Lecture Two

What are biogeochemical cycles?

Biogeochemical cycles are processes through which matter moves from organism to organism and between living organisms and the abiotic environment.

What are nutrient cycles?

Nutrient cycles are another name for biogeochemical cycles.

What does “bio” mean in biogeochemical?

“Bio” means life.

What does “geo” mean in biogeochemical?

“Geo” means earth.

What is a nutrient?

A nutrient is a substance that an organism needs to live, grow, and reproduce.

What are the two types of nutrients?

Macronutrients and micronutrients.

What are macronutrients?

Macronutrients are nutrients needed by organisms in large quantities.

What are examples of macronutrients?

Carbohydrates, proteins, and fats.

What do macronutrients provide?

Macronutrients provide energy or calories.

What are micronutrients?

Micronutrients are nutrients needed by organisms in smaller amounts.

What are examples of micronutrients?

Vitamins such as C and K and minerals such as iron and zinc.

What are the four major biogeochemical cycles?

Carbon, nitrogen, phosphorus, and water cycles.

What is the carbon cycle?

The carbon cycle is the movement of carbon through living organisms, the atmosphere, oceans, rocks, and other parts of Earth.

Why is carbon important to living organisms?

Carbon is a basic building block of carbohydrates, fats, proteins, and nucleic acids such as DNA.

What is the main source of carbon for living organisms?

Atmospheric carbon dioxide or carbon dioxide dissolved in surface water.

What is the largest carbon reservoir?

Earth’s rocks are the largest carbon reservoir.

What are other major carbon reservoirs?

Fossil fuels and ocean beds.

What is photosynthesis in the carbon cycle?

Photosynthesis is the process by which plants use carbon dioxide to make carbohydrates.

What natural process removes carbon dioxide from the environment?

Photosynthesis.

How does carbon move from plants to animals?

Animals obtain carbon by consuming plants or other organisms.

How does respiration affect the carbon cycle?

Respiration returns carbon to the atmosphere as carbon dioxide.

How does decomposition affect the carbon cycle?

Decomposition returns carbon to the atmosphere.

How does combustion affect the carbon cycle?

Burning coal, oil, natural gas, and wood releases carbon back into the atmosphere.

What is diffusion in the carbon cycle?

Diffusion moves carbon between the atmosphere and oceans.

What happens during burial and compaction in the carbon cycle?

Carbon deposited on land or in oceans can become buried and compacted over long periods, forming materials such as limestone, coal, and oil.

How is limestone formed in the carbon cycle?

Shells and coral in shallow coastal waters can form limestone, which is calcium carbonate.

How is coal formed?

Buried plant matter is compacted by soil and pressure over millions of years to form coal.

How is oil formed?

Buried and compacted animal material in oceans can form oil.

What human activities affect the carbon cycle?

Deforestation, clearing grasslands and green areas, and burning fossil fuels and wood.

How does deforestation affect atmospheric carbon dioxide?

It reduces the amount of vegetation available to absorb carbon dioxide.

How does burning fossil fuels affect the carbon cycle?

It adds excess carbon dioxide to the atmosphere.

How do human activities contribute to global warming?

They add excess carbon dioxide to the atmosphere, contributing to global warming.

How can replanting trees help the carbon cycle?

Trees absorb carbon dioxide through photosynthesis.

How can renewable energy help reduce carbon-cycle problems?

Solar, wind, and hydropower reduce the amount of carbon dioxide released from burning fossil fuels.

Why is nitrogen important to organisms?

Nitrogen is an essential component of proteins and nucleic acids.

What percentage of the atmosphere is nitrogen gas?

About 78%.

Why is atmospheric nitrogen difficult for organisms to use?

Nitrogen gas (N₂) is very stable and does not readily combine with other elements.

How many major steps are in the nitrogen cycle?

Five.

What are the five major steps of the nitrogen cycle?

Nitrogen fixation, nitrification, assimilation, ammonification, and denitrification.

What is nitrogen fixation?

Nitrogen fixation converts atmospheric nitrogen gas (N₂) into ammonia (NH₃), with some ammonia becoming ammonium (NH₄⁺).

How can nitrogen fixation occur?

It can occur through combustion, volcanic action, lightning, and biological activity.

What organisms carry out most biological nitrogen fixation?

Nitrogen-fixing bacteria.

Where are nitrogen-fixing bacteria found?

In soil and aquatic environments.

What is nitrification?

Nitrification converts ammonium (NH₄⁺) and ammonia (NH₃) into nitrate (NO₃⁻).

What organisms carry out nitrification?

Soil bacteria.

Why is nitrate important to plants?

Nitrate can be readily absorbed by plant roots.

What is assimilation in the nitrogen cycle?

Assimilation occurs when plant roots absorb nitrate or ammonia and incorporate nitrogen into proteins and nucleic acids.

What is ammonification?

Ammonification converts biological nitrogen compounds into ammonia.

When does ammonification occur?

It occurs when plants and animals return nitrogen compounds as waste or when organisms die and decompose.

What bacteria carry out ammonification?

Ammonifying bacteria.

What happens to ammonia after ammonification?

Ammonia can re-enter the nitrogen cycle at the nitrification stage.

What is denitrification?

Denitrification returns nitrogen gas to the atmosphere through the action of denitrifying bacteria.

