Our Environment - Lakhmir Singh Manjit Kaur Solutions Pg No. 240 Class 10 Biology

Solutions of Our Environment Lakhmir Singh Manjit Kaur VSAQ, LAQ and HOTS Pg No. 240 Class 10 Biology

Solutions of Our Environment Lakhmir Singh Manjit Kaur VSAQ, LAQ and HOTS Pg No. 240 Class 10 Biology

Very Short Answer Type Questions-Pg-240

1. What percentage of the solar energy is trapped and utilized by the plants?

Answer

→ 1-2% of energy is trapped and used by the plant to make food. Rest of the 99-98% of solar energy that reaches the earth is reflected from surface of leaves and is absorbed by certain molecules which convert the energy into heat.

2. What percentage of energy available at the producer level is transferred at successive trophic levels in a food chain?

Answer

→ 10% of energy is transferred from producer to the next trophic level in food chain. As little as 10 percent of energy is transferred at each trophic level. The rest is lost in metabolic processes through heat.

3. Name the process in which a harmful chemical enters the food chain and gets concentrated at each trophic level.

Answer

→ Chemicals, pesticides and heavy metals move up the food chain, get into aquatic bodies and are eaten by organisms like fishes which are in turn eaten by hawks/eagles. This process where the chemical enters the food chain and gets concentrated at each trophic level is known as Biological Magnification.

4. In a food chain consisting of grass, frog, bird and insects, where will the concentration of the harmful chemical be maximum?

Answer

→ Out of above mentioned animals, birds will have maximum concentration of harmful chemicals. Birds are tertiary consumes/ carnivores, they are at top in a food chain so due to biological magnification, the concentration of harmful chemicals will be maximum in birds.

5. If a harmful chemical enters a food chain comprising cat, mice and plants, which one of these organisms is likely to have the maximum concentration of the harmful chemical in its body?

Answer

→ Cat will have the maximum concentration of harmful chemicals in its body because mice will feed on plants and cats feed on mice. The concentration of chemicals increases with increase in each trophic level.

6. Which radiations are absorbed by ozone layer?

Answer

→ Ozone layer absorbs harmful ultraviolet radiations coming from the sun and prevent it from reaching the surface of the earth.

7. Name the group of chemical compounds which damages the ozone layer.

Answer

→ Chlorofluorocarbon damages the ozone layer by destroying the ozone molecules.

8. Name two waste materials which can be recycled.

Answer

→ Paper, plastic, cardboard, aluminum foil can be recycled in mixed recycling containers.

9. Name the process by which the volume of solid wastes can be reduced.

Answer

→ Incineration is a process by which solid waste can be reduced by burning.

10. If 5 joules of energy is available at producer level (plants), then how much energy will be transferred to the lion in the following food chain?

Answer

→ 0.05joule of energy will be passed from plant to lion because only 10% of energy is transferred at each trophic level. So Goat will get 0.5joule of energy from plants and lion will get 0.05joule of energy from goat.

11. State whether the following statement is true or false:
Only 10 per cent of the light energy given by the sun is available for transfer at each higher trophic level a food chain.

Answer

→ False; Pants absorb only 1% of sun energy. 10% of this one percent energy absorbed by the plants is transferred at each trophic level.

12. Where does all the energy in living organisms originate from?

Answer

→ Sun is the major source of energy for all living organisms. Plants absorb sun’s energy to make food through photosynthesis. All the other components of a food chain obtain energy from plants.

13. Why are there rarely more than five links (or five organisms) in a food chain?

Answer

→ There are rarely more than five organisms in a food chain because there is a decrease in energy with every transfer to next trophic level and energy availability will be so small that animals will not be able to survive with small amount of energy.

14. Name two predators of snakes in a food web operating in a forest ecosystem.

Answer

→ In a forest ecosystem, peacock and hawk feed on snake.

15. Fill in the following blanks with suitable words :
(a) Ultraviolet rays can cause skin.................
(b) Pesticides enter the food chain at the ..............level
(c) Grass → ……………………….  Human
(d) lettuce  ………………………….  Fox
(e) Plants  Antelope  ……………….

