I85PREP
⌘ K
MCAS Grade 8 Science study materials
MCAS Grade 8 Science study resources

MCAS Grade 8 Science practice questions

One question at a time. Build your MCAS Grade 8 Science understanding.

First 50 of 200 questions. Each one lists the choices, the correct answer, and an explanation. The checker at the top of this page saves progress in this browser when it is available.

Continue in the practice tool above to load more questions, 50 at a time.

Question 1Grade 8 Science (Massachusetts learning standards for science)

A student drops a rock from a cliff and uses a stopwatch to measure how long it takes to hit the ground. Which step should come immediately after collecting the timing data?

  1. Write a conclusion about gravity
  2. Change the hypothesis to match the data
  3. Publish the results in a journal
  4. Record the measurements in a data table Correct answer.

Explanation

Scientific investigations follow a logical sequence in which observations and measurements are gathered and organized before they are interpreted. Recording data in an organized table or chart preserves the raw evidence so it can later be analyzed. Conclusions and any changes to hypotheses must be based on that organized evidence, not made before it is recorded.

Question 2Grade 8 Science (Massachusetts learning standards for science)

A student wants to know whether fertilizer affects the height of bean plants. Which setup is the best controlled experiment?

  1. Use different types of seeds for each fertilizer treatment
  2. Water all plants daily and give each plant a different amount of fertilizer Correct answer.
  3. Give all plants fertilizer and place them in different rooms
  4. Measure plant height once at the end and ignore the starting height

Explanation

A controlled experiment changes only one independent variable while keeping all other conditions constant. Here the amount of fertilizer is the variable being tested, so light, water, soil, and seed type must stay the same for every plant. That allows any difference in height to be attributed to fertilizer rather than to another factor.

Question 3Grade 8 Science (Massachusetts learning standards for science)

A sealed glass jar contains a burning candle. When the candle goes out, a student claims the candle used up all the oxygen. Which observation would best support this claim?

  1. A glowing splint placed in the jar after the candle goes out does not relight Correct answer.
  2. The candle wax melts and drips down the side
  3. The candle flame produces light and heat
  4. The jar feels warmer after the candle burns

Explanation

Combustion requires oxygen, and a glowing splint relights only in an oxygen-rich atmosphere. If the splint will not relight inside the jar after the flame dies, oxygen has been consumed or greatly reduced. This directly tests the presence of oxygen rather than merely observing heat or light from the flame.

Question 4Grade 8 Science (Massachusetts learning standards for science)

Which statement correctly describes what happens to the mass of the substances during a chemical reaction in a closed container?

  1. The total mass decreases because gas is produced
  2. The total mass changes depending on the temperature of the reaction
  3. The total mass increases because a new substance forms
  4. The total mass stays the same because atoms are rearranged, not created or destroyed Correct answer.

Explanation

The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction. Atoms of the reactants are simply rearranged into new combinations, so the total mass of products equals the total mass of reactants. A closed container ensures no matter escapes, making this balance measurable.

Question 5Grade 8 Science (Massachusetts learning standards for science)

A substance melts at 80 degrees Celsius and does not conduct electricity when solid, but its melted form conducts electricity. Which type of substance is it most likely to be?

  1. A metal such as copper
  2. A molecular compound such as sugar
  3. An ionic compound such as a salt Correct answer.
  4. A noble gas such as argon

Explanation

Ionic compounds form crystal lattices of fixed ions that cannot move, so the solid does not conduct electricity. When melted, the ions become free to move and carry charge, which allows conduction. A high melting point and conductivity only in the liquid state are classic signs of an ionic substance.

Question 6Grade 8 Science (Massachusetts learning standards for science)

A student mixes baking soda and vinegar in an open cup and observes bubbles. What evidence indicates a chemical change occurred?

  1. The temperature of the mixture remains constant
  2. A gas forms that was not present in either starting material Correct answer.
  3. The mixture becomes cloudy and then clears
  4. The baking soda dissolves into the vinegar

Explanation

A chemical change produces a new substance with different properties from the reactants. The bubbles are carbon dioxide gas, which was not present in the solid baking soda or the vinegar. Formation of a new gas is strong evidence of a chemical reaction rather than a physical change.

