Water is a medium for life processes. Substances can dissolve in it, move through it, and react in it. This supports early life in oceans and modern cell chemistry in cytoplasm and body fluids.

Water remains the medium for most life processes and forms much of cell mass.

Early oceans gave first cells liquid conditions and helped shield them from UV radiation.

In modern organisms, aqueous solution enables transport, diffusion, and metabolism.

Which sentence best explains why water is called a medium for life?

Choose

Inside one water molecule, oxygen and hydrogen are joined by O-H covalent bonds. Because the molecule is polar, neighbouring water molecules attract each other by hydrogen bonds. Those hydrogen bonds explain many unusual water properties.

O-H covalent bonds are inside one water molecule.

Hydrogen bonds form between water molecules, not within one molecule.

Hydrogen bonding explains many unusual water properties, including cohesion and high specific heat capacity.

The diagram separates bonds inside a water molecule from attractions between water molecules.

Label the diagram using the rule: inside one molecule or between molecules?

Label

Labels

5

Label the diagram using the rule: inside one molecule or between molecules?

Choose

1. O-H covalent bond inside one molecule

2. hydrogen bond between molecules

3. δ- oxygen

4. δ+ hydrogen

5. polar V-shaped water molecule

Choose the word by asking what water is attracted to: water-to-water is cohesion; water-to-surface is adhesion.

In IB answers, the mark usually comes from linking the attraction to the biological effect, not just naming the term.

Surface tension: cohesion between water molecules at the surface supports droplets and small insects.

Xylem water column: cohesion helps the column resist breaking under tension.

Capillary action: adhesion helps water attach to polar or charged surfaces such as cellulose walls.

Sort each example by the attraction that matters most.

Sort

Unsorted

5

cohesion

0

adhesion

0

Use this when a question asks why water forms droplets, supports surface organisms, moves in xylem, or rises in narrow spaces.

Define the attraction: water-to-water for cohesion, water-to-surface for adhesion.

Name hydrogen bonding when explaining cohesion.

Link the property to the biological effect: surface tension, xylem column continuity, or capillary action.

Use this when a question asks why water forms droplets, supports surface organisms, moves in xylem, or rises in narrow spaces.

Naming cohesion or adhesion without saying what is attracting what.

Water is a solvent when its partial charges can interact with the solute. Ions are surrounded by hydration shells. Polar molecules can hydrogen-bond with water. Non-polar molecules do not interact strongly, so they are hydrophobic and have low solubility.

Water dissolves ions and polar molecules by hydration and hydrogen bonding.

Aqueous solution enables diffusion, transport, enzyme activity, and metabolism.

Non-polar molecules are hydrophobic; O2 and N2 have low solubility in water.

Water dissolves charged or polar solutes better than non-polar molecules.

Match each case to the reason water helps or limits it.

Match

Reasons

0/4

Match each case to the reason water helps or limits it.

Choose

sodium ion in blood plasma

glucose in cytoplasm

enzyme-catalysed metabolism

oxygen and nitrogen gases

Aquatic-animal adaptations are explained by the relevant water property. High specific heat capacity stabilizes temperature. High thermal conductivity increases heat loss. Buoyancy supports bodies. Viscosity creates drag. The property should be linked directly to the adaptation.

Specific heat capacity stabilizes aquatic temperatures and body temperature.

Thermal conductivity, buoyancy, and viscosity shape aquatic adaptations.

Compare black-throated loon and ringed seal adaptations for diving, insulation, and movement.

Use the named water property first, then explain the adaptation it selects for.

Compare the loon and the seal using this sentence frame: Because water has ____, the animal needs _____.

Compare

A

black-throated loon

B

ringed seal

diving

insulation

movement

Compare the loon and the seal using this sentence frame: Because water has ____, the animal needs _____.

Choose

Models

black-throated loonringed seal

Compare By

divinginsulationmovement

For HL, keep two claims separate. Source claim: Earth water may have been delivered by asteroids, supported by isotope comparisons with carbonaceous chondrites and Vesta meteorites. Retention claim: cooler temperatures allowed water vapour to condense and gravity helped Earth keep it.

Asteroid delivery is the syllabus hypothesis for Earth’s water origin.

Carbonaceous chondrites and Vesta meteorites provide isotope evidence.

Gravity and cooler temperatures allowed water vapour to condense and be retained.

Separate source evidence from retention conditions; the evidence supports a hypothesis rather than proving a single source.

