Chapter 7. Chapter 7: Ecosystems and Nutrient Cycling

How do important nutrients like carbon, nitrogen, and phosphorus cycle...

Interactive Study Guide
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Guiding Question 7.4

How do important nutrients like carbon, nitrogen, and phosphorus cycle through ecosystems?

Why You Should Care

As you have learned, the Earth is a closed system for matter; elements required for life travel through the biosphere in cycles. Understanding the carbon cycle is important because it relates directly to food production and global climate change. The nitrogen and phosphorous cycles are essential for plant growth, and when not functioning properly can lead to eutrophication—pollution caused by "fertilizing" bodies of water, which can cause fish kills and poisonous red tides.

Question Test Your Vocabulary

Choose the correct term for each of the following definitions:

Term Definition
rmWpVP86ek69WRC/zudbI3WGPBUneUwx2c5HiYElFUZP2OoufR3g2DP0yCH70GZRR/T0csceQQ3vPx+g4+GVGu12hTmYiSbjKVV7Lqi3nKBvo2pM4gRGmwWv3M43RtAYCJrjGj8DdbV5YuFU5L9AJwXSYb7vrDpmj5c+KIjTqQSdxYs8qZA4mNu+Y+5NZflECpwb3w== The process in which all organisms break down sugar to release its energy, using oxygen and giving off CO2 as a waste product.
sl+cOTkfbTSbv3z7Ka/fnptHVQm/WikAnB2G+BhKHBq7Fp+eEch7j34Lg83ovt3fWc53YvbhyZngq3bTXt4O63wak3ryx7c9qBmEEKqNxvsxV4LvaIuRdE9tgcJVmVMtv0fq6KU7S4vnm9s0WONqH56nBheddPy/46Ez4gCqPjXyZWgngYe0gbHEvBOr7old0OhaFQ== Movement of carbon through biotic and abiotic parts of an ecosystem. Carbon cycles via photosynthesis and cellular respiration as well as in and out of other reservoirs such as the oceans and soil. It is also released by human actions such as fossil fuel burning.
MnznlQ8ef6GN1Mpq8pTrvfa33wkHc87sg7VzyYS9uE/NZKeg3mtIseP2WaW2tDSYoSb65durdDk1rWVbegc4u9Rt9ODwqFsOmUm8sU7EAje3Lsq1YOmAO8eeBjqHQPhq6pb1MUM2k/AvxExemfAzt6aOMPEgPHc0FN5GZTVEVxcgwOUn1HsLFCWM14/Y4XFvhA73uQ== An organism that converts solar energy to chemical energy via photosynthesis.
ENu/9HNr4IWBG8QGwPehxrE8TN8WlHvvSSvIK2T5+MuqBcIJhvR7QURKdmMp3X+z9c6Y0aus9YA1nRZSKqEQNgVNhtyEHjJMLSq0iDKRJFs+8yXqIouZgFz4ro6dUUDAgzkZtVCemPHo0thLQ19kPWRGjDxbiaUrCWyjlu5LhIYPvGwDMOpgE/un2LIfLhsjJylNjw== Series of natural processes by which the nutrient phosphorus moves from rock to soil or water, to living organisms, and back to the soil.
rCBnUqI54vVsyvobA/7J2iMusmSoKfDF7U3FMPokElCvlEwCxL5eNg4tLuvfy64f1sEvA5ZVfYhtaU0v+IBnlQCHN2gWvvnxb+mSqFtJJ3X5fUHiYjbVZKFI2DROwMTNLEBsDl2UwPPrd5pXshz22O5u9SXYArKiQ2FtVoDPg7NyNOAaugWzUbvy2z+adkU0EFxIaQ== The living (organic) components of an ecosystem, such as the plants and animals and their waste (dead leaves, feces).
uHDXECrDWFfECriHXnhiuLBtMHkSyIbWLzwnKX4lBcFj85KX5htqGRWwElI/PvJx3nmGgOJKYM28cJ6dUjRO1qtbI0O8r04q0czE8FrxZPHD0DcMlq4duU/tBIjIvmat2lz3qKLil5HiWih6cBp4t2tfKxBhGRvdJuyT/Kq2hcNcZNEJRUYsQ8Kyn5dwccBA2ymOTA== Continuous series of natural processes by which nitrogen passes from the air to the soil, to organisms, and then returns back to the air or soil through decay or denitrification.
H/H7SEXATpXWubkzLMnFSEJXD0NvHRszDB1QZueU5kqFunNOkQV5B9RSx4NTG0XtiZfsOdYMHrykBA2+hDLdQxtwM1Q+M7mynsY9B6eqMuf/ooI9roRaoA4QJN7/whFZ4QfjAzTuCjmmukeKcgFIiB2M5NabXHdn9NLpeqj9xUooIihkz6+2k5VWeBDLgG+SqhgUFA== Abiotic or biotic component of the environment that serves as a storage place for cycling nutrients.
Vne8Q9UAlnHjRZoIq67dKFMVK/zf9ItN9okz0S0neRLguKIwKSE5ixS8SgkPtXL3/Pnru57taEwP2eZhGcZdoTJO85hScbjlVyNXpO3FzEKIDs7XHM0J3JZfan9P83cc3uNt21LtbaBziBcXMaxCPDzUFiv7u27PcSaynBOJW06FXpbKD2xbzqYSe3caqa88zJV0tw== An organism that obtains energy and nutrients by feeding on another organism.
NeAttSypM9jwwxPJuN5Ej5MOwhCC/nN93aGpIqZGYGIH4UQArxRsBX802TVALPTAfII3S3wQ+MXy52mePL9KFouCmHZUlz4llwFRYpY3LUIr4MS/XX8Klgd/d8AdSjcVTSJaPOgJr4AaU+nJHXbWh6rhkmXJDmiQX+7wFpSfPwRLARu9j9YVB8sq/IB9bylzrBUsIg== The nonliving components of an ecosystem, such as rainfall and mineral composition of the soil.
GlkjPdO9mGQduObtUEve7uydJI6SvVOF4Ir5goRuAikQbXMDpb+VnRZGCdbfTi2JGqHidzar/nBovnFpqBkV/th/KVcBA8bfN3TsPZqpJREHnBo9cf3LW/rx/nplBjZ24TKFQaoWqa+AQx8j7WDlMRITEGcLqSX8EfLOTeQqb+tSjTzZvryRXYROLdTYfcd3I+sNaw== Conversion of atmospheric nitrogen into a biologically usable form, carried out by bacteria found in soil or via lightning.
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Infographic 7.7 Animation