What organisms carry out denitrification?

Denitrifying bacteria.

What is the overall role of denitrification?

It reverses the actions of nitrogen-fixing and nitrifying bacteria by returning nitrogen to the atmosphere.

How do humans affect the nitrogen cycle?

Through excessive use of nitrogen-based fertilizers and release of nitrogenous gases from burning fossil fuels.

What can excessive nitrogen and phosphorus cause?

Eutrophication.

What is eutrophication?

Eutrophication is the over-nourishment of aquatic ecosystems with plant nutrients, mainly nitrates and phosphates.

What are sources of nutrients that cause eutrophication?

Agriculture, urbanization, industrial discharges, and sewage-treatment discharges.

How can organic fertilizers reduce nitrogen pollution?

Animal manure, green manure, and compost release nutrients more slowly because decomposition is required.

Why can organic fertilizers reduce nutrient washout?

The slower release of nutrients reduces the amount washed into aquatic ecosystems by rain.

How can renewable energy help the nitrogen cycle?

Solar, wind, and hydropower reduce nitrogen oxides produced by burning fossil fuels.

Why is phosphorus important?

Phosphorus is an essential nutrient for plant and animal growth and is used in bones, teeth, and plant and animal membranes.

Is phosphorus renewable or non-renewable?

Phosphorus is a non-renewable resource.

Why must phosphorus be used efficiently?

Because phosphorus is a non-renewable resource.

Does phosphorus have a biologically important gaseous form?

No, phosphorus has no biologically important gaseous compounds.

What is weathering in the phosphorus cycle?

Weathering breaks inorganic phosphate rocks into fragments.

What is erosion in the phosphorus cycle?

Erosion is the movement of phosphate-containing particles by ice, water, wind, or animals.

What is runoff in the phosphorus cycle?

Runoff is water moving over land into surface water bodies, carrying soil and dissolved phosphorus.

What is absorption in the phosphorus cycle?

Absorption occurs when organisms absorb or ingest inorganic phosphates.

What is assimilation in the phosphorus cycle?

Assimilation is the incorporation of phosphorus into cellular components.

What is consumption in the phosphorus cycle?

Consumption transfers phosphorus to other organisms through the food web.

What is decomposition in the phosphorus cycle?

Decomposers release phosphorus as inorganic phosphate when organisms die.

What is leaching?

Leaching is the removal of a solute by a liquid, usually water, passing through soil.

How do humans disrupt the phosphorus cycle?

Through excessive mining of phosphate rocks for fertilizers and detergents and through transporting food away from farms.

How can transporting food from farms to cities affect phosphorus?

Phosphorus can be lost as effluent or sewage in cities.

How can excessive phosphorus fertilizer cause eutrophication?

Excess inorganic phosphorus can enter aquatic ecosystems and over-nourish them.

How can organic fertilizers help reduce phosphorus pollution?

They release nutrients more slowly and can reduce nutrient loss.

How can composting help the phosphorus cycle?

Composting helps keep phosphates in the local area.

How can consuming locally produced food help the phosphorus cycle?

It helps keep phosphates near their original source.

How does exporting food crops affect phosphorus?

It moves phosphates away from the area where they originated.

How can lost phosphorus nutrients be replaced?

The notes state that importing fertilizers is the way to regain nutrients that have been lost through food export.

Why can the phosphorus cycle be considered a “dead end”?

Phosphorus can be moved away from its original location through processes such as food export, and there is no major atmospheric reservoir to easily return it.

What is the hydrological cycle?

The hydrological or water cycle is the continuous movement of water between the ocean, atmosphere, and land.

What percentage of Earth’s water is available as liquid freshwater?

About 0.024%.

Why is most of Earth’s water unavailable as accessible freshwater?

Most water is too salty, stored as ice in glaciers and icebergs, or too deep underground to extract affordably.

Why is the hydrological cycle important?

It provides a renewable supply of purified water on land.

What is precipitation?

Precipitation is water moving from the atmosphere to land or oceans as rain, snow, sleet, or hail.

What are the four forms of precipitation?

Rain, snow, sleet, and hail.

What is evaporation?

Evaporation is the process in which water from oceans, soil, streams, rivers, and lakes enters the atmosphere as water vapor.

What is transpiration?

Transpiration is the loss of water from plants through stomata, or pores, contributing to cloud formation.

What is evapotranspiration?

Evapotranspiration is the combined process of evaporation and transpiration.

What is condensation?

Condensation is the process in which water vapor changes into liquid water.

What is infiltration?

Infiltration is the movement of water into the soil.

What is percolation?

Percolation is the downward movement of water through soil and rock to become groundwater.

What are aquifers?

Aquifers are underground areas that store groundwater.

What is runoff?

Runoff is water that does not evaporate or infiltrate and instead flows over land into rivers and streams.

What is a watershed?

A watershed is an area of land drained by runoff.

What is sublimation?

Sublimation is the movement of water directly from a solid to a gas without passing through the liquid state.

How do humans affect the hydrological cycle?

By withdrawing freshwater faster than it can be replaced and by clearing vegetation.

How can human activities slow or stop parts of the water cycle?

Water withdrawals, vegetation clearing, buildings, concrete, and pavement can interfere with natural water movement.