Answer

→ a) Caner;
UV rays can cause skin cancer as they damage the genetic material of the skin cells causing the cells to grow out of control.
b) Producer;
Pesticides enter the food chain at the producer level as plants are the producers which are fed with pesticides.
c) Goat (or any herbivore);
Herbivores feed on Producers; herbivores are in turn eaten by consumers.
d) Rabbit ;
Rabbits feed on Lettuce which are in turn eaten by Fox
e) Lion; Plants are eaten by Antelope and Antelope are eaten by carnivores (consumers).

Short Answer Type Questions-Pg-241

16. What is ten per cent law? Explain with an example.

Answer

→ According to this law, only 10% of energy entering into trophic level of energy will be available to be transferred to the next trophic level.
For example if 1000joule of sunlight energy falls on plants and is to be transferred to herbivore and then a carnivore.

The plants or first trophic level (producers) has only 10joule of energy because plants absorb only 1% of energy that they receive from sun and according to 10% law, only 10% of 10joule will be transferred from plants to the next higher trophic level (herbivores) which is 1joule. Now 10% of 1joule =0.1 Joule which will be transferred to next higher trophic level (carnivores). So carnivores will receive 0.1 joule of energy if 1000joule of sunlight energy falls on plants.

17. Write the full form of CFC. Give its one harmful effect.

Answer

→ CFC stands for chlorofluorocarbons
Chlorofluorocarbons released into the atmosphere gradually react with ozone gas present in ozone layer and destroys ozone layer slowly thus allowing ultraviolet radiations enter into the earth.

18. Explain how, harmful ultraviolet radiations of sunlight are prevented from reaching the earth's surface.

Answer

→ Ozone layer in the stratosphere absorbs the harmful ultra violet radiations coming from the sun and thus prevent from reaching the earth surface.

19. What are the causes of depletion of ozone layer? Which diseases are likely to be caused if the ozone layer will become thinner?

Answer

→ Chlorofluorocarbons and certain ozone depleting substances are responsible for depletion of ozone layer. If the ozone layer becomes thinner, ultraviolet radiations will penetrate through the layer and reach the surface of earth which when fall on humans will destroy the genetic material of skin cells thus causing their unlimited growth and thus resulting in skin cancer.

20. Explain how harmful chemicals enter our bodies.

Answer

→ Harmful Chemicals like pesticides are sprayed on crop plants to protect them from diseases. These sprayed pesticides are absorbed by the plants because they mix up in the soil with water. From soil and water, plants absorb these pesticides. Plants are producers, they make food. Herbivores like goat consume these plants which have pesticides in them. On consuming plants accumulated with pesticides herbivores get those harmful chemicals in them. Herbivores are further eaten by carnivores like lions. Carnivores thus receive these harmful chemicals from herbivores. Humans being omnivores (both herbivores and plant eater), when eat plants or herbivores, the harmful pesticides are transferred into their bodies. This process of accumulation of harmful chemicals through each trophic level in food chain is known as biological magnification and this is how harmful chemicals reach into the bodies of humans.

21. If we excessively use pesticides to protect the crops from diseases, then it may cause long -term damage to mankind'. Justify this statement.

Answer

→ Pesticides are used to protect the crops from diseases. In this process pesticides mix up in the soil and water which are absorbed by plants. Producers are eaten by herbivores, and herbivores are eaten by carnivores. Man occupies the topmost level in a food chain as a omnivore, it eats plants as well as herbivores. The maximum amount of pesticide are accumulated at the topmost level of a food chain (biological magnification) and since human beings occupy the topmost level, the pesticides get accumulated in humans at maximum level which causes serious health issues.

22. What is meant by biological magnification? With the help of a food chain, explain how biological magnification of harmful chemicals can occur.

Answer

→ Chemicals, pesticides and heavy metals move up the food chain, get into aquatic bodies and are eaten by organisms like fishes which are in turn eaten by hawks/eagles. This process where the chemical enters the food chain and increase in concentration with increasing trophic level is known as biological magnification.


For example in the above food chain, Grass is a producer; it grows by consuming harmful chemicals from the soil. Grass is eaten by grasshopper which is further eaten by frog. Frog is eaten by snake and peacocks feed on snake. Since peacock is at the highest trophic level it will have the maximum concentration of harmful chemicals in its body, according to bio-magnification. The chemicals enter from soil to grass and they increase in concentration with increasing trophic level.

23. What is meant by bio-concentration of pesticides? Which common pesticide has accumulated in human body in considerable amounts?

