Solution of Our Environment (Page No - 241 - Biology by Lakhmir Singh, Class 10 | Extra Documents, Videos & Tests for Class 10 PDF Download

Question 16:
What is ten per cent law ? Explain with an example.
Solution :
Ten PerCent Law – According to ten per cent law, only 10 per cent of the energy entering a particular trophic level of organisms is available for transfer to the next higher trophic level.Example – Suppose 1000 Joules of light energy emitted by the sun falls on the plants. Consider a food chain: 

Plants               --->      Deer          --->   Lion

(Producer)               (Herbivorse)                 (Carnivorse)

The plants or first trophic level has 10 joules of energy in it. Now according to 10 percent law, only 10% of 10 joules of energy (which is 1 joule) will be available for transfer to the next trophic level, so that the herbivore will have only 1 joule of energy stored as food at the second trophic level. 10% of the remaining 1 joule will be transferred to third trophic level of carnivore. So, the energy available in the lion as food will be only 0.1 joule.

Question 17:
Write the full form of CFC. Give its one harmful effect.
Solution :
CFC – Chlorofluorocarbons. Chlorofluorocarbons released into the air react with ozone gas present in the ozone layer and destroy it gradually.

Question 18:
Explain how, harmful ultraviolet radiations of sunlight are prevented from reaching the earth’s surface.
Solution :
Ozone layer absorbs most of the harmful ultra violet radiations coming from the sun and prevents them from reaching the earth.

Question 19:
What are the causes of depletion of ozone layer ? Which diseases are likely to be caused if the ozone layer will become thinner ?
Solution :
The depletion of ozone layer is due to the use of chemicals called chlorofluorocarbons. Skin cancer is caused if the ozone layer will become thinner.

Question 20:
Explain how harmful chemicals enter our bodies.
Solution :
Pesticides are poisonous chemical substances which are sprayed over crop plants to protect them from pests (harmful small animals) and diseases. These chemical pesticides mix up with soil and water. From soil and water, these pesticides are absorbed by the growing plants alongwith water and other minerals. When herbivorous animals eat plant food, then these poisonous chemical pesticides go into their bodies through the food chain. And when the carnivore animals eat herbivores, then the pesticides get transferred to their bodies. Man being an omnivore; eat plant food as well as herbivores. So the pesticides present in plant food and herbivores also get transferred to the man’s body through food. Thus, pesticides enter the food chain at the producer level (plant level) and in the process of transfer of food through food chains these harmful chemicals get concentrated at each trophic level.

Question 21:
‘If we excessively use pesticides to protect the crops from diseases, then it may cause long-term damage to mankind’. Justify this statement.
Solution :
Pesticides are non – biodegradable chemicals, so they get accumulated at each trophic level. Since humans occupy the top level in any food chain, so the maximum amount of harmful chemical pesticides gets accumulated in our bodies. This damages our health gradually.

Question 22:
What is meant by biological magnification ? With the help of a food chain, explain how biological magnification of harmful chemicals can occur.
Solution :
The increase in concentration of harmful chemical substances like pesticides in the body of living organisms at each trophic level of a food chain is called biological magnification. The organism which occurs at the highest trophic level (on the extreme right side) in the food chain will have the maximum concentration of harmful concentration of harmful chemicals in its body. In this case grass is eaten by grasshopper; grasshopper is eaten by frog; frog is eaten by snake and finally snake is eaten by peacock. So, the food chain will be:

Grass   --->   Grasshopper   --->   Frog  --->     Snake    ---->   Peacock

Since the peacock occurs at the highest trophic level (on the extreme right side) in this food chain, it will have the maximum concentration of harmful chemicals in its body.

Question 23:
What is meant by bioconcentration of pesticides ? Which common pesticide has accumulated in human body in considerable amounts ?
Solution :
The accumulation of harmful chemicals such as pesticides in the living organisms like plants, animals and humans (men) through the food chain is called bio-concentration of pesticides. DDT has accumulated in human body through food chains.

Question 24:
What is garbage ? What does garbage consist of ?
Solution :
The household wastes are called garbage. It includes left -over food, fruit and vegetable peels, waste paper, unwanted plastic objects etc.

