General Science · Practice test 4

Correct answer: at the very bottom

Because sediment settles in order over time, the deepest layers in an undisturbed sequence were laid down first and are therefore the oldest, a principle called superposition.

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Correct answer: 6

A neutral atom has equal numbers of protons and electrons so their charges cancel out. Since carbon-12 has 6 protons, it also has 6 electrons.

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Correct answer: nitrogen fixation

Nitrogen makes up most of the air but plants cannot use it in gas form. Nitrogen-fixing bacteria, many living in nodules on the roots of legumes, convert it into ammonia and nitrates the plant can absorb.

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Correct answer: Jupiter

Jupiter, the largest planet, is made mostly of hydrogen and helium gas with no solid surface to stand on, unlike the smaller rocky planets Mercury, Mars, and Earth.

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Correct answer: recessive

A recessive trait is masked whenever a dominant allele is present, so it shows only when both copies are recessive. A dominant trait needs just one copy to appear.

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Correct answer: refraction

Light changes speed when it enters a denser medium and so changes direction, which is refraction. It is why a straw looks bent at the surface of a glass. Reflection is light bouncing back instead.

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Correct answer: Earth passes between the Sun and the Moon

In a lunar eclipse Earth sits in the middle and its shadow falls across the full Moon. The second choice describes a solar eclipse, where the Moon blocks the Sun from our view.

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Correct answer: taiga

The taiga, or boreal forest, stretches across northern regions and is dominated by cold-tolerant coniferous trees like pine and spruce. The tundra, further north still, is too cold for trees at all.

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Correct answer: biodiversity

Biodiversity counts the variety of life present. A population is the members of one species, and a habitat is the place an organism lives rather than the variety within it.

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Correct answer: organic humus

Humus, the decayed organic material in soil, holds nutrients and water that plant roots need, which is why dark, humus-rich topsoil supports the best plant growth.

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Correct answer: Nimbostratus

Nimbostratus is a thick grey sheet that produces continuous rain. Cirrus is thin and high with no rain, cumulus is the fair-weather puffy cloud, and cumulonimbus is the towering thunderstorm cloud, which brings violent but brief rain.

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Correct answer: The ribosome

Ribosomes, free-floating or attached to the endoplasmic reticulum, translate the mRNA sequence into a chain of amino acids. The nucleus only holds the original DNA instructions.

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Correct answer: Sedimentary

Sedimentary rock builds up as loose particles settle in layers and are gradually pressed and cemented into solid rock, often preserving fossils in the process.

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Correct answer: The Golgi apparatus

The Golgi apparatus receives proteins from the endoplasmic reticulum, modifies them, and wraps them for delivery. Ribosomes build the proteins in the first place and lysosomes break down waste.

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Correct answer: Fat

Fat carries about 9 calories per gram, while protein and carbohydrate each carry about 4. That is why fat is such a compact way for the body to store energy.

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Correct answer: carbon dioxide and water

Photosynthesis combines carbon dioxide from the air and water drawn up by the roots, using light energy, to produce sugar and release oxygen as a byproduct.

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Correct answer: Protein

Protein, along with carbohydrate and fat, is a macronutrient needed in relatively large daily amounts. Vitamins and minerals are needed only in small, or micro, amounts.

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Correct answer: The number of atoms of each element

Matter is neither created nor destroyed in a reaction, so every atom on the left must reappear on the right. The number of molecules often changes even when the atom counts match.

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Correct answer: Gravity

The Sun's gravity pulls each planet inward while the planet's own forward motion carries it sideways, and the balance of the two produces an orbit. Inertia is that forward motion rather than a force.

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Correct answer: returning nutrients from dead matter to the soil

Bacteria and fungi break down dead plants and animals, releasing the nutrients locked inside so that producers can use them again. Without them nutrients would stay trapped in dead matter.

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Correct answer: primary consumers

Primary consumers, typically herbivores, feed directly on producers such as plants. Secondary consumers then feed on the primary consumers, one step further along the chain.

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Correct answer: gravitational potential energy

Height above the ground gives an object gravitational potential energy; releasing the ball converts that stored energy into kinetic energy as it falls and speeds up.

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Correct answer: The electron

Electrons carry a negative charge and occupy the space around the nucleus, while protons in the nucleus carry a positive charge and neutrons carry none.

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Correct answer: one large central vacuole taking up most of its volume

Plant cells typically hold one big central vacuole that stores water and keeps the cell rigid, while animal cells, if they have vacuoles at all, carry several small ones.

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Correct answer: 100 degrees

Water boils at 100 degrees Celsius and freezes at 0. The values 212 and 32 are the same two points on the Fahrenheit scale.

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