3-Ecosystem

Question 1

ECOSYSTEM

Answer 1

a biotic community and its abiotic environment

• can be small or large
• ecosystem ecologists ask:
  
  • how does energy flow through a system
  • how do nutrients cycle between the abiotic and biotic components of a system?

Question 2

PRODUCERS

Answer 2

• aka autotrophs
• obtain their energy by using photosynthesis to convert solar energy to chemical energy

Question 3

CONSUMERS

Answer 3

• aka heterotrophs
• obtain energy by eating other organisms

Question 4

what are the two types of consumers that eat dead organic material

Answer 4

• detritvores—ingest dead organic material, break down material internally
  
  • earthworms, slugs
• decomposers—break down dead organic material, then absorb nutrients

Question 5

FOOD CHAIN

Answer 5

the linear transfer of food energy from one trophic level to the next trophic level

Question 6

food web

Answer 6

food web—series of interlocked food chains that allow for the possibility of omnivores (consumers of multiple trophic levels)

Question 7

primary productivity

Answer 7

• rate of conversation from solar energy to chemical energy by producers
  • biomass/area/time
  • energy/area/time

Question 8

gross primary productivity (GPP)

Answer 8

absolute rate of primary productivity

Question 9

net primary productivity (NPP)

Answer 9

rate of primary productivity after accounting for cellular respiration

Question 10

ten percent rule

Answer 10

approximately 10% of the chemical energy at one trophic level is transferred to the next trophic level

Question 11

why is energy lost between trophic levels?

Answer 11

• not all of the organisms at one trophic level are consumed by organisms at the next trophic level
  
  • ~90% of producer biomass is consumed by detritivores and decomposers
• not all food eaten is completely digested
• energy is lost as heat (by-product of metabolism)
• energy used for hunting
• this creates a biomass pyramid
  
  • it takes MAAANY primary producers to support only a few teritary consumers

Question 12

what are the nutrients that are chemicals needed for growth and maintenance for life

Answer 12

• N (nitrogen)
• P (Phosphorus)
• C (Carbon)
• O (Oxygen)
• Fe (iron)

nutrients do not come from outside the earth and instead have to be recycled

Question 13

pools

Answer 13

where nutrients are stored

Question 14

fluxes

Answer 14

movement in and out of pools

Question 15

Carbon

Answer 15

• essential nutrient that is required for growth and reproduction
• basic building block of organic molecules
• mainly stored in oceans and atmostphere
  
  • soils, living organisms, and fossil fuels are also important pools of C

Question 16

how does
Carbon enter and exit the food web?

Answer 16

• enters plant—C(CO2) captured by plants during photosynthesis, incorporated into organic molecules
• enter animals—Carbon is passed along the food chain/food web by consumers
• reenters the atmosphere
  • cellular respiration—occurs in the cells of all living things: producers (autotrophs) and consumers (heterotrophs)
  • humans are also emmiting carbon-based greenhouse gases to the atmosphere through deforestation and fossil fuel use

Question 17

Nitrogen

Answer 17

• essential nutrient that is required for survival and growth of all living organisms
• vast majority is stored in atmosphere as N2
  
  • 80% of the atmosphere!!
• soils, oceans, and living organisms are also important pools of N

Question 18

why is nitrogen a limiting factor?

Answer 18

• atmospheric nitrogen is largely inaccessible by most organisms
  
  • triple bond takes a lot of energy to break!
  • plants and animals cannot break these bonds
• sooooo N is a scarce resource
  
  • often limits primary productivity in many ecosystems

Question 19

limiting factor

Answer 19

a factor that limits the growth, abundance, or distribution of individuals and/or populations

Question 20

how does N become biologically available?

Answer 20

nitrogen fixation
- a process where N2 is converted into NH3
- ammonia

nitrification
process where NH3 is converted to nitrites (NO2) and then nitrates (NO3)

Question 21

how does nitrogen enter plants without symbiotic bacteria?

Answer 21

• some nitrogen-fixing bacteria are free-living in the soil or ocean while others form a symbiotic relationship with plants
  
  • free-living nitrogen-fixing bacteria that convert gaseous nitrogen to ammonia
  • nitrifying bacteria that convery ammonia to nitrites and nitrates
  • decomposing bacteria that breakdown dead organic material/tissues into basic components
• plants can uptake biologically available nitrogen via their roots

Question 22

how does nitrogen enter animals?

Answer 22

• plants eaten by primary consumers!
• passed along food chain/web

Question 23

other components of the nitrogen cycle

Answer 23

• when plants/animals die, tissues are decomposed by decomposing bacteria, which released nitrogen back into the ecosystem in a usable form
• when animals pee/poop, they release nitrogen into the environment in a usable form

Question 24

how does nitrogen return to the atmosphere?

Answer 24

• denitrification—process that converts nitrates to nitrogen gas
• denitrifying bacteria—strip O from NO3 (nitrates) and NO2 (Nitrites) and release N2 back to atmosphere

Question 25

how are Humans disrupting the nitrogen cycle

Answer 25

- increase the amount of biologically available nitrogen in ecosystems - excess nitrate is getting into water as a result of runoff from agricultural areas - resulting in **eutrophication** of water bodies - gradual increase in nitrogen (and other nutrients) in aquatic ecosystem - the addition of nitrogen due to human activities has lead to excessive plant and algae growth due to increased availability of nitrogen - can lead to decreased diversity - dead zones!