Nutrient Cycles, Energy and Ecosystems

What is each stage in the food chain referred to as

A trophic level

Name the 4 levels of the food chain

Tertiary Consumers - Feed on 2nd consumers

^

Secondary Consumers - Feed on 1st consumers

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Primary Consumers - Feed on Producers

^

Primary Producers - photosynthetic organisms that manufacture organic substances using light energy from the sun

What are saprobionts/decomposers

• Microorganisms that breakdown complex molecules in dead organisms to simple molecules

• Recycle minerals in a form so plants can absorb them

• E.g. some fungi and bacterium

What is a food web

Interconnection of food chains within an ecosystem —> most animals eat more than one food source

How can we determine energy transfer

Measuring biomass as biomass is the mass of carbon organisms contain

Why should we use dry biomass to determine energy

• Water content varies between organisms

• No energy in water

How can dry biomass be determined

• Weigh whole organism

• Dry in oven at 100C for 24 hours

• Reweigh

• Repeat drying process until there is a constant mass achieved

Why is light energy transfer from sun to primary producers is not 100% efficient

• Some is reflected by clouds and dust

• Some does not hit the leaves and therefore the chlorophyll

• Some is not the right wavelength to be absorbed by photosynthetic pigments (which absorb blue and red light but nor green)

Why is the energy transfer between producer (plant) to primary consumers is not 100% efficient

• Energy is lost in the form of heat during photosynthesis and respiration

• Not all of biomass is eaten

• Not all biomass can be digested (egestion)

• Energy lost due to excretion

Why is the energy transfer between primary consumer to secondary consumers is not 100% efficient

• Energy is lost in the form of heat as the animal is respiring

• Not all biomass is eaten

• Not all biomass can be digested

• Energy lost in excretion

What is Gross Primary Productivity and how can it be calculated as well as its units

The chemical energy store in plant biomass in a given area/volume, at a given time

Equation = Net Primary Productivity + Respiration energy

Units - kJ m^-1 y^-1

What is Net Primary Productivity and how can it be calculated as well as its units

The chemical energy store in plant biomass after respiratory losses to the environment; the energy in biomass that is available to the next trophic level

Equation = Gross Primary Productivity - Respiration

Units - kJ m^-1 y^-1

How is net production of consumers can be calculated

N = I - (F + R)

N = Net production

I = Energy ingested

F = Energy lost in faeces and urine

R = Energy lost in respiration

What is calorimetry

Technique used to estimate the chemical energy stored in dry biomass

How is a bomb calorimeter used to estimate chemical energy stored in dry biomass

• Dry sample is weighed

• This is then burnt in oxygen in a sealed chamber called a bomb cell

• The bomb is surrounded by water

• The combustion of the dry sample causes the temperature of the water increases

• If we know the volume of water and the temperature increase we can calculate the energy in the biomass

  q = mc ^ T

Why do plants rely on nitrification for survival

Nitrification converts nitrogen into nitrite and nitrate ions. Plants can only take up nitrogen into the form of nitrite/nitrate via active transport in the roots

Describe how nutrient cycles work in general

• Nutrients taken up by the producer as inorganic ion

• Producer incorporates nutrients into complex organic molecules (e.g. protein, DNA)

• Producer is eaten and nutrients passed along food chain

• When producer and consumer die, complex molecules are broken down by saprobionts which release the inorganic ions

What are saprobionts/decomposers

Organisms that obtain nutrients from dead or decaying organic matter (e.g. bacteria or fungi)

What is the role of bacteria in the nitrogen cycle

• Free-living nitrogen fixing bacteria reduces nitrogen gas to ammonia (nitrogen fixation) and uses this ammonia to make amino acids. Mutualistic bacteria live on roots of legumes and get carbs from plant and plants acquire amino acids from bacteria. The nitrogen rich compounds are released when they die

• Saprobionts break down dead organisms releasing ammonia

• Nitrosomas Bacteria oxidise ammonia and ammonium ions into nitrites

• Nitrobacter Bacteria oxidise nitrites into nitrates