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Energy Flow in Ecosystem

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Energy Flow in Ecosystem

An ecosystem is a biological community of organisms interacting with their biotic (other living organisms) and abiotic (physical environment) components. Ecosystems play a crucial role in climate regulation, soil, water and air quality.

The primary source of energy in the ecosystem originates from the sun. The energy from the sun transforms into chemical energy during photosynthesis. Plants in the terrestrial environment convert the sun's energy. Meanwhile, in aquatic ecosystems, aquatic plants, microalgae (phytoplankton), macroalgae and cyanobacteria convert the sun's energy. The consumers can then use transformed energy from the producers in the food web.

Energy transfer in the ecosystems


According to how they obtain nutrition, we can divide living organisms into three main groups: producers, consumers, and saprobionts (decomposers).


Producers

A producer is an organism that makes its food, such as glucose, during photosynthesis. These include photosynthetic plants. These producers are also termed autotrophs.

An autotroph is any organism that can use inorganic compounds, such as the carbon from carbon dioxide, to make organic molecules, such as glucose.

Some organisms will use both autotrophic and heterotrophic ways to obtain energy. Heterotrophs are organisms that ingest organic matter made from producers. For example, the pitcher plant will both photosynthesise and consume insects.


Autotrophs are not only photosynthetic organisms (photoautotrophs). Another group you may come across are the chemoautotrophs. Chemoautotrophs will use chemical energy to produce their food. These organisms usually reside in harsh environments, e.g., sulfur-oxidising bacteria found in marine and freshwater anaerobic environments.

Let's dive deeper into the ocean, where the sunlight does not reach. Here is where you will meet chemoautotrophs who dwell in deep-sea hot springs and hydrothermal vents. These organisms create food for deep-sea dwellers, such as deep-sea octopuses (Figure 1) and zombie worms. These dwellers do look quite funky!

In addition, organic particles, which can be living and non-living, sink to the bottom of the ocean to provide another food source. This includes tiny bacteria and sinking pellets produced by copepods and tunicates.

Energy Flow in Ecosystem, dumbo octopus, StudySmarterA dumbo octopus dwelling in the deep sea

Consumers


Consumers are organisms that obtain their energy for reproduction, movement and growth by consuming other organisms. We also refer to them as heterotrophs. There are three groups of consumers found in ecosystems:

  • Herbivores
  • Carnivores
  • Omnivores

Herbivores


Herbivores are organisms that eat the producer, such as plants or macroalgae. They are the primary consumers in the food web.


Carnivores


Carnivores are organisms that consume herbivores, carnivores and omnivores to obtain their nutrition. They are the secondary and tertiary consumers (and so on). There are a limited number of consumers in food pyramids because the transfer of energy decreases until it is not enough to sustain another trophic level. Food pyramids usually stop after the tertiary or quaternary consumer.

Trophic levels refer to the different stages in a food pyramid.


Omnivores


Omnivores are organisms that will consume both producers and other consumers. They can therefore be primary consumers. For example, humans are primary consumers when we eat vegetables. When humans consume meat, you will most likely be a secondary consumer (since you mainly consume herbivores).


Saprobionts


Saprobionts, also known as decomposers, are organisms that break down organic matter into inorganic compounds. To digest the organic matter, saprobiotics release digestive enzymes, which will break down the tissue of the decaying organism. The major groups of saprobionts include fungi and bacteria.

Saprobionts are extremely important in the nutrient cycles as they release inorganic nutrients such as ammonium and phosphate ions back into the soil, which producers can access once again. This completes the entire nutrient cycle, and the process starts again.

Mycorrhizal fungi form symbiotic relationships with plants. They can live in the root networks of the plants and provide them with essential nutrients. In return, the plant will provide sugars, such as glucose, for the fungi.

Energy transfer and productivity

Plants can capture only 1-3% of solar energy, and this happens due to four main factors:


  1. Clouds and dust reflect over 90% of the solar energy, and the atmosphere absorbs it.

  2. Other limiting factors may limit the amount of solar energy that can be taken, such as carbon dioxide, water, and temperature.

  3. The light may not reach the chlorophyll in chloroplasts.

  4. The plant can absorb only certain wavelengths (700-400nm). Non-usable wavelengths will be reflected.

Chlorophyll refers to pigments within plant chloroplasts. These pigments are necessary for photosynthesis.

Unicellular organisms, such as cyanobacteria, also contain photosynthetic pigments. These include chlorophyll-α and β-carotene.

Net primary production


Net primary production (NPP) is the chemical energy stored after what is lost during respiration, and this is usually around 20-50%. This energy is available to the plant for growth and reproduction.


