2.2 communities and ecosystems

Question 1

Define ecosystem and community

Answer 1

• Ecosystem = biological community that interact with each other and their environment + major input/output is energy
• Community = a group of populations living and interacting with each other in a common habitat

Question 2

trophic levels

Answer 2

describes the role an organism plays in the food chain

Question 3

Describe and explain the different groups of organisms – producers, consumers, and decomposers

Answer 3

Producers = organisms that nourish itself using an inorganic form of energy (sunlight/chemical compounds)
- e.g: plants
Primary consumers = animal that feeds off primary producers
- e.g: deer, cow
Secondary consumers = animal that feeds off primary consumer
- e.g: lion, wolf, humans
Decomposers = consume dead and non-living material
- e.g: dung beetles, worms, maggots

Question 4

Describe and explain respiration and photosynthesis as a system of inputs, processes, and outputs

Answer 4

Respiration ==> energy is released by cellular respiration of organic compounds
- word equation: glucose + oxygen → carbon dioxide + water
Photosynthesis ==> majority of ecosystems gain input of energy as light from the sun via photosynthesis
- word equation: carbon dioxide + water → glucose + oxygen

Question 4

output - heat - 2nd law

Answer 4

• living organisms can’t convert heat to other sources of energy –-> lost bc of second law of thermodynamics
  energy leaves areas of high concentration (living things) and moves towards a more equal concentration (out into space)
• means that energy trapped by photosynthesis is lost at every trophic level; energy flows through ecosystems, not recycled

Question 4

Describe and explain the different types of ecological pyramid

Answer 4

1. pyramid of numbers = the number of organisms at each trophic level - all organisms are counted as equal regardless of their size (1 oak tree counted as 1)
2. pyramid of biomass = a sample is collected, dried and then weighed
3. pyramid of productivity = shows the flow of energy over a period of time

Question 4

Why most ecological pyramids are pyramid-shaped with a wide base narrowing towards the top

Answer 4

2nd law of thermodynamics - energy is lost through heat - only 10% energy efficiency

Question 4

bioaccumulation and biomagnification

Answer 4

bioaccumulation = chemicals that aren’t broken down/expelled by the body
- typically associated with human-made chemicals (e.g. DDT)
biomagnification = process where top predators incur higher concentrations of bioaccumulating toxins (e.g. DDT)

Question 5

pyramids of energy

Answer 5

represent the energy that moves between trophic levels
- calculated over a year

Question 6

productivity

Answer 6

• conversion of energy into biomass over a period of time
• enables ecologists to compare the efficiency of photosynthesis between different biomes

Question 7

GPP, NPP, GSP, NSP

Answer 7

GPP = amount of energy that enters a trophic level
NPP = GPP - respiration (R) –> the amount of energy left over for growth and reproduction and available for consumers
GSP = the total energy/biomass taken by consumers –> food eaten - ‘fecal loss’
NSP = GSP - R

Question 8

factors regarding GPP and NPP

Answer 8

temperature, light and water availability

Question 9

MSY - maximum sustainable yield

Answer 9

max amount that can be taken (yield)

Question 10

human impacts on the nitrogen cycle

Answer 10

• we remove nutrients from the land and discharge them into aquatic environments
• leads to soil depletion, overabundance of nutrients, and pollution of water sources
• due to fertilizers and burning fossil fuels