1.1. In an investigation the carbon dioxide concentration in the air above a crop of maize plants was measured for 24 hours.

There was no wind blowing during the 24 hours of the investigation.

The results of this investigation are shown in Fig. 1.

Fig. 1

(i) State the two times, on Fig. 1, at which the carbon dioxide concentration in the air was 37 arbitrary units.

[1]

(ii) Calculate the difference in the carbon dioxide concentration in the air between 04:00 (sunrise) and 12:00 (midday) on Fig. 1. Give your answer in arbitrary units.

[1]

(iii) Explain why the concentration of carbon dioxide decreases between 04:00 and 09:00.

[3]

1.2. State two environmental factors that would affect the results of this investigation.

1.3. Extended Tier Only

Describe and explain the concentration of carbon dioxide between 16:00 and sunset in Fig. 1.

1.4. Extended Tier Only

The concentration of carbon dioxide was highest at sunrise.

Suggest a reason for this.