Answer

→ Bio-concentration of pesticides refers to accumulation of pesticides and harmful chemicals in organisms through food chain. Bio-concentration is also defined as increase in chemical concentration in aquatic organism more than the chemicals in water.
Dichlorodiphenyltrichloroethane (DDT) is an insecticidal pesticide that accumulates in human body through the food chain. Since human beings occupy the highest trophic level in a food chain, the pesticide concentration in humans is considerably greater than the other organisms in the food chain.

24. What is garbage? What does garbage consist of?

Answer

→ Garbage is defined as anything that cannot be re-used and is waste. It usually comprises of waste from household. Garbage consists of vegetable/fruit peels, paper, plastic, cans, used packaging material, left-over food, etc.

25. Name the various modes of waste disposal.

Answer

→ There are various modes of waste disposal. Few of them are- incineration, pyrolysis, sewerage, composting, landfill, recycling, burial, biogas plant, etc.

26. How can the wastes such as paper, plastic and metal objects be disposed of?

Answer

→ Waste paper can be recycled in industries where it is processed again to form new paper. Plastics can be discarded completely by incineration. Metals are even recycled depending on their nature i.e. ferrous or non-ferrous.

27. Give a method for the disposal of household wastes such as left-over food, fruit and vegetable peels, and leaves of potted plants.

Answer

→ The best method for disposal of left-over food, fruit, vegetable peels, leafs of potted plants is composting. Compost consists of organic matter in a composting pit which is dug deep into the ground and covered with earth to ground level. The compost acts as manure to the soil as organic nutrients will be returned back to the soil when the compost decomposes.

28. What is meant by incineration? For what purpose is it used?

Answer

→ Incineration is burning of waste materials at very high temperature, in an incinerator. Incineration is used mostly by hospitals for destruction of pathogen and sharp materials completely.

29. How are most of the solid wastes in urban areas disposed of?

Answer

→ Most of the solid waste in urban areas is disposed of by creating landfill sites. The solid waste (garbage, dump, trash etc.) is dumped into landfill sites (low line areas) and covered with earth to the ground. Waste material is disposed of by burial in this method.

30. State two advantages of using disposable paper cups over disposable plastic cups.

Answer

→ 1) Disposable paper cups are easily biodegradable. They breakdown without harming the environment and can be recycled into new paper. Whereas, disposable plastic cups are made of low grade plastics and does not decompose easily and pollute the environment.
2) Even on burning paper cups will not cause air pollution as much as will be caused by burning of plastic cups. Plastic on being burned will release toxic gases whereas paper will not.

31. What is sewage? How is sewage disposed of?

Answer

→ Sewage is defined as system of carrying waste matter such as water or human urine and faeces, through underground pipes/sewers.
Sewage can be disposed of by treating it first at the sewage treatment plant where contaminants are removed from sewage to produce environmentally safe waste which is then releases into the river.

32. Write the harmful effects of ozone depletion.

Answer

→ The harmful effects of ozone depletion are-
a) More skin cancer in humans due to ultraviolet radiations which will easily reach the skin cells through stratosphere if ozone layer depletes.
b) UV radiations would also damage parts of eyes thus causing cataracts, blindness and other diseases.
c) Immunosuppression. UV radiations could damage the immune system.

33. What would happen if the ozone layer in the atmosphere completely disappears?

Answer

→ If the ozone layer in the stratosphere disappears completely then ultraviolet radiations from the sun would easily reach the earth’s surface and damage skin cells in humans with radiations thus causing cancer. It will also lead to diseases in animals and damages in plants.

Long Answer Type Questions-Pg-241

34A. With the help of a flow diagram, describe how energy from the sun flows through various trophic levels.

Answer


The energy from sun flows from producers to herbivores to carnivores.
Producers (plants) absorb sun’s energy to make food by photosynthesis. In the presence of water, carbon dioxide and chlorophyll, plants absorb 1% of sun’s energy available to them to make food in form of carbohydrates and release oxygen as a by-product. This food in the form of chemical energy flows through the food chain.
In the next step, Plants are eaten by herbivores and according to 10% energy law only 10% of energy is transferred from plants to herbivores; the rest is lost in transfer and other activities. Herbivores utilize this energy in metabolic activities and release some of the energy in form of heat into the environment.
Further, herbivores are eaten by carnivores. 10% of energy from herbivores gets transferred to carnivores. Carnivores utilize this energy for activities like respiration etc. and release some part of the un-utilized energy into the environment.

