How can microbes remain alive in otherwise frozen environments?
(a)No survival anywhere in frozen environments
(b)Active growth in solid ice without liquid water
(c)Survival through freezing or active growth in pockets of liquid water
(d)Active growth in dry spaces without any water
Show answer
(c) Survival through freezing or active growth in pockets of liquid water
Some microbes can survive freezing. Active growth requires liquid water, which can occur in pockets within otherwise frozen environments.
The planets of the solar system
Question 2
Which description best fits the eight planets’ orbits around the Sun?
(a)They are straight lines moving away from the Sun.
(b)They are all extremely long, narrow ellipses.
(c)They are perfect circles with exactly the same radius.
(d)They are ellipses with different degrees of stretching, generally close to circular.
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(d) They are ellipses with different degrees of stretching, generally close to circular.
Planetary orbits are elliptical and differ in how far they depart from a circle. They are generally close to circular, although their distances from the Sun still vary. They do not all have the same shape or size.
Earth's magnetic field as a shield
Question 3
If Earth lost its magnetic field, which consequence is correctly described?
(a)The gases of the atmosphere would immediately escape into space.
(b)It would lose the deflection of many charged particles that interact with the atmosphere.
(c)Sunlight would newly reach the surface, because the magnetic field normally blocks it.
(d)Only that compasses would stop working, the atmosphere being unaffected.
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(b) It would lose the deflection of many charged particles that interact with the atmosphere.
Earth’s magnetic field deflects many charged particles and influences their interaction with the atmosphere. Losing it would remove this protection, not merely affect compasses. It would not make all atmospheric gas immediately escape.
Earth's size, its gravity and holding on to an atmosphere
Question 4
Which force helps keep Earth's atmosphere around the planet?
(a)Earth's magnetic force
(b)No force
(c)Earth's gravity
(d)Friction
Show answer
(c) Earth's gravity
Earth's gravity pulls gas particles towards the planet. This helps keep the atmosphere around Earth.
The biosphere and the interdependence of living things
Question 5
What role do decomposers play when dead plant and animal matter breaks down in soil?
(a)They store it unchanged until a plant comes to take it.
(b)They turn it into the sunlight that plants use.
(c)They only clear it away, leaving nothing behind them.
(d)They break down organic matter and help release nutrients for reuse.
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(d) They break down organic matter and help release nutrients for reuse.
Decomposers help release nutrients from dead organic matter. Plants can take up available mineral nutrients again. The rate of decomposition depends on conditions, so dead material can sometimes accumulate.
The ozone layer and shielding from ultraviolet rays
Question 6
The atmosphere contains both the oxygen used in breathing and the ozone that forms the ozone layer. How does ozone differ from the oxygen we breathe?
(a)It is not made of oxygen at all.
(b)It is oxygen in its liquid form.
(c)It does not differ. Ozone is another name for the oxygen we breathe.
(d)It is a three-atom oxygen molecule.
Show answer
(d) It is a three-atom oxygen molecule.
Ozone is a three-atom oxygen molecule. Some of the oxygen in the atmosphere gets converted into it, and that ozone forms the ozone layer.
Earth as a unique life-bearing planet
Question 7
Earth’s distance from the Sun, atmosphere, orbit and gravity all influence its conditions. Which statement best explains its ability to support life?
(a)Size alone explains habitability: the larger a planet is, the better it must be for life.
(b)None of them, since Earth counts as suitable because it is where we live.
(c)Its distance from the Sun alone, the others being minor details.
(d)Several conditions work together; distance from the Sun alone is not enough to explain it.
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(d) Several conditions work together; distance from the Sun alone is not enough to explain it.
Earth’s habitability reflects several interacting conditions, including liquid water and suitable temperatures. Distance alone is insufficient. This does not establish that every listed feature is individually indispensable to every possible form of life.
Earth's nearly circular orbit and steady conditions through the year
Question 8
A planet follows a strongly stretched orbit around a steadily shining star. How does the sunlight it receives change along its orbit?
(a)Its sunlight changes for exactly the same reason as Earth’s seasons: Earth also has a strongly stretched orbit.
(b)Only its speed can change; orbital shape cannot affect the sunlight it receives.
(c)The sunlight received is independent of its distance from the star.
(d)It receives more sunlight per unit area near the star and less when farther away.
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(d) It receives more sunlight per unit area near the star and less when farther away.
Sunlight becomes less intense with distance from a star. A strongly stretched orbit produces a larger variation in received sunlight. Actual temperatures also depend on the atmosphere and other factors, so scorching and freezing are not guaranteed.
Reproduction, genes and the continuity of life
Question 9
Reproduction keeps each kind of living thing going. What else does it make possible?
(a)A doubling of the instructions in each generation.
(b)Small changes in the instructions passed down.
(c)Nothing else. It can only ever make more of the same.
