IB Biology HL D4.2 Stability and Change Questions

a. recycling of nutrients/elements/components/materials

b. carbon/nitrogen/another example of recycled nutrient/element

c. decomposers/saprotrophs break down organic matter/release «inorganic» nutrients

d. energy supplied by the sun

OR

energy cannot be recycled «so ongoing supply is needed»

OR

energy is lost from ecosystems as heat

e. energy flow along food chains/through food web/through trophic levels

f. photosynthesis/autotrophs make foods/trap energy

OR

autotrophs supply the food that supports primary consumers

g. oxygen «for aerobic respiration» released by autotrophs/photosynthesis/plants

h. carbon dioxide «for photosynthesis» released by respiration

i. populations limited by food supply/predator-prey/interactions/competition OR

populations regulated by negative feedback

OR

fewer/less of each successive trophic level «along the food chain»/OWTTE

j. supplies of water from rainfall/precipitation/rivers/water cycle

(vaporization/evaporation) cools the atmosphere /(increased) rainfall/precipitation OR affects air flow OR increases in greenhouse effect/global warming;

Marking guidance:

a. conditions closer to levels experienced naturally by the organism
b. natural variation of abiotic variables
c. more natural behaviour/interactions
d. not harm organisms by removing them from natural habitat

a. has a disproportionate/large effect (on the community);

b. they maintain/regulate populations of other species

OR

they maintain species diversity/biodiversity

OR

the removal of the keystone species decreases species diversity/biodiversity of the ecosystem;

c. the removal of the keystone species can lead to collapse of the ecosystem;

Marking guidance:

Impact: [2 max]

a. overfishing can disrupt food chains/webs/ecosystems;

b. named example from the diagram;

c. decrease biodiversity / OWTTE;

Assessing: [2 max]

d. monitoring/measuring that the rate of harvesting of species is lower than the rate of replacement of species/OWTTE;

e. monitoring/enforcing application of regulations;

f. monitoring population size (over time)

OR

monitoring biodiversity (over time);

e. Accept monitoring of regulations, e.g., size/age of fish, number in a catch,
mesh size of nets, quotas, etc., but not setting of regulations.

a. the crocodile feeds on three different species of animals / OWTTE;

b. the crocodile can be a tertiary consumer while cormorant/tigerfish is a secondary consumer

OR

the crocodile has a higher trophic level than both the cormorant and tigerfish / vice versa;

c. DDT doesn't break down/biodegrade/metabolize

OR

(bio)accumulates/builds up (in the fat/adipose tissues/crocodile);

d. accumulation/biomagnification of DDT in the higher/across trophic levels;

c. Do not award this marking point for "accumulates in the food chain".

d. Trophic levels required.

(original) source of energy in a food chain is from (sun)light;
captured by plants/autotrophs/producers/first trophic level;
by means of photosynthesis/converted to chemical energy/organic molecules;
plants use part of energy for own energy requirements/lost through cell respiration;
consumers use energy for own requirements from organisms in previous trophic level;
energy travels between trophic levels/producer to 1st consumer/1st consumer to 2nd consumer/2nd consumer to 3rd consumer;
not all material is assimilated/consumed/not digested/lost in faeces / OWTTE;
only a small amount of energy/(approximately) 10–20% is passed between trophic levels / most/80–90%/a large amount of the energy of a trophic level is lost (and not transferred);
loss of energy from organisms in form of heat;
energy is not recycled in an ecosystem (but nutrients are);