Section 4: Ecology and the environment
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a) The organism in the environment
4.1: Understand the terms population, community, habitat and ecosystem
- All the organisms of a particular species found in an ecosystem at any one time form the population of that species in the ecosystem, for example, all of the koi fish in one pond form the koi fish population of that pond
- The populations of all species found in a particular ecosystem at any one time form the community in that ecosystem, for example, all of the animals in a mangrove form the community in that mangrove
- Within each ecosystem there is a range of habitats - these are the places where specific organisms live
- An ecosystem is a distinct, self-supporting system of organisms interacting with each other and with a physical environment
4.2: Recall the use of quadrats to estimate the population size of an organism in two different areas
When an ecologist wants to know how many organisms there are in a particular area, it would not be feasible to count them all. Instead, samples can be taken using quadrats to estimate the population size of an organism in a particular area.
When an ecologist wants to know how many organisms there are in a particular area, it would not be feasible to count them all. Instead, samples can be taken using quadrats to estimate the population size of an organism in a particular area.
4.3: Describe the use of quadrats as a technique for sampling the distribution of organisms in their habitats
Quadrats can be used for sampling the distribution of organisms in their habitats. Imagine you are trying to calculate how many daisies there are spread over an area of lawn. The quadrat is randomly placed on the lawn and the number of daisies inside the area are counted (e.g. eight daisies in the quadrat). The following formula can be used to calculate the amount of flowers spread over the lawn:
Quadrats can be used for sampling the distribution of organisms in their habitats. Imagine you are trying to calculate how many daisies there are spread over an area of lawn. The quadrat is randomly placed on the lawn and the number of daisies inside the area are counted (e.g. eight daisies in the quadrat). The following formula can be used to calculate the amount of flowers spread over the lawn:
number of plants per m2 = total number of plants counted รท total area sampled (in m2)
b) Feeding relationships
4.4: Recall the names given to different trophic levels to include producers, primary, secondary and tertiary consumers and decomposers
- Producers are plants which photosynthesize to produce food
- Primary consumers are animals that eat plants
- Secondary consumers are animals that eat primary consumers
- Tertiary consumers are animals that eat secondary consumers
- Decomposers decay dead material and help to recycle nutrients
4.5: Understand the concepts of food chains, food webs, pyramids of number, pyramids of biomass and pyramids of energy transfer
- Food chains show what is eaten in an ecosystem
- Food webs show how all the food chains are linked
- Pyramids of number compare how many organisms are present at each trophic level at a particular time
- Pyramids of biomass show the mass of living material at each trophic level
- Pyramids of energy transfer show how much energy is transferred at each trophic level
4.6: Understand the transfer of substances and energy along a food chain
4.7: Explain why only about 10% of energy is transferred from one trophic level to the next
Only 10% of energy is transferred from one trophic level to the next because for example, if a wolf is eating a rabbit, it does not eat the whole thing - it may only eat one leg and leave the rest of the body for decomposers. Also, the rabbit gives of 90% of its energy as heat while producing energy, so only 10% useful energy is left to be transferred between trophic levels.
Only 10% of energy is transferred from one trophic level to the next because for example, if a wolf is eating a rabbit, it does not eat the whole thing - it may only eat one leg and leave the rest of the body for decomposers. Also, the rabbit gives of 90% of its energy as heat while producing energy, so only 10% useful energy is left to be transferred between trophic levels.
c) Cycles within ecosystems
4.8: Describe the stages in the water cycle, including evaporation, transpiration, condensation and precipitation
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4.9: Describe the stages in the carbon cycle, including respiration, photosynthesis, decomposition and combustion
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4.10: Describe the stages in the nitrogen cycle, including the roles of nitrogen fixing bacteria, decomposers, nitrifying bacteria and denitrifying bacteria
The atmosphere contains 78% nitrogen gas which is highly unreactive. Plants need nitrogen in order to make nitrates for growth, and they get it from the soil.
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d) Human influences on the environment
4.11: Understand the biological consequences of pollution of air by sulfur dioxide and by carbon monoxide
Carbon monoxide is a product of incomplete combustion: when humans breathe it in, it binds with the hemoglobin in red blood cells to create carboxyhemoglobin instead of oxyhemoglobin. This means that the red blood cell is not carrying useful oxygen around the body, it is carrying carbon monoxide which doesn't do anything. Too much carboxyhemoglobin in the body can lead to carbon monoxide poisoning, which causes flu-like symptoms and even death.
