114 terms

8th grade science, Virginia SOL, key concepts, part 2

The living organisms within a specific area and their physical environment define an ecosystem. Characteristics of land, marine, and freshwater ecosystems vary with respect to biotic and abiotic factors.
The major terrestrial ecosystems are classified into units called biomes — large regions characterized by certain conditions, including a range of climate and ecological communities adapted to those conditions.
They have specific structures, functions, and behaviors that enable them to survive the biotic and abiotic conditions of the particular ecosystem in which they live. Organisms possess adaptations to both biotic and abiotic factors in their ecosystem that increase their chance of survival.
Relationship between organisms, populations, communities and ecosystems.
Organisms may exist as members of a population; populations interact with other populations in a community; and communities together with the physical environment form ecosystems.
Plants may respond to light by growing toward it or away from it, a behavior known as phototropism.
Animals may respond to cold conditions with a period of lowered metabolism, a behavior known as hibernation.
Organisms may respond to adverse conditions with a period of lowered or suspended metabolism, a behavior known as dormancy.
What environmental factors may cause the size of a population to increase or decrease.
Long-term changes may affect entire communities and ecosystems. Such large-scale changes include the addition of excess nutrients to the system (eutrophication), which alters environmental balance; dramatic changes in climate; and catastrophic events, such as fire, drought, flood, and earthquakes.
Role of humans in ecosystems.
Ecosystems are dynamic systems. Humans are a natural part of the ecosystem. Humans use the ecosystem to meet their basic needs, such as to obtain food.
Effect of humans on ecosystems.
Human interaction can directly alter habitat size, the quality of available resources in a habitat, and the structure of habitat components. Such interactions can be positive and/or negative. Human input can disturb the balance of populations that occur in a stable ecosystem. These disturbances may lead to a decrease or increase in a population. Since populations in an ecosystem are interdependent, these disturbances have a ripple effect throughout the ecosystem.The interaction of humans with the dynamic ecosystem may lead to issues of concern for continued ecosystem health in areas such as water supply, air quality, energy production, and waste management.
DNA is a molecule that includes different components — sugars, nitrogenous bases, and phosphates. The arrangement of the nitrogenous bases within the double helix forms a chemical code.
Chromosomes are strands of tightly wound DNA. Genes are sections of a chromosome that carry the code for a particular trait.
Mendelian genetics
The basic laws of Mendelian genetics explain the transmission of most traits that can be inherited from generation to generation.
A Punnett square
A model used to predict the possible combinations of inherited factors resulting from single trait crosses.
Dominant traits...
mask the expression (phenotype) of recessive traits.
The specific combination of dominant and recessive gene forms.
Difference between traits and characteristics
Traits that are expressed through genes can be inherited. Characteristics that are acquired through environmental influences, such as injuries or practiced skills, cannot be inherited.
Genetic engineering
Manipulation of the genetic code is manipulated to obtain a desired product. Genetic engineering has numerous practical applications in medicine, agriculture, and biology.
Mechanisms through which evolution takes place
A related set of processes that include mutation, adaptation, natural selection, and extinction. This results in changes in populations of organisms over time.
Inheritable changes because a mutation is a change in the DNA code. A mutation may result in a favorable change or adaptation in genetic information that improves a species' ability to exist in its environment, or a mutation may result in an unfavorable change that does not improve or impedes a species' ability to exist in its environment.
Structures, functions, or behaviors that enable a species to survive.
Natural selection
The survival and reproduction of the individuals in a population that exhibit the traits that best enable them to survive in their environment.
Evidence for evolution
The evidence for evolution is drawn from a variety of sources of data, including the fossil record, radiometric dating, genetic information, the distribution of organisms, and anatomical and developmental similarities across species.
Anything that has mass and occupies space. All matter is made up of small particles called atoms. Matter can exist as a solid, a liquid, a gas, or plasma.
Matter can be classified as...
elements, compounds, and mixtures.
The atoms of any element are alike but are different from atoms of other elements.
Consist of two or more elements that are chemically combined in a fixed ratio. Mixtures also consist of two or more substances, but the substances are not chemically combined.
Classifications of compounds
acids, bases, salts, inorganic and organic compounds.
Make up an important group of compounds that contain hydrogen ions. When acids dissolve in water, hydrogen ions (H+) are released into the resulting solution.
A substance that releases hydroxide ions (OH-) into solution. pH is a measure of the hydrogen ion concentration in a solution.
pH scale
ranges from 0-14. Solutions with a pH lower than 7 are acidic; solutions with a pH greater than 7 are basic. A pH of 7 is neutral. When an acid reacts with a base, a salt is formed, along with water.
Matter can be described by...
its physical properties, which include shape, density, solubility, odor, melting point, boiling point, and color. Some physical properties, such as density, boiling point, and solubility, are characteristic of a specific substance and do not depend on the size of the sample. Characteristic properties can be used to identify unknown substances.
