Ecosystems & Material Cycles

• What are the 4 different levels of organisation in an ecosystem and what do they mean ?

  Individual - a single organism

  Population - all the organisms of one species in a habitat

  Community - all the organisms of different species living in a habitat

  Ecosystem - a community of organisms along with all the non-living conditions
• Organisms in a community are interdependent - meaning that they depend on each other for things like food and shelter in order to survive and reproduce.
• What does it mean when organisms have a mutualistic relationship ?


  they depend on each other for things where both organisms benefit

  e.g. bees and flowering plants
• What does a parasite do ?


  takes what it needs to survive, but the host doesn't benefit
• What are the 4 abiotic factors that affect communities ?

  temperature

  amount of water

  light intensity

  levels of pollutants
• What are the 2 biotic factors that affect communities ?

  competition

  predation
• Method to study the distribution of small organisms using a quadrat:

  • place a 1 metre squared quadrat on the ground at a random point within the first sample area
  • count all of the organisms you are interested in within the quadrat
  • work out the mean number of organisms per quadrat within the first sample area
  • repeat steps 1 to 4 in other sample areas
  • finally, compare all of the means
• Method for studying the distribution of plants along a gradient using a belt transect:

  • mark out a line in the area you want to study
  • count the plants you are interested in along the line using quadrats placed next to each other
  • repeat steps 1 and 2 lots of times in different places along the line
  • find the mean number of organisms and plot graphs to show your data
• What is the source of energy for nearly all life on Earth ?

  The Sun
• Plants convert a small percentage of the light energy that falls on them into glucose. They use some of the glucose immediately in respiration and store some of the rest as biomass (the mass of living material that makes up an organism).
• What does a pyramid of biomass show ?

  shows how much the creatures are at each level of a food chain would weigh if you put them all together
• How do you calculate efficiency ?

  energy transferred to next level / energy available at previous level x 100
• What is biodiversity ?

  the variety of living organisms in an ecosystem
• Nitrates are put onto fields as fertilisers. If too much fertiliser is applied and it rains afterwards, nitrates easily find their way into rivers and lakes. The result of this is eutrophication.
• The steps of eutrophication:

  1. fertilisers enter the water, adding excess nitrates
  2. the excess nitrates causes algae to grow fast and block out the light
  3. plants can't photosynthesise due to the lack of light and they start to die and decompose
  4. with more food available, microorganisms that feed on decomposing plants increase in number and use up oxygen in the water
  5. organisms that need oxygen for aerobic respiration die
• Fish farms in areas of open water can reduce biodiversity in the surrounding area. Here's how:

  1. Food is added to the nets to feed the fish which produce huge amounts of waste. Both the food and the waste can leak into the open water, causing eutrophication and the death of wild species.
  2. Fish farms in open water often act as breeding ground for large numbers of parasites. These parasites can get out of the farm and infect wild animals, sometimes killing them.
  3. Predators are attracted to the nets and can become trapped in them and die.
• Sometimes fish are farmed in large tanks rather than in open water nets. These farms are low in biodiversity because often only one species is farmed, the tanks are often kept free of plants and predators and any parasites and microorganisms are usually killed.
• What is a non-indigenous species ?

  A species that doesn't naturally occur in an area.

  They can be introduced intentionally or unintentionally.
• Non-indigenous species compete with indigenous species for resources like food and shelter. Sometimes, they are better at getting these resources and out-compete the indigenous species, which decrease in number and eventually die out.

  Non-indigenous species sometimes bring new diseases to a habitat. These often infect and kill lots of indigenous species, reducing the habitat's biodiversity.
• What is reforestation ?

  when land where a forest previously stood is replanted to form a new forest.
• Forests generally have a high biodiversity because they contain a wide variety of trees and plants, and these provide food and shelter for lots of different animals and species.

  Deforestation reduces this biodiversity by removing the trees. Reforestation helps to restore it.
• Conservation schemes can help to protect biodiversity by preventing species from dying out.

  Conservation methods include:

  • protecting a species natural habitat
  • protecting species in safe areas outside of their natural habitat and introducing captive breeding programmes to increase numbers
  • the use of seed banks to store and distribute the seeds of rare and endangered plants
• What are the benefits of maintaining biodiversity ?

  protecting the human food supply

  ensuring minimal damage to food chains

  providing future medicines

  cultural aspects

  ecotourism

  providing new jobs
• What does ecotourism do ?

  helps to bring money into biodiverse areas where conservation work is taking place
• As the population of the world increases, so does the demand for food. So the more food needed to share out with a limited supply, the less food secure the world becomes.
• What are the 4 main biological factors affecting the level of food security ?

