ecosystems and material cycles

• Ecosystems

  All organisms that live and interact in an ecosystem form a community that is made up of populations of different species. These species depend on each other for resources, so we say they are interdependent. Abundance is a measure of how common something is in an area, such as its population size. Measuring population size by counting all the organisms in an area is often impossible. However you can estimate this by taking samples using a quadrant. Quadrants are placed randomly in an area, and the number of individuals in each quadrat is counted.
• Energy transfer

  Each year, photosynthesis over the whole Earth captures$3\times10^{20}$J of energy. Much of this energy is transferred into new biomass, the rest to the environment by heating (respiration). Other organisms cannot make use of the energy transferred to the environment. If we measure the biomass of all the organisms at each trophic level, we can display them as a pyramid of biomass. With less energy available, less biomass can be produced. We can calculate the percentage transfer of biomass between trophic levels in pyramids of biomass. There is a maximum length of food chain in an ecosystem.
• Abiotic factors

  Distribution is affected by abiotic factors. Abiotic factors are non-living conditions:

  • Physical e.g. light, rainfall, temperature, wind
  • Chemical e.g. pH of soil, pollutants

  Distribution can be measured using a belt transect. Quadrants are placed at regular intervals along a line in the habitat. Each species of organism is suited to particular conditions. If the abiotic factors change, the distribution of the organisms might change.
• Biotic factors

  Biotic factors are the organisms in an ecosystem that affect other living organisms.

  Predator prey cycles - numbers of predators and prey may be related. They may also be affected by biotic factors including food and competition. Changes in biotic factors may cause new habitats to be formed (beavers building dams), increasing the biodiversity.
• Assessing pollution (air pollution)

  Indicator species - the presence/absence shows pollutants e.g. Lichen Lecondora conizaeoides, these grow on tree, it is a mutualistic relationship between the fungus and the alga. It was the only lichen to be found in city centres and industrial areas, as if it is the only one that can tolerate polluted sulphur-containing gases. The distribution has changed as our air quality has improved. Other lichens have also changed their distribution as the levels of pollutants have changed e.g. increased nitrogen oxides due to vehicles. Lichens are not the only indicator of air quality. Black spot fungus - rose pathogen - cannot grow well where there is a lot of sulphur pollution, so roses in cities rarely suffer from an infection.
• Assessing pollution (water pollution)

  Some aquatic species of invertebrates are useful pollution indicators. Water pollution, poisonous substances released from factories (mercury detergent) or fertilisers and sewage causing eutrophication. These different species have adapted to different concentrations of oxygen. Both water and air  pollution can be accurately measured using sensors.
• Parasitism and mutualism

  Parasitism is a kind of feeding relationship in which one organism benefits by feeding off a host organism, causing harm. The parasite lives in or on the host. The host may survive for a long time and continues to be food for the parasite if it causes limited harm e.g. head lice and tape worms.

  Some organisms that live together both benefit from the relationship - it is mutualistic. For example, flowering plants depend on insects for pollination. Plants benefits from reproduction and insects benefits by collecting nectar/pollen for food. Other examples are sea anemones and clown fish and coral animal and algea.
• Biodiversity and humans (fish farming)

  Why:

  • 17% of protein eaten globally comes from fish
  • human population is increasing so more fish is needed
  • wild fish stocks damaged due to overfishing/ecosystems damaged

  Problems:

  • many fish kept in relatively small space
  • uneaten food/faeces sink and can change conditions for wildlife
  • parasites and diseases spread more easily
• Biodiversity and humans (introducing new species and eutrophication)

  Introducing new species:

  Why:

  • sheep/cattle/soybeans native to Asia but farmed all over the world for food
  • some species may be introduced to reduce populations of problem species

  Problems:

  • non-indigenous species may outcompete native species

  Eutrophication

  Why:

  • additions of more nutrients to help crops grow

  Problems:

  • other organisms will also increase in growth
• Preserving biodiversity

  Reforestation - planting new forests where old ones have been cut down. Plant a mixture of trees for more habitats and biodiversity, meaning they can recover quicker from natural disasters.

