biomass, production and productivity

what are producers?

• green plants

• they use light energy to produce organic molecules usch as carbohydrates

what are the 2 ways that organic molecules are used by plants?

• as respiratory substances

• to make other biological molecules (carbs, proteins and lipids)

  • these biological molecules form new biomass

in natural ecosystems, most of the light falling on producers is not used in photosynthesis; why is this?

• light is reflected

• light is wrong wavelength

what is biomass?

• the chemical energy stored in the plant

• energy stored within biomass can be passed along the food chain to different trophic levels

what do food chains show?

• how energy flows within a biological community

• producers are at the base of all food chains — they produce biomass

• consumers rely on producers as their source of energy

  • when they eat producers, the chemical energy stored in their biomass is transferred

examples of producers?

• plants and algae

how can we measure biomass?

• in terms of dry mass of tissue per unit area

OR

• mass of the carbon in organism

what apparatus is used to measure biomass?

• calorimeters

  • this burns biomass and calculates the chemical energy released per gram

  • the amount of heat given off tells you how much energy is in it

what is dry mass of an organism?

• the mass of an organism after its water has been removed

how to remove water from an organism?

• the organism is dried in an oven for several days

• the sample is then weighed at regular intervals

• once the mass becomes constant, you know all the water has been removed

mass of carbon?

• measure of the mass of carbon an organism has

• the water content of an individual is not taken into account

• the mass of carbon is usually about half the dry mass

how to calculate chemical energy of the dry biomass?

• a sample of dry biomass is burnt and the energy released is used to heat a known volume of water

• the change in temperature of water is used to calculate the chemical energy of the dry biomass

what happens as energy passes from one trophic level to the next?

• energy is lost

3 reasons for low efficiency of energy transfer from secondary consumers to tertiary?

• heat less from respiration

• food not digested

• excretion

what is gross primary production (GPP)?

• the chemical energy stored in plant biomass, in a given area or volume

  • during respiration, almost half the GPP is lost as heat.

  • this respiratory loss is called ‘R’

what is net primary production (NPP)?

• the chemical energy stored in plant biomass after respiratory loss to the environment have been taken into account

• equation: NPP = GPP - R

what is consumer production?

• secondary production that allows us to study how much energy consumers store in their biomass

what is net production of consumers?

• the production of new biomass by consumer

  • consumers can not convert all of the energy available from the previous trophic level into new biomass

2 primary ways that energy is lost?

• respiration

• excretion

how to calculate net production of consumers?

• N = I - (F + R)

  • N - net production of new biomass by consumers

  • I - chemical energy stored in ingested food

  • F - chemical energy lost to environment in faeces and urine

  • R - chemical energy used in respiration

how to calculate efficiency of energy transfer?

• net productivity / chemical energy stored in ingested food

what is productivity?

• the rate of production of new biomass

  • there are 2 categories: primary and secondary

what is primary productivity?

• refers to the rate of primary production by green plants

what is secondary productivity?

• refers to the rate of secondary production by consumers (herbivores and carnivores)

• herbivores have a lower secondary productivity than carnivores

why do herbivores have a lower secondary productivity than carnivores?

• this is because herbivores eat plant material which is higher in cellulose content than meat

• cellulose is harder to digest, so more energy is lost in excretion

measuring productivity?

• measured as biomass in a given area in a given time

• an example unit used for measuring productivity is kJ ha^-1 year^-1