ASVAB General Science Practice Test 1 3 — Questions and Answers

Question 1: What is the difference between a physical change and a chemical change?

Physical changes require heat; chemical changes require light
Physical changes alter matter's form without changing its chemical composition; chemical changes produce new substances (Correct answer)
Physical changes are reversible; chemical changes always produce gases
Physical changes affect only liquids; chemical changes affect only solids

Correct answer: Physical changes alter matter's form without changing its chemical composition; chemical changes produce new substances

A physical change alters the form, shape, or state of matter without changing its chemical identity (e.g., melting ice). A chemical change transforms matter into new substances with different chemical compositions (e.g., burning wood).

The distinction between physical and chemical changes is fundamental to chemistry: Physical changes alter the form, shape, size, or state of matter but do not change the substance's chemical identity. The molecules remain the same — only their arrangement or energy changes. Examples: melting ice (solid water → liquid water, same H2O molecules), tearing paper (different shapes, same cellulose), dissolving sugar in water (the molecules disperse but remain sucrose molecules), boiling water (liquid → gas, still H2O). Chemical changes (chemical reactions) transform substances into chemically different substances. New chemical bonds are formed and/or broken, resulting in new molecules with different properties. Examples: burning wood (cellulose + O2 → CO2 + H2O + ash — completely different substances), rusting iron (Fe + O2 → Fe2O3), cooking an egg (proteins denature — irreversible), baking soda + vinegar (NaHCO3 + CH3COOH → CO2 + H2O + NaCH3COO). Evidence of chemical change: color change (not explained by mixing), gas production (bubbles), precipitate formation (solid forms from solution), temperature change (significant heat release or absorption), light emission, and irreversibility in most cases. However, not all signs are definitive — dissolving some compounds releases heat (physical change) and some chemical changes are reversible (decomposition of HI is reversible). A key test: can you restore the original substance by physical means? If not, a chemical change likely occurred.

Question 2: What is the function of the mitochondria in a cell?

Store genetic information and control cell division
Produce proteins from amino acids via ribosomes
Produce ATP (adenosine triphosphate) through cellular respiration (Correct answer)
Regulate what enters and exits the cell

Correct answer: Produce ATP (adenosine triphosphate) through cellular respiration

Mitochondria are the cell's powerhouses — they generate ATP (the cell's primary energy currency) through cellular respiration, converting glucose and oxygen into usable energy, carbon dioxide, and water.

Mitochondria are membrane-bound organelles found in nearly all eukaryotic cells (cells with a nucleus — plants, animals, fungi, protists). They produce ATP (adenosine triphosphate), the universal energy currency of cells, through a process called cellular respiration. The overall reaction: C6H12O6 (glucose) + 6O2 → 6CO2 + 6H2O + ATP energy. Mitochondria extract this energy through three interconnected processes: Glycolysis (in cytoplasm, not mitochondria), Krebs cycle (in mitochondrial matrix), and Oxidative phosphorylation / electron transport chain (on inner mitochondrial membrane) — this last step produces most of the ATP. Mitochondria have a distinctive double-membrane structure: outer membrane (smooth, permeable to small molecules) and inner membrane (highly folded into cristae — these folds dramatically increase surface area for the electron transport chain, maximizing ATP production). Uniquely, mitochondria contain their own circular DNA (mtDNA) and ribosomes, suggesting they evolved from ancient bacteria that were engulfed by early eukaryotic cells (endosymbiotic theory). Mitochondrial DNA is inherited almost exclusively from the mother, making it useful for tracing maternal lineages in genetics and anthropology. Cells with high energy demands (muscle cells, nerve cells, liver cells) have thousands of mitochondria per cell. Red blood cells, which have no nucleus, also have no mitochondria.

Question 3: Which of the following best describes Newton's Third Law of Motion?

An object in motion stays in motion unless acted upon by an unbalanced force
Force equals mass times acceleration (F = ma)
For every action, there is an equal and opposite reaction (Correct answer)
The acceleration of an object is directly proportional to the net force and inversely proportional to mass

Correct answer: For every action, there is an equal and opposite reaction

Newton's Third Law states that for every action force, there is an equal magnitude but opposite direction reaction force. Forces always occur in pairs between two interacting objects.

Newton's Three Laws of Motion are foundational principles of classical mechanics: First Law (Inertia): An object at rest stays at rest, and an object in motion stays in motion at constant velocity, unless acted upon by a net external force. This describes inertia — the tendency of matter to resist changes in its state of motion. Second Law: F = ma. The net force on an object equals its mass times its acceleration. This quantifies how forces change motion — greater force produces greater acceleration; greater mass requires greater force for the same acceleration. Third Law (Action-Reaction): For every action (force), there is an equal and opposite reaction. When Object A exerts a force on Object B, Object B simultaneously exerts an equal force in the opposite direction on Object A. Forces always come in action-reaction pairs and act on different objects. Examples of Newton's Third Law: A rocket engine expels gas backward (action) → the gas pushes the rocket forward (reaction). Jumping — you push down on the ground (action), the ground pushes you upward (reaction). Swimming — you push water backward, water pushes you forward. Walking — foot pushes backward on floor, floor pushes foot forward. Gun recoil — bullet pushed forward, gun pushed backward. Important clarification: action-reaction pairs do NOT cancel each other out because they act on different objects. The ground pushing you up and you pushing down on the ground act on different bodies (you and the Earth, respectively).

