energy transfer and nutrient cycles

• Organism


  Gets energy from the Sun or other organisms
• Photosynthesis


  Plants use energy from sunlight and carbon dioxide from the atmosphere (or dissolved in water in aquatic ecosystems) to make glucose and other sugars
• Ecosystem


  Includes all the organisms living in a particular area and all the non-living (abiotic) conditions
• Components of an ecosystem


  • Producers (organisms that make their own food)
  • Consumers
  • Decomposers
• Some of the sugars produced during photosynthesis are used in respiration, to release energy for processes
• The rest of the glucose is used to make other biological molecules, such as cellulose (a component of plants)
• Biomass


  The mass of living material or the chemical energy stored in the plant
• Measuring biomass


  1. Dry mass (mass of organism with water removed)

  2. Using a calorimeter (to measure chemical energy stored)
• The mass of carbon present is generally taken to be 50% of the dry mass
• Gross primary production (GPP)


  The total amount of chemical energy converted to light energy by plants, in a given area
• Respiratory loss (R)


  Approximately 50% of the gross primary production is lost to the environment as heat when the plants respire
• Net primary production (NPP)


  The remaining chemical energy available to the plant for growth and reproduction, and to organisms at the next stage in the food chain
• Net primary production = Gross primary production - Respiratory loss
• Primary productivity


  When primary production is expressed as a rate (e.g. total amount of chemical energy per area per time)
• Net production of consumers


  Chemical energy in ingested food - Chemical energy lost in faeces and urine - Energy lost through respiration
• The net production of consumers can also be called secondary production (or secondary productivity when expressed as a rate)
• The percentage efficiency of energy transfer from one trophic level to another is calculated as (net production of consumers / net primary production) x 100
• Example food chain


  • Grass (13,883 kJ/m^2/yr)
  • Arctic hare (2,345 kJ/m^2/yr)
  • Arctic fox (137 kJ/m^2/yr)
• Farming Practices and Production
• Food Webs


  Show How Energy is Transferred Between Organisms
• Decomposing


  • A part of food webs
  • Decomposen break down dead or aged m
• Reducing Respiratory Losses Means Energy is Transferred More Efficiently
• One way that farmers increase the net production of their livestock

  1. is by controlling the conditions that they live in, so that more of

  2. their energy is used for growth and less is lost through respiration

  3. (and activities that increase the rate of respiration). For example:
• Movement increases the rate of respiration, so animals.


  • may be kept in pens where their movement is restricted.
  • The pens are often indoors and kept warm, so less
  • energy is wasted by generating body heat.
• • Increasing production was
  • not an issue that was easy
  • to raise with Herbert
• 1. This means that more biomass is produced and more chemical energy can be stored.
• increasing net production and the efficiency of energy transfer to humans.
• The benefits are that more food can be produced in a shorter space of time, often at lower cost.
• However, enhancing net production by keeping animals in pens raises ethical issues.
• • For example, some people think that the conditions intensively reared animals are kept in
  • cause the animals pain, distress or restricts their natural behaviour, so it shouldn't be done.
• Organisms don't need to worry about which recycling to use or have developed a mechanism to make sure necessary elements like nitrogen and phosphorus can be recycled and continue to be available
• Fungi and Bacteria


  • Have an important role in nutrient recycling
• A natural ecosystem is one that hasn't been changed by human activity
• In natural ecosystems, nutrients are recycled through the food web, but human activity often disrupts the cycling of nutrients
• Microorganisms, such as bacteria and fungi


  • Are an important part of food webs
  • Many are saprotrophs - they feed on the remains of dead plants and animals and on their waste products
  • Saprotrophs secrete enzymes and digest their food externally
• Saprobiotic nutrition


  Obtaining nutrients from dead organic matter using extracellular digestion
• Fungi


  • Are made up of long thin strands called hyphae
  • Hyphae connect to the plant's roots
  • Fungal hyphae also increase the uptake of water and phosphorus by the plants
  • In turn, fungi obtain organic compounds such as glucose from the plants
• The Nitrogen Cycle


  1. Plants and animals need nitrogen to make proteins and nucleic acids (DNA and RNA)

  2. The atmosphere is 78% nitrogen gas, which plants and animals can't use directly

  3. They need bacteria to convert nitrogen gas into usable compounds

  4. The nitrogen cycle shows how nitrogen is converted into a usable form and then passed on between different living organisms and the non-living environment
• Nitrogen fixation


  1. Carried out by bacteria such as Rhizobium

  2. They take nitrogen gas and convert it into ammonia, which goes on to form ammonium ions in solution that can then be used by plants
• Rhizobium bacteria


  • Form a symbiotic relationship with legume plants like peas, beans and clover
  • They provide the plant with nitrogen compounds and the plant provides them with carbohydrates