IB Biology Study Guide Ecology Test
1. Species are groups of organisms that can potentially interbreed to produce fertile offspring.
2. Members of a species may be reproductively isolated in separate populations.
3. Species have either an autotrophic or heterotrophic method of nutrition (a few species have both
methods).
4. Consumers are heterotrophs that feed on living organisms by ingestion.
5. Detritivores are heterotrophs that obtain organic nutrients from detritus by internal digestion.
6. Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms by external digestion.
7. A community is formed by populations of different species living together and interacting with each
other.
8. A community forms an ecosystem by its interactions with the abiotic environment.
9. Autotrophs obtain inorganic nutrients from the abiotic environment.
10. The supply of inorganic nutrients is maintained by nutrient cycling.
11. Ecosystems have the potential to be sustainable over long periods of time.
12. Most ecosystems rely on a supply of energy from sunlight.
13. Light energy is converted to chemical energy in carbon compounds by photosynthesis.
14. Chemical energy in carbon compounds flows through food chains by means of feeding.
15. Energy released from carbon compounds by respiration is used in living organisms and converted to
heat.
16. Living organisms cannot convert heat to other forms of energy.
17. Heat is lost from ecosystems.
18. Energy losses between trophic levels restrict the length of food chains and the biomass of higher
trophic levels.
19. Pyramids of number and biomass are not required. Students should be clear that biomass in terrestrial
ecosystems diminishes with energy along food chains due to loss of carbon dioxide, water and other
waste products, such as urea.
20. Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds. In aquatic
ecosystems carbon is present as dissolved carbon dioxide and hydrogencarbonate ions.
21. Carbon dioxide diffuses from the atmosphere or water into autotrophs. Carbon dioxide is produced by
respiration and diffuses out of organisms into water or the atmosphere.
22. Methane is produced from organic matter in anaerobic conditions by methanogenic archaeans and
some diffuses into the atmosphere or accumulates in the ground.
23. Methane is oxidized to carbon dioxide and water in the atmosphere.
24. Peat forms when organic matter is not fully decomposed because of acidic and/or anaerobic conditions
in waterlogged soils.
25. Partially decomposed organic matter from past geological eras was converted either into coal or into
oil and gas that accumulate in porous rocks.
26. Carbon dioxide is produced by the combustion of biomass and fossilized organic matter.
27. Animals such as reef-building corals and mollusca have hard parts that are composed of calcium
carbonate and can become fossilized in limestone.
28. Carbon dioxide and water vapour are the most significant greenhouse gases.
29. Other gases including methane and nitrogen oxides have less impact.
30. The impact of a gas depends on its ability to absorb long wave radiation as well as on its concentration
in the atmosphere.
31. The warmed Earth emits longer wavelength radiation (heat).
32. Longer wave radiation is absorbed by greenhouse gases that retain the heat in the atmosphere.
33. Global temperatures and climate patterns are influenced by concentrations of greenhouse gases.
34. There is a correlation between rising atmospheric concentrations of carbon dioxide since the start of
the industrial revolution 200 years ago and average global temperatures.
35. Recent increases in atmospheric carbon dioxide are largely due to increases in the combustion of
fossilized organic matter.
36. What are the units of energy for the pyramid of energy?
Possible Essays and Answers
Describe what is meant by a food chain using an example with four named
organisms.
food chains describe the feeding relationships between species;
arrows show (one) path of energy flow in an ecosystem / energy
flow described;
food chain with arrows pointing in the correct direction;
producer first step in chain;
three other named organisms making a realistic food chain;
Accept explicit common names exact enough to identify the food
source e.g. Oak not tree, sparrow not bird, rye grass not just grass, etc.
4 max
Outline how global warming may affect arctic ecosystems.
food chains describe the feeding relationships between species;
arrows show (one) path of energy flow in an ecosystem / energy
flow described;
food chain with arrows pointing in the correct direction;
producer first step in chain;
three other named organisms making a realistic food chain;
Accept explicit common names exact enough to identify the food
source e.g. Oak not tree, sparrow not bird, rye grass not just grass, etc.
