Download La biosphère : les cycles biogéochimiques

Name: ____________________________________________
Group: __________
Support activities – Second Year of Secondary Cycle Two
ACTIVITY 34
ANSWER KEY
Date: __________________
EST
STUDENT BOOK: Chapter 8, pages 254–261
RELATED HANDOUT: Concept review 34
The biosphere: biogeochemical cycles
1. Complete the following sentences, using the words or groups of words in the box below. You
may use some words more than once.
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air
algae
ammonia
ammonium
atmosphere
bacteria
biogeochemical
biogeochemical cycle
biosphere
calcium carbonate
carbonate rock
decomposed
decomposers
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decomposition
DNA
eat
erosion
essential
eutrophication
fossil fuels
fungi
glucose
herbivores
hydrogen
hydrosphere
lithosphere
live
living organisms
loops of recycling
methane
nitrates
nitrogen-rich fertilizer
oxidized
phosphates
photosynthesis
plankton
plant
proteins
respiration
• rock
• sediment
• soap
• solid
• spread manure
• sulphur
• take in
• teeth
• temperature
• volcanic eruptions
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biosphere
a) The ________________________
is the part of the Earth where human, animal or plant life
solid
is possible. It is composed of the lithosphere (the ________________________
outer
hydrosphere
covering of the Earth), the ________________________
(the layer of water) and the
air
atmosphere (the layer of ________________________
). In other words, the
biosphere
living organisms
________________________
is the entire system of ________________________
and
their habitats.
essential
b) The chemical elements ________________________
to life are found in the biosphere.
biogeochemical
loops of recycling
They move in infinite ________________________
called “________________________
biogeochemical cycle
cycles.” A ________________________
is a set of processes by which an element can
pass from one environment to another and eventually return to its original environment.
hydrogen
sulphur
Carbon, ______________________
, nitrogen, phosphorus and _______________________
are essential chemical elements because living organisms need to
take in
live
_______________________
considerable amounts of them to _______________________
and grow.
Observatory / Guide
11129-B
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ANSWER KEY
Support activities – Second Year of Secondary Cycle Two
ACTIVITY 34
The biosphere: biogeochemical cycles
Name: ____________________________________________
Group: __________
Date: __________________
c) Carbon is very important because it is a basic element in several complex substances, such
proteins
as ________________________
, lipids and carbohydrates. Carbon atoms are exchanged
atmosphere
between the ________________________
, the hydrosphere and the lithosphere.
photosynthesis
d) The carbon cycle can be described as follows: It starts with ________________________
,a
process by which plants capture carbon dioxide and transform it into
glucose
_______________________
. To take in the carbon they need, herbivores or carnivores
eat
respiration
_______________________
plants or other animals. Through _______________________
,
living organisms return the carbon they have ingested to the atmosphere. The rest of the
decomposed
carbon they have taken in is eliminated as waste and ________________________
by
methane
organisms called decomposers, producing carbon dioxide and _______________________
.
Forest fires also release large amounts of carbon dioxide into the atmosphere. Part of the
calcium carbonate
carbon dioxide dissolved in water becomes ________________________
. On the ocean
carbonate rock
floor, this substance is changed and gradually forms ________________________
. At the
surface, the rock can release part of the carbon it contains by melting on contact with
volcanic eruptions
Fossil fuels
magma during ________________________
. ________________________
also provide an
important supply of carbon dioxide.
atmosphere
e) The amount of carbon dioxide emitted in the ________________________
has increased
rapidly since the beginning of the industrial era. Human activities have upset the natural
balance of the carbon cycle, with the unfortunate consequences we know too well.
proteins
f) Nitrogen is essential in the formation of ________________________
and DNA. However,
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living organisms cannot use it in the form of molecular nitrogen (N2), as it exists in the air.
