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Can assimilated energy be simply lost from a trophic level?

Can assimilated energy be simply lost from a trophic level?


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I was reading Environmental Studies By B. S. Chauhan and there a diagram of a model of transfer of energy.

NU = Not used energy has been shown, energy that was neither stored or exported to the next level.

I wonder what physiological process causes this loss of energy at all trophic levels?


In this diagram, since this is the only loss between trophic levels (along with respiration and NA within each trophic level), NU represents dead organic matter, that is not transferred along the food chain. In other words, this represents dead leaves that are not eaten by herbivores, hares that die of old age and not predation, and foxes that are killed by falling rocks. So NU is the amount of energy that goes directly into the decomposer community (another flow to decomposers is coming from matter that is excreted by herbivores and predators), since this diagram only includes primary producers, herbivores and predators.

NA, on the other hand, represents energy that is consumed by the next trophic level but not assimilated (Not Aassimilated). So this represents faeces etc.


Ecosystems 2

As enemies consume their victims in a community, they digest the matter of their victim and use some of it for energy for their own growth and reproduction. For instance, when the squirrel eats the conifer seed in the food web above, the transfer of energy is not efficient because squirrel tissue composition is very different from seed tissue composition (for example, plant cells have a cell wall, while animal cells don’t). Much of the potential energy in the seed is spent in chemically processing the plant tissue, or it remains in the seed tissue as it moves through the squirrels digestive tract and is excreted into the environment. For the average trophic interaction, roughly 90% of energy is lost at each trophic level transfer, and this loss of energy to the consumer limits the length of food chains within a food web.

All the matter in living organisms, made up mostly of carbon, hydrogen, oxygen, and nitrogen in organic molecules, is either incorporated into the enemy that consumes it or left behind in the environment (see Frog Energy Flow Figure). Each atom ends up somewhere, as described below in the nutrient cycles section, below. The energy obtained by each organism is:

  • used for maintenance of the organisms
  • used for growth and reproduction
  • lost as heat or excreted waste from the organism

Frogs ingest energy that is used for metabolic processes (respiration), transformed into new frog biomass through growth and reproduction, or lost from the frog as feces. The energy flows from the frog into a predator, a parasite, or a detritovore. Energy is lost as it fuels the metabolic process that transform the energy and nutrients into biomass. (Source: “EnergyFlowFrog” by Thompsma – Own work. Licensed under CC BY-SA 3.0 via Commons)

This inefficient energy transfer from victim to enemy has population ecology implications. If only 10% of the energy makes it to the next trophic level, the population size of the top predator(s) remains small, while the population size and biomass of producers needs to be huge! In ecology, biomass is the combined mass of all the organisms of that species or group in the ecosystem. (Note that in the biofuel industry, the term biomass is used a little differently than in by an ecologist: ecologists refer to the entire organism, including roots and seeds, but biofuel biomass almost always refers to the mass of animal waste and harvested plant material used to make energy.)

While energy is transferred very inefficiently up a food chain, chemical toxins in the eaten organisms are incorporated into the consumer. Consumers eat many prey and retain all the toxins in those prey, accumulating higher toxin concentrations with each trophic position, a phenomenon called biomagnification (also called bioaccumulation).

While the energy pyramid for any ecosystem always narrows as the trophic levels increase (see Biomass and Energy figure below), the biomass pyramid can sometimes invert if the population ecology of the producers includes rapid generation times and little investment in building a physical body. For example, a single-celled aquatic algal species potentially reproduces every day, while a whale species cannot breed for several years after birth. Contrast that marine system with a terrestrial system such as Silver Springs, Florida (see figure) where plant tissue includes tree bark and roots from which many primary consumers cannot gain energy.

Ecological pyramids depict the (a) biomass, (b) number of organisms, and (c) energy in each trophic level. Biomass “pyramids” may be upright triangles, inverted triangles, or even diamond-shaped. Energy pyramids, however, are always upright. (Source: Excerpted from OpenStax Biology)


Can assimilated energy be simply lost from a trophic level? - Biology

The bacterium Neisseria gonorrhoeae causes infections related to the human reproductive system. The graph shows the percentage of samples in which this bacterium showed resistance to six antibiotics over a period of ten years.

What is a possible explanation for the total percentage resistance being larger than 100% in 2010?

