Biological Elements and Water

Question 1

All living things are made primarily from which four key elements?

Answer 1

Carbon (C)
Hydrogen (H)
Oxygen (O)
Nitrogen (N)

Question 2

In addition to the four key elements all living things are made primarily from, what other two elements play important roles in the biochemistry of cells ?

Answer 2

Phosphorus (P)
Sulphur (S)

Question 3

Five cations (+ve ions) that play important roles in organisms

Answer 3

Calcium ions (Ca2+)

Sodium ions (Na+)

Potassium ions (K+)

Hydrogen ions (H+)

Ammonium ions (NH4+)

Question 4

What roles do Calcium ions (Ca2+) play in organisms?

Answer 4

Nerve impulse transmission and muscle contractions.

Question 5

What roles do Sodium (Na+) play in organisms?

Answer 5

Nerve impulse transmission and kidney function

Question 6

What roles do Potassium (K+) play in organisms?

Answer 6

Nerve impulse transmission and stomatal opening

Question 7

What roles do Hydrogen ions (H+) play in organisms?

Answer 7

Catalysis of reactions, proton pump in photosynthesis, pH determination.

Question 8

What roles do Ammonium ions (NH4+) play in organisms?

Answer 8

Production of nitrate ions

Question 9

Five anions (-ve ions) that play important roles in organisms

Answer 9

Nitrate ions (NO3-)

Hydrogen carbonate ions (HCO3-)

Chloride ions (Cl-)

Phosphate ions (PO43-)

Hydroxide ions (OH-)

Question 10

What roles do Nitrate ions (NO3-) play in organisms?

Answer 10

Nitrogen supply to plants for amino acid and protein formation

Question 11

What roles do Hydrogen carbonate ions (HCO3-) play in organisms?

Answer 11

Maintenance of blood pH

Question 12

What roles do Chloride ions (Cl-) play in organisms?

Answer 12

Balance positive charge of sodium and potassium ions in cells

Question 13

What roles do Phosphate ions (PO43-) play in organisms?

Answer 13

Cell membrane formation, nucleic acid and ATP formation, and bone formation

Question 14

What roles do Hydroxide ions (OH-) play in organisms?

Answer 14

Catalysis of reactions, pH determination

Question 15

Which elements are found in carbohydrates?

Answer 15

Carbon, hydrogen and oxygen.

Question 16

Which elements are found in lipids?

Answer 16

Carbon, hydrogen and oxygen.

Question 17

Which elements are found in proteins?

Answer 17

Carbon, hydrogen, oxygen, nitrogen and sulphur.

Question 18

Which elements are found in nucleic acids?

Answer 18

Carbon, hydrogen, oxygen, nitrogen and phosphorus.

Question 19

Define the term ‘polar’ in relation to molecules. Why is this?

Answer 19

Molecules that have regions or negativity and regions of positivity

This is due to how electrons are distributed between elements joined by a covalent bond.

Question 20

Explain how polar molecules like water interact with each other.

What properties does this give water?

Answer 20

The positive and negative regions of the molecules attract each other and form hydrogen bonds.

These bonds give water its cohesive properties - it moves as one body because the molecules are attracted to each other.

These bonds also give water its adhesive properties - it molecules are attracted to other surfaces.

Question 21

Explain how the ‘skin’ of surface tension of water enables a pond skater to inhabit the surface of water?

Answer 21

The skin is caused by water molecules are more strongly cohesive to each other than to air, this skin supports the pond skater.

Question 22

Hydrogen bonds are…

What do they do, in terms of water?

Answer 22

Relatively weak interaction that form and break between the constantly moving water molecules.

There are large numbers of then though, which give water its unique characteristic that are essential for life on Earth.

Question 23

What are the unique characteristics of water that are essential for life on Earth? (5)

Answer 23

• Unusually high specific heat capacity (boiling point).
• Becomes less dense when it freezes.
• Cohesive properties
• Adhesive properties
• ‘Skin’ of surface tension

Question 24

Why is it good that water has a high specific heat capacity?

Answer 24

Keeps habitats stable for living things as a lot of energy is needed to change it by a degree.

Question 25

What makes it more difficult for water to become a gas?

Answer 25

Hydrogen bonding between molecules

Question 26

Water has a low viscosity. What does this mean?

Answer 26

It flows easily

Question 27

Due to water being a liquid at room temp what four things does this allow it to do? (4)

Answer 27

• Provide a habitat for living things
• Form a major component of the tissues in living organisms
• Provide a reaction medium for chemical reactions
• Provide an effective transport medium

Question 28

Because ice is less dense than water what two things does this allow it to do?

Answer 28

• Aquatic organisms have a stable environment in which to live throughout the winter
• Ponds and other bodies of water are insulated against extreme cold

Question 29

Because water is a good solvent it can do what two things?

Answer 29

• Molecules and ions can move around and react together in water
• Molecules and ions can be transported around living things while dissolved in water

Question 30

Why and How does water dissolve solutes?

Answer 30

• Water is able to dissolve solutes due to being polar.
• The negative parts of the water molecules attach to the positive parts of the solute.
• The positive parts of the water molecules attaches to the negative parts of the solutes.
• This keeps them away from each other eventually dissolving the solute into a solution.