Sort each statement as source evidence or retention condition.

Sort

Unsorted

4

source evidence

0

retention condition

0

Sort each statement as source evidence or retention condition.

Choose

Asteroid delivery is the hypothesis for Earth water origin.

Carbonaceous chondrites have isotope ratios compared with Earth water.

Cooler temperatures allowed water vapour to condense.

Gravity helped Earth keep water instead of losing it to space.

Liquid water is a filter for where to search, not proof that life exists. Goldilocks zones identify where surface liquid water could exist. Transit spectroscopy can then look for water signatures in exoplanet atmospheres.

Liquid water guides searches for extraterrestrial life.

Goldilocks zones mark where surface liquid water could exist.

Transit spectroscopy can detect water signatures in exoplanet atmospheres.

Distance can suggest liquid-water conditions; spectroscopy can provide atmospheric water evidence.

Which claim is safest?

Choose

Which claim is safest?

Choose

Water’s polar structure leads to hydrogen bonding. Hydrogen bonding and polarity create properties. Properties explain biological uses: transport, metabolism, temperature stability, xylem, and aquatic adaptations.

Structure: polar V-shaped water molecules form hydrogen bonds.

Properties: cohesion, adhesion, solvent ability, specific heat capacity, thermal conductivity, buoyancy, and viscosity.

Uses: xylem transport, aqueous metabolism, stable habitats, and aquatic animal adaptations.

Surface tension supports droplets and surface-skating insects.

Adhesion supports capillary action in soil channels and cellulose cell walls.

Cohesion is the stronger force in xylem transport; adhesion helps refill vessels.

Match each water idea to the biological consequence it supports.

Match

Reasons

0/5

Use this after retrieval when a question asks why water is important to organisms or how water properties support life. Short-answer writing belongs in the practice/question-bank flow; this card gives the answer framework.

Start from molecular cause: water is polar and forms hydrogen bonds.

Choose relevant properties: cohesion, solvent ability, specific heat capacity, thermal conductivity, buoyancy, or viscosity.

Link each property to a biological consequence such as xylem transport, metabolism, temperature stability, or aquatic adaptation.

Use this after retrieval when a question asks why water is important to organisms or how water properties support life. Short-answer writing belongs in the practice/question-bank flow; this card gives the answer framework.

Water is polar and forms hydrogen bonds, giving it properties useful to living organisms. Cohesion helps maintain continuous water columns in xylem, while water’s solvent properties allow ions and polar molecules to dissolve so they can be transported and used in metabolism. High specific heat capacity also helps aquatic environments remain temperature-stable.

The common mark loss is listing properties without explaining what they allow organisms to do. Use cause -> property -> consequence.

For HL, retrieve two separate chains. Earth-water origin uses asteroid delivery and isotope comparisons. Life-search questions use liquid water, Goldilocks zones, and spectroscopy as evidence filters.

Origin: asteroid delivery plus isotope evidence from carbonaceous chondrites and Vesta meteorites.

Retention: cooler temperatures and gravity allowed water to condense and remain.

Life search: liquid water guides investigation, but does not prove life.

Match each HL evidence idea to the claim it supports.

Match

Reasons

0/5

Use this for HL questions about Earth water origin, retention, or using water in the search for life.

For Earth origin, state asteroid delivery and support it with isotope evidence from meteorites.

For retention, state cooler temperatures allowed condensation and gravity helped retain water.

For life search, state liquid water guides investigation, but does not prove life; use Goldilocks zones and spectroscopy as evidence tools.

Use this for HL questions about Earth water origin, retention, or using water in the search for life.

Earth water may have an extraplanetary origin because asteroid delivery is supported by isotope comparisons with meteorites such as carbonaceous chondrites and Vesta meteorites. Water was retained because cooler temperatures allowed vapour to condense and Earth gravity helped keep it. In the search for extraterrestrial life, liquid water is used as a filter for promising targets, with Goldilocks zones and transit spectroscopy helping identify where water may exist.

Do not overclaim that water proves life, and do not mix origin evidence with retention conditions.

IB Biology HL A1.1 Water Notes

Water Is The Medium

Bonding Makes The Properties

Choose Cohesion or Adhesion

Solvent: What Dissolves And Why

Properties Explain Adaptations

HL: Earth Water Evidence

HL: Water Guides Life Search

Remember The SL Water Chain

Build The SL Exam Answer

HL: Retrieve And Transfer