A. People do not take the antibiotics as prescribed.

B. More people have been sampled in that year.

C. There was an epidemic of Neisseria gonorrhoeae in that year.

D. Some bacteria are resistant to more than one antibiotic.


Food Chains and Food Webs

The term “food chain” is sometimes used metaphorically to describe human social situations. In this sense, food chains are thought of as a competition for survival, such as “who eats whom?” Someone eats and someone is eaten. Therefore, it is not surprising that in our competitive “dog-eat-dog” society, individuals who are considered successful are seen as being at the top of the food chain, consuming all others for their benefit, whereas the less successful are seen as being at the bottom.

Figure 3. These are the trophic levels of a food chain in Lake Ontario at the United States-Canada border. Energy and nutrients flow from photosynthetic green algae at the bottom to the top of the food chain: the Chinook salmon.

The scientific understanding of a food chain is more precise than in its everyday usage. In ecology, a food chain is a linear sequence of organisms through which nutrients and energy pass: primary producers, primary consumers, and higher-level consumers are used to describe ecosystem structure and dynamics. There is a single path through the chain. Each organism in a food chain occupies what is called a trophic level. Depending on their role as producers or consumers, species or groups of species can be assigned to various trophic levels.

In many ecosystems, the bottom of the food chain consists of photosynthetic organisms (plants and/or phytoplankton), which are called primary producers. The organisms that consume the primary producers are herbivores: the primary consumers. Secondary consumers are usually carnivores that eat the primary consumers. Tertiary consumers are carnivores that eat other carnivores. Higher-level consumers feed on the next lower tropic levels, and so on, up to the organisms at the top of the food chain: the apex consumers. In the Lake Ontario food chain shown in Figure 3, the Chinook salmon is the apex consumer at the top of this food chain.

One major factor that limits the length of food chains is energy. Energy is lost as heat between each trophic level due to the second law of thermodynamics. Thus, after a limited number of trophic energy transfers, the amount of energy remaining in the food chain may not be great enough to support viable populations at yet a higher trophic level.

The loss of energy between trophic levels is illustrated by the pioneering studies of Howard T. Odum in the Silver Springs, Florida, ecosystem in the 1940s (Figure 4). The primary producers generated 20,819 kcal/m 2 /yr (kilocalories per square meter per year), the primary consumers generated 3368 kcal/m 2 /yr, the secondary consumers generated 383 kcal/m 2 /yr, and the tertiary consumers only generated 21 kcal/m 2 /yr. Thus, there is little energy remaining for another level of consumers in this ecosystem.

Figure 4. The relative energy in trophic levels in a Silver Springs, Florida, ecosystem is shown. Each trophic level has less energy available and supports fewer organisms at the next level.

There is a one problem when using food chains to accurately describe most ecosystems. Even when all organisms are grouped into appropriate trophic levels, some of these organisms can feed on species from more than one trophic level likewise, some of these organisms can be eaten by species from multiple trophic levels. In other words, the linear model of ecosystems, the food chain, is not completely descriptive of ecosystem structure. A holistic model—which accounts for all the interactions between different species and their complex interconnected relationships with each other and with the environment—is a more accurate and descriptive model for ecosystems. A food web is a graphic representation of a holistic, non-linear web of primary producers, primary consumers, and higher-level consumers used to describe ecosystem structure and dynamics (Figure 5).

Figure 5. This food web shows the interactions between organisms across trophic levels in the Lake Ontario ecosystem. Primary producers are outlined in green, primary consumers in orange, secondary consumers in blue, and tertiary (apex) consumers in purple. Arrows point from an organism that is consumed to the organism that consumes it. Notice how some lines point to more than one trophic level. For example, the opossum shrimp eats both primary producers and primary consumers. (credit: NOAA, GLERL)

A comparison of the two types of structural ecosystem models shows strength in both. Food chains are more flexible for analytical modeling, are easier to follow, and are easier to experiment with, whereas food web models more accurately represent ecosystem structure and dynamics, and data can be directly used as input for simulation modeling.

