subject notes

A1.1.1—Water as the medium for life

  • the first cells originated in water

  • most life processes occur in water

A1.1.2—Hydrogen bonds as a consequence of the polar covalent bonds within water molecules

water molecule is formed when one oxygen atom covalently bonds to 2 hydrogen atoms

but the difference in electronegativity means that the pair of electrons in each covalent bond isn’t shared equally between the oxygen & hydrogen atoms

  • oxygen = higher electronegativity than hydrogen

    • attracts the shared electrons more strongly than hydrogen atoms

      • so a polar covalent bond is formed

    • so oxygen has a partial negative charge & hydrogen has partial positive charge

a hydrogen bond between a hydrogen & oxygen, holds the water molecule together

  • is weak cuz the charges are partial & is represented in a diagram using a dashed line

A1.1.3—Cohesion of water molecules due to hydrogen bonding and consequences for organisms

cohesion occurs when “like” molecules are mutually attracted

  • the hydrogen bonds between water molecules, make water highly cohesive

ex: vascular plants use cohesion of water to transport water up its xylem, to the top of the plant

ex: the hydrogen bonds also allow water to resist an increase in its surface area, and some insects use this surface tension to create a habitat

  • Water striders reside on top of the bodies of calm water (the water is calm)

  • pollutants can disrupt this surface tension, causing the water strider to sink

A1.1.4—Adhesion of water to materials that are polar or charged and impacts for organisms

adhesion is the attraction between different types of substances

water is also attracted to any other polar or charged material

this adhesion (along with cohesion) has a positive impact for organisms, such as plants

  • if adhesion is greater than cohesion, capillary action will occur

    • means that water will be pulled through narrow tubes & space

    • is important in soil, as it prevents the soil from drying out

A1.1.5—Solvent properties of water linked to its role as a medium for metabolism and for transport in plants and animals

hydrophilic = molecules that are attracted to water

  • are usually polar or hv areas with an uneven distribution of positive & negative charges

  • water will dissolve polar substances

  • plasma (the water component of blood) uses water as a solvent in order to easily transport soluble materials, such as glucose

hydrophobic = substances that aren’t dissolvable in water cuz there’s not much attraction to water molecules

A1.1.6—Physical properties of water and the consequences for animals in aquatic habitats

Buoyancy - water has high density = high buoyancy, allowing less dense materials to float

  • water is less dense as a solid (ice) than as a liquid

    • is due to the hexagonal lattice formed when water freezes

    • there are large gaps between these hexagons, meaning ice is less dense?

  • cold liquid water=most dense

    • sinks to bottom of pond, allowing a layer of liquid water at the top, meaning life can continue to thrive

Viscosity - water has low viscosity compared to other liquids, but has a higher viscosity than air

Thermal heat conductivity - ability of substance to transfer heat when there’s a temperature difference

  • water has high compared to other liquids

  • air has lower compared to water

Specific heat capacity - how much energy is needed to raise the temperature of a substance

  • water has high specific heat capacity (meaning it can give off or absorb lots of heat without rlly changing temperature)

    • is due to hydrogen bonds, as these hv to be broken in order to temperature of water to rise

  • air has low compared to water

    • easily changes temp when there’s weather events

THE RINGED SEAL

property

water

air

Buoyancy

their low - density blubber increases the buoyant force (helps them float)

appear heavy on ice & land, cuz air is less buoyant

Viscosity

due to the viscosity of water, their hydrodynamic bodies can reduce drag and their powerful flippers exert force against water to propel them

Thermal

Conductivity

high thermal conductivity of water tends to take water from the seal’s body BUT their blubber has low thermal conductivity, which reduces heat loss & insulates the seal’s body

Specific Heat

Capacity

construct lairs under the snow where air (with its low specific heat capacity) can be easily warmed

  • snow has a low thermal conductivity compared to liquid water, so it’s a good insulator

    • this is especially important for young seals who can only survive in warm & insulated lairs cuz they’re born with little blubber

BLACK-THROATED LOON

property

water

air

buoyancy

has an aerodynamic body (and has large wings) which helps it generate lift during flight in less buoyant air (cold air is more dense, so less buoyant, compared to normal air)

viscosity

has a hydrodynamic body to reduce drag while swimming in more viscous water (cold water is more viscous than normal water)

Its aero dynamicity also helps the loon reduce drag when flying

thermal

conductivity

oiled exterior feathers exclude water

has an insulting layer of air & down feathers (which hv a low thermal conductivity)

specific heat

capacity

A1.1.7—Extraplanetary origin of water on Earth and reasons for its retention

presence of liquid water limits where life may exist & can help direct the search for extraterrestrial life

scientific evidence suggests that water was delivered to Earth through may collisions with water-rich asteroids

larger objects, like Earth, exert a greater gravitational force

  • as Earth began to cool, water condensed & the force of Earth’s gravity helped to retain water on the planet’s surface

  • temperatures also lowered enough to condense water

A1.1.8—Relationship between the search for extraterrestrial life and the presence of water

Goldilocks Zone - the orbital distance from a star where the conditions permit the presence of liquid water

Earth is in the Goldilocks Zone, as the distance from our Sun is enough to allow for liquid water