Biogeochemical Practice

Which statement about the cycling of materials through a stable ecosystem is true?

• Certain species of bacteria are responsible for cycling nitrogen from the atmosphere to plants.
• Carbon dioxide is continuously cycled through a stable ecosystem, but only bacteria can convert it to a usable form.
• Radiant energy and heat are continuously recycled from animals to plants.
• Water and energy are the only materials in an ecosystem that cannot be recycled.

If the decomposers were removed from the food web, which process for maintaining balance in an ecosystem would be altered first?

• maintenance of atmospheric quality
• maintenance of the hydrologic cycle
• generation of soils
• recycling of nutrients

Plants use several abiotic factors for the formation of leaves, stems, flowers, and fruits. How are the abiotic factors utilized by a plant eventually returned to the environment?

• Plant parts are eaten by animals to form energy molecules.
• Dead parts of the plant fall to the ground and are decomposed.
• Plants release heat and light through tiny pores in their leaves.
• Plant roots grow deep into the soil to absorb nutrients and water.

The image shows a model of the nitrogen cycle. How will the cycle be impacted if nitrogen-fixing bacteria are removed?

• Organisms will adapt to survive without nitrogen.
• Plants will lack nitrogen, which will harm the plants.
• Denitrification bacteria will grow in number.
• Plants will absorb nitrogen from the atmosphere.

How can the overuse of pesticides for farming practices impact the environment?

• Excess pesticides can decrease the amounts of crops harvested each year.
• Excess pesticides can increase the amount of carbon dioxide in the atmosphere.
• Excess pesticides can result in mass migrations of insects from farms to cities.
• Excess pesticides can contaminate nearby water sources.

The model shows the water cycle. Which process directly reduces water levels in plants?

• Condensation
• Precipitation
• Runoff
• Transpiration

A diagram outlining the phosphorus cycle in an ecosystem is shown. If the amount of phosphates present in water increased, what would be the most direct effect on the ecosystem?

• It will result in a decrease of phosphates in animal tissues and wastes.
• It will result in a decrease in the weathering of rocks.
• It will result in an increase in the rate of decomposition by bacteria and fungi.
• It will result in an increase in the incorporation of phosphates into sedimentary rocks.