How ecosystems work
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How Ecosystems Work. The Sun. Life depends on the sun The sun is the ultimate source of energy for almost all organisms Photosynthesis – a series of chemical reactions that use light to convert water and carbon dioxide into sugar and oxygen 6CO 2 + 6H 2 O → C 6 H 12 O 6 + 6O 2

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How Ecosystems Work

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How Ecosystems Work

The Sun

  • Life depends on the sun

  • The sun is the ultimate source of energy for almost all organisms

  • Photosynthesis – a series of chemical reactions that use light to convert water and carbon dioxide into sugar and oxygen

    • 6CO2 + 6H2O → C6H12O6 + 6O2

    • Plants, algae and some bacteria do photosynthesis

Producers & Consumers

  • Producers – organisms that make their own food

    • Autotrophs – self-feeders

    • Get their energy directly from the sun

  • Consumers – organisms that get their energy by eating other organisms

    • Heterotrophs – other-feeders

    • Get their energy indirectly from the sun by eating producers or other consumers

Producers & Consumers

The Exception to the Rule

  • Deep-ocean ecosystems thrive where there is no sunlight

  • Producers make food from hydrogen sulfide from the hot ocean vents instead of sunlight

  • Other organisms then eat these producers

Types of Consumers

  • Herbivores – consumers that eat only producers (plant-eaters)

  • Carnivores – consumers that eat only other consumers (meat-eaters)

  • Omnivores – consumers that eat both plants and animals (eaters of all)

  • Decomposers – consumers that break down dead organisms

What Eats What


  • Cellular respiration - gets the energy out of the food by using oxygen to break it down

  • All living things use cellular respiration to get energy from food

    • C6H12O6 + 6O2→ 6CO2 + 6H2O

    • Essentially the reverse of photosynthesis

Food Chains

  • Each time an organism eats another organism, energy is transferred

  • Food chain – a sequence in which energy is transferred from one organism to the next as each organism eats another

Food Webs

  • Ecosystems are much more complicated than a simple food chain

  • Food web – shows many feeding relationships in an ecosystem

Trophic Levels

  • Trophic level – each step in the transfer of energy through an ecosystem

  • Each time energy is transferred, less of it is available to organisms at the next level

  • Some energy is lost during the process of respiration; most is used for daily functions

  • About 90% of the energy is used; only 10% is left for the next trophic level

Trophic Levels

Water Cycle

  • Water moves between the Earth’s surface and the atmosphere

  • The sun provides the energy to drive the cycle

  • Evaporation – water changes from a liquid to a gas

  • Precipitation – water vapor cools and falls to Earth as rain, sleet, or snow

  • Groundwater – layer of water underground

Water Cycle

  • Living organisms move water about…

    • Carried within bodies (by drinking it or extracting it from food)

    • During respiration, water is excreted

    • Water also evaporates from the skin as sweat

    • Plant roots collect water from the soil

      • Some is used for photosynthesis

      • Some is evaporated or transpired from the leaves

Water Cycle

  • What are the 3 phases of water?

    • Solid

      • Ex. Glaciers, ice on the surface of a lake or pond

    • Liquid

      • Ex. oceans, rivers, streams, lakes

    • Gas

      • Ex. Water vapor

      • Water vapor cannot be seen, but we know that fog and clouds contain it

Water Cycle

Carbon Cycle

  • Carbon is an essential part of proteins, fats, and carbohydrates needed for life

  • Producers take CO2 from the atmosphere

  • Consumers eat the producers to obtain carbon

  • CO2 is released back to the atmosphere during cellular respiration

  • Fossil fuels store carbon that is then released when they are burned

Carbon Cycle

  • Four main reservoirs of carbon:

    • Atmosphere

      • Carbon dioxide, carbon monoxide

    • Terrestrial Biosphere

      • Includes freshwater, soil

    • Oceans

      • Dissolved carbon, living organisms in the ocean

    • Sediments

      • Fossil fuels

Carbon Cycle

  • Four processes involved in the carbon cycle:

    • Biological processes – photosynthesis, respiration & decomposition

    • Geochemical processes – release of carbon dioxide gas into the atmosphere by volcanoes

    • Mixed biogeochemical processes – burial of carbon-rich organisms and their conversion to fossil fuels

    • Human activity – mining, burning of fossil fuels

Carbon Cycle

Nitrogen Cycle

  • All organisms need nitrogen to build proteins

  • Nitrogen gas makes up 78% of the atmosphere

  • Nitrogen-fixing bacteria – Convert nitrogen from the air into ammonia (nitrogen fixation)

Nitrogen Cycle

  • Ammonia is converted into nitrates and nitrites, which plants and other producers can use (nitrification)

  • Bacteria convert nitrogen in the soil into atmospheric nitrogen (denitrification)

  • Decomposers return nitrogen to the soil

Nitrogen Cycle

Phosphorus Cycle

  • Phosphorus is an element that is part of many molecules that make up the cells of living organisms.

