Biology 5 Marks Questions

The ozone hole is more prominent over the region of Antarctica. It is formed due to an increased concentration of chlorine in the atmosphere.Chlorine is mainly released from chlorofluorocarbons (CFC's) widely used as refrigerants.

1. When released in stratosphere, these substances drift towards poles and get accumulated on the ice clouds formed at high altitudes.
2. Ice provides a surface on which breakdown of all the CFC compounds takes place to release chlorine atom.
3. These chlorine atoms breakdown ozone resulting in thinning of the ozone layer. Normally, the ozone layer plays a protective role by absorbing harmful UV radiations but reduction in its thickness allows UV rays to reach Earth's surface.

Effects of ultraviolet radiation on humans:

1. Early ageing of skin.
2. Increased incidences of cancer of the skin.
3. Cataract of the eyes.
4. Inflammation of cornea of the eye (known as snow blindness).
5. Weakened immune system.

Various constituents of domestic sewage are:

1. Solid wastes such as faecal matter, detergents etc, dissolved/ suspended in water from the kitchen, toilets, bathrooms and laundry.
2. Harmful pathogens including disease causing microbes-bacteria, viruses, fungi etc.
3. Dissolved minerals such as phosphates, nitrates, sodium ions, ammonia etc.

Discharge of untreated sewage in water bodies leads to:

1. Contamination of water in the water bodies with the faecal matter rendering it unfit for future usage.
2. Accumulation of various pathogens in the water bodies that can cause water borne diseases.
3. Increase in the Biological Oxygen Demand (BOD) of the water body thereby deteriorating the quality of water.
4. Excessive accumulations of minerals causes accelerated aging of the water bodies due to rapid growth of algae, called eutrophication.
5. Negative impact on the flora and fauna of the particular water body. Number of fishes are found to be less in water bodies with high BOD.

As an individual, we can take certain steps to reduce environmental pollution such as:

1. Using CNG instead of petrol, diesel. Opting more for either public transport or encouraging more and more carpooling.
2. Minimising the solid waste generation and recycling the plastic, metal and glass commodities.
3. Using the biodegradable waste generated in the kitchen to prepare compost.
4. Avoiding the usage of plastic bags wherever possible and opting for the jute or cotton bags.
5. Avoiding tinned food products.
6. Celebrating a cracker-free Diwali and encouraging others to follow it as well.
7. Using catalytic converters in the automobiles. Getting them checked for pollution on a regular basis.
8. Educating everyone and encouraging them to opt for renewable sources of energy.

Column A		Column B
a	Catalytic converter	ii	Carbon monoxide and nitrogen oxides
b	Electrostatic precipitator	i	Particulate matter
c	Earmuffs	iii	High noise level
d	Landfills	iv	Solid wastes

1. Value point conveying importance of clean environment/surrounding.
2. Social attitude/co-ordination/financial issues/disposal of collected garbage/separation of biodegradable and non-degradable waste/lack of awareness.
3. Campaigning/creating awareness/organising competitions/giving incentives/provision of imposing penalty/complaining to appropriate authority/publicity through mass media/using masks or gloves for separation and disposal of various categories of garbage.

1. Two causes of air pollution:

1. Burning of fossil fuels.
2. Smoke released from vehicles.
3. Industrial effluents.
4. Smoke stacks of thermal power plants.

2. Harmful effects of air pollution:

1. It affects respiratory system of humans and of animals.
2. It also reduces growth and yield of crops & cause premature death of plants.

3.  

1. Encouraging public transport i.e. buses & using CNG instead of diesel.
2. Planting more trees to curb pollution.

1. According to Central Pollution Control Board (CPCB), particulate size of 2.5 micrometers or less in diameter (PM 2.5) are responsible for causing the greatest harm to the human health. These fine particulates cause breathing and respiratory symptoms, irritation, inflammations and damage to the lungs and premature death.
2. About 40% of human deaths occur due to air pollution.
3. Causes increase in susceptibility to diseases.
4. Causes cancer and genetic mutations.
5. Causes respiratory ailments like asthma, hay fever and other allergic diseases.
6. Causes cardiovascular diseases and damage to CNS resulting in premature death.
7. Causes immediate effects like inflammation, nausea, headache, irritation to the eyes and nose.

It is true that if dissolved oxygen level drops to zero, the water will become septic. Absence of oxygen in water means the water will no longer be able to sustain living beings because aquatic plants and animals use dissolved oxygen for respiration.
When sewage is discharged into water body, microorganisms feed on organic impurities. In this process, they consume most of the oxygen present in water. This reduced the level of dissolved oxygen to negligible level.

