TIMSS 2019 Science Framework

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Science Content Domains–Eighth Grade

Four major content domains define the science content for the TIMSS Science eighth grade assessment: biology, chemistry, physics, and Earth science. Exhibit 2.3 shows the target percentages for each of the four content domains in the TIMSS 2019 science assessment.

Exhibit 2.3: Target Percentages of the TIMSS 2019 Science Assessment Devoted to Content Domains at the Eighth Grade

Eighth Grade Content Domains	Percentages
Biology	35%
Chemistry	20%
Physics	25%
Earth Science	20%

Each of these content domains includes several major topic areas, and each topic area in turn includes one or more topics. Each topic is further described by specific objectives that represent the students’ expected knowledge, abilities, and skills assessed within each topic. Across the eighth grade assessment, each objective receives approximately equal weight in terms of assessment items. The verbs used in the objectives are intended to represent typical performances expected of eighth grade students, but are not intended to limit performances to a particular cognitive domain. Each objective can be assessed drawing on each of the three cognitive domains (knowing, applying, and reasoning).

Biology

At the eighth grade, students build on the foundational life science knowledge they learned in the primary grades, and develop an understanding of many of the most important concepts in biology. The biology domain includes six topic areas:

• Characteristics and life processes of organisms
• Cells and their functions
• Life cycles, reproduction, and heredity
• Diversity, adaptation, and natural selection
• Ecosystems
• Human health

Concepts learned in each of these topic areas are essential for preparing students for more advanced study. Eighth grade students are expected to understand how structure relates to function in organisms. They also should have a foundational understanding of cell structure and function and the processes of photosynthesis and cellular respiration. At this level, the study of reproduction and heredity provides a foundation for later, more advanced study of molecular biology and molecular genetics. Learning the concepts of adaptation and natural selection provides a foundation for understanding evolution, and an understanding of processes and interactions in ecosystems is essential for students to begin to think about how to develop solutions to many environmental challenges. Finally, developing a science-based understanding of human health enables students to improve the condition of their lives and the lives of others.

Characteristics and Life Processes of Organisms

1. Differences among major taxonomic groups of organisms:

AIdentify the defining characteristics that differentiate among major taxonomic groups of organisms (i.e., plants, animals, fungi, mammals, birds, reptiles, fish, amphibians, and insects).

BRecognize and categorize organisms that are examples of major taxonomic groups of organisms (i.e., plants, animals, fungi, mammals, birds, reptiles, fish, amphibians, and insects).

2. Structures and functions of major organ systems:

ALocate and identify major organs (e.g., lungs, stomach, brain) and the components of major organ systems (e.g., respiratory system, digestive system) in the human body.

BCompare and contrast major organs and major organ systems in humans and other vertebrates.

CExplain the role of major organs and major organ systems in sustaining life, such as those involved in circulation and respiration.

3. Physiological processes in animals:

ARecognize responses of animals to external and internal changes that work to maintain stable body conditions (e.g., increased heart rate during exercise, feeling thirsty when dehydrated, feeling hungry when requiring energy, sweating in heat, shivering in cold).

Cells and Their Functions

1. The structures and functions of cells:

AExplain that living things are made of cells that both carry out life functions and reproduce by division.

BIdentify major cell structures (i.e., cell wall, cell membrane, nucleus, chloroplast, vacuole, and mitochondria) and describe the primary functions of these structures.

CRecognize that cell walls and chloroplasts differentiate plant cells from animal cells.

DExplain that tissues, organs, and organ systems are formed from groups of cells with specialized structures and functions.

2. The processes of photosynthesis and cellular respiration:

ADescribe the basic process of photosynthesis (i.e., requires light, carbon dioxide, water, and chlorophyll; produces glucose/sugar; and releases oxygen).

BDescribe the basic process of cellular respiration (i.e., requires oxygen and glucose/sugar; produces energy; and releases carbon dioxide and water).

Life Cycles, Reproduction, and Heredity

1. Life cycles and patterns of development:

ACompare and contrast the life cycles and patterns of growth and development of different types of organisms (i.e., mammals, birds, amphibians, insects, and plants).

2. Sexual reproduction and inheritance in plants and animals:

ARecognize that sexual reproduction involves the fertilization of an egg cell by a sperm cell to produce offspring that are similar but not identical to either parent; relate the inheritance of traits to organisms passing on genetic material to their offspring.

BRecognize that an organism’s traits are encoded in its DNA; recognize that DNA is genetic information found in chromosomes located in the nucleus of each cell.

CDistinguish inherited characteristics from acquired or learned characteristics.

