rays) travel through space.
In a vacuum all electromagnetic waves travel at the speed of light, about 300,000 km/s.
Reflection bounces a wave off a surface; refraction bends a wave as it changes speed entering a new medium; absorption transfers energy to the material.
Sound travels faster in solids than in gases because particles are closer together; it cannot travel through a vacuum.
Digital signals encode information as discrete values (0s and 1s), which resist noise better than analog signals and can be stored and transmitted reliably.
From Molecules to Organisms: Structures and Processes
Cells are the basic unit of structure and function in living things; cells contain specialized structures called organelles.
The cell membrane controls what enters and leaves the cell; the nucleus holds genetic material and directs activities.
Mitochondria release energy from food (cellular respiration); chloroplasts capture light energy for photosynthesis in plant cells.
Photosynthesis uses carbon dioxide, water, and light energy to make glucose and release oxygen.
Cellular respiration breaks down glucose using oxygen to release energy, producing carbon dioxide and water.
Body systems work together: the circulatory, respiratory, digestive, and nervous systems cooperate to supply cells with oxygen and nutrients.
Multicellular organisms are organized from cells to tissues to organs to organ systems to the whole organism.
Sensory receptors detect stimuli and send signals through the nervous system, which coordinates a response.
Ecosystems: Interactions, Energy, and Dynamics
Producers (plants, algae) make their own food; consumers eat other organisms; decomposers break down dead material and recycle nutrients.
Food chains and food webs trace energy flow; arrows point in the direction energy transfers, from eaten to eater.
Energy pyramids show that only about 10% of energy passes to the next trophic level; most is lost as heat.
Matter cycles through ecosystems (carbon, nitrogen, water cycles), but energy flows one way and is not recycled.
Population size is affected by food, water, shelter, predators, disease, and competition for resources.
Carrying capacity is the largest population an ecosystem can support over time with available resources.
Mutualism benefits both species, commensalism benefits one and does not affect the other, and parasitism benefits one while harming the other.
Changes such as drought, fire, or species removal can disrupt an ecosystem; biodiversity increases resilience to change.
Heredity: Inheritance and Variation of Traits
Genes are segments of DNA on chromosomes that carry instructions for traits; alleles are different versions of a gene.
A dominant allele is expressed when at least one copy is present; a recessive allele is expressed only when two copies are present.
Genotype is the genetic makeup (e.g., Bb); phenotype is the observable trait (e.g., brown eyes).
Punnett squares predict the probability of offspring genotypes from the parents' alleles.
In sexual reproduction, each parent contributes half the genetic material, producing offspring with unique trait combinations.
Asexual reproduction produces offspring genetically identical to the parent (clones).
Mutations are changes in DNA that can create new traits and are a source of genetic variation.
Traits result from both genes and environmental factors, such as nutrition or sunlight affecting growth.
Earth's Place in the Universe and Earth's Systems
Earth's rotation on its axis (about 24 hours) causes day and night; its revolution around the Sun (about 365 days) with a tilted axis causes seasons.
The Moon's phases result from the changing angle between Earth, the Moon, and the Sun; the Moon completes a phase cycle about every 29.5 days.
Gravity keeps planets in orbit around the Sun and moons in orbit around planets; orbits are elliptical.
The solar system has eight planets; inner planets are small and rocky, outer planets are large and mostly gas or ice.
Earth's layers are the crust, mantle, and core; the lithosphere is broken into tectonic plates that move on the mantle.
Plate boundaries are divergent (moving apart), convergent (colliding), and transform (sliding past); earthquakes and volcanoes cluster at boundaries.
The rock cycle describes how igneous, sedimentary, and metamorphic rocks change through melting, cooling, weathering, and pressure.
Weathering breaks rock down, erosion moves the material, and deposition lays it down to form new landforms.
The water cycle moves water through evaporation, condensation, precipitation, and runoff, driven mainly by energy from the Sun.
Matter and Its Interactions
Atoms are the smallest unit of an element that keeps that element's properties; molecules are two or more atoms bonded together.
In a chemical reaction, atoms are rearranged but never created or destroyed (conservation of mass), so total mass of reactants equals total mass of products.
Subscripts show how many atoms of an element are in a formula (H2O has 2 H, 1 O); coefficients show how many molecules (2H2O has 4 H, 2 O).
A balanced chemical equation has equal numbers of each type of atom on both sides of the arrow.
Physical changes alter form or state but not identity (ice melting); chemical changes produce new substances with new properties (rusting).
Evidence of a chemical change includes gas production, color change, precipitate formation, light or heat release, and odor change.
In a solid, particles are closely packed and vibrate in place; in a liquid they slide past each other; in a gas they move freely and far apart.
Adding thermal energy generally increases particle motion, which can raise temperature or cause a phase change such as melting or boiling.
Synthetic materials are designed by chemists to have specific properties; the properties of a material determine its best use.
Motion and Stability: Forces and Interactions
Speed = distance ÷ time; velocity is speed in a stated direction; acceleration is a change in velocity, including a change in direction.
Newton's first law: an object at rest or in uniform motion stays that way unless a net force acts on it (inertia).
Newton's second law: net force = mass × acceleration (F = ma); greater mass means less acceleration for the same force.
Newton's third law: every action force has an equal and opposite reaction force acting on a different object.
Forces are balanced when the net force is zero (no change in motion) and unbalanced when the net force is nonzero (motion changes).
