Science Study Guide for the GED Test

General Information

You will be allowed to use a calculator for this section of the GED test. See our Mathematical Reasoning Study Guide for calculator guidelines and a peek at the reference sheet, to which you will also have access during the test.

Types of Questions

When taking the Science section of the GED test, you will have 90 minutes to complete the entire section. It includes answering multiple-choice questions as well as items of these types:

• Fill-in-the-blank: These items require you to type a word or short phrase in an answer box.

• Drag-and-drop: This type of question asks you to move an item on the screen from one place to another. It enables you to place an event in sequence or an object in a category.

• Drop-down: After you choose your answer from a drop-down menu, the text on the screen will change to show how your answer fits in the item text.

• Hot spot: This type of question will require you to mark a particular spot on the screen by clicking on it.

There are no longer any short answer questions on the GED Science Test. These were discontinued in 2018.

Subject Areas Covered

Within the subject of science, you must be able to read and understand passages concerning various science topics. You will also need to solve problems related to three topics. The questions fall into the following fields of study in this manner:

• Life science: 40%

• Physical science: 40%

• Earth and space science: 20%

About half of the Science questions refer to a passage or graphic (graph or chart), and the remaining questions are stand-alone items.

Science Practices

As you study, become comfortable using the scientific method in these ways:

• Scientific presentations: Understand the symbols, terms, and phrases used in both textual (written) and non-textual (graphic) reports or documents.

• Investigation design: Be able to work with hypotheses, errors, and variables.

• Reasoning from data: Use sampling techniques and review data to state conclusions and make predictions based on the data presented.

• Be able to assess the findings of an investigation (observation or experiment) and come to conclusions about it.

• Use words, symbols, and graphics to express the results of an investigation.

• Be able to understand and use scientific theories.

• Use statistics to describe and solve data problems, including combinations and permutations.

Science Concepts

To do well on the Science section of the test, you must have a basic understanding of the following topics and related concepts:

Life Science Topics to Know for the GED

• Human Body and Health: body systems, homeostasis, nutrition, disease transmission and prevention, pathogens.

• Life Functions and Energy: photosynthesis, respiration, fermentation.

• Energy Flows in Ecologic Networks (Ecosystems): flow and sources of energy, the flow of matter in ecosystems, the effects of changes in communities or environment, carrying capacity, symbiosis, and disruption of ecosystems.

• Essential Functions of Life: chemical reactions, preproduction, metabolism, parts of a cell, cell theory, cell organization, mitosis, meiosis.

• Molecular Basis for Heredity: DNA, chromosomes, genotypes, phenotypes, Punnett squares, pedigree charts, alleles, mutations, epigenetics.

• Evolution: common ancestry and cladograms, selection, adaptation, selection pressure, speciation.

Structure and Function of Living Things

Amino Acids

Biological molecules are classified based on the type of atoms they contain and their arrangement. Most biologically important molecules are made of carbon, oxygen, and hydrogen atoms. Amino acids have an amino group (\(NH_2\)) and a carboxyl group (a carbon-oxygen double bond plus OH). Amino acids are the building blocks of proteins.

Proteins

Proteins are an important class of macromolecules used by every living organism. Proteins are built from basic units called amino acids. The type and order of amino acids will determine the structure and function of the protein. In turn, the sequence of amino acids is encoded in DNA. DNA has basic units called nucleotides. A sequence of 3 nucleotides (codon) specifies a particular amino acid that will be incorporated into the protein. A sequence of these triplets will encode the amino acids for an entire protein.

Multicellular Organisms

Multicellular organisms are organized into systems of specialized cells that perform the specific functions needed to keep the organism alive. The systems have components, usually organs, that interact and depend on each other and on other systems to perform their functions. For example, the proper functioning of the intestines depends on the stomach digesting food adequately, but it also depends on the nervous and endocrine systems for correct signals.

Homeostasis

Homeostasis refers to the ability of an organism to maintain stable conditions. If these conditions change, the organism activates processes to return to the proper levels. For example, if the body temperature drops, muscles will shiver to generate heat. If it is too warm, perspiration will occur to help lower the body temperature. The animal may also change its behavior to facilitate these changes, such as moving between shady and sunny areas.

