Question 1
What is the main reason that liquid water is described as the medium for most processes of life?
A.
It stores genetic information in early living cells.
B.
It allows dissolved substances to move, collide and react.
C.
It supplies most enzymes with chemical bond energy.
D.
It prevents all biological molecules from changing shape.
Question 2
What hypothesis for the origin of much of Earth’s water is included in the syllabus?
A.
Water formed only by photosynthesis in the first cells.
B.
Water was produced from nitrogen in Earth’s early atmosphere.
C.
Water-containing asteroids collided with the young Earth.
D.
Water arrived mainly as ice from modern polar glaciers.
Question 3
A diagram shows two water molecules. The oxygen atom of one molecule is labelled and a hydrogen atom of the neighbouring molecule is labelled . run What interaction should be shown between these two labelled atoms?
A.
A hydrogen bond between water molecules
B.
A non-polar bond with equal electron sharing
C.
A covalent bond within a water molecule
D.
An ionic bond formed by electron transfer
Question 4
Water evaporates from leaf cell walls and creates tension in xylem vessels. What property of water helps transmit this pull down the xylem column?
A.
Low density of water compared with air
B.
High thermal conductivity of water in leaves
C.
Solubility of non-polar gases in xylem sap
D.
Cohesion due to hydrogen bonding between water molecules
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Question 5
Water moves through tiny pores in soil and plant cell walls partly against gravity. What best explains this capillary action?
A.
Water breaks covalent bonds in cellulose and soil minerals.
B.
Water adheres to polar or charged surfaces in narrow spaces.
C.
Water becomes non-polar when confined in small pores.
D.
Water loses all hydrogen bonds at solid surfaces.
Question 6
What combination best explains Earth’s long-term retention of abundant water?
A.
Strong enough gravity and temperatures low enough for condensation
B.
Weak gravity and temperatures high enough for continuous evaporation
C.
Lunar gravity and temperatures low enough to freeze all water
D.
No atmosphere and temperatures high enough to boil all oceans
Question 7
What is meant by the Goldilocks zone around a star?
A.
A region where asteroids are absent from planetary orbits
B.
A region where all planets must contain living organisms
C.
A region where water vapour cannot condense into liquid water
D.
A region where surface temperatures could allow liquid water to exist
Question 8
Cells of a dormant seed become metabolically active after water is absorbed during germination.
State one meaning of the term medium in the context of water and life.
[1]
Outline why liquid water is needed for metabolism in the germinating seed.
[2]
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Question 9
A substance dissolves readily in blood plasma and can be transported as individual particles in aqueous solution. What property is it most likely to have?
A.
It is non-polar and strongly hydrophobic.
B.
It is charged or polar and hydrophilic.
C.
It is insoluble and forms a membrane interior.
D.
It is uncharged and unable to interact with water.
Question 10
A ringed seal, Pusa hispida, swims in water whereas a black-throated loon, Gavia arctica, flies in air. What contrast between water and air best explains why the seal gains more support from its surrounding medium?
A.
Water is denser than air, so it provides greater buoyancy.
B.
Water is less viscous than air, so it provides greater lift.
C.
Water conducts heat more slowly than air, so it prevents sinking.
D.
Water has lower specific heat capacity, so it changes depth slowly.
Question 11
A star is more luminous than the Sun. How would the position of its Goldilocks zone most likely compare with that of the Sun?
A.
It would be farther from the star.
B.
It would be inside the star.
C.
It would be absent from all orbits.
D.
It would be closer to the star.
Question 12
Liquid water is used as a criterion when searching for extraterrestrial life. What is the best reason for using this criterion?
A.
All planets with liquid water have identical atmospheres.
B.
Liquid water prevents chemical reactions from occurring.
C.
All known life uses liquid water as a medium for metabolism.
D.
Liquid water proves that organisms are already present.
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Question 13
The diagram shows two water molecules. The solid lines represent bonds within each molecule. No partial charges are shown.
Annotate the diagram to show the polarity of each water molecule and one hydrogen bond between the two molecules.
[3]
Explain why the O-H bonds within a water molecule are polar covalent bonds.
[1]
Question 14
Water moves through microscopic spaces in soil and in plant cell walls.
Distinguish adhesion from cohesion in water.
