Nutrient cycles：练习题

Besides carbon dioxide, which of the following gases is a significant contributor to the greenhouse effect and is often released through agricultural activities such as rice cultivation and cattle farming?

Which statement correctly describes the role of Rhizobium bacteria in the nitrogen cycle?

The graph shows atmospheric carbon dioxide concentrations measured over a period of five years. There is a clear upward trend with smaller annual fluctuations. What is the most likely biological explanation for the decrease in \(CO_2\) concentration observed during the summer months in the Northern Hemisphere?

Which process in the nitrogen cycle involves the conversion of nitrogen-containing compounds from dead organisms into ammonium ions by saprobionts?

Saprobionts play a vital role in nutrient recycling. How do these microorganisms typically obtain nutrients from dead organic matter?

Identify two greenhouse gases mentioned in the carbon cycle that contribute to global climate change and are influenced by human activity.

Explain why nitrogen gas \( (N_{2}) \) in the atmosphere is chemically unavailable to most producers and identify the specific enzyme used by nitrogen-fixing bacteria to convert it into a usable form.

During eutrophication, explain why the rapid growth of algae on the surface of a lake leads to the death of plants growing on the lake bed.

Fertilisers are used to ensure that crop growth is not limited by nutrient availability.
a) Explain why a high concentration of nitrate ions \( (NO_3^-) \) in the soil can cause water to leave the roots of a plant by osmosis.
b) Explain why the leaching of nutrients is generally more severe in sandy soils than in soils with a high clay content.
c) Identify one form of natural organic fertiliser and explain why it must be broken down by saprobionts before its nitrogen can be used by crops.<\/p>

The nitrogen cycle involves various groups of bacteria that convert nitrogen into different chemical forms.
a) Describe the process of nitrification and identify the environmental conditions that allow this process to occur at an optimal rate.
b) A farmer finds that his soil has become heavily waterlogged after a period of flooding. Explain the likely effect of these conditions on the nitrate concentration of the soil, referring to the specific biological process involved.