A1.1: Biology IB HL

why is covalent bonding in water polar

polarity of covalent bonding within water molecules is due to unequal

sharing of electrons and that hydrogen bonding due to this polarity occurs between water molecules

draw a water molecule

one oxygen (-) and two hydrogen (+)

Define buoyancy

An upward force exerted by a fluid that opposes the weight of a partially or fully immersed object.

Define viscosity

A fluid's resistance to flow, or resistance to an object moving through it.

Define thermal conductivity

The ability of a substance to transfer heat.

Define Specific Heat Capacity

The energy in joules required to raise the temperature of 1 kg of a substance by 1°C

Why is water a good solvent?

• water molecules are polar

• water forms hydrogen bonds with polar substances

• positive pole of water attracted to negative ions

• negative pole attracted to positive ions

• sodium chloride/other example dissolves because ions are attracted to water

• glucose/other example dissolves because it is polar

What is Cohesion?

molecules of the same type (in this case water) are attracted to one another.

What is Surface Tension?

due to cohesion between water molecules and those immediately next to and below them. This must be broken in order for an object to enter the water from above

What is adhesion?

attraction between two different types of molecule (in this case water and another polar molecule) due to hydrogen bonding.

Describe capillary action.

movement of a liquid (in this case water) upwards against gravity within a narrow tube. Due to adhesion between the water molecules and the inner wall of the tube, and cohesion pulling more water molecules up with them

What physical and chemical properties of water make it essential for life?

• Polar covalent bonds

• Cohesive forces

• Adhesive forces

• Excellent solvent properties

What are the challenges and opportunities of water as a habitat?

Buoyancy - keeping aquatic organisms on or near the surface Viscosity - overcome by adaptations to body shape

Thermal conductivity - adaptations to overcome the conduction of heat away from the body

High specific heat capacity - protects from cooler surrounding air temperatures.

HL - surface temps must allow it to exist in liquid form and gravity must be sufficient to prevent water escaping

Black throated loon