Energy transfers in and between organisms

• Outline the process of Eutrophication.

  1. Naturally low [nitrate] in lakes and rivers - limiting factor.

  
  

  2. As [nitrate] increases as a result of leaching, no longer a limiting factor for growth of plants and algae ---> populations grow.

  
  

  3. Algae grow mostly at the surface, the upper layers of water become densely populated with algae => algal bloom forms.

  
  

  4. Preventing light from reaching lower depths.

  
  

  5. Light then becomes limiting factor for growth of plants algae at lower depths and so they eventually die.

  
  

  6. Lack of dead plants and algae no longer a limiting factor for saprobiontic bacteria so their populations grow.

  
  

  7. Saprobiontic bacteria require oxygen for their respiration, creating an increased demand for oxygen.

  
  

  8. [O2] decreases and nitrates released from decaying organisms.

  
  

  9. Oxygen then becomes the limiting factor for populations of aerobic organisms such as fish ---> ultimately die as oxygen used up altogether.

  
  

  10. Without aerobic organisms, there is less competition for anaerobic organisms whose populations now increase.

  
  

  11. Anaerobic organisms further decompose dead material, releasing more nitrates and some toxic wastes such as hydrogen sulphide, making the water putrid.

  
  

  
  

  NB => organic manures, animal slurry, human sewage, ploughing old grassland and natural leaching can all contribute to eutrophication, but the leaching of artificial fertilisers is the main cause.
• Define Eutrophication.


  = The process by which nutrient concentrations increase in bodies of water.
• Define leaching.

  = When water-soluble compounds in soil are washed away by rain or irrigation systems ---> often washed in nearby ponds and rivers.

  
  

  => Can lead to eutrophication
• What are the environmental issues related to fertiliser use?

  1. Excess fertiliser in soils can lead to leaching into the waterways.

  
  

  2. This can lead to eutrophication.

  
  

  3. Leaching is more likely if fertiliser applied just before heavy rainfall.

  
  

  4. Leaching of phosphates is less likely as phosphates are less water-soluble than nitrates.

  
  

  5. Using fertilisers also changes the balance of nutrients in the soil ---> an excess of a particular nutrient can cause crops and other plants to die.
• What is the role of fertilisers? Outline the differences between artifical and natural fertilisers.

  = Added to replace lost nutrients ---> more energy from the ecosystem can be used for growth, increasing the efficiency of energy transfer.

  
  

  Artificial fertilisers are inorganic ---> pure chemicals (ammonium nitrate, for example) as powders or pellets.

  ---> Inorganic ions present in chemical fertilisers are soluble so excess minerals more likely to be leached into waterways.

  
  

  
  

  Natural fertilisers are organic matter ---> include manure, composted vegetables, crop residues and sewage sludge.

  ---> Nitrogen and Phosphorus are still contained in organic molecules that need to be decomposed by microorganisms before they can be absorbed by plants ---> release into soil is more controlled ---> leaching is less likely.
• How are nutrients lost when crops are harvested?

  1. Crops take in minerals from the soil as they grow and use them to build their tissues.

  
  

  2. When crops are harvested - they can no longer die and decompose in the field in which they were grown ---> mineral ions they contain not returned to soil by decomposers in N / P Cycles.

  
  

  3. Phosphates and Nitrates are also lost from the system when animals or animal products are removed from the land ---> when animals are taken for slaughter, the nutrients they took up when eating are not replaced through their remains or waste products.
• Outline the processes of the phosphorus cycle (PC).

  1. Phosphate ions in rocks released into soil by weathering.

  
  

  2. Phosphate ions absorbed through roots - mycorrhizae greatly increase the rate at which phosphorus can be assimilated.

  
  

  3. Phosphate ions transferred through the food chain as animals eat the plants and are in turn eaten by other animals.

  
  

  4. Phosphate ions lost from animals in waste products.

  
  

  5. When plants and animals die, saprobionts involved in breaking down the organic compounds, releasing phosphate ions into soil for assimilation by plants. These microorganisms release phosphate ions from urine and faeces.

  
  

  6. Weathering of rocks also releases phosphate ions into seas / lakes / rivers ---> taken up by aquatic producers such as algae and passed along food chain to birds.

  
  

  7. Guano (sea bird waste) contains a high [phosphate ion] ---> guano returns a significant amount of phosphate ions to soils (particularly in coastal areas) => guano is therefore often used as a natural fertiliser.
• Draw out the phosphorus cycle (PC).

  soil <- rock -> seas / lakes / rivers.

