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School · Science Class (Physics, Chemistry, Biology) · Card 001/010easy
When a swimmer pushes backward against the water with their arms and legs, they move forward through the pool. Which law of motion explains why pushing on the water propels the swimmer in the opposite direction?
ANewton's First Law -- an object stays at rest or keeps moving at a constant speed unless a force acts on it
BNewton's Third Law -- every force one object exerts on a second object is matched by an equal and opposite force from the second object back on the first
CThe law of conservation of energy -- energy is transferred from the swimmer's muscles into the water without ever being created or destroyed
DNewton's Second Law -- the acceleration produced depends on the size of the force and the mass being pushed
Why B? And why not the others?
Correct answer: B. Newton's Third Law -- every force one object exerts on a second object is matched by an equal and opposite force from the second object back on the first
A swimmer moving forward relies on Newton's Third Law: pushing backward on the water with hands and feet is an action force, and the water pushes back on the swimmer with an equal and opposite reaction force, propelling them forward through the pool. The option describing the law of inertia is wrong because that law only describes how an object behaves when no net force acts on it, and says nothing about paired forces between two interacting objects. The option describing conservation of energy is wrong because it addresses how energy moves and changes form, not why two objects experience opposite forces of the same size. The option describing the relationship between force, mass and acceleration is wrong because that law explains how a single object accelerates under a given force, not why the water exerts a force back on the swimmer in the first place.
Source: BBC Bitesize GCSE Physics: Newton's Laws of Motion
School · Science Class (Physics, Chemistry, Biology) · Card 002/010easy
In science fiction films, huge explosions in space are often shown with a loud roar. In real space, far from any planet, why would that explosion actually make no sound at all to a nearby astronaut?
ALight travels faster than sound, so the explosion would be seen long before any sound reached the astronaut, though the sound would eventually arrive
BSound waves are absorbed by the astronaut's spacesuit before they can be heard, unlike light waves which pass straight through
CThe human ear cannot detect sound at the extremely high frequencies produced by explosions, even though the sound does travel through space
DSound waves need particles of matter, like the molecules in air or water, to vibrate and carry the wave, and space is a near-total vacuum with essentially no particles to vibrate
Why D? And why not the others?
Correct answer: D. Sound waves need particles of matter, like the molecules in air or water, to vibrate and carry the wave, and space is a near-total vacuum with essentially no particles to vibrate
Sound is a mechanical wave, meaning it travels by making particles of a medium, like the molecules in air, water or a solid, bump into their neighbours and pass the vibration along. In outer space there is only a near-total vacuum with essentially no particles to carry that vibration, so an explosion there would be silent to any nearby observer no matter how powerful it was. The option about light outrunning sound is wrong because it assumes the sound eventually arrives, when in reality there is no medium present for it to travel through at all. The option about a spacesuit absorbing sound is wrong because it ignores that the sound could not reach the suit in the first place, since it cannot propagate through the vacuum surrounding it. The option about frequency is wrong because it wrongly assumes the sound is produced and simply inaudible, rather than never transmitted beyond the explosion itself.
Source: BBC Bitesize GCSE Physics: Sound waves
School · Science Class (Physics, Chemistry, Biology) · Card 003/010easy
A student dips a strip of universal indicator paper into three unknown liquids and gets three different colours: red, green, and purple. What does this range of colours tell the student that a single strip of litmus paper could not?
AThe universal indicator shows roughly how acidic or alkaline each liquid is across the whole pH scale, while litmus paper can only show whether a liquid is acidic or alkaline, not its strength
BUniversal indicator only works on liquids containing water, while litmus paper works equally well on liquids and gases
CThe colours show which liquid conducts electricity best, a property litmus paper is not sensitive to at all
DUniversal indicator changes colour permanently, while litmus paper's colour change reverses itself back to its original colour after a few minutes
Why A? And why not the others?
Correct answer: A. The universal indicator shows roughly how acidic or alkaline each liquid is across the whole pH scale, while litmus paper can only show whether a liquid is acidic or alkaline, not its strength
Universal indicator is a mixture of several dyes that produces a whole range of colours corresponding to different pH values, so it can show roughly how strongly acidic or alkaline a liquid is anywhere across the pH scale. Litmus paper contains only a single dye that turns one colour in acids and another in alkalis, so it can only tell you which side of neutral a liquid falls on, not its strength. The option claiming universal indicator only works on liquids is wrong because both indicators are typically used to test liquids and solutions, and this is not the property that explains the difference in colour range. The option about electrical conductivity is wrong because neither indicator measures conductivity at all; that would require a completely different piece of equipment. The option about permanent versus reversible colour change is wrong because neither indicator's colour change works that way; both simply respond to the pH of whatever they are currently dipped in.
