General Science · Practice test 8

Correct answer: Watson and Crick

James Watson and Francis Crick, building on X-ray data from Rosalind Franklin, proposed the double helix structure of DNA in 1953.

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Correct answer: genes

A gene is a stretch of DNA coding for one product, usually a protein. Proteins are what genes produce rather than the units of the code itself.

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Correct answer: Every force is matched by an equal force in the opposite direction

The third law says forces always come in pairs: push on a wall and the wall pushes back just as hard on you. The first choice paraphrases the first law and the third the second law, while the last is conservation of energy, which is not one of Newton's laws at all.

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Correct answer: Left ventricle

The left ventricle drives oxygen-rich blood into the aorta and around the whole body, which is why its wall is the thickest. The right ventricle sends blood only as far as the lungs.

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Correct answer: their outer electron shells are already full

Atoms react in order to reach a full outer shell of electrons. The noble gases in the last column already have one, so they have nothing to gain by bonding, which is why helium and neon are used where an inert gas is needed.

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Correct answer: poles

Field lines crowd together at the north and south poles, making the pull strongest there and weakest around the middle of a bar magnet.

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Correct answer: filter waste products from the blood

The kidneys strain waste and excess water out of the blood to make urine, and in doing so they also balance the body's salts and fluid levels.

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Correct answer: how much of its sunlit side faces Earth

Half the Moon is always lit by the Sun; the phase depends on how much of that lit half we can see from where we stand. Earth's shadow explains a lunar eclipse, not the ordinary monthly phases.

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Correct answer: cell membrane

The cell membrane is selectively permeable: it lets some molecules pass freely while blocking or actively transporting others. A cell wall, where present, is a rigid outer layer rather than the regulating barrier.

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Correct answer: is neither created nor destroyed, only transformed

Energy changes form constantly, from chemical to kinetic to heat and so on, but the total amount in a closed system stays the same rather than being created or lost.

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Correct answer: existing rock is altered by heat and pressure

Metamorphic means changed in form: heat and pressure reshape rock that already existed, turning limestone into marble or shale into slate, without melting it. Melting and cooling gives igneous rock instead.

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Correct answer: Right atrium

Blood from the body enters the right atrium first, then passes to the right ventricle, which pumps it to the lungs to pick up oxygen.

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Correct answer: Ice melting into water

Melting changes only the state; the substance is still water and freezing reverses it. The other three produce new substances and cannot be undone, which makes them chemical changes.

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Correct answer: half the number of chromosomes

Meiosis halves the chromosome count so that when two sex cells join at fertilisation, the full number is restored rather than doubled with every generation.

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Correct answer: 60 to 100 beats per minute

A healthy resting adult heart typically beats between 60 and 100 times a minute; well-trained athletes often sit toward the lower end of that range.

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Correct answer: condensation

Condensation is the step in the water cycle where rising water vapour cools enough to form tiny liquid droplets, which gather as clouds before eventually falling as precipitation.

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Correct answer: frequency

Frequency, measured in hertz, counts how many wave cycles pass a fixed point per second. A higher frequency sound wave is heard as a higher pitch.

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Correct answer: conduct heat and electricity well

Metals hold their outer electrons loosely, and those free-moving electrons carry both heat and current. The same loose hold means metals lose electrons in reactions rather than gaining them.

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Correct answer: The common cold

The common cold is caused by viruses, which is why antibiotics have no effect on it. Strep throat, tuberculosis, and most urinary tract infections are bacterial.

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Correct answer: velocity

Acceleration measures how quickly velocity changes over time, whether that change is speeding up, slowing down, or turning. A constant speed in a straight line means zero acceleration.

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Correct answer: let oxygen and carbon dioxide diffuse across easily

Alveolar walls are only one cell thick and surrounded by capillaries, so gases can diffuse quickly between the air sac and the blood. Warming and filtering happen earlier, in the nose and upper airway.

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Correct answer: an ionic bond

Transferring electrons leaves one atom positive and the other negative, and the opposite charges attract, forming an ionic bond as in table salt. A covalent bond shares electrons rather than handing them over.

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Correct answer: Every bulb in the circuit goes out

A series circuit gives current only one path, so a single break stops the flow everywhere. In a parallel circuit each bulb has its own path and the others keep working.

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Correct answer: niche

A niche describes an organism's full functional role, while a habitat is simply the physical place it lives. Two species rarely occupy the exact same niche in the same place for long.

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Correct answer: Veins

Veins carry blood back toward the heart, generally at lower pressure than arteries, and many contain valves that stop blood from flowing backward.

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