  Increasing consumption of meat and fish, and increasing animal farming.

  Environmental changes caused by human activity.

  Sustainability.

  New pests and pathogens.
• Materials are recycled through both the biotic and abiotic components of ecosystems:

  • living things are made of elements they take from the environment
  • they turn these elements into the complex compounds that make up living organisms, elements are passed along food chains when animals eat the plants and each other
  • the elements are recycled - waste products and dead organisms are broken down by decomposers and the elements in them are returned to the soil or air, ready to be taken in by new plants and put back into the food chain.
• What are the main parts of The Carbon Cycle ?

  There is only one arrow going down from carbon dioxide in the air. The whole thing is powered by photosynthesis.

  Eating passes the carbon compounds in the plant along to the animals in a food chain.

  Both plant and animal respiration while the organisms are alive releases CO2 back into the air.

  Plants and animals eventually die and decompose or are killed and turned into useful products.

  When plants and animals decompose they are broken down by microorganisms.

  These decomposers release CO2 back into the air.
• The process of The Water Cycle:

  • Energy from the Sun makes water evaporate from the land and sea, turning it into water vapour. Water also evaporates from plants - this is known as transpiration.
  • The warm water vapour is carried upwards. When it gets higher up it cools and condenses to form clouds.
  • Water falls from the clouds as precipitation but sometimes onto land, where it provides fresh water for plants and animals.
  • It then drains into the sea and the whole process starts again.
• What is desalination ?

  It removes salts from salt water.

  There are a few different methods of desalination. One really simple method is thermal desalination.

  This is where salt water is boiled in a large enclosed vessel, so that the water evaporates. The steam rises to the top of the vessel, but the salts stay at the bottom. The steam then travels down a pipe from the top of the vessel and condenses back into pure water.
• What is osmosis ?

  the net movement of water across a partially permeable membrane, from an area of high water concentration to an area of low water concentration.
• The higher the salt concentration in a solution, the lower the water concentration, so you could also say that osmosis is the net movement of water from an area of low salt concentration to an area of high salt concentration.
• Reverse osmosis removes impurities from water. Here's how:

  • salt water is first treated to remove solids, before being fed at a very high pressure into a vessel containing a partially permeable membrane
  • the pressure causes the water molecules to move in the opposite direction to osmosis - from a higher salt concentration to a lower salt concentration.
  • as the water is forced through the membrane, the salts are left behind, removing them from the water
• The atmosphere contains 78% nitrogen gas. This is very unreactive and so it can't be used directly by plants or animals. Nitrogen is needed for making proteins for growth, so living organisms have to get it somehow.
• Nitrogen in the air has to be turned into mineral ions such as nitrates before plants can use it. Plants absorb these mineral ions from the soil and use the nitrogen in them to make proteins. Nitrogen is then passed along food chains in the form of proteins, as animals eat plants.
• Decomposers break down proteins in rotting plants and animals, and urea in animal waste. This returns the nitrogen to the soil - so the nitrogen in these organisms is recycled.
• Nitrogen fixation is a the process of turning nitrogen from the air into the nitrogen-containing ions in the soil which plants can use.

  There are 2 main ways that this happens:

  • Lightning - there is so much energy in a bolt of lightning that it is enough to make nitrogen react with oxygen in the air to give nitrates.
  • Nitrogen-fixing bacteria in roots and soil.
• There are 4 different types of bacteria involved in the nitrogen cycle:

  Decomposers -> Decompose proteins and urea and turn them into ammonia. Ammonia forms ammonium ions in solution that plants can use.

  Nitrifying Bacteria -> Turn ammonia in decaying matter into nitrates.

  Nitrogen-fixing Bacteria -> Turn atmospheric nitrogen into ammonia, which forms ammonium ions.

  Denitrifying Bacteria -> Turn nitrates back into nitrogen gas. This is no benefit to living organisms.
• What are the 2 ways of increasing the amount of nitrates in the soil ?

  Crop Rotation - different crops are grown each year in a cycle in the same field which helps to put nitrates back into the soil to help the next crop grow the next year

  Fertilisers - spreading animal manure or compost on fields to recycle the nutrients left in plant and animal waste and returns them to the soil through decomposition.
• What are the 2 things that indicator species show the level of ?

  water pollution

  air pollution