Energy and biomass in ecosystems

First law of thermodynamics - energy can be transformed from one to another but cannot be lost or created.

Second law - as energy is transformed, some is transformed into a less useful form ( as heat)

Energy transformations in an ecosystem are inefficient.

  • Sunlight from the sun is transformed into many other types of energy.

  • But as it does so energy is ‘wasted’ in the form of heat.

  • The biggest losses in ecosystems comes from cellular respiration.

  • The more stages, the more transformation, and therefore more heat loss.

  • Hence energy transfers are not 100% efficient.

Photosynthesis

  • The conversion of light energy to chemical energy (glucose)

  • Carried out by plants, algae and photosynthetic bacteria.

  • These organisms are autotrophs - they make their own food.

  • They form the first trophic level in food chains - producers

  • Some of the chemical energy is stored as biomass - the mass living or recently living organisms.

  • Carbon dioxide + water → glucose + oxygen

  • Carbon dioxide and water have relatively low chemical energy.

  • Plants use sunlight to convert these into glucose (which has a lot more chemical potential energy).

Respiration

  • Respiration transforms both energy and matter

  • The process by which living organisms convert oxygen and glucose into a useful energy form, releasing carbon dioxide and water in the process.

  • Glucose + oxygen → carbon dioxide + water

  • The chemical potential energy of the glucose is released during this reaction.

  • It is converted from one form to another.

  • The energy is ‘stored’ within the chemical bonds of the glucose, and as the glucose is broken the energy released is used to create another chemical, ATP, which our cells can already use.

Trophic levels

Obtaining carbon compounds:

  • Herbivores - eat plants

  • Predators - eat prey

  • Scavengers - eat dead animals (carrion)

  • Detritivores - eat dead organic matter, have a digestive system

  • Parasites - feed from their hosts

  • Saprotrophs - secrete enzymes to break down and then absorb organic matter

Food chains and webs show the flow of energy between organisms.

Boxes represent stored energy and the arrows represent a transfer of energy.

Productivity and biomass:

  • Gross - the total amount of something made e.g your salary.

  • Net - the amount left after deductions (e.g. your salary after taxes, bills, food etc)

  • Gross productivity - the total gain in energy or biomass, per unit area per time. Plants - all energy they absorb from the sun. Animals - the food they eat.

  • Net productivity - all organisms need to respire to stay alive. This means that not all energy taken in is used for growing (gaining biomass). Basically like salary after taxes, bills etc.

Measuring biomass:

  • Biomass - the living mass of organisms, sometimes referred to as dry mass.

  • Biomass is taken as the mass of an organism minus water content (as it can vary between organisms and is not organic matter)

  • Other inorganic material is usually only present in insignificant quantities.

Ecologically pyramids:

  • Pyramid of numbers

  • Pyramid of biomass - snap shot into a community, total mass of each species (per m²). Unit is g/m² or gm-² . May show greater quantities at higher trophic levels because they are a snap shot, and seasonal variation may be prevalent.

  • Pyramid of productivity (energy) - show the amount of energy flowing from each trophic level to the next, not just a snap shot, but dynamic. Energy is lost at each stage due to heat loss. Unit is J/m²/yr.

Non - biodegradable vs biodegradable pollutants

Non-biodegradable:

  • Cannot be broken down by living organisms, therefore pass along food chains.

  • Persistent organic pollutants (PoP’s)

  • E.g. mercury

Biodegradable:

  • Can be broken down, therefore are not stored in living organisms nor pass along food chains.

  • E.g. sewage