Question 7.1

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Question 7.2

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Question 7.3

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Question 7.4

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Infographic 7.7: Carbon Cycles Via Photosynthesis and Cellular Respiration
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Question 7.5

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Infographic 7.7: Carbon Cycles Via Photosynthesis and Cellular Respiration
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Question 7.6

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Infographic 7.7: Carbon Cycles Via Photosynthesis and Cellular Respiration
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Question 7.7

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Infographic 7.7: Carbon Cycles Via Photosynthesis and Cellular Respiration
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Question 7.8

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The answer is no. Plants do take up CO2 to make carbohydrates and release oxygen by photosynthesis, but they also need to break down those carbohydrates, using oxygen and releasing CO2 by cellular respiration.

Question 7.9

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It's called the carbon cycle because carbon, in the form of carbon dioxide, is moved from the atmosphere into organisms, initially as sugars, but then as many different kinds of molecules, through photosynthesis. It is then released back to the atmosphere as carbon dioxide when sugars and other molecules are broken down to produce energy through cellular respiration.

Question 7.10

Choose whether "releasing" or "taking up" carbon dioxide is correct for each of the following:

  • Photosynthesis in plants YJInoU3XqQwqFs7hiSFdUvqpfoAxsU1oUKS+Pw==
  • Cellular respiration in plants S+mcF+WGc123WlK1X6acxvR3bGdoBqmd
  • Decomposition of animal bodies TbgufEkYWX9akJu6Tgm2ckw8+YyoAuRD3L93aw==
  • Utilizing prey as a source of energy TbgufEkYWX9akJu6Tgm2ckw8+YyoAuRD3L93aw==
  • Burning fossil fuels TbgufEkYWX9akJu6Tgm2ckw8+YyoAuRD3L93aw==
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Question 7.11

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Carbon that is in the body of trees is normally kept out of the atmosphere for a long time: until the tree dies and decomposes. Therefore, long-lived plants can be an important "sink," or storage medium, for carbon. Burning trees produces a net gain in carbon dioxide in the atmosphere because the carbon is released more quickly than by cellular respiration and because the plants that would normally take it back up have been destroyed.

Question 7.12

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In most ecosystems, the order would be decomposers, consumers, plants. Is this surprising? Although decomposing microbes are microscopic, collectively, there is a greater mass of them than consumers in most ecosystems, so they contribute the most CO2. In fact, in areas where the soil is mostly organic material instead of minerals, the soil can literally be lost to the atmosphere over a period of years if whatever keeps the microbes in check is removed (examples include melting permafrost in the Arctic tundra and drained swampland in the Everglades).

Since plants also take up carbon dioxide for photosynthesis, they usually contribute little, if any, net CO2 back to the atmosphere.
Infographic 7.10 Interactive

Question 7.13

Remember, it's best to try to do review questions without the help of your text the first time.

Which of the following are forms of nitrogen that plants can use as a nutrient? (Check all that apply.)

Molecular nitrogen (N2) s87TBEH0BM9yDZCI

Ammonia (NH3) 9PufMCe/gaVcshPB

Amonium (NH4+) 9PufMCe/gaVcshPB

Nitrate (NH3-) 9PufMCe/gaVcshPB

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Question 7.14

Which of the following are sources of nitrogen that are usable by plants? (Check all that apply.)

Lightning 9PufMCe/gaVcshPB

Decomposition 9PufMCe/gaVcshPB

Nitrogen fixation 9PufMCe/gaVcshPB

Denitrification s87TBEH0BM9yDZCI

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Question 7.15

Which of the following processes convert organic nitrogen from animal and plant matter back to ammonium (NH4+), a form that is usable by plants? (Check all that apply.)

Denitrification s87TBEH0BM9yDZCI

Nitrogen fixation s87TBEH0BM9yDZCI

Decomposition 9PufMCe/gaVcshPB

Nitrification s87TBEH0BM9yDZCI

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Question 7.16

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Obviously, nitrogen does not enter organisms until it is fixed by microbes, so there is a case for this being the starting point. But nitrogen doesn't really enter the food web in appreciable amounts until it is taken up by producers, so the case could also be made for producers being the start.
Infographic 7.11: The Phosphorus Cycle

Question 7.17

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Question 7.18

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Question 7.19

Which of the following are ways in which phosphorous enters ecosystems in a form that is usable by plants? (Check all that apply.)

Phosphorylation s87TBEH0BM9yDZCI

Decomposition 9PufMCe/gaVcshPB

Weathering of rocks 9PufMCe/gaVcshPB

Consumption s87TBEH0BM9yDZCI

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Question 7.20

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• In both cycles, decomposition releases the element for re-uptake by plants.

• The main source of nitrogen is the atmosphere; the main source of phosphorous is phosphate-containing rock.

• Abiotic nitrogen enters the ecosystem through nitrogen fixation; abiotic phosphate enters the ecosystem dissolved in water from weathered rock.

• Soil microbes play a large role in both cycles.