STAAR Grade 8 Science — Practice Test 1

Matter & Energy

Choose the best answer or type the correct number.

1. An atom of carbon-12 has 6 protons and 6 neutrons. How many electrons does a neutral carbon-12 atom have?

2. On the periodic table, elements in the same vertical column are called a:

3. Which change is a CHEMICAL change rather than a physical change?

4. Water (H₂O) is an example of a:

5. In the reaction 2H₂ + O₂ → 2H₂O, if 4 g of hydrogen react with 32 g of oxygen, how many grams of water should be produced (according to the law of conservation of mass)?

6. Which of the following is a HOMOGENEOUS mixture (a solution)?

7. Sodium (Na) is in Group 1 of the periodic table. The Group 1 elements are known as the alkali metals. Based on this group placement, sodium is most likely to:

8. A metal cube has a mass of 50 grams and a volume of 10 cubic centimeters. What is its density (g/cm³)? (Type a number.)

Force, Motion & Energy

Choose the best answer or type the correct number.

9. A car travels 240 kilometers in 4 hours at a constant speed. What is its average speed?

10. A book sits motionless on a table. Two forces act on it — gravity pulling down and the table pushing up. The forces are described as:

11. Newton's third law states that for every action there is an equal and opposite reaction. When a swimmer pushes water backward with her hands, the reaction force is:

12. A roller coaster car is at the top of the first hill, momentarily at rest. As it begins to descend, its potential energy is mostly converted into:

13. Which of the following is an example of a simple machine that is an INCLINED PLANE?

14. A 10 kg backpack and a 5 kg backpack are dropped from the same height in the same room (ignore air resistance). Which statement is true?

15. A runner travels 200 meters in 25 seconds. What is her average speed in meters per second? (Type a number.)

Earth — Geology & Atmosphere

Choose the best answer.

16. Two tectonic plates moving toward each other, where one slides beneath the other, form which type of boundary?

17. The Mid-Atlantic Ridge is an underwater mountain range where new ocean crust is being formed. This is evidence of:

18. In the rock cycle, igneous rock can become sedimentary rock through which sequence of processes?

19. The thickest layer of Earth, located between the crust and the outer core, is called the:

20. A topographic map shows contour lines very close together on one side of a mountain and farther apart on the other side. The side with the closely-spaced contour lines is:

21. Which best describes the difference between weather and climate?

Space

Choose the best answer.

22. Earth experiences seasons primarily because of:

23. A SOLAR eclipse occurs when:

24. An HR (Hertzsprung-Russell) diagram plots stars by their temperature versus their luminosity (brightness). Most stars, including our Sun, fall on a diagonal band called the:

25. A light-year is a unit of:

26. Which of the following correctly orders these from smallest to largest?

Organisms & Environments

Choose the best answer.

27. Which organelle is found in PLANT cells but NOT in animal cells?

28. Which sequence correctly orders the levels of biological organization from smallest to largest?

29. The simplified word equation for photosynthesis is: carbon dioxide + water → glucose + oxygen. The energy source that drives this reaction is:

30. In a typical food chain — grass → grasshopper → frog → snake — the grasshopper is best described as a:

31. An ecosystem's BIOTIC factors are:

32. A pea plant has the genotype Pp for flower color, where P (purple) is dominant over p (white). The plant's PHENOTYPE will be:

33. Two purple-flowered pea plants, both heterozygous (Pp), are crossed. According to a Punnett square, what fraction of offspring are predicted to have WHITE flowers (genotype pp)?

34. A trait such as a bird being able to fly south for winter (migration), passed genetically from parent to offspring, is BEST classified as:

Lab-Data Interpretation

Read the lab description and the data table, then answer the questions that follow.

Lab: Comparing the Densities of Four Unknown Liquids

Ms. Chen's eighth-grade class designed an experiment to identify four unknown liquids labeled W, X, Y, and Z. The students measured a fixed volume of each liquid (50.0 mL) using the same graduated cylinder and recorded its mass on an electronic balance that had been zeroed (tared) with the empty cylinder. The classroom temperature was held constant at 22 °C. Each measurement was repeated three times and averaged. The students then calculated density using the formula density = mass ÷ volume.

Their averaged data is shown below. The students compared their results to a reference table of common laboratory liquids: water (1.00 g/mL), vegetable oil (about 0.92 g/mL), rubbing alcohol (about 0.79 g/mL), and a sugar-water solution (about 1.10 g/mL).

Liquid	Volume (mL)	Average mass (g)	Density (g/mL)
W	50.0	39.5	0.79
X	50.0	50.0	1.00
Y	50.0	46.0	0.92
Z	50.0	55.0	1.10

35. Based on the data and the reference values, which liquid is most likely RUBBING ALCOHOL?

36. If the four liquids were carefully poured into the same tall, narrow container and allowed to settle without mixing, which liquid would form the BOTTOM layer?

37. Which variable in this experiment is the INDEPENDENT variable (the one the students deliberately changed)?

38. Why did the students repeat each measurement three times and AVERAGE the results?

39. A student claims, "Liquid X must be pure water." The BEST evidence from the table to support this claim is:

40. If the students had used DIFFERENT volumes for each liquid (for example, 30 mL of W and 70 mL of Z), the calculated DENSITY values would:

41. Calculate the density of Liquid Y using the data shown. (Type a number in g/mL.)

42. Which CONCLUSION is BEST supported by the data?

Matter & Energy

Force, Motion & Energy

Earth — Geology & Atmosphere

Space

Organisms & Environments

Lab-Data Interpretation

Lab: Comparing the Densities of Four Unknown Liquids

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