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UNIT 3: ECOSYSTEMS
STRUCTURE AND FUNCTION
WHICH ARE COMPONENTS OF AN ECOSYSTEM?
Ecosystems are functional units composed of all the living things in a place, their biotic
components, and the physical and chemical factors which make up its non-living things, which
are their abiotic components. There are different interactions between the biotic and abiotic
factors as well as between the organisms living in a ecosystem.
The ecosystem is the higher level in the organisation and complexity of life. An organism from
a species is an individual. All individuals of one species which live in the same place and at the
same time are called population. And populations of different living things that live in the
same ecosystem and interact between them are called community.
All the ecosystems on Earth can be considered as
an only functional unit called Ecosphere, where the
biotic components are all the living things living in
our planet, which we call Biosphere, and the abiotic
components are the Geosphere, the Atmosphere
and the Hydrosphere.
The habitat of a population is the place that
supplies the needs of this population, such as water
or food. The habitat where a population lives and
the range of environmental conditions that are
suitable for the survival of the population
determine the ecological niche. Each species
occupies a specific niche in the ecosystem. If two
different populations have the same ecological niche, they will compete for it.
They are different interactions between the members of a community that keep the
functionality of the ecosystem. Some of them are: competition, when two living things need
the same resource; predation, an individual kills and eats another individual of a different
species; symbiosis, two or more individuals of different species live in close proximity to each
other and interact regularly in such a way as to benefit them; or cooperation.
HOW ABIOTIC FACTORS INFLUENCE ON LIVING THINGS?
There are two main types of environment, terrestrial and aquatic. The influence of the abiotic
factors is different in each one. These factors are important because they determine the living
things that live in an ecosystem. The main abiotic factors are water, light, temperature,
precipitation, salinity or soil chemistry.
Living things have limits of tolerance to
abiotic factors to survive. The abiotic
factor’s range in which a population can
live is called tolerance range. This range is
different for each population, and
everyone has a level or optimum, inside
the tolerance range, at which the
population grows and lives better.
Temperature and water are the most
influential abiotic factors in the
development of a population in a terrestrial environment. On the contrary, in aquatic
environments, as well as temperature, other factors such as light, salinity or dissolved oxygen
level limit life.
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UNIT 3: ECOSYSTEMS
ACTIVITIES
1. Answer the following questions.
a) What is the difference between an ecosystem and the Ecosphere?
b) What is the difference between population and community?
c) What is the difference between habitat and ecological niche?
d) What is the difference between biotic and abiotic components?
e) What is the difference between limits of tolerance and tolerance range?
2. Look at the picture and write four biotic components and four abiotic components.
http://4.bp.blogspot.com/_mYcBoE9RZdU/TS8NhyPHznI/AAAAAAAACNM/OoTWYNAzJtA/s1600/ecosystem.jpeg
3. Look at the picture in activity 2 and write two interrelationships between different biotic
components and write what abiotic factor is more limiting in the ecosystem. Give reasons
for your answer.
4. W.orking W.ith the W.eb: Plant and Animal Adaptation Research
Adaptations are behavioural and physical characteristics that organisms develop to survive
and reproduce in their environment. Choose a plant and an animal to study how they adapt
to abiotic factors in an ecosystem. Use the information on the Internet to write and
illustrate a fact sheet explaining how your plant and animal adapt to their habitats. Include
images and information about their habitat and behavioural or physical traits related to
each abiotic factor.
http://resources.education.tas.gov.au/item/edres/68652f50-0e7f-5e01-321a5680ee051f0d/1/I_eat_them.zip/bio.swf
http://bioactive.mrkirkscience.com/Part6Sim/swfs/Sim_06.swf
http://www.phs.d211.org/science/dahljl/Bio%20138/PPTs/flash%20unit%2011/Biomes.swf
http://www.biologyreference.com/A-Ar/Adaptation.html
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UNIT 3: ECOSYSTEMS
FOOD CHAINS AND FOOD WEBS
HOW ARE LIVING THINGS RELATED IN AN ECOSYSTEM?
Living things need matter and energy for their life processes. Matter and energy appear in the
ecosystem when autotrophs get them from soil, air and light. Then, matter and energy are
transferred to heterotrophs by trophic relationships. Thus, living things can be classified
according to the trophic level they occupy:

Producers are autotrophic organisms that transform the inorganic matter into organic by
photosynthesis.

Consumers are heterotrophic living things that feed on other organisms. The consumer
trophic level can subdivide depending on the type of organisms included. First-order
consumers eat producers, whereas second-order
consumers obtain food from first-order consumers.

