UNDERSTANDING
- Most ecosystems rely on a supply of energy from sunlight
- Light energy is converted to chemical energy in carbon compounds by photosynthesis
- Chemical energy in carbon compounds flows through food chains by means of feeding
- Energy released by respiration is used in living organisms and converted to heat
- Living organisms cannot convert heat to other forms of energy
- Heat is lost from ecosystems
- Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels
SKILLS
- Quantitative representations of energy flow using pyramids of energy
NATURE OF SCIENCE
- Use theories to explain natural phenomena: the concept of energy flow explains the limited length of food chains
SUNLIGHT AND ECOSYSTEMS
Most ecosystems rely on a supply of energy from sunlight
For most biological communities, the initial source of energy is sunlight. Living organisms can harvest this energy by photosynthesis: plants, eukaryotic algae including seaweeds that grow on rocky shores, and cyanobacteria. These organisms are often referred to by ecologists as producers.
Heterotrophs do not use light energy directly, but they are indirectly dependent on it. There are several groups of heterotrophs in ecosystems: consumers, saprotrophs and detritivores. All of them use carbon compounds in their food as source of energy.
The amount of energy supplied to ecosystems in sunlight verses around the world. The percentage of this energy that is harvested by producers and therefore available to other organisms also varies. In the Sahara Desert, for example, the intensity of sunlight is very high but little of it becomes available to organisms because there are very few producers.
ENERGY CONVERSION
Light energy is converted to chemical energy in carbon compounds by photosynthesis
Producers absorb sunlight using chlorophyll and others photosynthetic pigments. This converts the light energy to chemical energy, which is used to make carbohydrates, lipid and all the other carbon compounds in producers.
Producers can release energy from their carbon compounds by cell respiration and then use it for cell activities. Energy released in this way is eventually lost to the environment as waste heat. However, only some of the carbon compounds in producers are used in this way and the largest part remains in the cells and tissues of producers. The energy in these carbon compounds is available to heterotrophs.
- Most ecosystems rely on a supply of energy from sunlight
- Light energy is converted to chemical energy in carbon compounds by photosynthesis
- Chemical energy in carbon compounds flows through food chains by means of feeding
- Energy released by respiration is used in living organisms and converted to heat
- Living organisms cannot convert heat to other forms of energy
- Heat is lost from ecosystems
- Energy losses between trophic levels restrict the length of food chains and the biomass of higher trophic levels
SKILLS
- Quantitative representations of energy flow using pyramids of energy
NATURE OF SCIENCE
- Use theories to explain natural phenomena: the concept of energy flow explains the limited length of food chains
SUNLIGHT AND ECOSYSTEMS
Most ecosystems rely on a supply of energy from sunlight
For most biological communities, the initial source of energy is sunlight. Living organisms can harvest this energy by photosynthesis: plants, eukaryotic algae including seaweeds that grow on rocky shores, and cyanobacteria. These organisms are often referred to by ecologists as producers.
Heterotrophs do not use light energy directly, but they are indirectly dependent on it. There are several groups of heterotrophs in ecosystems: consumers, saprotrophs and detritivores. All of them use carbon compounds in their food as source of energy.
The amount of energy supplied to ecosystems in sunlight verses around the world. The percentage of this energy that is harvested by producers and therefore available to other organisms also varies. In the Sahara Desert, for example, the intensity of sunlight is very high but little of it becomes available to organisms because there are very few producers.
ENERGY CONVERSION
Light energy is converted to chemical energy in carbon compounds by photosynthesis
Producers absorb sunlight using chlorophyll and others photosynthetic pigments. This converts the light energy to chemical energy, which is used to make carbohydrates, lipid and all the other carbon compounds in producers.
Producers can release energy from their carbon compounds by cell respiration and then use it for cell activities. Energy released in this way is eventually lost to the environment as waste heat. However, only some of the carbon compounds in producers are used in this way and the largest part remains in the cells and tissues of producers. The energy in these carbon compounds is available to heterotrophs.
ENERGY IN FOOD CHAINS
Chemical energy in carbon compounds flows through food chains by means of feeding.
A food chain is a sequence of organisms, each of which feeds on the previous one. There are usually between two and five organisms in a food chain. It is rare for there to be more organisms in the chain. As they do not obtain food from other organisms, producers are always the first organisms in a food chain. The subsequent consumers are consumers. Primary consumers feed on producers; secondary consumers feed on primary consumers; tertiary consumers feed on secondary consumers, and so on. No consumers feed on the last organism in a food chain. Consumers obtain energy from the carbon compounds in the organisms on which they feed. The arrows in a food chain therefore indicate the direction of energy flow.