Source: RSC Education / BBC Bitesize GCSE Chemistry: Acids, alkalis and the pH scale
School · Science Class (Physics, Chemistry, Biology) · Card 004/010easy
A gardener notices that a plant kept in a dark cupboard for two weeks grows pale and weak, while an identical plant on a sunny windowsill stays green and healthy. Which raw ingredient is missing for the plant in the cupboard, stopping it from making its own food?
ACarbon dioxide, because a closed cupboard traps stale air that contains none of this gas at all
BWater, because the soil in a dark cupboard dries out far faster than soil in direct sunlight
CLight energy, which the green pigment chlorophyll needs to absorb before it can drive the reaction that turns carbon dioxide and water into glucose and oxygen
DWarmth, because a cupboard is always colder than a sunny windowsill, and the chemical reaction cannot start below room temperature
Why C? And why not the others?
Correct answer: C. Light energy, which the green pigment chlorophyll needs to absorb before it can drive the reaction that turns carbon dioxide and water into glucose and oxygen
Photosynthesis needs light energy, which the green pigment chlorophyll absorbs and uses to drive the reaction that combines carbon dioxide and water into glucose and oxygen; without light, a plant kept in a dark cupboard cannot carry out this reaction, so it grows pale and weak. The option about carbon dioxide is wrong because a cupboard's air still contains carbon dioxide, just like any other room; sealing a plant away from the sun does not remove this gas from the air around it. The option about water is wrong because a dark, enclosed cupboard would if anything slow down water loss compared to a sunny windowsill, not speed it up. The option about warmth is wrong because photosynthesis can proceed at ordinary room temperatures found in a cupboard; it is the absence of light, not a lack of warmth, that stops the reaction.
Source: BBC Bitesize GCSE Biology: Photosynthesis
School · Science Class (Physics, Chemistry, Biology) · Card 005/010easy
When a splinter breaks the skin and bacteria get into the wound, certain white blood cells travel to the site and begin engulfing the bacteria one by one. What is this type of white blood cell called, and what is it doing?
AA red blood cell, carrying oxygen to the wound so that the bacteria are starved of the air they need to survive
BA phagocyte, carrying out phagocytosis by surrounding each bacterium with its own cell membrane and digesting it
CA platelet, releasing chemicals that dissolve the bacteria's outer cell wall on contact
DAn antibody, physically trapping each bacterium inside a hard protein shell until it can be removed
Why B? And why not the others?
Correct answer: B. A phagocyte, carrying out phagocytosis by surrounding each bacterium with its own cell membrane and digesting it
The white blood cells described are phagocytes, and the process of surrounding and digesting a bacterium using their own cell membrane is called phagocytosis; this is one of the body's first lines of defence against infection at the site of a wound. The option describing red blood cells is wrong because their job is carrying oxygen around the body, not attacking bacteria, and bacteria are not destroyed simply by being deprived of air at a wound site. The option describing platelets is wrong because platelets are involved in clotting blood to seal a wound, not in dissolving the cell walls of invading bacteria. The option describing antibodies is wrong because antibodies are proteins that mark or neutralise pathogens rather than cells that physically trap them inside a shell; that description does not match how either antibodies or phagocytes actually work.
Source: BBC Bitesize GCSE Biology: The immune system
School · Science Class (Physics, Chemistry, Biology) · Card 006/010medium
Almost every liquid becomes denser as it cools and turns into a solid, so the solid sinks in its own liquid. Water breaks this pattern: ice floats on liquid water instead of sinking. What causes water to behave this way?
AIce contains tiny pockets of trapped air bubbles that make it buoyant, in the same way a boat floats despite being made of dense metal
BWater is lightest exactly at its freezing point of 0°C, and steadily gets denser again as it turns into ice
CGravity affects frozen water differently from liquid water because the molecules are no longer able to move at all
DWhen water freezes, its molecules lock into an open hexagonal lattice held apart by hydrogen bonds, which takes up more space than the same molecules do when moving freely as a liquid, making ice about 8-9% less dense
Why D? And why not the others?
