23.2 transfer of biomass through ecosystems

what is meant by trophic levels and what do they represent

stages in the food chain

» represents the transfer of energy between organisms

outline the key trophic levels

Producers - organisms that make their own food e.g. plants and algae perform photosynthesis converting light energy into chemical energy

Primary consumers - herbivores that consume P for food

Secondary consumers - organisms that consume PC for food.

Tertiary consumers/ Apex predator - organisms consume SC for food

what is the difference between food chain and food web

complex network of interconnected food chains

what is biomass and why is it useful

mass of living material in particular area/ in particular organism - measuring biomass serves as an indicator of energy content

what is the difference between fresh and dry biomass

dry biomass is when all the water of an organism is removed

how is dry biomass achieved

1. collect sample and kill it

2. place sample in an oven at low temperature to dry the organism (water is removed via evaporation but temp is not too hot so organism isn’t burnt) until it reaches a constant mass (when water no longer evaporates)

3. place dry biomass into calorimeter and burn it to estimate its energy content by seeing how much the sample heats up a tank of water

what is calorimetry

burning dry biomass to estimate the energy content in Joules/ KiloJoules

why is dry biomass more useful that fresh biomass

dry biomass is a more useful because its a more reliable measure as water content fluctuates all the time due to environmental changes e.g. hot temperature or physiological processes e.g. urinating

give the units of biomass for: land VS aquatic animals

land = gm^-2

aquatic = gm^-3

define GPP and NPP

GPP - gross primary production = amount of energy entering the food chain as a result of photosynthesis

NPP - net primary production = chemical energy available for the next trophic level (gross production from photosynthesis - energy lost in respiration):

NPP = GPP - R

how to calculate net production of consumers

N = I - (F + R)

net production = energy stored in ingested food - (energy lost to environment in urine and faeces + respiratory losses)

what is ecological efficiency

efficiency at which biomass/ energy is transferred from one trophic level to the next

how do you calculate ecological efficiency

why is ecological efficiency never 100%

energy is lost at each trophic level

state factors that contribute to energy loss at the trophic levels

producers: only 10% sunlight is actually used in photosynthesis, factors e.g. water availability impact photosynthesis, some energy is used up for photosynthesis to occur

between consumers: energy lost through respiration (as body heat), lost through excretion, some parts of food are not eaten e.g. bones

explain how farmers increase ecological efficiency/ reduce energy loss

keep animals indoors = less respiration required (less body heat needed so more energy used to build biomass)

build fences = reduce movement of animals (less respiration)

vaccinations = prevent animals getting sick (energy is used to fuel their immune system to defeat the pathogen)

when is (kJ m^-2 yr^-1) or (gm^-2yr^-1) used as a unit

kJ m^-2 yr^-1 = energy content, energy transfer, respiration losses

» kilojoules per meter squared per year

(energy flowing through the ecosystem in a particular area over an entire year)

g m^-2 yr^-1 = mass, biomass, dry weight

» grams per meter squared per year

why is productivity measured per year

finds the average of productivity over a whole year, accounts for seasonal changes which impact photosynthesis