4.2 Energy flow
Essential idea: Ecosystems require a continuous supply of energy to fuel life processes and to replace energy lost as heat.
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4.2.U1 Most ecosystems rely on a supply of energy from sunlight.
4.2.U1 Most ecosystems rely on a supply of energy from sunlight.
Be able to:
State how energy in carbon compounds enters most biological communities.
List three groups of autotrophs.
ln green plants, and some bacteria, are photoautotrophic – they use sunlight as a source of energy. This makes light the initial source of energy for almost all communities
In a few ecosystems the producers are chemoautotrophic bacteria, which use energy derived from chemical processes
Most ecosystems rely on a supply of energy from sunlight
Living organisms can harvest this energy through the process of photosynthesis
Autotrophs of plants, cyanobacteria, eukaryotic algae also carry out photosynthesis
4.2.U2 Light energy is converted to chemical energy in carbon compounds by photosynthesis.
4.2.U2 Light energy is converted to chemical energy in carbon compounds by photosynthesis.
Be able to:
Outline how light energy is converted to chemical energy.
Producers absorb sunlight using chlorophyll and other photosynthetic pigments.
Converts light energy to chemical energy used to make carbo hydrates, lipids, and other carbon compounds
Produces can release energy from their carbon compounds by cell respiration and the use it for cell activities
Energy released this way is eventually lost to environment as waste heat
Light energy is converted to chemical energy in carbon compounds by photosynthesis
Light energy is converted to chemical energy in order to make lipids, carbohydrates and other carbon compounds found in producers
In addition, the producers absorb the sunlight using photosynthetic pigments and chlorophyll
4.2.U3 Chemical energy in carbon compounds flows through food chains by means of feeding.
4.2.U3 Chemical energy in carbon compounds flows through food chains by means of feeding.
Be able to:
Define food chain and food web.
State the meaning of the arrow in a food web or chain.
Draw a food chain, labeling the producer, primary consumer, secondary consumer and tertiary consumer.
Energy enters most ecosystems as sunlight, where it is converted into chemical energy by producers (via photosynthesis). This chemical energy is stored in carbon compounds (organic molecules) and is transferred to heterotrophs via feeding
Food chain: a sequence of organisms, each of which feeds on the previous one.
Carbon compounds store chemical energy in C-C bond
Heterotrophs fed on living organisms by ingestion
Saprotrophs feed on dead organisms by external digestion
Usually 2-5 organisms in a food chain
Producers are always first (they do not obtain food from other organisms)
Subsequent organisms are consumers
Primary consumers feed on producers; secondary consumers feed on primary consumers; tertiary consumers feed on secondary consumers – so on.
4.2.U4 Energy released from carbon compounds by respiration is used in living organisms and converted to heat.
4.2.U4 Energy released from carbon compounds by respiration is used in living organisms and converted to heat.
Be able to:
List three reasons why living organisms need energy for cell activities.
State the function of ATP.
Outline how ATP is formed, referencing exothermic and endothermic reactions.
Outline the reason why respiration releases heat.
Energy stored in organic molecules (e.g. sugars and lipids) can be released by cell respiration to produce ATP
Living organisms need energy for cell activities:
Synthesizing large molecules (DNA, RNA, proteins)
Pumping molecules or ions across membranes by active transport
Moving things around inside cell (chromosomes or vesicles; muscle cells – protein fibers that cause muscle contraction)
ATP supplies energy for those activities. Every cell produces its own ATP supply
All cells can produce ATP by cell respiration
Carbohydrates and lipids are oxidized – exothermic. Energy released is used in endothermic reactions to make ATM
Cell respiration transfers chemical energy from glucose and other carbon compounds to ATP
Chemical energy in carbon compounds such as glucose is not immediately usable by the cell but chemical energy in ATP can be used directly for many different activities
Energy transformations are never 100% efficient – not all of the energy from the oxidation of carbon compounds in cell respiration is transferred to ATP.
Remainder is converted to heat
Some heat is produced when ATP is used in cell activities
4.2.U5 Living organisms cannot convert heat to other forms of energy.
4.2.U5 Living organisms cannot convert heat to other forms of energy.
Be able to:
Draw a flow chart to illustrate the energy conversions performed by living organisms.