Mitosis

Mitosis is the process of cell division and results in two identical cells. Genetic material is duplicated to pass a complete set of chromosomes to both cells. In this way, the organism can replace dead cells and grow. Through a differentiation process, cells can develop specialized functions, different from the cell that produced them. Differentiation occurs as specific genes are activated and deactivated in the cell. For example, all the different types of blood cells are differentiated from hematopoietic stem cells that have undergone mitosis.

Photosynthesis

Photosynthesis is the process used by plants and some other organisms to convert the energy in sunlight into chemical energy. The chemical energy is stored in the chemical bonds of carbohydrate molecules. The energy from sunlight is used to convert the reactants of water (\(H_2O\)) and carbon dioxide (\(CO_2\)) into the products of sugar molecules (\(C_6H_{12}O_6\)) and oxygen (\(O_2\)). Oxygen is released as a by-product. Photosynthesis occurs in the chloroplasts of eukaryotic cells.

Cellular Respiration

In cellular respiration, the chemical energy in the bonds of carbohydrate molecules is released and captured to be used to maintain the cell. The sugar molecules (\(C_6H_{12}O_6\)), oxygen (\(O_2\)), and water (\(H_2O\)) enter a series of reactions where energy from the bonds in the sugar molecule is captured by smaller molecules and delivered to sites where energy is required. In the process, carbon dioxide (\(CO_2\)) and more water (\(H_2O\)) are released as by-products.

Ecosystems

Carrying Capacity

The carrying capacity is defined for a given population of organisms for a specific area. It is the population level of that organism that the environment can support. The carrying capacity can change upward or downward depending on conditions such as food availability, room for territory, and the presence of competing species.

Biodiversity and Populations

Biodiversity measures the variety and abundance of different species in an ecosystem. A high level of biodiversity is considered an essential contributor to the stability of an ecosystem. Biodiversity can be affected by any factor that promotes or inhibits a variety of species. For example, more microclimates may enhance diversity by favoring various species. An invasive species may overrun an area, deplete resources for many other species, and decrease biodiversity.

Aerobic Conditions and Anaerobic Respiration

Anaerobic respiration occurs in the absence of oxygen. It was the original form of respiration among Earth’s first bacteria. Although anaerobic respiration may not be noticed in today’s oxygen-rich atmosphere, many bacteria still use these processes and provide essential links in global nutrient cycles. Examples of these cycles are the conversion of nitrates to nitrogen and methane production.

Carbon Cycles

Photosynthesis and cellular respiration are significant flows in the global carbon cycle. Photosynthesis removes carbon dioxide from the atmosphere and “fixes” the carbon in the form of plant structures (e.g., carbohydrate synthesis). Cellular respiration returns carbon dioxide to the atmosphere when the plant matter decays.

Changing Ecosystem Conditions

The variety and population levels of a species in an ecosystem result from many interactions among these species and environmental conditions. In a stable ecosystem, these populations remain relatively steady. However, change, such as removing a species, can radically alter an ecosystem’s composition. This change has been noted in studies where the keystone species was removed from ecosystems.

Human Impact on the Environment

Humans can reduce impacts on the global environment by increasing their understanding of ecological processes and interactions. Actions such as burning fossil fuels have changed the carbon cycle by adding more carbon dioxide to the air. Humans can reduce these trends and engage in other activities, such as promoting forest growth, which would help remove some excess carbon dioxide.

Survival in an Ecosystem

The survival of a species in an ecosystem depends on the ability of individuals of the species to reproduce. Both individual and group behaviors can enhance survival and reproduction. An individual that is more aggressive or inquisitive may survive better and reproduce more. Group behavior, such as living as part of a herd, can increase survivorship by providing better protection. Group behaviors often demonstrate interesting exceptions to the general rule of competition.

Genetics

Genetics studies how biological information is inherited from one generation to the next. It tells us how the information is encoded and transformed into the structures and functions of the organism. Genetics also studies variations within a species and what causes these variations.

DNA and Chromosomes

The chromosomes of a cell contain DNA. DNA is a molecule that encodes the instructions to make all the proteins in cells. These proteins perform the functions of cells and can make up important structures. These structures and functions are visualized as various traits of an organism. DNA can be thought of as a blueprint for the cells and instructions for every organism.