We will use the equation below to explain the NPP of the producers:


Energy Flow in Ecosystem Net primary production NPP equation for producers StudySmarter


Gross primary production (GPP) represents the total chemical energy stored in the plant biomass. The units for NPP and GPP are expressed as units of biomass per land area per time, such as g/m2/year. Meanwhile, respiration is the loss of energy. The difference between these two factors is your NPP. Approximately 10% of the energy will be available for primary consumers. Meanwhile, secondary and tertiary consumers will get up to 20% from the primary consumers.


This results due to the following:


  • The whole organism is not consumed - some parts are not eaten, such as the bones.

  • Some parts cannot be digested. For example, humans cannot digest cellulose present in the plant cell walls.

  • Energy is lost in materials excreted, including urine and faeces.

  • Energy is lost as heat during respiration.

Although humans cannot digest cellulose, it still aids our digestion! Cellulose will help whatever you have consumed to move through your digestive tract.


NPP of consumers have a slightly different equation:


Energy Flow in Ecosystem Net primary production NPP equation for consumers StudySmarter


As you now understand, the energy available will become lower and lower at each higher trophic level.

Trophic levels


A trophic level refers to a position of an organism within the food chain/pyramid. Each trophic level will have a different amount of biomass available. The units for biomass in these trophic levels include kJ/m3/year.

Biomass is the organic material made from living organisms, such as plants and animals.

To calculate the percentage efficiency of the energy transfer at each trophic level, we can use the following equation:


Energy Flow in Ecosystem percentage efficiency of the energy transfer StudySmarter


Food chains


A food chain/pyramid is a simplified way to describe the feeding relationship between producers and consumers. When the energy moves up to higher trophic levels, a large amount will be lost as heat (about 80-90%).


Food webs


A food web is a more realistic representation of the energy flow within the ecosystem. Most organisms will have multiple food sources, and many food chains will be linked. Food webs are extremely complex. If you take humans as an example, we will consume many sources of food.

We will use Figure 2 as an example of an aquatic food web. The producers here are coontail, cottontail and algae. The algae are consumed by three different herbivores. These herbivores, such as bullfrog tadpole, are then consumed by multiple secondary consumers. The apex predators (predators at the top of the food chain/web) are humans and the great blue heron. All waste, including faeces and dead organisms, will be broken down by decomposers, in the case of this particular food chain, bacteria.

Human impact on the food webs

Humans have had a significant impact on the food webs, often disrupting the energy flow between the trophic levels. Some examples include:


  • Excessive consumption. This has led to the removal of important organisms in the ecosystem (e.g., overfishing and illegal hunting of endangered species).
  • Removal of apex predators. This leads to an excess of lower-level consumers.
  • Introduction of non-native species. These non-native species disrupt native animals and crops.
  • Pollution. Excessive consumption will lead to excessive waste (e.g., littering and pollution by burning fossil fuels). A large number of organisms will be sensitive to pollution.
  • Excessive land use. This leads to the displacement and loss of habitats.
  • Climate change. Many organisms cannot tolerate changes in their climate, and this consequently leads to habitat displacement and biodiversity loss.

The Deepwater Horizon oil spill in the Gulf of Mexico was the largest. The oil rig exploded, and the oil spilled into the ocean. The total discharge was estimated at 780,000 , which had a detrimental impact on marine wildlife. The spill affected over 8,000 species, including coral reefs being discoloured or damaged up to 4000ft deep, bluefish tuna experiencing irregular heartbeats, cardiac arrests, among other issues.

Energy Flow in Ecosystem - Key takeaways

  • An ecosystem is an interaction between the organisms (biotic) and their physical environment (abiotic). Ecosystems regulate the climate, air, soil and water quality.
  • Autotrophs harvest energy from the sun/chemical energy sources. The producers transform the energy into organic compounds.
  • Energy is transferred from the producers when consumers consume them. The energy travels within the food web to different trophic levels. Energy is transferred back into the ecosystem by decomposers.
  • Humans have had a negative impact on food webs. Some of the effects include climate change, habitat loss, the introduction of non-native species and pollution.

Frequently Asked Questions about Energy Flow in Ecosystem

The autotrophs (producers) harvest energy from the sun or chemical sources. The energy moves through the trophic levels within the foodwebs when the producers are consumed.

Energy is transferred within the food web, and organisms use it to carry out complex tasks. Animals will use energy for growth, reproduction and life, in general.

Sun’s energy and chemical energy.

The energy will be harvested from physical sources such as chemical compounds and the sun. The energy will enter the ecosystem through the autotrophs.

The ecosystem is essential in regulating climate, air, water and soil quality.

Final Energy Flow in Ecosystem Quiz

Question

Name three examples of producers in the aquatic ecosystem.

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Answer

Aquatic plants, phytoplankton, cyanobacteria.

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Question

What is meant by the biotic and abiotic components of the ecosystem?

