2.2: Energy And Biomass In Ecosystems

Question 1

Example of energy loss in food chains

Answer 1

Caterpillars -> do not eat every leaf available to them
-> too many leaves, not enough caterpillars
-> or in a difficult to reach position

Caterpillar may not eat entire leaf
-> may eat only softer/more nutritious parts

Once caterpillar eats -> not all of nutrients are absorbed
-> indigestible or contain compound that the caterpillar cannot process
-> egested

Caterpillar digest leaves -> nutrients into energy
-> not all energy from leaves stored for growth/development
-> some energy lost as heat during cellular respiration

Question 2

Examples of chemicals than tend to biomagnify

Answer 2

DDT (dichlorodiphenyltrichloroethane):
Used as pesticide, kill mosquitoes
Rachel Carson ‘silent spring’

Heavy metals (mercury and lead)

PCBs (polychlorinated biphenyl):
Originally used in electrical transformers as electrical insulators

Question 3

Biomagnification case study: DDT

Answer 3

Dichlorodiphenyltrichloroethane

• Insecticide used in 40-60s to control mosquito population
• still used in poor countries with high malaria rates
• entered environment via runoff -> leached into waterway+ecosystem
• enter food chains via plankton
  -> accumulate in fish, biomagnify in birds
• banned globally in 1972 (bald eagle population crashed)
  -> DDT stopped shells of eagle eggs from forming properly -> offspring died often

Question 4

Biomagnification case study: mercury

Answer 4

Mercury: released through activities like coal-fired power plants, gold mining

Once in environment: mercury converted into highly toxic methylmercury

Accumulated in fish bodies
- large fish eat smaller fish -> concentration of methylmercury in tissue of fish increases -> potential harm for humans

Ex: 1956 Minamata, Japan
Chemical factory released toxic methylmercury into water water in minamata bay
- mercury accumulate in fish/shellfish

• mercury poisoning in people (severe symptoms: paralysis, death, birth defects, loss of sight/hearing, etc)
  -> birth defect because MM disguised as methionine (AA) and bind to cysteine -> absorbed in placenta+brain
• cats show symptoms first -> danced and died
  -> fish was primary food source
  -> cats were smaller + ate parts that had higher methylmercury concentrations
• Chisso corporation -> used acetaldehyde to make plastics -> mercury catalyst
• inorganic mercury is not dangerous -> contact with bacteria in bay turn into methylmercury
  -> bio available, fully absorbed in gut and cannot be removed (bio accumulation and magnification)
• 12 years after first death (1968) -> stopped dumping
• cleaned in 1977 and safe in 1997

Question 5

Human activities and ecosystem impacts: burning fossil fuels

Answer 5

Releases CO2 into atmosphere> contribute to global warming
Increased CO2 availability -> increase photsyntehsis rates
- but climate change effects can outweigh this benefit

Ex: burning coal to generate electricity -> emit CO2 + release SO2
-> pollutant contributes to acid rain, change in soil pH, impact plant health, nutrient availability
-> reduces photosynthesis rates

Question 6

Human activities and ecosystem impacts: deforestation, urbanization and agriculture

Answer 6

Deforestation:
- Clearing forest for agriculture, urbanization, etc. -> disrupt ecosystem
- Cause habitat loss, disruption of food web, deforestation, reduces the carbon sink capacity of forests
- contributes to climate change

Urbanization:
- urban development replace habitats with impervious surfaces (ex concrete) -> increased runoff and reduced infiltration
- generate ‘heat islands’ -> increase local temps

Agriculture:
- intensive agriculture (fertilizers, pesticides, monoculture practice)
- lead to soil degradation, water pollution, loss of biodiversity