La biosphère : les cycles biogéochimiques



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.

|• air |• decomposition |• live |• rock |

|• algae |• DNA |• living organisms |• sediment |

|• ammonia |• eat |• loops of recycling |• soap |

|• ammonium |• erosion |• methane |• solid |

|• atmosphere |• essential |• nitrates |• spread manure |

|• bacteria |• eutrophication |• nitrogen-rich fertilizer |• sulphur |

|• biogeochemical |• fossil fuels |• oxidized |• take in |

|• biogeochemical cycle |• fungi |• phosphates |• teeth |

|• biosphere |• glucose |• photosynthesis |• temperature |

|• calcium carbonate |• herbivores |• plankton |• volcanic eruptions |

|• carbonate rock |• hydrogen |• plant | |

|• decomposed |• hydrosphere |• proteins | |

|• decomposers |• lithosphere |• respiration | |

a) The ________________________ is the part of the Earth where human, animal or plant life is possible. It is composed of the lithosphere (the ________________________ outer covering of the Earth), the ________________________ (the layer of water) and the atmosphere (the layer of ________________________). In other words, the ________________________ is the entire system of ________________________ and their habitats.

b) The chemical elements ________________________ to life are found in the biosphere. They move in infinite ________________________ called “________________________ 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. Carbon, ______________________, nitrogen, phosphorus and _______________________ are essential chemical elements because living organisms need to _______________________ considerable amounts of them to _______________________ and grow.

c) Carbon is very important because it is a basic element in several complex substances, such as ________________________, lipids and carbohydrates. Carbon atoms are exchanged between the ________________________, the hydrosphere and the lithosphere.

d) The carbon cycle can be described as follows: It starts with ________________________, a process by which plants capture carbon dioxide and transform it into _______________________. To take in the carbon they need, herbivores or carnivores _______________________ plants or other animals. Through _______________________, living organisms return the carbon they have ingested to the atmosphere. The rest of the carbon they have taken in is eliminated as waste and ________________________ by organisms called decomposers, producing carbon dioxide and _______________________. Forest fires also release large amounts of carbon dioxide into the atmosphere. Part of the carbon dioxide dissolved in water becomes ________________________. On the ocean 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 magma during ________________________. ________________________ also provide an important supply of carbon dioxide.

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.

f) Nitrogen is essential in the formation of ________________________ and DNA. However, living organisms cannot use it in the form of molecular nitrogen (N2), as it exists in the air. ________________________ must first change it into ammonia (NH3), ________________________ (NH4+), nitrites (NO2–) or nitrates (NO3–). Nitrogen exchanges 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 capture nitrogen from the atmosphere and change it into ________________________ and ammonium. Bacteria also oxidize ammonium to form nitrites, which in turn can be ________________________ into nitrates. Then, plants can absorb ammonium and nitrates from the soil and from water. ________________________ eat plants, and carnivores absorb nitrogen by eating herbivores and other animals. Certain bacteria and ________________________ break down animal and plant waste, resulting in the transformation of nitrogen into ammonium. Finally, other bacteria convert ________________________ into molecular nitrogen, which returns to the atmosphere.

h) The nitrogen cycle can be disrupted by several natural factors, including ________________________, relative humidity and pH. Human activities have an impact 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) Phosphorus is also an essential element, especially as a basic component of ________________________. Many animals need it to form their bones, ________________________ and shells. Phosphorus is exchanged between the lithosphere, the hydrosphere and living organisms in the form of ________________________ (PO43-).

j) The phosphorus cycle can be described as follows: ________________________ of rocks by wind or rain wears away a part of the phosphorus in rocks, and it is changed into phosphates. The phosphates are absorbed by ________________________, herbivores and carnivores. Some phosphates return to the soil in animal waste (feces and urine), and others are released through the ________________________ of dead animals and plants by ________________________. These phosphates make their way into the oceans, where some promote the growth of ________________________ and others contribute to sedimentation. Over time, ________________________ containing phosphates forms ________________________, and phosphorus returns to its original state.

k) Human activities also disrupt the phosphate cycle when farmers ________________________ that is rich in phosphates on their land or when people dispose of wastewater containing phosphate-laden ________________________ residues. An excess of phosphorus in lakes and rivers accelerates ________________________ 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 |

| | |

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. 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 |

| | |

| |b) Les feuilles mortes laissées sur le gazon l’automne dernier. |

| | |

| |Les cycles du carbone, de l’azote et du phosphore. |

| | |

c) the fire of a charcoal barbecue

| |The carbon cycle |

d) the steak you ate for supper yesterday

| |The carbon, nitrogen and phosphorus cycles |

| | |

| |b) Les feuilles mortes laissées sur le gazon l’automne dernier. |

| | |

| |Les cycles du carbone, de l’azote et du phosphore. |

| | |

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phosphates

|EST |

| student BOOK: Chapter 8, pages 254–261 |

| Related Handout: Concept review 34 |

answer key

ACTIVITY 34

ammonia

temperature

EST

EST

spread manure

biogeochemical cycle

hydrogen

soap

eutrophication

algae

EST

decomposers

sediment

rock

Erosion

plants

decomposition

plankton

EST

DNA

teeth

fungi

nitrates

Support activities – Second Year of Secondary Cycle Two

nitrogen-rich fertilizer

oxidized

Herbivores

proteins

ammonium

Bacteria

lithosphere

atmosphere

decomposed

carbonate rock

volcanic eruptions

Fossil fuels

glucose

respiration

photosynthesis

eat

methane

calcium carbonate

proteins

atmosphere

sulphur

loops of recycling

biogeochemical

take in

live

essential

biosphere

solid

air

biosphere

hydrosphere

living organisms

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