¨ More than 95 percent of the body is made up of just four elements: oxygen, carbon, hydrogen, and nitrogen.
Recycling in the Biosphere
¨ Matter is recycled within and between ecosystems.
¨ Elements, chemical compounds and matter are passed from one organism
to another through biogeochemical cycles.
¨ Biogeochemical cycles connect biological,
geological, and chemical aspects of
the biosphere.
¨ Matter can cycle through the biosphere because biological systems
do not use up matter, they transform it.
¨ Biogeochemcial cycles pass the same molecules around again and again
within the biosphere.
The Water Cycle
¨ Water moves between the ocean, atmosphere, and land.
¨ How does this cycle work?
1. Water molecules enter the atmosphere as water vapor when they evaporate from the ocean or
other bodies of water.
¨ Evaporation is the process by which water changes
from liquid form to atmospheric gas.
¨ Transpiration is water evaporating from the leaves of plants.
2. During the day, the sun heats the atmosphere and as warm, moist air rises, it cools.
3. The water vapor condenses to form clouds and water returns to Earth in the form of precipitation—rain,
snow, sleet, or hail.
4. On land, the precipitation runs along the surface of the ground and enters a river or stream
that carries the runoff back to an ocean or lake.
5. Rain seeps into the soil and becomes ground water.
6. Water in the soil enters plants through the roots, and the water cycle begins again.
Nutrient Cycles
¨ Nutrients are all the chemical substances that an organism needs to
sustain life.
¨ Like water, nutrients are passed between organisms and the environment
through biogeochemical cycles.
¨ The three cycles especially important are:
1. carbon cycle
2. nitrogen cycle
3. phosphorus cycle
¨ Oxygen participates in all these cycles by combining with these
elements and cycling with them during various parts of their journey.
The Carbon Cycle
¨ Carbon is a key ingredient of living tissue.
¨ Four main types of processes move carbon through its cycle:
A. Biological processes – photosynthesis, respiration
and
decomposition, take up and release carbon and oxygen.
B. Geochemical processes – erosion and volcanic activity, release carbon dioxide
into the atmosphere and oceans.
C. Mixed biogeochemical processes – burial and decomposition of dead organisms
and their conversion under pressure into coal and petroleum, store carbon underground.
D. Human activities – mining, cutting and burning forests, and burning fossil
fuels, release carbon dioxide into the atmosphere.
¨ How does this cycle work?
1. In the atmosphere, carbon is present as carbon
dioxide
gas. Carbon dioxide is released into the atmosphere by volcanic activity, respiration,
burning fossil fuels and decomposition of organic matter.
2. Plants take in carbon dioxide and use the carbon
to build carbohydrates during photosynthesis.
3. The carbohydrates are passed along food webs to
animals and other consumers.
4. In
the oceans, carbon is found along with calcium
and
oxygen, in calcium carbonate, which is formed
by marine
organisms. It accumulates in marine sediments and in the bones and shells of organisms.
5.
Eventually these compounds break down and the
carbon
returns to the atmosphere.
The Nitrogen Cycle
¨ All organisms require nitrogen to make amino acids, which are used
to build proteins.
¨ Nitrogen can be found in many different forms:
a) nitrogen gas (N2) which makes up 78% of the Earth’s atmosphere
b) ammonia (NH3), nitrate ions (NO3-), nitrite ions (NO2-)
found in waste products and in dead and decaying organic matter
c) plant fertilizers
¨ How does this cycle work?
1. Bacteria, which live in the soil and on plant roots called legumes, convert nitrogen gas
into ammonia in a process known as nitrogen fixation. Other bacteria in the soil convert ammonia into nitrites and nitrates.
2. Producers can use them to make proteins.
3. Consumers then eat the producers and reuse the nitrogen to make their own proteins.
4. When organisms die, decomposers return nitrogen to the soil as ammonia.
5. The ammonia may be taken up again by producers.
6. Other soil bacteria convert nitrates into nitrogen gas in a process called denitrification.
7. By this process nitrogen is released into the atmosphere again.
The Phosphorus Cycle
¨ Phosphorus is important to living organisms because it forms part
of DNA and RNA.
¨ It is not very common in the biosphere and remains mostly on land
in rock and soil minerals, and in ocean sediments.
¨ Phosphorus exists in the form of inorganic phosphate and as the
rocks wear down, phosphate washes into rivers and streams where it dissolves and then eventually makes it way to the oceans.
¨ How does this cycle work?
1. The phosphate that stays on land cycles between
organisms and the soil.
2. Plants absorb phosphate from the soil or from water and bind the phosphate into organic
compounds.
3. Organic phosphate moves through the food web, from producers to consumers, and to the rest
of the ecosystem.
Nutrient Limitation
¨ Primary productivity is the rate at which organic matter is created by producers.
¨ The amount of available nutrients controls the primary productivity
of an ecosystem.
¨ If a nutrient is in short supply, it will limit an organism’s
growth.
¨ A limiting nutrient is a single nutrient that is scarce or cycles very slowly.
¨ Farmers apply fertilizers to their crops to boost their productivity.
¨ Fertilizers contain three important nutrients:
Ø nitrogen
Ø phosphorus
Ø potassium
¨ These nutrients help plants grow larger and more quickly.
¨ Areas where limiting nutrient occur:
v open oceans – nitrogen
v oceans – iron and silica
v streams, lakes and freshwater environments – phosphorus
¨ When an aquatic system receives a large amount of a limiting factor
– runoff from a heavily fertilized field – an immediate increase in the amount of algae and other producers occurs
resulting in an algal
bloom.
¨ The producers grow and reproduce quickly and if there are not enough
consumers to eat the excess algae, the surface of the water may become covered with algae.
