energy flow and energy loss in ecosystems: food...

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(c) McGraw Hill Ryerson 2007

2.1 Energy Flow in Ecosystems

• Biomass is the total mass of all living things in a given area.Biomass can also refer to the mass of a particular type of matter, such as organic materials used to produce biofuels.Biomass is generally measured in g/m2 or kg/m2 .

• Within an organism’s niche, the organism interacts with the ecosystem by:1. Obtaining food from the ecosystem2. Contributing energy to the ecosystemPlants are called producers because they produce carbohydrates from carbon dioxide, water, and the Sun’s energy.Consumers get their energy by feeding on producers or otherconsumers.Decomposition is the breakdown of wastes and dead organisms by organisms called decomposers through the process of biodegradation.

See pages 56 - 59

Bees are consumers.


Energy Flow and Energy Loss in Ecosystems:Food Chains

• Scientists use different methods to represent energy moving through ecosystems.

Food chainsFood websFood pyramids

• Food chains show the flow ofenergy in an ecosystem.

• Each step in a food chain is a trophic level

Producers = 1st trophic levelPrimary consumers = 2nd trophic levelSecondary consumers = 3rd trophic levelTertiary consumers = 4th trophic level

See pages 59 - 60

Examples of terrestrial and aquatic food chains


Energy Flow and Energy Loss in Ecosystems:Food Chains (continued)

• Consumers in a food chain can be classified as:1. Detrivores – consumers that obtain energy and nutrients from dead organisms and

waste matterExamples include earthworms, bacteria and fungi.Detrivores feed at every trophic level.Detrivores have their own, separate food chains and are very numerous.

2. Herbivores – primary consumersHerbivores eat plants (producers) only.

3. Carnivores – secondary or tertiary consumersSecondary consumers eat non-producers, such as herbivores.Tertiary consumers eat secondary consumers.

Also called top consumers or top carnivores.4. Omnivores – consumers that eat both plants and animals

Examples include humans and bears.See page 61

This dung beetle is a detrivore.


Energy Flow and Energy Loss in Ecosystems:Food Webs

• Most organisms are part of many food chains.Food webs represent interconnected food chains.Food webs are models of the feeding relationships in an ecosystem.Arrows in a food web represent the flow of energy and nutrients.Following the arrows leads to the top carnivore(s).

See page 62

This food web represents a

terrestrial ecosystem that

could be found in British Columbia.


Energy Flow and Energy Loss in Ecosystems:Food Pyramids

See page 63

• Food pyramids show the changes in available energy from one trophic level to another in a food chain.

Energy enters at the first trophic level (producers), where there is a large amount of biomass and therefore much energy.It takes large quantities of organisms in one trophic level to meet the energy needs of the next trophic level.

Each level loses large amounts of the energy it gathers through basic processes of living.80 – 90 percent of energy taken in by consumers is used in chemical reactions in the body and is lost as thermal energy.There is very little energy left over for growth or increase in biomass.

Ninety percent of this mouse’s food energy is used to maintain its life functions.


Energy Flow and Energy Loss in Ecosystems:Food Pyramids (continued)

See pages 63 - 64

• Food pyramids are also known as ecological pyramids.Ecological pyramids may show biomass, population, or energy numbers.The amount of life an ecosystem can contain is based on the bottom level of the ecological pyramid, where producers capture energy from the Sun.Each level in the energy pyramid = a loss of 90 percent of total energy available.

Lower trophic levels have much larger populations than upper levels.This shows the importance of maintaining large, biodiversepopulations at the lowest levels of the food pyramid.

Take the Section 2.1 Quiz

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2.2 Nutrient Cycles in Ecosystems

• Nutrients are chemicals required for growth and other life processes.Nutrients move through the biosphere in nutrient cycles or exchanges.Nutrients often accumulate in areas called stores.Without interference, generally the amount of nutrients flowing into a store equals the amount of nutrients flowing out.

• Human activities can upset the natural balance of nutrient cycles.Land clearing, agriculture, urban expansion, mining, industry, and motorized transportation can all increase the levels of nutrients more quickly than the stores can absorb them.Excess nutrients in the biosphere can have unexpected consequences.

• There are five chemical elements required for life.Carbon, hydrogen, oxygen, and nitrogen cycle between living things and the atmosphere.Phosphorus cycles in from sedimentary rock.

See pages 68 - 70


Nutrient Cycles:The Carbon Cycle

• Carbon atoms are a fundamental unit in cells of all living things.Carbon is also an essential part of chemical processes that sustain life.

• Carbon can be stored in many different locations.Short-term shortage is found in aquatic and terrestrial organisms, in CO2 in the atmosphere and in the top layers of the ocean.Long-term storage is found in middle and lower ocean layers as dissolved CO2 and in coal, oil, and gas deposits in land and ocean sediments.

• Sedimentation traps many long-term stores of carbon.Layers of soil and decomposing organic matter become buried on land and under the oceans.

Slowly, under great pressure over many years, coal, oil, and gas form.Layers of shells also are deposited in sediments on the ocean floor, forming carbonate rocks like limestone over long periods of time.