Scrubber:

1. It is used to remove gases like sulphur dioxide from industrial exhaust.
2. The exhaust is passed through a spray of water or lime.
3. Water dissolves gases and lime reacts with sulphur dioxide to form a precipitate of calcium sulphate and sulphide.

FOAM: Friends of Arcata Marsh

1. It is a citizens group responsible for the upkeep and safeguarding of a project of integrated waste water treatment in the town of Arcata in the northern coast of California.
2. Collaborating with the biologists of Humboldt State University, the people of the town created an integrated waste water treatment process within a natural system.
3. The cleaning occurs in two stages:

• The conventional sedimentation, filtration and chlorination are done, after this, the dangerous pollutants like dissolved heavy metals remain.
• The biologists developed a series of six connected marshes over 60 hectares of marshland; and seeded into them appropriate plants, algae, fungi and bacteria, which neutralise, absorb and assimilate the pollutants.

4. As water flows through the marshes, it gets purified naturally.
5. The marshes also constitute a sanctuary with a high level of biodiversity including fishes, birds and other animals which reside there now.

1. The impurities in the sewage water can be categorised as:

1. Suspended solids:

• e.g. clay, grit, sand.

2. Colloidal matter:

• e.g. faecal matter, cloth fibres, paper fibres, some bacteria.

3. Dissolved substances:

• e.g. ammonia, nitrates or sodium, calcium, phosphate (any one in each of the above).

2. Polyblend is a fine powder recycled and modified plastic.
3. A greenhouse warms up because the glass panel lets the light in, but does not allow the heat to escape.

Electrostatic precipitator:

• It is the most widely used method for removal of particulate matter, about 90% of particulate matter is removed from the exhaust of thermal power plants.
• It has electrode wires and a stage of collecting plates.
• The electrode wires are maintained at several thousand volts, which produce a corona that releases electrons.
• These electrons get attached to the (dust) particles and give them a net negative charge within a very small fraction of a second.
• The collecting plates are grounded and hence attract the charged particles.
• The velocity of air between the plates must be low enough to allow the particles to fall on them.

Ozone shield: The ozone layer in the stratosphere absorbs a portion of the radiation from the sun, preventing it from reaching the planet’s surface. Most importantly it absorbs the portion of UV light called UVB has been linked to many harmful effects, including skin cancers, cataracts, and harm to some crops and marine life.
These compounds contribute to ozone depletion, and are called ozone-depleting substances. ODS that release chlorine include (CFCs), (HCFCs).
Harmful Effects of UV Rays:

1. In the absence of ozone, DNA and proteins of living organisms preferentially absorb W-B rays and is high energy break the chemical bonds within these molecules. This causes

1. Damage to DNA and leads to mutation.
2. Damage to the skin cells.
3. Ageing of the skin.
4. Various types of cancers.

2. W-B rays are absorbed by human eye and in high dose, it causes inflammation of cornea. This is called snow-blindness cataract. It leads to diminishing of eye sight, photo burning and later permanent damage to cornea.

Methods of Solid Waste Disposal:

1. Open burning: Municipal waste is reduced by burning in open dumps but the unburnt waste serve as the breeding ground for rats and flies.
2. Sanitary landfills: Wastes are dumped in a depression or trench after compaction and covered with dirt. But seepage of chemicals from these landfills can pollute underground water resources.
3. Rag-pickers and kabadiwallahs: Wastes are collected and separated out into reusable or recyclable categories.
4. Natural breakdown: The biodegradable materials are kept into deep pits in the ground for natural breakdown.
5. Recycling: E-wastes can be recycled in specifically built factories or manually to recover important metals.
6. Incineration: Majority of e-wastes generated in developed world is exported to developing world where they are incinerated.

1. Catalytic converters are recommended in automobiles to reduce air pollution by their exhaust.

• Catalytic converters have metals like rhodium, palladium and platinum, which convert the unburnt hydrocarbons into carbon dioxide and water, carbon monoxide into carbon dioxide and nitric oxides into nitrogen.

2. Only unleaded petrol must be used in such vehicles as lead would inactivate the catalyst.
3. CNG is preferred as a fuel because:

• It burns efficiently in the vehicles and very little of it is left unburnt.
• It cannot be adulterated.