Two general types of food webs are often shown interacting within a single ecosystem. A grazing food web (such as the Lake Ontario food web in Figure 5) has plants or other photosynthetic organisms at its base, followed by herbivores and various carnivores. A detrital food web consists of a base of organisms that feed on decaying organic matter (dead organisms), called decomposers or detritivores. These organisms are usually bacteria or fungi that recycle organic material back into the biotic part of the ecosystem as they themselves are consumed by other organisms. As all ecosystems require a method to recycle material from dead organisms, most grazing food webs have an associated detrital food web. For example, in a meadow ecosystem, plants may support a grazing food web of different organisms, primary and other levels of consumers, while at the same time supporting a detrital food web of bacteria, fungi, and detrivorous invertebrates feeding off dead plants and animals.

Consequences of Food Webs: Biological Magnification

One of the most important environmental consequences of ecosystem dynamics is biomagnification. Biomagnification is the increasing concentration of persistent, toxic substances in organisms at each trophic level, from the primary producers to the apex consumers. Many substances have been shown to bioaccumulate, including classical studies with the pesticide dichlorodiphenyltrichloroethane (DDT), which was published in the 1960s bestseller, Silent Spring, by Rachel Carson. DDT was a commonly used pesticide before its dangers became known. In some aquatic ecosystems, organisms from each trophic level consumed many organisms of the lower level, which caused DDT to increase in birds (apex consumers) that ate fish. Thus, the birds accumulated sufficient amounts of DDT to cause fragility in their eggshells. This effect increased egg breakage during nesting and was shown to have adverse effects on these bird populations. The use of DDT was banned in the United States in the 1970s.

Figure 6. This chart shows the PCB concentrations found at the various trophic levels in the Saginaw Bay ecosystem of Lake Huron. Numbers on the x-axis reflect enrichment with heavy isotopes of nitrogen (15N), which is a marker for increasing trophic level. Notice that the fish in the higher trophic levels accumulate more PCBs than those in lower trophic levels. (credit: Patricia Van Hoof, NOAA, GLERL)

Other substances that biomagnify are polychlorinated biphenyls (PCBs), which were used in coolant liquids in the United States until their use was banned in 1979, and heavy metals, such as mercury, lead, and cadmium. These substances were best studied in aquatic ecosystems, where fish species at different trophic levels accumulate toxic substances brought through the ecosystem by the primary producers. As illustrated in a study performed by the National Oceanic and Atmospheric Administration (NOAA) in the Saginaw Bay of Lake Huron (Figure 6), PCB concentrations increased from the ecosystem’s primary producers (phytoplankton) through the different trophic levels of fish species. The apex consumer (walleye) has more than four times the amount of PCBs compared to phytoplankton. Also, based on results from other studies, birds that eat these fish may have PCB levels at least one order of magnitude higher than those found in the lake fish.

Other concerns have been raised by the accumulation of heavy metals, such as mercury and cadmium, in certain types of seafood. The United States Environmental Protection Agency (EPA) recommends that pregnant women and young children should not consume any swordfish, shark, king mackerel, or tilefish because of their high mercury content. These individuals are advised to eat fish low in mercury: salmon, tilapia, shrimp, pollock, and catfish. Biomagnification is a good example of how ecosystem dynamics can affect our everyday lives, even influencing the food we eat.


Food Webs

While food chains are simple and easy to analyze, there is a one problem when using food chains to describe most communities. Even when all organisms are grouped into appropriate trophic levels, some of these organisms can feed at more than one trophic level. In addition, species feed on and are eaten by more than one species. In other words, the linear model of trophic interactions, the food chain, is a hypothetical and overly simplistic representation of community structure. A holistic model&mdashwhich includes all the interactions between different species and their complex interconnected relationships with each other and with the environment&mdashis a more accurate and descriptive model. A food web is a concept that accounts for the multiple trophic interactions between each species (Figure (PageIndex<2>)).

