Ch 5 How Ecosystems Work Chapter 5 Objectives

Ch. 5 How Ecosystems Work

Chapter 5 Objectives List two examples of ecological succession. Explain how a pioneer species contributes to ecological succession. Explain what happens during old-field succession. Describe how lichens contribute to primary succession.

I. Energy Flow in Ecosystems § A. Life Depends on the Sun § Photosynthesis – when plants use sunlight to make sugar molecules § performed by plants, algae, and some bacteria § 6 CO 2 + 6 H 2 O + solar energy = C 6 H 12 O 6 + 6 O 2

I. Energy Flow in Ecosystems § Result of photosynthesis is energy rich molecules called Carbohydrates § When an animal eats a plant, some energy is transferred from the plant to the animal, and use this energy to grow, move, and reproduce.

I. Energy Flow in Ecosystems § Producer – an organism that makes its own food – an Autotroph -organisms that perform photosynthesis § Consumer – organisms that get their energy by eating other organisms – heterotrophs § All organisms get their energy from the sun either by using it directly through photosynthesis like producers, or indirectly by eating producers or other consumers

I. Energy Flow in Ecosystems § In 1977 scientists discovered areas on the bottom of the ocean that were full of life even though sunlight did not reach § -deep ocean communities got their energy from bacteria who could use hydrogen sulfide from the hot water vents to make their own food § -these bacteria served as the food for other organisms so a whole ecosystem could be supported

B. What Eats What § Organisms can be classified by the source of their energy § Herbivores – consumers that eat only producers – planteaters § Carnivores – consumers that eat other consumers – meat -eaters § Omnivores – consumers that eat both producers and consumers – all-eaters § Decomposers – consumers that get their food by breaking down dead organisms -bacteria and fungi

C. Cellular Respiration: Burning the Fuel § Your body gets the energy out of the food by using the oxygen you breathe to break down the food § -you are then able to use the energy stored in the food § Excess energy is stored as fat or sugar.

C. Cellular Respiration: Burning the Fuel § Cellular respiration – process of breaking down food to yield energy -occurs inside cells of most organisms including plant and animals § You use the energy to walk, breathe, think, or play a sport, to make more body tissues, fight disease, grow, stay healthy

D. Energy Transfer § Each time one organism eats another, a transfer of energy occurs § According to the second law of thermodynamics – at each energy transfer only 10% is available at the next level, the rest is lost as heat

§ You can trace the transfer of energy as it travels through an ecosystem by studying food chains, food webs, and trophic levels § Food chain – a sequence in which energy is transferred from one organism to the next as each organism eats another organism § In an ecosystem, energy flow is usually more complex because there are so many species interacting § Food web – shows many feeding relationships that are possible in an ecosystem

Food Web Food Chain

Trophic Levels § Trophic level – each step in the transfer of energy through a food chain or web § -each time energy is transferred from one organism to another, some of the energy is lost as heat and less is available to organisms at the next level § 90 percent of the energy at each trophic level is used to carry out the functions of living

Trophic Levels § 10 percent becomes used as part of the organisms body and stored in its molecules – this is what is available to the next trophic level when one organism consumes another § Energy pyramid is used to visualize the loss of energy from one trophic level to the next § -each layer represents one trophic level

Trophic Levels § producers form the base because they contain the most energy § -herbivores make up the next level because they contain less energy § -carnivores that feed on herbivores make up the next level § -omnivores that feed on carnivores and producers make up the top level

Trophic Levels

§ The decreased amount of energy at each trophic level affects the organization of an ecosystem § -because so much energy is lost at each level, there are fewer organisms at the higher trophic levels § -the loss of energy limits the number of trophic levels in an ecosystem

Objectives § § § List the three stages of the carbon cycle. Describe where fossil fuels are located. Identify one way that humans are affecting the carbon cycle. List the three stages of the nitrogen cycle. Describe the role that nitrogen-fixing bacteria play in the nitrogen cycle. Explain how the excess use of fertilizer can affect the nitrogen and phosphorus cycles.

II. The Cycling of Materials § A. The Carbon Cycle § Carbon is an essential part of all living things § Carbon cycle – a process by which carbon is cycled between the atmosphere, land, water, and organisms § Carbon is the essential component of proteins, fats, and carbohydrates, which make up all organisms.

The Carbon Cycle

The Long & Short Cycles of Carbon § a short term cycle is when producers like plants convert CO 2 in the air into glucose during photosynthesis § -some carbon enters a long-term cycle if carbon is converted into carbonates which make up the hard parts of bones and shells

As a Long Term Cycle § over millions of years carbonate deposits produce huge formations of limestone rocks -limestone is one of the largest carbon sinks or carbon reservoirs on Earth § -carbon can be released into the soil or air after an organism dies and decomposes and form deposits of coal, oil, and natural gas underground called fossil fuels

Humans affect the carbon cycle § When we burn fossil fuels, we release carbon into the atmosphere as carbon dioxide -cars, factories, and power plants rely on these fossil fuels to operate § -about 6 billion metric tons of carbon a year are released as CO 2

B. The Nitrogen Cycle § All organisms need protein which is essential for new cells - nitrogen is needed for proteins. § Nitrogen makes up 78% of the gases in the atmosphere, but organisms cannot take in and use atmospheric nitrogen