The top Carnivores obtain energy by feeding on the flesh of small carnivores and the transfer of energy keeps on happening.

34B. Explain why, the flow of energy in the ecosystem is said to be unidirectional.

Answer

→ Energy flows from plants to herbivores, then to carnivores in a food chain. Most of the energy is utilized by the organism for its activities and un-utilized energy is dissipated in the form of heat; this energy in the form of heat cannot be returned back to plant for photosynthesis. Therefore, The flow of energy in the ecosystem is said to be unidirectional.

35A. What is ozone? How is it formed?

Answer

→ Ozone is a toxic gas formed from reaction of ultraviolet radiations with oxygen. It differs from oxygen in having three molecules (O3) instead of two.
Ozone is formed when Ultraviolet radiations act on oxygen molecules. Oxygen molecules O2 are converted to ozone O3 when Ultraviolet radiations act upon them.

35B. How does ozone layer protect us from harmful effects in the environment?

Answer

→ Ozone layer protects by blocking the harmful ultraviolet radiations coming from the sun, reaching the earth and thus protecting from ailments like skin cancer, cataract and immunosuppression which occur when ultraviolet radiations reach humans.

35C. What is UNEP? What step has been taken by UNEP in 1987 to prevent too much damage to the ozone layer?

Answer

→ UNEP stands for United Nations Environment Program.
In 1987, UNEP signed an agreement to stop the CFC production at 1986 level, amongst its member countries. Montreal Protocol was signed in September 1987 which states to reduce the consumption and production of ozone depleting substances in order to reduce their quantity in the environment thus protecting the fragile ozone layer.

36A. How is energy introduced into the ecosystem?

Answer

→ Energy is introduced into the ecosystem from sun through the process of photosynthesis. Producers make their own food which flows as energy through the entire food chain. Producers use water, carbon dioxide in the presence of sunlight and chlorophyll to make food. This process is known as photosynthesis. This food then flows as energy in the entire ecosystem.

36B. Consider the following food chains:
(i) Plants → Mice →Snakes →Hawks
(ii) 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.

Answer

→ i) Plants→Mice→Snakes→Hawks.
If 100J is available at producer level (plants); mice will receive 10% of it- 10J.
10% of energy transfer will take from mice to snakes. 10% of 10J=1J. Snake will receive 1J of energy.
10% of energy will be transferred from snake to hawks. 10% of 1J=0.1J. Hawk will receive 0.1J of energy in this food chain.


ii) Plants—Mice—Hawks.
If 100J is available at producer level (plants); mice will receive 10% of it-10J
10% of 10J energy will be transferred from mice to hawks. 10% of 10J=1J.
The Hawks will receive 1J energy in this food chain.

Therefore, hawks will get more energy in the food chain which is equal to 1J and is more than 10% than the energy it is receiving in the first food chain. This is because in the first food chain Mice were being eaten by snakes, and hawks had to eat snakes, so it received less energy. In the second food chain, hawks directly ate mice, there were no snakes to consume energy in between so hawks received more energy.

37A. Explain why, a food chain usually cannot have more than three or four steps.

Answer

→ 10% energy transfer takes place from one trophic level to the next trophic level. Producers absorb one percent of sun’s energy to make food and then transfer 10% of it to the next trophic level and so on. There cannot be more than three or four steps in food chain because after that the energy availability to the organisms will be so less that the organism will not be able to survive with that less amount of energy available to them.

37B. 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

Answer

→ Food chain= Small algae—Zooplankton—Fish—Big fish
The algae receive 10,000J of energy out of which it absorbs only 1% i.e. 100J. 10% of 100J i.e. 10J is transferred to zooplankton. Fish receives 10% of this 10J= 1J. Out of 1J energy available to the fish, 10% is transferred to the next trophic level i.e. big fish. 10% of 1J is 0.1J. Hence, 0.1J of energy will be available to big fish if 10,000J of energy is available to small algae from the sun.

38A. Name and state the law given by Lindeman which tells us how much energy entering a particular trophic level of organisms is available for transfer to the next higher trophic level.

Answer

→ Raymond Lindeman in 1942 gave the Ten percent law. According to this law, only 10% of the energy transfer takes place from one trophic level to the next trophic level. The remaining energy is lost during transfer or broken down in respiration.

