IB DP Biology Option C: Ecology and conservation (Core topics) :C.2 Communities and ecosystems HL Paper 3

Date	May 2017	Marks available	6	Reference code	17M.3.HL.TZ2.17
Level	Higher level	Paper	Paper 3	Time zone	Time zone 2
Command term	Distinguish	Question number	17	Adapted from	N/A

Question

Distinguish between tropical rainforest and taiga in terms of nutrient stores, nutrient flows and climate. Gersmehl diagrams can be used to support your answer.

Markscheme

Date	May 2017	Marks available	1	Reference code	17M.3.HL.TZ2.15
Level	Higher level	Paper	Paper 3	Time zone	Time zone 2
Command term	State	Question number	15	Adapted from	N/A

Question

Most reef-building corals contain photosynthetic algae, called Zooxanthellae, that live in their cells. Coral bleaching can occur as a result of human-induced changes leading to the Zooxanthellae being ejected from the coral.

State the type of interaction that occurs between Zooxanthellae and reef-building corals.

[1]

State the trophic level of Zooxanthellae.

[1]

When coral is bleached, certain organisms become more common in the ecosystem such as the cnidarian Gorgonia, the echinoderm Diadema, other algae and certain sponges. State the term that is used for organisms whose presence provides evidence of the existence of a particular environmental condition.

[1]

A coat of algae builds up on coral reefs as a consequence of eutrophication. Explain the relationship between eutrophication and algal growth.

[2]

Explain how an excessive growth of algae on coral reefs can be controlled by top-down factors.

[2]

Markscheme

symbiosis/mutualism

producers

indicator species

a. eutrophication is nutrient enrichment of a body of water

b. example of nutrients eg: nitrates

c. «nutrients» serve as fertilizer for the algae «promoting growth»

a. top-down factors refer to predation/herbivory/trophic level above another one

b. which limit/control population growth

c. named example of a top-down predator eg: parrotfish. Do not accept general names, like “fish”.

Date	May 2017	Marks available	1	Reference code	17M.3.HL.TZ1.14
Level	Higher level	Paper	Paper 3	Time zone	Time zone 1
Command term	Determine	Question number	14	Adapted from	N/A

Question

Define indicator species.

[1]

Indicator species may be affected by biomagnification. Discuss biomagnification using a named example of a pollutant.

[3]

Determine whether islands are open or closed ecosystems.

[1]

Markscheme

organism that is present/absent when specific environmental conditions exist
OR
organism used to assess a specific environmental condition

a. example eg: DDT / mercury / cadmium

b. substance accumulates in «fat» tissue/not excreted «when consumed»

c. contaminated organisms consumed «in large quantities» by higher level consumers

d. pollutant becomes more concentrated at each higher trophic level / through the food chain

e. some pollutants are more likely to be biomagnified «accumulate in fat tissue»
OR
some organisms are more likely to be affected by biomagnification than others
OR
biomagnification not the same at each trophic level

Only [2] if verified example not given.

closed because islands do not exchange matter/nutrients with surroundings
OR
open because islands do exchange matter/nutrients with surroundings

Date	May 2017	Marks available	2	Reference code	17M.3.HL.TZ1.13
Level	Higher level	Paper	Paper 3	Time zone	Time zone 1
Command term	Distinguish	Question number	13	Adapted from	N/A

Question

The worm Branchiobdella italica lives on the external surface of the freshwater crayfish Austropotamobius pallipes. A study was carried out in a river in central Liguria, north-western Italy, of the range of sizes of B. italica found on adult A. pallipes.

Describe the body length frequency of the B. italica worms collected in this study.

[1]

The relationship between A. pallipes and B. italica is mutualistic.

A. pallipes feeds on algae and another worm, B. exodonta, lives inside A. pallipes as a parasite. State the trophic level of B. exodonta in this food chain.

[1]

Distinguish between mutualism and parasitism, providing another example of mutualism and another example of parasitism.

[2]

Markscheme

a. higher frequency of medium length worms
b. shows normal distribution
c. lower frequency at extremes

Allow correct numerical description of these points.

secondary consumer / third trophic level

a. in parasitism only one organism benefits whereas in mutualism both benefit
b. example for both parasitism AND mutualism

Do not allow B. italica or B. exodonta as examples.

eg parasitic: human tapeworms AND mutualism: bacteria in human digestive tract

Date	May 2016	Marks available	2	Reference code	16M.3.HL.TZ0.16
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Explain	Question number	16	Adapted from	N/A

Question

The graph is a model showing biomass and respiration levels in a field where farming stops at time zero and the abandoned land develops into forest.

