Science CRT Prep Slides 72 to 103

A tool used by scientists to identify the name of unknown organisms based on observable characteristics is called a

• dichotomous key.

• scientific name.

• taxonomic Tree.

• homologous structure

Answer explanation

A very important tool that is used in the world of taxonomy is a dichotomous key. This is a key that incorporates a set of choices that eventually leads to the naming of an organism. Even everyday common objects can be used to make a dichotomous key, but most often they are used in the field to help identify an unknown organism.A dichotomous key, regardless of complexity and subject, always begins with the very first set of choices available to the person utilizing it. Within every set of choices there exists the possibility of reaching a solution/identification to the “mystery” organism or a path to another set of choices. The process continues until the user can clearly identify from one of the choices the organism that they are attempting to name or classify. One advantage to a dichotomous key is that the user always has to decide on one of the choices provided in each set and if at any point in time neither choice seems appropriate for the unknown object, then a mistake was made somewhere earlier in the dichotomous key.

Which of the following provides the best evidence that organisms of two different species share a common ancestor?

• They live in the same ecosystem.

• They reproduce at the same time.

• They have similar DNA sequences.

• They have similar body movements.

Answer explanation

Biological evolution is the best scientific explanation for how life on Earth has changed and how it continues to change. Phylogeny is the classification of organisms based upon their evolutionary history. Evidence used to explain and determine phylogeny includes, but is not limited to fossils, biochemistry, and structure. DNA analysis and other molecular evidence available today provides the strongest evidence for classification based on evolutionary history. Organisms that have a more recent common ancestor will share more similar DNA sequences and are more closely related than species that have more ancient ancestors.

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Which of the following best explains how the fossil record provides evidence that evolution has occurred?

• It indicates that forms of life existed on Earth at least 3.5 billion years ago.

• It indicates the exact cause of structural and behavioral adaptations of organisms.  

• It shows how the embryos of many different vertebrate species are very similar.

• It shows that the form and structure of groups of organisms have changed over time.

Answer explanation

Fossils are the remains of once living organisms. The most common types of fossils form when shells, bones, or other parts of organisms are rapidly covered with layers of sediment. Sedimentary rocks are the richest source of fossils. Successive layers of sedimentary rock contain different groups of fossils, and in most cases, the lowest layer of rock is the oldest. The different types of fossils in the different layers provide evidence that changes have occurred in groups of living things through time. Therefore, the fossil record supports evolutionary theory by providing evidence that organisms that lived in the past have changed over time.

There are gaps in the branches of the fossil records of life. Gaps exist in the fossil record, in part because plants, microorganisms, and soft shelled organisms (majority of marine animals) are not likely to become fossilized. Even hard bodied organisms do not frequently become fossilized because conditions in the environment may not facilitate fossilization. In addition, changes in the land (erosion and geological events) can destroy fossils. However incomplete the fossil record may be, it does provide significant evidence of evolution and of the history of life on earth.

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NGSS.MS-LS4-1

Fossils are most commonly preserved in

• igneous rock.

• metamorphic rock.

• sedimentary rock.

• transitional rock.

Answer explanation

Fossils are the remains of once living organisms. The most common types of fossils form when shells, bones, or other parts of organisms are rapidly covered with layers of sediment. Sedimentary rocks are the richest source of fossils. Successive layers of sedimentary rock contain different groups of fossils, and in most cases, the lowest layer of rock is the oldest. The different types of fossils in the different layers provide evidence that changes have occurred in living things through time. Therefore, the fossil record supports evolutionary theory by providing evidence that organisms that lived in the past have changed over time.

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Scientists discovered fossils of whale ancestors that have well-developed hip and thigh bones, which are typically used for walking by mammals. Modern whales most likely evolved from ancestors who

• lived in the sea, and then became better adapted for land.

• lived on land, and then became better adapted for the sea.

• evolved in the sea and remained in the sea.

• evolved on land and remained on land.

Answer explanation

Fossils are the remains of once living organisms. The most common types of fossils form when shells, bones, or other parts of organisms are rapidly covered with layers of sediment. Sedimentary rocks are the richest source of fossils. Successive layers of sedimentary rock contain different groups of fossils, and in most cases, the lowest layer of rock is the oldest. The different types of fossils in the different layers provide evidence that changes have occurred in living things through time. Therefore, the fossil record supports evolutionary theory by providing evidence that organisms that lived in the past have changed over time.

Based upon the fossil record, scientists have concluded that modern whales evolved from land mammals. Paleontologists have discovered transitional fossils of whale ancestors that show the gradual loss of terrestrial adaptations with the gradual accumulation of aquatic adaptations that led to modern whales.

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The unifying concept that provides an explanation for the vast diversity of life on our planet is the

• theory of evolution.

• binomial nomenclature system.

• gene-chromosome theorem.

• cell theory

Answer explanation

Evolution is an essential topic within the biology curriculum as it explains the unity and diversity of life on Earth by using evidence from various fields such as biochemistry, paleontology, and ecology. In the scientific community, there is no debate whether or not evolution has occurred. Scientists regard evolution as a core theory that makes sense of everything we know about living organisms.

According to the National Center for Science Education, “In the biological sciences, evolution is a scientific theory that explains the emergence of new varieties of living things in the past and in the present; it is not a "theory of origins" about how life began. Evolution accounts for the striking patterns of similarities and differences among living things over time and across habitats through the action of biological processes such as natural selection, mutation, symbiosis, gene transfer, and genetic drift. Evolution has been subjected to scientific testing for over a century and has been (and continues to be) consistently confirmed by evidence from a wide range of fields.”For more information about evolution education visit

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Which term refers to the process by which organisms that are better adapted to their environment are more likely to survive and reproduce?

