A1.1 Water
Practice exam-style IB Biology questions for Water, aligned with the syllabus and grouped by topic.
Question 1
What causes a water molecule to be polar?
A.
Water molecules are linear, so charges are evenly distributed.
B.
Oxygen attracts the shared electrons more strongly than hydrogen.
C.
Water molecules contain ionic bonds between oxygen and hydrogen.
D.
Hydrogen atoms attract electrons more strongly than oxygen.
Question 2
A water strider remains on the surface of a pond without breaking through. What property of water is mainly responsible?
A.
High thermal conductivity resulting from rapid heat transfer
B.
Buoyancy resulting from density lower than air
C.
Surface tension resulting from cohesion between water molecules
D.
Solvent action resulting from attraction to ions
Question 3
What best describes adhesion of water in plant cell walls?
A.
Formation of covalent bonds between water and cellulose
B.
Repulsion of water from hydrophobic wall components
C.
Attraction between neighbouring water molecules in the xylem column
D.
Attraction between water molecules and polar cellulose molecules
Question 4
What is the syllabus-limited hypothesis for the extraplanetary origin of much of Earth’s water?
A.
Continuous creation of water by photosynthesis in early oceans
B.
Condensation of water from modern industrial emissions
C.
Conversion of nitrogen gas into water by lightning
D.
Delivery by water-containing asteroids colliding with the young Earth
Question 5
The diagram shows two water molecules.
Label the partial charge on the oxygen atom of one water molecule.
[1]
State the type of bond represented by a dashed line between the two water molecules.
[1]
Distinguish this dashed-line bond from an O—H bond within a water molecule.
[1]
Question 6
Glucose dissolves readily in cytoplasm. What property of water best explains this?
A.
Water breaks all covalent bonds in glucose molecules.
B.
Water molecules form attractions with polar groups on glucose.
C.
Water is non-polar, so it mixes with all organic molecules.
D.
Water prevents enzyme active sites from binding glucose.
Question 7
A ringed seal, Pusa hispida, can maintain depth in water with relatively little energy compared with a similarly sized terrestrial animal supporting itself in air. What physical property of water is most directly involved?
A.
Viscosity
B.
Buoyancy
C.
Thermal conductivity
D.
Specific heat capacity
Question 8
Why is liquid water described as a medium for life?
A.
It allows dissolved molecules to move, collide and react.
B.
It prevents all chemical reactions from occurring too quickly.
C.
It dissolves all molecules found in living cells.
D.
It replaces the need for enzymes in metabolism.
Question 9
What combination best explains Earth’s long-term retention of abundant water?
A.
Sufficient gravity and temperatures low enough for water vapour to condense
B.
Absence of an atmosphere and constant freezing of all water
C.
High solar radiation and low planetary mass
D.
Weak gravity and temperatures high enough to keep water as vapour
Question 10
What is meant by the Goldilocks zone around a star?
A.
The region where asteroid impacts cannot occur
B.
The region where all water is permanently frozen at the surface
C.
The region where surface temperatures could allow liquid water if pressure is suitable
D.
The region where planets must contain oxygen gas in their atmospheres
Question 11
A cooler, dimmer star is compared with a hotter, more luminous star. How would the Goldilocks zone usually differ?
A.
It would be farther from the cooler star.
B.
It would be closer to the cooler star.
C.
It would disappear because cool stars cannot have planets.
D.
It would be identical for all stars.
Question 12
A small rocky body with weak gravity loses water vapour more readily than Earth. What factor best explains the difference?
A.
Small bodies contain only hydrophobic water.
B.
Earth’s water molecules are larger than those on small bodies.
C.
Weak gravity makes water condense at higher temperatures.
D.
Earth’s larger mass gives stronger gravity to retain water and atmosphere.
Question 13
Define cohesion.
[1]
Explain how cohesion allows water to move under tension in xylem.
[1]
Question 14
Define adhesion.
[1]
Outline one role of adhesion in soil.
[1]
Outline one role of adhesion in plant cell walls.
[1]
Question 15
State why most active cells require liquid water.
[1]
Explain why dry biological material may be dormant rather than metabolically active.
[1]
Question 16
State the proposed extraplanetary source of much of Earth’s water.
[1]
Outline why timing after early cooling would favour retention of water.
[1]
Question 17
Explain two reasons why Earth has retained abundant water for billions of years.
Explain the role of gravity.
[1]
Explain the role of temperature.
[1]
Question 18
An investigation measured the force needed to pull a fine ring through the surface of pure water and water containing different concentrations of detergent.
Describe the relationship shown in the graph.
[1]
Identify the property of water being measured indirectly.
[1]
Explain why increasing detergent concentration could affect organisms that live at the water surface.
