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Praxis Middle School Science study materials
Praxis Middle School Science study resources

Praxis Middle School Science practice questions

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Question 1Science Content Knowledge

Which structure in a eukaryotic cell is the primary site of ATP production through aerobic respiration?

  1. Golgi apparatus
  2. Mitochondrion Correct answer.
  3. Ribosome
  4. Lysosome

Explanation

Mitochondria house the electron transport chain and ATP synthase, where most ATP is generated during oxidative phosphorylation. Ribosomes build proteins, the Golgi modifies and packages them, and lysosomes break down waste.

Question 2Science Content Knowledge

A student measures the mass of a rock as 24.0 g and its volume as 8.0 cm³. What is the density of the rock?

  1. 32.0 g/cm³
  2. 192 g/cm³
  3. 3.0 g/cm³ Correct answer.
  4. 0.33 g/cm³

Explanation

Density equals mass divided by volume, so 24.0 g ÷ 8.0 cm³ = 3.0 g/cm³. The units follow directly from dividing grams by cubic centimeters.

Question 3Science Content Knowledge

Which of the following is the correct chemical formula for table salt?

  1. CaCO₃
  2. KCl
  3. NaCl Correct answer.
  4. Na₂O

Explanation

Table salt is sodium chloride, formed from Na⁺ and Cl⁻ ions in a 1:1 ratio, giving the formula NaCl. The other formulas represent different compounds entirely.

Question 4Science Content Knowledge

Which force is responsible for keeping the planets in orbit around the Sun?

  1. Gravitational force Correct answer.
  2. Strong nuclear force
  3. Friction
  4. Electromagnetic force

Explanation

Gravity is a long-range attractive force between masses, and the Sun's gravity provides the centripetal pull that keeps planets in orbit. The other forces act over short ranges or require contact.

Question 5Science Content Knowledge

In a food chain, which organisms convert sunlight energy into chemical energy stored in sugars?

  1. Producers Correct answer.
  2. Decomposers
  3. Tertiary consumers
  4. Primary consumers

Explanation

Producers, such as plants and algae, perform photosynthesis to convert light energy into chemical energy. Consumers and decomposers obtain energy by eating or breaking down other organisms.

Question 6Science Content Knowledge

Which layer of Earth's atmosphere contains most of the planet's weather and clouds?

  1. Troposphere Correct answer.
  2. Stratosphere
  3. Mesosphere
  4. Thermosphere

Explanation

The troposphere is the lowest atmospheric layer and holds most of the water vapor, so nearly all weather occurs there. The other layers are higher and much drier.

Question 7Science Content Knowledge

Which particle carries a negative electric charge?

  1. Electron Correct answer.
  2. Neutron
  3. Proton
  4. Positron

Explanation

Electrons carry a negative charge and orbit the nucleus. Protons are positive, neutrons are neutral, and positrons are the positively charged antiparticles of electrons.

Question 8Science Content Knowledge

A marble is dropped from rest and falls freely for 3 seconds. Ignoring air resistance, approximately how far does it fall? (Use g = 10 m/s²)

  1. 15 m
  2. 30 m
  3. 90 m
  4. 45 m Correct answer.

Explanation

For an object starting from rest, distance equals ½gt². Substituting gives ½ × 10 m/s² × (3 s)² = 45 m.

Question 9Science Content Knowledge

Which process produces gametes with half the normal chromosome number?

  1. Mitosis
  2. Meiosis Correct answer.
  3. Budding
  4. Binary fission

Explanation

Meiosis involves two divisions that reduce the chromosome number by half, producing haploid gametes. Mitosis and the asexual processes preserve the full chromosome number.

Question 10Science Content Knowledge

A neutral atom of an element has 11 protons and 12 neutrons. What is its mass number?

  1. 11
  2. 12
  3. 23 Correct answer.
  4. 1

Explanation

Mass number is the sum of protons and neutrons in the nucleus, so 11 + 12 = 23. Protons alone give the atomic number, not the mass number.

Question 11Science Content Knowledge

Which type of rock forms when molten material cools and solidifies?