  • Plants get the phosphorus they need from soil and water, while animals get their phosphorus by eating plants or other animals that have eaten plants.

  • The phosphorus cycle is the cyclic movement of phosphorus in different chemical forms from the environment to organisms and then back to the environment.

Phosphorus Cycle Continued

  • Phosphorus may enter soil and water when rocks erode. Small amounts of phosphorus dissolve as phosphate, which moves into the soil.

  • Plants absorb phosphates in the soil through their roots.

  • Some phosphorus washes off the land and ends up in the ocean.

  • Because many phosphate salts are not soluble in water, they sink to the bottom and accumulate as sediment.

Fertilizers and the Nitrogen and Phosphorus Cycles

  • Fertilizers contain both nitrogen and phosphorus.

  • Excessive amounts of fertilizer can enter terrestrial and aquatic ecosystems through runoff.

  • Excess nitrogen and phosphorus can cause rapid growth of algae.

  • Excess algae can deplete an aquatic ecosystem of important nutrients such as oxygen, on which fish and other aquatic organisms depend.

Acid Precipitation

  • When fuel is burned, large amounts of nitric oxide is release into the atmosphere.

  • In the air, nitric oxide can combine with oxygen and water vapor to form nitric acid.

  • Dissolved in rain or snow, the nitric acid falls as acid precipitation.

Acid rain damage on gargoyle

Trees killed by acid rain

Sulfur Cycle

  • Sulfur is one of the components that make up proteins and vitamins.

  • Proteins consist of amino acids that contain sulfur atoms.

  • Sulfur is important for the functioning of proteins and enzymes in plants, and in animals that depend upon plants for sulfur.

  • Plants absorb sulfur when it is dissolved in water. Animals consume these plants, so that they take up enough sulfur to maintain their health.

Sulfur Cycle Continued

  • Most of the earth's sulfur is tied up in rocks and salts or buried deep in the ocean in oceanic sediments.

  • Sulfur can also be found in the atmosphere. It enters the atmosphere through both natural and human sources.

  • Natural recourses: volcanic eruptions, bacterial processes, evaporation from water, or decaying organisms.

  • When sulfur enters the atmosphere through human activity, this is mainly a consequence of industrial processes where sulfur dioxide (SO2) and hydrogen sulphide (H2S) gases are emitted on a wide scale.

Sulfur Cycle Continued

  • When sulfur dioxide enters the atmosphere it will react with oxygen to produce sulfur trioxide gas (SO3), or with other chemicals in the atmosphere, to produce sulfur salts.

  • Sulfur dioxide may also react with water to produce sulphuric acid (H2SO4). Sulphuric acid may also be produced from demethylsulphide, which is emitted to the atmosphere by plankton species.

  • All these particles will settle back onto earth, or react with rain and fall back onto earth as acid depostion.

Rock Cycle

  • Group of changes

  • Igneous rock can change into sedimentary rock or into metamorphic rock

  • Sedimentary rock can change into metamorphic rock or into igneous rock

  • Metamorphic rock can change into igneous or sedimentary rock

Igneous Rock

  • Igneous rock forms when magma cools and makes crystals.

  • Magma is a hot liquid made of melted minerals. The minerals can form crystals when they cool.

  • Igneous rock can form underground, where the magma cools slowly. Or, igneous rock can form above ground, where the magma cools quickly.

Sedimentary Rock

  • On Earth's surface, wind and water can break rock into pieces.

  • The rock pieces, called sediments, drop from the wind or water to make a layer.

  • After a long time the sediments can be cemented together to make sedimentary rock. In this way, igneous rock can become sedimentary rock.

Metamorphic Rock

  • Baked rock does not melt, but it does change. It forms crystals.

  • Because this rock changes, it is called metamorphic.

  • Metamorphosis can occur in rock when they are heated to 300 to 700 degrees Celsius.


  • A regular pattern of changes over time in the types of species in a community

  • May take hundreds or thousands of years

  • Climax community – the community that eventually forms if the land is left undisturbed

  • Two types of succession

    • Primary succession

    • Secondary succession

Primary Succession

  • Occurs on surfaces where no ecosystem existed before

    • New islands created by volcanic eruptions

    • Land exposed when a glacier retreats

  • No soil exists

    • It takes several hundred to several thousand years to produce soil naturally

  • Pioneer species – first organisms to populate an area (usually lichens)

    • Lichens → mosses → grasses → shrubs → trees

Primary Succession

Secondary Succession

  • Occurs on a surface where an ecosystem has previously existed

    • Volcanic eruption, forest fire, abandoned farmland

  • Occurs much more quickly than primary succession because there is already fertile soil

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