The Biological Importance of Water

Question 1

Define the term ‘Polar’

Answer 1

The uneven distribution of charge resulting in atoms within a molecule to have opposing charges (one having a partial negative charge, another having a partial positive charge).
i.e. A polar covalent bond is when electrons (negatively charged) have been shared unevenly between atoms.

Question 2

Define the term ‘Dipole’

Answer 2

A molecule that has both positive and negative charges due to an uneven distribution of charges.

Question 3

Define the term ‘Electronegativity’

Answer 3

Electronegativity is the measure of the tendency of an atom to attract bonding pairs of electrons. Some atoms have a much stronger electronegativity than others.

Question 4

Give examples of some atoms with a strong electronegativity.

Answer 4

Oxygen, Flourine, Nitrogen

Question 5

Explain what a hydrogen bond is, which types of atoms it can join together and where they occur in biology.

Answer 5

• A weak type of chemical bond (but collectively they are very strong)
• Occurs between a hydrogen atom and another strongly electronegative atom of a polar covalent bond in the same or another molecule.
• In water, the slightly negative oxygen atoms are attracted to the slightly positive hydrogen atoms in another molecule.

Question 6

Explain why water is a polar molecule.

Answer 6

A water molecule is formed by covalent bonds (the sharing of electrons) betweeen hydrogen and oxyen atoms. Because oxygen is more strongly electronegative than hydrogen it has a greater pull on the shared electrons than the hydrogen, resulting in an uneven distribution of charges.
This causes a partial negative charge on oxygen (due to the closeness of the electrons) and a partial positive charge on hydrogen, therefore it is a polar molecule. (Water forms polar covalent bonds)

Question 7

Gives some roles that water plays in life.

Answer 7

• Medium for transport
• Medium for chemical reactions
• Temperature control
• Support
• Reproduction (bringing the male and female gametes together for fertilisation)
• Habitat
• A reactant
• A solvent

Question 8

Describe the structure of a water molecule.

Answer 8

A water molecule consists of two hydrogen atoms and one oxygen atom. They are bonded by polar covalent bonds.

Question 9

What is the bond that links two water molecules together?

Answer 9

A hydrogen bond.

Question 10

Draw two water molecules and label the bond that links them together.

Answer 10

Draw and look up in text book.

Question 11

Explain why water is a polar molecule.

Answer 11

Water is a polar molecule because oxygen is more strongly electronegative than hydrogen, so it has a greater pull on the shared electrons. This results in oxygen having a slightly negative charge and hydrogen having a slightly positive charge, therefore, it is polar.

Question 12

Explain how the polar nature of water makes it’s freezing point 0 and it’s boiling point 100.

Answer 12

Because water is polar, hydrogen bonds form between the molecules. Collectively, these bonds require a lot of energy to break and separate the water molecules. This means that water has a high boiling.

Question 13

Explain the biological significance of water’s freezing and boiling point.

Answer 13

Because water’s boiling point is 100 degrees it stays as a liquid at most envrionmental temperatures, and so provides a stable aquatic environment and medium for chemical reactions.

Question 14

Explain how the polar nature of water gives it a high specific heat capacity.

Answer 14

Hydrogen bonds give water a high specific heat capacity. The hydrogen bonds between the water molecules can absorb a lot of energy so it takes a lot of energy to heat water up.

Question 15

What is high specific heat capacity?

Answer 15

The energy needed to raise the temperature of one gram of a substance by 1 degrees celsius.

Question 16

Explain the biological signifcance in having a high specific heat capacity.

Answer 16

Water temperature remains fairly stable, reducing fluctuations in organisms and environments. Cells and aquatic environments slow to freeze.

Question 17

Explain how the polar nature of water gives it a high latent heat of vaporisation.

Answer 17

Water is polar, so it has hydrogen bonds between molecules. It takes a lot of energy to break the hydrogen bonds between water molecules because hydrogen bonds absorb a lot of energy, so a lot of energy is used up when trying to evaporate water.

Question 18

What is the biological significance of water having a high latent heat of vaporisation?

Answer 18

It is effective as a coolant, through sweating because a large amount energy is expended in evaporating sweat from the surface of our skin. This also happens in panting and transpiration.

Question 19

Explain how the polar nature of water means that it has a lower density when a solid.

Answer 19

Water molecules are held further apart in ice than in liquid water because each water molecule forms four hydrogen bonds to other water molecules making a lattice shaper. This means that ice takes up a greater volume with the same mass, and so it is less dense.

Question 20

When is water at its highest density?

Answer 20

At 4 degrees Celsius.

Question 21

What is the biological significance of water being less dense as a solid?

Answer 21

Because ice floats water freezes on the surface first, this forms an insulating layer over the rest of the water meaning that water under the ice does not freeze. This means that the aquatic environment of organisms does not freeze over completely.

Question 22

Explain how the polar nature of water makes it a good solvent for other ionic and polar molecules.

Answer 22

The polar nature of water means that one side of the water molecule is delta positive and one side is delta negative. They attract to ionic and polar compounds because the delta negative side attracts to the positive ion in the compound (e.g. Oxygen is attracted the negative Na+ in NaCL) and delta positive side is attracted to the negative ion in the compound (e.g hydrogen is attracted to CL-). The individual charged ions are pulled away from the compound and are surround by water molecules to form a hydration sphere, so the compound is dissolved.

Question 23

Explain the biological significance of water being a good solvent for polar and ionic compounds.

Answer 23

Enables transport of substances in solution (i.e. in the human circulatory system and in the vascular bundles of plants). Oxygen and other essential nutrients can dissolve in water in aquatic environments.

Question 24

Define hydrophilic

Answer 24

When something is hydrophilic, it can interact with water. It will readily dissolve or absorb water.

Question 25

Define hydrophobic

Answer 25

When something is hydrophobic, it repels water. It is insoluable in water.

Question 26

Explain how the polar nature of water makes it cohesive.

Answer 26

Cohesion is the attraction of molecules of the same type. Water molcules are very cohesive because they have the attraction of hydrogen bonds between them (due to them being polar)

Question 27

Explain the biological significance of water being cohesive?

Answer 27

Creates water collumn of transpiration stream, through the xylem of a plant. Creates a surface on which small organisms can live. The shape of rain drops.

Question 28

Explain how the polar nature of water makes it adhesive.

Answer 28

Adhesion is when water adheres non- water molecules surfaces. This is because it forms hydrogen bonds to other polar molecules.

Question 29

What is the biological significance of water being adhesive?

Answer 29

It allows capillary action, which is when water rises up narrow tubes because it has adhered to the surfaces of them. For example, when water rises up the xylem of a plant and through air spaces between particles in the soil.

Question 30

What are the properties that are not related to water’s polar nature?

Answer 30

• Reactivity
• Transparency
• Poor conductivity
• Low viscosity

Question 31

The biological significance of reactivity.

Answer 31

Water can take part in reactions. It takes part in hydrolysis and condensation reactions and is a major part in photosynthesis.

Question 32

The biological significance of transparency

Answer 32

Allows light to pass through water into aquatic environments so submerged organisms can photosynthesize.
Allows light to penetrate cells so photosynthesis can take place.

Question 33

The biological significance of low viscosity

Answer 33

Water molecules slide past eachother readily so water flows readily. This allows transport through vessels e.g. xylem and blood vessels

Question 34

Explain how the polar nature of water allows water to form a dome above the level of the glass container it is.

Answer 34

Because water is polar, it forms hydrogen bonds and becomes cohesive. This means water molecules do not separate very easily, and so when they rise about over the level of their container they form a dome. This is called surface tension.