[1]
Question 19
What is a consequence of water having higher viscosity than air for aquatic animals?
A.
They lose less heat to the surrounding medium.
B.
They are unable to float because water provides no upward force.
C.
They experience greater drag when moving through their habitat.
D.
They experience larger daily temperature fluctuations.
Question 20
Why are lipids useful in forming the internal region of cell membranes?
A.
Their hydrophobic parts are insoluble in water and help separate aqueous compartments.
B.
They are strongly attracted to water and dissolve freely in cytoplasm.
C.
Their covalent bonds are broken by water to release ions.
D.
They form hydrogen bonds with all dissolved ions.
Question 21
A planet orbits within the Goldilocks zone of its star. What conclusion is justified?
A.
Water cannot exist there because the planet is too close to the star.
B.
The planet must have no atmosphere because water is liquid.
C.
Life must be present because liquid water always contains cells.
D.
Liquid water may be possible, but life is not demonstrated.
Question 22
Why would water delivered to Earth after the hottest stages of formation be more likely to remain?
A.
The planet’s gravity would become zero after cooling.
B.
Asteroids would prevent all atmospheric escape by blocking sunlight.
C.
The surface could cool enough for water vapour to condense to liquid.
D.
Water molecules would stop being polar at low temperature.
Question 23
Why is liquid water used as a first filter in the search for extraterrestrial life?
A.
Water only occurs on planets with animals.
B.
Water prevents chemical reactions from occurring on planets.
C.
All known life uses liquid water as a medium for metabolism and transport.
D.
Water proves that DNA and proteins are already present.
Question 24
State what is meant by a hydrophilic substance.
[1]
Explain why water dissolves many ions.
[1]
State one biological transport fluid in which hydrophilic substances are carried.
[1]
Question 25
Compare water and air as habitats for animals.
State one advantage of water over air for body support.
[1]
State one disadvantage of water compared with air for movement.
[1]
Explain one thermal challenge for warm-blooded animals in water.
[1]
Question 26
A detergent spill reaches a pond surface.
State the water property most directly reduced by detergent at the surface.
[1]
Suggest why mosquito larvae hanging below the surface may be affected.
[1]
Question 27
Define the Goldilocks zone.
[1]
State two planetary factors, other than distance from the star, that affect whether liquid water can persist at the surface.
[1]
Question 28
An exoplanet has spectral evidence of water vapour but no confirmed surface liquid water.
State why the water vapour does not prove life is present.
[1]
Suggest two additional conditions that would make liquid water more likely at the surface.
[1]
Question 29
Two stars have different luminosities. Star X is cooler and dimmer than Star Y.
State which star would have a Goldilocks zone closer to it.
[1]
Explain why the position of the Goldilocks zone differs between the stars.
[1]
Question 30
A rocky exoplanet is closer to its star than the inner edge of the Goldilocks zone.
Suggest the likely state of surface water on this planet.
[1]
Explain why this affects its priority in a search for life as we know it.
[1]
Question 31
The table compares physical properties of water and air relevant to animal habitats.
| Property | Water | Air |
|---|---|---|
| Density / kg m^-3 | 998 | 1.20 |
| Dynamic viscosity / Pa s | 1.00 × 10^-3 | 1.81 × 10^-5 |
| Thermal conductivity / W m^-1 K^-1 | 0.60 | 0.026 |
| Specific heat capacity / J kg^-1 K^-1 | 4180 | 1005 |
Identify the medium that provides greater buoyant support.
[1]
State which property would make rapid swimming more energetically costly than flying at the same speed through air.
[1]
Explain why a small warm-blooded animal in cold water may require more insulation than one in cold air.
[1]
Suggest one advantage of high specific heat capacity for aquatic animals.
[1]
Question 32
Strips of paper made from cellulose were dipped into liquids and the height reached by each liquid after the same time was recorded.
Identify the liquid that shows the greatest capillary rise.
[1]
Describe how pore width affects capillary rise in the data.
[1]
Suggest why water rises in cellulose paper.
[1]
Question 33
Temperature loggers recorded daily water temperature in a shallow pond and air temperature above it.
Describe the difference in daily temperature variation between water and air.
[1]
Identify the physical property of water responsible for this difference.
[1]
Explain how this property benefits aquatic animals.
[1]
Question 34
Isotope ratios in water from several meteorites and Earth’s oceans were compared. The meteorites are fragments of water-containing asteroids.
| Sample | D/H ratio / ×10⁻⁶ |
|---|---|
| Earth oceans | 156 |
| Asteroid sample A | 123 |
| Asteroid sample B | 151 |
| Asteroid sample C | 169 |
| Asteroid sample D | 202 |
| Asteroid sample E | 137 |
Identify the asteroid sample with an isotope ratio most similar to Earth ocean water.