Equal volumes of different substances usually have...
different masses.
Chemical property
Matter can also be described by its chemical properties, which include acidity, basicity, combustibility, and reactivity. A chemical property indicates whether a substance can undergo a chemical change.
Parts of atoms
The atom is the basic building block of matter and consists of subatomic particles (proton, neutron, electron, and quark) that differ in their location, charge, and relative mass. Protons and neutrons are made up of smaller particles called quarks.
Bohr model of an atom
The Bohr model does not depict the three-dimensional aspect of an atom, and it implies that electrons are in static orbits.
Electron cloud model of an atom
The "electron cloud" model better represents our current understanding of the structure of the atom.
How many elements and how produced?
There are more than 110 known elements. No element with an atomic number greater than 92 is found naturally in measurable quantities on Earth. The remaining elements are artificially produced in a laboratory setting. Elements combine in many ways to produce compounds that make up all other substances on Earth.
Periodic table of elements
A tool used to organize information about the elements. Each box in the periodic table contains information about the structure of an element. The periodic table of elements is an arrangement of elements according to atomic number and properties. The information can be used to predict chemical reactivity. The boxes for all of the elements are arranged in increasing order of atomic number.
From left to right on periodic table, how do elements change?
The elements have an increasing nonmetallic character as one reads from left to right across the table. Along the stair-step line are the metalloids, which have properties of both metals and nonmetals.
How is an atom's identity determined
An atom's identity is directly related to the number of protons in its nucleus. This is the basis for the arrangement of atoms on the periodic table of elements.
The vertical columns in the period table are called...
groups or families.
The horizontal rows on the periodic table are called...
What do elements in the same column (family) have?
Elements in the same column (family) of the periodic table contain the same number of electrons in their outer energy levels. This gives rise to their similar properties and is the basis of periodicity — the repetitive pattern of properties such as boiling point across periods on the table.
On the periodic table, the nonmetals are located...
to the right of the stair-step line on the periodic table.
Metals tend to...
lose electrons in chemical reactions, forming positive ions.
Nonmetals tend to...
gain electrons in chemical reactions, forming negative ions.
Gaining or losing electrons makes an atom an ion.
Gaining or losing neutrons makes an atom an isotope. However, gaining or losing a proton makes an atom into a completely different element.
How are compounds formed
Compounds are formed when elements react chemically. When a metallic element reacts with a nonmetallic element, their atoms gain and lose electrons respectively, forming ionic bonds. Generally, when two nonmetals react, atoms share electrons, forming covalent (molecular) bonds.
Physical change of matter
In physical changes, the chemical composition of the substances does not change.
Chemical change of matter
In chemical changes, different substances are formed. Chemical changes are often affected by the surface area/volume ratio of the materials involved in the change.
The Law of Conservation of Matter (Mass)
states that regardless of how substances within a closed system are changed, the total mass remains the same. The Law of Conservation of Energy states that energy cannot be created or destroyed but only changed from one form to another.
A chemical equation
Represents the changes that take place in a chemical reaction. The chemical formulas of the reactants are written on the left, an arrow indicates a change to new substances, and the chemical formulas of the products are written on the right.
Chemical reactions in which energy is released (exothermic)
Chemical reactions in which energy is absorbed (endothermic).
Nuclear reactions
Nuclear energy is the energy stored in the nucleus of an atom. In nuclear reactions, a small amount of matter produces a large amount of energy. However, there are potential negative effects of using nuclear energy, including radioactive nuclear waste storage and disposal.
Nuclear fusion
Nuclear energy can be released by joining nuclei together (fusion)
Nuclear fission
Nuclear energy can be released by splitting nuclei (fission)
The ability to do work.
Potential energy
Stored energy based on position (height, for example) or chemical composition.
Kinetic energy
The energy of motion. The amount of kinetic energy depends on the mass and velocity of the moving object.
Important forms of energy include...
radiant, thermal, chemical, electrical, mechanical, and nuclear energy.
Visible light is a form of...
radiant energy
Sound is a form of...
mechanical energy.
Energy lost to the environment
Energy can be transformed from one type to another. In any energy conversion, some of the energy is lost to the environment as thermal energy.
Difference between heat and temperature
Heat and temperature are not the same thing. Heat is the transfer of thermal energy between substances of different temperature.
As thermal energy is added, the temperature of a substance...
A measure of the average kinetic energy of the molecules of a substance. Increased temperature means greater average kinetic energy of the molecules in the substance being measured, and most substances expand when heated. The temperature of absolute zero (-273oC/0 K) is the theoretical point at which molecular motion stops.
Atoms and molecules are...
perpetually in motion.
The transfer of thermal energy occurs in three ways:
by conduction, by convection, and by radiation.
When does the temperature not change despite adding or taking away thermal energy
There is no change in temperature during a phase change (freezing, melting, condensing, evaporating, boiling, and vaporizing) as this energy is being used to make or break bonds between molecules.