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Answer

Biotic refers to the living organisms, abiotic is the physical environment.

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Fill in the blanks about the energy in the ecosystems: 
The primary source of energy is the ________.  ___________ will harvest this energy during the process of _________. In the terrestrial environments, the ________ captures this energy. In the aquatic environments, an example would be _______. This energy is ________, and the _________ can use it within the food web.


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Answer

The primary source of energy is the sun. The photoautotrophs will harvest this energy during the process of photosynthesis. In terrestrial environments, this energy will be captured by the plant. In the aquatic environments, an example would be microalgae (phytoplankton)/macroalgae/aquatic plant/cyanobacteria/any other producer within the aquatic environment. This energy is transformed, and the consumers can use it within the food web.

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Question

What are the three types of consumers?


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Answer

Herbivores, carnivores, and omnivores.

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Question

What is the difference between an autotroph and a heterotroph?

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Answer

An autotroph will use inorganic compounds to make its food. A heterotroph will use organic compounds (consume other organisms) to gain energy.

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Question

What is an apex predator? Give an example.

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Answer

An apex predator is a consumer on top of the food chain/web. Buzzard is an example of an apex predator within the terrestrial ecosystem.

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Question

Calculate the percentage efficiency transfer from a phytoplankton (level 1) (biomass 20 kg) to zooplankton (level 2) (biomass 2 kg). Energy transfer equation: Energy transfer (%) = Biomass in a higher trophic level/Biomass in a lower trophic level.

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Answer

1%

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The food chain is a realistic representation of the energy transfer within the ecosystem. True or False?


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Answer

False.

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Question

What are the other compounds required (other than the sun’s energy) to transform the energy via photosynthesis?


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Answer

Carbon dioxide and water.

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Question

How will excessive land use affect the food webs?

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Answer

Excessive land use can lead to loss or displacement of habitats which in turn will cause species loss.

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Question

Why would you consume a primary consumer instead of a secondary consumer?

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Answer

Since the primary consumer is at a lower trophic level, you would gain more energy from its consumption than the secondary consumer.

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What is the source of energy loss when it moves to higher trophic levels?


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Answer

80-90% of energy is lost as heat.

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Give an example of an organism that is both an autotroph and a heterotroph.


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Answer

The pitcher plant. It will both photosynthesise and catch insects.

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Question

What do the specialised producers use as an energy source within harsh, often anaerobic environments?

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Answer

Chemical sources of energy.

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Question

What do unicellular cyanobacteria contain for photosynthesis (instead of the chloroplast)?


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Answer

Photosynthetic pigments.

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Biomass is made up of inorganic matter. True or False?

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Answer

False.

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Why is biomass within the ecosystem hard to measure?

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Answer

Biomass is measured as carbon/dry mass of the living organisms. Animals will first need to be killed to be measured.

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Why is biomass measured in grams per cubic metre in the aquatic environment?


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Answer

Aquatic environments are three-dimensional and so the volume is measured.

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What is a biological pyramid of biomass?


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Answer

Biological pyramid shows the energy movement within a given area and time.

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What is the type of reaction (exothermic or endothermic) that happens when biomass is burned?


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Answer

Exothermic (heat is released).

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What is a bomb calorimeter used for?

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Answer

Bomb calorimeter is used to measure the heat released from a specific biomass sample.

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What is biomass referred to as in the fuel industry?


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Answer

Biomass is a renewable, sustainable fuel source derived from organic matter.

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Why is biomass sustainable?


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Biomass is sustainable because the nutrients are cycled back into the environment.

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What is the biggest source of biomass within the fuel industry?


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Answer

Wood.

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What are three disadvantages of using biomass as a fuel?


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Examples of disadvantages:

  1. Higher cost compared to other renewables such as wind.
  2. Possible deforestation for wood biomass.
  3. Biomass is not as efficient as fossil fuel.

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Why would you rather use C4 plants rather than C3 plants for fuel?


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Answer

C4 plants such as wheatgrass, are more efficient due to their higher rate of photosynthesis and a reduced rate of photorespiration. Photorespiration is a wasteful pathway.

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What is biological farming?


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Answer

Biological farming is a chemical free method of farming.

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What practises are incorporated to increase the efficiency of energy transfer in the human food chain?


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Answer

Reduction in respiratory losses by reducing animal movement and simplification of human food chains to increase energy transfer efficiency.

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How would organic farming increase biodiversity at an ecosystem level?

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Answer

Organic farms can act as refugee spots for wild plant species. Use of organic fertilisers will allow species such as birds and pollinators to return.

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What are three disadvantages of organic farming?

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Answer

Examples of disadvantages:

  1. Lower yield of crops/livestock.
  2. Higher costs of the final product.
  3. Quality of the crop can also fluctuate seasonally depending on the soil quality and other external factors.

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