Diversity, Adaptation, and Natural Selection

1. Variation as the basis for natural selection:

ARecognize that variations in physical and behavioral characteristics among individuals in a population give some individuals an advantage in surviving and passing on their characteristics to their offspring.

BRelate species survival or extinction to reproductive success in a changing environment (natural selection).

2. Evidence for changes in life on Earth over time:

ADraw conclusions about the relative length of time major groups of organisms have existed on Earth using fossil evidence.

BDescribe how similarities and differences among living species and fossils provide evidence of the changes that occur in living things over time, and recognize that the degree of similarity of characteristics provides evidence of common ancestry.

Ecosystems

1. The flow of energy in ecosystems:

AIdentify and provide examples of producers, consumers, and decomposers; draw or interpret food web diagrams.

BDescribe the flow of energy in an ecosystem (i.e., energy flows from producers to consumers, and only part of the energy is passed from one level to the next); draw or interpret energy pyramids.

2. The cycling of water, oxygen, and carbon in ecosystems:

ADescribe the role of living things in cycling water through an ecosystem (i.e., plants take in water from the soil and give off water through their leaves; and animals take in water and release water during respiration and as waste).

BDescribe the role of living things in cycling oxygen and carbon through an ecosystem (i.e., plants take in carbon dioxide from the air and release oxygen into the air as part of photosynthesis and store carbon in their cells; and animals take in oxygen from the air and release carbon dioxide into the air as part of respiration).

3. Interdependence of populations of organisms in an ecosystem:

ADescribe and provide examples of competition among populations or organisms in an ecosystem.

BDescribe and provide examples of predation in an ecosystem.

CDescribe and provide examples of symbiosis among populations of organisms in an ecosystem (e.g., birds or insects pollinating flowers, birds eating insects on deer or cattle).

4. Factors affecting population size in an ecosystem:

ADescribe factors that affect the growth of plants and animals; identify factors that limit population size (e.g., disease, predators, food resources, drought).

BPredict how changes in an ecosystem (e.g., changes in the water supply, the introduction of a new population, hunting, migration) can affect available resources, and thus the balance among populations.

5. Human impact on the environment:

ADescribe and explain ways in which human behavior (e.g., re-planting forests, reducing air and water pollution, protecting endangered species) can have positive effects on the environment.

BDescribe and explain ways in which human behavior (e.g., allowing factory waste water to enter water systems, burning fossil fuels that release greenhouse gases and pollutants into the air) can have negative effects on the environment; describe and provide examples of the effects of air, water, and soil pollution on humans, plants, and animals (e.g., water pollution can reduce plant and animal life in the water system).

Human Health

1. Causes, transmission, and prevention of, and resistance to diseases:

ADescribe causes, transmission, and prevention of common diseases (e.g., influenza, measles, malaria, HIV).

BDescribe the role of the body’s immune system in resisting disease and promoting healing (i.e., antibodies in the blood help the body resist infection and white blood cells fight infection).

2. The importance of diet, exercise, and other lifestyle choices:

AExplain the importance of diet, exercise, and other lifestyle choices in maintaining health and preventing illness (e.g., heart disease, high blood pressure, diabetes, skin cancer, lung cancer).

BIdentify the dietary sources and roles of nutrients in a healthy diet (i.e., vitamins, minerals, proteins, carbohydrates, and fats).

Chemistry

At the eighth grade, students’ study of chemistry extends beyond developing an understanding of everyday phenomena to learning the central concepts and principles that are needed for understanding practical applications of chemistry and undertaking later, more advanced study. The chemistry domain includes three topic areas:

• Composition of matter
• Properties of matter
• Chemical change

The composition of matter topic area focuses on differentiating elements, compounds, and mixtures and understanding the particulate structure of matter. Included in this area also is the use of the periodic table as an organizing principle for the elements. At a more macroscopic level, the properties of matter topic area focuses on distinguishing between physical and chemical properties of matter and understanding the properties of mixtures and solutions and the properties of acids and bases. The study of chemical change focuses on the characteristics of chemical changes and the conservation of matter during chemical changes.

Composition of Matter

1. Structure of atoms and molecules:

ADescribe atoms as composed of subatomic particles (i.e., negatively charged electrons surrounding a nucleus containing positively charged protons and neutrons with no charge).

BDescribe the structure of matter in terms of particles (i.e., atoms and molecules) and describe molecules as combinations of atoms (e.g., H₂O, O₂, CO₂).

