biology paper 2

• An ecosystem is the interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment
• Organisms require a supply of materials from their surroundings and from other living organisms to survive and reproduce
• Plants in a community or habitat often compete for light, space, water, and mineral ions from the soil
• Animals often compete for food, mates, and territory within a community
• Within a community, each species depends on other species for food, shelter, pollination, seed dispersal, etc.
• If one species is removed from a community, it can affect the whole community, known as interdependence
• A stable community is one where all species and environmental factors are in balance, keeping population sizes fairly constant
• Abiotic - non living
• Abiotic factors

  • light intensity

  • temperature

  • moisture levels

  • soil pH and mineral content

  • wind intensity and direction

  • carbon dioxide levels for plants

  • oxygen levels for aquatic animals.
• Biotic - living
• Biotic factors

  • availability of food

  • new predators arriving

  • new pathogens

  • one species outcompeting another so the numbers are no longer sufficient to breed.
• Organisms have features (adaptations) that enable them to survive in the conditions in which they normally live
• Adaptations can be structural, behavioural, or functional
• Some organisms live in extreme environments, such as high temperature, pressure, or salt concentration
• Organisms living in extreme environments are called extremophiles
• Bacteria living in deep sea vents are extremophiles
• photosynthetic organisms are the producers of biomass for life on Earth.
• Feeding relationships within a community can be represented by food chains
• All food chains begin with a producer which synthesises molecules. This is usually a green plant or alga which makes glucose by photosynthesis.
• A range of experimental methods using transects and quadrats are used by ecologists to determine the distribution and abundance of species in an ecosystem.
• Producers are eaten by primary consumers, which in turn may be eaten by secondary consumers and then tertiary consumers
• Consumers that kill and eat other animals are predators, and those eaten are prey
• In a stable community the numbers of predators and prey rise and fall in cycles
• The carbon cycle returns carbon from organisms to the atmosphere as carbon dioxide to be used by plants in photosynthesis
• The water cycle provides fresh water for plants and animals on land before draining into the seas. Water is continuously evaporated and precipitated
• the role of microorganisms in cycling materials through an ecosystem is returning carbon to the atmosphere as carbon dioxide and mineral ions to the soil
• Biodiversity is the variety of all the different species of organisms on earth, or within an ecosystem
• A great biodiversity ensures the stability of ecosystems by reducing the dependence of one species on another for food, shelter and the maintenance of the physical environment.
• The future of the human species on Earth relies on us maintaining a good level of biodiversity
• Many human activities are reducing biodiversity and only recently have measures been taken to try to stop this reduction
• Rapid growth in the human population and an increase in the standard of living mean that increasingly more resources are used and more waste is produced
• Unless waste and chemical materials are properly handled, more pollution will be caused
• Pollution can occur

  • in water, from sewage, fertiliser or toxic chemicals

  • in air, from smoke and acidic gases

  • on land, from landfill and from toxic chemicals.
• Pollution kills plants and animals which can reduce biodiversity.
• Humans reduce the amount of land available for other animals and plants by building, quarrying, farming and dumping waste.
• The destruction of peat bogs, and other areas of peat to produce garden compost, reduces the area of this habitat and thus the variety of different plant, animal and microorganism species that live there
• The decay or burning of the peat releases carbon dioxide into the atmosphere.
• Large-scale deforestation in tropical areas has occurred to:

  • provide land for cattle and rice fields

  • grow crops for biofuels
• Levels of carbon dioxide and methane in the atmosphere are increasing, and contribute to ‘global warming’.
• Scientists and concerned citizens have put in place programmes to reduce the negative effects of humans on ecosystems and biodiversity. These include:

  • 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.