  1. Fossiliferous
  2. Sedimentary
  3. Metamorphic
  4. Igneous Correct answer.

Explanation

Igneous rock forms from the cooling and crystallization of magma or lava. Sedimentary rock forms from deposited sediments, and metamorphic rock forms from heat and pressure altering existing rock.

Question 12Science Content Knowledge

A 2 kg cart moving at 3 m/s collides with and sticks to a stationary 4 kg cart. What is the velocity of the combined carts immediately after the collision?

  1. 1.5 m/s
  2. 1 m/s Correct answer.
  3. 3 m/s
  4. 2 m/s

Explanation

Momentum is conserved: (2 kg)(3 m/s) = (2 kg + 4 kg)v, so v = 6/6 = 1 m/s. The masses combine because the carts stick together.

Question 13Science Content Knowledge

Which property of water allows insects such as water striders to rest on its surface?

  1. High specific heat
  2. Low density as a solid
  3. Surface tension Correct answer.
  4. Universal solvency

Explanation

Hydrogen bonding between water molecules creates cohesive forces that produce surface tension, a skin-like layer strong enough to support small objects. The other properties do not create a supportive surface.

Question 14Science Content Knowledge

In a cross between two heterozygous tall pea plants (Tt × Tt), what fraction of the offspring is expected to show the recessive short phenotype?

  1. 1/2
  2. 3/4
  3. 0
  4. 1/4 Correct answer.

Explanation

A Tt × Tt cross yields a 1:2:1 genotypic ratio (TT:Tt:tt), so only the tt genotype shows the recessive trait, which is 1/4 of offspring. The dominant phenotype accounts for the remaining 3/4.

Question 15Science Content Knowledge

Which change would most likely increase the rate of a chemical reaction between a solid and a dilute acid?

  1. Diluting the acid further
  2. Grinding the solid into a fine powder Correct answer.
  3. Cooling the reaction mixture
  4. Adding more liquid to the mixture

Explanation

Grinding increases the surface area of the solid exposed to the acid, raising the collision frequency and reaction rate. Cooling and diluting reduce the rate by lowering particle energy or concentration.

Question 16Science Content Knowledge

A student observes that a distant mountain appears hazy and bluish. Which atmospheric effect best explains this?

  1. Total internal reflection in the atmosphere
  2. Scattering of shorter wavelengths by air molecules Correct answer.
  3. Absorption of blue light by the mountain
  4. Reflection of light off the mountain's snow

Explanation

Air molecules scatter shorter wavelengths of visible light more strongly than longer ones, a process called Rayleigh scattering. This scattered blue light reaches the observer, giving distant objects a bluish haze.

Question 17Science Content Knowledge

Which of the following best describes the role of decomposers in an ecosystem?

  1. They produce oxygen through photosynthesis.
  2. They transfer energy directly to top predators.
  3. They return nutrients from dead organisms to the soil. Correct answer.
  4. They convert nitrogen gas into usable compounds.

Explanation

Decomposers break down dead organic matter, releasing nutrients such as carbon and nitrogen back into the environment for reuse by producers. Nitrogen fixation and photosynthesis are carried out by other organisms.

Question 18Science Content Knowledge

Which statement correctly describes the relationship between wavelength and frequency for a wave traveling at constant speed?

  1. As wavelength increases, frequency increases.
  2. As wavelength increases, frequency decreases. Correct answer.
  3. Wavelength and frequency are unrelated.
  4. As wavelength increases, frequency stays constant.

Explanation

Wave speed equals wavelength times frequency. For a fixed speed, wavelength and frequency are inversely proportional, so increasing wavelength lowers frequency.

Question 19Science Content Knowledge

Which of the following is an example of a chemical change?

  1. Sugar dissolving in water
  2. Ice melting into liquid water
  3. Glass shattering into pieces
  4. Iron rusting in moist air Correct answer.

Explanation

Rusting forms a new substance, iron oxide, indicating a chemical change. Melting, dissolving, and shattering are physical changes that do not create new substances.

Question 20Science Content Knowledge

A population of rabbits is introduced to an island with abundant food and no predators. Which growth pattern is most likely in the short term?