2. Elements, compounds, and mixtures:

ADescribe the differences among elements, compounds, and mixtures; differentiate between pure substances (i.e., elements and compounds) and mixtures (homogeneous and heterogeneous) on the basis of their formation and composition.

3. The periodic table of elements:

ARecognize that the periodic table is an arrangement of the known elements; recognize and describe that the elements are arranged in order of the number of protons in the nuclei of the atoms of each element.

BRecognize that an element’s properties (e.g., metal or non-metal, reactivity) can be predicted from its location in the periodic table (i.e., row, or period, and column, or group/family) and that elements in the same group have some properties in common.

Properties of Matter

1. Physical and chemical properties of matter:

ADistinguish between physical and chemical properties of matter.

BRelate uses of materials to their physical properties (e.g., melting point, boiling point, solubility, thermal conductivity).

CRelate uses of materials to their chemical properties (e.g., tendency to rust, flammability).

2. Physical and chemical properties as a basis for classifying matter:

AClassify substances according to physical properties that can be demonstrated or measured (e.g., density, melting or boiling point, solubility, magnetic properties, electrical or thermal conductivity).

BClassify substances according to their chemical properties (e.g., whether the substance is a metal or a nonmetal).

3. Mixtures and solutions:

AExplain how physical methods can be used to separate mixtures into their components.

BDescribe solutions in terms of substance(s) (i.e., solid, liquid, or gas solutes) dissolved in a solvent and relate the concentration of a solution to the amounts of solute and solvent present.

CExplain how temperature, stirring, and surface area in contact with the solvent affect the rate at which solutes dissolve.

4. Properties of acids and bases:

ARecognize everyday substances as acids or bases based on their properties (e.g., acids have pH less than 7; acidic foods usually have a sour taste; bases usually do not react with metals; bases feel slippery).

BRecognize that both acids and bases react with indicators to produce different color changes.

CRecognize that acids and bases neutralize each other.

Chemical Change

1. Characteristics of chemical changes:

ADifferentiate chemical from physical changes in terms of the transformation (reaction) of one or more pure substances (reactants) into different pure substances (products).

BProvide evidence (i.e., temperature changes, gas production, precipitate formation, color change, or light emission) that a chemical change has taken place.

CRecognize that oxygen is needed in oxidation reactions (i.e., combustion, rusting, and tarnishing) and relate these reactions to everyday activities (e.g., burning wood, preserving metal objects).

2. Matter and energy in chemical reactions:

ARecognize that matter is conserved during a chemical reaction and that all of the atoms present at the beginning of the reaction are present at the end of the reaction, but they are rearranged to form new substances.

BRecognize that some chemical reactions release energy (heat) while others absorb it, and classify familiar chemical reactions (e.g., burning, neutralization, the mixing of substances in a chemical cold pack) as either releasing heat or absorbing energy (heat).

CRecognize that chemical reactions occur at different rates and that the rate of reaction can be affected by changing the conditions under which the reaction is taking place (i.e., surface area, temperature, and concentration).

3. Chemical bonds:

ARecognize that a chemical bond results from the attraction between atoms in a compound and that the atoms’ electrons are involved in this bonding.

Physics

As in the chemistry domain, students’ study of physics at the eighth grade extends beyond understanding the scientific basis of common everyday observations to learning many of the central physics concepts that are needed for understanding practical applications of physics or for undertaking advanced study later in their education. The physics domain includes five topic areas:

• Physical states and changes in matter
• Energy transformation and transfer
• Light and sound
• Electricity and magnetism
• Motion and forces

Eighth grade students are expected to be able to describe processes involved in changes in the state of matter and relate states of matter to the distance and movement among particles. They also should be able to identify different forms of energy, describe simple energy transformations, apply the principle of conservation of total energy in practical situations, and understand the difference between thermal energy (heat) and temperature. Students at this level also are expected to know some basic properties of light and sound, relate these properties to observable phenomena, and solve practical problems involving the behavior of light and sound. In the topic area of electricity and magnetism, students should be familiar with the electrical conductivity of common materials, current flow in electric circuits, and the difference between simple series and parallel circuits. They also should be able to describe properties and uses of permanent magnets and electromagnets. Students’ understanding of motion and forces should include knowing general types and characteristics of forces and how simple machines function. They should understand the concepts of pressure and density and be able to predict qualitative changes in motion based on the forces acting on an object.

Physical States and Changes in Matter

1. Motion of particles in solids, liquids, and gases:

ARecognize that atoms and molecules in matter are in constant motion and recognize the differences in relative motion and distance between particles in solids, liquids, and gases; apply knowledge about the movement of and distance between atoms and molecules to explain the physical properties of solids, liquids, and gases (i.e., volume, shape, density, and compressibility).