Genetic Variations

Genetic variations are the basis of change in a species, allowing it to adapt to its environment. As DNA is replicated and passed on to new generations, changes can occur in the DNA sequence causing variation in the species. This can occur during meiosis as copies of DNA are made in the reproductive cells. Errors can also be introduced when DNA is replicated during cell division or when an environmental factor damages DNA.

Statistics and Probability in Genetics

The principles of genetics predict the distribution of genes and traits in a population. Different genetic processes will cause different distributions. Statistics can be used to test an observed set of traits in a population against various genetic models to see which genetic process is most likely responsible. Examples of this are dominant and recessive genes.

Unity and Diversity

Ancestry and Biological Evolution

Modern DNA analysis has given us the most direct way to establish relationships and show trends in evolution. The same DNA sequences can be seen in various organisms and show a relationship between them. Other clues to similar ancestry include anatomical structures and patterns of development in embryos.

Natural Selection

The argument for natural selection is based on four observations:

1. All organisms produce far more offspring than can survive in a given environment.

2. The traits that help them survive are variable among the individuals.

3. These traits can be passed to offspring.

4. Traits that favor survival will allow that individual to reproduce more, passing those favorable traits on in greater numbers to the next generation.

Adaptation

Changes in the environment will allow individuals better adapted to those changes to survive and pass on that trait. The population will change as this trait becomes more common. This was demonstrated by the researchers Rosemary and Peter Grant, who examined the beak sizes of Galapagos finches and compared them to the available food sources. Beak size determines what food the birds can access.

Traits and Environmental Changes

An organism’s traits allow it to adapt (or not adapt) to environmental changes. Some species are generalists, can adapt to environmental changes, and can increase after a change. Others are specialists and may not be able to adapt to extreme changes and disappear from an area. A drastic change may cause favorable conditions that allow a new species to move into an area.

Human Impact on Biodiversity

Human actions can impact biodiversity, usually decreasing it as an unintended effect. Human-induced changes can occur too rapidly, and species don’t have time to adapt. Humans can intentionally or accidentally introduce new species to an area. These new species can overrun an area because there are no natural checks and balances. Humans can also intentionally restore habitats and improve biodiversity.

Physical Science Topics to Know for the GED

• Conservation, Transformation, and Flow of Energy: heat, temperature, conduction, convection, endothermic and exothermic reactions, types of energy (kinetic, mechanical, chemical), transformation between types of energy, energy sources (nuclear, sun, fossil fuels), waves and wavelengths, electromagnetic radiation.

• Work, Motion, and Forces: speed, velocity, acceleration, momentum, collisions, force, Newton’s laws, gravity, mass and weight, work simple machines, mechanical advantages.

• Chemical Properties and Reactions Related to Living Systems: structure of matter, physical and chemical properties, changes of state, density, balancing chemical equations, conservation of mass, solubility, solutions.

Energy

Energy is commonly defined as the ability to do work. The conversion and transfer of energy are at the heart of economic activity and biological and ecological processes. The energy content in molecular bonds will determine whether a particular reaction will occur.

Energy in a System

Energy is neither created nor destroyed. If the energy in one component of a system changes, energy changes will also occur in other parts of the system. In principle, if all of these can be measured, it is possible to calculate the change in one component if all of the other changes and the energy flows are known. An energy budget for the system can describe this process quantitatively.

Particles and Energy

The total energy of an object is the sum of its energy due to motion (kinetic energy) and its energy due to its position. For example, a ball that has been thrown upward has kinetic energy due to its motion and potential energy due to its height above the ground. As it gains altitude, it loses speed, and the kinetic energy decreases. However, since it is higher, it has gained equal potential energy, and the sum of potential and kinetic energy remains constant.

Energy Conversion

Energy can be converted from one form to another. For example, the chemical potential energy in a battery can be converted into electrical energy. The electrical energy might power a motor that converts electrical energy to mechanical energy to do work. However, these conversions are never 100% efficient. Some energy is always lost as heat energy. The efficiency of a process is the ratio of the total useful energy output compared to the original energy input.