38B. 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?

Answer

→ Food chain will be = Paddy—Mice—Snake—Hawk
10,000J of energy is available to paddy from sun, out of which only 1% is absorbed, 1% of 10,000J is 100J. 100J energy is absorbed by Paddy. 10% of this 100J is transferred to mice, 10% of 100J is 10J; mice receives 10J energy. 10% of 10J i.e. 1% reaches the next trophic level i.e. snake. Snake will transfer 10% of 1J to hawks; 10% of 1J is 0.1J.
Thus, 0.1J of energy will be available to hawks in the given food chain.

Multiple Choice Questions (MCQs)-Pg-242

39. What provides the energy which then flows through a food chain?
A. Glucose
B. Oxygen
C. Respiration
D. Sunlight

Answer

→ Plants that are producers in a food chain synthesize food using water and carbon dioxide in the presence of chlorophyll and sunlight which then flows in the form of energy through the food chain.

40. Which pollutant released into the air during refrigeration and air-conditioning is the greatest contributor to the depletion of ozone layer?
A. BHC
B. DDT
C. CFC
D. UNEP

Answer

→ Chlorofluorocarbon, released from refrigerators and air-conditioners are the greatest contributor in depleting the ozone layer.

41. In the food chain given below, if the amount of energy available at fourth trophic level is 5 kJ, what was the energy available at the producer level?
GrassGrasshopper  Frog  Snake  Hawk
A. 500 kJ
B. 50 kJ
C. 5000 kJ
D. 5 kJ

Answer

→ According to the 10% energy law, 10% of energy is transferred at each trophic level. So, when 5000 kJ energy is available at producer, 10% of it will be transferred to second trophic level, i.e. 500 kJ. Now, 10% of this 500 kJ will be transferred to the third trophic level i.e. 50 kJ. 10% of 50kJ will be transferred to the fourth trophic level, i.e. 5kJ.

42. Which of the following limits the number of trophic levels in a food chain?
A. Insufficient food supply from producer level
B. Decrease in energy at higher trophic levels
C. Increase in the number of organisms at higher trophic levels
D. Accumulation of harmful chemicals at higher trophic levels

Answer

→ Since only 10% of energy is transferred at each trophic level, the higher trophic level get very low amount of energy which is not sufficient for the organisms to sustain life. So, the trophic level gets restricted to amount of energy available at which the organisms at that trophic level can sustain life.

43. What percentage of sun's energy falling on the leaves of green plants is utilized by the plants in the process of photosynthesis and stored as chemical energy of food?
A. 99 per cent
B. 10 per cent
C. 1 per cent
D. 20 per cent

Answer

→ Out of all the energy that falls on leaves of green plants, only one percent is utilized by plants to make food through photosynthesis, the rest is reflected back by the leaves.

44. The depletion of ozone layer in the upper atmosphere is mainly due to the emission of:
A. Un-burnt hydrocarbons
B. Chlorofluorocarbons
C. Greenhouse gases
D. Ultraviolet radiations

Answer

→ Chlorofluorocarbon that is emitted by refrigerators and air-conditioners are responsible for depletion of ozone layer in the stratosphere.

45. In an ecosystem, the ten per cent energy available for transfer from one trophic level to the next is in the form of:
A. Heat energy
B. Light energy
C. Chemical energy
D. Mechanical energy

Answer

→ According to 10% energy rule, 10% of total energy available at each trophic level is transferred to the next trophic level in the form of food i.e. chemical energy.

46. The flow of energy in an ecosystem is always:
A. Unidirectional
B. Bidirectional
C. Cyclic
D. Multidirectional

Answer

→ The energy enters the plants from sun, during the making of food. This energy is passed from one trophic level to another in food chain.

47. The excessive exposure of humans to ultraviolet rays results in:
(i) Damage to immune system
(ii) Damage to lungs
(iii) Skin cancer
(iv) Peptic ulcers
A. (i) and (ii)
B. (ii) and (iv)
C. (i) and (iii)
D. (iii) and (iv)

Answer

→ Damage to immune system and skin cancer
Excessive exposure of UV radiations to human skin cells results in destruction of genetic material thus leading to uncontrolled growth of cells and hence causing cancer. Exposure to UV radiations also causes immunosuppression and hence damage to immune system.

