Earthlabs: Carbon Cycle– Lab 1 STUDENT ANSWERS http://serc.carleton.edu/eslabs/carbon/lab1.html Living in a Carbon World PART A. Trees - The Carbon Storage Experts 1: Using the tree diagram above to help you, explain why trees (and all plants) represent a small but complete carbon cycle. Draw your own diagram to help you illustrate your answer. Key Points: Trees take in carbon when they absorb CO2 from the air for photosynthesis. In cell respiration, CO2 is produced as a byproduct moving from leaves into the atmosphere. That CO2 released via respiration can be used by plants for photosynthesis. Earthlabs: Carbon Cycle– Lab 1 http://serc.carleton.edu/eslabs/carbon/lab1.html PART B. Carbon Storage in Local Trees 1: Carbon dioxide (CO2) is a greenhouse gas that naturally warms the atmosphere as part of the greenhouse effect. Unfortunately, the amount of CO2 in the atmosphere has been increasing over the past hundred years. According to scientists, this increase in atmospheric CO2 has caused the average global temperature on Earth to increase by about 0.8° Celsius (1.4° Fahrenheit) since 1880. Two-thirds of the warming has occurred since 1975, at a rate of roughly 0.15-0.20°C per decade. (NASA) Explain how planting and growing more trees could mitigate (slow down ) this warming trend in global temperature. Key Points: CO2 is a greenhouse gas that naturally warms the atmosphere. Trees not only absorb a lot of CO2 for photosynthesis, they store that carbon in their cells and tissues for hundreds of years. Thus, photosynthesis and carbon storage reduce the amount of fossil fuel CO2 emitted to the atmosphere. Earthlabs: Carbon Cycle– Lab 1 http://serc.carleton.edu/eslabs/carbon/lab1.html PART C. Building Carbon Compounds 1. Explain why the carbon atoms in carbon compounds such as proteins and DNA originally came from CO2 molecules in the atmosphere. Key points: Plants absorb CO2 from the atmosphere during photosynthesis and use those carbon atoms to make glucose molecules. When glucose molecules are broken down, plants use these carbon atoms to build all of their other carbon compounds – including DNA and proteins. The only source of carbon to make all of the new carbon compounds is the CO2 –photosynthesis-glucose pathway. 2. Explain why a lack of soil nutrients (ex. nitrogen, phosphorus, sulfur and magnesium) limits a tree's ability to grow and store carbon. Key Points: Important biomolecules such as proteins and DNA are required for carrying out all of life’s activities (including growing). Plants need nitrogen atoms to build their proteins and nitrogen, phosphorus and sulfur atoms to build their DNA molecules. Chlorophyll is a pigment that plants use to absorb the sunlight needed to power photosynthesis. Plants need magnesium atoms to build their chlorophyll pigment molecules. Lack of chlorophyll means that photosynthesis does not occur and glucose is not produced. 3. Explain how trees and all other organisms in the biosphere are able to make millions of different configurations of carbon compounds. Key Points: Because carbon atoms can form 4 bonds and can bond easily with hydrogen and oxygen atoms, producing many different structures and sizes of carbon compound molecules. The atoms in these carbon compounds can be continually rearranged into new configurations. By bonding with nitrogen, phosphorus and sulfur atoms, even more configurations are possible, producing biomolecules that can be very large and very complex (ex. Proteins, DNA). Earthlabs: Carbon Cycle– Lab 1 http://serc.carleton.edu/eslabs/carbon/lab1.html PART D. Fossil Fuels, Hydrocarbons and CO2 1: Describe how combustion can move carbon atoms from being stored deep in the ground to the atmosphere. Key Points: Fossil fuels (oil, natural gas, coal) have been stored for millions of years deep within the ground. Fossil fuels are made of hydrocarbon molecules. When hydrocarbons are burned (combustion) in the presence of oxygen, the carbon, hydrogen and oxygen atoms are rearranged producing CO2 and H2O molecules. The CO2 molecules are released to the surrounding air. 2: Identify and explain at least one piece of evidence supporting or refuting the claim that humans are changing the carbon chemistry of the atmosphere. Key points: (supporting) Burning fossil fuel produces CO2. Atmospheric CO2 has been increasing since humans began burning fossil fuels. CO2 that has been produced by burning fossil fuels has a chemical signature that differs from CO2 released by photosynthesis, respiration and volcanoes. This evidence tells scientists how much of the CO2 increase since the beginning of the industrial revolution comes directly from the combustion of fossil fuels.