  1. Linear decline
  2. Oscillating cycles
  3. Exponential growth Correct answer.
  4. Logistic growth with an early plateau

Explanation

With abundant resources and no limiting factors initially, the population can grow exponentially as each generation reproduces at a high rate. Logistic growth and plateaus occur once carrying capacity is approached.

Question 21Science Content Knowledge

Which statement about the conservation of energy is correct for a closed system?

  1. Energy can be created but not destroyed.
  2. Energy can change forms but cannot be created or destroyed. Correct answer.
  3. Energy always decreases over time in any system.
  4. Energy is lost whenever work is done.

Explanation

The law of conservation of energy states that total energy in a closed system remains constant, though it may convert between forms such as kinetic, potential, and thermal. Energy is neither created nor destroyed.

Question 22Science Content Knowledge

A solution has a hydrogen ion concentration of 1 × 10⁻³ M. What is its pH, and is it acidic or basic?

  1. pH 11, basic
  2. pH 3, basic
  3. pH 11, acidic
  4. pH 3, acidic Correct answer.

Explanation

pH is the negative logarithm of hydrogen ion concentration, so −log(10⁻³) = 3. A pH below 7 indicates an acidic solution.

Question 23Science Content Knowledge

Two identical resistors of 6 ohms each are connected in parallel across a 12 V battery. What is the total current drawn from the battery?

  1. 2 A
  2. 1 A
  3. 6 A
  4. 4 A Correct answer.

Explanation

For two equal resistors in parallel, equivalent resistance is 6/2 = 3 ohms. Using Ohm's law, I = V/R = 12 V / 3 ohms = 4 A.

Question 24Science Content Knowledge

A dihybrid cross between two individuals heterozygous for both traits (AaBb × AaBb) is performed with independent assortment. What fraction of offspring is expected to be homozygous recessive for both traits?

  1. 1/8
  2. 1/16 Correct answer.
  3. 9/16
  4. 3/16

Explanation

Each trait independently yields a 1/4 chance of the recessive homozygote. Multiplying the independent probabilities gives 1/4 × 1/4 = 1/16 for the double recessive.

Question 25Science Content Knowledge

A block slides down a frictionless incline. Which statement about its energy is correct?

  1. The sum of kinetic and potential energy remains constant. Correct answer.
  2. Total mechanical energy increases as the block descends.
  3. Potential energy is converted entirely into thermal energy.
  4. Kinetic energy decreases as potential energy increases.

Explanation

On a frictionless incline, no energy is dissipated, so gravitational potential energy converts into kinetic energy while total mechanical energy stays constant. The block speeds up as it loses height.

Question 26Science Content Knowledge

Which organelle is the primary site of ATP production in a eukaryotic cell?

  1. Ribosome
  2. Golgi apparatus
  3. Mitochondrion Correct answer.
  4. Lysosome

Explanation

Mitochondria carry out oxidative phosphorylation, generating most of the cell's ATP through the electron transport chain. Other organelles perform different specialized functions.

Question 27Science Content Knowledge

A runner travels 100 meters east in 20 seconds. What is the runner's average velocity?

  1. 20 m/s east
  2. 0.2 m/s east
  3. 5 m/s east Correct answer.
  4. 2000 m/s east

Explanation

Average velocity equals displacement divided by time, so 100 m ÷ 20 s = 5 m/s in the direction of displacement.

Question 28Science Content Knowledge

Which gas makes up the largest fraction of Earth's atmosphere by volume?

  1. Nitrogen Correct answer.
  2. Carbon dioxide
  3. Argon
  4. Oxygen

Explanation

Nitrogen accounts for roughly 78% of the atmosphere by volume, making it the most abundant gas. Oxygen is second at about 21%.

Question 29Science Content Knowledge

Which type of chemical bond forms when electrons are transferred from one atom to another?

  1. Covalent bond
  2. Ionic bond Correct answer.
  3. Hydrogen bond
  4. Metallic bond

Explanation

An ionic bond results from the electrostatic attraction between oppositely charged ions formed by electron transfer. Covalent bonds instead involve electron sharing.

Question 30Science Content Knowledge

Which structure in the human body filters blood and produces urine?

  1. Pancreas
  2. Kidney Correct answer.
  3. Spleen
  4. Liver

Explanation

The kidneys contain nephrons that filter blood, reabsorb needed materials, and excrete wastes as urine. Other listed organs serve different physiological roles.

