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Ok, most of us have learned this¡K. Those of you that were in Reta last year, I hope you went over this.

 

This Chapter focuses mainly the transfer of energy through an ecosystem and various cycles that occur on earth.

 

Transfer of Energy:

 

Recap: Ecosystem = living + nonliving factors

 

Energy cannot be recycled. So¡K our sun is like a giant battery, continuously providing energy.

 

Plants use this energy and other material to create organic matter. Then, other organisms eat a portion(1/10th) of this matter to acquire energy from it. The cycle continues as smaller organisms help to support larger organisms.

 

Trophic levels, obviously, there are five main ones:

 

Sun ¡V the Almighty battery

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  1. Primary producers ¡V plants and photosynthetic organisms. They convert the sunlight into matter, which can later be used by other organisms.

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  1. Primary consumers ¡V small organisms that get their energy from the primary producers. Basically, they eat the plants or the small photosynthetic organisms.

Note: Since most of them eat plants, they are usually herbivores.

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  1. Secondary consumers- These eat the herbivores, or primary consumers. Since they eat meat, they¡¦re usually carnivores.

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  1. Tertiary consumers- The top of the food chain. These animals eat other carnivores. Note: I believe Quaternary consumers eat Tertiary consumers.

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  1. Finally¡K there is the almighty decomposer, which eats everything that dies.

 

Sun > photosynthetic plant/organism > herbivore > carnivore > carnivore>¡K. ^ \/ \/ \/ \/

\-----------------------------Decomposer-----------------------------------------/

Look at figure 54.1 on page 1132 for more info.

 

Note: Omivores like humans could eat both vegetation as well as animals.

 

Food chain vs. Food web:

 

What¡¦s the main difference?

 

Food chain is one pathway showing how energy is transferred from one trophic level to another. Such as¡K

 

Plant> grasshopper> mouse> owl

 

Food web on the other hand is much more complex. It is several food chains put together.

 

Too hard to make one¡K so look on page 1133 figure 54.2

 

 

 

Now I¡¦ll explain the each trophic levels further.

 

Trophic levels:

 

Primary Producers: Autotrophs

 

There are two main kinds. Those that derive their energy from the sun, and those that are chemoautotrophic, meaning they derive energy from the oxidation of hydrogen sulfide.

 

Those that get energy from sun are plants and some photosynthetic organisms. They use photosynthesis to create matter.

 

Chemoautotrophic bacteria get it from chemical. However, they still rely on solar energy to create oxygen. Usually these bacteria live near hot water vents.

 

Primary/Secondary/Tertiary Consumers: Herbivore/Carnivore

 

Opportunistic feeders - usually would eat anything available, namely the plants around them.

 

Decomposers: mainly prokaryotes and fungi.

 

They break down dead material to be reused by autotrophs.

 

Primary Productivity:

 

Sun = Very Very Big battery. 1022 J a day¡K. that¡¦s with 22 0¡¦s

if 1J = 0.239 calories. 239 x 1019 calories¡K 2,390,000,000,000,000,000 Calories.

 

Now¡K a person needs about 2000 Calories a day¡K

2,390,000,000,000,000,000 / 2000 = ???? you do the math.

 

Main point is Sun provides a lot of energy.

 

However, not all of the solar radiation reaches earth because of other variables like dust, cloud, etc.

 

Ultimately, a small portion(1-2%) of the energy becomes used in photosynthesis:

 

NPP = GPP ¡V Rs

 

NPP = Net Primary Productivity

 

GPP = Gross Primary Productivity

 

Rs = energy used in cellular respiration

 

Gross, in math, means addition, or all. So Gross primary is everything.

 

Imagine it¡¦s a factory making toys to sell.

Net, is like the profit. Earning ¡V cost of making the toy= profit.

 

GPP ¡V NPP ratio : the percentage of NPP that remains from the GPP after Rs is subtracted.

 

Bigger producers have higher Rs, so their ratio is smaller, meaning they keep less of the GPP as NPP.

 

There are two ways to show Primary productivity:

 

  1. energy per unit area per unit time (J/m2/yr)

 

  1. biomass, weight of vegetation added to ecosystem per unit per unit time (g/m2/yr)

 

note: water not included in biomass, since it does not include usable energy and can vary.