Decomposers transform organic matter into
inorganic substances which are used by producers.
A food chain is a sequence of organisms that shows the
feeding relationships between them. A food chain always
begins with producers. But, these relationships are not
always so simple because a consumer can feed from
several lower levels. This means that several food chains
become connected forming complex food webs.
Higher trophic levels have fewer organisms than lower
levels. This is because when nutrients are recycled within
an ecosystem, energy is lost with each transfer to a
higher trophic level. So, energy must be continually
generated in an ecosystem by photosynthesis.
HOW ARE TROPHIC RELATIONSHIPS REPRESENTED?
As well as food chain or food web, the relationships between living things can be represented
by trophic pyramids. These pyramids show the amount of energy, biomass or the number of
organisms there are in every trophic level.
An ecological pyramid places the producers at
the base, the next higher level consist of firstorder consumers, the next higher level of
second-order consumers, and so on. There are
different types of ecological pyramids:

The energy pyramid shows the total amount
of energy present in each trophic level. This
is the only representation that always has a
pyramidal form, because of the progressive
energy loss.

A biomass pyramid represents the biomass
or amount of organic matter at each trophic
level of a food web. Usually these pyramids
have a pyramidal form, but some of them
can be inverted. This pattern is often attributed to different sizes of producers, such as
plankton producers in some aquatic ecosystems.

A pyramid of number shows the number of organisms at each trophic level. This pyramid
also can be inverted, such as the number of insects living on a tree.
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UNIT 3: ECOSYSTEMS
ACTIVITIES
1. Match each concept with its definition.
-
They are herbivores
- Food chain
-
They do photosynthesis
- Energy pyramid
-
It is a sequence of feeding relationships
- Producers
-
It never is inverted
- Decomposers
-
It can be inverted
- Food web
-
It is formed by several food chains
- Biomass pyramid
-
They produce inorganic matter
- Second-order consumers
-
They eat herbivores
- First-order consumers
2. Look at the following food web and give reasons for your answer.
(http://king.portlandschools.org/files/houses/y2/animalmaineia/files/species/wfrogkm/foodweb/foodwebexample.gif)
a) What do you think will happen if you take
the foxes out of the food web?
b) Which are the producers?
c) Which are the first-order consumers?
d) Which are the second-order consumers?
e) What is the biggest order of consumers in
the food web? What animal/s occupy/ies
this order?
f)
Write the biggest food chain you can find.
3. Complete the sentences with the words below.
autotrophs – herbivore – carnivore – plants – heterotrophs – omnivore – produce
a) Plants _____________ their own food.
b) A __________ eats only plants.
c) __________ provide food for all the animals in the world.
d) __________ are animals that do not produce their own food.
e) Plants are called producers or _____________.
f)
An animal or human being that eats meat and plants is an ______________.
g) A ______________ eats only meat.
4. W.orking W.ith the W.eb: Food chain game
Play one of the following on-line games and write two different food chains. Identify the
second-order consumer in each chain and explain what would happen if they disappeared.
http://www.ecokids.ca/pub/eco_info/topics/frogs/chain_reaction/index.cfm
http://www.sheppardsoftware.com/content/animals/kidscorner/games/foodchaingame.htm
http://www.bbc.co.uk/schools/ks2bitesize/science/living_things/food_chains/play.shtml
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UNIT 3: ECOSYSTEMS
WORLD’S BIOMES
HOW ARE ECOSYSTEMS DISTRIBUTED AROUND THE WORLD?
There are many similarities between the different ecosystems around the world. Scientists
classified ecosystems into categories called biomes. The American scientist Neil Campbell
defined biome as “the world’s major communities, classified according to the predominant
vegetation and characterized by adaptations of organisms to that particular environment”. The
terrestrial biome distribution is determined by temperature and precipitation patterns. Thus,
the world’s biomes can be classified according to three climate zones: low-latitude climates
(tropical rainforest, savanna, desert), mid-latitude climate (Mediterranean biome, grasslands,
deciduous forest) and high-latitude climates (taiga, tundra, alpine biome).
These are the characteristics
of the main world’s biomes:

The tropical rainforest has
the greatest diversity of
species. It occurs near the
equator. Temperature and
humidity are relatively
high through the year.

The savanna is a grassland
ecosystem with scattered
individual
trees.
This
biome has only two very
different seasons: a very
dry season and a very wet season. The savanna is located on extensive areas on either side
of the equator on the edges of tropical rainforest.

Desserts cover about one fifth of the Earth’s surface and occurs where annual rainfall is
less than 25 cm and, in some years, zero. Desserts are classified into hot and dry, semiarid,
coastal and cold. This last type of dessert occurs in the high-latitude such as Antarctic or
Greenland.

The Mediterranean biome is found between 32º and 40º latitude North and South on the
west coast of the continents. The annual rainfall averages from about 300 to 1000
millimeters. Summers are dry and winters are wet.

Grassland biomes are areas dominated by grass or grasslike vegetation. There two main
kinds of grassland: prairies, with tall grasses, and steppes, with short grasses.

The deciduous forest is characterised by a moderate climate and deciduous trees.
Normally, large areas are dominated by a single species. Abundant precipitation falls
throughout the year, increasing in the summer season. There is not a dry season.

The taiga or boreal forest represents the largest terrestrial biome. It occurs between 50º
and 60º North latitude and it is dominated by conifers. It has long, very cold winters and
short, cool summers. Precipitation is small, increasing during summer months.

