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

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

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.

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

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

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

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

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

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

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

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

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

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)

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

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

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

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)

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

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

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-)

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

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

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

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

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

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)

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

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