BRelate changes in temperature of a gas to changes in its volume and/or pressure and changes in the average speed of its particles; relate expansion of solids and liquids to temperature change in terms of the average spacing between particles.

2. Changes in states of matter:

ADescribe changes of state (i.e., melting, freezing, boiling, evaporation, condensation, and sublimation) as resulting from an increase or decrease of thermal energy.

BRelate the rate of change of state to physical factors (e.g., surface area, the temperature of the surroundings).

3. Physical changes:

ARecognize that physical changes do not involve the formation of new substances.

BExplain that mass remains constant during physical changes (e.g., change of state, dissolving solids, thermal expansion).

Energy Transformation and Transfer

1. Forms of energy and the conservation of energy:

AIdentify different forms of energy (e.g., kinetic, potential, light, sound, electrical, thermal, chemical).

BDescribe the energy transformations that take place in common processes (e.g., combustion in an engine to move a car, photosynthesis, the production of hydroelectric power); recognize that the total energy of a closed system is conserved.

2. Thermal energy transfer and thermal conductivity of materials:

ARecognize that temperature remains constant during melting, boiling, and freezing, but thermal energy increases or decreases during a state change.

BRelate the transfer of thermal energy from an object or an area at a higher temperature to one at a lower temperature to cooling and heating; recognize that hot objects cool off and cold objects warm up until they reach the same temperature as their surroundings.

CRecognize that conduction, convection, and radiation are all types of thermal energy transfer; compare the relative thermal conductivity of different materials.

Light and Sound

1. Properties of light:

ADescribe or identify basic properties of light (i.e., speed; transmission through different media; reflection, refraction, absorption, and splitting of white light into its component colors); relate the apparent color of objects to reflected or absorbed light.

BSolve practical problems involving the reflection of light from plane mirrors and the formation of shadows; interpret simple ray diagrams to identify the path of light.

2. Properties of sound:

ARecognize that sound is a wave phenomenon caused by vibration and is characterized by loudness (amplitude) and pitch (frequency); describe some basic properties of sound (i.e., the need for a medium for transmission, reflection and absorption by surfaces, and relative speed through different media which is always slower than light).

BRelate common phenomena (e.g., echoes, hearing thunder after seeing lightning) to the properties of sound.

Electricity and Magnetism

1. Conductors and the flow of electricity in electrical circuits:

AClassify materials as electrical conductors or insulators; identify electrical components or materials that can be used to complete circuits.

BIdentify diagrams representing complete circuits; describe factors that affect electrical current in series or parallel circuits (e.g., the number of batteries and/or bulbs).

2. Properties and uses of permanent magnets and electromagnets:

ARelate properties of permanent magnets (i.e., two opposite poles, attraction/repulsion, and strength of the magnetic force varies with distance) to uses in everyday life (e.g., a directional compass).

BDescribe the properties that are unique to electromagnets (i.e., the strength varies with current, number of coils, and type of metal in the core; the magnetic attraction can be turned on and off; and the poles can switch) and relate properties of electromagnets to uses in everyday life (e.g., doorbell, recycling factory).

Motion and Forces

1. Motion:

   ARecognize the speed of an object as change in position (distance) over time and acceleration as change in speed over time.

2. Common forces and their characteristics:

ADescribe common mechanical forces (e.g., gravitational, normal, friction, elastic, buoyant); recognize and describe weight as a force due to gravity; differentiate between contact and non-contact forces (e.g., friction, gravity).

BRecognize that forces have strength and direction; recognize that for every action force there is an equal and opposite reaction force; recognize and describe the difference in the force of gravity on an object when it is located on different planets (or moons).

3. Effects of forces:

ADescribe the functioning of simple machines (e.g., levers, inclined planes, pulleys, gears).

BExplain floating and sinking in terms of density differences and the effect of buoyant force.

CDescribe pressure in terms of force and area; describe effects related to pressure (e.g., water pressure increasing with depth, a balloon expanding when inflated).

DPredict qualitative one-dimensional changes in motion (speed and direction) of an object based on the forces acting on it; recognize and describe how the force of friction affects motion (e.g., the contact area between surfaces can increase friction and impede motion).