[2]
Outline how adhesion contributes to capillary action in soil or plant cell walls.
[2]
Question 15
One hypothesis proposes that much of Earth's water was delivered by water-containing asteroids during the early history of the Solar System.
State the proposed extraplanetary source of much of Earth's water.
[1]
Explain two reasons why Earth has retained abundant water for billions of years.
[2]
Suggest why water delivered before the young Earth cooled may have been lost more easily.
[1]
Question 16
The diagram shows a star with three planets at different orbital distances. A shaded band marks the region where surface liquid water could exist if atmospheric pressure is suitable.
Define the Goldilocks zone.
[1]
Using the diagram, explain why the middle planet would be a higher priority target in a search for extraterrestrial life than the inner or outer planet.
[2]
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Question 17
Capillary rise was measured in narrow tubes made from different materials. Each tube had the same internal diameter and was placed vertically with its lower end in water. The height reached by the water after five minutes is shown in the bar chart.
State which material showed the greatest capillary rise.
[1]
Compare the capillary rise in cellulose paper with that in the non-polar plastic.
[1]
Explain why capillary action is important in plant cell walls.
[2]
Question 18
Dried yeast cells were placed in glucose solutions with different water contents. Carbon dioxide production was used as an indicator of enzyme-catalysed metabolism. The results are shown in the graph.
Describe the effect of increasing water content on carbon dioxide production.
[1]
Calculate the increase in rate of carbon dioxide production between the lowest and highest water contents tested.
[1]
Explain why liquid water is needed for normal metabolic activity in yeast cells.
[1]
Question 19
An exoplanet orbits within the Goldilocks zone of its star but has very low mass and weak gravity. What is the most reasonable inference about its potential to retain surface liquid water over long periods?
A.
Retention is impossible because all water-containing asteroids avoid low-mass planets.
B.
Retention will increase because weak gravity condenses water vapour more rapidly.
C.
Retention is guaranteed because orbital position is the only factor that matters.
D.
Retention may be limited because weak gravity makes atmospheric and water-vapour loss more likely.
Question 20
The diagram represents water movement in a tall plant during transpiration.
State the property of water that helps maintain a continuous column in the xylem.
[1]
Explain how this property allows water to be transported under tension in xylem.
[2]
Suggest why a large air bubble entering xylem would reduce water transport.
[1]
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Question 21
Glucose, sodium ions and lipids are transported differently in animals because they interact differently with water.
State why glucose and sodium ions are hydrophilic.
[1]
Explain how the polarity of water allows sodium ions to dissolve.
[2]
Suggest why lipids are not transported simply dissolved in blood plasma.
[1]
Question 22
Two rocky bodies receive water from asteroid impacts. Body X is small with weak gravity. Body Y is larger, has stronger gravity and cools to temperatures at which water can condense.
Suggest which body is more likely to retain surface water for a long period.
[1]
Explain the role of gravity in the retention of water on a planet.
[1]
Explain the role of temperature in the retention of water on a planet.
[1]
Suggest why asteroid delivery alone is not sufficient to explain long-term abundance of water on Earth.
[1]
Question 23
The early Earth was initially very hot but later cooled while asteroid impacts continued.
Outline why late asteroid impacts could contribute to the accumulation of liquid water on Earth.
[2]
State one reason why long-term retention of this water was important for the evolution of life.
[1]
Question 24
A student investigated the effect of a detergent on the surface tension of water. Small metal discs were placed carefully on the water surface. The maximum total mass supported before the surface film broke was measured at different detergent concentrations. The results are shown in the graph.
Describe the relationship shown in the graph.
[1]
Calculate the percentage decrease in mean maximum mass supported between and detergent concentration.
[1]
Explain why adding detergent can affect organisms such as water striders that live on the surface of ponds.
[2]
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Question 25
Researchers used artificial xylem tubes to test how different solutions behaved when pulled under tension. The maximum tension before the water column broke was recorded. The results are shown in the table.
Solution | Maximum tension before break / MPa |
|---|---|
Pure water | 1.8 |
Salt solution | 1.6 |
Sucrose solution | 1.5 |
Surfactant solution | 0.4 |
Identify the solution that would be least effective at maintaining a continuous column in xylem.
