Biodiversity

• The earth is a closed system, there is a fixed number of atoms. Life has evolved to constantly recycle important nutrients like carbon and nitrogen.
• Decomposers play a vital role in the recycling of nutrients. They are a group of organisms which have adapted to feed on waste and dead animals and plants. They use them as food and in the process release the nutrients back into the environment as useful compounds like carbon dioxide into the air and nitrates into the water. Plants can then absorb the nitrates through their roots and carbon dioxide through their leaves.
• Most decomposers are microorganisms like bacteria and fungi. Others, called detritus feeders (or detritivores) start the process of decay off. Examples include maggots, worms and beetles. Microorganisms can even live off the waste and corpses of detritivores.​
• Carbon is an essential element for life on Earth and parts of each of the cells in our bodies are made from it. The carbon cycle shows how atoms of this element can exist within different compounds at different times.
• Photosynthesis: Carbon dioxide is absorbed by producers to make carbohydrates.
• Respiration: Carbon enters the atmosphere as carbon dioxide from respiration.
• Animals feed on plants, passing the carbon compounds along the food chain.
• Most carbon consumed by animals is exhaled as carbon dioxide during respiration.
• Bacteria and other detritivores also respire, releasing carbon dioxide back to the atmosphere.
• Decomposition: The animals and plants eventually die, and their bodies are digested by decomposers, returning the carbon compounds to the atmosphere as carbon dioxide, from respiration.
• Combustion: In some conditions, decomposition is stopped as the conditions for decay are not present.
• The plant and animal material may then be available as fossil fuel in the future for combustion.
• Combustion in the presence of oxygen, as in Chemistry, releases carbon dioxide and water.
• Most carbon consumed by animals is exhaled as carbon dioxide during respiration.
• The water cycle is also known as the hydrological cycle. It describes how water moves on, above or just below the surface of our planet.​

  Water can change state.  Water molecules move between various locations - such as rivers, oceans and the atmosphere - by specific processes. 
• Precipitation: If enough condensed water droplets join together they become heavy enough to fall out of the sky. This is precipitation.
• Evaporation - Energy from the Sun heats the Earth’s surface and water evaporates from oceans, rivers and lakes. The warm air rises, carrying water vapour with it.
• Transpiration  -  Plants release water vapour into the air.
• Condensation - The moist air cools down as it rises. Water vapour condenses back into liquid water and this condensation process produces clouds.
• Percolation – Water that falls on the ground passes through soil and rocks.
• Decomposition relies on decomposing organisms to digest the tissue.
• Decay happens faster if there is a plentiful supply of oxygen.
• These organisms can digest faster under certain conditions:

  Temperature: Decomposers use enzyme-controlled reactions, making them very sensitive to temperature changes.
• Too cold and the rate of reaction will be slow, too hot and the enzymes will denature killing the decomposers.
• Nearly all decomposers respire aerobically.
• Decay happens much faster when there is enough water.
• Decomposers need a plentiful oxygen supply to allow them to respire efficiently.
• Dead tissues are easier to digest when wet.
• Microorganisms grow much faster in moist conditions.
• The household compost bin is a common example of the value of decomposing in nutrient recycling. The compost bin is often a dark colour, which allows it to absorb infra-red radiation from the sun, warming it up. It also has vents to allow oxygen in and a lid to prevent water loss. ​

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  Gardeners and farmers improve the quality of their soil by adding compost.  Compost recycles minerals needed for healthy growth, including nitrogen. 
• Bacteria can decompose waste material anaerobically (in the absence of oxygen). When they do this, they produce biogas. Biogas is mainly methane and made in a biogas generator, a large pit designed to decompose animal and agricultural waste anaerobically. The gas produced is used to heat homes, cook or as a fuel for vehicles. This is a good strategy for agricultural communities in developing countries. 
• In 2019 there are 7.7 billion people on the earth, with an increase of 82 million people each year. This was not always the case 200 years ago the global population was under 1 billion people. The increase in the population is mainly due to the increase in medicine,  technology and the availability of food. This had led to a large rise in life span and a huge reduction in infant mortality (the rate at which new born children die).
• As the population has grown the demand humans place on the environment have increased. We have reduced biodiversity and destroyed ecosystems by using the land for:​

  • Building of houses, roads and other infrastructure.​
  • Farming to provide us with the plants and animals we eat.​
  • Mining to remove the vast quantities of oil and metal ores needed to build the modern world​

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• Humans don’t just affect the environment by what we remove. Humans also release a huge amount of waste as sewage, litter and as a by-product of industrial processes. These can have a massive effect on ecosystems and biodiversity.
• Environmental changes affect the distribution of species in an ecosystem.  These changes include:​

  • Temperature​
  • Availability of water​
  • Composition of atmospheric gases​

  The changes may be seasonal (eg, in the summer atmospheric CO2 levels fall and in winter they increase), geographic (eg, temperatures increase as you move towards the equator) or caused by human interaction.
• Deforestation involves the removal of large areas of trees.  This is done to provide resources for building, land for cattle and rice-fields and to grow crops for biofuels.  The consequence of removing large numbers of trees is the increase in CO2 in the atmosphere through lack of photosynthesis, combustion of timber to clear spaces and burning of fossil fuels by machinery used to remove the trees.  Forest habitats are destroyed, reducing biodiversity.
• We can protect biodiversity by:​

  • breeding programmes for endangered species
  • protection and regeneration of rare habitats
  • reintroduction of field margins and hedgerows in agricultural areas where farmers grow only one type of crop ​
  • reduction of deforestation and carbon dioxide emissions by some governments
  • recycling resources rather than dumping waste in landfill.
• Most land pollution is either the result of deliberate pollution from toxic industrial by-products, human sewage or from farming. Also the use of fertilisers, pesticides (chemicals the kill insects) and herbicides (chemicals that kill weeds) can significantly pollute the land if used in high levels. 
• If fertilisers build up in a lake, they can cause the algae to grow incredibly quickly. They cover the surface of the pond blocking out the light to the plants at the bottom. These underwater plants die and are fed on by decomposers which use up all the oxygen in the water. The lack of oxygen kills the fish and other aquatic animal life. This process is called eutrophication.​
• Pesticides and herbicides can cause a problem due to bioaccumulation. This is when the chemicals that are in low levels in the water begin to build up in producers and primary consumers. These levels are still too low to kill the organisms, but the consumers above them eat many and the toxins begin to build up as they flow up the food chain.  By the time the top carnivore has fed the amount of chemical is in much higher concentration and kills them.