Figure (PageIndex<2>) This food web shows the interactions between organisms across trophic levels. Arrows point from an organism that is consumed to the organism that consumes it. All the producers and consumers eventually become nourishment for the decomposers (fungi, mold, earthworms, and bacteria in the soil). (credit "fox": modification of work by Kevin Bacher, NPS credit "owl": modification of work by John and Karen Hollingsworth, USFWS credit "snake": modification of work by Steve Jurvetson credit "robin": modification of work by Alan Vernon credit "frog": modification of work by Alessandro Catenazzi credit "spider": modification of work by "Sanba38"/Wikimedia Commons credit "centipede": modification of work by &ldquoBauerph&rdquo/Wikimedia Commons credit "squirrel": modification of work by Dawn Huczek credit "mouse": modification of work by NIGMS, NIH credit "sparrow": modification of work by David Friel credit "beetle": modification of work by Scott Bauer, USDA Agricultural Research Service credit "mushrooms": modification of work by Chris Wee credit "mold": modification of work by Dr. Lucille Georg, CDC credit "earthworm": modification of work by Rob Hille credit "bacteria": modification of work by Don Stalons, CDC)


4.1 – Communities and Ecosystems

Species – A group of organisms that can interbreed and produce fertile offspring.

They are a group of individuals of common ancestry that closely resemble each other and that are normally capable of interbreeding to produce fertile offspring.

Habitat – The environment in which a species normally lives or the location of a living organism.

If this area is extremely small, we call it a microhabitat, such as the crevices in the bark of a tree in which some insects live. Conditions in a microhabitat are different to those of the surrounding habitat.

Population – A group of organisms of the same species who live in the same area at the same time.

The members of a population have a high chance of interbreeding, assuming the species concerned reproduces sexually. The boundaries of populations are often hard to define.

Community – A group of populations living and interacting with each other in the same area.

Ecosystem – A community and its abiotic environment.

It is a stable, settled unit of nature consisting of a community of organisms, interacting with each other and with their surrounding physical and chemical environment. These vary greatly in size.

Ecology – The study of relationships between living organisms and their environment

4.1.2 – Distinguish between autotroph and heterotroph

Autotroph – An organism that synthesizes its organic molecules from simple inorganic substances

Heterotroph – An organism that obtains organic molecules from other organisms

4.1.3 – Distinguish between consumers, detritivores and saprotrophs

Consumers – An organism that ingests other organic matter that is living or recently killed

Detritivore – An organism that ingests non-living organic matter, also known as a decomposer.

Saprotroph – An organism that lives on or in non-living organic matter, secreting digestive enzymes into it and absorbing the products of digestion

4.1.4 – Describe what is meant by a food chain, giving three examples, each with at least three linkages (four organisms)

A food chain is a representation of the relationships between organisms based on their diet. A → B indicates that A is ‘eaten’ by B (that is, the arrow indicates the direction energy flow). Each food chain should include a producer and consumers, but not decomposers. Named organisms at either species or genus level should be used. Common species names can be used instead of binomial names. However, general names such as ‘tree’ or ‘fish’ should not be used.

4.1.5 – Describe what is meant by a food web

A food web is a diagram that shows how food chains are linked together in to more complex feeding relationships. Advantages of a food web include:

Advantages of a food web include:

  • Shows the much more complex interactions between species within a community or ecosystem
  • There is more than one producer supporting a community, which this shows
  • It shows that a single producer can be a food source for a number of primary consumers
  • A consumer may have a number of different food sources on the same or different trophic levels
  • A consumer can be an omnivore, feeding as a primary consumer and at also at higher trophic levels

Food webs, as they are very detailed and complicated, often reflect the interest of its author. Species of interest are detailed by name, whereas less important or interesting species are grouped into a large family.

4.1.6 – Define trophic level

The trophic level of an organism defines the feeding relationship of that organism to other organisms in a food chain. In a food web, a consumer can occupy a number of different trophic levels, depending on which organism is the prey.

4.1.7 – Deduce the trophic level of organisms in a food chain and a food web

Looking at the food web, assess the trophic level by looking at how many previous organisms it feeds off. You should also be able to identify them with the levels of producer, primary consumer, secondary consumer, and so on. The terms herbivore and carnivore are not always applicable.

4.1.8 – Construct a food web containing up to 10 organisms, using appropriate information

Where possible, identify the trophic levels for each organism.

4.1.9 – State that light is the initial energy source for almost all communities

To maintain food chains, food webs, communities and all their interactions, energy is required. Sunlight is the source of this energy for most communities, both aquatic and terrestrial. The principle trap of sunlight energy is the protein molecule chlorophyll, found in the chloroplasts of producers cells, mainly green plants.

