2.2: communities & ecosystems

Question 1

community:

Answer 1

group of populations living and interacting w/ each other in a common habitat

Question 2

ecosystem:

Answer 2

community and physical environment it interacts in

Question 3

respiration:

Answer 3

glucose + oxygen = carbon dioxide + water, releasing energy as a byproduct

large amounts of energy are dissipated as heat. increasing entropy in the ecosystem while enabling organisms to maintain low entropy.

Question 4

photosynthesis:

Answer 4

carbon dioxide + water = glucose + oxygen.

produces raw material for producing biomass

Question 5

trophic level:

Answer 5

position that an organism occupies in a food chain

Question 6

how the second law of thermodynamics applies to food chains -

Answer 6

• second law of thermodynamics states that the entropy/disorder of a system increases over time
• conversions/transformations in energy aren’t 100% efficient
• available energy is lost to environment between trophic levels, for eg. lost as heat from cell respiration
• often only 10% of available energy is passed on and 90% is lost between trophic levels

Question 7

bioaccumulation:

Answer 7

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

eg. DDT

Question 8

biomagnification:

Answer 8

increase in concentration of persistent or non-biodegradable pollutants along a food chain

Question 9

types of pyramids:

Answer 9

• productivity
• biomass
• numbers

Question 10

pyramid of biomass

Answer 10

represents the standing stock or storage (biomass) of each trophic level / quantity of dry organic matter.

biomass is the mass of each individual multiplied by the number of individuals.

(measured in units such as grams of biomass per square metre)

advantage: overcomes some of the problems of the pyramid of numbers

disadvantages: only uses samples because it is impossible to measure biomass, organisms must be killed to measure the dry mass, time of the year affects the results, organisms w/ same mass do not have the same energy content

Question 11

pyramid of productivity:

Answer 11

refers to the flow of energy through a trophic level

(the rate at which a stock or storage is being generated)

10% is passed to the next, so each bar will be 10% of the lower one

advantages: most accurate, allows comparison, pyramids are not inverted, energy from solar radiation can be added

disadvantages: very difficult to collect data, problem of assigning a species to a particular trophic level when they are omnivores

Question 12

pyramid of numbers:

Answer 12

shows the number of organisms at each trophic level in a food chain at one time

advantage: simple, easy method of giving an overview. is good at observing changes in numbers

disadvantages: all organisms are included regardless of their size, does not allow for juveniles or immature forms, numbers can be too great to represent accurately

Question 13

three key ecological concepts

Answer 13

• photosynthesis
• respiration
• productivity

Question 14

compensation point

Answer 14

when all CO2 that plants produce in respiration is used up in photosynthesis, the rates of the two processes are equal and there is no net release of either oxygen or carbon dioxide

Question 15

food chain

Answer 15

flow of energy from one organism to the next (feeding relationships b/w species)

Question 16

classification of organisms:

Answer 16

producers (autotrophs/chemosynthetic organisms)
consumers (heterotrophs)

Question 17

function of primary producers -

Answer 17

• provide energy requirement for all energy requirement for all other trophic levels
• habitat
• supplies nutrients to soil
• binds the soil/ stops soil erosion

Question 18

functions of primary consumers -

Answer 18

• disperse seeds

Question 19

functions of secondary & tertiary consumers -

Answer 19

• pollinate flowers
• remove old and deceased animals from the population

Question 20

decomposers:

Answer 20

obtain their energy from dead organisms by secreting enzymes that break down organic matter

Question 21

detritivores:

Answer 21

derive their energy from decomposing organic matter

eg. shed skin from a snake

Question 22

functions of decomposers & detritivores

Answer 22

• break down dead organisms
• release nutrients into cycle
• controls spread of disease

Question 23

ecological pyramids:

Answer 23

quantitative models usually measured for a given area in time

advantages: allows easy examination of energy transfers and loses

Question 24

advantages of ecological pyramids:

Answer 24

• allows easy examination of energy transfers and loses
• gives an idea of what feeds on what and what organisms exist on different trophic levels
• demonstrates that ecosystems are systems that are in balance

Question 25

why the top of a food chain is always vulnerable to the effects of changes further down the chain -

Answer 25

• top carnivores often have a limited diet so a change in their food prey has a knock-on effect.
• their population numbers are low due to the fall in efficiency along a food chain, therefore their ability to withstand negative influences is more limited than species lower in the food chain with larger populations.