  
  

  -> algae and other primary producers.

  
  

  -> fish (feeding) -> birds (feeding).

  
  

  -> guano (excretion).

  
  

  
  

  
  

  -> soil -> plants -> animals (feeding).

  
  

  -> decaying organisms -> soil.

  AND

  -> faeces and urine -> soil.
• Suggest other ways of getting Nitrogen into an ecosystem (NC).

  1. Lightning - fixes atmospheric nitrogen.

  
  

  2. Artificial fertilisers - produced from atmospheric nitrogen on an industrial scale in the Haber process.
• Outline the process of Denitrification (NC).

  1. Nitrates in soil converted into N2 gas by denitrifying bacteria - they use nitrates in the soil to carry out respiration and produce N2 gas.

  
  

  2. Happens under anaerobic conditions, such as those present in waterlogged soils.
• Outline the process of Nitrification (NC).

  1. NH4+ ions in the soil are changed into N compounds that can be used by plants (-> nitrites -> nitrates).

  
  

  2. Nitrifying bacteria called Nitrosomonas change NH4+ ions into nitrites.

  
  

  3. Other nitrifying bacteria called Nitrobacter then turn nitrites into nitrates.
• Outline the process of Ammonification (NC).

  1. Nitrogen compounds from dead organisms are turned into NH3 by saprobionts, which goes on to form NH4+ ions.

  
  

  2. Animal urine and faeces also contain N compounds ---> also turned into NH3 by saprobionts, which goes on to form NH4+ ions.
• Outline the process of Nitrogen Fixation (NC).

  1. N2 gas in atmosphere converted to N-containing compounds by bacteria.

  
  

  2. Bacteria found inside root nodules of leguminous plants.

  
  

  3. Bacteria there form a mutualistic relationship with the plants - they provide the plant with nitrogen compounds and the the plant provides them with carbohydrates.
• Draw out the Nitrogen Cycle.

  Atmospheric N ---> N-compounds in plants (nitrogen fixation).

  
  

  ---> N compounds in animals (feeding).

  
  

  ---> to NH3 (ammonification by saprobionts).

  
  

  ---> NH4+ -> Nitrites -> Nitrates (nitrification).

  
  

  ---> Atmospheric nitrogen (denitrification)

  OR

  ---> nitrogen compounds in plants again.
• Comment on the necessity of the Nitrogen Cycle.

  - Plants and animals need nitrogen for proteins and nucleic acids.

  
  

  - They need bacteria to convert nitrogen in air to N-containing compounds.
• Define saprobiotic nutrition.

  = The process of obtaining nutrients from dead organic matter using extracellular digestion.
• Comment on the symbiotic relationships that some fungi form with plant roots.


  = These relationships are called Mycorrhizae.

  
  

  - Fungi made up of long, thin strands called hyphae, which connect to the plant's roots.

  
  

  - The hyphae greatly increase the surface area of the plant's root system, helping the plant to absorb usually scarce ions from the soil - phosphates.

  
  

  - Hyphae also increase water uptake by plant.

  
  

  - In turn, the fungi obtain organic compounds, such as glucose from the plant.
• Outline the role of fungi and bacteria (saprobionts) in nutrient recycling.

  - In natural ecosystems (hasn't been changed by human activity), nutrients recycled through food webs.

  
  

  - Some microorganisms are saprobionts (a type of decomposer) - feed on remains of dead plants and animals and on their waste products (faeces / urine), breaking them down ---> allows important chemical elements in the remains to be recycled.

  
  

  - Saprobionts excrete enzymes and digest their food externally and then absorb the nutrients they need - extracellular digestion. Organic molecules ---> inorganic ions.
• Outline how farmers can reduce respiratory losses to increase the efficiency of energy transfer.

  1. Can control conditions livestock is kept in ---> more energy used for growth and less is lost through respiration (and activities that increase the rate of respiration):

  
  

  - Animals kept in pens where movement is restricted.

  
  

  - Pens often kept indoors and kept warm so less energy wasted by generating body heat.

  
  

  2. Therefore, more biomass produced and more chemical energy can be stored, increasing productivity and efficiency of transfer to humans:

  
  

  - Benefits are that more food can be produced in a shorter space of time, often at a lower cost.

  
  

  - However enhancing productivity by keeping animals in pens raises ethical issues ---> intensively reared animals kept in conditions cause animals pain, distress or restricts their natural behaviour, so it shouldn't be done.
• Outline how simplifying the food web reduces the energy loss to other organisms.

