Energy Transfers & Nutrient Cycles

• What 2 sources of CO2 do plants use?

  Aquatic and atmospheric.
• Why are energy transfers never 100% efficient?

  Each stage transfers energy to surroundings as heat via respiration and chemical energy via excretion.
• In which 2 ways can biomass be measured?

  In terms of mass of carbon or dry mass of tissue per given area.
• What can calorimetry be used to measure?

  Amount of chemical energy stored in dry biomass.
• What is gross primary production (GPP)?

  Chemical energy store in plant biomass, in given area or volume. (Total chemical energy converted from light energy in given area). Some lost as heat via respiration.
• What is net primary production (NPP)?

  Chemical energy store in plant biomass after respiratory losses to environment taken into account.
• What is an ecosystem?

  All organisms living in a particular area & abiotic conditions.
• What is a plant's biomass?

  Mass of living material (biological molecules). (Chemical energy stored in plant).
• Biomass can be measured in terms of...

  Mass of carbon organism contains or dry mass of its tissue per unit area.
• How can you measure biomass?

  Measure dry mass. Organism sample dried & weighed at regular intervals. Once mass constant, all water has been removed. (Mass of carbon present generally 50% of dry mass. Scale up result of sample to give biomass of population of area investigated).
• Equation for NPP?


  NPP = GPP - R
• How do you calculate consumers' net production?

  N = I - ( F + R ) ( F is energy lost in faeces & urine) (I is energy ingested in food)
• How do consumers get energy?

  Ingesting plant material or animals that have eaten plant material. Not all chemical energy stored in food transferred to next trophic level (90% available energy lost (disappearing energy)).
• Why is energy transfer more efficient moving up the food chain?

  Producers contain more indigestible matter than animals.
• How do you calculate % efficiency of energy transfer?

  Net production of trophic level / net production of previous trophic level x 100
• What do food chains show?

  Feeding relationships & energy transfer between trophic levels.
• What do detritivores do?

  Eat dead organic material (detritus) & digest internally.
• What are saprobionts?

  Decomposers (bacteria & fungi). Breakdown dead remains & waste products externally. Allow chemical elements in remains & waste to be recycled. Secrete enzymes & digest food externally (extracellular digestion). Organic molecules broken down into inorganic ions.
• How else can you measure biomass?

  Bomb calorimeter used to measure chemical energy store in biomass (dry organic material). Heat given off = how much energy is in it. Sample burnt & energy released used to heat known volume of water. Change in temperature of water used to calculate chemical energy of dry biomass.
• What is disappearing energy?

  Not all food eaten due to feeding limitations. Some energy lost in urine & faeces. Some energy used for movement. Much of the energy absorbed is used in respiration & transferred as heat energy. Energy from sun lost as its reflected as light.
• What is ecological efficiency?

  Efficiency with which energy transferred from 1 trophic level to the next.
• What do decomposers do?

  Breakdown dead or undigested material, allowing nutrients to be recycled.
• How can farmers increase energy available in food produced?

  Increase NPP & NP. Energy lost to other organisms (e.g, pests) can be reduced through simplification of food webs. Energy lost through respiration of livestock can be reduced.
• What is NP?

  Energy in consumers that's available to next trophic level.
• What are pests?

  Organisms that reduce energy available for crop growth & NPP of crops. Reduces energy available for humans.
• What happens when you simplify a food web?

  Remove chains not involving humans. Energy losses will be reduced & NPP of crop will increase.
• How can you remove pests?

  Chemical pesticides (pest control).
• What are insecticides?

  Kill insect pests that eat & damage crops. Less biomass lost from crops, so grow larger, so NPP greater.
• What are herbicides?

  Kill weeds (unwanted plant species). Can remove direct competition with crop for energy from sun. Also remove preferred habitat or food source of insect pests (simplifies food web).
• What do biological agents do?

  Reduce number of pests, so crops lose less energy & biomass, increasing efficiency of energy transfer to humans. E.g, parasites, pathogenic bacteria & viruses kill pests or reduce its ability to function.
• Why do farmers try to reduce respiratory loss?

  To increase NP of livestock by controlling conditions they live in, so more of their energy used for growth & less lost through respiration or activities that increase rate of respiration.
• Why are animals kept in warm indoor pens?

  Movement restricted (movement increases respiration rate). Less energy wasted by generating body heat. Therefore more biomass produced & more chemical energy stored-increases NP & efficiency of energy transfer to humans. (More food produced in shorter time at lower cost, however ethical issues).
• What is a symbiotic relationship?

  2 species live closely together & 1 or both depends on the other for survival.
• What are mycorrhizae?

  Symbiotic relationships formed by fungi with roots of plant. Fungi made of long, thin strands (hyphae)-connect to plant's roots. Greatly increase surface area of plant's root system, helping plant absorb ions from soil that are usually scarce. Increase uptake of water by plant. Fungi obtain organic compounds from plant (e.g, glucose).
• Where is phosphorus found?

  Rocks & dissolved in oceans as phosphate ions. Ions dissolved in water in soil can be assimilated by plants. Need phosphorus to make biological molecules.
• First step of the phosphorus cycle:

  Phosphate ions in rocks released into soil by weathering.
• 2nd step of phosphorus cycle:

  Ions taken into plants through roots. Mycorrhizae greatly increases rate at which phosphorous assimilated.
• 3rd step of phosphorous cycle:

  Ions transferred through food chain as animals eat plants & are in turn eaten by other animals. Ions lost from animals in waste products.
• 4th step of phosphorous cycle:

  Plants & animals die-saprobionts breakdown organic compounds, releasing phosphate ions into soil for assimilation by plants. These microorganisms also release phosphate ions from urine & faeces.
• 5th step of phosphorus cycle:

  Weathering of rocks releases phosphate ions into seas-taken up by aquatic producers & passed along food chain to birds.