Sound is produced by...
vibrations and is a type of mechanical energy. Sound travels in compression waves and at a speed much slower than light. It needs a medium (solid, liquid, or gas) in which to travel.
compression wave
matter vibrates in the same direction in which the wave travels.
All waves exhibit certain characteristics:
wavelength, frequency, and amplitude. As wavelength increases, frequency decreases.
The speed of sound depends on two things:
the medium through which the waves travel and the temperature of the medium.
The tendency of a system to vibrate at maximum amplitude at certain frequencies.
A compression (longitudinal) wave
consists of a repeating pattern of compressions and rarefactions. Wavelength is measured as the distance from one compression to the next compression or the distance from one rarefaction to the next rarefaction.
How are reflection and interference patterns used?
Reflection and interference patterns are used in ultrasonic technology, including sonar and medical diagnosis.
Visible light
A form of radiant energy that moves in transverse waves.
All transverse waves exhibit certain characteristics:
wavelength, crest, trough, frequency, and amplitude. As wavelength increases, frequency decreases. There is an inverse relationship between frequency and wavelength.
Radiant energy travels in straight lines until...
it strikes an object where it can be reflected, absorbed, or transmitted.
As visible light travels through different media...
it undergoes a change in speed that may result in refraction.
Electromagnetic waves are arranged on the electromagnetic spectrum by...
wavelength. All types of electromagnetic radiation travel at the speed of light, but differ in wavelength.
The electromagnetic spectrum includes...
gamma rays, X-rays, ultraviolet, visible light, infrared, and radio and microwaves.
Radio waves
The lowest energy waves and have the longest wavelength and the lowest frequency.
Gamma rays
The highest energy waves and have the shortest wavelength and the highest frequency.
Visible light
lies in between radio waves and gamma rays and makes up only a small portion of the electromagnetic spectrum.
Convex mirrors
diverge light and produce a smaller, upright image.
Concave mirrors
converge light and produce an upright, magnified image if close and an inverted, smaller image if far away.
when light waves strike an obstacle and new waves are produced.
Interference takes place when...
two or more waves overlap and combine as a result of diffraction.
the change in velocity per unit of time. An object moving with constant velocity has no acceleration. A decrease in velocity is negative acceleration or deceleration. A distance-time graph for acceleration is always a curve.
Newton's three laws of motion describe...
the motion of all common objects.
Difference between mass and weight
Mass is the amount of matter in a given substance. Weight is a measure of the force due to gravity acting on a mass. Weight is measured in newtons.
Measured in newtons. Force can cause objects to move, stop moving, change speed, or change direction.
Difference between velocity and speed
The change in position of an object per unit of time. Velocity may have a positive or a negative value depending on the direction of the change in position, whereas speed always has a positive value and is nondirectional.
Work is done when...
an object is moved through a distance in the direction of the applied force.
simple machine
a device that makes work easier. Simple machines have different purposes: to change the effort needed (mechanical advantage), to change the direction or distance through which the force is applied, to change the speed at which the resistance moves, or a combination of these.
Work efficiency
Due to friction, the work put into a machine is always greater than the work output. The ratio of work output to work input is called efficiency.
Formula for speed
Speed = distance/time (s = d/t)
Formula for force
Force = mass × acceleration (F = ma)
Formula for work
Work = force × distance (W = Fd)
Formula for power
Power = work/time (P = W/t).
Electrical Resistance
a property of matter that affects the flow of electricity. Some substances have more resistance than others.
Cause electrons to be transferred from one object to another. These static electrical charges can build up on an object and be discharged slowly or rapidly. This is often called static electricity.
Relationship between electricity and magnetism.
Magnetic fields can produce electrical current in conductors. Electricity can produce a magnetic field and cause iron and steel objects to act like magnets.
temporary magnets that lose their magnetism when the electric current is removed. Both a motor and a generator have magnets (or electromagnets) and a coil of wire that creates another magnetic field.
A generator
A device that converts mechanical energy into electrical energy. Most of the electrical energy we use comes from generators. Electric motors convert electrical energy into mechanical energy that is used to do work. Examples of motors include those in many household appliances, such as blenders and washing machines.
A conductor
a material that transfers an electric current well.
An insulator
material that does not transfer an electric current.
A semiconductor
in-between a conductor and an insulator.
A semiconductor device that acts like a one way valve to control the flow of electricity in electrical circuits. Solar cells are made of semiconductor diodes that produce direct current (DC) when visible light, infrared light (IR), or ultraviolet (UV) energy strikes them. Light emitting diodes (LED) emit visible light or infrared radiation when current passes through them. An example is the transmitter in an infrared TV remote or the lighting course behind the screen in an LED TV or notebook computer screen.
Semiconductor devices made from silicon, and other semiconductors. They are used to amplify electrical signals (in stereos, radios, etc.) or to act like a light switch turning the flow of electricity on and off.