Question 31Science Content Knowledge

Which planet in the solar system is closest to the Sun?

  1. Mars
  2. Earth
  3. Venus
  4. Mercury Correct answer.

Explanation

Mercury orbits at the smallest average distance from the Sun. Venus is the second planet and Earth the third.

Question 32Science Content Knowledge

Which instrument is used to measure the mass of a sample most directly?

  1. Graduated cylinder
  2. Barometer
  3. Thermometer
  4. Balance Correct answer.

Explanation

A balance compares an unknown mass against known masses or calibrated forces, giving a direct mass reading. The other instruments measure temperature, volume, and pressure.

Question 33Science Content Knowledge

Which term describes the variety of species living in an ecosystem?

  1. Biomass
  2. Biodiversity Correct answer.
  3. Succession
  4. Carrying capacity

Explanation

Biodiversity refers to the variety of life, including species richness and genetic diversity, within a given area. The other terms describe quantity or change in populations.

Question 34Science Content Knowledge

A student heats 200 g of water and its temperature rises by 10 °C. If the specific heat of water is 4.18 J/(g·°C), how much heat energy is absorbed?

  1. 20 900 J
  2. 836 J
  3. 8360 J Correct answer.
  4. 4180 J

Explanation

Using q = mcΔT gives q = 200 g × 4.18 J/(g·°C) × 10 °C = 8360 J.

Question 35Science Content Knowledge

Which statement best explains why the Moon shows phases to an observer on Earth?

  1. The Moon rotates at a rate that hides part of its surface.
  2. The Moon emits varying amounts of light over a monthly cycle.
  3. The changing angle between Earth, the Moon, and the Sun alters the portion of the lit half we see. Correct answer.
  4. Earth's shadow falls on different parts of the Moon each night.

Explanation

The Moon is always half illuminated by the Sun, but as it orbits Earth the geometry changes how much of that lit half faces us. Phases are not caused by Earth's shadow.

Question 36Science Content Knowledge

A sealed container holds a gas at constant temperature. If the volume is halved, what happens to the pressure?

  1. It decreases to one quarter.
  2. It doubles. Correct answer.
  3. It halves.
  4. It stays the same.

Explanation

Boyle's law states that pressure and volume are inversely proportional at constant temperature, so halving the volume doubles the pressure.

Question 37Science Content Knowledge

Which adaptation most directly helps a desert plant reduce water loss?

  1. Shallow roots that spread widely near the surface
  2. Broad flat leaves with many stomata
  3. Thick waxy coating on leaves Correct answer.
  4. Brightly colored flowers that attract insects

Explanation

A thick waxy cuticle limits evaporation from leaf surfaces, conserving water in dry environments. Features that increase surface area or stomatal number would increase water loss.

Question 38Science Content Knowledge

In a food web, a hawk eats snakes that eat mice that eat seeds. Which trophic level does the hawk occupy?

  1. Primary consumer
  2. Secondary consumer
  3. Quaternary consumer Correct answer.
  4. Producer

Explanation

Seeds are the producer level, mice are primary consumers, snakes are secondary consumers, and hawks that eat snakes are quaternary consumers.

Question 39Science Content Knowledge

Which change to a periodic table position generally corresponds to an element with greater metallic character?

  1. Moving left to right across a period
  2. Moving toward the noble gases
  3. Moving up a group
  4. Moving down a group Correct answer.

Explanation

Metallic character increases down a group as the outer electrons are farther from the nucleus and more easily lost. It decreases left to right across a period.

Question 40Science Content Knowledge

Which process in the water cycle returns water vapor from plants directly to the atmosphere?

  1. Condensation
  2. Infiltration
  3. Precipitation
  4. Transpiration Correct answer.

Explanation

Transpiration is the release of water vapor through plant stomata, contributing to atmospheric moisture. The other processes move water in liquid or solid form.

Question 41Science Content Knowledge

A 12 V battery is connected to a single 4-ohm resistor. What power is dissipated by the resistor?