Discarded computers and other electronic items comprise electronic waste. E-waste contains various metals; like copper, iron, nickel, gold, silver, etc. and plastic.Sources of E-waste: Computers, printers, scanners, webcam, mobile phones, music players, e-reader, etc.
Problems associated with disposal of e-waste:

• Dumping of e-waste will result in accumulation of plastic on land.
• Extraction of metals; like iron or gold involves incineration of plastic components which creates many polluting substances.

Manual handling of e-waste can be harmful for workers.

1. There is a continuous increase in DDT content in different trophic levels of the chain, this is known as biological magnification in the aquatic food chain. This happens because a toxic substance accumulated by an organism cannot be metabolised or excreted and is thus passed on to the next higher trophic level. Thus, concentration of DDT is increased at successive tropic levels.
2. Biomagnification.

Chipko Movement: Chipko movement (Hug the Trees Movement) was an organised resistance to the destruction of forests. It started in 1974 in Reni village of Garhwal. A contractor was allowed to cut trees in a forest near the village. When the contractor’s workers appeared, the women of the village reached the forest quickly and clasped the tree trunks with their arms, preventing the workers from cutting down the trees. Mr. Sunder Lal Bahuguna, a Gandhian activist and philosopher was the leader of Chipko Movement.

1. Ozone layer in the stratosphere acts as a shield to absorb the ultraviolet radiation from the sun, which is highly injurious to living organisms.

• Chlorofluorocarbons (CFCs), from refrigerators and aerosol sprays, degrade the ozone layers.
• The UV rays act on the CFCs and release CI atoms, which degrade ozone to molecular oxygen.

2. In the absence of ozone, which absorbs the ultraviolet radiation, the UV rays reach the earth and cause the following ill-effects.

• (i) UV-B damages DNA and causes mutation in living organisms.
• (ii) It causes ageing of skin, damage to skin cells and various types of skin cancers.
• (iii) A high dose of UV-B causes inflammation of cornea, called snow blindness, cataract and even permanent damage to cornea.

The use of Biofertilisers in agriculture is called organic farming. Biofertilisers are organisms that enrich the nutrient quality of the soil. The main sources of biofertilisers are bacteria, fungi and cyanobacteria. The nodules on the roots of leguminous plants formed by the symbiotic association of Rhizobium. These bacteria fix atmospheric nitrogen into organic forms, which is used by the plant as nutrient. Other bacteria can fix atmospheric nitrogen while free-living in the soil (examples Azospirillum and Azotobacter), thus enriching the nitrogen content of the soil.
Currently, in our country, a number of biofertilisers are available commercially in the market and farmers use these regularly in their fields to replenish soil nutrients and to reduce dependence on chemical fertilisers.

Slash and bum agriculture, commonly called as Jhum cultivation in the north-eastern states of India, has also contributed to deforestation. In slash and bum agriculture, the farmers cut down the trees of the forest and bum the plant remains. The ash is used as a fertilizer and the land is then used for farming or cattle grazing. After cultivation, the area is left for several years so as to allow its recovery. The farmers then move on to other areas and repeat this process. In earlier days, when Jhum cultivation was in prevalence, enough time-gap was given such that the land recovered from the effect of cultivation. With increasing population, and Treated cultivation, this recovery phase is done away with, resulting in deforestation.

1. Biomagnification is a cumulative increase in the concentrations of a persistent substance (e.g. pesticides, metals, etc.) as it moves up the food chain. This occurs when agricultural, industrial, or human waste pours into the ocean directly or via rivers, sewage, etc. Some of the most dangerous of these toxins settle in the sediment of the sea floor and are consumed by bottom feeders.

With each step up the food chain, there is an increase in the concentration of these chemicals. This affects humans because a large percentage of the fish we consume are higher on the food chain and therefore likely to carry a high concentration of potentially harmful chemicals.

2. Biomagnification in the aquatic food chain. Biomagnification refers to increase in concentration of the toxicant at successive trophic levels. This happens because a toxic substance accumulated by an organism cannot be metabolised or excreted, and is thus passed on to the next higher trophic level. This phenomenon is well-known for mercury and DDT. Figure 16.5 shows biomagnification of DDT in an aquatic food chain. In this manner, the concentration of DDT is increased at successive trophic levels; say if it starts at 0.003 ppb (ppb = parts per billion) in water, it can ultimately can reach 25 ppm (ppm = parts per million) in fish-eating birds, through biomagnification. High concentrations of DDT disturb calcium metabolism in birds, which causes thinning of eggshell and their premature breaking, eventually causing decline in bird populations.