• Variation

• Competition

• Overproduction

• Natural selection

Answer explanation

Evidence suggests that species change over time. This process of change is called biological evolution and can be attributed to genetic and/or environmental influences. Individuals that are better suited to their environment are more likely to survive and reproduce than other less fit members of the same species. In essence, nature “selects” those individuals with beneficial traits. This mechanism of biological evolution is called natural selection and was developed by Charles Darwin. Natural selection is affected by the following factors: overproduction, competition for survival, variation, adaptation, and genetic mutation. Additionally, differences among individuals within a species can yield advantages and/or disadvantages in survival and/or reproduction.

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NGSS.MS-LS4-4

Which statement best describes how climate conditions in Nevada would be different if the tilt of Earth’s axis was at 0°?

• The seasons in Nevada would be opposite from the current seasons.

• Nevada would experience climate conditions that change very little throughout the year.

• Climate conditions in Nevada would be coolest when Earth is closest to the sun.

• Nevada would receive the most energy from the sun in the summer and the least in the winter.

Answer explanation

The tilt of the Earth is the reason we experience seasonal changes in climate in most parts of the world. In the summer, the northern hemisphere (which includes Nevada) faces more towards the sun, causing the sun to rise earlier in the morning, be higher in the sky at noon, and set later in the evening. Due to the longer daylight hours and more direct sunlight, the ground and air become warmer, and we call it summer. The seasons are the opposite in the southern hemisphere: December 21 is the first day of summer and June 21 is the first day of winter.

If there were no tilt to the earth's axis, the sun would rise and set at the same time every day, and the weather would remain constant throughout the year. Nevada’s climate conditions would experience little change throughout the year.

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NGSS.MS-ESS1-1

Which of the following is not a contributing factor to the uneven warming of Earth’s surface?

• Different surfaces warm at different rates.

• Different surfaces retain energy differently.

• The Sun is farther from Earth during winter.

• The Sun’s rays hit the surface at varied angles.

Answer explanation

Based on the fact that the Sun is the major source of energy for the Earth, it becomes imperative for the students to understand that for seasons to exist, all parts of the Earth cannot receive the same amount of energy from the Sun.  If the energy from the Sun were evenly distributed over the surface of the Earth then variations in temperature would be limited to the variation in the Earth’s surface.  

Earth unevenly warms primarily due to the 23.5 degree tilt of its axis resulting in varying intensities received from the Sun. The tropics region (latitudes near the Equator) receive more intense rays than latitudes farther from the Equator. Students should also understand that the materials comprising Earth’s various surfaces affect how well sunlight is absorbed or reflected. Also, due to differences in specific heat of the materials making up Earth’s surface, the rate of increase or decrease in temperature varies. Water has a higher specific heat than land, and thus takes longer to increase in temperature as it absorbs energy than does land. Conversely, even though land will heat up quicker than water, the land will also cool down quicker.

Students mistakenly believe that it is the Earth’s distance from the Sun that controls the seasons. Although the Earth’s orbit is not circular, it is very close to being circular. The variation in the distance the Earth is from the Sun during Perihelion (closest point to the sun) verses aphelion (furthest distance from the sun) is only about 3.5 percent. This minimal variation is not sufficient to cause the massive fluctuation in seasonal temperatures that Earth experiences.  

One decisive factor in refuting this misconception is the fact that during the Northern Hemisphere’s summer, Earth is at its furthest point from the Sun (152 million kilometers), and during the Northern Hemisphere’s winter, Earth is at its closest point in its orbit around the Sun (147 million kilometers).Earth is closest to the Sun in winter in the Northern Hemisphere.  If the distance from the Earth to the Sun were the deciding factor for the cause of seasons, the seasons would be reversed for the Northern Hemisphere.

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What is the primary energy source behind the water cycle?

• Earth’s internal energy

• Sun’s electromagnetic radiation

• Moon’s gravitational attraction

• Radioactive decay of elements

Answer explanation

While Earth’s internal energy is considerable, it accounts for less than 1% of the Earth’s energy budget. Energy from the Sun accounts for more than 99% of the Earth’s energy budget and drives the water cycle.Tidal forces from the Moon’s gravity have virtually no effect on the atmosphere. Although sea and lake tides are often reported with the weather forecast, there is no appreciable relationship between weather, climate, and tides.The Earth’s internal energy comes from two sources. The first is the warming caused by the formation of the planet. Scientific evidence indicates Earth and the other planets were formed by accretion (collisions and sticking) of planetesimals. The kinetic energy of these impacts raised the planet’s temperature as it formed, so much so, that early Earth consisted of melted rock and metal. Since that time, Earth has been slowly cooling as this primordial internal energy is radiated back to space. The second source of internal energy is from decay of radioactive elements present in Earth materials. For example, the decay of Uranium-238 in the Earth’s crust, mantle, and core releases energy that ultimately warms surrounding material.

The Earth’s internal energy drives plate tectonics, which can results in amazing effects such as tearing apart continents and creating new mountain ranges. But plate tectonics works slowly (i.e., on a geologic time scale), with average movement of only a few centimeters per year. Energy from the Sun drives drastic changes to Earth’s atmosphere—called weather—causing the precipitation and wind that erodes these mountain ranges. Additionally, the atmosphere retains enough of the Sun’s energy to raise the Earth’s surface temperature by more than 30 degrees Celsius (60 degrees Fahrenheit). This is called the greenhouse effect and is a common occurrence on planets with relatively thick atmospheres.

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