Deduce factors influencing soil air, compare soil and atmospheric gases, explain porosity/bulk density relationships, and identify gases in experiments.

1.1.1 Deduce TWO factors that influence storage and movement of soil air from the scenario above.

• Water content (volume of soil not occupied by liquid)
• Porosity (total porosity / condition of soil affecting diffusion)

1.1.2 Compare the levels of gases mentioned in the scenario above with those in the atmosphere.
In soil air, the level of oxygen is generally lower than in the atmosphere, especially in lower horizons due to poor diffusion. The level of carbon dioxide in soil air is generally higher than in the atmosphere.

1.1.3 Explain the relationship between porosity and bulk density.
Porosity and bulk density are inversely related. Higher porosity (more pore space) means there is less solid material per unit volume, resulting in a lower bulk density. Conversely, lower porosity leads to higher bulk density.

1.2 A soil scientist conducted an experiment to test the influence of soil gas in plants.

1.2.1 Indicate the gas that is deficient in experiment No.1.

• Oxygen

1.2.2 Explain the role that the gas mentioned in QUESTION 1.2.1 could have played if it was not deficient.
Oxygen is essential for root respiration, which provides energy for the roots to absorb water and nutrients, and for overall plant growth.

1.2.3 Name the gas that is high in soil as a result of activities in experiment No 2.

• Carbon dioxide

1.2.4 Explain the reason for the high amount of gas mentioned in QUESTION 1.2.3.
The high amount of carbon dioxide in experiment No. 2 is due to root respiration from the well-rooted plants and the decomposition of organic matter by microorganisms, both of which release $\text{CO}_2$ into the soil.