  Pests reduce the productivity of crops by reducing the amount of energy available for crop growth ---> reduces energy available for humans.

  
  

  => By removing food chains that don't involve humans, energy losses reduced and crop productivity increased.

  
  

  1. Chemical pesticides:

  
  

  - Insecticides kill insect pests that eat and damage crops ---> killing pests means less biomass lost - crops grow larger so productivity (rate at which chemical energy is stored) is greater.

  
  

  - Herbicides kill weeds (unwanted plant species) - killing weeds removes direct competition for light and resources etc. Also removes habitats for insect pests helping to further reduce their numbers and simplify the food web.

  
  

  2. Biological pesticides:

  
  

  - Parasites live in or lay their eggs on a pest insect. Parasites either kill insect or hinder its ability to function.

  
  

  - Pathogenic (disease-causing) bacteria and viruses are used to kill pests.

  
  

  
  

  => Farmers can use integrated systems that combine both chemical and biological methods. Combined effect of using both can reduce pest numbers even more than one method alone, increasing productivity even more.
• Farming practices aim to increase the efficiency of energy transfer by? (2 factors).


  1. Reducing energy lost to other organisms.

  
  

  2. Reducing energy lost through respiration.
• How can food chains / food webs show how energy is transferred between organisms?

  Food chains - show simple lines of energy transfer between trophic levels.

  
  

  Food webs - show many food chains in an ecosystem, and how they interact and overlap.

  
  

  
  

  Decomposers (such as fungi) are also part of food webs - break down dead or undigested material, allowing nutrients to be recycled.
• How would we calculate the efficiency of energy transfer?


  (NP / total energy received) x 100.
• Give the equation for the net production of consumers.

  N = I - (F + R).

  
  

  Where:

  
  

  N = Net production.

  I = Chemical energy in ingested food.

  F = Chemical energy lost in faeces and urine.

  R = Energy lost through respiration.

  
  

  All units in = kj / m2 / yr.
• Comment on the energy transfer between producers and consumers / consumers and consumers.

  1. Consumers get energy by eating plant material or animals that have eaten plant material.

  
  

  2. Not all chemical energy stored in consumer's food is transferred to the next trophic level (only around 10%).

  
  

  3. Firstly, not all food is eaten - plant roots / bones etc. so the energy these things contain is not transferred as they are not ingested.

  
  

  4. Of the parts that are ingested,

  
  

  - Some are indigestible, so are egested in faeces => chemical energy stored in these parts is therefore lost to the environment.

  
  

  - Some energy lost to the environment through respiration or excretion of urine.

  
  

  5. Energy left after all this is stored in the consumers' biomass and is available to the next trophic level. Energy = consumers net production.
• Give the equation for NPP.

  NPP = GPP - R.
• Define Net Primary Production (NPP). Units?

  = Remaining chemical energy - energy available to plant for growth and reproduction, i.e. energy stored in plant's biomass.

  
  

  = Energy available to organisms at the next trophic level.

  
  

  
  

  kj / m2 / yr.
• Define Respiratory Loss (R). Units?

  = (Approx 50% of) GPP lost to the environment as heat when the plants respire.

  
  

  
  

  kj / m2 / yr.
• Define Gross Primary Production (GPP). Units?

  = Total amount of chemical energy converted from light energy by plants in a given area, in a given time.

  
  

  kj / m2 / yr.
• How can we measure biomass using calorimeter.


  - Can estimate the amount of chemical energy stored in biomass by burning biomass in a calorimeter.

  
  

  => heat given off tells you how much energy is in it.

  
  

  1. Sample of dry biomass burnt and energy released to heat a known volume of water.

  
  

  2. Temperature change of water is calculated the chemical energy of the dry biomass.
• How can we measure biomass as dry mass?

  - Measured in terms of the mass of carbon that an organism contains or the dry mass of its tissue per unit area per unit time.

  
  

  1. Dry mass is the mass of the organism with the water removed.

  
  

  2. To measure dry mass, sample of the organism dried, often in an oven set to a low temperature. Sample then weighed at regular intervals (every day). Once mass remains constant, all water removed.

  
  

  3. If necessary, result from sample can be scaled up to give dry mass (biomass) of the total population or the area being investigated. Typical units for dry mass => kg / m2

  
  

  4. Mass of carbon present is generally taken to be 50% of dry mass.

  
  

  5. Biomass changed over time ---> deciduous trees lose their leaves in winter, for example.

  => useful to give biomass over a particular time period ---> typical biomass units kg / m2 / yr.
• List 2 methods of measuring biomass.