  Conservation - attempt to protect endangered species. How is it managed; organisms can be bred in captivity and released, removal of predators, laws to protect the species.

  Preserving biodiversity is also important for plants and animals we use for food or medicines. In the future we may need new varieties of plants and animals so we need to preserve them all.
• Food security Pt.1

  Food security - having access to safe + healthy food at all times. Many places have increased food security due to better agriculture. Food security is a problem in poor countries, areas of conflict and it may become a problem in the future due to the population increasing. As countries become wealthier, people prefer to eat more fish and meat. Environmental effects as up to 15X more protein from soybean than meat in the same area. Changing farming practices can help. Some think fish and meat protein should be replaced with more vegetable protein.
• Food security Pt.2

  Growing crops also has problems associated, fertilisers use has increased 700% over the last 50 years. Most fertilisers is made using chemical processes, using energy and releasing $CO_2$​ so there are sustainability issues. Planting biofuels can decrease $CO_2$ emissions. This is because they are carbon neutral. Pests and pathogens are moving into new areas. Midges are vectors for blue tongue disease and are killed by cold temperatures. These were first seen in the UK in 2007, since then is has spread to sheep and cattle across the country.
• The carbon cycle

  Carbohydrates, fats and proteins all contain carbon atoms. When eaten some of these compounds are digested and taken into the body, the rest leaves as faeces. Some of the absorbed compounds will be used for respiration and the carbon will return to the atmosphere as$CO_2$. $CO_2$ is taken in by plants by photosynthesis and made into glucose, which can be made into other molecules. Decomposers are an important part of the cycle as they break down waste and dead material. If plants and animals are not eaten and just die, their bodies are broken down by decay. Decay is caused by microorganisms that we call decomposers. Decomposers include fungi and bacteria, which break down carbon compounds in animal waste and dead bodies. Decomposers use some of the carbon compounds they absorb for respiration and to make more complex compounds in their cells.
• The nitrogen cycle

  78% of the air is nitrogen. Plants and animals contain nitrogen compounds in proteins and DNA. To grow well plants need nitrogen to make more of these compounds. Plants cannot absorb nitrogen directly from the air. They can only absorb nitrogen compounds (nitrates from the soil). Nitrates in the soil can be increased by; crop rotation, manure and artificial fertilisers. Bacteria are responsible for fixing nitrogen (making nitrogen based compounds) from the air. A small quantity is also formed by lightning.
• The nitrogen cycle (crop rotation)

  Crop rotation involves crops of peas (or related plants) and then digging in the roots after the crop has been harvested. The peas/legumes have a mutualistic relationship with nitrogen fixing bacteria which live in nodules inside the plant's roots. The following year, a different crop will benefit from addition nitrogen compounds in the soil. Farmers may spread artificial fertilisers or manure onto the fields to increase soil fertility. The nitrogen compounds in fertilisers are soluble and dissolve in soil water.
• The water cycle

  Water makes up the majority of an organisms' body mass. The water cycle shows how the water moves through the biotic parts of an ecosystem. Fresh water (river/lakes/underground) has to be made potable by filtering and treating with chemicals. It may also be treated for taste. In areas of drought drinking water may be collected from the air or extracted from saltwater (desalination)

  1. sea
  2. clouds
  3. rain
  4. plants and trees
  5. rivers
  6. back to the sea
• Rates of decomposition

  Usually the soft tissue of organisms are decayed by decomposers. These microorganisms grow best in warm, moist conditions. Most preservation methods rely on reducing temperature, reducing water concentration, irradiation of packaged foods and reducing oxygen. Decomposers on dead plant material can be useful. Gardeners collect waste garden material in a heap and keep it until it is well-decayed in compost. Compost contains many nutrients that were in plant tissues, but the decay process leaves them in a form that plants can absorb easily. Spreading compost increases soil fertility. The way a compost heap is constructed affects the conditions inside and rate of formation.