8th Grade Science Benchmark Review

The Law of Conservation of Mass states that mass cannot be created or destroyed in ordinary chemical and physical changes, but only transformed from one form to another. The Law of Conservation of Energy states that energy can be neither created nor destroyed in a closed system, but only transformed from one form to another. In living systems, these laws mean that matter and energy are constantly being transferred within and between organisms and their environment. For example, plants take in sunlight and use it to convert carbon dioxide and water into glucose and oxygen, demonstrating the transformation of energy and mass.

The carbon cycle is a natural process that involves the exchange of carbon within and between organisms and the physical environment. It includes processes like photosynthesis, respiration, decomposition, and fossil fuel combustion. In photosynthesis, plants absorb carbon dioxide and use it to create energy. Respiration releases carbon dioxide back into the atmosphere. Decomposition breaks down dead organisms and releases carbon. The burning of fossil fuels also releases carbon into the atmosphere.

The periodic table is organized based on elements' properties. Elements within a group share similar behaviors such as reactivity or the number of electrons in their outer shell. Elements in the same period have the same number of electron shells.

There are a limited number of elements that exist naturally. These elements combine in various ways to form countless compounds. All living and non-living things are made up of these compounds. For example, water is made up of hydrogen and oxygen, salt is made up of sodium and chlorine. These are just two examples, but there are countless compounds formed from combining different elements.

Physical properties of a substance are those that can be observed or measured without changing the substance's chemical composition. They include features like density, electrical conductivity, magnetic properties, melting and boiling points, and solubility. These properties are intrinsic to the substance and do not depend on the amount of the sample. For instance, the density of water is always 1 g/mL, regardless of whether you have a drop or a gallon.

Density measures how much mass is packed into a given volume. It is calculated by dividing the mass of a substance by its volume. Different materials have different densities. For instance, a block of wood is less dense than a block of lead of the same size.

Technology plays a vital role in advancing scientific understanding. It provides tools for accessing remote locations like outer space, collecting samples, making measurements, storing and analyzing data, and communicating information. For example, telescopes allow us to study distant planets, satellites help us monitor weather patterns, and computers enable us to process and share scientific discoveries.

The vastness of space means that objects are incredibly far apart. Our understanding of light and space travel helps us comprehend these distances. Light travels at a finite speed, so it takes time for light from distant objects to reach us. It also takes years for spacecraft to travel vast distances, highlighting the scale of the universe. For instance, the light from the nearest star to us, Proxima Centauri, takes over four years to reach Earth!

Scientific investigations involve a systematic process of gathering evidence, applying logic, and using imagination. Scientists first define a problem and then develop hypotheses, predictions, and models based on their observations. They collect relevant data, analyze it, and draw conclusions. By constantly testing their assumptions and refining their understanding, scientists make progress in unraveling natural phenomena.

Repeated trials ensure that the results of an experiment are reliable and not due to chance. Each trial is conducted under the same conditions to minimize variations and identify patterns. For example, if you are testing the effect of fertilizer on plant growth, you would need to repeat the experiment with multiple plants and compare the results to ensure that the fertilizer is truly causing the growth.

Replication involves repeating an experiment by someone else, often in a different location, to verify the original findings. Replication strengthens the reliability of the results and increases confidence in the scientific discovery. If another scientist can repeat the experiment and obtain similar results, it adds weight to the validity of the findings.

A scientific problem is a question or issue that motivates a scientific investigation. Scientists use reference materials like textbooks, scientific journals, and online databases to gain knowledge and understanding of the problem. They then plan and design experiments to investigate the problem, gathering data, analyzing it, and drawing conclusions based on their findings. Problems can range from understanding the effect of pollution on plant growth to investigating the properties of a newly discovered material.

Producers, consumers, and decomposers play distinct roles in energy transfer within a food web. Producers are organisms that capture energy from the sun through photosynthesis (like plants). Consumers, like animals, cannot produce their own food and get energy by consuming other organisms. Decomposers, such as fungi and bacteria, break down dead organisms and waste, releasing nutrients back into the ecosystem. All these roles are interconnected in a complex web of energy flow, demonstrating the interdependence of living organisms in an ecosystem.