Question 4: What is the pH scale, and what pH value indicates a neutral solution?

pH measures temperature; pH 50 is neutral
pH measures acidity/basicity on a scale of 0-14; pH 7 is neutral (Correct answer)
pH measures electrical conductivity; pH 1 is neutral
pH measures concentration of molecules; pH 10 is neutral

Correct answer: pH measures acidity/basicity on a scale of 0-14; pH 7 is neutral

The pH scale measures the hydrogen ion concentration in a solution on a scale from 0 to 14. pH 7 is neutral (pure water), pH below 7 is acidic, and pH above 7 is basic (alkaline).

The pH scale is a logarithmic measurement of the concentration of hydrogen ions (H⁺ or H3O⁺) in a solution. The scale runs from 0 to 14 (though values outside this range are possible in extreme concentrated solutions). PH 7 = Neutral (pure water at 25°C). [H⁺] = [OH⁻] = 10⁻⁷ mol/L. Below 7 = Acidic. Higher H⁺ concentration. Common acids: stomach acid (~pH 1-2), lemon juice (~pH 2), vinegar (~pH 3), coffee (~pH 5), rainwater (~pH 5.6). Above 7 = Basic (alkaline). Lower H⁺ concentration (higher OH⁻). Common bases: baking soda (~pH 9), milk of magnesia (~pH 10), bleach (~pH 12.5), drain cleaner (~pH 14). The logarithmic nature is critical: each whole number change in pH represents a 10× change in hydrogen ion concentration. pH 3 is 10× more acidic than pH 4, and 100× more acidic than pH 5. This is why even small pH changes in biological systems can be significant — the human blood pH must stay between 7.35-7.45 for proper function; a drop to 7.0 or rise to 7.8 is life-threatening. The pH formula: pH = -log₁₀[H⁺]. Neutral means [H⁺] = 10⁻⁷ M, so pH = -log(10⁻⁷) = 7.

Question 5: What is the primary role of the ozone layer in Earth's atmosphere?

Trap heat to maintain Earth's surface temperature
Absorb most of the sun's harmful ultraviolet (UV) radiation (Correct answer)
Produce oxygen through photosynthesis
Regulate carbon dioxide levels in the atmosphere

Correct answer: Absorb most of the sun's harmful ultraviolet (UV) radiation

The ozone layer (O3) in the stratosphere absorbs most of the sun's harmful ultraviolet radiation, particularly UV-B and UV-C wavelengths, protecting life on Earth from radiation damage.

The ozone layer is a region of Earth's stratosphere approximately 15-35 km (9-22 miles) above Earth's surface where ozone (O3) molecules are present in relatively high concentrations. Each ozone molecule consists of three oxygen atoms bonded together. The ozone layer's primary function is absorbing UV radiation. Solar radiation includes UV-A (320-400nm, least harmful), UV-B (280-320nm, causes sunburn and skin cancer), and UV-C (100-280nm, most energetic, potentially lethal). The ozone layer absorbs most UV-B and essentially all UV-C radiation before it reaches Earth's surface. Without the ozone layer, UV radiation at Earth's surface would be intense enough to cause rapid DNA damage in living organisms, dramatically increasing rates of skin cancer, cataracts, and immune suppression in humans, and damaging plants, algae, and marine organisms that form the base of food chains. Ozone depletion became a significant concern in the late 20th century due to chlorofluorocarbons (CFCs) and other halogenated compounds used in refrigerants and aerosols. These compounds release chlorine atoms in the stratosphere that catalytically destroy ozone molecules. The Montreal Protocol (1987), an international agreement to phase out ozone-depleting substances, has been remarkably successful — the ozone layer has been gradually recovering. Note: the ozone layer is different from ground-level ozone, which is a pollutant formed in smog.

Question 6: Which type of rock forms when molten rock (magma or lava) cools and solidifies?

Sedimentary rock
Metamorphic rock
Igneous rock (Correct answer)
Limestone

Correct answer: Igneous rock

Igneous rock forms when molten rock (magma below ground or lava above ground) cools and solidifies. The word 'igneous' comes from the Latin word for fire.

Rocks are classified into three major types based on how they form — the rock cycle connects all three: Igneous Rocks: Form from cooling and solidifying molten rock. Intrusive (plutonic) igneous rocks form when magma cools slowly underground — slow cooling allows large crystals to grow (e.g., granite with visible mineral grains). Extrusive (volcanic) igneous rocks form when lava cools quickly at the surface — rapid cooling produces fine-grained or glassy textures (e.g., basalt, obsidian). Examples: granite, basalt, obsidian, pumice, rhyolite, gabbro. Sedimentary Rocks: Form when sediments (fragments of other rocks, minerals, shells, organic material) accumulate and compact over time. Examples: sandstone, limestone, shale, conglomerate, coal. Most fossils are found in sedimentary rocks. They often have visible layers (strata). Metamorphic Rocks: Form when existing rocks (any type) are transformed by heat, pressure, or chemically active fluids without melting. Examples: marble (from limestone), slate (from shale), quartzite (from sandstone), schist, gneiss. The Rock Cycle: Magma cools → igneous rock → weathering and erosion → sediments → compaction → sedimentary rock → heat/pressure → metamorphic rock → melting → magma again. All rock types can transform into the others given sufficient geological time and conditions.

ASVAB General Science Practice Test 1 3

What is the difference between a physical change and a chemical change?