48. Which of the following gets the minimum energy through the food chain in an ecosystem?
A. Carnivore
B. Large carnivore
C. Producer
D. Herbivore

Answer

→ According to the ten percent energy rule, 10% energy is transferred at each trophic level; so the organism that is at the top in a food chain will receive the lowest amount of energy. Hence, large carnivore which will be at the top in food chain will get minimum amount of energy through the food chain.(Producer-herbivore-carnivore-large carnivore).

49. A food chain comprises of cat, seed-eating bird, plants, and dog. The organism which will have the maximum concentration of harmful pesticides coming through the food chain is most likely to be:
A. Cat
B. Plants
C. Dog
D. Seed-eating bird

Answer

→ Biological magnification is the accumulation of harmful chemicals and pesticides at trophic levels in a food chain, and it is the maximum at the topmost trophic level. In this food chain, plant-seed eating bird-cat-dog; dogs are at the top so they will have the maximum concentration of harmful pesticides.

50. An aquatic food chain comprises of the organisms like tadpoles, weeds, fish and water beetles. The organism which gets the minimum energy through this food chain is:
A. Water beetles
B. Tadpoles
C. Weeds
D. Fish

Answer

→ According to 10% energy rule, the organism at the topmost level in a food chain will receive minimum energy because of 10% energy transfer at each trophic level. So in this food chain, fish being at the topmost trophic level will get minimum amount of energy through the food chain.

51. Most of the water surface of a lake is covered with algae. This algae is part of the food chain which also includes small fish, bird, larvae and big fish. Which of the following will obtain the maximum energy?
A. Big fish
B. Bird
C. Larvae
D. Small fish

Answer

→ According to 10% energy rule, 10% of energy is transferred at each trophic level. In this food chain, larvae will have the maximum amount of energy because they are at the second trophic level in a food chain and we already know that energy decreases as it moves or flows in a food chain, so after algae, larvae will have maximum energy.

52. If the energy available at the producer level in a food chain is 150 J, how much energy will be transferred to: tertiary consumer?
A. 15 J
B. 10 J
C. 1.50 J
D. 0.15 J

Answer

→ According to ten percent energy rule- 10% of energy available at producer is transferred to primary consumer, so primary consumer receives 15J energy. 10% of 15J is transferred to secondary consumer. The secondary consumer receives 1.5J energy. The tertiary consumer will receive 10% of 1.5J i.e. 0.15J.

53. If the energy transferred to a tertiary consumer in a food chain is 10 J, how much energy was available to the primary consumer?
A. 100 J
B. 500 J
C. 1000 J
D. 5000 J

Answer

→ According to 10% energy law, 10% energy is transferred at each trophic level. So if tertiary consumer gets 10J, primary consumer would have had 1000 J of energy out of which, 10% i.e. 100J gets transferred to secondary consumer, 10% of 100J will be transferred to tertiary consumer i.e. 10J.

54. In addition to wheat plants, a crop field ecosystem has organisms such as snake, peacock, eagle and mice. If the wheat plants are sprayed with pesticides periodically, which of the following will have the minimum concentration of pesticides in the body?
A. Snake
B. Eagle
C. Mice
D. Peacock

Answer

→ The food chain will be [wheat plants-mice-snake-peacock-eagle]. Mice will have the minimum concentration of pesticides. This is because, biological magnification is the increasing concentration of pesticides and harmful chemicals in organisms at higher levels in a food chain. So, eagle will have the maximum concentration and mice will have the minimum concentration of pesticide.

55. Which of the following is the best method to dispose of biological wastes from hospitals?
A. Landfill
B. Recycling
C. Incineration
D. Composting

Answer

→ Disposal of bio-medical waste i.e. waste from hospitals is best done by incineration as it destroys pathogen and sharp materials completely.

56. In an ecosystem:
(i) The flow of energy is unidirectional
(ii) The flow of materials is unidirectional
(iii) The flow of materials is cyclic
(iv) The flow of energy is cyclic
A. (i) and (ii)
B. (ii) and (iii)
C. (i) and (iv)
D. (i) and (iii)

Answer

→ The flow of energy is unidirectional. The flow of materials is cyclic. Energy enters a food chain through producers and transfer of energy takes place from producers to decomposers through the food chain on the basis of ten percent energy rule, and is unidirectional.
The flow of materials takes place in a cyclic manner. Materials like water, carbon dioxide and nitrogen are taken up by plants to make food. This food passes from producers to herbivores and carnivores. After the death of animals, these materials are returned back to the soil from where they were taken. The materials hence are re-used for growth of new plants. Hence, flow of nutrients is cyclic in food chain.

