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.Briefly write down all the natural cycle of gases (Carbon

dioxide, Nitrogen, sulphur and Oxygen).
Q2.What are Ozone Layer Depletion and the consequent effects it
has on the Earth? Briefly explain some resilient measures that can
be taken to mitigate the effects.
Q3. Which substances are responsible for Ozone layer depletion?
Write Chemical Equation to show how it happens.
Q4.What are greenhouse gases and their roles? List some
examples of greenhouse gases from most toxic to least toxic.

1 answer

Q1. Natural Cycles of Gases

Carbon Dioxide Cycle:

  1. Photosynthesis: Plants absorb CO2 from the atmosphere and convert it into glucose and oxygen.
  2. Respiration: Animals breathe in oxygen and exhale CO2, which is returned to the atmosphere.
  3. Decomposition: Dead organisms are broken down by decomposers, releasing CO2.
  4. Combustion: Burning fossil fuels and biomass releases CO2 into the atmosphere.

Nitrogen Cycle:

  1. Nitrogen Fixation: Nitrogen gas (N2) is converted into ammonia (NH3) by bacteria and lightning.
  2. Nitrification: Ammonia is converted to nitrites (NO2-) and then to nitrates (NO3-) by soil bacteria.
  3. Assimilation: Plants absorb nitrates and use them to create proteins and nucleic acids.
  4. Ammonification: Decomposition of organic matter releases ammonia back into the soil.
  5. Denitrification: Microbes convert nitrates back into nitrogen gas, releasing it into the atmosphere.

Sulfur Cycle:

  1. Weathering: Sulfur from rocks is released into soil and water.
  2. Uptake: Plants absorb sulfate ions (SO4²-) for use in amino acids.
  3. Decomposition: The decay of organic matter returns sulfur to the soil.
  4. Volcanic Activity: Sulfur dioxide (SO2) is released into the atmosphere from volcanic eruptions.
  5. Atmosphere: Sulfur compounds can fall back to Earth as acid rain.

Oxygen Cycle:

  1. Photosynthesis: Plants produce oxygen (O2) from CO2 and water.
  2. Respiration: Animals and plants use oxygen for cellular respiration, producing CO2.
  3. Decomposition: The breakdown of organic matter in the absence of oxygen produces CO2, and sometimes methane (CH4).

Q2. Ozone Layer Depletion and Resilient Measures

Ozone Layer Depletion: The ozone layer, located in the stratosphere, absorbs the majority of the sun's harmful ultraviolet (UV) radiation. Depletion leads to increased UV radiation reaching the Earth's surface, which can cause skin cancer, cataracts, and harm to ecosystems and wildlife.

Consequent Effects:

  • Increased rates of skin cancer and eye cataracts.
  • Harmful effects on biodiversity, including damage to phytoplankton and plant growth.
  • Disruption of food chains due to harmful UV exposure.

Resilient Measures:

  1. Regulation of Ozone-Depleting Substances: Implementation and enforcement of international agreements like the Montreal Protocol to phase out the use of chlorofluorocarbons (CFCs).
  2. Promotion of Alternative Chemicals: Encourage the use of less harmful alternatives for industrial and household products.
  3. Public Awareness: Educate the public about the importance of the ozone layer and the need to take protective measures.
  4. Research and Monitoring: Continued scientific research to monitor ozone levels and the effects of UV radiation on health and the environment.

Q3. Substances Responsible for Ozone Layer Depletion

Substances responsible for ozone layer depletion include:

  • Chlorofluorocarbons (CFCs)
  • Halons
  • Carbon tetrachloride
  • Methyl chloroform
  • Hydrochlorofluorocarbons (HCFCs)

Chemical Equation: The breakdown of CFCs leads to ozone depletion: \[ \text{CCl}_3\text{F} \rightarrow \text{Cl} + \text{CCl}_2\text{F} \] The chlorine atom then catalyzes the destruction of ozone (O3): \[ \text{Cl} + \text{O}_3 \rightarrow \text{ClO} + \text{O}_2 \] \[ \text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2 \] This cycle results in the depletion of ozone molecules.

Q4. Greenhouse Gases and Their Roles

Greenhouse Gases: These are gases that trap heat in the atmosphere, contributing to the greenhouse effect which warms the Earth’s surface. They allow sunlight to enter the atmosphere but prevent some of the heat that the Earth emits from escaping back into space.

Roles:

  • Regulation of the Earth's temperature.
  • Affecting weather patterns and climate.

Examples of Greenhouse Gases (from most toxic to least toxic):

  1. Methane (CH4): Highly potent, 25 times more effective than CO2 over a 100-year period.
  2. Nitrous Oxide (N2O): Approximately 298 times more effective than CO2 over a 100-year period.
  3. Hydrofluorocarbons (HFCs): Synthetic gases used in refrigeration and air conditioning, with high global warming potential.
  4. Carbon Dioxide (CO2): The most prevalent greenhouse gas, primarily from fossil fuel combustion.
  5. Water Vapor (H2O): Naturally occurring and the largest contributor to the greenhouse effect, but not directly human-caused.

Note: The classification of toxicity may vary, as greenhouse gases aren’t strictly toxic but are measured by their Global Warming Potential (GWP).