3. The insidious aspect of this phenomenon is that large concentrations of chlorinated hydrocarbons do not usually kill the bird outright. Rather, DDT and its relatives alter the bird's calcium metabolism in a way that results in thin eggshells.
4. Health awareness, eco-friendly nature and boldness for the right cause.

1. The ecological term used to describe the DDT accumulation at different trophic levels is called biomagnifications.
2. High concentrations of DDT disturb calcium metabolism in birds, which causes thinning of egg shell and their premature breaking, eventually causing decline in bird populations.
3. Yes, DDT accumulation can lead to eutrophication.
4. It increases the BOD, resulting in a decrease in dissolved oxygen in the water body.
5. Eating fish that has accumulated mercury, a heavy metal, causes a disease called Minamata. It is characterized by diarrhoea, haemolysis, numbness, deafness, mental derangement, meningitis and death

Integrated Waste Water Treatment:

• In the town of Arcata situated on northern coast of California, an integrated waste water treatment process was developed with the help of biologists from Humboldt State University.
• The cleaning occurs in two stages:

1. The conventional sedimentation, filtration and chlorine treatments are given. The treated water still contains lots of heavy metals and other dangerous pollutants.
2. Appropriate plants, algae, fungi and bacteria were grown in a marshland through which water was flowed. The various life forms neutralise, absorb and assimilate the pollutants and purify the water naturally.

• ‘Ecosan’ toilets have been developed in areas of Kerala and Sri Lanka for ecological sanitation.
• Advantages of ecological sanitation:

1. It is a practical, hygienic and efficient method of waste disposal.
2. It is cost effective.
3. Human excreta can be recycled into natural fertiliser to replace chemical fertiliser.

Due to biomagnification of DDT, i.e., excess presence of DDT in the body of the bird, interferes with calcium metabolism and causes thinning of eggs shell; hence the eggs break prematurely and there is a decline in the bird population.

Radioactive wastes: Radioactive wastes such as uranium, are used as fuel in the atomic power plant. The accidental leakage and disposal of radioactive wastes are the most serious problems. All safety measures for this purpose should be strictly enforced. Highlevel radioactive wastes generate a lot of heat and thus require cooling, as well as special protective shield during handling and transport. Radiation, that is given off by nuclear wastes is extremely harmful to the organisms, because it causes mutation at a very high rate. At high doses, nuclear radiation is lethal but at lower doses, it creates various disorders, the most frequent of all being cancer. Therefore, nuclear waste is an extremely potent pollutant and has to be dealt with utmost caution.

The thin layer of ozone around the atmosphere that prevents entry of harmful UV rays is called ozone shield. Methane and CFCs are the two ozone depleting substances.
Chlorofluorocarbons (CFCs) release active chlorine (Cl atom) when acts with UV rays and Cl atoms degrade ozone releasing molecular oxygen. Depletion of ozone allows the entry of UV-B radiation to the earth which damages DNA causes mutation leading to skin cancer in humans and also rate of photosynthesis decreases in plants.

Characteristic of a modern landfill site is as follows:

1. Methods to contain leachate such as lining clay or plastic liners: This helps in preventing the leachate from seeping into the underground aquifers. This prevents soil population and groundwater pollution.
2. Compaction and covering of the waste to prevent it from being blown by wind: Compaction helps in better space utilization because more waste can be accommodated in smaller area. Covering prevents spread of dust and harmful germs and is thus safer from health perspective.
3. Installation of a landfill gas extraction system to extract the gas for use in generation of power: This enables faster generation of methane which can be used for power generation. In some countries, landfill sites have become important contributors to power generation.

Causes of water logging and soil salinity: Many canals were built to implement Green Revolution. This made for easy availability of water for irrigation. Excess use of water during irrigation results in water logging. This draws salt to the soil surface and increases soil salinity. Also, excess use of fertilizers has lead to accumulation of many unused salts resulting in soil salinity.
Effects of Water Logging:

1. Increases soil salinity.
2. Many crops cannot survive in water logged conditions.
3. Prolonged period of water logging will reduce the number of microorganism and creatures in soil. This will reduce biodiversity in soil.
4. Decomposition of organic matter in stagnant water will release methane which is a potent greenhouse gas.

Effects of Soil Salinity:

1. Most of the plants cannot survive in saline soil.
2. Soil will become barren.
3. Desertification may take place.

Electrostatic precipitator has electrode wires that are maintained at several thousand volts, which produce a corona that releases electrons. These electrons attach to dust particles giving them a net negative charge. The collecting plates are grounded and attract the charged dust particles. The velocity of air between the plates must be low enough to allow the dust to fall.