4.3 Carbon Cycle

Question 1

Name the four spheres.

Answer 1

Atmosphere (air)
Lithosphere (ground)
Hydrosphere (water / oceans)
Biosphere (living things)

Question 2

Name the 4 forms carbon is exchanged through.

Answer 2

Atmospheric gases (carbon dioxide, methane)
Oceanic carbonates (calcium carbonates) 
Organic materials (carbohydrates, lipids, proteins, nucleic acids)
Non-living remains (detritus, fossil fuels)

Question 3

How do autotrophs convert inorganic carbon dioxide into organic compounds?

Answer 3

Through photosynthesis.

Question 4

Should carbon dioxide always be at a lower or higher concentration in the atmosphere?

Answer 4

Higher.

Question 5

Where does diffusion occur in terrestrial plants?

Answer 5

In the stomata.

Question 6

How do heterotrophs obtain carbon compounds?

Answer 6

Through feeding, as they cannot synthesise their own organic molecules.

Question 7

How is carbon dioxide produced? Name the process.

Answer 7

Through respiration, and it diffuses out of organisms, into water/the atmosphere.

Question 8

How is ATP produced?

Answer 8

Through respiration.

Question 9

What is the meaning of ‘compensation point’?

Answer 9

The uptake of CO2 by photosynthesis being balanced by the production of CO2 by respiration.

Question 10

How is carbon present in aquatic ecosystems?

Answer 10

It is present as dissolved carbon dioxide and hydrogen carbonate ions.

Question 11

Fill in the blank. Carbon dioxide dissolves in water and some of it will remain as a dissolved gas, however the remainder will combine with water to form ________.

Answer 11

Carbonic acid.

Question 12

State the equation of carbon dioxide forming carbonic acid.

Answer 12

(CO2 + H2O ⇄ H2CO3)

Question 13

State the equation of carbonic acid forming hydrogen carbonate ions.

Answer 13

(H2CO3 ⇄ HCO3– + H+)

Question 14

Why does pH change when CO2 is dissolved in water?

Answer 14

Because hydrogen ions (H+) are released.

Question 15

What do hydrogen carbonate ions require when they come into contact with rocks and sediment on the ocean floor?

Answer 15

Metal ions.

Question 16

Fill in the blank. Living animals may also combine the ____ ____ ions with ____to form ____ _____.

Answer 16

Hydrogen carbonate
Calcium
Calcium carbonate

Question 17

What forms the hardened exoskeleton of coral?

Answer 17

Calcium carbonate.

Question 18

When do organisms become fossilized in limestone?

Answer 18

When the organism dies and settles to the sea floor.

Question 19

What are methanogens?

Answer 19

Archaean microorganisms that produce methane (CH4) as a metabolic by-product in anaerobic conditions.

Question 20

Name 3 anaerobic conditions where methanogens may be found.

Answer 20

Wetlands (swamps and marshes)
Marine sediments (mud of lake beds)
Digestive tract of ruminant animals (cows, sheep)

Question 21

How do methanogens produce methane?

Answer 21

From the by-products of anaerobic digestion - mainly acetic acid and CO2.

Question 22

Name two things that can happen to methane.

Answer 22

It can accumulate under the ground

It can diffuse into the atmosphere

Question 23

What happens when organic matter is buried in anoxic conditions?

Answer 23

Deposits of methane may form underground.

Question 24

What is the impact of rising global numbers of domesticated cattle?

Answer 24

There will be increased levels of methane being released into the atmosphere.

Question 25

What decomposes dead organisms and returns nutrients to the soil for cycling?

Answer 25

Sapotrophic bacteria and fungi.

Question 26

True or false: cell respiration isn’t required to fuel digestive reactions.

Answer 26

False.

Question 27

What do waterlogged regions lack?

Answer 27

Oxygenated air spaces within the soil.

Question 28

Why are there acidic conditions in waterlogged regions?

Answer 28

Due to anaerobic respiration, producing organic acids (eg. acetate)

Question 29

Why is decomposition prevented in anaerobic/acidic conditions?

Answer 29

Saprotrophic bacteria and fungi can’t function effectively in the conditions.

Question 30

Outline the 3-step process of coal/peat formation.

Answer 30

1. Carbon rich molecules remain in soil and form peat, as organic matter isn’t fully decomposed.
2. The heat and pressure force out impurities and remove moisture when deposits of peat are compressed under sediments.
3. The remaining material has a high carbon concentration, and undergoes a chemical transformation, producing coal.

Question 31

How is oil and natural gas formed?

Answer 31

It forms as the result of the decay of marine organisms on the ocean floor.

Question 32

What results in hydrocarbons forming?

Answer 32

Burial and compaction, and the organic material being heated.

Question 33

Are fossil fuels renewable or non renewable?

Answer 33

Non-renewable, as the formation of fossil fuels takes place over millions of years.

Question 34

What is needed for hydrocarbons to undergo combustion?

Answer 34

O2.

Question 35

What is produced from the combustion reaction?

Answer 35

CO2 and H2O.

Question 36

Name two sources of hydrocarbons.

Answer 36

Fossilized organic matter (coal, oil and gas)

Biomass (bioethanol/biofuels)