57. The ten per cent law is associated with.
A. Transfer of energy from various trophic levels to decomposers in a food chain
B. Transfer of ATP energy into muscular energy
C. Transfer of chemical energy from one organism to another
D. Transfer of sun's energy to the organisms called producers.

Answer

→ According to ten percent law, 10% of total energy available at a trophic level is transferred to the next trophic level. Transfer of energy begins from producers and continues up to decomposers in a food chain.

58. The harmful chemical which is accumulating in human beings through food chain is:
A. Benzene hexa-chloride
B. Dichlorodiphenyltrichloroethane
C. Chlorofluorocarbon
D. Abscisic acid

Answer

→ DDT (dichlorodiphenyltrichloroethane) is an insecticide that is used to kill insects. Plants absorb it through soil and pass it up in the food chain. Because of biological magnification, it gets accumulated in human beings and may accumulate in large amount too.

59. O2 is converted into O3 by the action of:
A. Infrared radiations
B. Ultraviolet radiations
C. Gamma radiations
D. Cosmic radiations

Answer

→ Oxygen released from the plants, floats upwards into the atmosphere and is converted into ozone by ultraviolet radiations. Formation of ozone thus blocks ultraviolet radiations from reaching the earth surface.

60. Which of the following cannot be added in a composting pit to prepare compost?
A. Sunflower plants
B. Fruit and vegetable peels
C. Flowers of plastic
D. Red worms

Answer

→ Compost consists of organic matter, and plastic is not organic in nature, moreover plastic is non-degradable. To prepare compost, organic matter is added in a composting pit.

Questions Based on High Order Thinking Skills (HOTS)-Pg-243

61. The gas A is used by most of the animals to obtain energy from food by the process of respiration. When A is acted upon by radiation X, it gets converted into another gas B which is an allotrope of A but poisonous when inhaled. B forms a kind of layer C in the upper atmosphere which absorbs radiations X coming from a source Y and prevents them from reaching the earth. Some chemicals Z released from the various devices on the earth are destroying the layer C slowly. In fact, a hole has already been formed in layer Cover the area D of the earth.
(a) What are gases?
(i) A, and
(ii) B? Write their molecular formulae.
(b) Name the layer C.
(c) What are (i) X, (ii) Y, and (iii) Z?
(d) Name the area D.
(e) Name any two human ailments which may be caused by X.

Answer

→ a) i) The gas A used by animals to obtain energy from food by respiration is Oxygen O2.
ii) The gas B is Ozone O3. Radiations X (ultraviolet) when act on oxygen, convert oxygen to ozone.
b) The layer C is Ozone layer. Gas B i.e. Ozone forms ozone layer in the stratosphere.
c) i) X- Ultraviolet radiations
ii) Y- Sun. Ultraviolet radiations come from the sun
iii) Z- Chlorofluorocarbons. CFC’s are released from refrigerator and air-conditions which are destroying the ozone layer.
d) Ozone hole has been formed over Antarctica’s upper atmosphere.
e) The radiations X i.e. ultraviolet radiations cause skin cancer, when they fall on skin; they destroy the genetic material of the cells, thus resulting in uncontrolled growth of cells. These radiations are also absorbed by the lens of the eyes which leads to formation of free radicals inside the lens that causes cataract over time. Ultraviolet radiations also cause immunosuppression.

62. The surface of water in a lake appears green due to a layer of tiny free-floating organisms X on its surface. The lake water also contains organisms like water beetle, fish and tadpole. The sun shines over the lake water and provides energy for the functioning of this lake ecosystem.
(a) What could organisms X be?
(b) Write a food chain comprising of all the four organisms mentioned.
(c) What is the general name of the food chains like the one written above?
(d) Name
(i) Secondary consumer
(ii) Producer
(iii) Tertiary consumer, and
(iv) Primary consumer in the above food chain
(e) If the tertiary consumer gets 0.2 J of energy from the secondary consumer, then how much energy was radiated by the sun to the producer?