Bacteria
________________________
must first change it into ammonia (NH3),
ammonium
________________________
(NH4+), nitrites (NO2–) or nitrates (NO3–). Nitrogen exchanges
lithosphere
take place between the atmosphere, the hydrosphere and the _______________________
.
g) The nitrogen cycle can be described as follows: Certain bacteria in the ground or water
ammonia
capture nitrogen from the atmosphere and change it into ________________________
and
ammonium. Bacteria also oxidize ammonium to form nitrites, which in turn can be
oxidized
________________________
into nitrates. Then, plants can absorb ammonium and nitrates
Herbivores
from the soil and from water. ________________________
eat plants, and carnivores
absorb nitrogen by eating herbivores and other animals. Certain bacteria and
fungi
________________________
break down animal and plant waste, resulting in the
transformation of nitrogen into ammonium. Finally, other bacteria convert
nitrates
________________________
into molecular nitrogen, which returns to the atmosphere.
Observatory / Guide
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ANSWER KEY
Support activities – Second Year of Secondary Cycle Two
ACTIVITY 34
The biosphere: biogeochemical cycles
Name: ____________________________________________
Group: __________
Date: __________________
h) The nitrogen cycle can be disrupted by several natural factors, including
temperature
________________________
, relative humidity and pH. Human activities have an impact
nitrogen-rich fertilizer
on this cycle through farming, when ________________________
is applied to the soil to
increase productivity, and through industrial processes, when factories discharge ammonia
in their wastewater. In the long term, this imbalance can interfere with plant growth.
i)
EST Phosphorus is also an essential element, especially as a basic component of
DNA
________________________
. Many animals need it to form their bones,
teeth
________________________
and shells. Phosphorus is exchanged between the
lithosphere, the hydrosphere and living organisms in the form of
phosphates
________________________
(PO43-).
j)
EST The phosphorus cycle can be described as follows:
Erosion
________________________
of
rocks by wind or rain wears away a part of the phosphorus in rocks, and it is changed into
plants
phosphates. The phosphates are absorbed by ________________________
, herbivores
and carnivores. Some phosphates return to the soil in animal waste (feces and urine), and
decomposition
others are released through the ________________________
of dead animals and plants
decomposers
by ________________________
. These phosphates make their way into the oceans,
plankton
where some promote the growth of ________________________
and others contribute to
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sediment
sedimentation. Over time, ________________________
containing phosphates forms
rock
________________________
, and phosphorus returns to its original state.
k) EST Human activities also disrupt the phosphate cycle when farmers
spread manure
________________________
that is rich in phosphates on their land or when people
soap
dispose of wastewater containing phosphate-laden ________________________
residues.
algae
An excess of phosphorus in lakes and rivers accelerates ________________________
eutrophication
growth. This surplus can trigger ________________________
in aquatic environments. The
affected bodies of water suffer an oxygen shortage due to the presence of organisms like
algae that consume the dissolved gas.
2. Name two processes by which carbon dioxide is captured and used to produce other
substances.
Photosynthesis and calcium carbonate synthesis
Observatory / Guide
11129-B
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ANSWER KEY
Support activities – Second Year of Secondary Cycle Two
ACTIVITY 34
The biosphere: biogeochemical cycles
Name: ____________________________________________
Group: __________
Date: __________________
3. How have human activities contributed to disrupting the carbon cycle?
Through the combustion of fossil fuels, used in cars, and through various industrial processes.
4. EST Which biochemical cycle or cycles are involved in each of the following situations?
a) sheep grazing in fields
The carbon, nitrogen and phosphorus cycles
b) the dead leaves left on the lawn last fall
The carbon, nitrogen and phosphorus cycles
c) the fire of a charcoal barbecue
The b)
carbon
Les cycle
feuilles mortes laissées sur le gazon l’automne dernier.
d) the steak
atedufor
supperdeyesterday
Les you
cycles
carbone,
l’azote et du phosphore.
The carbon, nitrogen and phosphorus cycles
b) Les feuilles mortes laissées sur le gazon l’automne dernier.
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solely for classroom use with Observatory.
Les cycles du carbone, de l’azote et du phosphore.
Observatory / Guide
11129-B
4
ANSWER KEY
Support activities – Second Year of Secondary Cycle Two
ACTIVITY 34
The biosphere: biogeochemical cycles