Correct answer: D. When water freezes, its molecules lock into an open hexagonal lattice held apart by hydrogen bonds, which takes up more space than the same molecules do when moving freely as a liquid, making ice about 8-9% less dense
When water freezes, its molecules arrange themselves into an open, hexagonal lattice held apart by hydrogen bonds, and this structure takes up more space than the same molecules do when they are free to move closely together as a liquid; the result is that ice ends up roughly 8-9% less dense than liquid water, which is why it floats. The option about trapped air bubbles is wrong because the density difference comes from the arrangement of the water molecules themselves, not from air pockets, and ice would still float even without any dissolved air at all. The option claiming water is lightest at 0°C and gets denser again as ice is wrong because it has the pattern backwards; liquid water is actually densest at 4°C and becomes less dense both as it cools further and once it freezes. The option about gravity acting differently on frozen water is wrong because gravity treats ice and liquid water identically; buoyancy, not gravity behaving differently, is what determines whether ice floats.
Source: BBC Bitesize GCSE Physics / GCSE Chemistry: Density and states of matter
School · Science Class (Physics, Chemistry, Biology) · Card 007/010medium
A student reacts a strip of magnesium with dilute hydrochloric acid in a test tube and collects the gas given off. When they hold a lit wooden splint near the mouth of the tube, they hear a sharp squeaky pop. What does this result confirm about the gas, and why does the pop happen?
AThe gas is hydrogen: the flame supplies enough energy for the hydrogen to react rapidly with oxygen in the air, and the sudden release of hot gas and water vapour produces the popping sound
BThe gas is oxygen: the splint's flame burns more brightly in the gas, and the pop is simply the sound of the wood catching fire faster than normal
CThe gas is carbon dioxide: the pop happens because the gas extinguishes the flame instantly, and the sound is the splint's ember cracking as it cools
DThe gas is chlorine: the pop is caused by the bleaching reaction between the gas and the burning wood fibres of the splint
Why A? And why not the others?
Correct answer: A. The gas is hydrogen: the flame supplies enough energy for the hydrogen to react rapidly with oxygen in the air, and the sudden release of hot gas and water vapour produces the popping sound
A lit splint held near hydrogen gas provides the activation energy needed for the hydrogen to react rapidly with oxygen in the surrounding air, and the sudden release of hot gas and water vapour from that fast reaction produces the sharp squeaky pop; this reaction is the standard confirmatory test for hydrogen gas. The option describing oxygen is wrong because the standard test for oxygen is a glowing splint relighting in the gas, not a popping sound, since oxygen supports combustion rather than being the fuel that combusts. The option describing carbon dioxide is wrong because carbon dioxide is tested by turning limewater cloudy, and a splint held in carbon dioxide is extinguished quietly rather than producing any pop. The option describing chlorine is wrong because chlorine is identified by bleaching damp litmus paper white, and it does not react explosively with a flame the way hydrogen does.
Source: RSC Education / BBC Bitesize GCSE Chemistry: Tests for gases
School · Science Class (Physics, Chemistry, Biology) · Card 008/010medium
During a slow jog, a runner's muscles get enough oxygen delivered to release energy from glucose. When the same runner sprints flat out, their muscles cannot get oxygen fast enough, yet the muscles keep working for a while before starting to ache and tire. What is happening in the muscles during the sprint?
AThe muscles briefly stop respiring altogether and rely only on the oxygen already stored in the blood from before the sprint began
BThe muscles switch to burning stored fat directly, a process that also happens to require no oxygen at all
CThe muscles switch to anaerobic respiration, breaking down glucose without oxygen to release energy more quickly, but producing lactic acid as a waste product that builds up and causes the aching, tired feeling
DThe muscles increase their rate of aerobic respiration only, extracting extra oxygen that was previously unused in the surrounding tissue
Why C? And why not the others?
Correct answer: C. The muscles switch to anaerobic respiration, breaking down glucose without oxygen to release energy more quickly, but producing lactic acid as a waste product that builds up and causes the aching, tired feeling
When the demand for energy outpaces the oxygen the blood can deliver, muscle cells switch to anaerobic respiration, breaking down glucose without oxygen to release energy faster; the trade-off is that this process produces lactic acid as a waste product, which builds up in the muscles and causes the aching, tired feeling the runner notices. The option claiming the muscles stop respiring is wrong because muscle cells must keep respiring to keep producing energy; stopping respiration entirely would mean the muscles could no longer function at all. The option about burning stored fat is wrong because breaking down fat for energy actually requires oxygen, so it is not a pathway the body can rely on when oxygen is in short supply during a sprint. The option about increasing aerobic respiration alone is wrong because the whole problem during a sprint is that oxygen delivery cannot keep up with demand, so relying only on the oxygen-using pathway cannot explain how the muscles keep working.