Question 25:
Name the various modes of waste disposal.
Solution :
The various modes of waste disposal are:

1. Recycling
2. Preparation of compost
3. Incineration
4. Landfill
5. Sewage treatment

Question 26:
How can the wastes such as paper, plastic and metal objects be disposed of ?
Solution :
The solid wastes like papers, plastics and metals are recycled. For example – waste paper is send to paper mills where it is reprocessed to form new paper once again.

Question 27:
Give a method for the disposal of household wastes such as left-over food, fruit and vegetable peels, and
leaves of potted plants.
Solution :
Preparation of compost is a method in which the disposal of household wastes such as left-over food, fruit and vegetable peels and leaves of potted plants can be converted into compost by burying in a pit dug into the ground and is used as manure.

Question 28:
What is meant by incineration ? For what purpose is it used ?
Solution :
Incineration means reducing to ashes. It is used to destroy the household waste, chemical waste and biological waste.

Question 29:
How are most of the solid wastes in urban areas disposed of ?
Solution :
Most of the solid waste in urban areas is dumped in low line areas of ground and covered with earth to level the uneven ground. This method is called landfill.

Question 30:
State two advantages of using disposable paper cups over disposable plastic cups.
Solution :
The advantages of using disposable paper cups over disposable plastic cups are:

1. Paper cups are biodegradable. So, even if paper cups are thrown away after use, they will decompose (break down) automatically by the action of micro-organisms in due course of time. On the other hand, plastic cups are non-biodegradable. They will remain as such and pollute the environment.
2. Paper cups can be disposed off by burning without causing much air pollution. On the other hand, burning of plastic cups produces toxic gases (poisonous gases) which causes too much air pollution.

Question 31:
What is sewage ? How is sewage disposed of ?
Solution :
The dirty drain water containing urine and faeces which is carried from our homes by the underground pipes (called sewers) is called sewage. Sewage is disposed off by treating it at the sewage treatment plant (or sewage works). The treatment of sewage produces clean water which is discharged into the river. The organic matter present in sewage is ‘digested’ in the digesters of sewage treatment plant to produce ‘sewage gas’ (which is kind of biogas) and manure.

Question 32:
Write the harmful effects of ozone depletion.
Solution :
Harmful effects of ozone depletion are:

1. It can cause skin cancer.
2. It damages the eyes by causing the eye disease called cataract.
3. It damages the immune system by lowering the body’s resistance to diseases.

Question 33
What would happen if the ozone layer in the atmosphere completely disappears ?
Solution :
If the ozone layer in the atmosphere disappears completely, then all the extremely harmful ultraviolet radiations coming from the sun would reach the earth. These ultraviolet radiations would cause skin cancer and other ailments in men and animals, and also damage the plants.

Question 34:
(a) With the help of a flow diagram, describe how energy from the sun flows through various trophic levels.
(b) Explain why, the flow of energy in the ecosystem is said to be unidirectional.
Solution :
(a) The energy from sun flows through various trophic levels. The food and energy are transferred from producer organisms to herbivores and from herbivores to carnivores, through the food chain. First Step – The green plants trap solar energy with the help of green pigment called chlorophyll which converts the sunlight energy into chemical energy. This gets stored as carbohydrates in the plants. About 1% of the sun’s energy falling on the leaves is used by the plants in the process of photosynthesis and stored as chemical energy of food. The plants utilize the stored energy for their metabolic activities like respiration and growth. Some of the energy is not utilised and it is released as unusable heat into the environment. Second Step – The plants are eaten up by herbivores and the chemical energy of plants is transferred to them. The herbivores utilize this energy for various metabolic activities and release unused energy as heat energy to the environment.
Third Step – The herbivores are eaten up by carnivores. The chemical energy stored in the flesh of herbivores is transferred to the carnivores and they utilise this energy for their metabolic activities like respiration and growth and some of the energy which remains unutilised, is released into the environment. This process of transfer of energy is repeated with large carnivores and so on.

Diagram to show the transfer of energy in a food chain

(b) The flow of energy in the ecosystem is said to be unidirectional because the energy lost as heat from the living organisms of a food chain cannot be reused by plants in photosynthesis.

