Ecosystems: How They Work

Objectives

At the end of the session the students should be able to:

1. Show the correct way of explaining the relation of matter and energy.

2. Can identify the Laws of Thermodynamics.

3. Show correct way of explaining the energy flow in ecosystems. 

4. Can enumerate the various biogeochemical cycles in the ecosystem.

5. Show comparison between carbon, nitrogen, sulfur and phosphorus cycle within the ecosystem.

What is matter? 

• Matter- materials of which things are made

• Can be solid, liquid, or gas

• Law of Conservation of Matter- matter cannot be created nor destroyed- recycled or transformed

• All life is made of matter

What is energy?

• Provides the force to hold matter together, tear it apart, & move from one place to another.

• Kinetic energy- energy in moving objects

• Potential energy- stored energy; latent & ready for use.

• Chemical energy- energy stored in food or carbon compounds

What is the difference between high quality energy and low quality energy?

• High quality- intense, concentrated, & high in temperature

  • Ex:  energy in fossil fuels

• Low quality- diffused, dispersed, low in temperature

  • Ex:  low heat energy of ocean is huge but hard to capture & use

How is energy transfer related to Thermodynamics?

• 1st law of thermodynamics:  energy is conserved, neither created nor destroyed

• 2nd law of thermodynamics: entropy (disorder) increases in all natural systems; less energy is available to do work; it has not been destroyed, only dissipated.

Why do organisms need a constant supply of energy?

• Needed to replace energy that is dissipated as used.

• If no constant supply of energy, cells can’t perform work or it causes death.

How do organisms get energy?

•  Chemosynthesis- use chemicals like sulfur to create organic food compounds.

  • EX:  chemosynthetic bacteria near hydrothermal vents in ocean; no sunlight in this ecosystem= no producers

• Photosynthesis- use radiation energy from sun to create organic food compounds.

  • EX: plants make glucose from sunlight

• Cellular respiration- use ATP to breakdown glucose to store energy in chemical bonds of more ATP

  • EX:  all living organisms

 How is energy transferred in an ecosystem? 

•  Tertiary consumers- top carnivores or omnivores

• Secondary Consumers- carnivores

• Primary Consumers- herbivores

• Primary Producers- plants

•  Scavengers- eat dead carcasses with mouth

  • Ex:  vulture, crow

• Detritivores- eat leaf litter, dung, debris

  • Ex:  ants, beetles

• Decomposers- absorb nutrients from dead or dung thru cell wall

  • Ex:  fungus, bacteria

• Occupy any level

• Clean up and recycle nutrients to soil

 How can we show this transfer of energy?  

• Food chains show one possible relationship

• Food Webs more complex- show all feeding relationships in ecosystem

• Length can indicate health, harshness of ecosystem

  • Ex:  arctic food webs smaller than tropical food webs

  • Diversity=stability 

 How can we show this transfer of energy? 

• Pyramid of Numbers- shows actual numbers of organisms at each level 

 How can we show this energy transfer? 

• Pyramid of Biomass- shows mass of available nutrients at each level 

What happens to the energy at each level?

• Energy decreases at each level (2nd law of thermodynamics)

• Where does it go?

  • Used in organisms own daily life functions

  • Lost as heat

  • Lost as feces

• 90% used- 10% stored in organism and passed to next level when organism gets eaten- “ECOLOGICAL RULE OF THUMB”

• As a result, less energy = fewer organisms at top of food chain.

• This is why there are not 6, 7, 8th level consumers. 

• Energy is NOT recycled in an ecosystem

• BUT…

• Matter is… which leads us to the biogeochemical cycles! 

Biogeochemical Cycles

• Refers to any of the natural circulation pathways of chemical elements and compounds between living organisms and the physical environment. 

• Chemicals absorbed or ingested by organisms are passed through the food chain and returned to the soil, air, and water by such mechanisms as respiration, excretion, and decomposition. 

Types of Biogeochemical Cycle

1. Gaseous Cycles

• Cycling elements in which the reservoir is the air or the oceans (via evaporation).

• Nitrogen - atmosphere

• Oxygen - atmosphere

• Carbon - atmosphere

• Water - ocean

2. Sedimentary Cycles

   • Cycling elements in which the reservoir is the earth’s crust.

     • Phosphorus – rocks

     • Sulfur – earth’s crust

Gas Composition of the Atmosphere

• Nitrogen (N2) 78%

• Oxygen (O2) 21% 

• Other gases 1%

• Argon (Ar) 

• Carbon dioxide CO2) 

• Methane (CH4) 

• Helium (He) 

• Hydrogen (H2) 

• Krypton (Kr) 

• Neon (Ne) 

• Nitrous oxide (N2O) 

Carbon Cycle

• Carbon

  • Essential for PHOTOSYNTHESIS

  • Part of LIFE’s BIOMOLECULES

  • Part of FOSSIL FUELS

  • Major cause of GLOBAL WARMING

Carbon Cycle

• Carbon moves from the atmosphere to plants through photosynthesis.

• Carbon moves from plants to animals through food chain.

• Carbon moves from plants and animals to the ground through decomposition.

  • Some becomes buried miles underground and will become fossil fuels in millions and millions of years.

• Carbon moves from living things to the atmosphere through respiration.