Question 7Grade 8 Science (Massachusetts learning standards for science)

Two atoms both have 17 protons, but one has 18 neutrons and the other has 20 neutrons. What is the relationship between these two atoms?

  1. They are different elements with the same mass number
  2. They are isotopes of the same element Correct answer.
  3. They are ions of different elements
  4. They are identical atoms with different charges

Explanation

The number of protons determines the element's identity, so both atoms are chlorine because each has 17 protons. Atoms of the same element with different numbers of neutrons are isotopes. Neutron count affects mass number but not the chemical identity of the element.

Question 8Grade 8 Science (Massachusetts learning standards for science)

In a neutral atom of carbon-12, how are the electrons arranged?

  1. Two electrons fill the first energy level and four occupy the second Correct answer.
  2. Four electrons fill the first energy level and two occupy the second
  3. All six electrons are in the nucleus with the protons
  4. Six electrons are shared equally in the outermost energy level

Explanation

Electrons occupy energy levels outside the nucleus, and the first level holds a maximum of two electrons. Carbon has six electrons, so two fill the first level and the remaining four go into the second level. These four valence electrons explain carbon's ability to form four bonds.

Question 9Grade 8 Science (Massachusetts learning standards for science)

Why does sodium (atomic number 11) react so readily with chlorine (atomic number 17) to form sodium chloride?

  1. Both atoms lose electrons and become positively charged
  2. Sodium gains one electron and chlorine loses one electron
  3. Sodium loses one electron and chlorine gains one, producing oppositely charged ions that attract Correct answer.
  4. Both atoms share two electrons equally

Explanation

Sodium has one valence electron that it loses easily, forming a stable positive ion with a full inner level. Chlorine needs one electron to complete its outer level, so it gains that electron and becomes a negative ion. The oppositely charged ions attract each other and form an ionic bond in a crystal lattice.

Question 10Grade 8 Science (Massachusetts learning standards for science)

A pot of water is heated on a stove. Which statement best explains why the water at the top of the pot eventually becomes hot?

  1. Heat travels upward through the water by radiation
  2. Water molecules move from the bottom to the top without changing temperature
  3. The metal pot conducts heat directly through the water
  4. Warm water near the bottom rises and cooler water sinks, forming convection currents Correct answer.

Explanation

Heating water at the bottom decreases its density, so the warm water rises while cooler, denser water sinks to be heated. This circulation of fluid is called convection and distributes thermal energy through the pot. Convection requires a fluid in which warmer material can physically move.

Question 11Grade 8 Science (Massachusetts learning standards for science)

A ball rolls across a floor and gradually slows to a stop. Which statement best explains the ball's motion?

  1. A force such as friction acts opposite to the ball's motion Correct answer.
  2. The ball's inertia decreases as it slows down
  3. The ball stops because no forces act on it
  4. Gravity pulls the ball backward along the floor

Explanation

According to Newton's first law, an object in motion stays in motion unless a net force acts on it. Friction between the rolling ball and the floor acts opposite to the direction of motion, producing a net force that reduces speed. Without friction or another opposing force, the ball would keep rolling.

Question 12Grade 8 Science (Massachusetts learning standards for science)

A 4 kg cart is pushed with a net force of 12 N. What is the cart's acceleration?

  1. 0.33 m/s squared
  2. 3 m/s squared Correct answer.
  3. 48 m/s squared
  4. 8 m/s squared

Explanation

Newton's second law relates force, mass, and acceleration as force equals mass times acceleration. Rearranging gives acceleration equals force divided by mass, or 12 N divided by 4 kg. This equals 3 meters per second squared, the rate at which the cart's speed increases each second.

Question 13Grade 8 Science (Massachusetts learning standards for science)

A student pushes a heavy box across a rough floor and then across a smooth floor using the same effort. On which floor does the box slide farther, and why?

  1. The rough floor, because rough surfaces store energy
  2. The smooth floor, because less friction opposes the motion Correct answer.
  3. The rough floor, because friction helps objects keep moving
  4. Both floors equally, because the push is the same

Explanation

Friction is a contact force that opposes sliding motion and converts kinetic energy into thermal energy. A smooth floor has less friction, so less of the box's motion is resisted and it travels farther before stopping. The applied push is the same in both cases, so the difference comes from the opposing friction.

