2.2 – Water – Sciences for IGCSE & IB

1.Which property of water accounts for its moderating effects on the Earth’s atmosphere?

Cohesive
Thermal
Transparency
Adhesive

2. Cladograms can be created by comparing DNA or protein sequences. The cladogram on the left is based on DNA sequences and the cladogram on the right is based on comparing protein sequences.

What is the reason that cladograms based on DNA sequences are more reliable predictors of the phylogenetic relationship of species than cladograms based on protein sequences?

Amino acids are not as chemically stable as DNA nucleotides
DNA mutates but amino acids do not
Several different triplets of bases can code for the same amino acid
There are 20 different amino acids but only 4 nucleotides

3. The bacterium Neisseria gonorrhoeae causes infections related to the human reproductive system. The graph shows the percentage of samples in which this bacterium showed resistance to six antibiotics over a period of ten years.

What is a possible explanation for the total percentage resistance being larger than 100% in 2010?

People do not take the antibiotics as prescribed
More people have been sampled in that year
There was an epidemic of Neisseria gonorrhoeae in that year
Some bacteria are resistant to more than one antibiotic

4. Which can be explained by the solvent properties of water?

Sodium chloride is transported as Na+ and Cl– in blood
Movement of water occurs under tension in the xylem
Water is the coolant in sweat
Ice floats on liquid water

5. Which properties explain the ability of water to dissolve solutes? I. Polarity of water molecules II. High specific heat capacity of water III. Hydrogen bonding

I and II only
I and III only
II and III only
I, II and III

6. Why is sweat a good coolant for the body?

The arterioles that transfer water to sweat move closer to the skin surface when it is hot
Breaking H bonds between water molecules in sweat requires energy from body heat
Sweat contains minerals such as sodium chloride
Sweat is non-polar

7. What property of water makes it suitable as a coolant?

It takes a lot of energy to increase the temperature of water
It takes a lot of energy for water to evaporate
Water molecules are cohesive and stick to the skin
Water is a good solvent so it can transport heat from the body

8. What is a consequence of the specific heat capacity for liquid water, ice and water vapour?

Less energy is needed to warm water vapour than liquid water
Salt dissolves more readily in liquid water than in ice
Small insects can walk on liquid water
Ice floats on liquid water

9. Water shows strong cohesive properties. Which of the following can occur because of the cohesive properties of water?

Water can be pulled up a plant through the xylem
Enzymes can react with their substrates in cells
Sweating cools the body on a hot day
Salt can dissolve in sea water

10. What property makes water an important coolant in the natural world?

It is cohesive
It requires much energy to evaporate
It has a lower temperature than blood
It has a low specific heat

11. Between which atoms do hydrogen bonds form in water?

Oxygen and hydrogen atoms in the same water molecule
Oxygen and hydrogen atoms in different water molecules
Hydrogen atoms in the same water molecule
Oxygen atoms of different water molecules

12. Which statements correctly explain properties of water? I. Water is a useful medium for metabolic reactions as many substances dissolve in water. II. Water is useful as a coolant as it takes a small amount of heat energy to change its temperature. III. Water molecules are cohesive which helps water transport in the roots and stems of plants.

I and II only
I and III only
II and III only
I, II and III

13. What property of water makes it a good evaporative coolant?

High latent heat of evaporation
Relatively low boiling point
Volatility
Transparency

14. Which statement about water is correct?

The atoms within a molecule of water are held together by hydrogen bonds
Water has a low heat capacity allowing enzymatic reactions to happen at a wide range of temperatures
Water molecules are polar, therefore fatty acids do not dissolve
Ice has a higher density than liquid water, therefore some organisms can live under the ice

15. Which of these molecules is a disaccharide?

Galactose
Sucrose
Cellulose
Ribose

16. Which diagram represents the polarity of a water molecule?

A
B
C
D

17. Which of the following is true about a polar amino acid and cellulose?

Both are polysaccharides
Both contain nitrogen
Both are hydrophobic
Both contain hydrogen atoms

18. Blood is a water-based transport medium. Which property of water makes it a good transport medium?

High specific heat
Transparency
Versatility as a solvent
It has its greatest density at 4°C

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