Unit 2 - Biological Elements & 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⁺) - Nerve impulse transmission and muscle contractions

Sodium ions (Na⁺) - Nerve impulse transmission and kidney function

Potassium ions (K⁺) - Nerve impulse transmission and stomatal opening

Hydrogen ions (H⁺) - Catalysis of reactions, proton pump in photosynthesis, pH determination.

Ammonium ions (NH₄⁺) - Production of nitrate ions

Question 4

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

Answer 4

Nitrate ions (NO₃^-) - Nitrogen supply to plants for amino acid and protein formation

Hydrogen carbonate ions (HCO₃^-) - Maintenance of blood pH

Chloride ions (Cl^-) - Balance positive charge of sodium and potassium ions in cells

Phosphate ions (PO₄^3-) - Cell membrane formation, nucleic acid and ATP formation, and bone formation

Hydroxide ions (OH^-) - Catalysis of reactions, pH determination

Question 5

Which elements are found in carbohydrates?

Answer 5

Carbon, hydrogen and oxygen.

Question 6

Which elements are found in lipids?

Answer 6

Carbon, hydrogen and oxygen.

Question 7

Which elements are found in proteins?

Answer 7

Carbon, hydrogen, oxygen, nitrogen and sulphur.

Question 8

Which elements are found in nucleic acids?

Answer 8

Carbon, hydrogen, oxygen, nitrogen and phosphorus.

Question 9

Define the term ‘polar’ in relation to molecules.

Answer 9

Molecules that have regions or negativity and regions of positivity

This is due to the way in which electrons are distributed between elements joined by a covalent bond.

Question 10

Explain how polar molecules like water interact with each other.

Answer 10

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 11

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

Answer 11

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

Question 12

Hydrogen bonds are…

Answer 12

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 13

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

Answer 13

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

Question 14

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

Answer 14

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

Question 15

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

Answer 15

Hydrogen bonding between molecules

Question 16

Water has a low viscosity. What does this mean?

Answer 16

It flows easily

Question 17

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

Answer 17

1. Provide a habitat for living things
2. Form a major component of the tissues in living organisms
3. Provide a reaction medium for chemical reactions
4. Provide an effective transport medium

Question 18

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

Answer 18

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

Question 19

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

Answer 19

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

Question 20

How does water dissolve solutes?

Answer 20

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.