Biogeochemical Cycles Worksheet - AP Biology

Flashcards covering water conservation, carbon cycle (including sinks and human impact), nitrogen cycle (fixation, nitrification, denitrification, symbiosis, limiting nutrients), and phosphorus cycle as described in the notes.

Why do we need to conserve water despite ¾ of Earth's surface being water?

Only about 0.78% of Earth's water is freshwater; the rest is saltwater, so freshwater is scarce.

What would happen to the carbon cycle if there were no decomposers?

Dead matter would not be decomposed, reducing cellular respiration and limiting the amount of carbon released to the atmosphere.

How does carbon enter living systems?

Through photosynthesis.

How does carbon leave living systems?

Via cellular respiration and burning fossil fuels (combustion).

What is the role of microorganisms in carbon cycling?

Decomposition of organic matter, releasing carbon back into the cycle.

List the reservoirs of carbon.

Atmosphere, fossil fuels, soils, oceans, and plant/animal biomass.

Are peat, coal, and oil considered carbon sinks, and how can they return to the cycle?

Yes, they store carbon as sinks; geological processes can return these deposits to the surface where carbon is released (oxidized) back into the cycle.

What is the effect of human activity on the amount of carbon stored in sinks?

Human activities reduce the amount of carbon stored in natural sinks.

Describe two global effects resulting from reduced carbon storage in sinks.

Global warming and ocean acidification.

What could be done to prevent or alleviate these effects?

Develop and use alternative energy sources to reduce fossil fuel emissions.

How does carbon get into the oceans?

Dissolving carbon dioxide from the atmosphere into surface waters.

Why are oceans considered carbon sinks?

They absorb CO2 from the atmosphere, storing carbon in dissolved forms.

Why is nitrogen essential to life?

Nitrogen is needed to build essential biomolecules like proteins and nucleic acids.

How do plants and animals obtain usable nitrogen?

Nitrogen-fixing bacteria convert atmospheric N2 into usable forms (ammonia/nitrates) that plants can uptake; animals obtain nitrogen by consuming plants or other organisms.

What is nitrogen fixation?

The conversion of atmospheric N2 into ammonia, a usable nitrogen form for plants.

What is nitrification?

Conversion of ammonia to nitrates that plants can take up.

What is denitrification?

Nitrates and nitrites are converted to nitrogen gas and returned to the atmosphere.

Give an example of a symbiotic relationship that helps plants with nitrogen acquisition.

Legume plants and nitrogen-fixing bacteria in root nodules; bacteria provide usable nitrogen to the plant, while the plant supplies carbohydrates.

Why is nitrogen often the most limiting nutrient for plants?

Most nitrogen is in unusable N2 gas; fixed nitrogen (ammonium/nitrate) is often in limited supply.

What is the main reservoir for nitrogen?

The atmosphere (N2 gas).

Why might farmers plough a crop of legumes into the ground rather than harvest it?

Legumes fix atmospheric nitrogen, enriching soil nitrogen for subsequent crops.

List one other method of increasing nitrogen in the soil besides adding fertilizers.

Use legume cover crops or crop rotation to enhance natural nitrogen fixation.

List the reservoirs for phosphorus.

Sedimentary rocks and soils (and marine sediments).

What is the role of microorganisms in phosphorus cycling?

They release phosphorus from organic matter back into the soil as inorganic phosphate, making it available to plants.