Ecosystems

• Define ecosystem


  A community and the non-living components of its environment (biotic and abiotic factors). Ecosystems can vary from being very small (ponds) to very large (African savannah)

  
• Give examples of ecosystems


  Moorland ecosystem (terrestrial)

  Rocky shore ecosystem (marine)

  Pond ecosystem (freshwater)
• Define population


  Group of organisms of the same species living in the same habitat at the same time

  
• Give examples of populations


  Population of mute swan in a mere

  Population of bluebells in a deciduous wood in the spring
• Define community


  All the populations of different species in the same area at the same time

  
• Give an example of a community


  A woodland community including all the plants (e.g. trees, grasses, flowering plants), animals (e.g. mice, voles, birds), microorganisms and fungi

  
• Define habitat


  Part of an ecosystem in which a particular organisms live

  
• Define niche


  An organism's role in an ecosystem, including their position in the food web and habitat. Each species occupies their own niche governed by adaptation to both abiotic and biotic conditions

  
• Define carrying capacity


  The maximum population size an ecosystem can support

  
• Define biotic factors


  The living components of an ecosystem (consisting of living organims)

  
• Give examples of biotic factors

  Predation

  Competition (inter-specific) for space, food, water, light

  Disease - For example, pathogenic disease caused by microorganisms (such as cholera, or carried by vectors - malaria)

  Humans (mankind) - In terms of habitat loss, hunting, farming
• Define abiotic factors


  The physical and chemical components of an ecosystem (non-living)

  
• Give examples of abiotic factors


  Light intensity

  Temperature

  Availability of water

  Soil pH

  Humidity
• Ecosystems are...


  dynamic (constantly changing)
• Give examples of different-sized ecosystems


  A rock pool

  Playing field

  Large tree
• What is a trophic level?


  The position an organism occupies in a food chain

  
• Define producers


  Autotrophs that convert light energy to chemical energy. Examples include: plants and some bacteria

  
• Define primary consumers


  Herbivores that usually eat plant material. Examples include: rabbits, caterpillars, cows and sheep

  
• Define secondary consumers


  Carnivores that eat primary consumers. Examples include: leopards, wolves and lions

  
• Define predators


  Animals that kill for food. They are either secondary or tertiary consumers

  
• Define prey


  The animal that predators feed on

  
• Define scavengers

  Animals that feed on dead/decaying matter. Examples include: vultures and hyenas

  
• Define decomposers


  Microbes which break down dead/decaying matter and the undigested parts of plant and animal matter in faeces to release nutrients into the soil

  
• What do food webs show?


  The direction of energy flow

  
• How efficient are energy transfers in animals?


  Energy is lost at each trophic level. Energy is lost as heat in endotherms (mammals and birds), released in respiration and used for life processes.

  Energy is also "locked up" in waste and dead matter and indigestible parts (it is available to decomposers only). The remaining energy is used to form biomass
• As energy is lost there is less to sustain organisms at a higher trophic level...


  so there are fewer organisms at each successive stage
• How efficient are energy transfers in plants?


  Of all the sunlight falling onto a plant, only a small percentage (around 1-3%) is converted into chemical energy:

  - Some light misses the leaf and falls onto the ground

  - Some sunlight is reflected from the leaf surface

  - Chlorophyll only absorbs certain wavelengths of light

  - Energy is lost in chemical reactions as carbohydrates are produced during photosynthesis
• What maximises the efficiency of energy transfer in plants?


  Plenty of water, light, warmth and green plants will maximise the rate of photosynthesis and therefore result in more carbohydrates being produced in the plants
• How can humans manipulate the transfer of biomass to reduce energy at each trophic level?


  Restricting the movement (and therefore respiration) of animals

  Providing animals with higher energy food (increasing energy input)

  Keeping animals indoors to reduce the energy transferred as heat
• How can the efficiency of biomass transfers between trophic levels be calculated?

  
• Why is the nitrogen cycle important?


  Nitrogen is needed for making proteins and nucleic acids.

  Animals and plants cannot use nitrogen from the air - it must be converted to nitrates to be taken up by plants and later pass along the food chain

  
• Which biological molecules contain nitrogen?


  Proteins

  ATP

  Nucleic acids
• What are the 4 processes carried out by bacteria in the nitrogen cycle?

  Nitrogen fixation

  Ammonification

  Nitrification

  Denitrification
• What other ways can nitrogen enter the ecosystem?


  Lightning (fixes atmospheric nitrogen)

  Addition of artificial fertilisers (made by industrial processes)
• (1) Nitrogen fixation


  Rhizobium bacteria in the root nodules of legumes convert nitrogen gas to ammonia (NH3) which can be used by plants.

  Azotobacter bacteria are found in the soil and use nitrogen gas to make amino acids

  
• (2) Ammonification


  Decomposers convert nitrogen compounds from dead organic matter and animal urine/faeces into ammonium compounds (NH4+)
• (3) Nitrification


  Nitrification is an oxidation reaction. Nitrifying bacteria (nitrosomonas) oxidises ammonium compounds in the soil into nitrites (NO2-). Then Nitrobacter oxidises nitrites into nitrates (NO3-)
• (4) Denitrification


  Denitrifying bacteria convert nitrates in the soil into nitrogen gas via respiration under anaerobic conditions (e.g. waterlogged soils)
• Why is the carbon cycle important?


  Carbon is a component of all major organic molecules present in living organism such as fats, carbohydrates, and proteins.

  There is a constant cycling of carbon between the atmosphere, land and living organisms

  
• What are the main processes of the carbon cycle?


  Photosynthesis

  Respiration

  Feeding

  Combustion

  Death and decomposition