4.1.10 – Explain the energy flow in a food chain

Energy losses between trophic levels include material not consumed or material not assimilated, and heat loss through cell respiration. Essentially the loss of heat from respiration

Photosynthesis converts light into energy. Not all solar energy will come into contact with chlorophyll and will therefore not be trapped in the synthesis of organic compounds.

Death and the consumption of dead organisms by detritivores, or as food not assimilated because of incomplete digestion.

Energy loss can occur in undigested food, which is used by saprophytes (decomposers), or in the reactions of respiration. Ultimately, all energy will be lost as heat.

4.1.11 – State that energy transformations are never 100% efficient

The transfer of energy from one trophic level to the next in inefficient. Only 10-20% of the energy on one trophic level will be assimilated at the next higher level.

In extreme environments like the arctic, the initial trapping of energy by producers is low, making the food chains much shorter. Likewise, in tropical rainforests, where the trapping of energy is more efficient, the food chains are longer, and the food webs are more complex.

This explains why larger predators at the top of the food chain are so rare. The energy loss throughout the food chain means that the number of organisms decreases at each step. In the higher trophic levels, organisms become less and less common. They are also more prone to extinction as they rely on the organisms below them. Any decrease in numbers in these organisms cause a chain reaction, resulting in possible extinction.

4.1.12 – Explain reasons for the shape of pyramids of energy

A pyramid of energy shows the flow of energy from one trophic level to the next in a community. The units of pyramids of energy are, therefore, energy per unit area per unit time, such as kJ m-2 yr-1

In a typical pyramid of energy, the initial solar energy is not shown. The narrowing shape shows the gradual loss of energy as you move up the food chain to the higher trophic levels. The scale to which it is drawn (energy/area/unit time) is written at the base of the pyramid.

4.1.13 – Explain that energy enters and leaves ecosystems, but nutrients must be recycled

Energy Flows

At every trophic level, energy is lost as heat. The narrowing of the energy pyramid shows that all energy is eventually radiated into space as heat.

Matter Cycles

New matter is not created, nor is it lost the way energy is. Instead, producers (autotrophs) take organic molecules and convert them into organic compounds, helping them to be recycled and re-used. Consumers then take in this organic matter as they feed and use it for their own growth. Such cycles of matter include the carbon, nitrogen and oxygen cycles.

4.1.14 – State that saprotrophic bacteria and fungi (decomposers) recycle nutrients

Nutrients, unlike energy, are not lost, but are recycled and re-used. Decomposers (saprotrophic bacteria and fungi) recycle organic molecules (nutrients) found in dead organisms. This is a complex process, serving many functions. These include the formation of soil, recycling nutrients stored in organic molecules, and reduction of high energy carbon compounds. Mineral elements are absorbed by plants as ions from the soil solution. This cycling process is called biogeochemical cycles, in which all essential elements take part. The biological process of decomposition begins when saprotrophic bacteria and

The biological process of decomposition begins when saprotrophic bacteria and fungi secrete extra-cellular digestive enzymes onto the dead organism. The enzymes hydrolyse the biological molecules that the dead organism is composed of. The hydrolysed molecules are soluble, and are absorbed by the fungi or bacteria. Organic molecules are oxidised to release carbon dioxide back into the atmosphere, and nitrogen in the form of nitrate, nitrite and ammonium. This also produces energy for the saprophyte, but returns in the various forms of matter to the abiotic environment.


Can assimilated energy be simply lost from a trophic level? - Biology

The food chain is the pathway along which food is transferred from one trophic or feeding level to another.

Energy, in the form of food, moves from the producers to the herbivores to the carnivores. Only about 10 percent of the energy stored in any trophic level is converted to organic matter at the next trophic level. This means that if you begin with 1,000g of plant matter, the food chain can support 100g of herbivores (primary consumers), 10g of secondary consumers, and only lg of tertiary consumers. As a result of the loss of energy from one trophic level to the next, food chains never have more than four or five trophic levels.

Examples of food chain: An example of simple food chain operating in a grassland or forest. In a grassland or forest, there is a lot of grass. This grass is eaten up by animals like deer,and deer is then consumed by a lion.

This food chain tells us that grass is the starting point of this food chain. The grass is eaten up by deer and the deer is then eaten up by a lion. In this food chain, grass is the producer which uses sunlight energy to prepare food like carbohydrates by the process of photosynthesis. This grass is then consumed by a herbivore called deer. And the deer is consumed by a carnivore called lion. The food chain represents a single directional or unidirectional transfer of energy.