  1. 3 W
  2. 36 W Correct answer.
  3. 0.33 W
  4. 48 W

Explanation

Power can be found with P = V²/R = (12 V)²/4 Ω = 144/4 = 36 W.

Question 42Science Content Knowledge

Which statement correctly distinguishes mitosis from meiosis?

  1. Mitosis produces four varied cells, while meiosis produces two identical cells.
  2. Both processes produce cells with half the chromosome number.
  3. Mitosis occurs only in gametes, while meiosis occurs in body cells.
  4. Mitosis produces two genetically identical cells, while meiosis produces four genetically varied cells. Correct answer.

Explanation

Mitosis yields two daughter cells with the same chromosome number and genetic content as the parent, supporting growth and repair. Meiosis halves the chromosome number and generates four genetically distinct gametes.

Question 43Science Content Knowledge

A ball is thrown straight up with an initial velocity of 20 m/s. Ignoring air resistance and using g = 10 m/s², how long does it take to reach its highest point?

  1. 2 s Correct answer.
  2. 4 s
  3. 10 s
  4. 0.5 s

Explanation

At the highest point the velocity is zero, so t = v/g = 20 m/s ÷ 10 m/s² = 2 s.

Question 44Science Content Knowledge

Which observation provides the strongest evidence that a chemical reaction has occurred?

  1. A liquid changes color when diluted
  2. A new gas forms that was not present before Correct answer.
  3. A mixture becomes colder when stirred
  4. A solid dissolves in water

Explanation

Formation of a new substance, such as a gas not previously present, indicates that reactants have rearranged into products. Dissolving and dilution are typically physical changes.

Question 45Science Content Knowledge

A sound wave has a frequency of 500 Hz and a wavelength of 0.68 m. What is its speed?

  1. 500 m/s
  2. 735 m/s
  3. 340 m/s Correct answer.
  4. 0.0014 m/s

Explanation

Wave speed equals frequency times wavelength, so 500 Hz × 0.68 m = 340 m/s.

Question 46Science Content Knowledge

Which factor most limits the size of a population that an environment can support indefinitely?

  1. The mutation rate of the species
  2. The average lifespan of individuals
  3. The number of chromosomes in the species
  4. Availability of resources such as food and space Correct answer.

Explanation

Carrying capacity is determined by limiting resources such as food, water, and space, which constrain population growth. Genetic and lifespan factors influence individuals but not the resource ceiling.

Question 47Science Content Knowledge

A sample of rock contains 25% of its original radioactive parent isotope. If the half-life is 10 million years, how old is the sample?

  1. 25 million years
  2. 40 million years
  3. 10 million years
  4. 20 million years Correct answer.

Explanation

After one half-life 50% remains, and after two half-lives 25% remains. Two half-lives of 10 million years each give an age of 20 million years.

Question 48Science Content Knowledge

Two objects with masses m and 2m are pushed with equal forces on a frictionless surface. How do their accelerations compare?

  1. Both objects accelerate equally.
  2. The less massive object accelerates four times as much.
  3. The more massive object accelerates twice as much.
  4. The less massive object accelerates twice as much. Correct answer.

Explanation

Newton's second law gives a = F/m, so for equal forces acceleration is inversely proportional to mass. The object with mass m has twice the acceleration of the object with mass 2m.

Question 49Science Content Knowledge

A buffer solution resists large pH changes when small amounts of acid or base are added. Which component pair best provides this behavior?

  1. Pure water and a neutral salt
  2. A strong acid and a strong base
  3. A weak acid and its conjugate base Correct answer.
  4. Two strong acids in equal amounts

Explanation

A weak acid and its conjugate base form a buffer that neutralizes added acid or base through shifts in the equilibrium. Strong acid-base mixtures react completely and cannot buffer.

Question 50Science Content Knowledge

In a pedigree, a trait appears in every generation and affects about half of the offspring of an affected parent regardless of sex. Which inheritance pattern is most consistent with these observations?

  1. X-linked recessive
  2. Y-linked
  3. Autosomal recessive
  4. Autosomal dominant Correct answer.

Explanation

Autosomal dominant traits typically appear in each generation and affect males and females equally, with roughly half of offspring of an affected heterozygous parent inheriting the trait. Recessive traits often skip generations.