The tundra is located in the northern hemisphere, poleward of 60º North latitude. The
climate is so cold in winter that soils of this biome are usually permafrost.

The alpine biome is quite similar to the tundra but there are not permafrost and it
presents a better drainage. Alpine biomes are found in the mountain regions all around
the world.
The world’s aquatic ecosystems can be classified into freshwater (ponds and lakes, rivers) and
marine (oceans, coral reefs).
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UNIT 3: ECOSYSTEMS
ACTIVITIES
1. Tick the sentences T (true) or F (false). Then correct the false sentences.
T
F
a. Aquatic biomes are distributed according to climate.
b. Steppes are a type of Mediterranean biome.
c. The tropical rainforest occurs near to equator.
d. There are desserts in Greenland.
e. The coral reef is a type of freshwater biome.
2. Answer the following questions.
a. Which terrestrial biome occupies one fifth of the Earth’s surface?
b. What is the difference between prairies and steppes?
c. Which terrestrial biome is between 50º and 60º North latitude?
d. In which hemisphere is the tundra located?
e. In which latitude can the Mediterranean biome be found?
3. Identify the type of biome. What animals can you see in each ecosystem?
savanna
a.
desert
b.
coral reef
Mediterranean forest
c.
d.
tundra
desert
e.
W.orking W.ith the W.eb: My favourite aquatic ecosystem
In groups, design a poster about your favourite aquatic ecosystem using information on the
Internet. Include a map where you can locate the ecosystem in the world and a fact file of its
characteristics: climate, animals and plants. Write a possible food chain or food web in the
ecosystem.
Suggested websites:
http://www.mbgnet.net/fresh/
http://www.ucmp.berkeley.edu/exhibits/biomes/index.php
http://www.schools.indiawaterportal.org/sites/schools.indiawaterportal.org/files/ppt/c
p/Aquatic_Ecosystems/Aquatic_Ecosystems.swf
http://www.limpoporak.com/UserFiles/Interactive/en/FoodWeb/food_web3.swf
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UNIT 3: ECOSYSTEMS
KEY POINTS
Temperature – Light – Water – Salinity –
Precipitation – Soil chemistry
Organism – Population – Community
Biotic
components
Abiotic
components
What is an ecosystem
made up of?
ECOSYSTEM
How are the
relationships in an
ecosystem
represented?
Food chain
Food web
What are the
world’s
ecosystems?
Ecological
pyramids
Energy
Biomass
Number
Terrestrial
ecosystems
Low-latitude: tropical rainforest,
savanna, desert
Mid-latitude: Mediterranean biome,
grasslands, deciduous forest
High-latitude: taiga, tundra, alpine
biome
Aquatic
ecosystems
Freshwater:
ponds and
lakes
Marine:
oceans and
coral reefs.
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UNIT 3: ECOSYSTEMS
PROGRESS CHECK
Choose the correct answer:
1. _________ is all the individuals of the same species that live in an ecosystem.
a) Organism
b) Community
c) Population
2. _________ are limiting factors in a terrestrial environment.
a) Water and temperature
b) Light and water
c) Light and temperature
3. The interaction between two populations for the same resource is called ________.
a) Cooperation
b) Symbiosis
c) Competition
4. The living things that make their own food by photosynthesis are called __________.
a) Producers
b) Consumers
c) Decomposers
5. A food chain always starts with a __________.
a) Producers
b) Consumers
c) Decomposers
6. The true sentence is ___________.
a) The food chain is formed by several food webs
b) The food web is formed by several food chains
c) The food web is formed by one food chain.
7. A __________ pyramid shows how many organisms there are at each trophic level.
a) Biomass.
b) Number.
c) Energy.
8. The Mediterranean biome is located in the ___________ climate zone.
a) Low-latitude
b) High-latitude
c) Mid-latitude
9. The taiga biome is located in the ___________ climate zone.
a) Low-latitude
b) High-latitude
c) Mid-latitude
10. The tropical rainforest is located in the ___________ climate zone.
a) Low-latitude
b) High-latitude
c) Mid-latitude
ANSWERS: 1-c; 2-a; 3-c; 4-a; 5-a; 6-b; 7-b; 8-c; 9-b; 10-a.
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UNIT 3: ECOSYSTEMS
Figure 1:
http://www.exploringnature.org/graphics/ecology/ecology_vocabulary.jpg
Figure 2:
http://3.bp.blogspot.com/_sob8E7nEtu0/SlVVhzbMrLI/AAAAAAAAAfo/3VxEnHANBT0/s
320/tolerance+limits.jpg
Figure 3:
http://media-2.web.britannica.com/eb-media/99/95199-036-D579DC4A.jpg
Figure 4:
http://www.sciencelearn.org.nz/var/sciencelearn/storage/images/contexts/life-in-thesea/sci-media/images/marine-trophic-pyramid/169349-5-eng-NZ/Marine-trophic-pyramid.png
Figure 5:
http://luchipaiz.blogspot.es/img/biome.jpg