Gravity is an attractive force between masses; on Earth it pulls objects downward with an acceleration of about 9.8 m/s².
Friction opposes motion between surfaces in contact and converts kinetic energy into thermal energy.
Weight is the gravitational force on an object (changes with location); mass is the amount of matter (stays the same).
Energy
Energy is the ability to cause change and is measured in joules; it cannot be created or destroyed, only transferred or transformed.
Kinetic energy depends on mass and speed (KE = ½mv²); doubling speed quadruples kinetic energy.
Potential energy is stored energy due to position or condition; gravitational PE increases with height and mass.
Energy forms include kinetic, potential, thermal, chemical, electrical, radiant (light), and sound.
In every energy transformation some energy spreads as thermal energy, so no system is 100% efficient.
Conduction transfers heat by direct contact, convection by moving fluids, and radiation by electromagnetic waves.
Heat flows spontaneously from warmer objects to cooler objects until thermal equilibrium is reached.
Total mechanical energy (potential plus kinetic) stays constant in a system with no friction; friction reduces it as thermal energy.
Waves and Their Applications in Technologies for Information Transfer
A wave transfers energy, not matter, from place to place; the medium (if any) vibrates and returns to its rest position.
Amplitude relates to a wave's energy; greater amplitude means more energy (brighter light, louder sound).
Wavelength is the distance between corresponding points on consecutive waves; frequency is the number of waves passing a point per second (hertz).
Wave speed = frequency × wavelength; in a given medium, changing frequency changes wavelength inversely.
Mechanical waves (sound, water) need a medium; electromagnetic waves (light, radio, X-rays) travel through space.
In a vacuum all electromagnetic waves travel at the speed of light, about 300,000 km/s.
Reflection bounces a wave off a surface; refraction bends a wave as it changes speed entering a new medium; absorption transfers energy to the material.
Sound travels faster in solids than in gases because particles are closer together; it cannot travel through a vacuum.
Digital signals encode information as discrete values (0s and 1s), which resist noise better than analog signals and can be stored and transmitted reliably.
From Molecules to Organisms: Structures and Processes
Cells are the basic unit of structure and function in living things; cells contain specialized structures called organelles.
The cell membrane controls what enters and leaves the cell; the nucleus holds genetic material and directs activities.
Mitochondria release energy from food (cellular respiration); chloroplasts capture light energy for photosynthesis in plant cells.
Photosynthesis uses carbon dioxide, water, and light energy to make glucose and release oxygen.
Cellular respiration breaks down glucose using oxygen to release energy, producing carbon dioxide and water.
Body systems work together: the circulatory, respiratory, digestive, and nervous systems cooperate to supply cells with oxygen and nutrients.
Multicellular organisms are organized from cells to tissues to organs to organ systems to the whole organism.
Sensory receptors detect stimuli and send signals through the nervous system, which coordinates a response.
Ecosystems: Interactions, Energy, and Dynamics
Producers (plants, algae) make their own food; consumers eat other organisms; decomposers break down dead material and recycle nutrients.
Food chains and food webs trace energy flow; arrows point in the direction energy transfers, from eaten to eater.
Energy pyramids show that only about 10% of energy passes to the next trophic level; most is lost as heat.
Matter cycles through ecosystems (carbon, nitrogen, water cycles), but energy flows one way and is not recycled.
Population size is affected by food, water, shelter, predators, disease, and competition for resources.
Carrying capacity is the largest population an ecosystem can support over time with available resources.
Mutualism benefits both species, commensalism benefits one and does not affect the other, and parasitism benefits one while harming the other.
Changes such as drought, fire, or species removal can disrupt an ecosystem; biodiversity increases resilience to change.
Heredity: Inheritance and Variation of Traits
Genes are segments of DNA on chromosomes that carry instructions for traits; alleles are different versions of a gene.
A dominant allele is expressed when at least one copy is present; a recessive allele is expressed only when two copies are present.
Genotype is the genetic makeup (e.g., Bb); phenotype is the observable trait (e.g., brown eyes).
Punnett squares predict the probability of offspring genotypes from the parents' alleles.
In sexual reproduction, each parent contributes half the genetic material, producing offspring with unique trait combinations.
Asexual reproduction produces offspring genetically identical to the parent (clones).
Mutations are changes in DNA that can create new traits and are a source of genetic variation.
Traits result from both genes and environmental factors, such as nutrition or sunlight affecting growth.
Earth's Place in the Universe and Earth's Systems
Earth's rotation on its axis (about 24 hours) causes day and night; its revolution around the Sun (about 365 days) with a tilted axis causes seasons.
The Moon's phases result from the changing angle between Earth, the Moon, and the Sun; the Moon completes a phase cycle about every 29.5 days.
Gravity keeps planets in orbit around the Sun and moons in orbit around planets; orbits are elliptical.
The solar system has eight planets; inner planets are small and rocky, outer planets are large and mostly gas or ice.
Earth's layers are the crust, mantle, and core; the lithosphere is broken into tectonic plates that move on the mantle.
Plate boundaries are divergent (moving apart), convergent (colliding), and transform (sliding past); earthquakes and volcanoes cluster at boundaries.
The rock cycle describes how igneous, sedimentary, and metamorphic rocks change through melting, cooling, weathering, and pressure.
Weathering breaks rock down, erosion moves the material, and deposition lays it down to form new landforms.
The water cycle moves water through evaporation, condensation, precipitation, and runoff, driven mainly by energy from the Sun.