Question 35:
(a) What is ozone ? How is it formed ?
(b) How does ozone layer protect us from harmful effects in the environment ?
(c) What is UNEP ? What step has been taken by UNEP in 1987 to prevent too much damage to the ozone layer ?
Solution :
(a) Ozone is a poisonous gas. It is made up of three atoms of oxygen combined together. It is formed high up in the atmosphere by the action of ultraviolet radiation on oxygen gas. The high energy ultraviolet radiation (UV radiation) coming from the sun splits oxygen gas into free oxygen atoms.

O₂                                  O           +           O

(Oxygen Molecule)          (Oxygen atom)         (Oxygen atom)

(b) Ozone layer protect us from harmful effects as it absorbs most of the ultraviolet radiations coming from the sun and prevents them from reaching the earth.
(c) UNEP – United Nation Environment Program. In 1987, in an attempt to protect ozone layer, the United Nations Environment Program (UNEP) forged an agreement among its member countries to freeze CFC production at 1986 levels.

Question 36:
(a) How is energy introduced into the ecosystem ?
(b) Consider the following food chains :

1.  Plants —-> Mice —-> Snakes —-> Hawks
2.  Plants —-> Mice —-> Hawks
   If energy available at the producer level in both the food chains is 100 J, in which case will hawks get more energy as food and by how much ? Justify your answer.

Solution :
(a) The energy enters the living components of the ecosystem through the process of photosynthesis.
(b) (i) The producer level in the food chain are plants, so 100 J of energy is available in plants as food. Applying the 10% law to the above food chain:

1.  According to the 10% law, 10% of energy of plants will be available as food in mice. Thus, the energy available to mice will be 10% of 100 J, which is 10 J.
2. The energy available to snakes will be 10% of 10 J, which is 1 J.
3. The energy available to hawks will be 10% of 1 J, which is 0.1 J.

(ii) The producer level in the food chain is plants, so 100 J of energy is available in plants as food. Applying the 10% law to the above food chain:

1. According to the 10% law, 10% of energy of plants will be available as food in mice. Thus, the energy available to mice will be 10% of 100 J, which is 10 J.
2. The energy available to hawks will be 10% of 10 J, which is 1 J.

Hawks will get more energy in food chain

1. because in this food chain there are three trophic levels so the energy available will be more as compared to food chain
2. which has four trophic levels.

Question 37:
(a) Explain why, a food chain usually cannot have more than three or four steps.
(b) Calculate the amount of energy that will be available to big fish in the following food chain, if 10,000 J of energy is available to small algae from the sun :
Small algae —-> Zooplankton —-> Fish —-> Big fish
Solution :
(a) Food chain generally consists of three or four steps because after that the energy available for the next organism will be so small that it will be insufficient to sustain the life of that organism.
(b)

1.  Small algae can trap only 1% of the sun’s energy falling on them. 1% of 10,000 J is 100 J, so the small algae have 100 J of energy available.
2. Small algae are eaten up by zooplankton. According to the 10% law, 10% of 100 J is 10 J of energy which is available in zooplankton.
3. The zooplankton will transfer 10% of its 10 J energy to the fish. Thus, the food energy available to the fish will be 10% of 10 J, which is 1 J.
4. 10% of 1 J will be transferred to big fish which will be 0.1 J. The above result can be clearly shown as:

Question 38:
(a) Name and state the law given by Lindeman which tells us how much energy entering a particular trophic
level of organisms is available for trasnsfer to the next higher trophic level.
(b) How much energy will be available to hawks in the food chain comprising hawk, snake, paddy and mice, if 10,000 J of energy is available to paddy from the sun ?
Solution :
(a) The law given by Lindeman is 10% law. According to 10% law, only 10% of the energy entering a particular trophic level of organisms is available for transfer to next higher trophic level.
(b)

1. Paddy can trap only 1% of the sun’s energy falling on them. 1% of 10,000 J is 100 J, so paddy have 100 J of energy available in them as food.
2. Paddy is eaten up by mice. Now according to the 10% law, 10% of 100 J is 10 J of energy which is available in mice.
3. The mice will transfer 10% of its 10 J energy to the snake. Thus, the food energy available to the snake will be 10% of 10 J, which is 1 J.
4. 10% of 1 J will be transferred to hawk which will be 0.1 J.