Bio HL 1.1

Water as a medium of life

The first cells originated in water. Water is the universal solvent allowing it to dissolve and transport molecules around a body. Water is needed in condensation and hydrolysis reactions. Water is a temperature buffer in bodies and ecosystems. Water maintains biological structures such as phospholipid bilayer/proteins/DNA.

The structure of the water molecule

1 slightly negative oxygen and 2 slightly positive hydrogens

The water molecule polar since

It contains 1 slightly negative oxygen atom and 2 slightly positive hydrogen atoms

Bond between oxygen and hydrogen atom

covalent bond

Bond between water and water molecules

hydrogen bond

Cohesion

the attraction between the same kind of substance (water molecules) by hydrogen bonding

Adhesion

the attraction between water molecules and other polar surfaces

Transport of water in xylem of plants

water molecules join together by hydrogen bonding forming a continuous unbroken column of water within the xylem vessels to be transported to leaves for photosynthesis

Surface tension on surface of ponds

water molecules at the surface are attracted by adhesive hydrogen bonding creating a strong surface layer with high surface tension allowing light-weighted organisms like bond skates to walk on water without sinking

Capillary action

water molecules are attracted to the polar walls of narrow tubes such as xylem vessels allowing water to rise against gravity in the xylem

Attraction to cellulose

cellulose in xylem is polar so it forms a hydrogen bond with water so helping in maintaining water movements across roots and up-through the plant

Hydrophilic

the molecule that is attracted to water like glucose

Hydrophobic

the molecule that is not attracted to water like oil

Water as a transport medium

blood carries nutrient gases and waste all of which are dissolved in the water of the blood

Transportation of sodium chloride in plasma

NaCl will be dissociating into positive Na and negative Cl ions which can dissolve in water and get transported

Transportation of amino acids/glucose in plasma

both are polar molecules so they are transported and dissolved in the liquid part of the blood

Transportation of oxygen in plasma

its a small non polar molecule so its solubility in blood plasma is low so its transported through binding to the hemoglobin in red blood cells

Transportation of fat molecules in plasma

they are non polar molecules which cannot dissolve in water so they are transported through lipoproteins

Thermal properties of water

high specific heat capacity (4.18) as a lot of energy is required to break the bonds between the water molecules this is so waters temperature doesn't change easily making it stable for aquatic life. high latent heat of vaporization since water (in sweat) needs a lot of energy to break the hydrogen bonds to evaporate making it an excellent cooling agent. and a high boiling point of 100 degrees celsius.

Buoyancy of water

The less dense an object is to water the more it floats. Most organisms have more or less the same density of water to help them float, so they don’t need to exert energy to float. Air pockets in any organism adds to its ability to float. Air is much less dense than water. Animals are more dense than air so they need energy to fly.

Viscosity

The resistance to flow. Honey is more viscous than water. The more viscosity of a medium, the more internal friction leading to difficulty in movement within the medium. Aquatic animals need energy to swim underwater because of its viscosity.

Thermal conductivity

water has high thermal conductivity than air. water can conduct heat with ease compared to air that acts as an insulator (not conducting heat). blood which is 70% of water can conduct heat from the internal organs and transfer this heat to the extremities. aquatic animals may lose heat to the surrounding water so much adapt to reduce heat loss