Science 8 STAAR Practice Part 6

Even though these puppies have the same parents, they do not all look alike because —

• they were produced by asexual cloning

• some of the puppies have genetic material from only one of the parents

• each puppy has a different combination of genetic material as a result of sexual reproduction

• all the puppies developed from the same fertilized egg

Answer explanation

Sexual reproduction causes variations in genetic makeup. Even though the puppies all have the same two parents, they each have different combinations of the parents’ genes. This results in some differences in observable physical characteristics, such as fur color patterns

Tags

NGSS.MS-LS3-2

2. Sodium and lithium have similar chemical properties. What characteristic of these elements explains why they are chemically similar?

• Their atoms both have one valence electron.

• Their atoms both have more neutrons than protons.

• Their atoms have the same number of energy levels.

• Their atoms contain equal numbers of protons and electrons.

Answer explanation

Both lithium (Li) and sodium (Na) are in Group 1 of the Periodic Table (located in the first column of the Periodic Table). Elements in the same group have the same number of valence electrons that determine their bonding behavior. Both Li and Na have 1 valence electron in their outer energy level (or electron shell).

Which location around Green Peak is likely to experience the most erosion over time?

• Location W, because location W has the gentlest slope

• Location X, because location X is near the bottom of a slope

• Location Y, because location Y has the steepest slope

• Location Z, because location Z is the flattest slope

Answer explanation

The lines in the map are called contour lines. Contour lines help indicate elevation and steepness. The closer the contour lines are together, the steeper the slope. The close contour lines around location Y indicate a steep slope. As the steepness of a slope increases, the rate of erosion increases.

Tags

NGSS.MS-ESS2-2

Based on the dichotomous key, in which order does the insect belong?

• Diptera

• Isoptera

• Ephemeroptera

• Zoraptera

Answer explanation

The Isoptera is the insect identified when the dichotomous key is followed correctly. A dichotomous key is a tool that helps scientists classify organisms. It consists of a series of steps with descriptions of physical characteristics. The absence or presence of a given characteristic at each step directs the user closer to the identification of the organism.

Which statements best describe the charges on the particles in this model?

• Both particles X and Y have a positive charge. Particle Z has a negative charge.

• Both particles X and Y have a negative charge. Particle Z has a positive charge.

• Either particle X or particle Y has a positive charge. Particle Z has a negative charge.

• Either particle X or particle Y has a negative charge. Particle Z has a positive charge.

Answer explanation

Particles X and Y must consist of one proton (positive charge) and one neutron (no charge). Protons and neutrons are found in the nucleus at the center of the atom. Particle Z represents electrons, which have a negative charge. Electrons are found in orbitals outside the nucleus.

Tags

NGSS.MS-PS1-1

Which description best identifies the action-reaction pair between the bird and the fence post?

• Action: The force of the bird on the wires Reaction: The force of the wires on the fence post

• Action: The force of the wires on the fence post Reaction: The force of the fence post on the bird

• Action: The force of the fence post on the bird Reaction: The force of the bird on the wires

• Action: The force of the bird on the fence post Reaction: The force of the fence post on the bird

Answer explanation

Based on Newton’s third law, for every action, there is an opposite and equal reaction. Therefore, interacting forces occur as action-reaction pairs. In this scenario, the bird is exerting a downward force on the fence post, while the fence post is exerting an upward force on the bird.

Tags

NGSS.MS-PS2-1

Farmers can best reduce negative effects on the water quality of nearby streams and lakes by planting crops that

• produce less oxygen

• produce less carbon dioxide

• need less fertilizer

• need less solar energy

Answer explanation

Planting a crop that requires fewer supplemental nutrients to grow would result in less fertilizer use and fewer nutrients in agricultural runoff that can flow into nearby waterways. Excess nutrients from fertilizers in agricultural runoff can negatively affect nearby waterways by causing harmful algal blooms.

Tags

NGSS.MS-ESS3-3

Buffelgrass is an invasive species of grass from Africa that outcompetes native Texas grasses for space and water. Which long-term change to a Texas grassland would most likely occur due to the introduction of buffelgrass?

• The population of native grasses will increase.

• The population of native grasses will decrease.

• Buffelgrass offspring will develop traits like those of native grasses.

• Buffelgrass offspring will develop traits like those of other invasive species.

Answer explanation

The native grass population will decrease since buffelgrass is competing against it for the same resources.

Tags

NGSS.MS-LS2-1

NGSS.MS-LS2-4

If the students continue at the same speed, which statement describes the total distance traveled after 90 seconds?

• Student 1 traveled 40 m, and student 2 traveled 20 m.

• Student 1 traveled 50 m, and student 2 traveled 30 m.

• Student 1 traveled 60 m, and student 2 traveled 30 m.

• Student 1 traveled 70 m, and student 2 traveled 25 m.

Answer explanation

Speed is a measure of distance over time. Student 1 travels 40 meters in 60 seconds. Student 2 travels 20 meters in 60 seconds. After an additional 30 seconds (90 seconds total), student 1 would travel another 20 meters for a total of 60 meters, and student 2 would travel another 10 meters for a total of 30 meters.

A star that has a luminosity of 10-2 and a temperature of 20,000 K is most likely a —

• Main sequence

• White dwarf

• Blue giant

• Red giant

Answer explanation

White dwarf stars are found to be around 20,000 K and 10-2 luminosity. The student correctly interpreted the H-R diagram to identify the white dwarfs.