Living organisms can perform various energy conversions:
Light energy -> chemical energy (photosynthesis)
Chemical energy -> kinetic energy (muscle contraction)
Chemical energy -> electrical energy (nerve cells)
Chemical energy -> heat energy (heat-generating adipose tissue)
Cannot convert heat energy into any other form of energy. Energy pyramids illustrate the quantity of energy within the biomass of each trophic level
only a portion of energy in any level is transferred to the next, commonly being 10-20%
of the plant biomass consumed by a typical herbivore:
50% is not assimilated: lost as feces (indigestible cellulose)
35% is assimilated but lost as heat during cellular respiration
15% is consumed and assimilated and incorporated into biomass
4.2.U6 Heat is lost from ecosystems.
4.2.U6 Heat is lost from ecosystems.
Be able to:
State the reason why heat created by living organisms is eventually lost from the ecosystem.
All of these reactions are exothermic and release thermal energy (heat) as a by-product
Living organisms cannot turn this heat into other forms of usable energy
This heat energy is released from the organism and is lost from the ecosystem (unlike nutrients, which are recycled)
Hence ecosystems require a continuous influx of energy from an external source (such as the sun)
Heat resulting from cell respiration makes living organisms warmer
Can be useful in making cold-blooded animals more active
Birds/mammals increase rate of heat generation if necessary to maintain constant body temperatures
Heat passes from hotter to cooler bodies – heat produced in living organisms is all eventually lost to abiotic environment
Heat may remain in ecosystem for a while but ultimately is lost
All energy released by respiration for use in cell activities will ultimately be lost from an ecosystem
4.2.U7 Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels.
4.2.U7 Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels.
Be able to:
Define biomass.
Define trophic level.
State the unit used for communicating the energy in each trophic level of a food chain.
Outline three reasons why the amount of energy decreases at higher trophic levels.
State the average amount of energy passed through each trophic level of a food chain.
A food web is the elaborate interconnected relationships within an ecosystem based on feeding and energy transfer
When energy transformations take place in living organisms the process is never 100% efficient
Most of the energy is lost to the organism – either used in respiration, released as heat, excreted in faeces or unconsumed
Typically energy transformations are ~10% efficient, with about 90% of available energy lost between trophic levels
The amount of energy transferred depends on how efficiently organisms can capture and use energy (usually between 5 – 20%
Biomass: the total mass of a group of organisms.
Consists of the cells and tissues of those organisms, including carbohydrates / other carbon compounds they contain
Carbon compounds have chemical energy, therefore biomass has energy
Can measure how much energy is added per year by groups of organisms to their biomass.
Results calculated per square meter of ecosystem (different trophic levels can be compared)
The energy added to biomass each successive trophic level is less.
Loss of energy between trophic levels:
Most of energy in food is digested and absorbed by a trophic level is released by them in respiration for use in cell activities – lost as heat
Organisms in a trophic level are not usually entirely consumed by organisms in the next trophic level.
Predators may not eat material from the bodies of their prey such as bones or hair.
Energy in uneaten material passes to saprotrophs or detritivores rather than passing to organisms in the next trophic level
Not all parts of food ingested by the organisms in a trophic level are digested and absorbed. Some material is indigestible and is egested in feces. – Passed on to saprotrophs or detritivores.
Only small proportion of energy in the biomass of organisms in one trophic level will ever become part of the biomass of organisms in the next trophic level.
As losses occur at each stage in the food chain, there is gradually less energy available to each successive trophic level.
Biomass (measured in grams) also diminishes along food chains due to loss of carbon dioxide and water from respiration and loss from the food chain of uneaten or undigested parts of organisms
Biomass of higher trophic levels is usually smaller than of lower levels
4.2.S1 Quantitative representations of energy flow using pyramids of energy.
4.2.S1 Quantitative representations of energy flow using pyramids of energy.
Be able to:
Describe the shape and units of a pyramid of energy.
Draw a pyramid of energy given data for an ecosystem.
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, for example, kJ m-2 yr-1. The pyramid demonstrates that energy transformations between trophic levels are never 100% efficient
Pyramids of energy will never appear inverted as some of the energy stored in one source is always lost upon transfer. Each level should be roughly one tenth of the size of the preceding level (as energy transformations are ~10% efficient). The bottom level will always represent the producers, with subsequent levels representing consumers (primary, secondary, etc.)
Rain forest Animation- Look at this site and answer the questions.
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