Earth Science

Topics covered in the teaching and learning of Earth science draw on the fields of geology, astronomy, meteorology, hydrology, and oceanography, and are related to concepts in biology, chemistry, and physics. Although separate courses in Earth science covering all of these topics are not taught in all countries, it is expected that understandings related to Earth Science topic areas will have been included in a science curriculum covering the physical and life sciences or in separate courses such as geography and geology. The TIMSS 2019 Science Framework identifies the following topic areas that are universally considered to be important for students at the eighth grade to understand as they learn about the planet on which they live and its place in the universe:

• Earth’s structure and physical features
• Earth’s processes, cycles, and history
• Earth’s resources, their use, and conservation
• Earth in the Solar System and the universe

Eighth grade students are expected to have some general knowledge about the structure and physical features of Earth, including Earth’s structural layers, and the atmosphere. Students also should have a conceptual understanding of processes, cycles, and patterns, including geological processes that have occurred over Earth’s history, the water cycle, and patterns of weather and climate. Students should demonstrate knowledge of Earth’s resources and their use and conservation, and relate this knowledge to practical solutions to resource management issues. At this level, the study of Earth and the Solar System includes understanding how observable phenomena relate to the movements of Earth and the Moon, and describing the features of Earth, the Moon, and other planets.

Earth’s Structure and Physical Features

1. Earth’s structure and physical characteristics:

ADescribe the structure of the Earth (i.e., crust, mantle, and core) and the physical characteristics of these distinct parts.

BDescribe the distribution of water on Earth in terms of its physical state (i.e., ice, water, and water vapor), and fresh versus salt water.

2. Components of Earth’s atmosphere and atmospheric conditions:

ARecognize that Earth’s atmosphere is a mixture of gases; identify the relative abundance of its main components (i.e., nitrogen, oxygen, water vapor, and carbon dioxide), relate these components to everyday processes.

BRelate changes in atmospheric conditions (i.e., temperature and pressure) to changes in altitude.

Earth’s Processes, Cycles, and History

1. Geological processes:

ADescribe the general processes involved in the rock cycle (e.g., the cooling of lava, heat and pressure transforming sediment into rock, weathering, erosion).

BIdentify or describe changes to Earth’s surface (e.g., mountain building), resulting from major geological events (e.g., glaciation, the movement of tectonic plates and subsequent earthquakes and volcanic eruptions).

CExplain the formation of fossils and fossil fuels; use evidence from the fossil record to explain how the environment has changed over long periods of time.

2. Earth’s water cycle:

ADescribe the processes in Earth’s water cycle (i.e., evaporation, condensation, transportation, and precipitation) and recognize the Sun as the source of energy for the water cycle.

BDescribe the role of cloud movement and water flow in the circulation and renewal of fresh water on Earth’s surface.

3. Weather and climate:

ADistinguish between weather (i.e., day-to-day variations in temperature, humidity, precipitation in the form of rain or snow, clouds, and wind) and climate (i.e., long-term typical weather patterns in a geographic area).

BInterpret data or maps of weather patterns to identify climate types.

CRelate the climate and seasonal variations in weather patterns to global and local factors (e.g., latitude, altitude, geography).

DIdentify or describe evidence for climate changes (e.g., changes that occur during ice ages, changes that are related to global warming).

Earth’s Resources, Their Use and Conservation

1. Managing Earth’s resources:

AProvide examples of Earth’s renewable and nonrenewable resources.

BDiscuss advantages and disadvantages of different energy sources (e.g., sunlight, wind, flowing water, geothermal, oil, coal, gas, nuclear).

CDescribe methods of conservation of Earth’s resources and methods of waste management (e.g., recycling).

2. Land and water use:

AExplain how common methods of land use (e.g., farming, logging, mining) can affect land and water resources.

BExplain the importance of water conservation, and describe methods for ensuring that fresh water is available for human activities (e.g., desalination, purification).

Earth in the Solar System and the Universe

1. Observable phenomena on Earth resulting from movements of Earth and the Moon:

ADescribe the effects of the Earth’s annual revolution around the Sun, given the tilt of its axis (e.g., different seasons, different constellations visible at different times of the year).

BRecognize that tides are caused by the gravitational pull of the Moon, and relate phases of the Moon and eclipses to the relative positions of Earth, the Moon, and the Sun.

2. The Sun, stars, Earth, Moon, and planets:

ARecognize that the Sun is a star and provides light and heat to each member of the Solar System; explain that the Sun and other stars produce their own light, but that other members of the Solar System are visible because of light reflected from the Sun.

BCompare and contrast certain physical features of Earth with those of the Moon and other planets (e.g., presence and composition of an atmosphere, average surface temperature, presence of water, mass, gravity, distance from the Sun, period of revolution and rotation, ability to support life); recognize that the force of gravity keeps planets and moons in their orbits.