Biomass Transfer Through An Ecosystem

What do all organisms found within an ecosystem require?

A source of energy to perform the functions needed to survive.

What is the source of energy for almost all ecosystems on earth?

The sun, which’s light energy is converted into chemical energy through photosynthesis. This chemical energy is then transferred to other non-photosynthetic organisms as food.

What are food webs and food chains?

Diagrams that scientists use to show how the transfer of biomass and therefore energy, through the organisms in an ecosystem.

What is each stage in a food chain known as?

A trophic level.

What is always the first trophic level?

A producer.

What is a producer?

An organism that converts light energy into chemical energy by photosynthesis.

What are all the subsequent consumers in the food chain following the producer?

Consumers.

What are consumers>

Organisms that obtain their energy by feeding on other organisms.

What is the second trophic level?

A primary consumer.

What is a primary consumer?

An animal that eats a producer.

How are the trophic levels after the primary consumer labelled?

Successively - secondary, tertiary and quaternary consumers.

What is a secondary consumer?

An animal that eats a primary consumer.

What is teriary consumer?

An animal that eats a secondary consumer.

What is a quaternary consumer?

An animal that eats a tertiary consumer.

What do food chains rarely have more trophic levels after quaternary consumers?

There is not sufficient biomass and stored energy left to support any further organisms.

What are decomposers?

Important components of food webs - they break down dead organisms releasing nutrients back into the ecosystem.

How can food chains be presented diagrammatically?

As a pyramid of numbers, which each level representing the number of organisms at each trophic level. The producers are always placed at the bottom.

What is biomass?

The mass of living material present in a particular place of in particular organisms. It is an important measure in the study of food webs and chains as it can be equated to energy content.

How is biomass calculated at each trophic level?

By multiplying the biomass present in each organism by the total number of organisms in that trophic level.

What is the easiest way to measure biomass?

By measuring the mass of fresh material present. However, water content must be discounted and the presence of varying amounts of water in different organisms makes this technique unreliable unless very large samples are used. Scientists therefore usually calculate the ‘dry mass‘ of organisms present.

What are the problems with calculating dry mass?

Organisms have to be killed in order to be dried. The organisms are place din an oven at 80C until all water has evaporated. To minimise the destruction of organisms, only a sample is taken but this may not be representative of the entire population.

What is biomass measured in?

Grams per square metre for areas of land, or grams per cubic metre for areas of water.

Why is the biomass in each trophic nearly always less than the trophic level below?

Because biomass consists of all the cells and tissues of the organisms present, including the carbohydrates and other carbon compounds the organisms contain. As carbon compounds are a store of energy, biomass can be equated to energy content. When animals eat, only a small proportion of food they ingest is converted into re tissue, it is only this part of the biomass which is available for the next trophic level to eat.

What is the energy available at each trophic level measured in?

Kilojoules per metre squared per year, to allow for changes in photosynthetic production and consumer feeding patterns throughout the year,

What happens as biomass is transferred between trophic levels?

The energy contained is transferred.

What is ecological efficiency?

The efficiency with which biomass or energy is transferred from one trophic level to the next.

How much of the sunlight received by producers is converted into chemical energy/biomass?

1-3%.

Why is only 1-3% of solar energy converted into biomass by producers?

• Not all of the solar energy available is used for photosynthesis - approximately 90% is reflected, some is transmitted through the leaf, and some is of unusable wavelength.

• Other factors may limit photosynthesis, such as water availability.

  • A proportion of the energy is ‘lost‘, as it is used for photosynthetic reaction.

What is the total solar energy that plants convert to organic matter called?

Gross production. However, plants use 20-50% of this energy in respiration. The remaining energy is converted into biomass. This is the energy available to the next trophic level and is known as the net production.

How can the energy available to the next trophic level be calculated?

Net production = gross production - respiratory losses.

How much biomass do consumers at each level convert into their own organic tissue?

10% at most.

Why is that consumers at each trophic level convert at most 10% of the biomass in their food to their own organic tissue?

• Not all of the biomass of an organism is eaten, for example plant roots or animal bones may not be consumed.

• Some energy is transferred to the environment as metabolic heat, as a result of movement and respiration.

• Some energy is lost from the animal in excretory materials such as urine.

• Some parts of an organism are eaten but are indigestible, which are egested as faeces.

How much of the total energy originally present in the incident sunlight is finally embodied as biomass in a tertiary consumer?

Only around 0.001%.

How can the efficiency of the energy transfer between each trophic level of a food chain be calculated?

Energy or biomass available after the1 transfer/ energy or biomass available before the transfer x 100.

What does human civilisation depend on?

Agriculture.

What does agriculture involve?

Manipulating the environment to favour plant species that we can eat (crops) and to rear animals for food or their produce. Plants and animals are provided with the abiotic conditions they need to thrive. Competition from other species is removed as well as the treat of predators.

What would happen in a natural ecosystem?

Humans would occupy the second, third or even fourth tropic level.

What does agriculture create?

Very simple food chains. In farming animals or animal produce for human consumption, only three trophic levels are present - products, primary and secondary consumers.

What is involved in cultivating plants for human livestock?

Just two trophic levels - producers and primary consumers. This means that the minimum energy is lost as there are fewer tropic levels present than in the natural ecosystem. This ensures that as much energy as possible is transferred into biomass that can be eaten as humans.