Water (CIE AS Biology)

Water is a very important component of cells and performs a variety of functions within living organisms.

Explain the role of water within a cell.

Fig.1 shows a diagram of three water molecules.

Fig. 1

Identify Y in Fig.1 and describe how it forms.

Contrast covalent bonds and hydrogen bonds with one another.

Describe the properties of water that enable it to dissolve solutes.

Explain, with reference to bonding, how the relatively high specific heat capacity of water enables it to buffer temperature changes.

Explain the importance of the high latent heat of vaporisation of water to living organisms.

The relatively high specific heat capacity of water is of great biological significance to organisms.

Give one example of the biological importance of this property.

Fig.1 is a transmission electron micrograph showing two adjacent cells in a leaf.

Fig. 1

Cellulose is the main polysaccharide in cell walls of plants.

Describe the structure of cellulose.

[3]

ii)

State one feature visible in Fig. 1, other than the cell wall, that identifies the cells as plant cells.

[1]

iii)

Outline the role of ATP in a leaf cell.

[3]

Water is a main component of plant cells.

Fig. 2 shows two water molecules linked by a hydrogen bond.

Fig. 2

Explain how hydrogen bonding occurs between water molecules.

Suggest why water is an excellent solvent for ions.

A group of students wanted to investigate the thermal properties of water. They poured hot water into two thin plastic cups and measured the rate of cooling of each cup. The sides of one cup were covered with tissue paper soaked in hot water while the sides of the other cup were left uncovered. The temperature of the water was recorded with a thermometer every two minutes over a 10 minute time period.

The results of this experiment is shown in Fig. 1.

Fig. 1

Describe the results shown in Fig. 1.

Calculate the percentage decrease in temperature of the covered cup in the first 4 minutes.

State two control variables for the experiment described in part (a), other than any that have been mentioned in the question above.

Explain how the experiment in part (a) can demonstrate how humans respond to overheating, with reference to the thermal properties of water.

Explain the properties of water that make it a useful component of blood.

A group of scientists investigated the cooling effect of transpiration on the surface temperature of leaves from the species Eucalyptus saligna.

Fig. 1 shows their results.

Fig. 1

Describe the results shown in Fig. 1.

Explain how the properties of water contribute to the cooling effect of transpiration in a leaf.

Calculate the decrease in temperature when the transpiration rate increases from 1 mmol H₂O m^-2 s^-1 to 2 mmol H₂O m^-2 s^-1.

Suggest and explain one advantage to ecosystems of solid water (ice) being less dense than liquid water.

Fig. 1 shows a water molecule with its bond angle labelled as 104.49°.

Fig. 1

The bond angle that would be expected in a molecule of this shape would usually be larger, around 109°.

Use information in Fig. 1 to suggest why water's bond angle is less than that of the expected geometric shape of a water molecule.

Water reaches its maximum density of 1 000 kg m^-3 at 4 °C, while the density of ice is 917 kg m^-3.

Density can be calculated using the formula:

Density = mass ÷ volume

Use the formula provided to calculate the percentage volume expansion that occurs when 1 000 kg of water freezes from 4 °C to below its freezing point. 

State your answer to the nearest whole number.