Exam 1: Energy-flow through ecosystems
The study of the flow of energy through the ecosystem is known as ecological energetics. The energy from the sun enters the food chain at the producer level during photosynthesis and is the source of energy for the ecosystem. The sun’s energy is passed from one feeding or trophic level to another through the ecosystem. Energy is passed along a hierarchy of trophic levels with primary producers (plants or for example photosynthetic phytoplankton/algae) at the starting point of the chain. All animals are consumers. Primary consumers eat plants and are also called herbivores. Secondary consumers are carnivores, they feed on primary consumers. Tertiary consumers are carnivores that eat other consumers. Eventually the energy leaves the system as heat.
The following summarises the flow of energy through the ecosystem:
• Green plants trap solar energy and manufacture sugars from simple raw materials by the process of photosynthesis.
• Herbivores (primary consumers) are animals which feed on plants. Carnivores are animals that feed on other animals.
• Each of these groups forms a feeding or trophic level with energy passing from each level to a higher one as material is eaten. Only a small amount of the total energy that reaches the plant as light is incorporated into plant tissues. As energy is passed along the food chain there is a large loss of energy at each level.
• At each trophic level energy is lost through cellular respiration (e.g. glucose is respired inside cells and some heat energy is released from the process), through the excretion of waste products (e.g. ammonia/urea which still contain some chemical enegry) and the egestion of faeces (e.g. cointaining undigested cellulose which also has lots of chemical energy in it) so the amount of energy available to the next trophic is reduced compared to the energy that entered that particular trophic level.
• The sequence from plant to herbivore to carnivore is a food chain and is the route by which energy passes between trophic levels. It is the loss of energy at each level which limits the length of a food chain so the number of links in the chain is normally limited to four or five trophic levels.
• On the death of producers and consumers, some energy remains locked up in the organic compounds of which they are made. Detritivores (holozoic heterotrophs) and decomposers (saprophytic bacteria and fungi) contribute to the recycling of nutrients.
The study of the flow of energy through the ecosystem is known as ecological energetics. The energy from the sun enters the food chain at the producer level during photosynthesis and is the source of energy for the ecosystem. The sun’s energy is passed from one feeding or trophic level to another through the ecosystem. Energy is passed along a hierarchy of trophic levels with primary producers (plants or for example photosynthetic phytoplankton/algae) at the starting point of the chain. All animals are consumers. Primary consumers eat plants and are also called herbivores. Secondary consumers are carnivores, they feed on primary consumers. Tertiary consumers are carnivores that eat other consumers. Eventually the energy leaves the system as heat.
The following summarises the flow of energy through the ecosystem:
• Green plants trap solar energy and manufacture sugars from simple raw materials by the process of photosynthesis.
• Herbivores (primary consumers) are animals which feed on plants. Carnivores are animals that feed on other animals.
• Each of these groups forms a feeding or trophic level with energy passing from each level to a higher one as material is eaten. Only a small amount of the total energy that reaches the plant as light is incorporated into plant tissues. As energy is passed along the food chain there is a large loss of energy at each level.
• At each trophic level energy is lost through cellular respiration (e.g. glucose is respired inside cells and some heat energy is released from the process), through the excretion of waste products (e.g. ammonia/urea which still contain some chemical enegry) and the egestion of faeces (e.g. cointaining undigested cellulose which also has lots of chemical energy in it) so the amount of energy available to the next trophic is reduced compared to the energy that entered that particular trophic level.
• The sequence from plant to herbivore to carnivore is a food chain and is the route by which energy passes between trophic levels. It is the loss of energy at each level which limits the length of a food chain so the number of links in the chain is normally limited to four or five trophic levels.
• On the death of producers and consumers, some energy remains locked up in the organic compounds of which they are made. Detritivores (holozoic heterotrophs) and decomposers (saprophytic bacteria and fungi) contribute to the recycling of nutrients.
Detritivores are organisms which feed on small fragments of organic debris from plants and animals. This organic material is referred to as detritus and is made up of non-living organic material, such as faeces, fallen leaves and the remains of dead organisms. Examples of detritivores are earthworms and woodlice.
Decomposers are microbes, bacteria and fungi that obtain nutrients from dead organisms and faeces. They complete the process of decomposition started by detritivores.
Saprobionts include bacteria and fungi that feed by secreting enzymes on the food substrate absorbing the resulting products of this extracellular digestion.
Decomposers are microbes, bacteria and fungi that obtain nutrients from dead organisms and faeces. They complete the process of decomposition started by detritivores.
Saprobionts include bacteria and fungi that feed by secreting enzymes on the food substrate absorbing the resulting products of this extracellular digestion.
The ultimate source of energy for ecosystems is the sun from which energy is released in the form of electromagnetic waves.
• A good deal of the solar energy reaching the Earth’s atmosphere does not penetrate it. It is reflected or absorbed and radiated back into space by the ozone layer, dust particles and clouds.
• Also about 90% of the energy reaching the surface of the Earth is reflected by vegetation, soil, and water or absorbed and radiated to the Earth’s atmosphere as infrared heat.
• This means that only about 10% of the solar energy that reaches the earth's surface is left for producers to make use of. Therefore, only a small part of the total amount of energy reaching the Earth’s atmosphere enters ecosystems. Also, the quantity absorbed by plants varies considerably at different latitudes.
Of this light energy hitting a plant only 1% to 5% is utilised by the plant in photosynthesis; alot of the light energy hitting the plant is lost, partly by:
1. By being transmitted straight through the plant (not hitting the photosynthetic pigments in the chloroplasts inside the mesophyll cells of the leaves
2. By reflection of green light which is not of the corrcet wavelength for absorption by the photosyntheitc pigments (chlorophyll a for example is the primary photosynthetic pigment and absorbs red and blue light only but reflects greeen)
3. By the evaporation of water inside the air chambers of the leaves during transpiration
• A good deal of the solar energy reaching the Earth’s atmosphere does not penetrate it. It is reflected or absorbed and radiated back into space by the ozone layer, dust particles and clouds.
• Also about 90% of the energy reaching the surface of the Earth is reflected by vegetation, soil, and water or absorbed and radiated to the Earth’s atmosphere as infrared heat.
• This means that only about 10% of the solar energy that reaches the earth's surface is left for producers to make use of. Therefore, only a small part of the total amount of energy reaching the Earth’s atmosphere enters ecosystems. Also, the quantity absorbed by plants varies considerably at different latitudes.
Of this light energy hitting a plant only 1% to 5% is utilised by the plant in photosynthesis; alot of the light energy hitting the plant is lost, partly by:
1. By being transmitted straight through the plant (not hitting the photosynthetic pigments in the chloroplasts inside the mesophyll cells of the leaves
2. By reflection of green light which is not of the corrcet wavelength for absorption by the photosyntheitc pigments (chlorophyll a for example is the primary photosynthetic pigment and absorbs red and blue light only but reflects greeen)
3. By the evaporation of water inside the air chambers of the leaves during transpiration