Lesson 6 - Water

Question 1

Definition of polar

Answer 1

Polar molecules have regions of negativity and regions of positivity.

Question 2

Explanation of polar

Answer 2

The atom with a greater share of negative electrons will be slightly negative, compared with the other atom in the bond which is positive.

Question 3

How come electrons are not shared equally in water?

Answer 3

Oxygen has a much greater share of electrons in the O-H bond. So hydroxyl molecules are slightly polar.

Water contains two hydroxyl bonds.

Question 4

How do hydrogen bonds occur in water?

Answer 4

Polar molecules interact with each other, as positive and negative regions attract each other and form bonds. These are called hydrogen bonds.

Question 5

Hydrogen bonds are weak:

Answer 5

Break and reform between constantly moving water molecules

Question 6

How come hydrogen bonds are effective?

Answer 6

Occur in high numbers

Question 7

Characteristics of water:

Answer 7

• high boiling point
• Cohesive
• Adhesive

Question 8

Compare boiling point of water to other small molecules?

Answer 8

Carbon dioxide is a gas at room temperature, but water is a liquid

Question 9

Freezing of water:

Answer 9

Water becomes less dense as a solid (unlike most molecules). This is because hydrogen bonds are formed.

As water is cooled below 4 degrees, the hydrogen bonds fix the positions of the water molecules slightly further apart than the average distance in liquid state.

Question 10

Structure of ice:

Answer 10

Giant, rigid, but open structure. Every oxygen atom is at the centre of a tetrahedral arrangement of hydrogen atoms.

Question 11

Result of low density of ice:

Answer 11

It floats

Question 12

Cohesion definition:

Answer 12

Molecules are attracted to each other.

Question 13

Result of water’s cohesive nature:

Answer 13

Water moves as one mass.
- Plants are able to draw water up their roots
- Can drink through a straw

Question 14

Adhesive definition:

Answer 14

Molecules are attracted to other materials.

Question 15

Result of water being adhesive:

Answer 15

Can wash hands and hands become wet, water doesn’t run off.

Question 16

Why does water have a ‘skin’ surface tension?

Answer 16

Water molecules are more attracted to each other than the air.

Question 17

Results of water acting as a solvent:

Answer 17

• Cytosol of prokaryotes and eukaryotes are mostly water
• Water acts as a medium for chemical reactions and helps to transport dissolved compounds into and out of cells.

Question 18

Other polar molecules:

Answer 18

• Amino acids
• Proteins
• Nucleic Acids

Question 19

What does adhesion of water occur between?

Answer 19

• Other water molecules
• Other polar molecules
• Surfaces

Question 20

Results of adhesion and cohesion:

Answer 20

Capillary action

Question 21

What is capillary action?

Answer 21

This is the process by which water can rise up a narrow tube against the force of gravity.

Question 22

How is water an effective transport medium:

Answer 22

Cohesion between water molecules means that water is transported through the body and molecules will stick together.

Question 23

Effect of water as a coolant:

Answer 23

Buffer temperature changes during chemical reactions in prokaryotic and eukaryotic cells because of the large amounts of energy required to overcome hydrogen bonds.

Question 24

Why is it important for water to maintain temperatures in cellular environments?

Answer 24

Enzymes are only active in a small range of temperatures

Question 25

Results of ice floating:

Answer 25

Forms an insulating layer above the water below.

Question 26

Why is the insulating layer of ice important?

Answer 26

Aquatic organisms would not be able to survive freezing temperatures if their environment froze solid.

Question 27

How is surface tension good for some insects?

Answer 27

The surface tension is strong enough to support small insects such as pond skaters.

Question 28

How does water provide a constant environment?

Answer 28

It does not change temperature easily.