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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The sun
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 & 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

The exception to the rule
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
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


  • 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
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
Food Webs

  • Ecosystems are much more complicated than a simple food chain

  • Food web – shows many feeding relationships in an ecosystem

Trophic levels
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

Water cycle
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 cycle1
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 cycle2
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

Carbon 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 cycle1
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 cycle2
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

Nitrogen 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 cycle1
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

Phosphorus 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 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 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
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.

How ecosystems work

Acid rain damage on gargoyle

Trees killed by acid rain

Sulfur cycle
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
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 continued1
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
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

  • 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
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
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
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

Secondary 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