In the above example, the food chain tells us that the transfer of energy takes place from grass to deer and then to lion. It cannot take place in the reverse direction form lion to deer to grass. The study of food chains in an area or habitat helps us in knowing various interactions among the different organisms and also their interdependence.


What is the 10 rule in biology?

Explanation: When energy moves between trophic levels , 10% of the energy is made available for the next level. Some of that energy is also lost through heat loss. Thus, when a predator eats that consumer, all of the energy the consumer gained from the plant is not available to the predator: it has been used and lost.

Similarly, what happens to the other 90% in the 10% rule? Ten Percent Rule: What happens to the other 90% of energy not stored in the consumer's body? Most of the energy that isn't stored is lost as heat or is used up by the body as it processes the organism that was eaten.

Accordingly, why is the 10 rule important?

The 10-percent rule (10PR) is one of the most important and time-proven principles in running. It states that you should never increase your weekly mileage by more than 10 percent over the previous week. The 10PR gains its importance from the fact that the vast majority of running injuries are overuse injuries.

The Ten percent law of transfer of energy from one trophic level to the next was introduced by Raymond Lindeman (1942). According to this law, during the transfer of energy from organic food from one trophic level to the next, only about ten percent of the energy from organic matter is stored as flesh.


Can assimilated energy be simply lost from a trophic level? - Biology

1. Discuss the definition of the term species. (8 marks)

  • a species is a group of organisms
  • a species shares a common gene pool
  • showing similar morphology / characteristics
  • capable of interbreeding
  • and producing fertile offspring
  • but dissimilar organisms sometimes interbreed
  • mule formed by crossing horse and donkey / other example of interspecific hybridisation
  • interspecific hybrids are sometimes fertile
  • sometimes organisms that are very similar will not interbreed
  • Drosophila pseudoobscura and persimilis / other example of sibling species
  • reference to the problem of defining fossil species
  • reference to the problem of species that only reproduce asexually
  • reference to the problem of isolated populations gradually diverging

2. Compare the ways in which autotrophic, heterotrophic and saprotrophic organisms obtain energy. (6 max)

  • autotrophs use an external / non-organic energy source
  • (some) autotrophs use light / (some) autotrophs use photosynthesis
  • (some) autotrophs use inorganic chemical reactions / (some) autotrophs use chemosynthesis
  • heterotrophs obtain energy from other organisms
  • heterotrophs (usually) ingest food / consume food
  • saprotrophs obtain energy from non-living matter / dead organisms
  • saprotrophs digest organic matter extracellularly

(Award 1 mark for the meaning)

  • feeding level for an organism in a food chain
  • naming of habitat (1 mark)
  • naming three trophic levels correctly (1 mark)
  • three examples forming a food chain from the named habitat (1 mark)

4. Outline the energy flow between trophic levels in a food chain. 6 marks

  • (original) source of energy in a food chain is from (sun)light
  • captured by plants/autotrophs/producers/first trophic level
  • by means of photosynthesis/converted to chemical energy/organic molecules
  • plants use part of energy for own energy requirements/lost through cell respiration
  • consumers use energy for own requirements from organisms in previous trophic level
  • energy travels between trophic levels/producer to 1st consumer/1st consumer to 2nd consumer/2nd consumer to 3rd consumer
  • not all material is assimilated/consumed/not digested/lost in faeces / OWTTE
  • only a small amount of energy/(approximately) 10–20% is passed between trophic levels / most/80–90%/a large amount of the energy of a trophic level is lost (and not transferred)
  • loss of energy from organisms in form of heat
  • energy is not recycled in an ecosystem (but nutrients are)

(Award any of the above marking points in a correctly annotated diagram.)

5. Ecologists sometimes display data from an ecosystem using a diagram called a pyramid of energy. Describe what is shown in pyramids of energy. 6 marks

  • pyramid of energy shows the flow of energy from one trophic level to the next (in a community)
  • units of pyramids of energy are energy per unit area per unit time/kJ m –2 yr –1
  • bar width is proportional to the energy stored (in the biomass) in that trophic level
  • the first/lowest trophic level is producers
  • second level is primary consumers/herbivores
  • third level of secondary consumers/carnivores
  • only a small amount (10 to 20 %) of energy of one level is passed to the next
  • bar width/energy stored in the trophic level decreases (proportionally) as you go up each level
  • pyramid shows that there is a limit to the length of food chains

(Award any of the above marking points to a correctly drawn and clearly labelled pyramid.)