(d)Nothing else, since an animal changes its own body to suit where it lives instead.
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(b) Small changes in the instructions passed down.
Reproduction does more than create more of the same. It allows small changes in the instructions passed down, and over many generations those changes can lead to new features or even completely new types of living beings.
The four spheres and the balance that keeps Earth habitable
Question 10
Earth's air, water, solid ground and living things are counted as four systems. How do they stand in relation to one another?
(a)They take turns, only one of them acting at a time.
(b)They are separate systems that do not affect one another.
(c)They are connected, so damage to one can affect the others.
(d)They interact, but a small local change can never have effects beyond its starting place.
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(c) They are connected, so damage to one can affect the others.
The atmosphere, hydrosphere, geosphere and biosphere are connected, so damage to one can affect the others. Earth is a vast living system in which land, air, water and living things support and affect one another.
The greenhouse effect
Question 11
Gases in Earth's atmosphere hold in some of the heat the surface gives off. What does that do for conditions on Earth?
(a)It keeps the Sun's rays out, which is what stops the surface overheating.
(b)It supplies the oxygen that living things breathe.
(c)Nothing but harm, since holding in heat is always harmful.
(d)It raises the average surface temperature and helps support conditions for liquid water.
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(d) It raises the average surface temperature and helps support conditions for liquid water.
The natural greenhouse effect warms Earth’s surface compared with conditions without it. This helps support liquid water. Increasing greenhouse gas concentrations strengthens warming and can disrupt climate; the effect does not set one fixed ideal temperature.
The Earth's crust, the thin layer where life exists
Question 12
How does Earth’s crust compare in thickness with the radius of the whole planet?
(a)It is about as thick as each of the other layers of the Earth.
(b)It is a thin outer layer compared with the planet’s radius.
(c)It is about a tenth of the planet.
(d)It extends all the way to Earth’s centre.
Show answer
(b) It is a thin outer layer compared with the planet’s radius.
Earth’s crust is its thin rocky outer layer. The apple-skin comparison illustrates its small thickness relative to the whole planet. Life also occupies water and parts of the atmosphere; crust and biosphere are different terms.
The geosphere: soil, rocks, minerals and geodiversity
Question 13
What can soil naturally supply that plants need for growth?
(a)Nutrients such as nitrogen and potassium.
(b)The oxygen that plants use when they make their food.
(c)Nothing plants need. It is just dirt.
(d)Only what people have added to it, since nutrients have to be put in.
Show answer
(a) Nutrients such as nitrogen and potassium.
Soil can supply mineral nutrients, including usable forms of nitrogen and potassium. Nutrient amounts vary between soils; they need not all be rich, and nutrients do not come only from added fertilisers.
Air, water and sunlight sustaining life
Question 14
In a simple comparison, Earth’s atmosphere is removed while the sunlight absorbed by the surface is held fixed. What happens to atmospheric greenhouse warming?
(a)It is lost, so the average surface temperature would be lower.
(b)Only a barrier against cold is lost; an atmosphere warms solely by blocking cold from space.
(c)It becomes stronger because removing greenhouse gases increases their effect.
(d)It stays unchanged because greenhouse warming needs no gases.
Show answer
(a) It is lost, so the average surface temperature would be lower.
Greenhouse warming involves atmospheric absorption and emission of infrared radiation. Removing the atmosphere removes this contribution. With absorbed sunlight held fixed, the comparison predicts a lower average surface temperature, not one uniform temperature everywhere.
Asexual reproduction
Question 15
A sugarcane stem cutting with a bud is planted and develops into a new plant. How did this new plant arise?
(a)From the roots of entirely different plants nearby.
(b)By vegetative propagation from part of the parent plant.
(c)From spores carried in on the wind.
(d)From seeds too small to notice, since every new plant must start from a seed.
Show answer
(b) By vegetative propagation from part of the parent plant.
A suitable stem cutting can grow into a new sugarcane plant. This is vegetative propagation. It does not mean sugarcane never produces seeds or that every part of every plant can grow this way.
Common misconception in Our Home: Earth, a Unique Life Sustaining Planet
Does being closer to the Sun always make a planet hotter at its surface?
Wrong
Mercury must have a hotter average surface than Venus because it is closer to the Sun.
Why it feels right. I use distance from the Sun as the only factor.
Right
An atmosphere can change how easily a planet loses heat to space.
Worked example
Mercury
Nearer the Sun→Almost no atmosphere→Cooler average surface
Venus
Farther from the Sun→Thick CO₂-rich atmosphere→Hotter average surface
Mercury is nearer the Sun. Venus still has a hotter average surface because its atmosphere strongly limits heat loss.
Mercury is closer to the Sun and has almost no atmosphere.
Venus has a thick atmosphere rich in carbon dioxide and a higher average surface temperature.
Distance alone misses the role of the atmosphere.
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