4.2 Energy Flow Flashcards
What does it mean if an organism is photoautotrophic? give examples
All green plants, and some bacteria, are photoautotrophic – they use sunlight as a source of energy
What is the initial source for most communities?
This makes light the initial source of energy for almost all communities
What is an exception to a community that uses sunlight as its primary energy source?
In a few ecosystems the producers are chemoautotrophic bacteria, which use energy derived from chemical processes
What process makes use of light energy?
Light energy is absorbed by photoautotrophs and is converted into chemical energy via photosynthesis
What is light energy used for?
This light energy is used to make organic compounds (e.g. sugars) from inorganic sources (e.g. CO2)
Why do heterotrophs consume autotrophs?
Heterotrophs ingest these organic compounds in order to derive their chemical energy (ATP)
What happens when organic compounds are broken down?
When organic compounds are broken down via cell respiration, ATP is produced to fuel metabolic processes
What is light energy converted into?
Energy enters most ecosystems as sunlight, where it is converted into chemical energy by producers (via photosynthesis)
How is chemical energy stored?
This chemical energy is stored in carbon compounds (organic molecules) and is transferred to heterotrophs via feeding
What is a trophic level?
The position an organism occupies within a feeding sequence is known as a trophic level
What occupies the first trophic level?
Producers always occupy the first trophic level in a feeding sequence
What occupies the second trophic level?
Primary consumers feed on producers and hence occupy the second trophic level
What occupies the consequent trophic levels (2+)?
Further consumers (e.g. secondary, tertiary, etc.) may occupy subsequent trophic levels
What is a food chain?
A food chain shows the linear feeding relationships between species in a community
What do arrows in a food chain represent?
Arrows represent the transfer of energy and matter as one organism is eaten by another (arrows point in direction of energy flow)
What is the sequence of organisms in a food chain?
The first organism in a food chain is always a producer, followed by consumers (primary, secondary, tertiary, etc.)
How can energy stored in organic molecules be released?
Energy stored in organic molecules (e.g. sugars and lipids) can be released by cell respiration to produce ATP
What is ATP used for?
This ATP is then used to fuel metabolic reactions required for growth and homeostasis
What is a by-product of respiration?
A by-product of these chemical reactions is heat (thermal energy), which is released from the organism
In what ways can energy be lost?
Not all energy stored in organic molecules is transferred via heterotrophic feeding – some of the chemical energy is lost by:
Being excreted as part of the organism’s faeces
Remaining unconsumed as the uneaten portions of the food
Into what 3 forms can energy produced by an organism be converted into?
kinetic, electrical and light energy
What is an example of a use of kinetic energy?
during muscular contractions
What is an example of a use of electrical energy?
during the transmission of nerve impulses
What is an example of a use of light energy?
producing bioluminescence
What type of reaction are the reactions in a food chain?
Living organisms cannot turn this heat into other forms of usable energy
What is the consequence of these reactions being exothermic?
This heat energy is released from the organism and is lost from the ecosystem (unlike nutrients, which are recycled)
What does the constant loss of energy from an ecosystem result in?
Hence ecosystems require a continuous influx of energy from an external source (such as the sun)
What percentage of energy transformations are efficient?
Typically energy transformations are ~10% efficient, with about 90% of available energy lost between trophic levels
What does the amount of energy transferred depend on?
The amount of energy transferred depends on how efficiently organisms can capture and use energy (usually between 5 – 20%)
What does the loss of energy between trophic levels say about higher trophic levels?
As energy is lost between trophic levels, higher trophic levels store less energy as carbon compounds and so have less biomass
What is biomass?
Biomass is the total mass of a group of organisms – consisting of the carbon compounds contained in the cells and tissues
How can scientists measure the amount of energy added to organisms?
Because carbon compounds store energy, scientists can measure the amount of energy added to organisms as biomass
How does biomass change along food chains and why?
Biomass diminishes along food chains with the loss of carbon dioxide, water and waste products (e.g. urea) to the environment
Can there be an unlimited number of trophic levels? why?
Because energy and biomass is lost between each level of a food chain, the number of potential trophic levels are limited
How much energy do higher trophic levels receive? What does this result in?
Higher trophic levels receive less energy / biomass from feeding and so need to eat larger quantities to obtain sufficient amounts
How is energy lost by these higher trophic level organisms?
Because higher trophic levels need to eat more, they expend more energy (and biomass) hunting for food
Why aren’t there more trophic levels?
If the energy required to hunt food exceeds the energy available from the food eaten, the trophic level becomes unviable
What is a pyramid of energy?
A pyramid of energy is a graphical representation of the amount of energy at each trophic level of a food chain
What is the unit of a pyramid of energy?
They are expressed in units of energy per area per time (e.g. kJ m–2 year–1)
Do pyramids of energy always have the same general structure?
YES
Pyramids of energy will never appear inverted as some of the energy stored in one source is always lost upon transfer
What is the rough change in size in pyramids of energy?
Each level should be roughly one tenth of the size of the preceding level (as energy transformations are ~10% efficient)
What will the bottom level of a pyramid of energy usually represent?
The bottom level will always represent the producers, with subsequent levels representing consumers (primary, secondary, etc.)
