Energy and ecosystems

• Define trophic level:

  Positions of each organism in the food chain

  e.g. producer = 1st trophic level, primary consumer=2nd trophic level
• How much energy is transferred from solar energy into chemical energy in producers?

  1-3%
• Why are producers not very efficient?

  • energy is reflected
  • wrong wavelength for photosynthesis
  • energy is transmitted through leaves
• What are decomposers known as?

  Saprobiontic microorganisms
• Efficiency of primary consumers vs secondary/tertiary consumers:

  Primary- 10%

  Secondary/tertiary- 20%
• Why are primary consumers not very efficient?

  • energy lost via heat through respiration
  • energy lost in waste products- faeces that contain cellulose
• Reasons for inefficiency in secondary/tertiary consumers:

  • energy lost via heat through respiration
  • waste products- faeces and urine
  • some energy cannot be obtained e.g. bones
• Equation for energy efficiency:

  after / before X 100
• Why are producers called producers?

  They produce their own nutrients i.e. glucose via photosynthesis
• Define productivity:

  The rate at which biomass is produced.
• What is GPP and how is it measured?

  Gross Primary Productivity- the chemical energy store in plant biomass in a given area in a given time

  kJ m-2 year-1
• 5 factors increasing GPP:

  1. Increased light intensity
  2. Increased leaf surface area
  3. Increased co2 concentration
  4. Increased temperature
  5. More mineral ions
• What is NPP?

  Net Primary Productivity- the chemical energy store in plant biomass after respiratory losses are accounted for
• Equation for NPP:

  NPP = GPP - R

  where R is respiration
• The temperature and gross productivity of the plants in a field were highest in July. Explain why. (2)

  The rate of photosynthesis increases so the chemical energy store increases. Light is not a limiting factor.
• The NPP of the plants was higher in August than in July. Suggest why (2)

  As the temperature decreases, the rate of respiration decreases. This means that there are less respiratory losses.
• Define net production:

  The energy available to make new animal tissues.
• Equation for net production:

  N = I - ( F + R )

  where I is chemical energy in ingested food

  f is chemical energy lost in faeces and urine

  r is energy lost as heat during respiration
• How can net production be increased?

  By intensive farming practices.
• The energy lost in respiration: energy absorbed from gut is higher in mammalian primary consumers. Why?

  More heat loss through respiration as mammals maintain their body temperature above the environment.
• Effect of restricting animal movement:

  Less heat energy lost during movement (muscle contraction) so more available for growth.
• Effect of keeping animals warm:

  Less heat energy lost maintaining body temperature so more available for growth.
• Effect on feeding animals high nutritive value food:

  A higher proportion of digested food is absorbed from the gut so more is used in growth and less is lost in faeces and urine.
• Effect of using hormones on animals:

  Hormones can increase growth rates of animals, increasing biomass.
• What does calorimetry do?

  Measures the chemical energy store in dry biomass.
• Equation for bomb calorimetry:

  energy = m X c X deltaT
• Units for calorimetry:

  Joules or kilojoules
• Biomass: the ecologists dried the samples in an oven at 103 degrees for 24 hours. Describe how the ecologists could have determined whether or not this drying method removed all the water from the sample of wood. (2)

  Measure initial mass of sample of wood. Repeat process of measuring mass and drying until a constant mass is reached/ no further change in mass.
• In calorimetry, how does a stirrer, air, and presence of water enable a valid measurement of total heat energy released?

  stirrer- distributes heat

  air- reduces loss of heat

  water- has a high specific heat capacity
• What is biomass?

  The mass of carbon or dry mass of tissue per given area in a given time.

  Measured in kg m-2 year-1
• Why do biologists measure dry mass for biomass?

  The water content of organisms varies.
• Describe the 2 types of fertilisers:

  1. Artificial/inorganic- contain no3- , po43- and k+ ions
  2. Natural- dead organic matter from living organisms e.g. manure
• Effect of using fertilisers:

  Increases crop productivity.
• Why are fertilisers needed? (3)

  • crops are grown and harvested repeatedly in the same area of land
  • this removes mineral ions from soil
  • mineral ions are not returned to the soil as plants do not undergo decomposition
• Advantages of inorganic fertilisers:

  • faster acting as they are water soluble
  • higher concentration of NPK ions
  • less smelly than organic fertilisers
  • easier to apply with machinery
• Suggest why , after a certain point the addition of fertiliser no longer improves crop productivity. (2)

  Factors other than mineral ions begin to limit the crop plant's rate of photosynthesis. e.g. lack of light energy, low co2 concentration, low water availability
• Define eutrophication:

  The addition of mineral ions to a body of water.
• What is an algal bloom?

  The rapid growth of algae caused by algae absorbing mineral ions.
• What is BOD?

  biochemical oxygen demand- it is a measure of the amount of oxygen needed by bacteria to break down organic matter in a given time.
• Reeds have hollow, air-filled tissue in their stems, which supplies oxygen to their roots. Explain how this enables the roots to take up nitrogen-containing substances:

  The oxygen is used in aerobic respiration, which releases energy in the form of ATP. This can be used in active transport to absorb nitrate ions.