Nitrogen Fixation § Nitrogen must be altered, or fixed, before organisms can use it § The only organisms that can fix nitrogen is bacteria called nitrogen-fixing bacteria § -all organisms depend on these bacteria to supply nitrogen § Bacteria are an important part of nitrogen cycle

Nitrogen Cycle

Nitrogen cycle § Nitrogen cycle– a process in which nitrogen is cycled between the atmosphere, bacteria, and other organisms § -bacteria take nitrogen from the air and transforms it into molecules that living things can use § -the bacteria live within nodules on the roots of plants called legumes – beans, peas, clover § -they use sugars provided by the legumes to produce nitrogen-containing compounds like nitrates § -the excess nitrates are released into the soil

§ Animals get nitrogen by eating plants or other animals § After nitrogen cycles from the atmosphere into living things, it is returned to the atmosphere by bacteria § -decomposers are essential to the nitrogen cycle because the break down wastes such as urine, dung, leaves, and other decaying plant and animal matter and return the nitrogen that these organisms and wastes contain to the soil § -after decomposers return the nitrogen to the soil, bacteria transform a small amount of the nitrogen into nitrogen gas which returns to the atmosphere

C. The Phosphorus Cycle § Phosphorus is part of many molecules that make up the cells of living organisms § Essential in forming bones and teeth § Plants get phosphorus from soil and water, and animals get it by eating plants or plant-eaters

Phosphorus cycle § Phosphorus cycle – the movement of phosphorus from the environment to organisms and then back to the environment § -this cycle is slow and does not normally occur in the atmosphere because phosphorus rarely occurs as a gas § -phosphorus enters the cycle when rocks erode, small amounts of phosphorus dissolve as phosphate in soil and water § -plants absorb phosphates in the soil through their roots

Phosphorus cycle § -phosphorus also enters the cycle when added to soil and water when excess phosphorus is excreted in waste § from organisms and when organisms die and decompose § -some phosphorus also washes off the land eventually ends up in the ocean § -phosphate salts are not soluble in water and so they sink to the bottom of the ocean and accumulate as sediment

Phosphorus Cycle

Human effects § Humans effect the Nitrogen and Phosphorus cycle § -people often apply fertilizers to stimulate and maximize plant growth § -fertilizers contain both nitrogen and phosphorus § -the more nitrogen and phosphorus available to a plant, the faster and bigger the plant tends to grow § If excessive amounts of fertilizer are used, the fertilize can enter terrestrial and aquatic ecosystems through runoff

Phosphorus cycle § -this can cause rapid and over-abundant growth of algae resulting in an algal bloom – a dense, visible patch of algae that occurs near the surface of the water (Eutrophication) § -bacteria break down the dead algae and plants depleting the oxygen from the water causing fish and other aquatic organisms to die

Nutrient Cycles can be harmful § When we burn coal, wood, or oil, a large amount of nitric oxide is release into the atmosphere § -this is a harmful gas and when it combines with oxygen and water vapor to form nitric acid (NOX) § -nitric acid dissolves in rain and snow contributing to acid precipitation

Bellringer

Objectives § List two examples of ecological succession. § Explain how a pioneer species contributes to ecological succession. § Explain what happens during old-field succession. § Describe how lichens contribute to primary succession.

III. How Ecosystems Change § A. Ecological Succession § Ecological succession – a gradual process of change and replacement of the types of species in a community § Primary succession – a type of succession that occurs on a surface where no ecosystem existed before -rocks, cliffs, sand dunes

Secondary succession § Secondary succession – the more common type of succession where succession occurs on a surface where an ecosystem has previously existed -areas that have been disturbed by humans, animals or natural processes such as storms, floods, fires, earthquakes, volcanoes § Example – Mount St. Helens eruption wiped out everything

Mount St. Helens Succession § the first species to regrow were pioneer species – the first organisms to colonize any newly available area and begins the process of ecological succession § -pioneer species makes the area habitable for other species § -tend to be smaller species like mosses and grasses § -they are replaced by larger and larger organisms

climax community § -climax community – a final and stable community § Natural fires caused by lightening are a necessary part of secondary succession § -some trees release seeds only when exposed to the heat of a fire § -minor fires remove the brush and deadwood that would otherwise contribute to major fires burning out of control § -some animal species feed on vegetation that only sprouts after fires

Ecological Succession

Old-field succession § Example of secondary succession is old-field succession § Old-field succession – occurs when farmland is abandoned when a farmer stops cultivating a field § § -grasses and weeds quickly build up -over time taller plants move into the area -taller plants gradually replace smaller ones -finally the slower growing trees like oaks, hickory, beech, and maple take over

Primary succession § Primary succession is much slower than secondary succession because it begins where there is no soil § -it can take several hundred to several thousand years to produce fertile soil § -lichens are usually the first pioneer species because they can live with no soil § Lichens are composed of a fungus and an algae

How it happens § as the lichen grows it breaks down the rock and soil slowly accumulates as dust particles in the air are trapped in cracks in the rock § -dead remains of lichens and bacteria accumulate in the cracks § -mosses may grow larger and break the rock even more, then they die and decay and add material and nutrients to the growing soil § -fertile soil is formed from broken rock, decayed organisms, water, and air

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