Question 14Grade 8 Science (Massachusetts learning standards for science)

A 2 kg book rests on a shelf 1.5 m above the floor. Using g = 10 m/s squared, what is the book's gravitational potential energy relative to the floor?

  1. 20 J
  2. 3 J
  3. 15 J
  4. 30 J Correct answer.

Explanation

Gravitational potential energy equals mass times the gravitational acceleration times height above the reference level. Multiplying 2 kg by 10 m/s squared by 1.5 m gives 30 joules. The reference level matters, so the energy is measured relative to the floor as stated.

Question 15Grade 8 Science (Massachusetts learning standards for science)

A pendulum swings back and forth. At the lowest point of its swing, which statement best describes its energy?

  1. Kinetic energy is converted entirely into heat at the lowest point
  2. Both kinetic and potential energy are zero
  3. Kinetic energy is greatest and potential energy is at its minimum Correct answer.
  4. Potential energy is greatest and kinetic energy is zero

Explanation

As a pendulum falls toward its lowest point, gravitational potential energy is converted into kinetic energy. At the bottom of the swing, the pendulum moves fastest, so kinetic energy is at a maximum and potential energy is at its minimum. The total mechanical energy stays approximately constant if friction is negligible.

Question 16Grade 8 Science (Massachusetts learning standards for science)

Which of these is an example of a renewable energy resource?

  1. Coal
  2. Petroleum
  3. Wind Correct answer.
  4. Natural gas

Explanation

Renewable resources are naturally replenished on a human timescale and are not used up permanently. Wind is driven by solar heating of the atmosphere and will continue to be available. Fossil fuels such as coal, natural gas, and petroleum form over millions of years and are consumed faster than they are replaced.

Question 17Grade 8 Science (Massachusetts learning standards for science)

A food chain in a pond contains algae, small fish, and herons. If a disease kills most of the small fish, what is the most likely short-term effect?

  1. The algae population will decrease and the heron population will increase
  2. The algae population will increase and the heron population will decline Correct answer.
  3. Both algae and heron populations will decrease
  4. Both algae and heron populations will increase

Explanation

Small fish eat algae, so fewer fish means less predation on algae and the algae population can grow. Herons eat small fish, so with fewer fish available, the herons have less food and their numbers should fall. This illustrates how removing one population affects both its prey and its predators.

Question 18Grade 8 Science (Massachusetts learning standards for science)

In a forest ecosystem, which organism is best described as a producer?

  1. A mushroom growing on a fallen log
  2. A deer grazing on shrubs
  3. A moss that carries out photosynthesis Correct answer.
  4. A hawk that hunts mice

Explanation

Producers are organisms that make their own food, usually through photosynthesis, and form the base of the food web. Moss contains chlorophyll and produces sugars from sunlight, carbon dioxide, and water. Mushrooms are decomposers, while deer and hawks are consumers.

Question 19Grade 8 Science (Massachusetts learning standards for science)

Bacteria that are resistant to an antibiotic survive treatment and reproduce, so the next generation is mostly resistant. Which process does this describe?

  1. Inheritance of traits acquired during an organism's lifetime
  2. Random mutation that occurs only when antibiotics are present
  3. Natural selection acting on variation in a population Correct answer.
  4. Individual bacteria changing their genes on purpose to survive

Explanation

Populations contain variation, and some individuals have traits that help them survive and reproduce in a given environment. Antibiotics act as a selective pressure, so resistant bacteria survive and pass on the genes that cause resistance. Over generations, the frequency of resistant traits increases in the population.

Question 20Grade 8 Science (Massachusetts learning standards for science)

A scientist finds a fossil of a fish-like organism in a rock layer, and in a layer below it finds fossils of simpler sea creatures. What can be reasonably inferred?

  1. The simpler creatures lived after the fish-like organism
  2. The layers were deposited at exactly the same time
  3. The lower layer is younger because it is deeper
  4. The fish-like organism is younger than the simpler creatures Correct answer.

Explanation

In undisturbed sedimentary rock, lower layers are deposited first and are therefore older than the layers above them. Fossils in an upper layer come from organisms that lived after those in lower layers. This principle of superposition lets scientists establish relative ages of fossils.

