Correct Answer: (1) increased burning of fuels

The increase in concentration of carbon dioxide in the atmosphere has started ever since the Industrial Revolution. This is due to the combustion of fossil fuels and wood (removed by deforestation). The carbon dioxide concentration in the atmosphere continues to increase up to this date. The rising carbon dioxide concentration in the atmosphere affects immensely the Earth's heat budget. Much of the solar radiation that strikes the planet is reflected back to the space. Even if carbon dioxide and water vapor in the atmosphere are transparent to visible light, they intercept and absorb much of the reflected infrared radiation, rereflecting it back to the Earth's surface.  This process keeps some of the solar heat. This is known as the greenhouse effect.

Incorrect Answers:

Increased productivity by vegetation is one potential consequence of increasing carbon dioxide concentrations. It has been tested in experimental greenhouses that when the carbon dioxide concentration was increased, C₃ plants increased in growth. Thus, C₃ species may spread to areas previously inhabited by C₄ plants.

Mineral availability has no direct effect on global warming.

Correct Answer: (4) increasing human population

More food must be produced in order to sustain the increasing human populatison. Because of this, more natural habitats were disrupted and used for agriculture. Agriculture also disrupts the nitrogen cycle. This also causes great loss of biodiversity.

When fossil fuels are burned (for human activities like in factories, vehicles, etc.), the concentration of carbon dioxide in the atmosphere increases. This further causes global warming that induces dramatic climate changes in the whole planet.

Humans also dump toxic materials in the environment which causes biological magnification of toxic products accumulation in organisms at the topmost level of the food chain.

These are just some of the several activities of humans that greatly affect the ecosystems of the Earth.

Incorrect Answers:

Use of air pollution controls and use of natural predators to control insect pests have no negative effects on the ecosystem, consequently, they prevent the disruption of ecosystems.

Recycling of glass, plastic and metals were also done to prevent ecosystem disruption. However, there were some studies that they can also be harmful to the environment, especially when they are combusted during the process.

Correct Answer: Significant amount of chemical toxin release may cause imbalance the amount of the toxins and antitoxins in the environment. If the amount of toxins would decrease, there would be an excess in the amount of antitoxins. These antitoxins could have been used for metabolic processes.

Correct Answer: This might be the time when laws were passed to decrease the amount of chemical toxins released in the environment. Since it became stricter during this time, industries could just decrease the amount of toxins released easily and so the graph remained constant.

Correct Answer: Chlorinated hydrocarbons are synthetic compounds produced industrially. These include pesticides such as DDT and PCBs (polychlorinated biphenols). Studies have shown that these chemicals damage the endocrine systems of a large number of animals, including humans.    These toxins are dangerous because as they become more concentrated as they go beyond the different trophic levels. Because of this, DDT has been banned in the United States (since 1970s).

Biodiversity refers to the variety of life in n area which is usually measured as the number of species that live in an area. Loss of biodiversity is the main problem of the wide destruction of natural habitat, especially in tropical rainforests. In fact, IUCN reported that 73% of the extinct, endangered, vulnerable and rare species were concerned by habitat destruction.   Biodiversity is a crucial natural resource, and the threatened species could provide important crops, fibers, and medicines. Areas with high biodiversity should not be converted into industrial or agricultural sites to prevent loss of biodiversity.