[1]
State what this similarity suggests about the origin of some of Earth’s water.
[1]
Explain why this evidence alone cannot prove that all Earth’s water came from asteroids.
[1]
Question 35
The graph models the state of water on early Earth as surface temperature decreased over time after formation.
Identify the time period in which liquid water first becomes stable at the surface.
[1]
Describe the change in dominant water state as temperature falls.
[1]
Explain why this change would increase water retention on Earth.
[1]
Question 36
Distinguish between hydrophilic and hydrophobic substances.
[1]
Explain why the hydrophobic nature of some cell molecules is biologically useful.
[1]
Question 37
A space mission reports a subsurface ocean on an icy moon.
State why this finding is relevant to the search for extraterrestrial life.
[1]
Give two reasons why it is still insufficient evidence for life.
[1]
State one further observation that could strengthen the case for habitability.
[1]
Question 38
Explain why a smaller planet with weaker gravity would be less likely than Earth to retain water vapour.
[1]
Explain why condensation of water vapour aids long-term retention of water.
[1]
Question 39
A student measured the solubility of four substances in water at 25 °C.
| Substance | Charge/polarity category | Solubility at 25 °C / g per 100 g water |
|---|---|---|
| Sodium chloride | Ionic | 35.9 |
| Glucose | Polar, uncharged | 91 |
| Glycine | Zwitterionic, polar | 25.0 |
| Tristearin | Mostly non-polar | <0.001 |
Identify the substance most likely to be hydrophobic.
[1]
Describe the relationship between charge/polarity and solubility shown in the table.
[1]
Explain why water dissolves the ionic substance.
[1]
Suggest one limitation of using solubility alone to classify biological molecules as hydrophilic or hydrophobic.
[1]
Question 40
The graph shows the Goldilocks zones for three stars of different luminosity and the orbital distances of one planet around each star.
Identify the planet most likely to have temperatures permitting liquid surface water.
[1]
Describe how stellar luminosity affects the position of the Goldilocks zone.
[1]
Explain why a planet in the Goldilocks zone may still lack liquid water.
[1]
State one reason why finding liquid water would not be proof of life.
[1]
Question 41
A model estimates the percentage of water retained by rocky planets of different masses after a period of heating.
Describe the relationship between planetary mass and water retention in the model.
[1]
Explain this relationship using gravity.
[1]
Suggest why temperature must also be considered when predicting water retention.
[1]
Question 42
Outline the bonding and polarity within a water molecule.
[1]
Explain how hydrogen bonding between water molecules gives rise to cohesion and two biological consequences of cohesion.
[1]
Question 43
Define adhesion and capillary action.
[1]
Explain how adhesion and cohesion of water affect plants and soils.
[1]
Question 44
Data from four exoplanets are shown: orbital position relative to the Goldilocks zone, estimated mass, atmospheric pressure and evidence for water.
| Planet | Orbit vs GZ | Mass / Earth masses | Atmos. pressure | Water evidence |
|---|---|---|---|---|
| A | Inside inner edge | 0.7 | Very low | Water vapour detected |
| B | Within GZ | 3.8 | Very high | Water vapour detected |
| C | Within GZ | 1.1 | Moderate | Surface signal consistent with liquid water |
| D | Beyond outer edge | 0.9 | Low | Surface ice detected |
Identify the planet that is the strongest candidate for liquid surface water.
[1]
Give two features from the data that support this choice.
[1]
Evaluate the claim that this planet must contain life.
[1]
Question 45
Distinguish between hydrophilic and hydrophobic substances.
[1]
Discuss the importance of water’s solvent properties for metabolism, transport and cell structure.
[1]
Question 46
State two physical properties of water that differ from air and are important for animals.
[1]
Compare and contrast the opportunities and challenges of water and air as habitats for animals, using named examples where appropriate.
[1]
Question 47
Outline the asteroid hypothesis for the origin of much of Earth’s water.
[1]
Evaluate why Earth, unlike many smaller bodies, has retained abundant water for billions of years.
[1]
Question 48
Define the Goldilocks zone and state why its position varies between stars.
[1]
Discuss the use of liquid water as a criterion in the search for extraterrestrial life.
[1]
Question 49
Outline two conditions required for a planet to retain water over long periods.
[1]
Compare and contrast a young Earth-like planet and a small hot rocky body in terms of water origin and retention.
[1]
Question 50
A mission identifies a rocky exoplanet in the Goldilocks zone with water vapour in its atmosphere.
State three reasons why the planet is a candidate for further investigation.
[1]
Evaluate the claim that this evidence is sufficient to infer the presence of life.
[1]
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