Question 21Grade 8 Science (Massachusetts learning standards for science)

Which statement best describes the role of cell division in a multicellular organism?

  1. It allows growth and repair by producing new cells Correct answer.
  2. It removes waste products from the organism
  3. It creates new species over time
  4. It produces energy for the organism's cells

Explanation

Mitosis produces new cells that are genetically identical to the parent cell, which supports growth and replaces damaged tissues. The process also maintains the chromosome number in body cells. Energy production and waste removal are carried out by other cell processes, not by division itself.

Question 22Grade 8 Science (Massachusetts learning standards for science)

A plant is placed in a dark closet for a week. Which change is most likely to be observed when it is compared with an identical plant kept in sunlight?

  1. The dark plant will be paler and grow less because photosynthesis is limited Correct answer.
  2. The dark plant will produce more chlorophyll to compensate
  3. The dark plant will produce more oxygen than the lit plant
  4. The dark plant will grow taller but with darker leaves

Explanation

Photosynthesis requires light to produce sugars and to support chlorophyll production. Without light, the plant cannot make as much food, so growth slows and existing chlorophyll breaks down, giving pale leaves. Oxygen production also drops because photosynthesis is limited.

Question 23Grade 8 Science (Massachusetts learning standards for science)

A student uses a hand lens to observe a leaf and then a microscope to observe cells in the leaf. Which statement best explains why the microscope reveals structures the hand lens cannot?

  1. The microscope uses brighter light to change the leaf's color
  2. The hand lens is too small to hold steady
  3. The microscope provides greater magnification and resolution Correct answer.
  4. The microscope changes the leaf cells into different structures

Explanation

A microscope has higher magnification, making small objects appear larger, and better resolution, allowing closely spaced details to be distinguished. Cell structures such as chloroplasts are too small to be resolved by a hand lens. The instrument improves the ability to see detail rather than altering the specimen.

Question 24Grade 8 Science (Massachusetts learning standards for science)

A town near a river experiences heavy rain, and the water level rises quickly. Which human action would most likely increase the risk of flooding downstream?

  1. Building terraces on nearby slopes
  2. Restoring wetlands near the river
  3. Paving large areas of land for parking lots Correct answer.
  4. Planting trees along the riverbanks

Explanation

Paved surfaces are impermeable, so rainwater runs off quickly instead of soaking into the ground. This rapid runoff raises the amount and speed of water entering streams downstream, increasing flood risk. Trees, wetlands, and terraces slow runoff and increase infiltration.

Question 25Grade 8 Science (Massachusetts learning standards for science)

Which process is the main way water moves from the surface of oceans and lakes into the atmosphere?

  1. Evaporation Correct answer.
  2. Runoff
  3. Precipitation
  4. Condensation

Explanation

Evaporation occurs when liquid water gains energy and changes into water vapor, which rises into the atmosphere. This vapor later cools and condenses to form clouds. Precipitation and runoff return water to the surface rather than moving it into the atmosphere.

Question 26Grade 8 Science (Massachusetts learning standards for science)

A student observes a model of a molecule of water, H2O. Which statement correctly describes the atoms that make up one water molecule?

  1. Two hydrogen atoms are chemically bonded to one oxygen atom. Correct answer.
  2. One hydrogen atom shares an electron pair with another hydrogen atom only.
  3. Two oxygen atoms are chemically bonded to one hydrogen atom.
  4. Hydrogen and oxygen atoms are mixed but not bonded to each other.

Explanation

A water molecule has the formula H2O, meaning two hydrogen atoms are chemically combined with one oxygen atom. The atoms are held together by chemical bonds, so the substance has properties different from either element alone.

Question 27Grade 8 Science (Massachusetts learning standards for science)

A sealed jar contains a mixture of small iron filings and sulfur powder. A magnet removes the iron filings without changing either substance. This behavior shows that the mixture:

  1. has the same properties as a pure element
  2. has chemically reacted to produce a gas
  3. retains the properties of each original substance Correct answer.
  4. has formed a new compound with new properties

Explanation

In a mixture, substances are combined physically and each keeps its own properties, so the iron can still be attracted by a magnet. A compound would have different properties and the original substances could not be separated this way.