• Carbon stores are also known as carbon sinks.

See pages 71 - 72


Nutrient Cycles:The Carbon Cycle (continued)

• Carbon is cycled through ecosystems in a variety of ways.Photosynthesis: energy from the sun allows CO2 and H2O to react

6CO2 + 6H2O + sunlight → C6H12O6 + 6O2Carbon in the atmosphere is transformed by plants into carbohydrates.Photosynthesis also occurs in cyanobacteria and algae in oceans.

Cellular respiration: carbohydrates release energy in consumersC6H12O6 + O2 → 6CO2 + 6H2O + energyThe energy released is used for growth, repair, and other life processes.

Decomposition: decomposers break down large quantities of celluloseCellulose is a carbohydrate most other organisms cannot break down.

Ocean processes: CO2 dissolves in cold, northern waters and sinksOcean currents flow to the tropics where the water rises and releases CO2.This process is called ocean mixing.

Eruptions and fires – volcanic eruptions can release CO2.Forest fires also release CO2. See pages 73 - 76



See page 76

The Carbon Cycle



• Many human activities can influence the carbon cycle.Since the start of the Industrial Revolution (160 years ago), CO2 levels have increased by 30 percent due to the increased burning of fossil fuels.

The increase in CO2 levels in the previous 160 000 years was 1 - 3 percentCarbon is being removed from long-term storage more quickly than it naturally would as we mine coal and drill for oil and gas.CO2 is also a greenhouse gas, which absorbs heat in the atmosphere.

Clearing land for agriculture and urban development reduces plants that can absorb and convert CO2.

Farmed land does not remove as much CO2 as natural vegetation does.

See page 77

Clearing Land for

Agriculture

Urban

Expansion


Nutrient Cycles:The Nitrogen Cycle

• Nitrogen is very important in the structure of DNA and proteins.In animals, proteins are vital for muscle function.In plants, nitrogen is important for growth.

• The largest store of nitrogen is in the atmosphere in the form N2.

Approximately 78 percent of Earth’s atmosphere is N2 gas.Nitrogen is also stored in oceans, and as organic matter in soil.Smaller nitrogen stores are found in terrestrial ecosystems and waterways.

• Nitrogen is cycled through processes involving plants.1. Nitrogen fixation2. Nitrification3. Uptake

See page 78

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Nutrient Cycles:The Nitrogen Cycle (continued)

• Nitrogen fixation is the conversion of N2 gas into compounds containing nitrate (NO3

–) and ammonium (NH4+).

Both nitrate and ammonium compounds are usable by plants.Nitrogen fixation occurs in one of three ways.1. In the atmosphere – lightning provides the energy for N2 gas to react with

O2 gas to form nitrate and ammonium ions.Compounds formed by these ions then enter the soil via precipitation.This provides only a small amount of nitrogen fixation.

2. In the soil – nitrogen-fixing bacteria like Rhizobium convert N2 gas into ammonium ions

These bacteria grow on the root nodules of legumes like peas.The plants provide sugars, while bacteria provide nitrogen ions.

3. In the water – some cyanobacteria convert N2 into ammonium during the process of photosynthesis.

See pages 78 - 79



• Nitrification occurs when certain soil bacteria convert ammonium.Ammonium is converted into nitrates (NO3

–) by nitrifying bacteria.Ammonium is converted to nitrite (NO2

–), which is then converted to nitrate.• Nitrates enter plant roots through the process of uptake.

These nitrogen compounds compose plant proteins.Herbivores then eat plants and use nitrogen for DNA and protein synthesis.

• Nitrogen is returned to the atmosphere via denitrification.

Nitrates are converted back to N2by denitrifying bacteria.N2 is also returned to the atmosphere through volcanic eruptions.

See page 80Nitrification



See page 81

• Excess nitrogen dissolves in water, enters the waterways, and washes into lakes and oceans. The nitrogen

compoundseventually becometrapped insedimentary rocksand will not bereleased againuntil the rocksundergo hundredsof years ofweathering.



• Human activities can also affect the nitrogen cycle.Due to human activities, the amount of nitrogen in the ecosystem has doubled in the last 50 years.Burning fossil fuels and treating sewage releases nitrogen oxide (NO) and nitrogen dioxide (NO2).

Burning also releases nitrogen compounds that increase acid precipitation in the form of nitric acid (HNO3).

Agricultural practices often use large amounts of nitrogen-containing fertilizers.

Excess nitrogen is washed away, or leaches, into the waterways.• This promotes huge growth in aquatic algae called algae blooms.• Algae blooms use up all CO2 and O2

and block sunlight, killing many aquatic organisms.• Algae blooms can also produce neurotoxins that poison animals.

See pages 82 - 83

Acid rain damaged these trees


Nutrient Cycles:The Phosphorous Cycle

• Phosphorus is essential for life processes in plants and animals.Phosphorus is a part of the molecule that carries energy in living cells.Phosphorus promotes root growth, stem strength, and seed production.In animals, phosphorous and calcium are important for strong bones.

• Phosphorus is not stored in the atmosphere.Instead, it is trapped in phosphates (PO4

3–, HPO42–, H2PO4

–) found in rocks and in the sediments on the ocean floor.