Describe the movement of energy and nutrients in an ecosystem.
ecosystem is a community and its abiotic environment;
solar energy collected by autotrophs/plants (via photosynthesis);
moves through trophic levels via food;
4 max
only 5 to 20% transferred from one trophic level to next / never
100% efficient;
lost as metabolic heat/organic waste;
energy flow can be illustrated by pyramid shape;
organisms absorb nutrients from food/environment;
nutrients occur as complex organic matter in living organisms;
after death, saprotrophic bacteria and fungi (decomposers) breakdown
complex organic matter;
breakdown products are simpler substances;
absorbed into plants for resynthesis into complex organic matter/recycled;
6 max
0utline the consequences of an increased greenhouse effect on arctic ecosystems.
melting of permafrost;
increased detritus decomposition;
expansion of temperate species / reduced range for arctic species;
example of an affected species;
examples of human activity;
rise in sea levels;
change in climatic patterns;
loss of ice habitat;
more pests / pathogens;
disturbance to food chains / webs / trophic levels;
6 max
Explain how the emission of gases, both naturally and through human activity,
can alter the surface temperature of the Earth.
increase in temperature is called global warming;
this is caused by the greenhouse effect;
a natural phenomenon that has occurred over millions of years;
main gas responsible is carbon dioxide;
other gases like methane/nitrous oxide also cause effect;
shortwave radiation from the Sun enters atmosphere;
warms the surface of the Earth;
longwave radiation emitted by the surface of the Earth;
is absorbed by carbon dioxide/greenhouse gases;
human use of fossil fuels has increased levels of atmospheric carbon dioxide;
rapid rise in temperatures over (approximately) hundred years;
cows/animals/peat bogs release methane;
greenhouse gases emitted by volcanic activity;
Describe what is meant by a food chain and a food web.
Accept examples of the points below, provided that the terms underlined
are clearly identified. Accept only named examples (Latin or common
names) from natural ecosystems only. Do not award marks for general
names such as “fish” or “tree”.
food chain shows transfer of nutrients/energy in an ecosystem /
arrows from one trophic level to the next in examples;
between different trophic levels / shown in a correct chain or web;
starting with a producer;
followed by at least two levels of consumers / shown in a correct
chain or web;
food web is the (branched) interaction of multiple food chains /
cross arrows in examples;
using (multiple) producers as a source;
transferring nutrients/energy to consumers from different food chains;
same consumer could be at different trophic levels in a food web;
Explain the relationship between rises in concentration of atmospheric gases
and the enhanced greenhouse effect.
Award [2 max] from the following list of greenhouse gases:
water vapour;
carbon dioxide;
methane;
oxides of nitrogen;
all (of these gases) occur naturally;
and human activity has increased the normal level of these gases in
recent years;
incoming shorter wave radiation from the Sun;
is re-radiated as longer wave radiation/infrared;
(mainly) in the form of heat;
captured by greenhouse gases;
which increases the atmospheric/ocean temperature;
at a higher rate than normal / creating a positive imbalance;
which threatens ecosystems/climatic patterns/ocean patterns;
Earth’s history had many fluctuations in gas levels/global
temperature / some scientists are skeptical about enhanced
greenhouse effect;
Living organisms at every trophic level are part of the carbon cycle. Draw a
labelled diagram of the carbon cycle to show the processes involved.
diagram of food chain showing at least three organisms and two
linkages with arrows showing direction of energy flow;
trophic level is a step/position in the movement/flow of energy
through an ecosystem;
(in a field situation) observe which organisms eat each other;
producer/name from example (first trophic level) does not eat other
organisms/captures energy through photosynthesis;
primary consumer/name from example (second trophic level) feeds
on producers;
secondary consumer/name from example (third trophic level) feeds
on primary consumers;
Since the command term is explain, the answer must be explicit to
gain marking points d–f. Named examples for producer and
consumers in diagram or explained example must represent
a coherent food chain. Reject chains using general names
such as fish or tree or grass. But, accept sardine or oak.
4 max
Explain, using an example of a food chain, how trophic levels can be deduced.
measure production of oxygen;
because oxygen is a by-product of photosynthesis;
example of technique for measuring oxygen production (count
bubbles/use sensors/other);
measure uptake of carbon dioxide;
because carbon dioxide is used during photosynthesis;
example of technique for measuring carbon dioxide production
(sensor, aquatic pH shift);
measure biomass of (batches of) plants;
increase in biomass gives (indirect) measure of rate of photosynthesis;
Since the command term is explain, reasons must be given to
receive full marks.