Describe the change in biomass over the 100 year period.

[2]

Outline the evidence from the graph that the area had plentiful rainfall.

[2]

Explain the changes in biomass.

[2]

Explain why biomass continues to increase after the respiration levels plateau.

[2]

Markscheme

Increases

At a greater rate early on

Seems to plateau/levels off

Forest developed

Increase in biomass «over years» requires rainfall

Water is a limiting factor to photosynthesis

Initially there is low competition for sunlight/resources

Photosynthesis allows accumulation of biomass

Biomass rises as larger plants replace smaller plants

«In later stages» biomass increase limited due to competition for resources
OR
biomass stabilizes as climax community reached

Development of mature trees requires xylem/wood

Xylem/wood contributes to biomass but not respiration

Photosynthesis/production greater than respiration

Photosynthesis/production continues to accumulate biomass
OR
accumulated biomass remains/increases

Date	May 2015	Marks available	1	Reference code	15M.3.HL.TZ1.11
Level	Higher level	Paper	Paper 3	Time zone	Time zone 1
Command term	State	Question number	11	Adapted from	N/A

Question

Distinguish between the use of a quadrat and a transect in gathering field data.

[2]

State the change in species diversity and the change in production during primary succession.

Species diversity: ………………………………………..
Production: ………………………………………………..

[1]

b (i).

State one difficulty in classifying organisms into trophic levels.

[1]

b (ii).

Markscheme

Accept any horizontal set of ideas, up to two sets.

Species diversity: rises
Production: rises
Both needed for [1].

b (i).

an organism can occupy/feed at more than one trophic level

b (ii).

Date	November 2015	Marks available	3	Reference code	15N.3.HL.TZ0.11
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Explain	Question number	11	Adapted from	N/A

Question

Outline how habitat corridors can aid conservation of biodiversity in a nature reserve.

[1]

Explain how living organisms can change the abiotic environment during primary succession.

[3]

Markscheme

a. they allow species to travel between habitats / OWTTE;

b. outline of an example of a habitat corridor;

a. lichens secrete chemicals/acid which break down inorganic material/rock;

b. lichens/plants/litter change pH of the soil (which prevents/assists some species to establish);

c. organisms increase the mineral/organic/humus content of the soil when they decompose;

d. (organic matter and humus) can increase water retention;

e. plant roots can bind soil preventing erosion / break down soil particles;

Date	May 2012	Marks available	1	Reference code	12M.3.HL.TZ1.11
Level	Higher level	Paper	Paper 3	Time zone	Time zone 1
Command term	Define	Question number	11	Adapted from	N/A

Question

In a grassland ecosystem, the amount of energy captured by the photosynthetic organisms was 100 000 kJ m–2 yr–1. Construct a pyramid of energy indicating the predicted energy levels for four trophic levels, including the producers.

[3]

Define biomass.

[1]

Markscheme

Values: primary consumers: 10 000 kJ m–2 yr–1, secondary consumers: 1000 kJ m–2 yr–1 and tertiary consumers: 100 kJ m–2 yr–1
correct values; (allow 20 % error)
correct trophic level labels; (do not accept trophic level 1, trophic level 2 etc.)
drawing showing proper proportions; (height of each step the same, each bar no more than one quarter of the one below)

the dry mass / organic material (of a group) of organisms in a given area/habitat

Date	May 2012	Marks available	2	Reference code	12M.3.HL.TZ2.11
Level	Higher level	Paper	Paper 3	Time zone	Time zone 2
Command term	Outline	Question number	11	Adapted from	N/A

Question

Outline changes in species diversity during primary succession.

[2]

Describe a method used to estimate the size of a mouse population.

[3]

(i) Describe the environmental impact of a named invasive alien species.

(ii) State an example of biological control of the invasive alien species named above.