  1. Using dry mass.

  
  

  2. Using a calorimeter.
• Outline how energy is "produced" and transferred throughout an ecosystem.

  1. In an ecosystem there are producers - organisms that make their own food - plants / algae, via photosynthesis.

  
  

  2. Some sugars produced during photosynthesis used in respiration, to release energy for growth.

  
  

  ---> rest used to make other biological molecules such as cellulose. These molecules make up the plant's biomass = mass of living material / stored chemical energy of plant.

  
  

  3. Energy is transferred through the living organisms of an ecosystem when organism eat other organisms ---> producers eaten by primary consumers, eaten by secondary consumers, eaten by tertiary consumers = food chain.
• Define ecosystem.

  = All the organisms living in a particular area along with all the abiotic conditions.
• How can other respiratory substrates be used in aerobic respiration?

  Some products from the breakdown of other molecules such as fatty acids from lipids, and amino acids from proteins can be converted into molecules that are able to enter the Krebs Cycle (usually converted to acetylcoA).
• How do mitochondrial diseases affect ATP production?

  1. Affect the functioning of mitochondria - can affect how proteins involved in oxidative phosphorylation or the Krebs Cycle function, reducing ATP production.

  
  

  2. May cause anaerobic respiration to increase in order to compensate for some of the ATP shortage.

  
  

  3. => Lots of lactate produced, which can cause muscle fatigue and weakness.

  
  

  4. Some lactate will also diffuse into bloodstream, leading to high lactate concentrations in the blood.
• Calculate how much ATP can be made from one glucose molecule.

  Glycolysis 1 ---> 2 ATP.

  Glycolysis 2 ---> 2 NADH ---> 2x2.5 => 5 ATP.

  
  

  Link Reaction x 2 ---> 2NADH ---> 2x2.5 => 5 ATP.

  
  

  Krebs Cycle x 2 ---> 2ATP.

  ---> 6 NADH ---> 6x2.5 => 15 ATP.

  ---> 2 FADH2 ---> 2x1.5 => 3 ATP.

  => 32 ATP.
• Outline the process of oxidative phosphorylation.

  1. H atoms released from NADH and FADH2 (oxidation). The H atoms split into protons (H+) and electrons (e-).

  
  

  2. Electrons move down ETC (made up of electron carriers) losing energy at each carrier.

  
  

  3. This energy used by the electron carriers to actively transport H+ from the mitochondrial matrix into the intermembrane space.

  
  

  4. [H+] now higher in the intermembrane space than in mitochondrial matrix ---> forms an electrochemical gradient.

  
  

  5. Protons then move down electrochemical gradient into mitochondrial matrix via ATP-synthase (embedded in the inner mitochondrial membrane).

  => movement drives ADP + Pi ---> ATP.

  
  

  => process called chemiosmosis.

  
  

  6. In the mitochondrial matrix at the end of the ETC, the protons, e- and O2 from blood combine to form water.

  
  

  => O2 said to be the final electron acceptor.
• Some products of the Krebs Cycle are used in oxidative phosphorylation.

  
  

  List the products of the Krebs Cycle and outline where they go.

  1 x coenzymeA ---> reused in next link reaction.

  
  

  Oxaloacetate ---> regenerated for use in next Krebs Cycle.

  
  

  2 x CO2 ---> released as waste product.

  
  

  1 x ATP ---> used for energy.

  
  

  3 x NADH ---> oxidative phosphorylation.

  
  

  1 x reduced FAD ---> oxidative phosphorylation.
• Outline the Krebs Cycle.

  = Series of oxidation-reduction reactions which take place of the mitochondria.

  
  

  = Takes place once for every pyruvate, so goes around twice for every glucose molecule.

  
  

  1. AcetylcoA from the link reaction combines with 4C oxaloacetate to form 6C citrate.

  
  

  2. Coenzyme A goes back to the link reaction to be used again.

  
  

  3. 6C citrate molecule converted to a 5C molecule. -CO2 / NAD--->NADH.

  
  

  4. 5C molecule converted to 4C oxaloacetate molecule.

  
  

  NAD--->NADH.

  
  

  ADP + Pi--->ATP = produced by direct transfer of a phosphate group from an intermediate compound to ADP (substrate-level phosphorylation).

  
  

  FAD--->reduced FAD.

  
  

  NAD--->NADH.

  
  

  
  

  
  

  => Krebs therefore produces reduced coezymes and ATP.