Answer

→ a) Phytoplankton- Algae are tiny free floating organisms on surface of water.
b) Food chain= Algae- tadpole- water beetle- fishes.
c) Aquatic food chain is the name given to the above food chain because this food chain exists in aquatic bodies where algae are producers, tadpoles are primary consumers, water beetles are secondary consumers and fishes are tertiary consumers.
d) i) Water beetles- secondary consumer
ii) Algae-producers
iii) Fishes- tertiary consumer
iv) Tadpole- primary consumer
e) If the tertiary consumer gets 0.2J of energy from the secondary consumer, then the producer would have received 20000J of energy from the sun. This is because of the 10% energy law. Producer receives 20,000J energy from sun and uses 1% of it to make food. 200J of energy is available at the producer. 10% of 200J is transferred to primary consumer which is 20J. Secondary consumer will obtain 10% of 20J=2J. The tertiary consumer will at last receive 10% of 2J which is equal to 0.2J. Thus, 20,000J energy was radiated from sun to producer.

63. A forest ecosystem having a lot of green plants has some foxes, lions and rabbits in it.
(a) Write a food chain comprising all the four organisms mentioned above.
(b) Name
(i) one herbivore, and
(ii) two carnivores, in this food chain.
(c) Name the link which is a predator as well as a prey.
(d) Name
(i) second trophic level, and
(ii) third trophic level.
(e) Which link of this food chain can feed on second trophic level as well as third trophic level, independently?
(f) If the sun provides 1000 J of energy to the plants, then how much energy will be transferred to fox through the food chain.

Answer

→ a) Food Chain= Green plants- rabbits-fox-lions
b) i)Herbivore- Rabbit is a herbivore
ii) Carnivore- Fox and lion are carnivores.
c) Fox is a predator as well as a prey. It eats rabbits as well as gets eaten by lion
d) i) Second trophic level- Rabbits
ii) Third trophic level- Fox.
e) Lion can feed on rabbits (secondary trophic level) as well as Fox (third trophic level), because they are carnivores.
f) If 1000J of energy is provided by sun to plants, the plant will absorb only 1% of this energy to make food. 1% of 1000J = 10J. Further, applying the ten percent rule,
The rabbits will receive 10% of 10J i.e. 1J.
10% of 1J= 0.1 J will be passed on to the foxes,.

64. A food chain consists of fish, larvae, phytoplankton and birds. The level of pesticides in water in which the fish, larvae and phytoplankton live is quite high.
(a) In which organisms the pesticides enter from the polluted water? What is this level of organisms known as?
(b) Which organism will have the maximum amount of pesticides accumulated through the food chain? What is this process known as?
(c) Write the food chain comprising all the organisms mentioned above.
(d) Which other organism you could write in place of bird in the above food chain?

Answer

→ a) Pesticides enter the Phytoplankton from the polluted water. This level of organism is known as producers. They produce their own food through the process of photosynthesis.
b) Birds will have the maximum amount of pesticides accumulated through the food chain because they are at the top in the food chain.
The process of accumulation of substances like pesticides where they move up the food chain, enter the aquatic organisms which are in turn are eaten by birds or humans is known as biological magnification.
c) Food chain= Phytoplankton-Larvae-Fish-Birds.
d) Human being can be considered in place of birds in the above food chain since they are omnivore too like certain birds; they eat food both of plant and animal origin.

65. Every household produces a lot of material A daily. In one of the methods of disposal B, material A is burned at a very high temperature of about 1000°C in a structure called C. During this process, the organic matter present is removed as D and E whereas F is left behind (which can be dumped in a landfill site).
(a) What is material A
(b) Name the method of disposal B.
(c) What is structure C known as?
(d) What are
(i) D
(ii) E, and
(iii) F?
(e) This method is especially suitable for the disposal of materials produced by certain institution. Name such institutions.

Answer

→ a) A-Garbage; Every household produces a lot of garbage daily.
b) B-Incineration; it is a method of destroying waste material by burning at high temperature.
c) C-Incinerator; incineration is carried out in an incinerator.
d) (i) D-Carbon dioxide; CO2 is the organic matter that is removed by burning of garbage.
(ii) E- Water is left behind after burning of garbage.
(iii) F- Ash is also left behind after burning of garbage.
e) Hospitals use incineration for disposal of biomedical wastes. An efficient incinerator will destroy pathogens and sharp materials and the source materials are not found in the ash that is left behind.

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