Question 28Grade 8 Science (Massachusetts learning standards for science)

An atom of an element has 8 protons, 8 neutrons, and 10 electrons. What is the electric charge of this particle?

  1. 2- (negative) Correct answer.
  2. 0 (neutral)
  3. 8+ (positive)
  4. 2+ (positive)

Explanation

Protons carry positive charge and electrons carry negative charge; neutrons are neutral. With 8 protons and 10 electrons, there are two more negative charges than positive charges, so the net charge is 2-.

Question 29Grade 8 Science (Massachusetts learning standards for science)

In the periodic table, elements in the same column (group) tend to have similar chemical properties. Which best explains this pattern?

  1. They have identical atomic masses.
  2. They have the same total number of electrons.
  3. They have the same number of valence electrons. Correct answer.
  4. They have the same number of neutrons.

Explanation

Elements in a group share the same number of electrons in their outermost energy level, and these valence electrons determine how an element reacts. That shared outer arrangement is why group members behave similarly.

Question 30Grade 8 Science (Massachusetts learning standards for science)

A student wants to compare how quickly sugar dissolves in water at different temperatures. Which change would make the investigation a controlled experiment?

  1. Stir one sample and leave the other samples still.
  2. Keep the amount of sugar and water the same and change only the temperature. Correct answer.
  3. Change both the temperature of the water and the amount of sugar used.
  4. Use different amounts of water for each temperature tested.

Explanation

A controlled experiment changes only the independent variable, which here is water temperature. All other factors, such as sugar amount, water volume, and stirring, must be held constant so any difference in dissolving time can be attributed to temperature.

Question 31Grade 8 Science (Massachusetts learning standards for science)

A runner moves at a constant speed of 5 m/s for 20 seconds. How far does the runner travel?

  1. 4 m
  2. 100 m Correct answer.
  3. 25 m
  4. 0.25 m

Explanation

Distance equals speed multiplied by time, so 5 m/s × 20 s = 100 m. The units of seconds cancel, leaving meters as the unit of distance.

Question 32Grade 8 Science (Massachusetts learning standards for science)

A student graphs the motion of a car and sees that the line is horizontal on a distance-versus-time graph. What does this graph show about the car?

  1. The car is not changing its position during that time. Correct answer.
  2. The car is moving at a constant high speed.
  3. The car is speeding up steadily.
  4. The car is slowing down to a stop.

Explanation

On a distance-versus-time graph, slope represents speed. A horizontal line has zero slope, meaning distance is not changing as time passes, so the object is at rest.

Question 33Grade 8 Science (Massachusetts learning standards for science)

Two students push on a box in opposite directions. One pushes with 30 N to the right and the other with 10 N to the left. What is the net force on the box?

  1. 20 N to the left
  2. 40 N to the right
  3. 20 N to the right Correct answer.
  4. 0 N

Explanation

Forces in opposite directions partially cancel, so subtract the smaller force from the larger one: 30 N − 10 N = 20 N. The net force points in the direction of the larger force, which is to the right.

Question 34Grade 8 Science (Massachusetts learning standards for science)

A crate is lifted straight up onto a shelf at a steady speed. Which statement best describes the work done on the crate by the lifting force?

  1. No work is done because the crate moves at a steady speed.
  2. Work is done only if the crate accelerates while being lifted.
  3. No work is done because the force is upward and the motion is upward.
  4. Work is done because the force and the motion are in the same direction. Correct answer.

Explanation

Work is done when a force causes displacement in the direction of the force, calculated as force times distance. Lifting the crate upward with an upward force satisfies this condition regardless of whether the speed is steady.

Question 35Grade 8 Science (Massachusetts learning standards for science)

A metal spoon is left in a cup of hot soup. After a few minutes the handle of the spoon feels warm. Which process transfers thermal energy along the spoon?

  1. Convection within the metal
  2. Conduction through the metal Correct answer.
  3. Evaporation of soup onto the handle
  4. Radiation from the soup to the handle

Explanation

Conduction is the transfer of thermal energy through direct contact as particles collide and pass energy along a material. Metal is a good conductor, so energy travels from the hot end of the spoon to the cooler handle.

Question 36Grade 8 Science (Massachusetts learning standards for science)

A student adds a small amount of salt to 100 mL of water at room temperature and stirs. The salt disappears and the liquid stays clear. What happened to the salt?