Source: BBC Bitesize GCSE Biology / PE: Aerobic and anaerobic respiration
School · Science Class (Physics, Chemistry, Biology) · Card 009/010hard
Two identical bulbs are connected to the same battery, once in series and once in parallel. In the series circuit, the current is measured as 0.5 A everywhere in the loop. In the parallel circuit, each branch is measured separately. Which statement correctly compares current and voltage in the two circuits?
AIn both the series and parallel circuits, the current is shared out equally between the two bulbs while the voltage across each bulb stays the same as the battery's voltage
BIn the series circuit, the same 0.5 A flows through both bulbs one after another, while in the parallel circuit the total current from the battery splits between the two branches, with the full battery voltage appearing across each branch
CIn the series circuit, the voltage is the same across both bulbs while the current splits between them, and in the parallel circuit the current is the same everywhere while the voltage splits between the branches
DThe parallel circuit only works if the current is reduced to exactly half of the series circuit's current, because splitting the wire path always halves the current automatically
Why B? And why not the others?
Correct answer: B. In the series circuit, the same 0.5 A flows through both bulbs one after another, while in the parallel circuit the total current from the battery splits between the two branches, with the full battery voltage appearing across each branch
In a series circuit, there is only one path for charge to flow, so the same current passes through every component one after another; in a parallel circuit, the current from the battery splits between the separate branches, but the full battery voltage appears across each branch because each one connects independently back to the battery. The option claiming current is shared and voltage stays the same as the battery's voltage in both circuit types is wrong because that describes only the parallel case, not the series one, where the current instead stays constant throughout the single loop. The option describing the series circuit as having equal voltage and split current, and the parallel circuit as having equal current and split voltage, is wrong because it has the two circuit types' behaviour completely swapped. The option claiming a parallel circuit always exactly halves the current is wrong because how the current divides between branches depends on the resistance of each branch, not a fixed automatic halving rule.
Source: BBC Bitesize GCSE Physics: Series and parallel circuits
School · Science Class (Physics, Chemistry, Biology) · Card 010/010hard
Two pea plants, each carrying one dominant allele for tall stems (T) and one recessive allele for short stems (t), are crossed with each other. Using a Punnett square for this Tt x Tt cross, what proportion of their offspring would be expected to have short stems, and why?
ANone of the offspring, because the dominant tall allele always completely replaces the recessive short allele in every offspring's genetic makeup
BHalf of the offspring, because each parent contributes one allele, and exactly half of all combinations must contain the recessive allele
CAll of the offspring, because both parents carry the recessive allele, so it is guaranteed to be passed on and expressed in every offspring
DOne quarter of the offspring, because the only combination that produces a short phenotype is the one where an offspring inherits the recessive allele from both parents (tt), which happens in one of the four equally likely combinations in the Punnett square
Why D? And why not the others?
Correct answer: D. One quarter of the offspring, because the only combination that produces a short phenotype is the one where an offspring inherits the recessive allele from both parents (tt), which happens in one of the four equally likely combinations in the Punnett square
Crossing two Tt parents produces four equally likely combinations in the Punnett square: TT, Tt, Tt and tt; only the tt combination, where an offspring inherits the recessive allele from both parents, produces the short-stem phenotype, and that combination makes up one of the four boxes, giving a quarter of the expected offspring. The option claiming none of the offspring would be short is wrong because it ignores that two carriers of the recessive allele can still produce offspring with two recessive alleles between them. The option claiming half the offspring would be short is wrong because it correctly identifies that half of the offspring carry at least one recessive allele through the Tt combinations, but a single recessive allele paired with a dominant one still produces the tall phenotype, since the dominant allele is expressed. The option claiming all offspring would be short is wrong because carrying the recessive allele is not the same as having two copies of it; the dominant allele from either parent is still enough to produce a tall plant unless both parents happen to contribute the recessive allele to the same offspring.
Source: BBC Bitesize GCSE Biology: Monohybrid crosses and Punnett squares