[1]
Calculate the difference in maximum tension between pure water and the surfactant solution.
[1]
Explain how the molecular properties of water allow xylem sap to be transported under tension.
[2]
Question 26
The solubility of several biologically important substances in water was compared at the same temperature. The results are shown in the table.
Substance | Solubility in water / g L |
|---|---|
Glucose | 910 |
Sodium chloride | 360 |
Glycine | 250 |
Cholesterol | 0.002 |
Triglycerides | 0.0001 |
Identify one substance in the table that is hydrophilic.
[1]
Calculate how many times more soluble glucose is than cholesterol in water.
[1]
Suggest why triglycerides are not transported in blood plasma simply as dissolved molecules.
[2]
Question 27
The ratio of deuterium to hydrogen in water can be used to compare possible sources of Earth’s water. Samples from Earth’s oceans and from different Solar System materials were analysed. The results are shown in the graph.
Identify the source of water most consistent with the composition of Earth’s oceans.
[1]
Calculate the percentage difference between the mean asteroid ratio and the Earth ocean ratio.
[1]
Suggest why these data support, but do not prove, an asteroid origin of Earth’s water.
[2]
Question 28
The position of the Goldilocks zone was modelled for three stars of different luminosities. The orbits of selected planets are also shown.
Star | Luminosity / | Inner Goldilocks limit / AU | Outer Goldilocks limit / AU | Planet | Planet orbit / AU |
|---|---|---|---|---|---|
Star 1 | 0.25 | 0.40 | 0.60 | A | 0.20 |
Star 2 | 1.0 | 0.90 | 1.40 | B | 1.60 |
Star 3 | 4.0 | 1.80 | 2.80 | C | 2.40 |
Describe the relationship between star luminosity and the distance of the Goldilocks zone from the star.
[1]
Identify the labelled planet that is most likely to have surface temperatures allowing liquid water, according to the model.
[1]
Explain why the Goldilocks zone is useful in the search for extraterrestrial life.
[2]
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Question 29
A model was used to estimate the likelihood that rocky exoplanets retain surface liquid water. The model includes planet mass and equilibrium temperature. The results are shown as a heat map.
Planet mass / Earth masses | 220 K | 260 K | 280 K | 320 K | 380 K |
|---|---|---|---|---|---|
0.1 | 2 | 5 | 8 | 4 | 1 |
0.5 | 8 | 18 | 30 | 15 | 4 |
1.0 | 20 | 45 | 60 | 30 | 8 |
5.0 | 30 | 70 | 95 | 50 | 10 |
State the combination of conditions that gives the highest predicted likelihood of retaining surface liquid water.
[1]
Explain why very low-mass planets have low predicted likelihood even at suitable temperatures.
[1]
Explain why very hot planets have low predicted likelihood even if their mass is high.
[1]
Question 30
The table compares some physical properties of water and air that affect animal movement and heat exchange.
Property / unit | Water | Air |
|---|---|---|
Density / | 1000 | 1.2 |
Viscosity / | ||
Thermal conductivity / | 0.60 | 0.024 |
Specific heat capacity / | 4180 | 1000 |
Using the table, explain one opportunity and one challenge for a seal swimming in water rather than moving in air.
[2]
Compare the consequences of water's thermal conductivity and specific heat capacity for aquatic animals.
[2]
Question 31
Spectroscopic observations of an exoplanet suggest the presence of water vapour in its atmosphere. Its orbit lies near the outer edge of its star's Goldilocks zone.
Explain why the observation would interest scientists searching for extraterrestrial life.
[2]
Evaluate whether detection of water vapour is evidence that life is present on the exoplanet.
[2]
Question 32
A smaller, cooler star has a Goldilocks zone closer to the star than that of the Sun. A planet is discovered within this zone, but its mass is low.
Explain why the Goldilocks zone of a cooler star is closer to the star.
[1]
Discuss whether being in the Goldilocks zone is sufficient for the planet to be considered likely to have surface liquid water.
[3]
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Question 33
Physical properties of water and air were compared to model some challenges faced by aquatic and flying animals. The data are shown in the table.
