4.2

ENERGY PYRAMIDS

(TB and sheets)

Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels.

When biomass (the total dry mass of organisms within an area or volume) is consumed, energy is transferred. Energy transfers between tropic levels is inefficient. Only about 10% of the energy available at one trophic level is passed on to the next.

Chemical energy in carbon compounds flows through food chains by means of feeding.

-Food chain is a sequence of organisms, each of which feeds on the previous one -Two- five organisms in a chain is normal -Arrow indicates the direction of energy flow -consumers obtain energy from the carbon compounds in the organism on which they feed

There are three ways, shown in the flow chart by which food and energy can be passed to detritivores or saprotrophs rather than to next stage in the food chain:

-Some organisms die before they are eaten by the organism in the food chain. For example, foxes do not eat every rabbit in their community and some rabbits die from disease. -Some parts of organisms are not eaten, such as bones, hair and gall bladders. -Some parts of organisms are indigestible, such as cellulose in food eaten by humans. The undigested parts are egested faeces.

Heat is lost from ecosystems.

-heat passes from hotter to cooler bodies (laws of thermodynamics) -heat produced in living organisms (including plants) is lost to the abiotic environment -heat is radiated from the environment into the atmosphere -all energy released by respiration will be ultimately lost from an ecosystem

Most ecosystems rely on a supply of energy from sunlight.

-initial source of energy in most biological communities is sunlight -producers like plants, eukaryotic algae and cyanobacteria use photosynthesis (AUTOTROPHS) -consumers, detrivores and saprotrophs use the carbon in their food (heterotrophs)

Energy released from carbon compounds by respiration is used in living organisms and converted to heat.

-organisms use chemical energy for life processes (ATP) -cells produce ATP by cell respiration -Carbohydrates and lipids are oxidised and the chemical energy is transferred to ATP -Energy transformation is not 100% efficient. Some is lost as heat.

ENERGY LOSSES- Food containing energy is passed along food chains when the primary consumer feeds on the producer, the secondary consumer feeds on the primary consumer and so on

. At each successive stage in food chain less food is available and therefore less chemical energy. This is due to looses of food and energy between the stages in a food chain.

Energy released by respiration is used in living organisms and converted to heat Living organisms need energy for cell activities such as these: - Synthesizing large molecules like DNA, RNA and proteins - Pumping molecules or ions across membranes by active transport - Moving things around inside the cell, such as chromosomes or vesicles, or in muscle cells the protein fibers that cause muscle contraction.

ATP supplies energy for these activities. Every cell produces its own ATP supply. All cells can produce ATP by cell respiration. In this process carbon compounds such as carbohydrates and lipids are oxidized. These oxidation reactions are exothermic and the energy released is used in endothermic reactions to make ATP. So cell respiration transfers chemical energy from glucose and other carbon compounds to ATP. The second law of thermodynamics states that energy transformations are never 100% efficient. Not all of the energy from the oxidation of carbon compounds in cell respirations is transferred to ATP. The remainder is converted to heat.

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Consumers, detritivores and saprotrophs obtain energy from their food. There is a chemical energy in the food. Carbon compounds and the energy contained in them can pass from organism to organism along food chains start with a producer that originally made the carbon compounds by photosynthesis. Light is therefore the initial energy source for the whole community. (PIC)

So, energy in the bodies of dead organisms, parts of organisms and in faeces passes to detritivores or saprotrophs. The other cause of energy losses is cell respiration. All organisms release energy from carbon compounds by cell respiration and use the energy for essential processes such as muscle contraction or active transport.

Energy used in this way is converted into heat which is lost from the organism. No organisms can convert the heat energy back into chemical energy, and the hear is eventually lost from the ecosystem. For this reason ecosystems need an energy source to replace energy lost. For most ecosystems the energy source is sunlight.

Living organisms cannot convert heat to other forms of energy.

Living organism can perform various energy conversions -light energy to chemical energy in phs -chemical energy to kinetic energy in muscle contraction -chemical energy to electrical energy in nerve cells -chemical energy to heat energy in heat generating adipose tissue CANNOT CONVERT HEAR ENERGY INTO ANY OTHER FORM OF ENERGY

The organisms in a community all need a supply of energy. Most organism obtain their energy in one of two ways.

Plants, algae and some bacteria absorb light energy and convert it into chemical energy in carbon compounds. Because these organisms make their own food they are called producers.

Light energy is converted to chemical energy in carbon compounds by photosynthesis.

Producers capture the sun's light energy and convert it in to chemical energy in the process of photosynthesis. CO2+H20+ light (light energy is captured!) --> C6H12O6 (and converted to chemical energy!) + O2 Chemical energy (ATP) is used to make carbs, lipids and all other carbon compounds in producers

Each species in a food chain feeds on the previous one, apart from the producer at the start that makes its own food by photosynthesis. Producer, primary consumer, secondary consumer and tertiary consumer are trophic levels. The trophic level of an organism is its position in the food chain. Food chains commonly contain three or four trophic levels and rarely more then five.

The limited length of food chains can be explained by the theories of energy flow and energy losses. Only a small proportion of energy and biomass is passed on from one trophic level to the next. The percentage is very variable but is unlikely to be more then 10%.

Trophic level

The position of the organism in a food chain. Producers on the first trophic level, primary consumers on the second.