Journal Entry #5
The Carbon Cycle
A) Background
Why is Carbon important to life?
Carbon forms the backbone of all organic molecules essential to life (Carbohydrates, proteins, lipids, and
nucleic acids).
Where is Carbon found?
In the oceans (dissolved carbon compounds), the atmosphere (as CO2), in animals and plants (as organic
molecules) and in fossil fuels (as CO2 emissions). There is also a large reservoir of carbon in sedimentary rock,
such as limestone, but this pool turns over very slowly.
What are the Key Processes of the Carbon Cycle?
Rapid: Photosynthesis and cellular respiration
Over longer periods of time: Burning of fossil fuels and volcanic activity.
B) Exploring the Carbon Cycle on Land
See if you can find six separate carbon pathways in the animation
Carbon is obtained from the
Carbon is returned to the
atmosphere by …
atmosphere by …
1
2
3
4
5
6
Trace the steps of the carbon cycle for each scenario:
1.
2.
3.
4.
5.
6.
Attach this sheet to a page in your journal (right after JE #4 – The Nitrogen Passport Activity).
C) Carbon Pathways in the Oceans
Exploring the Carbon Cycle
Watch the video and follow the text below:
Oceans are carbon sinks because they take up carbon (in the form of CO2) from the atmosphere.
Phytoplankton, living in the ocean, take up this C through photosynthesis (they are therefore producers
in the marine environment). C then moves through the food chain through various levels of consumers.
When phytoplankton die, they may fall to the ocean floor, which over time has made it the largest carbon
reservoir on the planet. In a process called upwelling, ocean currents bring nutrients and C up to the
surface. Carbon is then released as a gas (CO2) back into the atmosphere, thus continuing the carbon
cycle.
The amount of CO2 in the atmosphere has increased mainly due to the burning of fossil fuels and
deforestation (not to be confused with reforestation). CO2 and other greenhouse gases trap heat from the
Sun which can raise temperatures and lead to a phenomenon known as “global warming”. Atmospheric
CO2 has increased about 30 % over the past two centuries and the level of CO2 in the atmosphere is the
highest it has been in several million years.
About one-third of CO2 emissions dissolves in the oceans. This has resulted in warmer ocean
temperatures (and warmer water holds less C than cold water). Marine ecosystems can be adversely
affected by these warmer temperatures. In addition, oceans can become less effective at removing CO2
from the atmosphere.
D) Summary Questions
Answer the following questions in complete sentences in your journal. Refer to the information in A-C
above and textbook pages 76-77.
1. In what compound is carbon found in the environment?
2. Name three ways that carbon is returned to the atmosphere. (These are called carbon sources).
3. a) Only plants in the legume family can fix atmospheric nitrogen.
Which plants take carbon out of the atmosphere and how do they do it?
b) How do animals obtain their carbon?
4. A carbon sink is a reservoir where carbon accumulates. Identify two carbon sinks, one for land and
one for the ocean.
5. a) List as many ways as you can in which humans impact the carbon cycle. (You have already listed at
least some of these in your “Ecological Address”).
b) Where is most of this carbon accumulating and in what form is it found?