Chemical energy in carbon compounds flows through food chains by means of feeding.
A food chain is a sequence of organisms, each of which feeds on the previous one. There are usually between two and five organisms in a food chain. It is rare for there to be more organisms in the chain. As they do not obtain food from other organisms, producers are always the first organisms in a food chain. The subsequent consumers are consumers. Primary consumers feed on producers; secondary consumers feed on primary consumers; tertiary consumers feed on secondary consumers, and so on. No consumers feed on the last organism in a food chain. Consumers obtain energy from the carbon compounds in the organisms on which they feed. The arrows in a food chain therefore indicate the direction of energy flow.
RESPIRATION AND ENERGY RELEASE
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.
HEAT ENERGY IN ECOSYSTEMS
Living organisms cannot convert heat to other forms of energy.
Living organisms can perform various energy conversions:
- Light energy to chemical energy in photosynthesis
- 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.
They cannot convert heat energy into any other form of energy
HEAT LOSSES FROM ECOSYSTEMS
Heat is lost from ecosystems.
Heat resulting from cell respiration makes living organisms warmer. This heat can be useful in making cold-blooded animals more active. Birds and mammals increase their rate of heat generation. if necessary to maintain there constant body temperatures.
According to the laws of thermodynamics in physics, heat passes from hotter to cooler bodies, so heat produced in living organisms is all eventually lost to the abiotic environment. The heat may remain in the ecosystem for a while, but ultimately is lost, for example when heat is radiated into the atmosphere.
ENERGY LOSSES AND ECOSYSTEMS
Energy losses between trophic levels restrict the length of food cans and the biomass of higher trophic levels.
Biomass is the total mass of a group of organisms. It consists of the cells and tissues of those organisms, including the carbohydrates and other carbon compounds that they contain. Because carbon compounds have chemical energy, biomass has energy. Ecologists can measure how much energy is added per year by groups of organisms to their biomass. The results are calculated per square metre of the ecosystem so that different trophic levels can be compared. When this is done, the same trend is always found: the energy added to biomass by each successive trophic level is less. In secondary consumers, for example, the amount of energy is always less per yearner square metro of ecosystem than in primary consumers.
Because of these losses, only a small proportion of the 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 the losses occur at each stage in a food chain, there is less and less energy available to each successive trophic level. After only a few stages in a food chain the amount of energy remaining would not be enough to support another trophic level.
Biomass, measured in grams, also diminishes along food chains, due to loss of carbon dioxide and water from respiration and loss form the food chain of uneaten or undigested parts of organisms.
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.
HEAT ENERGY IN ECOSYSTEMS
Living organisms cannot convert heat to other forms of energy.
Living organisms can perform various energy conversions:
- Light energy to chemical energy in photosynthesis
- 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.
They cannot convert heat energy into any other form of energy
HEAT LOSSES FROM ECOSYSTEMS
Heat is lost from ecosystems.
Heat resulting from cell respiration makes living organisms warmer. This heat can be useful in making cold-blooded animals more active. Birds and mammals increase their rate of heat generation. if necessary to maintain there constant body temperatures.
According to the laws of thermodynamics in physics, heat passes from hotter to cooler bodies, so heat produced in living organisms is all eventually lost to the abiotic environment. The heat may remain in the ecosystem for a while, but ultimately is lost, for example when heat is radiated into the atmosphere.
ENERGY LOSSES AND ECOSYSTEMS
Energy losses between trophic levels restrict the length of food cans and the biomass of higher trophic levels.
Biomass is the total mass of a group of organisms. It consists of the cells and tissues of those organisms, including the carbohydrates and other carbon compounds that they contain. Because carbon compounds have chemical energy, biomass has energy. Ecologists can measure how much energy is added per year by groups of organisms to their biomass. The results are calculated per square metre of the ecosystem so that different trophic levels can be compared. When this is done, the same trend is always found: the energy added to biomass by each successive trophic level is less. In secondary consumers, for example, the amount of energy is always less per yearner square metro of ecosystem than in primary consumers.
Because of these losses, only a small proportion of the 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 the losses occur at each stage in a food chain, there is less and less energy available to each successive trophic level. After only a few stages in a food chain the amount of energy remaining would not be enough to support another trophic level.
Biomass, measured in grams, also diminishes along food chains, due to loss of carbon dioxide and water from respiration and loss form the food chain of uneaten or undigested parts of organisms.