6. Draw a labeled diagram of the carbon cycle. 6 marks

(Award [1] for each of the following shown using labelled arrows or notes on a diagram. Accept carbon dioxide or CO 2 throughout.)

  • carbon dioxide/CO 2 in atmosphere/water
  • (cell) respiration producing CO 2 in atmosphere
  • photosynthesis (fixing) CO 2 from atmosphere into producers/plants
  • death/decomposition transforming C in plants/animals to C in bacteria/fungi/saprotophs
  • fossilization converting carbon in organisms to fossil fuels/coal/oil/natural gas
  • combustion/burning of fossil fuels/coal/oil/natural gas/peat producing CO 2 / weathering of shells/rocks releasing CO 2
  • combustion/burning of producers/forests producing CO 2
  • feeding (organic C) in producers/plants to (organic C) in consumers/animals
  • feeding (organic C) in consumers to other consumers

7. All organisms in an ecosystem are involved in the carbon cycle. Outline the roles of living organisms in the carbon cycle. (8 marks)

  • plants/producers fix carbon (dioxide)/use carbon (dioxide) in photosynthesis
  • sugars/carbon compounds (produced) in plants/producers from photosynthesis
  • (carbon compounds in) plants/producers eaten by animals/primary consumers/herbivores
  • (carbon compounds in) primary consumers eaten by secondary consumers/ passed along food chain
  • carbon compounds/sugars/organic molecules digested and absorbed by consumers
  • carbon dioxide released by cell respiration (in plants/animals/consumers)
  • plants/animals die and are decomposed by (saprotrophic) bacteria/fungi
  • carbon dioxide released by cell respiration in bacteria/fungi/decomposers
  • enzymes released to digest/hydrolyse carbon compounds in organic matter
  • forest fires/combustion releases carbon dioxide
  • humans burn fossil fuels adding carbon dioxide to the atmosphere

Award any of the above points if clearly drawn in an annotated diagram.

8. Describe the relationship between the rise in the concentration of atmospheric carbon dioxide and the enhanced greenhouse effect. 5 marks

  • CO2 is a greenhouse gas
  • increases in CO2 increase/enhance the greenhouse effect
  • greenhouse effect is a natural phenomenon but not its increase
  • Earth receives short wave radiation from the sun
  • reradiated from Earth as longer wave radiation/infra red/heat
  • CO2 /greenhouse gases trap/absorb longer wave radiation/infra red/heat
  • global warming happened during same time/period as CO2 rise
  • CO2 concentration correlated (positively) with global temperature / global temperature
  • increases as CO2 concentration increases
  • (causal) link accepted by most scientists
  • no proof that man-made increases in CO2 have caused global warming

9. Outline the causes and consequences of the enhanced greenhouse effect. 4 marks

  • a. burning of (fossil) fuels/coal/oil/gas releases carbon dioxide
  • b. deforestation/loss of ecosystems reduces carbon dioxide uptake
  • c. methane emitted from cattle/livestock/melting permafrost/waste dumps
  • d. heating of the atmosphere/global warming/climate change
  • e. melting of ice caps/glaciers/permafrost / sea level rise / floods / droughts / changes in ocean currents / more powerful hurricanes / extreme weather events / other abiotic consequence
  • f. changes in species distributions/migration patterns / increased decomposition rates / increases in pest/pathogen species / loss of ice habitats / other biotic consequence

10. Outline the consequences of a global temperature rise on arctic ecosystems. 6 marks


Section Summary

Organisms in an ecosystem acquire energy in a variety of ways, which is transferred between trophic levels as the energy flows from the bottom to the top of the food web, with energy being lost at each transfer. The efficiency of these transfers is important for understanding the different behaviors and eating habits of warm-blooded versus cold-blooded animals. Modeling of ecosystem energy is best done with ecological pyramids of energy, although other ecological pyramids provide other vital information about ecosystem structure.


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