• Weathering releases these phosphates from rocks.Chemical weathering, via acid precipitation or lichens, releases phosphates.Physical weathering, including wind, water and freezing, releases phosphates.Phosphates are then absorbed by plants, which are then eaten by animals.Weathering does not occur until there is geologic uplift, exposing the rock to chemical and physical weathering.

See pages 83 - 84


Nutrient Cycles:The Phosphorous Cycle (continued)

• Humans add excess phosphorus to the environment through mining for fertilizer components.

Extra phosphorus, often along with potassium, then enters the ecosystems faster than methods can replenish the natural stores.

See page 85

• Humans can also reduce phosphorus supplies.

Slash-and-burning of forests removes phosphorus from trees, and it then is deposited as ash in waterways.

The Phosphorus Cycle

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How Changes in Nutrient Cycles Affect Biodiversity

See pages 86 - 87

• Any significant changes to any of these nutrients (C, H, O, N, or P) can greatly affect biodiversity.

Carbon cycle changes contribute to climate change and global warming.

Slight temperature fluctuations and changes in water levels can drastically change ecosystems.Changes influence other organism in the food webs.

Increased levels of nitrogen can allow certain plant species to outcompete other species, decreasing resources for every species in the food webs.Decreased levels of phosphorus can inhibit the growth of algae that are very important producers in many food chains.

Take the Section 2.2 Quiz

Salmon are sensitive to temperature changes.


2.3 Effect of Bioaccumulation on Ecosystems

• Amphibians live on both land and in the water.Amphibians are sensitive to chemical changes in the environment.They are therefore valuable indicators of environmental health.Since the 1980s, many of the world’s amphibian species have suffered declines in population.There also have been alarming increases in amphibian birth deformities.Many theories attempt to explain these changes, including drought, increased UV rays, pollution, habitat loss, parasites, and diseases.

See pages 92 - 93

Amphibians, like this frog, have exhibited drastic changes since the 1980s.


Bioaccumulation

• Bioaccumulation refers to the gradual buildup ofchemicals in living organisms.

Many harmful chemicals cannot be decomposed naturally.These chemicals can be eaten or absorbed and sometimes cannot be removed from the body of the organism effectively.If a keystone species suffers a chemical bioaccumulation, it can affect every other organism in its far-reaching niches.

A keystone species is a vital part of an ecosystem.• Biomagnification is the process by which

chemicals become more concentrated at each trophic level.

At each level of the food pyramid, chemicals that do not get broken down build up in organisms.When a consumer in the next trophic level eats organisms with a chemical accumulation, it receives a huge dose of the chemical(s).

See page 94

Organisms are sometimes exposed to toxic chemicals.


Bioaccumulation (continued)

• An example of bioaccumulation in British Columbia is the effect of PCBs on the Orca.

PCBs are chemicals that were used for many industrial and electrical applications in the mid-20th century.PCBs were banned in 1977 because of their environmental impact.

PCBs bioaccumulate and have a long half-life (they break down very slowly).PCBs will affect the reproductive cycles of orcas until at least 2030.

See page 95The bioaccumulation of PCBs begins with the absorption of the chemicals by microscopic plants and algae.



• Chemicals like PCBs and DDT are called persistent organic pollutants (POPs).

POPs contain carbon, like all organic compounds, and remain in water and soil for many years.Many POPs are insecticides, used to control pest populations.

DDT was introduced in 1941 to control mosquito populations, and is still used in some places in the world.Like PCBs, DDT also bioaccumulates and has a long half-life.Even at low levels (5 ppm), DDT in animals can cause nervous, immune,and reproductive system disorders.• ppm = parts per million

See page 96Spraying DDT, 1958(c) McGraw Hill Ryerson 2007


• Heavy metals are metallic elements that are toxic to organisms.Levels of lead in the soil have increased due to human activities.

Lead is not considered safe at any level.Many electronics contain lead and must be recycled carefully.Lead can cause anemia and nervous and reproductive system damage.

Cadmium is also found in low levels naturally.Cadmium is used in the manufacture of plastics and nickel-cadmium batteries.It is toxic to earthworms and causes many health problems in fish.In humans, the main source of cadmium is exposure to cigarette smoke.• Cadmium causes lung diseases, cancer,

and nervous and immune system damage.See page 97

Electronics Waste Contains Lead.

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Mercury also is found naturally.Mercury has entered ecosystems through the burning of fossil fuels, waste incineration, mining, and the manufacture of items like batteries.

Coal burning accounts for 40 percent of the mercury released into the atmosphere.

Mercury bioaccumulates in the brain, heart and kidneys of many animals.Mercury compounds bioaccumulate in fish, adding risk for any organisms eating fish.

• Reducing the effects of chemical pollutionBioremediation is the use of micro-organisms or plants to help clean up toxic chemicals.

Example: the oil industry uses bacteria to “eat” oil spills.By trapping chemicals in the soil, they cannot enter the food chains as easily.

See pages 98 - 99Take the Section 2.3 Quiz

energy flow and energy loss in ecosystems: food...

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