  1. The salt turned into a gas and escaped.
  2. The salt melted into a liquid metal.
  3. The salt dissolved, forming a solution with the water. Correct answer.
  4. The salt chemically reacted and became water.

Explanation

When a solid dissolves, its particles separate and spread evenly among the liquid particles, forming a solution. The salt is still present in the clear liquid even though it is no longer visible as solid crystals.

Question 37Grade 8 Science (Massachusetts learning standards for science)

A balloon rubbed with wool cloth sticks to a wall. Which statement best explains this behavior?

  1. The balloon becomes magnetized and is attracted to metal in the wall.
  2. The balloon's mass decreases, so air pressure pushes it against the wall.
  3. The balloon becomes heavier and falls against the wall.
  4. The balloon gains a static electric charge that attracts it to the neutral wall. Correct answer.

Explanation

Rubbing transfers electrons between the wool and the balloon, giving the balloon a net static charge. This charged balloon can attract neutral objects such as a wall through electric forces.

Question 38Grade 8 Science (Massachusetts learning standards for science)

A simple series circuit contains a battery and two identical light bulbs. If one bulb is removed so the circuit is broken, what happens?

  1. The battery reverses its polarity.
  2. Both bulbs go out because the path for current is broken. Correct answer.
  3. The remaining bulb stays lit at the same brightness.
  4. The remaining bulb becomes brighter.

Explanation

In a series circuit there is only one path for current. Removing a bulb breaks that path, so current stops flowing and all bulbs go out.

Question 39Grade 8 Science (Massachusetts learning standards for science)

A student builds an electromagnet by wrapping wire around an iron nail and connecting it to a battery. Which change would most likely make the electromagnet stronger?

  1. Using a thinner wire with fewer turns
  2. Replacing the iron nail with a plastic rod
  3. Removing the battery from the circuit
  4. Increasing the number of wire turns around the nail Correct answer.

Explanation

The strength of an electromagnet increases with more turns of wire and greater current. Adding turns strengthens the magnetic field produced around the coil.

Question 40Grade 8 Science (Massachusetts learning standards for science)

A light ray strikes a mirror and reflects. If the angle between the incoming ray and the mirror surface is 30 degrees, what is the angle of reflection measured from the normal?

  1. 60 degrees Correct answer.
  2. 30 degrees
  3. 0 degrees
  4. 90 degrees

Explanation

Angles in reflection are measured from the normal, the line perpendicular to the mirror. The angle of incidence is 90° − 30° = 60°, and the angle of reflection equals the angle of incidence, so it is also 60°.

Question 41Grade 8 Science (Massachusetts learning standards for science)

A student looks at a pencil placed in a glass of water and sees it appear bent at the surface. Which statement explains this observation?

  1. Light is absorbed completely at the water surface.
  2. Light travels faster in water than in air and reverses direction.
  3. The pencil physically bends when it gets wet.
  4. Light changes speed and direction when it passes from water into air. Correct answer.

Explanation

Refraction occurs because light travels at different speeds in different materials, bending as it crosses the boundary between water and air. The bent appearance is an optical effect, not a change in the pencil itself.

Question 42Grade 8 Science (Massachusetts learning standards for science)

In a population of beetles, some are green and some are brown. Birds more easily see and eat the brown beetles on green leaves. Over many generations, what is most likely to happen?

  1. Both color forms will disappear from the population.
  2. The proportion of brown beetles will increase.
  3. The proportion of green beetles in the population will increase. Correct answer.
  4. The beetles will learn to change color during their lifetime.

Explanation

Green beetles are better camouflaged and survive to reproduce more often, so their inherited color trait becomes more common over generations. This is natural selection acting on variation already present in the population.

Question 43Grade 8 Science (Massachusetts learning standards for science)

Two populations of the same bird species live on opposite sides of a wide river and have not interbred for thousands of years. Each population has developed different songs and plumage. Which statement best describes their relationship?

  1. They are certainly the same species because they are both birds.
  2. They will immediately merge into one population again.
  3. They may be diverging into separate species because they no longer interbreed. Correct answer.
  4. They have identical genes because they live near the same river.

