food chains and energy transfers

topic 5.3

producer

photosynthetic organisms that make organic substances

primary consumer

organisms that consume the producer

secondary consumer

organisms that eat animal material (carnivores)

tertiary consumer

consume secondary consumers

quarternary consumer

consume tertiary consumers

trophic level

position occupied by a group of organisms in a food chain/web/pyramid (each feeding stage)

the three groups organisms are divided into to based on how they use/obtain their energy

• autotrophs/producers

• heterotrophs/consumers

• saprobionts/decomposers (+detrivores)

autotrophs

use energy from sunlight to produce glucose which is converted into organic compounds (i.e fats, carbs, proteins etc.)

heterotrophs

organisms that cannot fix carbon so obtains organic carbon (by eating other organisms) for growth

saprobionts

(micro)organisms that feed by releasing enzymes outside of their body, digesting the food externally and then absorbing the digested products

detrivores

organisms that feed on detritus (dead or decaying material) giving it a bigger surface area for saprobionts to work on

what does a food chain show

it shows how energy is passed through series of organisms

what is constantly being recycled within the ecosystem

matter and nutrients for growth and other metabolic activities

e.g nutrient cycles → nitrogen cycle etc.

what is NOT being recycled within the ecosystem

energy is not recycled in the ecosystem but flows through it

what percentage of the sun’s radiation is absorbed by producers

1-3%

why is so little of the sun’s radiation absorbed by producers

bc over 90% of the sun’s energy is reflected back into space by clouds and dust or absorbed by the atmosphere

what is gross primary production (GPP)

the total quantity of chemical energy stored in plant biomass in a given area or volume in a given time

suggest a suitable unit for GPP

kJ m^-2 year^-1 or any suitable unit for energy, area and time

why isn’t all the GPP available to the plant itself, let alone the next trophic level (4)

• some of the organism is not consumed

• some is lost in urine

• some parts of the organism are consumed but can’t be digested so are lost as faeces

• energy is lost as heat from respiration to the environment

what is net primary productivity (NPP)

the chemical energy stored in plant biomass after respiratory losses to the environment

equation for NPP in plants

NPP = GPP - R

equation for NPP in animals

NPP = I - (F + R)

I = chemical energy stored in ingested food
F = chemical energy lost to the environment in faeces and urine
R: respiratory losses to the environment

equation for percentage efficiency of energy transfer from one trophic level to another

(energy available after the transfer/energy available before the transfer) x 100

biomass

the total dry mass of an organism in a given area at a given time

how is biomass measured in terms of

in terms of carbons or dry mass of tissue per given area per given time

why is dry mass used to calculate biomass

the water content can vary, depending on environmental conditions

how to obtain biomass

place material in oven at 100C to evaporate all water
mass must be weighed periodically till constant madd

pyramids of biomass

where the area of the bars is proportional to the dry mass of all the organisms at that trophic level

bomb calorimeter is used when

when estimating the chemical energy stored in dry biomass

the calorimeter contains known volume of water and known dry mass is burned inside it

the apparatus is well insulated to ensure as much as the heat energy as possible is transferred to the water

formula for estimating chemical energy stored in dry biomass

E = MCΔT