Property | Water at | Air at |
|---|---|---|
Density / kg | 1000 | 1.2 |
Thermal conductivity / W | 0.60 | 0.026 |
Dynamic viscosity / Pa s |
Calculate how many times greater the thermal conductivity of water is than that of air.
[1]
State one opportunity for an aquatic animal resulting from the density of water.
[1]
Explain one challenge for a ringed seal, Pusa hispida, caused by the thermal properties of water.
[2]
Suggest why streamlined body shape is more important for a fast-swimming animal than for an animal moving at the same speed through air.
[1]
Question 34
Scientists compared four rocky bodies in the Solar System to investigate why some have retained abundant water and others have not. The data are shown in the table.
Body | Surface gravity / m | Mean surface temperature / | Surface liquid water / % |
|---|---|---|---|
Mercury | 3.7 | 167 | 0 |
Venus | 10.0 | 465 | 0 |
Earth | 9.8 | 15 | 71 |
Mars | 3.7 | -63 | 0 |
State the body in the table that has retained the greatest abundance of surface liquid water.
[1]
Identify two factors in the table that are associated with long-term retention of water on Earth.
[2]
Explain why Venus is not expected to retain surface liquid water despite having stronger gravity than Earth.
[2]
Question 35
A model of early Earth shows changes in surface temperature and the rate of impacts by water-containing asteroids over time. The results are shown in the graph.
Time / billion years ago | Surface temperature / | Asteroid impact rate / impacts per million years |
|---|---|---|
4.5 | 320 | 20 |
4.4 | 220 | 16 |
4.3 | 130 | 12 |
4.2 | 90 | 9 |
4.1 | 75 | 6 |
4.0 | 60 | 3 |
Identify the time at which the model first predicts that water vapour could condense at Earth’s surface.
[1]
Describe the change in asteroid impact rate after this time.
[1]
Explain how the data support the hypothesis that asteroids contributed to Earth’s oceans.
[2]
Question 36
Some small freshwater animals live at the water surface rather than within the bulk water below it.
Discuss how hydrogen bonding in water creates a surface habitat for small organisms.
I.
State the property of water that allows the surface to resist being broken.
[1]
II.
Explain the molecular basis of this property.
[2]
Evaluate the advantages and limitations of living at the water surface for a small animal such as a water strider.
[3]
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Question 37
Earth has had abundant surface water for much of its history. This long-term presence is considered important in explaining the evolution of life.
Discuss how the origin and retention of water on Earth are separate parts of the explanation for Earth's oceans.
I.
State the proposed extraplanetary source of Earth's water in this topic.
[1]
II.
Distinguish delivery of water from retention of water.
[2]
Discuss why long-term water retention would have increased the opportunity for life to evolve.
[3]
Question 38
Four exoplanets orbiting the same star were studied using telescope observations. Their positions relative to the Goldilocks zone and some atmospheric data are shown in the table.
Planet | Orbital position relative to Goldilocks zone | Atmospheric pressure / kPa | Water vapour detected |
|---|---|---|---|
A | Too close to star (inside inner edge) | 2 | No |
B | Within Goldilocks zone | 98 | Yes |
C | Too far from star (outside outer edge) | 0.8 | No |
D | Far outside Goldilocks zone | 650 | No |
Identify the planet that is the best candidate for surface liquid water.
[1]
Give two pieces of evidence from the table that support this choice.
[2]
Suggest why the detection of water vapour in the atmosphere of an exoplanet is not sufficient evidence for life.
[2]
Question 39
Water moves through xylem vessels as a continuous column under tension from roots to leaves.
Explain how the structure of water molecules allows hydrogen bonding between neighbouring water molecules.
I.
Outline why a water molecule is polar.
[2]
II.
Explain how polarity leads to cohesion between water molecules.
[2]
Explain how cohesion contributes to transport of water under tension in xylem.
[3]
Question 40
Water can move through narrow spaces in soil and plant cell walls even when gravity opposes the movement.
Explain why water adheres to some surfaces in soil and plant cell walls.
I.
Identify the type of surfaces to which water adheres strongly.
[1]
II.
Explain the attraction between water and these surfaces.
[2]
Explain how adhesion and cohesion together contribute to capillary action in a plant cell wall.
[3]
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Question 41
A researcher compares the movement of different substances in blood plasma and across cell membranes.
