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15 Human and Ecosystem
#148 The human influences on the ecosystem
Increasing use of pesticides, fertilizers and herbicides à ↑ levels of nutrients in the soil, kill insect pests, kill weeds à ↑ crop yields.
Use of modern machinery (tractors, combined harvesters) à manage land and crop more efficiently.
Artificial selection to produce varieties of plants suited to particular climates and soil types, and breeds of animal for specific purposes (optimum meat, milk, wool production).
Use of yeast and bacteria in the large-scale production of breads, beer and wine, yoghurt and cheese. Single-cell protein and fungi are used to produce meat substitutes.
Use of medicines such as antibiotics, hormones and artificial insemination techniques in intensive animal rearing.
Use of plant hormones in plant growing and fruit production.
Use of genetic engineering and cloning techniques to produce organisms to produce hormones…
Development of systems to water plants in greenhouses automatically and to grow plants in nutrient solutions (hydroponics).
Use of satellites to monitor crop development, observe crop diseases and assess the need for additional fertilizer.
Development of intensive farming and automated feeding mechanisms.
#149 Undesirable effects of deforestation
Deforestation is the removal of large areas of forest to provide land for farming and roads, and to provide timber (wood) for building, furniture and fuel. Deforestation has a number of undesirable effects on the environment.
Deforestation:
Reduction of habitats or food sources for animals, which can result in their extinction. Animal and plant diversity is reduced, and food chains are disrupted.
Loss of plant species and their genes which may be important for medical use or genetic engineering in the future.
Removal of trees means there are no roots to hold soil, which can result in soil erosion and leaching of minerals. Desertification can eventually occur.
Lack of roots and soil à flooding and mudslides. Lakes can become silted up.
Leaching of nutrients into lakes and rivers à eutrophication.
Less CO 2 is absorbed from the atmosphere, more CO 2 build up à increase the greenhouse effect.
Less O 2 is produced à atmospheric O 2 level can drop.
Less transpiration à reduced rainfall.
Answer
- i) B
ii) A
iii) Column for F drawn to 550. Column shaded in the same way as the others, and labeled. Column drawn an equal width and distance from the others.
- i) 30 years
ii) 2 reasons from:
to clear land for agriculture, housing, industry or roads. to collect timber for housing to collect timber for fuel.
iii) 2 suggestions from:
plants have gone so there are no roots to bind the soil. wind blows soil away rain washes soil away.
- Increased CO 2 can lead to global warming, or flooding, or desertification. O 2 : organisms need O 2 for respiration to release energy.
#150 Overuse of fertilisers, water pollution by sewage
It is very tempting for farmers to increase the amount of fertilisers applied to crops to try and increase crop yields. However, this can lead to the eutrophication of rivers and lakes and the sequence occurs.
1. Overuse of fertilisers
fertilisers (very soluble) are easily leached out of the soil fertilisers are washed into a water system (river or lake) algae absorb fertiliser and grow rapidly (algal bloom) algae form a blanket on the surface of the water, blocking light from algae below algae die without light bacteria decompose dead algae, using up O 2 in the water for respiration animals in water die through lack of O2.
Fishermen row a boat in a algae-filled lake in China. Credit: Totallycoolpix.com
feathers they swallow the oil, which poisons them. Oil also disrupts food chains.
Try this
Figure below shows part of a river into which sewage is pumped. The river water flows form W to Z , with the sewage being added at X.
Some of the effects of adding sewage to the river are shown in picture below.
Try this
- Describe the changes in the levels from W to Z of: i) nitrates [2 marks] ii) suspended solid [2 marks]
- Suggest why the level of O2:
i) drops at X [1 mark] ii) increase again toward Z [1 mark]
- Suggest 2 reasons why levels of algae drop: i) when sewage is added to the river [2 marks] ii) towards Z [2 marks]
- A farm at Z used herbicides on the field next to the river. Suggest why this could cause further problems in the river. [1 mark]
Answer
- i) Constant level between W and X, or starts off quite low, or at point X it start to drop then increases toward Y before dropping again toward Z.
ii) Level starts off quite low, then at point X it increases sharply; level returns nearly to original level between Y and Z.
