A1.1 WaterIB Biology HL: Flashcards

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Question

Why is water polar?

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Why is water polar?: Oxygen attracts shared electrons more strongly than hydrogen, making O δ− and H δ+.
What is a hydrogen bond between water molecules?: Attraction between the δ+ H of one molecule and the δ− O of another.
Cohesion vs adhesion?: Cohesion: water attracted to water. Adhesion: water attracted to other polar or charged materials.
Where does capillary action matter to plants?: In soil (water moving between particles to roots) and in cellulose cell walls of leaves.
How does cohesion help xylem transport?: It keeps the water column unbroken under tension, so the pull from evaporation reaches the roots.
Name two functions that depend on molecules being hydrophobic.: Phospholipid membranes as barriers; triglyceride energy storage (also waxy cuticles).
Name four physical properties that differ between water and air.: Buoyancy, viscosity, thermal conductivity and specific heat capacity.
Why do seals need blubber in cold water?: Water conducts heat far faster than air, so insulation is needed to reduce heat loss.
HL: What is the hypothesised origin of Earth's water?: Extraplanetary: delivered by asteroids colliding with the early Earth.
HL: Why did Earth retain its water?: Gravity strong enough to hold it, and temperatures low enough for water vapour to condense.
HL: Why is the long-term abundance of water important?: Water has been present for billions of years, giving a continuous medium in which life originated and evolved.
HL: What is the Goldilocks zone?: The region around a star where temperatures allow liquid water on a planet's surface.
HL: Why is water the focus of the search for extraterrestrial life?: All known life depends on liquid water as its medium.