A1.1 Water

Question 1

In what medium are the first cells believed to have evolved?

Answer 1

The first cells are believed to have evolved in a watery environment, specifically in the deep oceans close to hydrothermal vents in the earth’s crust.

Question 2

Why is liquid water important for life processes?

Answer 2

Liquid water allows dissolved molecules to move around, enabling them to easily collide and react with each other; this is crucial for most life processes.

Question 3

What is hydrogen bonding?

Answer 3

Hydrogen bonds are weak electrostatic attractive forces between a slightly positive hydrogen atom of one molecule and a slightly negative atom (usually oxygen or nitrogen) of another molecule.

Question 4

Which area of a water molecule is δ- and which area is δ+?

Answer 4

In a water molecule the oxygen atom is δ- and the hydrogen atoms are δ+.

Question 5

How does the polarity of water molecules lead to hydrogen bonding?

Answer 5

The polarity of water molecules leads to hydrogen bonding because the slightly positive hydrogen atoms of one water molecule are attracted to the slightly negative oxygen atoms of adjacent water molecules.

Question 6

Why is cohesion important for living organisms?

Answer 6

Cohesion is important for living organisms because it allows, e.g.:

• transport of water under tension in xylem vessels
• the use of water surfaces as habitats due to surface tension

Question 7

Define the term cohesion in relation to water molecules.

Answer 7

Cohesion is the strong attraction between water molecules that is present due to hydrogen bonding.

Question 8

What is adhesion in the context of water?

Answer 8

Adhesion is when water molecules forms hydrogen bonds with other polar or charged molecules.

Question 9

What is an example of adhesion in living organisms?

Answer 9

An example of adhesion in living organisms is the capillary action that allows water movement in:

• xylem
• soil
• plant cell walls

Question 10

Why is water considered a universal solvent?

Answer 10

Water is considered a universal solvent because most biological molecules are hydrophilic and can be dissolved in it; this is due to water’s polarity.

Question 11

Define the term specific heat capacity.

Answer 11

Specific heat capacity is a measure of the energy required to raise the temperature of 1 kg of a substance by 1 °C.

Question 12

How does water’s high specific heat capacity benefit living organisms?

Answer 12

Water’s high specific heat capacity means that it can absorb a lot of heat energy without wide temperature fluctuations. This means that it can provide temperature-stable aquatic habitats where it is easy for organisms to maintain the optimum temperature for enzyme activity.

Question 13

Define the term thermal conductivity.

Answer 13

Thermal conductivity refers to the ability of a substance to conduct heat.

Question 14

How does the thermal conductivity of water compare to that of the air?

Answer 14

The thermal conductivity of water is higher than that of air, which makes air a very good insulator for organisms living in colder climates.

Question 15

What is viscosity, and how does it affect aquatic organisms?

Answer 15

Viscosity is the resistance of a fluid to flow.

Aquatic organisms like seals and loons need body shapes adapted to move efficiently through viscous water.

Question 16

What are examples of adaptations of animals that live in water and in air?

Answer 16

Examples of adaptations of animals that live in water and in air are:

• the ability to regulate buoyancy
• streamlined body and webbed feet / flippers
• insulation that functions in water and in air