The theory of evolution by natural selection explains how species change over time. The inability of a species to adapt to a changing environment can lead to its extinction. This is because they may not possess the traits necessary to survive in the new conditions, such as a changing climate, competition for resources, or the introduction of new predators. These less-adapted species may struggle to find food, mates, or shelter, ultimately leading to their decline.

Heat energy always moves from warmer objects to cooler ones until they reach the same temperature. This is known as thermal equilibrium. For example, if you have a warm cup of coffee and place it on a cold table, the heat from the coffee will transfer to the table until both reach the same temperature. Similarly, if you hold a hot cup of coffee, heat will transfer from the cup to your hand until both reach a thermal equilibrium.

Adding heat to or removing heat from a system can cause changes in its temperature and possibly its state. For example, heating ice will cause it to melt into liquid water, and cooling water will cause it to freeze into ice. Similarly, heating liquid water will cause it to boil into steam or gas. These changes in state are directly related to the energy present in the system.

Different materials transmit waves at different speeds. Light travels at different speeds in air, water, and glass. Sound travels faster in solids compared to liquids and gases. For example, light travels faster in air than in water, which is why objects appear to be bent when submerged. Sound waves travel faster in steel than in air, so you hear sounds from a train passing by sooner if you are touching the tracks.

Light can be reflected, refracted, or absorbed depending on the material it interacts with. Reflection occurs when light bounces off a surface, like a mirror. Refraction happens when light bends as it passes from one medium to another, like from air to water. Absorption happens when light is taken in by a material and not reflected or transmitted. For example, a black surface absorbs most light, while a white surface reflects most light.

The theory of plate tectonics explains the movement of Earth's crustal plates. These plates move slowly, causing both slow and rapid changes on Earth's surface. Slow changes include the formation of mountains, continents, and ocean basins over millions of years. Rapid changes include earthquakes and volcanic eruptions. Earthquakes result from the sudden release of built-up energy at the plate boundaries. Volcanic eruptions occur when molten rock from Earth's mantle erupts through the surface.

Scientific theories are well-supported and widely accepted explanations of natural phenomena based on a large body of evidence. They are not simply guesses or claims but rather explanations that have been rigorously tested and verified. Laws, on the other hand, are statements that describe consistent patterns in nature, often expressed mathematically. Theories explain why these patterns occur, and laws describe what happens. For example, the theory of gravity explains why objects fall to the ground, while the law of gravity describes the force of attraction between objects with mass.

Scientific knowledge is dynamic and constantly evolving as new evidence and interpretations emerge. Throughout history, scientists have made discoveries that have challenged existing theories and led to new understandings. For example, the discovery of the atom challenged the idea that matter was infinitely divisible. Advancements in technology continually provide new tools and insights, prompting revisions to our understanding of the world.

The Sun's influence on Earth manifests in several ways, including seasons and gravitational attraction. The Earth's tilt on its axis and its revolution around the Sun cause different parts of the Earth to experience different amounts of sunlight throughout the year, resulting in seasons. The Sun exerts a gravitational pull on Earth, keeping it in orbit and being the dominant force in the Solar System.

The Moon's influence on the Earth is evident in phenomena like phases, tides, and eclipses. The Moon's phases are caused by the changing angles at which the Sun illuminates the Moon as it orbits the Earth. Tides are caused by the Moon's gravitational pull on Earth's oceans. Eclipses occur when the Moon passes between the Sun and the Earth (solar eclipse) or when the Earth passes between the Sun and the Moon (lunar eclipse) .

Mutualism, predation, parasitism, competition, and commensalism are different relationships among organisms. Mutualism benefits both organisms involved (example: bees pollinate flowers while gathering nectar). Predation involves one species hunting another (example: lions hunting zebras). Parasitism benefits one organism at the expense of the other (example: fleas on dogs). Competition occurs when organisms struggle for the same resources (example: plants competing for sunlight). Commensalism benefits one organism without harming or benefiting the other (example: barnacles on whales).