- i) One suggestion from:
- aerobic respiration by sewage fungus
- lack of algae to produce O 2
ii) One suggestion from:
- lack of sewage fungus
- photosynthesis by alge.
- i) Two suggestions from:
- presence of suspended solids blocks ligh for algae
- lack of nitrate in the water
- possible presence of toxins in sewage
- possible increase in temperature or unsuitable temperature.
ii) Two suggestions from:
- shortage of nitrates
- grazing by aquatic herbivores
- possible drop in temperature , or unsuitable temperature.
- One suggestion from:
- herbicides could leach into river and kill algae
- herbicides will kill algae and disrupt food chain
- herbicides may be toxic to other organisms in the river.
The main causes of acid rain are process that release SO 2 and oxides of nitrogen into the atmosphere. These include:
burning of fossil fuels , such as coal and gas, by power stations combustion of petrol in car engines.
Problems caused by acid rain include:
Damage to plant leaves , eventually killing the plants. Whole forests of pine trees have been destroyed by acid rain.
Plant leaves damaged by acid rain.
Acidification of lakes : as the water become more acidic, some animals such as fish cannot survive and fish stocks are destroyed. Increased risk of asthma attacks and bronchitis in humans. Corrosion of stonework on buildings. Release into soil of soluble aluminium ions that are toxic to fish when washed into lakes.
Ways of reducing the incidence of acid rain:
changing the types of power stations that generate electricity from coal and oil to gas or nuclear power , or using more renewable energy sources such as wind using ‘scrubbers’ in power station chimneys – these remove most of the SO 2 present in the waste gases using catalytic converters in car exhausts – these convert oxides of nitrogen to harmless nitrogen.
Common misconceptions
Remember that car engines do not make large amount of SO 2 – but they are responsible for producing large amount of oxides of nitrogen, CO 2 and CO.
Examiner’s tip
When describing the effects of car exhaust fumes on the environment, don’t make a list of the chemicals and then link them all to acid rain or global warming. Be specific:
oxides of nitrogen leas to acid rain; CO can reduce the ability of haemoglobin to carry O 2 ; CO 2 increases can lead to global warming.
Try this
- SO 2 is a major pollutant of the air. Which process is mainly responsible for the release of SO 2 into the air? [ mark]
- SO 2 is one of the gases which contributes to acid rain. Acid rain can affect trees and their surrounding soil in a variety of ways. Figure below shows where these effects can occur.
Suggest how each of the following affects the tree and explain how it can lead to its death. i) Damage of the leaves [2 marks] ii) Damage of the fine roots [2 marks] iii) Death of the soil microorganisms [2 marks]
#152 Greenhouse gases and global warming
Some gases in the Earth’s atmosphere stop heat radiating into space from the Earth. This is called the greenhouse effect and the gases involved are called greenhouse gases. They include: methane, CO 2 and water vapour. An increased greenhouse effect can lead to global warming and climate change.
The diagram shows how the greenhouse effect works.
- Electromagnetic radiation at most wavelengths from the Sun passes through the Earth’s atmosphere.
- The Earth absorbs electromagnetic radiation with short wavelengths and so warms up. Heat is radiated from the Earth as longer wavelength infrared radiation.
3.Some of this infrared radiation is absorbed by greenhouse gases in the atmosphere.
- The atmosphere warms up.
Source: BBC Bytesize
#153 Pesticides, herbicides, nuclear fallout and non-biodegradable plastics
Some pesticides are non- biodegradable and stay in the environment for a long time. For example, DDT has been a very effective insecticide, used to kill mosquitoes to reduce the spread of malaria. However, because it does not break down, it enters water systems such as lakes, where it is absorbed into plankton.
DDT spraying.
They are unable to excrete DDT. In a similar way to heavy metal, it is passed up the food chain and bioaccumulation occurs: the top carnivores suffer from it toxicity. For example, when fish eagles are exposed to DDT passed through the food chain, they produce eggs with very thin shells. When the adult birds sit on the nest, the eggs break, so they are unable to produce offspring.