 

Difference between Primary productivity and Standing crop biomass:

 

PP = rate of which NEW biomass is produced.

 

Standing crop biomass = basically, the biomass already there. It¡¦s the amount of biomass at a given time

 

Main factors affecting productivity: Type of ecosystem and seasonal changes.

 

This may include amount of water available, the temperature, how much light is available, and other resources such as inorganic materials, etc.

 

If a nutrient is not adequately available, it is called the limiting nutrient. It limits the Primary productivity.

 

Secondary Productivity:

 

Rate of chemical energy from food consumers eat convert into new biomass.

 

As we have learned before, much energy is wasted going from trophic level to level. Average 10% of energy is transferred. Plants only uses 1% of the energy from sunlight.

 

Ecological efficiency is this percentage of energy transferred. Ranges from 5% - 20%

 

Most systems are inefficient (80%-95% of energy lost), but some aquatic ecosystems are inverted. (see figure 54.6 on page 1137)

 

Why? Because phytoplankton have a short turnover time. In other words their productivity is greater compared to their standing biomass.

 

Turnover time= standing crop biomass/ productivity

 

or

 

= the biomass present/ the biomass created

 

Since so much energy is lost, the ecosystem can support only few top-level predators.

 

 

Cycles:

 

Sun is producing a seemingly endless supply of energy (although it should end in a few gazillion years)

 

The materials on earth are not endless. However, matter cannot be created or destroyed, so various cycles recycle these material.

 

Biogeochemical cycles ¡V involving both biotic and abiotic factors

 

The Water Cycle(pg 1139 Fig 54.9):

 

This one most people should be familiar with.

 

  1. evaporation and transpiration: solar energy cause water to evaporate and plants give off water molecules, called transpiration.

 

  1. condensation: water collects as it rises into cooler air, and falls back down as precipitation or travels across the land and precipitate as raindrops down to earth.

 

  1. percolation: collection of water in the soil

 

  1. evapotranspiration: water goes back to sea.

 

The Carbon Cycle(pg 1140 fig. 54.10):

 

Carbon is mainly acquired by plants in the form of CO2.

Organisms acquire carbon from plants or other herbivores.

 

  1. Burning of fuel, cellular respiration all put CO2? into the atmosphere

 

  1. Photosynthesis: changes CO2 back into organic matter

 

  1. Consumers: herbivores eat the vegetation, and then later becomes eaten by carnivores, transferring the carbon.

 

Detritus- recycles carbon from dead material and respires it into the atmosphere.

 

In aquatic environments, water and limestone become involved.

 

  1. CO2 + water = carbonic acid
  2. carbonic acid + limestone = bicarbonates and carbonate ions

 

note: check pg 1141 for exact equation.

 

The Nitrogen Cycle(pg 1141 fig. 54.11):

 

Nitrogen is acquired by plants from ammonium and nitrate.

 

The atmosphere is made up of 80% N2, not usable by plants.

 

How does Nitrogen go into plants?

 

  1. atmospheric deposition(5-10%) ¡V nitrogen is added to the soil through rain and dust that settles

 

  1. nitrogen fixation ¡V certain prokaryotes can convert N2 into minerals then used by plants.

 

  1. During nitrogen fixation, these prokaryotes fix nitrogen in order to fulfill their own needs. However, excess ammonia is created during the process.

 

  1. This ammonia(NH3) is then converted into ammonium(NH4+) by picking up a hydrogen ion H+?? from the soil.

 

or

 

The ammonia (NH3) goes back into the air and may form NH4+ in the atmophere, which is later brought down during rainfall at a different location.

 

  1. Plants absorb this ammonium.

 

Note: this is the reason for nitrogen in industrial fertilizers.

 

Recycling Nitrogen:

 

Herbivores that eat the plant with nitrogen then dies and decomposers convert the dead material back into ammonium.

 

Nitrification and Denitrification:

 

Some aerobic bacteria uses ammonium as an energy source. They convert ammonium to nitrite (NO2-) and then to nitrate (NO3-).

 

Nitrate is then assimilated by plants and turned into organic material.

 

As for denitrification, nitrate is converted back to N2 by bacteria.


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