Genetic variation, or differences in genes among individuals of a species, is essential for evolution by natural selection. This variation arises from mutations or changes in DNA. Environmental factors, such as climate change, food availability, or the presence of predators, can also influence how traits are selected for or against. Those individuals with traits best suited to the changing environment are more likely to survive, reproduce, and pass on their genes, leading to the gradual evolution of the species over generations.

The Sun's energy reaches Earth as radiation, including a wide range of wavelengths, such as infrared, visible, and ultraviolet light. White light is a combination of these different colors, as seen in a rainbow. Infrared light is a type of heat, while ultraviolet light has more energy and can be harmful to living organisms. It is the Sun's energy that drives the Earth's weather, climate, and life processes.

Replication, repetition, and multiple trials are terms used in research. Replication is when a scientist repeats an experiment independently from another scientist. Repetition is when a scientist repeats the same experiment multiple times usually to confirm the results are reliable and not due to errors. Multiple trials imply that the experiment is repeated numerous times, similar to repetition, to ensure the results are reproducible and statistically significant.

The Linnaean system is a hierarchical classification of organisms, grouping them into increasingly specific categories: kingdom, phylum, class, order, family, genus, and species. Recent advancements have led to the addition of a broader category called 'Domain.' This system is based on shared characteristics, such as physical structures, evolutionary relationships, and genetic similarities. Domain encompasses three main groups: Archaea, Bacteria, and Eukarya.

Cell theory is a unifying principle in biology that explains the fundamental basis of life. It has three main points: 1) All organisms are composed of cells, either single-celled or multicellular. 2) All cells arise from pre-existing cells through cell division. 3) Cells are the basic unit of life and perform all the functions that make life possible like metabolism, growth, and reproduction. It revolutionized our understanding of life and its fundamental building blocks.

Organisms are organized hierarchically, from the smallest level of atoms and molecules to the largest level of organisms. Atoms are the basic building blocks of matter and combine to form molecules. Molecules then assemble to form cells. Similar cells form tissues, tissues form organs, organs form organ systems, and lastly, organ systems work together to form a complete organism. This hierarchical organization reflects the complexity of life at different levels.

Energy provided by the Sun drives global patterns of atmospheric movement and temperature differences. The Sun unevenly heats different regions of the Earth, creating temperature differences between air, water, and land. This temperature disparity leads to air currents, winds, and ocean currents, influencing regional climates and weather patterns around the globe. The unequal heating of Earth is a major driving force in the Earth's climate system.

Physical changes alter a substance's appearance but not its chemical composition. For example, melting ice is a physical change because it changes the state of matter from solid to liquid, but the chemical composition remains the same. Chemical changes result in new substances with different chemical properties. For example, burning wood is a chemical change because it changes the wood into ash, carbon dioxide, and water vapor.

The Solar System is a collection of objects that orbit the Sun. These include planets, moons, asteroids, comets, and dwarf planets. Each of these objects has its own unique characteristics, including gravitational force, distance from the Sun, speed, movement, temperature, and atmospheric conditions. For example, Jupiter is a gas giant with a strong gravitational pull, while Mars is a rocky planet with a thin atmosphere.

Stars, the building blocks of galaxies, have physical properties that differentiate them. Apparent magnitude refers to the brightness of a star as seen from Earth. Temperature is measured by color, with hotter stars appearing bluer and cooler stars appearing redder. Size varies greatly among stars, ranging from small dwarfs to giant supergiants. Luminosity refers to the total energy output of a star, or its absolute brightness, determined by size and temperature.

The universe is organized hierarchically, with planets orbiting stars, stars forming galaxies, and galaxies forming clusters and superclusters. This organization also reflects the size and composition of these celestial objects. For example, our Solar System is a part of the Milky Way galaxy, which contains billions of stars and is just one of many galaxies in the universe.

Scientific explanations are pursued using different methods in various fields of science. Biologists use experiments, observations, and data analysis to understand life processes. Geologists use fieldwork, rock analysis, and Earth history to understand Earth's formation and evolution. Physicists use theoretical models, experiments, and mathematical equations to study the fundamental laws of nature. While the approaches may differ, all scientific fields aim to explain natural phenomena based on evidence and logical reasoning.