BM - Water

Question 1

What is the chemical structure of water, and how does this structure contribute to its properties?

Answer 1

• Water (H₂O) consists of two hydrogen atoms covalently bonded to an oxygen atom.
• The molecule has a bent shape due to the angle between the bonds.
• The oxygen atom is more electronegative than hydrogen, creating a partial negative charge on the oxygen atom and partial positive charges on the hydrogen atoms.
• This results in water being polar, leading to hydrogen bonding between molecules.
• This structure accounts for water’s high boiling and melting points, surface tension, cohesion, adhesion, and its ability to dissolve many substances (solvent properties).

Question 2

Explain how the properties of water contribute to its role as a solvent in biological systems.

Answer 2

1. Water’s polarity allows it to dissolve a wide range of ionic and polar substances.
2. The positive hydrogen atoms are attracted to negative ions, while the negative oxygen atoms are attracted to positive ions.
3. This makes water an effective solvent for many biological molecules
4. This property is crucial for processes like nutrient transport and waste removal in cells.

Question 3

What is the significance of water’s high specific heat capacity in living organisms?

Answer 3

1. Water has a high specific heat capacity, meaning it can absorb or release a large amount of heat energy with only a small change in temperature.
2. This is due to the hydrogen bonds between water molecules, which require a significant amount of energy to break.
3. This property helps maintain stable temperatures in organisms and environments, preventing rapid temperature fluctuations that could damage cells and tissues.

Question 4

How does the high latent heat of vaporization of water support living organisms?

Answer 4

1. The high latent heat of vaporization of water means that a large amount of energy is required to convert water from a liquid to a gas.
2. This helps organisms regulate their temperature through processes like sweating or transpiration, as heat is removed from the body or plant during the evaporation of water, cooling the organism.
3. This is crucial for thermoregulation in animals and plants, particularly in hot climates.

Question 5

Describe the importance of water’s cohesion and adhesion properties in plants.

Answer 5

• Cohesion refers to the attraction between water molecules, while adhesion is the attraction between water molecules and other substances.
• In plants, these properties are crucial for the movement of water through the xylem during transpiration.
• Cohesion allows water molecules to stick together, helping to form a continuous column of water.

Question 6

What is the role of water in maintaining turgidity in plant cells?

Answer 6

• Water enters plant cells via osmosis, and the cell wall exerts pressure to prevent the cell from bursting.
• The water inside the vacuole creates pressure known as turgor pressure.
• This pressure helps maintain the rigidity and shape of the plant cell, preventing wilting and enabling the plant to stand upright.

Question 7

Explain the process of osmosis in relation to water movement across cell membranes.

Answer 7

• Osmosis is the passive movement of water molecules from an area of higher water concentration (or lower solute concentration) to an area of lower water concentration (or higher solute concentration) across a semi-permeable membrane.
• This process does not require energy and continues until equilibrium is reached.

Question 8

How does water’s surface tension support life?

Answer 8

• This property allows small organisms, such as insects, to walk on water.
• It also plays a role in processes like the transport of water in plants and the formation of droplets in the environment.
• The surface tension of water helps maintain stability in various biological systems.

Question 9

Explain five properties that make water important for organisms.

5 marks

Answer 9

1. A metabolite in condensation/hydrolysis
2. A solvent so (metabolic) reactions can occur
3. High (specific) heat capacity so buffers changes in temperature;
4. Large latent heat of vaporisation so provides a cooling effect (through
   evaporation);
5. Cohesion (between water molecules) so supports columns of water
   (in plants);
6. Cohesion (between water molecules) so produces surface tension
   supporting (small) organisms;