1. Unit D – Living Systems Chapter 1 The biosphere of Life
Section 1.5
The Recycling of Matter

2. Ecosystem as an open system
Recall:
An open system involves the exchange of what two things?
Answer:
Energy
Matter
We have already looked at the exchange of energy
This section deals with the exchange of matter

3. Flow of energy vs. flow of matter
flows into an ecosystem from the sun
escapes from the ecosystem in the form of heat
survival of an ecosystem depends on a continual input of new energy from the sun
Matter (elements & compounds)
also moves through the trophic levels of an ecosystem
however, matter can move in either direction
 matter is recycled.

4. What’s the matter?
There are four types of matter that are cycled in an important way through an ecosystem
Two types of cycles occur
hydrologic cycle (water cycle)
the movement of water through an ecosystem
the most influential non-living component of an ecosystem

5. What’s the matter? biogeochemical cycles
the movement of elements and compounds between living and non living components
look at the roots of the word “biogeochemical”
“bio” = life
“geo” = Earth
geology is the study of the composition and physical properties of the planet
“chemical” = elements and compounds
there are three elements whose biogeochemical cycles we will look at:
carbon, nitrogen and oxygen

6. Hydrologic Cycle
natural and man-made processes recycle water through an ecosystem
sun’s energy causes water to…
evaporate from oceans and lakes
transpire from plants
when water vapour is added to the atmosphere, it increases the humidity

7. Hydrologic cycle
when water vapour enters the atmosphere, it cools and condenses
this causes it to fall as precipitation (rain or snow)
the water is absorbed by the ground and taken up by the roots of plants
plants use the water for photosynthesis

10. Hydrologic cycle Processes that use water from the atmosphere
condensation (cloud formation)
photosynthesis
Processes that add water to the atmosphere
evaporation
cellular respiration
transpiration

11. Impacts on the water cycle
There are both natural and man-made events that have a significant impact on the water cycle
wildfires
as organic matter burns, water vapour is produced
however, when a forest burns, it is no longer able to absorb and hold water
the total amount of water in that ecosystem is reduced
this affects the quality of the soil and usually prevents re-growth for about 2 years

12. Impacts on the water cycle
human impact
through industry, humans remove fresh water from the environment and return polluted, lower quality water back
this leaves less clean water to support aquatic ecosystems
deforestation (clear-cutting)
has a similar impact to a wildfire
hinders the area’s ability to regulate temperature and moisture content

13. Carbon cycle all life on Earth has carbon as its building blocks
carbon is the basis for the building blocks of living organisms:
proteins,
carbohydrates,
fats

14. Carbon cycle producers taken in CO2(g) for photosynthesis
all living organisms return CO2(g) to the atmosphere by cellular respiration
carbon is stored in various reservoirs such as
fossil fuels
animal fossils
calcium carbonate in the oceans

15. Carbon cycle carbon sink carbon source
a system that removes carbon dioxide from the atmosphere (e.g. photosynthesis)
carbon source
a system that adds carbon dioxide to the atmosphere (e.g. combustion of fossil fuels)

16. Carbon cycle sun causes plants to pull in CO2 for photosynthesis
plant and animal cells burn glucose in cellular respiration, returning the CO2 to the atmosphere
when living things die,
some carbon stored in their bodies is released by decomposers
some carbon may be trapped in fossils
see page 444 for a diagram of the carbon cycle

17. Human impact on the carbon cycle
burning fossil fuels
the combustion of coal, oil and gas
reverses millions of years of photosynthesis
increases atmospheric carbon dioxide
carbon was previously trapped in the Earth in the form of fossil fuels
increase in atmospheric CO2 is a cause of global warming and has resulted in climate change
deforestation
reduces trees that could be absorbing carbon dioxide from the atmosphere

19. Oxygen cycle processes that produce carbon dioxide take in oxygen
combustion
cellular respiration
processes that take in carbon dioxide release oxygen
photosynthesis

20. carbon / oxygen cycles Photosynthesis:
takes in carbon dioxide, produces oxygen
6CO2(g) + 6H2O(g)  C6H12O6(s) + 6O2(g)
Cellular respiration (Combustion):
takes in oxygen, produces carbon dioxide
C6H12O6(s) + 6O2(g)  6CO2(g) + 6H2O(g)

22. Human impact on the oxygen cycle
ozone layer
about 10km above the Earth’s surface is a layer of oxygen called ozone (O3(g))
when pollutants like CFCs are released into the atmosphere, they react with the oxygen in ozone
this makes the ozone layer thinner and less able to filter the sun’s UV radiation
wildfires
not only takes in oxygen as it burns
also removes oxygen-producing vegetation

24. Nitrogen cycle
nitrogen is a critical element in biological structures because it forms the basis for both protein and DNA
the atmosphere is composed of 78% nitrogen (N2(g))
notice the Bohr diagram of N2 below
the bond between N’s is a triple bond

25. Nitrogen cycle
this means that nitrogen molecules are very stable and hard to break apart
plants cannot get usable nitrogen from the atmosphere because it takes too much energy to break the triple bonds between nitrogens
instead, plants rely on bacteria to convert nitrogen gas into forms they can use
ammonia (NH3)
nitrate and nitrite ions (NO3- and NO2-)

26. Nitrogen fixation
converting nitrogen gas into usable compounds requires two steps
Nitrogen fixation
the process of bacteria converting nitrogen gas into ammonia
Nitrification
convert the ammonia into nitrate and nitrite ions that are usable for the plant
this step is done by nitrifying bacteria

27. Nitrogen cycle
By definition, a cycle must be able to return to the starting point
Denitrification
requires a third type of bacteria, denitrifying bacteria,
convert excess nitrates back into atmospheric nitrogen gas

28. Natural impacts on the nitrogen cycle
Lightning
converts nitrogen gas into nitrates
often a lawn will be noticeably greener after a lightning storm
the electricity from the lightning floods the lawn with a new supply of nitrates

29. Natural impacts on the nitrogen cycle
Wildfires
break down complex nitrogen compounds into smaller compounds like nitrates and ammonia
a wildfire has the same effect as nitrogen fixation
the heat from a fire makes the soil more livable for nitrogen fixing bacteria
plants that thrive in soils with a high nitrogen content are the first to grow back after a wildfire

31. Human impact on nitrogen cycle
fertilizers
the main ingredient in most fertilizers is nitrogen
over-reliance on fertilizers can pollute water sources
industry
some emissions from smokestacks and car exhaust also produce nitrogen compounds

32. Effect of wildfires: water carbon some water vapour is produced
burning of trees means less retention of water in the soil
carbon
combustion produces carbon dioxide (carbon source)
lack of plants to do photosynthesis (loss of a carbon sink)

33. Effect of wildfires: oxygen: nitrogen: combustion uses oxygen
lack of plants to do photosynthesis (loss of an oxygen source)
nitrogen:
dramatic increase in nitrogen levels in soil
heat breaks nitrogen compounds down into simpler molecules
soil is more viable for nitrogen fixing bacteria

34. Practice problems Page 443 #33, 35 Page 446 #37 Page 447 #39, 41
Cycles Wkst in your notes package
Decomposition video: Planet Earth, Jungles 24:00