Some insecticides are non-specific : when applied to kill an insect pest, they also kill all the other insects that are exposed to it. This may include useful insects, such as bees that are needed to pollinate crops. Food webs can be affected, threatening the extinction of top carnivores such as birds of prey.
Herbicides are used to kill weeds in a crop, to reduce competition to increase crop yield. However, herbicides may also kill rare plants species near the field being sprayed.
Nuclear fallout can be the result of a leak from a nuclear power station, or from a nuclear explosion. Radioactive particles are carried by the wind or water and gradually settle in the environment. If the radiation has a long half-life, it remains in the environment and is absorbed by living organisms. The radio active material bioaccumulates in food chains and can cause cancer in top carnivores.
#154 Conservation of species, recycling sewage and paper
Koala is an endangered animal
Conservation is the process of looking after the natural environment. Conservation attempts to maintain or increase the range of different species living in an area, known as biodiversity.
The need for conservation of species
- Many species of animals and plants are in danger of extinction, due to factors such as habitat destruction, the introduction of other species, international trade and pollution.
- Loss of a species also means that its genes are lost: these may be important in the future for genetic engineering (e.g. to improve crops) and the production of useful chemicals such as medicines.
- The presence of rare species can be an important source of money for poor communities, through tourism.
- The species may play an important role in a food chain: its loss could endanger other species.
The need for conservation of habitats
- If habitat is lost, so are the species that live in them, so habitat destruction poses the greatest threat to the survival of species.
- A habitat maybe conserved by:
using laws to protect the habitat
using wardens to protect the habitat reducing or controlling public access to the habitat controlling factors, such as water drainage and grazing, that may otherwise contribute to destruction of the habitat
The need for conservation of natural resources
Some natural resources (the material we take from Earth) are not replaceable (renewable). For example, fossil fuels such as coal took millions of years to form. Increasing demands for energy are depleting these resources.
Ways of conserving natural resources:
- Increase the use of renewable energy (wind farms, solar power, hydroelectric power…).
- Improve the efficiency of energy use (better insulation, smaller car engines, more public transports…).
- Grow tree specifically for fuel, then replant as they are cut down --> the greenhouse effect is not increased, and habitats can be maintained when trees felling is carefully managed.
The principle of recycling sewage (water) and paper
Sewage is mainly water, contaminated with organic material, solids, bacteria and minerals such as phosphates. In places where water is in short supply, the sewage is treated to provide water that is clean enough to drink. Any treated effluent that is returned to water system such as a river will not cause problems such as eutrophication.
Treatment of sewage:
- Large object such as sticks screened out of raw sewage.
- Suspended grit allowed to settle out by gravity in grit settling tank.
- Organic matter allowed to settle out by gravity in sludge-settling tank – after digestion in a sludge digester , sludge can be used as fertiliser on farmland – methane gas can also be generated for use as a fuel.
- Remaining liquid sprinkled on to the top of an aeration tank containing stone – microorganisms (protoctists and aerobic bacteria) on surface of stones digest any remaining organic mater.
- Water passing out may be chlorinated to kill any bacteria, so it is safe to drink.
#155 Summary of Human and Ecosystem
CO 2 and methane are greenhouse gases , trapping outgoing long
wavelength radiation in the atmosphere and warming the Earth. Increased concentrations of these gases are causing global warming.
SO 2 is produced when coal and other fossil fuels burn.
SO 2 and nitrogen oxides dissolves and react in water droplets in the atmosphere, and fall to the ground as acid rain. This leaches aluminum ions from soils, and kills plants and aquatic organisms.
Fall-out from accidents at nuclear reactions emits ionising radiation, which damages DNA and can cause mutations, cancer and radiation burns.
Deforestation reduces the amount of CO 2 that is taken out of the atmosphere for photosynthesis, and so may increase global warming. Combustion of the felled trees releases CO 2 into the atmosphere. Deforestation also destroys habitats for animals, possibly leading to their extinction. It increases soil erosion and flooding.
Water pollution by fertilisers or raw sewage can cause eutrophication, in which large populations of aerobic bacteria form, reducing the amount of dissolved O 2 in the water and making it impossible for most animals to live there. Other chemical wastes, such as heavy metals, can also cause water pollution.
