Model Answer:

An individual’s “ecological footprint” is represented as the amount of land (generally given in hectares) needed to supply all the resources and energy that person uses. Consider your favorite actor. His ecological footprint would take into account all the land (or water) needed to: 1) provide the electricity to power all the lights and appliances in his house(s); 2) produce the oil or gas needed to heat his home(s) and run his car or jet; 3) cultivate the crops which provide his favorite fruits and vegetables, and grow the fish used in his favorite sushi roll; and 4) provide the cotton which is used to make his shirts. Depending on who your favorite actor is, he may have a very large ecological footprint!

Model Answer:

Carbon dioxide can be introduced into the atmosphere by both natural and man-made processes. The burning of fossil fuels and forests (to make way for crops) are both major sources of man-made CO₂. On the other hand, volcanic eruptions are natural processes that introduce CO₂ into the atmosphere.

Model Answer:

Carbon dioxide is a greenhouse gas that is normally present in the Earth’s atmosphere. This gas absorbs solar radiation reflected off the Earth’s surface and re-emits it, ultimately warming the planet. The problem arises when excess CO₂ is introduced into the atmosphere by human activities (e.g., burning fossil fuels). Excess CO₂ in the atmosphere results in more of this reflected radiation being absorbed and re-emitted, resulting in an increase in temperature. Thus, higher levels of CO₂ in the atmosphere can translate into an increase in mean global temperature.

Model Answer:

Recall from Chapter 25 that different materials (such as forest vegetation or the oil used to heat a house) are composed of three primary carbon isotopes (¹²C, ¹³C and ¹⁴C). These isotopes are present in distinct ratios depending on the source; some sources have lots of ¹²C but little ¹⁴C. When these materials are burned (or used in other processes), they can generate CO₂ composed of different carbon isotopes. As scientists (remember Hans Suess?) studied atmospheric CO₂ levels, they determined that even though more CO₂ was present in the atmosphere, the composition of this CO₂ had changed. When researchers compared previous and modern measurements, they realized that the level of ¹⁴C in the atmosphere had decreased, as had the ratio of ¹³C to ¹²C. What sources could have produced the amounts of ¹²C, ¹³C and ¹⁴C now present in the atmosphere? The answer was fossil fuels. Thus, scientists concluded that humans are in fact contributing to increased CO₂ through industrial practices.

Model Answer:

CO₂-induced changes in temperature (both in the atmosphere and in the ocean) and ocean acidity can have serious consequences for many organisms. Some organisms can respond to temperature changes while remaining in the same environment; often, these organisms have to modify their behavior (i.e., like plants changing their flowering times). However, other organisms are forced to migrate to more suitable climates. For example, recall that corals require symbiotic algae for survival. As sea temperature rise, these algae migrate (presumably to waters with more favorable temperatures); however, the corals can’t migrate with the algae, as they build skeletons and are anchored to a particular location. Without the algae, the corals die. Interestingly, corals are also susceptible to CO₂-induced changes in ocean acidity. As the seas become more acidic (the result of increased aquatic CO₂ levels), corals can’t construct their unique skeletons and eventually die.

Model Answer:

Although excess CO₂ in the atmosphere is a serious problem, several steps can be taken to reduce our contribution to greenhouse gases. Efforts are being made to both remove CO₂ from the environment, and to limit our CO₂ output. Remember that trees naturally use CO₂ during photosynthesis. Thus, planting more trees via reforestation efforts helps to remove excess CO₂ already in the atmosphere. The use of alternative energy sources such as wind power also means that less fossil fuels (one of the mainsources of human-generated CO₂) are burned. For example, an electric or hybrid car is powered mostly by electricity rather than gas (a fossil fuel). Less gas means that less CO₂ will be introduced into the atmosphere. So by turning to alternative energy sources, we can limit the amount of man-made CO₂ introduced into the environment in the first place.

Model Answer:

To increase crop yields, farmers often treat their land with nitrogen or phosphate-based fertilizers. However, a large percentage of this fertilizer (and the nutrients it contains) is carried off by rainfall to rivers and lakes. This nitrogen and phosphate-rich run-off unintentionally “fertilizes” bodies of water. As a result, the native cyanobacteria and algae living in rivers or lakes experience population explosions. This overgrowth of cyanobacteria and algae in response to excess (human-introduced) nutrients is known as eutrophication, and can be remarkably detrimental to the environment. Excess cyanobacteria and algae provide a robust food source for aquatic bacteria, and as bacteria feed they rapidly deplete the oxygen (via aerobic respiration) in their environment. This process can result in the appearance of “Dead Zones” – areas literally devoid of life - in rivers or lakes. Without the proper amount of oxygen in the water, fish, crustaceans and other aquatic life can’t survive.

Model Answer:

Increasing crop yields is one way to assure that a growing global population can be fed. This can be accomplished through devoting more land to agriculture and utilizing fertilizer. Other solutions include genetically engineering plants that are resource-efficient or resistant to predators or diseases. However, all of these methods carry with them certain dangers: increasing atmospheric CO₂ levels, jeopardizing aquatic environments due to eutrophication, or selecting for hardier pests. Providing for a growing human population will likely require the integration of these methods.

Model Answer:

Human activities can have positive or negative effects on specific species. Many invasive species, which are introduced into new environments either inadvertently (e.g., through shipping) or purposefully (e.g., as food sources), have been positively affected by human actions. Such species include the Zebra Mussel, the Kudzu plant, and Brown Tree Snake. All of these invasive species have taken root in new environments where natural predators do not necessarily exist, and where endogenous organisms are not equipped to deal with competition from these invaders. As a result, the populations of these invasive species have skyrocketed.

In contrast, many species are also negatively impacted by human activities. These include: 1) certain species of frogs, whose life cycles are disrupted by the introduction of agricultural pesticides into the environment; 2) corals, which experience “bleaching” in response to changes in ocean temperature (the result of excess CO₂); and 3) numerous species of trees in the rainforest, which have been negatively impacted by deforestation.

Model Answer:

Both amphibians and canaries are remarkably responsive to certain changes in their environment. Much like canaries once warned miners of excess carbon monoxide levels underground, so too can amphibians warn us about dangerous levels of pesticides in the environment. In fact, we are already beginning to see the effects of excess pesticides (such as atrazine) on the life cycles of frogs. Recall that over-exposure of frogs to atrazine severely affects their ability to reproduce and/or results in deformed offspring. Such observations in frogs warned scientists that atrazine may also negatively affect human reproduction, a hypothesis confirmed by evaluating the response of human placental cells to atrazine exposure.