Thermal Energy

Thermal energy will always move from areas of higher temperature to regions of lower temperature. Suppose two objects of different temperatures are in a closed system (heat cannot enter or leave). In that case, thermal energy will flow from the hotter to the cooler object, resulting in an intermediate temperature. If liquids of different temperatures are mixed, the resulting liquid will be at a medium temperature.

Interactions with Electric and Magnetic Fields

Objects interacting through electrical charges or magnetic fields can attract or repel each other. Opposite charges or magnetic poles attract; similar charges or poles repel. These forces follow an inverse square law and diminish rapidly when the distance between the particles increases. When the space gets too great, the force is so weak that it will not affect the motion of the particles. Less than this distance, there is a zone where the particles cannot stay. They will be repelled farther away until the force is too weak to affect them, or they will be attracted to each other if the distance between them is zero.

Waves and Technology

Light, radio, and microwaves are all forms of electromagnetic radiation. Along with sound, they travel as waves. Understanding the nature of waves was vital in the widespread use of sound waves and electromagnetic radiation in our modern technologies.

Frequency, Wavelength, and Speed

For any wave, the speed of the wave is the product of its frequency and its wavelength. If you know any two of these variables, you can calculate the third one. The speed of a wave is a constant in any given medium. For example, the rate of sound waves in the air is 330 to 350 meters per second, depending on the temperature. Any sound’s frequency and wavelength will multiply to this constant speed, no matter what the pitch or frequency of the sound is.

Digital Transmission and Storage

Digital transmission and storage of information are done by encoding the data as a series of 0s and 1s (binary code). The code itself does not degrade over time, as might happen with the pages of a book. Digital information can be copied and transmitted repeatedly without any loss. Each copy is just as high quality as the original. Digital information can easily be stolen, and it is also very easy to erase by accident.

Electromagnetic Radiation

Light is an example of electromagnetic radiation. Other examples are microwaves, radio waves, and x-rays. Electromagnetic radiation exhibits many properties of waves. They have wavelengths and frequencies and show behaviors such as diffraction and interference. However, electromagnetic radiation also shows the properties of being a particle. In this case, a particle of light is called a photon. An example of particle behavior is the photoelectric effect, where light striking a material will cause an electric current in that material.

Waves and Technological Devices

Many modern devices use the properties of waves in some way. The interaction of microwaves with water molecules is the basis for microwave cooking. GPS technology must account for the behavior of waves in Earth’s gravitational field. Cell phones are a network of radio wave communications.

Matter

The Periodic Table

The periodic table organizes the chemical elements according to their atomic structure and chemical behavior. The smallest atoms are at the top and the largest ones at the bottom. Atoms increase in size from left to right in each row. Elements in the same column have similar atomic structures, usually because the number of electrons in their outermost shell is the same. This gives elements in each column similar chemical properties and reactions.

Simple Chemical Reactions

Simple chemical reactions are based on the number of electrons in the outer shell. Atoms will donate, accept, or share electrons to end up with eight electrons in the outer shell (the exception is Hydrogen, whose outer shell has two electrons).

For example, sodium (\(Na\)) has one electron in the outer shell, and chlorine (\(Cl\)) has seven. One atom of sodium will donate an electron to one atom of chlorine, forming sodium chloride, \(NaCl\).

Oxygen (\(O\)) has six outer electrons and will accept or share two others. Hydrogen (\(H\)) has only one outer electron, so two atoms of \(H\) are needed to complete the outer shell of \(O\), resulting in water, \(H2O\).

Electrical Forces Between Particles

Electrical forces occur between particles. Negative and positive charges act on the particles to attract and repel them from each other. The strength of these forces will determine a substance’s phase (solid, liquid, gas) and properties, such as melting and boiling points. Stronger attractive forces require higher temperatures to separate the particles. For example, substances with strong attractive forces between the molecules will tend to be solid at room temperature and have a higher boiling point.

Energy in Chemical Reactions

A chemical reaction may require a net input of energy or yield a net output of energy. If the energy in the reactants’ chemical bonds (bond energy) is greater than the bond energy in the products, the reaction will release energy. The reaction will consume energy if the products have a greater bond energy than the reactants. Energy is conserved, so the energy consumed or released will match the difference in energy between reactants and products. Note that many reactions require an initial activation energy, even if they eventually release energy.