[2]

Markscheme

few colonizing species establish themselves in harsh conditions/volcanic ash/ sand/areas devoided of life/bare rock;
e.g. moss/lichens/marram grass/bacteria;
more organic material accumulates/soil develops;
increasing species diversity;

capture-mark-release-recapture / OWTTE;
mice are trapped in a given area, counted, marked and released (without damage);
a second capture is made in the same area and marked and unmarked mice counted;
use of Lincoln index /

(accept valid alternatives for equation)
assumes marked mice randomly distributed / other valid comment on limitations;

(i) name of invasive alien species and impact
e.g.:
water hyacinth is an invasive plant with explosive growth that blocks waterways/kills other aquatic organisms

(ii) example of biological control organism e.g.: weevils/moths/fungus/mites have been used to control the water hyacinth growth Do not award the mark if the example of the control does not correspond to the species named.

Date	May 2010	Marks available	1	Reference code	10M.3.HL.TZ1.11
Level	Higher level	Paper	Paper 3	Time zone	Time zone 1
Command term	Identify	Question number	11	Adapted from	N/A

Question

The following figure represents a terrestrial food web.

Identify the trophic level of the toad.

[1]

Outline a method that could be used to estimate the population of rabbits in this environment.

[4]

The Simpson diversity index is used to calculate the species richness in an ecosystem.

Define the terms N and n in the formula above.

N =

n =

[2]

Markscheme

tertiary consumer / fourth trophic level

capture – mark – release – recapture method;
marked unit area;
apply a paint spot/ear tag/leg ring/radio transmitter to the captured rabbits;
sufficient time must elapse to allow mixing of population to occur;
second capture must be from same marked area;
calculate the Lincoln index / population size
n1=first capture, n2= second capture, n3= number marked in second capture;

N = total number of organisms of all species found;
n = number of individuals of a particular species/per species;

Date	November 2011	Marks available	1	Reference code	11N.3.HL.TZ0.11
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Identify	Question number	11	Adapted from	N/A

Question

In 1988 a fire destroyed large portions of forest in Yellowstone National Park, USA. Photograph A was taken soon after the fire and photograph B one year later. The photographs are of the same area.

Identify, with a reason, the type of succession that has taken place.

[1]

Outline a method that could be used to sample the plant population shown in photograph B.

[2]

Yellowstone National Park was the first national park in the world and is a designated biosphere reserve site. Outline the biogeographical features of nature reserves that promote conservation of diversity.

[3]

Markscheme

secondary succession as some plants/organic components were present before fire

describe method for ensuring random placement of quadrats in a grid; (do not accept transect)
different species present in quadrat identified and counted;
used to estimate species density/frequency/abundance/cover;

size:
large nature reserves usually promote conservation better than small ones;
large areas needed for far-ranging animals (e.g. grizzly bear);
larger areas have proportionally smaller perimeters/less affected by edges;

edge effect:
ecology of edges of ecosystems is different from central areas due to edge effects;
fragmentation (of forests) leads to increase in edges which will favour some species over others;

habitat corridor:
habitat/movement/wildlife corridors allow organisms to move between different parts of fragmented habitat;

To award [3] responses must refer to size, edge effect and habitat corridor.

Date	November 2012	Marks available	1	Reference code	12N.3.HL.TZ0.11
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Define	Question number	11	Adapted from	N/A

Question

Define the term biomagnification.

[1]

Define the term biomass.

[1]

b (ii).

Describe one technique used to estimate the population size of mice.

[2]

Markscheme

Process by which chemical substances become more concentrated at each trophic level.

total dry mass of organic matter in organisms/trophic level

b (ii).

(mice are) are captured marked and released (in first cycle);
(mice are) are recaptured and number of marked ones recorded (in second cycle);
population size
(accept other symbols)

Date	November 2010	Marks available	1	Reference code	10N.3.HL.TZ0.11
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	State	Question number	11	Adapted from	N/A

Question

Earthworms are primary consumers that can be grown on household food waste such as fruit and salad leftovers. Outline their potential as an energy-containing food source for humans.

[3]

State the units used in a pyramid of energy.

[1]

Markscheme

a. much loss of energy / 10–20 % loss of energy;

b. low down food chain so efficient;

c. loss of energy through respiration/heat;

d. loss of energy through egestion;

e. less valuable as a food source than primary producers;

f. converts undigestible material into digestible materials;

kJ m–2 yr–1 / kilojoules per meter squared per year