Explanation

When populations are separated and cannot interbreed, genetic differences can accumulate over time, which can lead to speciation. Different songs and plumage are signs of divergence between the groups.

Question 44Grade 8 Science (Massachusetts learning standards for science)

A cell in a plant leaf is compared with a cell from a human cheek. Which structure is present in the leaf cell but absent in the cheek cell?

  1. Cytoplasm
  2. Cell wall Correct answer.
  3. Ribosomes
  4. Cell membrane

Explanation

Plant cells have a rigid cell wall made largely of cellulose outside the cell membrane, providing support and shape. Human cheek cells lack a cell wall but share membranes, cytoplasm, and ribosomes with plant cells.

Question 45Grade 8 Science (Massachusetts learning standards for science)

A student measures the heart rate of a classmate before and after one minute of jumping jacks. The heart rate rises after exercise. Which body system interaction best explains this change?

  1. The nervous system stops sending signals to the heart during exercise.
  2. The digestive system breaks down more food to cool the blood.
  3. The muscular system increases its activity, and the circulatory system delivers more oxygen to muscles. Correct answer.
  4. The skeletal system produces extra blood cells during exercise.

Explanation

Muscles working harder need more oxygen and nutrients, so the circulatory system responds by increasing heart rate and blood flow. This reflects interaction between the muscular and circulatory systems, coordinated by the nervous system.

Question 46Grade 8 Science (Massachusetts learning standards for science)

During photosynthesis, a green plant takes in carbon dioxide and water and releases oxygen. Which statement best describes the overall purpose of photosynthesis for the plant?

  1. It breaks down sugar to release energy for movement.
  2. It produces sugar that stores energy for the plant's use. Correct answer.
  3. It produces carbon dioxide for the plant to breathe out.
  4. It converts oxygen directly into water inside the leaves.

Explanation

Photosynthesis uses light energy to combine carbon dioxide and water into sugar, storing energy in chemical bonds, while oxygen is released. The sugar can then be used for growth or broken down later for energy.

Question 47Grade 8 Science (Massachusetts learning standards for science)

A baker mixes yeast, sugar, and warm water in a bowl and covers it. After a while the mixture bubbles and gives off a gas. Which statement best explains the source of the bubbles?

  1. Yeast cells break down sugar and release carbon dioxide gas. Correct answer.
  2. The bowl absorbs oxygen from the air and releases it as bubbles.
  3. The water boils because of the sugar added to it.
  4. The sugar melts and turns into a gas when warmed.

Explanation

Yeast are living single-celled organisms that use sugar as food and release carbon dioxide as a waste product, which forms the bubbles. This is evidence of a living process producing a gas.

Question 48Grade 8 Science (Massachusetts learning standards for science)

A scientist finds that a certain trait in a population of plants is controlled by genes. Which statement best describes how a gene influences a trait?

  1. A gene is passed only from the mother plant to its offspring.
  2. A gene is a type of cell that builds the plant's leaves.
  3. A gene carries instructions that help determine a trait, which the environment can also affect. Correct answer.
  4. A gene directly determines a trait with no other influences at all.

Explanation

Genes are segments of DNA that carry instructions for traits, and offspring inherit them from both parents. Traits also depend on environmental factors such as light, water, and nutrients, so genes are not the only influence.

Question 49Grade 8 Science (Massachusetts learning standards for science)

A rock layer contains fossils of shells and coral. Which conclusion about the past environment of that area is best supported by this evidence?

  1. The area was once covered by lava flows.
  2. The area has always been a high mountain peak.
  3. The area was once covered by water. Correct answer.
  4. The area was once a desert with no water.

Explanation

Shells and coral are produced by organisms that live in water, so their fossils indicate the area was once underwater. Fossils provide evidence about past environments and organisms.

Question 50Grade 8 Science (Massachusetts learning standards for science)

A river carries sediment downstream and deposits it where the river slows at its mouth. Over a long time, this process most likely builds:

  1. a deep canyon cut into bedrock
  2. a volcanic mountain
  3. a delta of layered sediment Correct answer.
  4. a glacier-carved valley

Explanation

When a river slows at its mouth, it can no longer carry as much sediment, so the material is deposited in layers that build a delta. This is an example of erosion and deposition shaping landforms over time.