Temperature and Chemical Reactions

The rate at which a chemical reaction occurs depends on the interactions between the reacting particles. There are two ways to speed up these reactions: increase the speed of the particles or increase the number of particles so they find each other faster. The speed of particles increases by raising the temperature. Increasing the concentration of the reactants will increase the number of particles.

Creating Equilibrium

Le Chatelier’s Principle states that if the equilibrium of a reaction is disturbed by changing the conditions, the equilibrium will move to counteract these changes. For example, if more reactants are added, the system will counteract this and increase the rate at which these extra reactants are converted into products. This principle can be used to manipulate reactions to yield products at a faster pace.

Showing Conservation of Mass

Mass can not be created or destroyed. Atoms interact during a chemical reaction, and their mass is unchanged by the chemical reaction. A balanced chemical reaction is a visual model showing that mass is conserved in a chemical reaction. For any atom in the reaction, the total number on the left side of the equation before the reaction is the same as the total number on the right side after the reaction. Atoms are not created or destroyed in a reaction. The atoms only change how they are combined with other atoms.

Fission, Fusion, and Radioactive Decay

In fission, fusion, or radioactive decay, the actual structure of the atom changes, and it gains or loses electrons, protons, or neutrons. If the number of protons changes, the atom is transformed into a different type of atom. Matter is converted directly into energy in these reactions. A minimal amount of matter releases enormous energy in these processes, as summarized in Einstein’s famous equation \(E =mc^2\).

Motion and Forces

Newton’s Second Law of Motion

Newton’s second law of motion describes the relationship between the net force on an object (\(F\)), its mass (\(m\)), and the acceleration of the object (\(a\)) as the mathematical relationship \(F = ma\). We can calculate the third one if we know any of these properties. We will see a distinct pattern because of this relationship if we plot these three quantities for a moving object.

Momentum

The momentum of an object is defined as the product of its mass and velocity, \(momentum = mv\). The total momentum is conserved for any pair of objects with no outside forces acting on them. If these objects interact with each other, such as in a collision, any momentum gained by one of the objects is balanced by a loss of momentum from the other object.

Collision Force

When an object collides, its momentum changes. The change in momentum is caused by force exerted for a duration of time. The product of the force and the time duration is called impulse.

The formula for impulse (\(J\)) = \(force (F) \cdot time (t)\).

Since momentum is conserved, the impulse is equal to the initial momentum of the object. The product \(Ft\) is constant for any given collision, and \(F\) and \(t\) balance each other. If the time of the collision can be increased, the force will decrease so that the product \(Ft\) remains the same. Cushioning works to protect objects during impact because it lengthens the time of the crash, thus reducing the force of impact.

Newton’s Law of Gravity and Coulomb’s Law

Newton’s law of gravity states that \(F = \frac{Gm_1m_2}{d_2}\), where:

• \(F\) is the gravitational force between the objects
• \(G\) is a constant
• \(m_1\) and \(m_2\) are the masses of the objects
• \(d\) is the distance between them

This formula shows force will increase if the mass of either object increases and the force gets much smaller when the distance grows. If the distance increases by a factor of three, the force decreases by a factor of \(32 = 9\). This is known as an inverse square law.

Coulomb’s law for electrostatic force is very similar: \(F = \frac{kq_1q_2}{d_2}\), where:

• \(q_1\) and \(q_2\) represent the electrostatic charges
• \(k\) is a different constant
• \(F\) is electrostatic force
• \(d\) is the distance

Magnetic Fields and Electric Currents

Magnetism and electricity are closely interrelated. A magnetic compass near a working electric circuit will change its heading, showing a magnetic field around the flowing electricity. A magnet moved through a coil of wire will produce an electric current, which can be seen if a bulb is connected in a circuit with the wire coil. This is the basis of how electricity is generated in homes and industries.

Molecular Structure and Design

Molecular structure and the electrostatic charges of molecules will often determine how a given material might function. Long, chained molecules such as cellulose in plants produce strong, light structures such as wood. The electrical properties of molecules will determine if they can be used as conductors or insulators. This is usually related to how well electrons can move within the material.