Substance | Charge / polarity | Water solubility | Transport in blood |
|---|---|---|---|
Sodium ion | positive charge | very soluble | dissolved in plasma |
Glucose | polar | soluble | dissolved in plasma |
Oxygen | non-polar | slightly soluble | mostly bound to haemoglobin |
Triglyceride | non-polar | insoluble | transported in lipoproteins |
Explain why many hydrophilic substances dissolve in water.
I.
State what is meant by hydrophilic.
[1]
II.
Explain how water molecules dissolve ions or polar molecules.
[2]
Evaluate the statement: water is a universal solvent for transport in animals.
[4]
Question 42
Seeds of some desert plants can survive for long periods in a dry state but resume growth rapidly after rainfall. The graph shows enzyme activity in seed extracts at different water contents.
Explain why liquid water is required for most metabolic activity.
I.
State what is meant by metabolism.
[1]
II.
Explain why drying reduces metabolic activity.
[3]
Discuss how the data support the idea that water is the medium for life, without implying that dry seeds are dead.
[3]
Question 43
One hypothesis is that much of Earth's water was delivered after the young Earth formed.
Explain the asteroid hypothesis for the origin of water on Earth.
I.
State the type of body proposed to have delivered water to Earth.
[1]
II.
Explain why delivery after the hottest stage of Earth's formation is plausible.
[2]
Explain two reasons why Earth retained abundant water over billions of years.
[3]
Question 44
The diagram shows the estimated Goldilocks zones around three stars of different luminosities. Several rocky planets are shown orbiting each star.
Explain how the position of the Goldilocks zone depends on the star.
I.
Define the Goldilocks zone.
[1]
II.
Explain why the zone is farther from a more luminous star.
[2]
Evaluate the use of the Goldilocks zone as a criterion in the search for extraterrestrial life.
[4]
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Question 45
The ringed seal, Pusa hispida, spends much of its life in seawater. The black-throated loon, Gavia arctica, flies in air but also feeds in water.
Compare the consequences of density and viscosity of water and air for animal movement.
I.
Explain one advantage of the density of water for an aquatic animal.
[2]
II.
Explain one challenge caused by the viscosity of water.
[2]
Compare the thermal consequences of living in water rather than air for a warm-blooded animal.
[4]
Question 46
Astronomers detect three rocky exoplanets around a nearby star. The table summarizes evidence relevant to the possibility of liquid water.
Planet | Surface temperature / | Mass / Earth masses | Pressure / bar | Water vapour detected |
|---|---|---|---|---|
A | 300 | 0.9 | 0.01 | No |
B | 5 | 0.20 | 0.01 | Yes |
C | 15 | 1.05 | 1.00 | No |
Use the information to assess which planet is most likely to have liquid water at its surface.
I.
Identify one factor from the table that would favour liquid water.
[1]
II.
Explain why a low-mass planet may fail to retain surface water even if water was delivered to it.
[3]
Evaluate whether the detection of water vapour in the atmosphere of one planet would be sufficient evidence for extraterrestrial life.
[4]
Question 47
The Moon, Mars and Earth differ in gravity and surface temperature. These differences affect whether water can be retained as liquid at the surface.
Body | Gravity / | Mean surface temp / | Atmosphere | Liquid water at surface |
|---|---|---|---|---|
Earth | 9.8 | 15 | dense | stable, abundant |
Mars | 3.7 | -63 | thin | not stable |
Moon | 1.6 | -20 | negligible | not stable |
Compare how gravity affects the retention of water on Earth and on a smaller body such as the Moon or Mars.
I.
State why gravity is relevant to water retention.
[1]
II.
Explain why a smaller body is less likely to retain abundant surface water.
[3]
Contrast the effect of temperature on water retention with the effect of gravity.
[3]
Question 48
A space mission is designed to choose one target planet for a future search for extraterrestrial life. Mission planners initially propose selecting the planet with the strongest evidence of water.
Explain why water is a logical starting point in a search for extraterrestrial life.
I.
State the form of water most directly linked to life as known on Earth.
[1]
II.
Explain two biological reasons why liquid water is important for life as known on Earth.
[3]
Discuss why choosing only the planet with the strongest evidence of water could lead to an unreliable conclusion about life.
[4]
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