2.2 Communities and ecosystems

Question 1

Community

Answer 1

All populations living and interacting in a common habitat at a specific time (only biotic)

Question 2

Ecosystem

Answer 2

a community and the physical environment it interacts with (biotic interacting w/ abiotic)
→ divided into terrestrial, marine, and freshwater

Question 3

Photosynthesis and respiration

Answer 3

all organisms respire, only producers photosynthesise
Photosynthesis → process by which a plant converts light energy from the Sun into usable chemical energy stored in organic matter. Produces the raw material for biomass.

Question 4

Photosynthesis

Answer 4

Inputs: sunlight as energy, CO2, H2O
Outputs: glucose (foundation for other organic molecules)
Transformations: light energy → chemical energy stored in biomass

Question 5

Respiration

Answer 5

conversion of organic matter to carbon dioxide and water in all living organisms, releasing energy for life processes. “Wasted” energy is lost as heat, increasing the entropy in the ecosystem while allowing organisms to maintain low entropy.

Question 6

Respiration 2

Answer 6

Inputs: organic matter (glucose) and oxygen
Outputs: release of energy to maintain order (counteract entropy) and heat
Transformations: stored chemical energy → kinetic energy and heat energy

Question 7

Producers

Answer 7

autotrophs - organisms that convert abiotic components (sunlight) into living matter. Support the ecosystem through constant input of energy and new biomass.
→ convert sunlight energy to chemical energy using photosynthetic pigments

Question 8

Consumers

Answer 8

organisms that eat other organisms to obtain energy and matter
→ pass energy and biomass from producers through to apex predators

Question 9

Decomposers

Answer 9

break down tissue of dead organic matter and release nutrients for reabsorption by producers
→ improves the ability of soil to retain nutrients - the organic byproducts of decomposed matter contribute to the humus in soil
→ essential for cycling matter within ecosystems, esp. in carbon and nitrogen cycles

Question 10

Efficiency of energy transfer

Answer 10

Only ~10% of energy is transferred to the next trophic level - trophic efficiency = 10%.
→ 2nd law of thermodynamics states energy transformations inefficient, so energy is lost at each level
→ most energy is lost as heat energy through respiration
→ each trophic level has a smaller energy pool from which it can withdraw energy, thus limiting the amount of trophic levels in a food web

Question 11

Ecological pyramid

Answer 11

quantitative differences between the trophic levels of an ecosystem, measured for a given area and time. Shows feeding relationships in a community

Question 12

Pyramid of numbers

Answer 12

records number of individuals at each trophic level in an ecosystem
→ numbers tend to decrease along food chain and pyramid tends to narrow at apex
→ can be inverted when size of individuals at lower trophic levels is large (eg. tree)
Advantages: easy method of comparing changes in population numbers over different times
Disadvantages: numbers too great to be accurate, doesn’t represent energy flow accurately

Question 13

Pyramid of biomass

Answer 13

the standing or storage of each trophic level
→ can depend on seasonal variations as they are a snapshot in certain time
Advantages: overcomes problems w/ pyramid of numbers
Disadvantages: only uses sample populations, organisms must be killed to measure dry mass, subject to seasonal variations, gives no indication of productivity over time

Question 15

Pyramid of productivity

Answer 15

, the rate at which biomass is being generated.
→ shows amount of energy available as food to next trophic level, more useful in measuring a system’s changes over time
→ always show a decrease, as transfer of energy is inefficient
Advantages: shows rate of productivity of a system

Question 16

First law

Answer 16

energy cannot be created or destroyed, only transformed.

Question 17

Second law

Answer 17

energy transformations result in a loss of energy, leaving less energy to maintain order, thus increasing entropy over time.

Question 18

Bioaccumulation

Answer 18

build up of persistent / non-biodegradable pollutants within an organism/trophic level because it cannot be broken down

Question 19

Biomagnification

Answer 19

increase in concentration of persistent / non-biodegradable pollutant along a food chain.

Question 20

DDT

Answer 20

on-biodegradable pollutant used as a pesticide by farmers.
→ producers take in DDT, organisms in 2nd trophic level retain the pesticide in their body tissue from the producers (bioaccumulation) as it is unable to be broken down
→ process continues, with more DDT accumulated at each level. Top carnivores are ultimate accumulators, and are the most vulnerable to ecosystem disruption due to their small population and high doses of toxins they receive.