Pollution: A Rising Environmental Problem — ICSE Class 10 Biology Important Questions

Answer: (b) Carbon dioxide.

Carbon dioxide ($CO_2$CO₂) is the main greenhouse gas; it traps heat radiated from the Earth's surface and raises the atmospheric temperature, causing global warming.

Answer: (b) $SO_2$SO₂ and oxides of nitrogen.

Sulphur dioxide and oxides of nitrogen from burning fossil fuels dissolve in rain water to form sulphuric and nitric acids, producing acid rain.

Answer: (b) Chlorofluorocarbons (CFCs). CFCs from old refrigerators, air conditioners and aerosol sprays release chlorine in the stratosphere, which breaks down ozone. A thinner ozone layer lets more harmful ultraviolet rays reach the Earth, causing skin cancer and cataracts.

Answer: (b) Thermal pollution. Warm water holds less dissolved oxygen and raises the temperature above what aquatic animals can tolerate, so fish die.

Answer: (a) Because plastics are non-biodegradable, decomposers cannot break them down, so they accumulate in the soil, block air and water movement and harm soil life; R correctly explains A.

(i) A pollutant is any substance or form of energy that, when added to the environment in harmful amounts, causes an undesirable change and damages living things. Example: sulphur dioxide (or smoke).

(ii) Biodegradable waste is waste that can be broken down (decomposed) by microorganisms into harmless substances. Example: kitchen or vegetable waste (or paper).

(i) Radiation pollution: careless use of X-rays, or radioactive fall-out from nuclear plants and tests. It can damage cells and genes and cause cancer.

(ii) Biomedical waste: used needles and syringes, soiled dressings and discarded medicines from hospitals. It can spread infections such as hepatitis and HIV if not disposed of safely (for example by incineration).

Three major air pollutants from motor vehicles and their effects:

1. Carbon monoxide ($CO$CO): it combines with haemoglobin more readily than oxygen, reducing the oxygen-carrying capacity of blood and causing suffocation or headache.
2. Oxides of nitrogen ($NO_x$NO_x): they irritate the lungs and eyes and contribute to acid rain and photochemical smog.
3. Lead compounds / particulate matter: lead is a poison that damages the nervous system, while fine particles cause breathing (respiratory) problems.

(Unburnt hydrocarbons and $SO_2$SO₂ are also acceptable.)

How sewage pollutes water: sewage contains organic matter, disease-causing microbes and nutrients (nitrates and phosphates). When it is discharged into a river it makes the water dirty, foul-smelling and unfit for use, and it spreads water-borne diseases such as cholera and typhoid.

How it kills fish: the organic matter and nutrients encourage the rapid growth of bacteria and algae. These microbes use up the dissolved oxygen in the water while decomposing the waste (a high biological oxygen demand). As the dissolved oxygen level falls, fish and other aquatic animals cannot get enough oxygen to breathe and they die.

The greenhouse effect is the natural trapping of heat in the atmosphere by greenhouse gases such as carbon dioxide, methane and water vapour. These gases allow sunlight to reach the Earth but absorb the heat (infra-red radiation) given off by the warmed surface, keeping the planet warm enough for life.

Leading to global warming: burning of fossil fuels and deforestation add extra $CO_2$CO₂ and other greenhouse gases to the air. This thicker blanket of gas traps more heat than before, so the average temperature of the Earth slowly rises. This gradual rise is called global warming.

One harmful consequence: the rise in temperature melts glaciers and polar ice caps, raising sea levels and flooding low-lying coastal areas (it also disturbs climate and rainfall patterns).

The four main types of pollution are air pollution, water pollution, soil (land) pollution and noise pollution.

1. Air pollution

• Cause: burning of fossil fuels in vehicles and factories, releasing smoke, $CO$CO, $SO_2$SO₂ and $NO_x$NO_x.
• Control: fit chimneys with scrubbers and electrostatic precipitators and vehicles with catalytic converters; use cleaner fuels (CNG) and plant more trees.

2. Water pollution

• Cause: discharge of untreated sewage, industrial effluents and fertiliser run-off into rivers and lakes.
• Control: treat sewage and effluents before releasing them, and use bio-fertilisers instead of chemical fertilisers.

3. Soil pollution

• Cause: excessive use of pesticides and chemical fertilisers and dumping of plastics and industrial waste.
• Control: use bio-pesticides and manure, and reduce, reuse and recycle solid waste instead of dumping it.

4. Noise pollution

• Cause: loud vehicle horns, machinery, loudspeakers and crackers.
• Control: ban loud horns in silent zones, use silencers and sound-proofing, and plant trees to absorb sound.

Acid rain is rain (or snow) that is more acidic than normal because it contains dissolved acids formed from air pollutants; its pH is lower than about 5.6.

Formation: sulphur dioxide ($SO_2$SO₂) and oxides of nitrogen ($NO_x$NO_x) from burning coal, oil and vehicle fuel rise into the atmosphere. There they react with water vapour and oxygen to form sulphuric acid ($H_2SO_4$H₂SO₄) and nitric acid ($HNO_3$HNO₃), which come down dissolved in rain as acid rain.

Two harmful effects:

1. It makes the water of lakes and rivers acidic, killing fish and other aquatic life.
2. It corrodes buildings, statues and metal structures (for example, it damages marble monuments such as the Taj Mahal) and harms plants and soil.

Two ways to reduce it:

1. Burn less fossil fuel and remove sulphur from fuels; use cleaner energy such as solar and wind power.
2. Fit factory chimneys with scrubbers and vehicles with catalytic converters to remove $SO_2$SO₂ and $NO_x$NO_x before they enter the air.

(i) The phenomenon is smog (a smoke-plus-fog mixture; a form of air pollution).

(ii) Two contributing pollutants are smoke or particulate matter and oxides of nitrogen ($NO_x$NO_x) (unburnt hydrocarbons and $SO_2$SO₂ are also acceptable).

(iii) One harmful effect on health seen in the passage is breathing difficulty and coughing (respiratory irritation) along with watering of the eyes.

(iv) One measure to reduce it is to cut vehicle and factory emissions by using catalytic converters and cleaner fuels such as CNG (and to control the burning of waste and crop residue).