Sulfur dioxide dissolves in the water vapor in the air to create sulfuric acid, which normally has a low pH. This causes acid rain which can be damaging to ecosystems and to humans when consumed.
Carbon monoxide is a product of incomplete combustion: when humans breathe it in, it binds with the hemoglobin in red blood cells to create carboxyhemoglobin instead of oxyhemoglobin. This means that the red blood cell is not carrying useful oxygen around the body, it is carrying carbon monoxide which doesn't do anything. Too much carboxyhemoglobin in the body can lead to carbon monoxide poisoning, which causes flu-like symptoms and even death.
Sulfur dioxide dissolves in the water vapor in the air to create sulfuric acid, which normally has a low pH. This causes acid rain which can be damaging to ecosystems and to humans when consumed.
4.12: Recall that water vapor, carbon dioxide, methane and CFCs are greenhouse gases
Water vapor, carbon dioxide, methane and CFCs are all greenhouse gases because they prevent heat from escaping the earth through the atmosphere.
Water vapor, carbon dioxide, methane and CFCs are all greenhouse gases because they prevent heat from escaping the earth through the atmosphere.
4.13: Understand how human activities contribute to greenhouse gases
- Water vapor is produced through evaporation and transpiration
- Carbon dioxide is produced when fossil fuels are burnt and when trees are cut down
- Nitrous oxides are produced when car engines get hot enough for nitrogen to chemically bond with oxygen
- Methane is produced from rotting plants, the growing of rice, and cow farts
- CFCs (or chlorofluorocarbons) are manmade chemicals that were once used to make aerosol sprays and fridges; they damage the ozone layer and CFCs still leak from old fridges today
4.14: Understand how an increase in greenhouse gases results in an enhanced greenhouse effect and that this may lead to global warming and its consequences
The greenhouse effect is a natural process which prevents Earth from getting too cold. However, when additional greenhouse gases are added to the atmosphere, the greenhouse effect is enhanced. These gases reflect heat back to the Earth's surface, which increases the general temperature as well as melting polar ice caps. This results in an increase in sea level which, along with the increased temperature, causes more evaporation. More evaporation means more rain, which leads to natural disasters such as typhoons and hurricanes.
The greenhouse effect is a natural process which prevents Earth from getting too cold. However, when additional greenhouse gases are added to the atmosphere, the greenhouse effect is enhanced. These gases reflect heat back to the Earth's surface, which increases the general temperature as well as melting polar ice caps. This results in an increase in sea level which, along with the increased temperature, causes more evaporation. More evaporation means more rain, which leads to natural disasters such as typhoons and hurricanes.
4.15: Understand the biological consequences of pollution of water by sewage, including increases in the number of microorganisms causing depletion of oxygen
When sewage, urine and feces are released into bodies of water, eutrophication occurs.
- Sewage contains phosphates from detergents
- Urine and feces contain nitrates
When sewage, urine and feces are released into bodies of water, eutrophication occurs.
4.16: Understand that eutrophication can result from leeched minerals from fertilizer
- Nitrates and phosphates from fertilizers leech into water when it rains; they speed up the growth of algae on the pond's surface
- More algae on the pond surface prevents plants in the deep from getting sunlight for photosynthesis - they die
- Decomposers break down the dead plants and this releases carbon
- Decomposers increase in number because of increased food supply and they use up all the oxygen in the water for respiration
- Fish die from lack of oxygen - tertiary consumers (e.g. larger fish) are also affected by lack of food
4.17: Understand the effects of deforestation, including leeching, soil erosion, disturbance of the water cycle and of the balance in atmospheric oxygen and carbon dioxide
- Trees take nutrients from soil. These nutrients are returned to the soil when trees die; when they are cut down, nutrients are not returned to the soil, leaving it infertile. This is called leeching
- Soil erosion is when soil is loose because of a lack of tree roots holding it together
- If there are no trees, there is less transpiration which leads to a lack of precipitation; this means that the climate will get drier
- Forests absorb oxygen and release carbon dioxide; when trees are cut all of their carbon dioxide is released at once rather than slowly as they decompose; overall, this leads to less photosynthesis which disrupts the balance of atmospheric oxygen and carbon dioxide