• Carbon moves from fossil fuels to the atmosphere when fuels are burned.

  • When humans burn fossil fuels to power factories, power plants, cars and trucks, most of the carbon quickly enters the atmosphere as carbon dioxide gas. 

• Carbon moves from the atmosphere to the oceans. 

  • The oceans, and other bodies of water, soak up some carbon from the atmosphere. 

Nitrogen Cycle

• Nitrogen (N2)

  • MOST ABUNDANT GAS in the atmosphere

  • Converted into several form with the aid of different bacteria while in the cycle.

  • All plants and animals need nitrogen to make;

    • Amino acids 

    • DNA

• Most of the nitrogen on Earth is in the atmosphere. Approximately 78% of the molecules in Earth's atmosphere are made of two nitrogen atoms bonded together (N2). 

• All plants and animals need nitrogen to make amino acids, proteins and DNA, but the nitrogen in the atmosphere is not in a form that they can use. 

• The molecules of nitrogen in the atmosphere can become usable for living things when they are broken apart during lightning strikes, or by certain types of bacteria.

Types of bacteria that plays an important role in the  Nitrogen Cycle

1. Nitrogen-fixing bacteria 

   • ex: Azotobacter and Rhizobium

2. Nitrifying bacteria

   • ex: Nitrosomonas and Nitrobacter

3. Denitrifying bacteria

   • ex: Thiobacillus and Pseudomonas

Processes in the Nitrogen Cycle

1. Fixation 

• Fixation is the first step in the process of making nitrogen usable by plants (atmospheric nitrogen to ammonium)

• Types 

1. Atmospheric fixation – with the aid of lightning

2. Industrial fixation – due to extremely high temperature

3. Biological fixation – with the aid of bacteria

2. Nitrification 

• This is the process by which ammonium gets changed into nitrates by bacteria. Nitrates are what the plants can then absorb.

3. Assimilation 

• This is how plants get nitrogen. They absorb nitrates from the soil into their roots. Then the nitrogen gets used in amino acids, nucleic acids, and chlorophyll.

4. Ammonification 

• This is part of the decaying process. 

• When a plant or animal dies, decomposers like fungi and bacteria turn the nitrogen back into ammonium so it can reenter the nitrogen cycle.

5. Denitrification 

• Extra nitrogen in the soil gets put back out into the air. 

Phosphorus Cycle

• Phosphorus

  • Component of DNA(Deoxyribonucleic Acid), RNA, ATP(Adenosine Triphosphate), proteins and enzymes. 

  • Source: ROCK

  • Released into the cycle through MINING and WEATHERING  

  • It is taken up by plant roots, and then travels through food chains then return to sediment. 

• Plants absorb phosphorous from water and soil into their tissues, tying them to organic molecules (RNA, DNA, CHON)

• Once taken up by plants, phosphorus is available for animals when they consume the plants. 

• When plants and animals die, bacteria decompose their bodies, releasing some of the phosphorus back into the soil. 

• Phosphate is lost when it accumulated in sediments until millions of years go by and the old sediments are uplifted and eroded.

Sulfur Cycle

• Component of protein

• The source of Sulfur is the lithosphere(earth's crust)

• Sulfur (S) enters the atmosphere as  hydrogen sulfide (H2S) during fossil fuel combustion, volcanic eruptions and decomposition.

• H2S is immediately oxidized to sulfur dioxide (SO2).

• SO2 and water vapor makes sulfuric acid (H2SO4) which is then carried to the ground in rainfall.

• Sulfur in soluble form is taken up by plant roots and incorporated into amino acids. 

• It then travels through the food chain and is eventually released through decomposition. 

Oxygen Cycle 

• 2nd abundant gas in the atmosphere

• WASTE product of PHOTOSYNTHESIS

• Essential for ENERGY PRODUCTION.

• Oxygen is one of the important compounds found in the atmosphere of the Earth. 

• Plants take in carbon dioxide and combine it with water to create sugars and oxygen molecules. 

• Animals breathe that oxygen and both plants and animals use the sugars for energy. 

• Through the process of metabolism, the sugars are broken down into water and carbon dioxide. 

Then the cycle begins again.

Water Cycle

• The water cycle, also known as the hydrologic cycle, describes the continuous movement of water on, above and below the surface of the Earth. 

• Since the water cycle is truly a "cycle," there is no beginning or end. Water can change states among liquid, vapor, and ice at various places in the water cycle. 

Different Processes involved in the Water Cycle

1. Precipitation

• Condensed water vapor that falls to the Earth's surface. 

• Most precipitation occurs as rain, but also includes snow. 

2. Runoff

• The variety of ways by which water moves across the land. 

3. Infiltration

• The flow of water from the ground surface into the ground. 

4. Evaporation

• The transformation of water from liquid to gas phases as it moves from the ground or bodies of water into the overlying atmosphere.

• The source of energy for evaporation is primarily solar radiation. 

5. Condensation

• The transformation of water vapor to liquid water droplets in the air, producing clouds and fog.  

6. Transpiration

• The release of water vapor from plants into the air. 

7. Snowmelt

• The runoff produced by melting snow

8. Sublimation

• The state change directly from solid water (snow or ice) to water vapor.