biomass and farming

• trophic levels


  the hierarchical levels of the food chain through which energy flows from primary producers to primary consumers, secondary consumers and so on
• what are trophic levels numbered based on?

  how far along the food chain the organisms in the trophic levels are
• trophic level 1


  producers: the organisms at the starting point of the food chain (e.g. plants and algae) that make their own good by photosynthesis using energy from the sun
• trophic level 2


  primary consumers: herbivores that eat plants and algae
• trophic level 3


  secondary consumers: carnivores (or omnivores) that eat primary consumers and are meat eaters (omnivores are meat and plant eaters)
• trophic level 4


  tertiary consumers: carnivores (or omnivores) that eat secondary consumers
• apex predators


  also known as "top carnivores", the animals in any ecosystem occupying the top trophic level; apex predators do not have any natural predators
• decomposers


  organisms (e.g. bacteria and fungi) that break down wastes and dead organisms and return raw materials to the environment
• How do decomposers break down dead matter?

  by releasing enzymes which catalyse the breakdown of dead material into smaller soluble molecules that diffuse into the microorganisms
• ... decreases as you go up the food chain

  energy and biomass
• biomass


  total amount of living tissue within a given trophic level
• why is there not always less organisms as you go up the food chain?

  many smaller organisms may feed on a larger organism (e.g. 500 fleas feeding on one fox)
• pyramid of biomass


  illustrates the relative amount of living organic matter available at each trophic level in an ecosystem
• what do pyramids of biomass show?

  the relative masses of trophic levels and what organisms feed on other organisms
• what does each bar on a pyramid of biomass show?

  the relative mass of living material at a trophic level
• what does the order of organisms on a pyramid of biomass show?

  the trophic levels in a food chain, showing the flow of energy and biomass from producers to consumers - the large bar along the bottom represents the producer, and the bars above it will go in order of trophic level
• drawings pyramids of biomass

  should be to scale based on actual numerical values, the order of organisms must follow the order of the food chain and each bar must be labelled with the organism that it is representing
• Why is biomass lost between trophic levels?

  - organisms don't always eat every single part of the organism they're consuming

  - organisms don't absorb all of the stuff in the food they ingest - the stuff they don't absorb is egested as faeces

  - some of the biomass taken in is converted into other substances that are lost as waste
• why may organisms not eat every single part of the organism that they are consuming?

  some material making up the organisms may be inedible (e.g. bones)
• how many biomass taken in by an organism be converted into other substances that are lost as waste?

  organisms that use a lot of glucose (obtained from the biomass) in respiration to provide energy for movement and keeping warm, etc. rather than to make more biomass - this process produces lots of waste carbon dioxide and water as by-products. urea is another waste substance, which is released in urine with water when the proteins in the biomass are broken down
• efficiency of biomass transfer (%)

  (biomass transferred to next level/biomass available at previous level) x 100
• food security


  people's ability to access sufficient, safe, nutritious food to maintain a healthy and active life
• factors threatening food security

  - increasing world population and birth rates

  - demand for certain foods from developing countries increasing with diets developing resulting in scarce foods becoming more scarce

  - farming being affected by new pests and pathogens or changes in environmental conditions resulting in the loss of crops and livestock and potentially widespread famine

  - high costs for farming making it too expensive for some countries to start or maintain food production, meaning that there may not be enough food in these areas

  - conflicts between countries that affect the availability of food and water
• what is needed for enough food to be available to feed everyone now and in the future?

  sustainable methods of food production, meaning making enough food without using resources faster than they renew
• what is overfishing resulting in?

  decease in fish stocks, meaning there are fewer fish available for consumption, the ocean's food chains being affected and some species of fish being at risk from going extinct
• how can fish stocks be maintained?

  - fishing quotas: limits to the number and size of fish caught (prevents over fishing)

  - net size: using a bigger mesh size for nets reduces unwanted and discarded fish catches and allows younger fish to slip through the net so they can reach breeding age
• how can food production be made more efficient?

  limiting the movement of livestock and keeping them in a temperature-controlled environment reduces the transfer of energy from livestock to the environment so that more energy is available for growth, so more food can be produced from the same input
• examples of food production made to be efficient

  - like stock like calves and chickens can be factory farmed, involving raising them in small pens

  - fish can be factory farmed in cages where their movement is restricted

  - some animals are fed high-protein food to further increase their growth
• why are some factory farming methods controversial?


  because the animals are kept so close together, disease can spread between them easily. there are also ethical objections, as some people think that making animals live in unnatural and uncomfortable conditions is cruel
• biotechnology


  a form of technology that uses living organisms, usually genes, to modify products, to make or modify plants and animals, or to develop other microorganisms for specific purposes
• how can bacteria be engineered to produce human insulin?

  1. a plasmid (a loop of DNA) is removed from a bacterium.

  2. the insulin gene is cut out of a human chromosome using a restriction enzyme. restriction enzymes recognise specific sequences of DNA and cut the DNA at these points. the cut leaves one of the DNA strands with unpaired bases — this is called a 'sticky end'

  3. the plasmid is cut open using the same restriction enzyme - leaving the same sticky ends

  4. the plasmid and the human insulin gene are mixed together

  5. ligase (an enzyme) is added. this joins the sticky ends together to produce recombinant DNA (two different bits of DNA stuck together)

  6. the recombinant DNA is inserted into a bacterium

  7. the modified bacterium is grown in a vat under controlled conditions. you end up with millions of bacteria that produce insulin.the insulin can be harvested and purified to treat people with diabetes
• mycoprotein


  a food made from the fungi family which contains all the essential amino acids needed by the body; suitable for lacto-ovo vegetarians
• what is mycoprotein used for?

  to make high-protein meat substitutes for vegetarian meals (e.g. Quorn)
• what is mycoprotein made from?

  the fungus Fusarium which is grown in aerobic conditions on glucose syrup, which it uses as food - the fungal biomass is harvested and purified to produce the mycoprotein
• why may crops be genetically modified?

  to improve crop yields by producing crops resistant to pests and crops that grow better in drought conditions or to provide more nutritional value to crops
• arguments against genetic modification of crops

  - many people argue that people go hungry because they can't afford to buy food, not because there isn't any food about: so they argue that you need to tackle poverty first

  - there are fears that countries may become dependent on companies who sell genetically modified seeds

  - sometimes poor soil is the main reason why crops fail, and even genetically modified crops won't survive