Biology Ecology Unit (Pre-IB Science 10)
Compare energy and nutrient flow in ecosystems.
Energy flow:
Energy in an ecosystem originates from the sun and flows through the system in a LINEAR or ONE-WAY DIRECTION.
This energy transfer continues up the food chain, from autotrophs to primary consumers to secondary consumers and so on. However, at each transfer, a significant amount of energy is LOST, primarily as HEAT.
Once the energy reaches the top of the food chain, it does not cycle back but is LOST FROM THE SYSTEM. Therefore eventually there is not enough energy to support another trophic level.
Nutrient flow:
Nutrients are the elements and compounds that organisms need to live, grow, and reproduce. These include elements like carbon, nitrogen, and phosphorus. Unlike energy, nutrients are RECYCLED within and between ecosystems.
They are taken up by plants from the soil or water, transferred to consumers when they eat the plants, and then returned to the soil or water when the organisms die and DECOMPOSE. This cycle can continue INDEFINITELY, with nutrients being reused and recycled within the system.
Both:
Both energy flow and nutrient cycling are essential for maintaining the structure and function of an ecosystem. They determine the types and distribution of organisms, the productivity of the ecosystem, and its overall stability.
Both energy and nutrients flow through energy pyramids or food chains/webs, starting from autotrophs/producers and moving through different trophic levels.
What are autotrophs and heterotrophs?
Autotrophs, or primary producers, are organisms that can produce their own food from natural sources like water, light energy, carbon dioxide (CO2) and chemical energy.
Heterotrophs, also known as consumers, are organisms that cannot produce their own food and must obtain it by consuming other heterotrophs or autotrophs.
Draw an energy pyramid and label it. Include energy and nutrient flow.
Has detailed energy flow:
https://images.nationalgeographic.org/image/upload/v1638892193/EducationHub/photos/energy-flow-in-an-ecosystem.jpg
Also had nutrient cycling labeled:
https://upload.wikimedia.org/wikipedia/commons/d/d4/Ecological_Pyramid.png
What is a trophic level?
Trophic levels are the steps in a food chain of an ecosystem. The organisms of a chain are classified into these levels on the basis of their feeding behaviour.
True or false; organisms can feed on more than one trophic level.
TRUE. Example: Some carnivores also consume plant materials and are called omnivores.
Explain incomplete consumption.
Organisms in a trophic level are not usually entirely consumed by organisms in the next trophic level (ex. bones, hair, etc.) and the energy stored in these compounds are lost from the food chain. Saprotrophs and detritivores will consume these parts.
Explain incomplete digestion.
Not all parts of food ingested by organisms are digested and absorbed (some animals do not digest tough fibrous plant matter containing cellulose) --> egested in faeces and passes to saprotroph or detritivores.
True or false: It is often said that 10% of energy is lost between trophic levels.
FALSE. It is usually said that 90% of energy is lost, but there is variation between food chains.
Compare saprotrophs and detritivores.
Both: Both saprotrophs and detritivores are decomposers, meaning they break down dead organic material.
Both contribute to nutrient cycling by releasing nutrients from dead organic matter back into the environment.
Saprotrophs: Digest dead organic matter EXTERNALLY using enzymes that break down the material, and then absorb the resulting nutrients. (ex. bacteria and fungi)
Detritivores: Ingest and digest dead organic matter internally, within their digestive systems. (ex. earthworms and dung beetles)
Why is there energy loss between trophic levels?
- Incomplete digestion and consumption, cell respiration, heat loss, and movement or temperature regulation.
What is the significance of the 90% energy loss estimate between trophic levels?
It illustrates that most energy is lost as heat or other forms, limiting the number of trophic levels in an ecosystem.
How does heat loss effect energy transfer in ecosystems?
Some chemical energy is converted into heat which cannot be used in the next trophic level, resulting in energy loss.
How does incomplete digestion contribute to energy loss?
Not all ingested food is digested and absorbed, with some parts egested as faeces to saprotrophs or detritivores. The energy from these parts is lost and cannot be reused.
How does incomplete consumption contribute to energy loss?
Incomplete consumption occurs when organisms are not entirely eaten, leaving parts like bones or hair that contain stored energy and are lost from the food chain.
What organisms are typically found at each trophic level of an energy pyramid?
Producers/autotrophs at the base, primary consumers above them, secondary consumers next, and tertiary consumers at the top. (The consumers are AKA heterotrophs)
From where do an organism's energy requirements (ATP) originate?
An organism's energy requirements come from the release of energy stored in carbon bonds through cellular respiration.
How does a food web differ from a food chain?
A food web shows multiple feeding relationships where many consumers eat more than one species and are preyed upon by more than one species.
What is the chemical equation for photosynthesis?
CO₂ + H₂O + light energy → C₆H₁₂O₆ + O₂
What is the equation for cellular respiration?
C₆H₁₂O₆ + O₂ → CO₂ + H₂O + ATP
What is biomass?
The total mass of all living organisms in a given area or ecosystem at a given time.
What is a carbon sink? What is a carbon source?
Carbon sink: A natural system that absorbs more carbon than it releases (e.g., forests, oceans, permafrost).
Carbon source: Anything that releases more carbon into the atmosphere than it absorbs (e.g., burning fossil fuels).
What are homologous structures?
Structures within different organisms that have different functions and the same structure.
What are analogous structures?
Structures within different organisms that have the SAME function but different structures.
True or false: Analogous structures come from divergent evolution.
False. Analogous structures come from convergent evolution.
What are open and closed systems?
Open system- both energy and chemical substances can enter and exit.
Closed system- energy can enter or exit, but chemical resources cannot be removed or replaced.
What is primary production and secondary production?
Primary: Accumulation of carbon compounds by autotrophs by growing and reproducing.
Secondary: Accumulation of carbon compounds by heterotrophs by growing and reproducing but less than primary production.