Back to AI Flashcard MakerBiology /Edexcel Biology Gcse - Natural Cycles and Decomposition Part 4
Crop rotation and improved soil fertility
Farmers often grow crops such as peas, beans or clover as these crops can form nitrate, as they have nitrogen-fixing bacteria in their roots. This will increase the nitrate content and fertility of the soil. Crop plants will take in the nitrate and use it to make proteins for growth. One year the farmer will grow one of these crops and then the following years, the farmer will plant another crop in the nitrate rich soil. Growing different crops each year in a cycle is called crop rotation.
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Key Terms
Term
Definition
Crop rotation and improved soil fertility
Farmers often grow crops such as peas, beans or clover as these crops can form nitrate, as they have nitrogen-fixing bacteria in their roots. This wil...
Using fertilisers
Natural fertilisers such as manure or compost are used by farmers to provide a source of nitrate to increase crop yield. Expensive artificial fertilis...
Pollution indicators
The level of pollution in air or water can be indicated by the species living there. This is known as an indicator species. Data obtained using indica...
Species that indicate water pollution levels
If water is polluted by raw sewage or fertilisers, eutrophication can happen, which decreases the oxygen concentration in the river or lake. Some fres...
Species that indicate air pollution
Pollutants in the air such as sulfur dioxide are released from power stations. Air pollution can be monitored by indicator species. Some species of li...
Decomposition | detailed
Decomposition is the breakdown of dead matter, which is often called rotting. Decomposing bacteria and fungi are organisms that help the process of de...
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| Term | Definition |
|---|---|
Crop rotation and improved soil fertility | Farmers often grow crops such as peas, beans or clover as these crops can form nitrate, as they have nitrogen-fixing bacteria in their roots. This will increase the nitrate content and fertility of the soil. Crop plants will take in the nitrate and use it to make proteins for growth. One year the farmer will grow one of these crops and then the following years, the farmer will plant another crop in the nitrate rich soil. Growing different crops each year in a cycle is called crop rotation. |
Using fertilisers | Natural fertilisers such as manure or compost are used by farmers to provide a source of nitrate to increase crop yield. Expensive artificial fertilisers such as ammonium nitrate can be applied to the fields. |
Pollution indicators | The level of pollution in air or water can be indicated by the species living there. This is known as an indicator species. Data obtained using indicator species will only show if an area is polluted or not. Indicator species cannot measure pollution levels only chemical analysis using electronic meters and laboratory tests can do this. |
Species that indicate water pollution levels | If water is polluted by raw sewage or fertilisers, eutrophication can happen, which decreases the oxygen concentration in the river or lake. Some freshwater animals are very sensitive to the oxygen levels such as stonefly larvae and freshwater shrimps. If these animals are found in a river, it shows that the river is clean. However, some animals are adapted for surviving in polluted conditions and can survive in low oxygen concentrations. Examples are blood worms and sludge worms. The presence of these species indicates there is a high level of water pollution. |
Species that indicate air pollution | Pollutants in the air such as sulfur dioxide are released from power stations. Air pollution can be monitored by indicator species. Some species of lichens and blackspot fungus are very sensitive to sulfur dioxide, if there are very high levels in the air then they will not be able to grow. By looking at the number and type of lichens present in various locations, scientists can determine how clean or how polluted the air is. |
Decomposition | detailed | Decomposition is the breakdown of dead matter, which is often called rotting. Decomposing bacteria and fungi are organisms that help the process of decomposition. Decomposition is crucial to the cycling of elements, such as carbon from one living organism to another. You can learn more about the carbon and water cycles here. |
The rate of decay | The rate of decay is the speed at which dead matter is broken down by decomposers. The rate can be estimated by measuring changes in pH, (for example in milk), change in mass (decaying fruit and vegetables) or change in temperature (grass cuttings). Rates of decay are affected by a number of key factors. |
The effect of temperature, water & oxygen on the rate of decay Temperature | At colder temperatures decomposing organisms will be less active, therefore the rate of decomposition remains low. This is why we keep food in a fridge. As the temperature increases, decomposers become more active and the rate of decay increases. When decomposers break compost down, the compost heap becomes warmer due to the respiration of the bacteria and fungi generating heat. At extremely high temperatures decomposers will be killed and decomposition will stop. |
The effect of temperature, water & oxygen on the rate of decay Water | With little or no water there is less decomposition because decomposers cannot survive. As the volume of available water increases, the rate of decomposition also increases. Many decomposers secrete enzymes onto decaying matter and then absorb any dissolved molecules. Without water these reactions cannot occur. The Egyptians mummified their dead kings and queens. This process removed all water from the mummy and so stopped decomposers from breaking down the dead tissue. |
The effect of temperature, water & oxygen on the rate of decay Oxygen | Similar to water, decomposers need oxygen to survive and without it there is little or no decomposition. Oxygen is needed for many decomposers to respire, to enable them to grow and multiply. This is why we often seal food in bags or cling film before putting it in the fridge. As the volume of available oxygen increases, the rate of decomposition also increases. Some decomposers can survive without oxygen. These are used in biogas generators. |
The effect of temperature, water & oxygen on the rate of decay Oxygen example: peat bogs | Archaeologists have found very old remains of people who have fallen into peat bogs. A famous example of this was the Tollund man. In peat bogs there is low oxygen, a low temperature and acidic water which can naturally mummify dead remains. |
Rate of change equation | Rate of change = change in value ÷ Change in time |
Rate of change can also be calculated from graphs. Here we use this equation: | x axis = time (hours) y axis = pH Rate of change = vertical change ÷ horizontal change |
Which process removes carbon dioxide from the atmosphere? | Photosynthesis |
Which conditions make decay happen at a faster rate? | Warm and moist |
What do nitrogen-fixing bacteria do? | Nitrogen-fixing bacteria convert nitrogen gas into nitrates. |
What does Denitrifying bacteria do? | Denitrifying bacteria convert nitrates into nitrogen gas. |
What do nitrifying bacteria do? | Nitrifying bacteria convert ammonia into nitrates. |
Which process releases water vapour into the atmosphere? | Transpiration from the leaves of plants releases water vapour into the atmosphere. |
Which gas is needed for decomposers to respire? | Oxygen |
What is potable water? | Safe to drink |