Energy Transfers, Nutrient Cycles and Fertilisers

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

^

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

Describe the process of nitrification

• Ammonia and ammonium ions in the soil are changed into nitrogen compounds by nitrifying bacteria

• Nitrosomonas oxidate ammonium ions into nitrites

• Nitrobacter oxidate nitrites into nitrates

Describe the process of denitrification

• Denitrification happens when the soil has a low oxygen concentration which leads to a change in the species of microorganisms

• Therefore there are less aerobic nitrifying bacteria and more anaerobic denitrifying bacteria

• These convert nitrates in soil to nitrogen gas which reduces nitrogen availability for plants

• Soil must be aerated to prevent denitrification

Describe the process of ammonification

• Nitrogen compounds from dead organisms are turned into ammonia and ammonium ions by saprobionts

• Animal waste which also contains nitrogen compounds which are also turned into ammonia and ammonium ions by saprobionts

Describe the process of nitrogen fixation

• Nitrogen gas in atmosphere is converted into ammonia and ammonium ions

• Three ways this can happen

  • Lightning

  • Free-living nitrogen fixing bacteria - reduces gaseous nitrogen to ammonia which is used by bacteria to make amino acids, nitrogen rich compounds released when they die

  • Mutualistic nitrogen fixing bacteria - live in nodules on roots of legumes, bacterium get carbohydrates from the plant and plant acquires amino acids from bacteria

Why is the phosphorous cycle different from the carbon and nitrogen cycle

They don’t have a gaseous phase

Explain the phosphorous cycle

1. Phosphorous ions in rocks are released to the soil by erosion and weathering

2. Phosphate ions are taken into plants by the roots and incorporated into their biomass - absorption rate is increased by Mycorrhizae

3. Plants are eaten and digested by herbivores, phosphate ions incorporated into their biomass

4. Some phosphate ions are lost through excretion and decomposition

5. Saprobionts break down organic compounds in waste and release phosphate ions to the soil

What is Mycorrhizae

• Association between fungi and roots of plants

• Fungi acts as an extension of the plants roots

  • Increases surface area

  • Increases rate of absorption of water and nutrients

• Also acts as a sponge to hold water and minerals

  • Plants can better resist dry conditions

• This is a mutualistic relationship between plant + fungi as plant gains nutrients/water and fungus receives organic compounds (e.g. carbs)

Why do farmers use fertilisers

• Replaces nutrients lost from the soil e.g. phosphorus and nitrogen ​

• These Crops take nutrients from the soil and incorporate them into their biomass ​

• As DNA, RNA, ATP etc contain nitrogen or phosphorous or both ​

• When crops are harvested they are removed from the field they cannot be decomposed ​

• Therefore do not release the nutrients they absorbed from the soil. ​

• Farm animals that graze on plants are taken from the field to an abattoir ​

• Therefore cannot be decomposed to release the nutrients from the soil. ​

• Therefore phosphates and nitrogen are lost from the cycle ​

• They therefore increase productivity of agricultural land​

• Improves efficiency of energy transfers.

What are the two types of fertilisers

Artificial fertilisers ​

• Inorganic ​

• Contain pure chemicals (ammonium nitrate) ​

​

Natural fertilisers ​

• Organic ​

• Manure, composted veggies, sewage, crop residual

How does adding nitrogen to soil via fertilisers increase productivity

Nitrogen is a component in ​

• Amino acids ​

• ATP, DNA, FAD, NAD (nitrogenous bases)​

  So these molecules are essential for growth ​

  Which means ​

• plants can grow taller ​

• Produce more leaves​

• Rate of Photosynthesis can increase​

• More sugars can be stored in the biomass, so NPP increases

How does adding phosphates to soil via fertilisers increase productivity

• Used to make phosphate ​

  Phosphate is a component in ​

• GP ​

• TP ​

• RuBP ​

• NADP ​

• These molecules required for photosynthesis to occur. So can increase the rate of photosynthesis. ​

• Therefore more glucose production, this increases the rate of respiration. So the plant makes more ATP. This can provide energy for the plant to grow. So NPP increases.

How can farmers increase yield without the use of fertilisers

Selective breeding ​

• Can grow individuals that produce the greatest yield ​

  Ploughing soils for aeration ​

• Allows for nitrification ​

• Prevents dentification ​

• Increases yield ​

​

Crop rotation ​

• Some plants can perform nitrogen fixation so add nitrogen containing compounds to the soil ​

• Crops use different ions and minerals from the soil ​

• Crops have different pests and pathogens ​

• So increases yield

What are the 3 main negative impacts of using fertilisers

• Reduces species diversity

  • Species like grasses and nettles favour nitrogen rich soil and outcompete other plant species

• Leaching

• Eutrophication

What is leaching and how does it occur from fertilising crops

• Leaching of nutrients ​

• Occurs when more fertiliser is added to the field than used​

• Therefore when it rains the water soluble compounds are washed out of the soil into waterways ​

• Leads to eutrophication ​

• Pollution of drinking water​

• Also means there is less nitrogen and phosphorous so plants grow less ​

• Less likely with natural fertilisers ​

• Nitrogen and phosphorous contained in organic molecules ​

• Need to be decomposed by micro-organisms before nitrogen and phosphorous are released.

What is eutrophication

1. Mineral ions leached from fertilised fields which results in the rapid growth of algae in ponds and rivers ​

2. Algae blocks the light preventing it from reaching plants below ​

3. Results in the death of the plants as they cannot photosynthesise ​

4. Saprobionts decompose the dead plant matter, reducing oxygen concentration of the water as bacteria respire aerobically ​

5. Leads to the death of aquatic organisms due to a lack of dissolved oxygen

What are the pros and cons of organic/natural fertilisers

Advantages ​

• Contains lots of other elements ​

• Add structure to the soil and increases organic content of the soil​

• Provide a useful means of ​
  disposing of farm waste​

• Slow releasing so nutrients not readily leached ​
  from the soil

  Disadvantages ​

• Offensive smells​

• May be difficult to spread ​

• Mineral release slow​