Class 8th Science Term 3 Tamilnadu Board Solution
Evaluation- Choose the best answer: a. Species with low population numbers that are in considerable…
- In India, Social Forestry was started in 1976. Its aim is to promote natural forests and…
- Wildlife is essential for ecological balance and is a big attraction to tourism. Support…
- People tried several methods to keep wild animals away from the fields and villages. Power…
- Planting trees is known as afforestation and cutting down trees is deforestation. Is there…
- Deforestation leads to many changes in the following but they are not in the right order.…
- What will happen if: a. we go on cutting down trees? b. the habitat of an animal is…
- Indiscriminate cutting of trees will lead to deforestation. How does it reduce rainfall on…
- Choose the best answer: a. Species with low population numbers that are in considerable…
- In India, Social Forestry was started in 1976. Its aim is to promote natural forests and…
- Wildlife is essential for ecological balance and is a big attraction to tourism. Support…
- People tried several methods to keep wild animals away from the fields and villages. Power…
- Planting trees is known as afforestation and cutting down trees is deforestation. Is there…
- Deforestation leads to many changes in the following but they are not in the right order.…
- What will happen if: a. we go on cutting down trees? b. the habitat of an animal is…
- Indiscriminate cutting of trees will lead to deforestation. How does it reduce rainfall on…
Evaluation
Question 1.Choose the best answer:
a. Species with low population numbers that are in considerable danger of elimination are termed as ––––––––––(endangered species / extinct)
b. All non-domesticated and non-cultivated biota in the natural environment are termed –––––––––––––(wildlife / ordinary life)
c. The natural vegetation in a particular area is termed as –––––––––– (flora / forest)
d. All the organisms of the animal kingdom are termed as ––––––––––– (fauna / protozoans)
e. The word ‘dinosaur’ means –––––––––––––– (terrible lizard / dragon lizard)
Answer:a. Species with low population numbers that are in considerable danger of elimination are termed as endangered species
When the population of a species continues becoming less in number, with danger of elimination, they are referred to as ‘endangered species’.
When no more individuals of that species is alive anywhere in the world, the species is defined as ‘extinct species’.
b. All non-domesticated and non-cultivated biota in the natural environment are termed wildlife
We often say that, “we are going to the zoo to look at wildlife.” The definition of wildlife is also structured in the same context. Wildlife refers to non-domesticated (when referring to animals) and non-cultivated (plants) biota in the natural environment.
For example: Lions, birds, deer, etc. are largely non-domesticated and present in the natural environment (i.e forests). Hence, they would come under the definition of wildlife. Similarly, plants such as sunflower, thyme, etc. are also considered wildlife.
Note: Biota refers to a grouping of animals, plants, or other organisms that share the same geographical region on Earth.
c. The natural vegetation in a particular area is termed as flora.
Flora is a term used to collectively refer to all the plants occurring in a particular region. For example, the flora of India will refer to all the species of plants in India.
A forest mostly refers to a large area covered chiefly with trees.
The diagram below shows an example of flora on an island: (the flora of this island has four species of plants)
d. All the organisms of the animal kingdom are termed as fauna.
All Life on this planet has been divided into broad categories or “kingdoms” according to the cell structure, nutrition requirements and body organisation of different organisms. The animal kingdom includes all animals.
Protozoans are unicellular organisms belonging to the animal kingdom.
Hence, protozoans refer to only few organisms of animal kingdom; and all organism of animal kingdom are called as fauna.
e. The word ‘dinosaur’ means terrible lizard
The term dinosaur is derived from Greek; ‘dienos’ meaning terrible, and ‘sauros’ meaning lizard. Hence, the literal meaning of the word dinosaur becomes “terrible lizard”.
Question 2.In India, Social Forestry was started in 1976. Its aim is to promote natural forests and create man made forests on unused lands. Suggest some steps to convert a sterile land into a cultivable one.
Answer:a) Use organic compost to nourish the sterile land by adding materials like leaves, wood chips, bark, hay or even discarded fruits and vegetables. This will add nutrient content to the superficial layers of the soil, making it more suitable for cultivation.
b) Add animals such as earthworms, ants, or other arthropods to the soil. These animals break down organic matter in the soil into small particles readily absorbed by plants, making the soil more fertile
c) Water the soil regularly
d) Start growing plants. Even if the plants die, continue efforts to grow new plants, as the old dead plants will nourish the soil and make it more fertile for the subsequent crops.
Question 3.Wildlife is essential for ecological balance and is a big attraction to tourism. Support the statement with your suggestions.
Answer:Ecology deals with the relations of organisms to one another and to their physical surroundings. The ecosystem of earth is a very complex one, with many species directly and indirectly depending upon each other for survival.
For example, the lion eats the sheep, the sheep eats grass, and the grass eats the decomposed lion and sheep which ultimately become part of the soil. (the interactions among thousands of species are much more complex)
While considering the prosperity of one species, we must not ignore the health of other species, as we all depend on each other indirectly. These complex interactions form the basis of our ecosystem.
The huge biodiversity in particular regions, such as that of the ‘Big Cats in India’ like Lion, Tiger, Leopard, etc. make it a great tourist attraction and is of great value to people.
Question 4.People tried several methods to keep wild animals away from the fields and villages. Power fences were erected around the fields against animals.
Is it a healthy practice? Do you have any alternative that would help both animals and man?
Answer:No, it is not a healthy practice. Man must be empathetic to other species on earth. The wild animals attempt to enter fields and villages as their natural habitat was destroyed due to deforestation by man. These animals wander around searching for food, water and new places to inhabit to avoid starvation and death.
As an alternative, we can attempt to restore the habitat of the wildlife by transporting them to natural parks or wildlife sanctuaries and attempt to provide basic food, water, and shelter for the wildlife.
Also, in the long run, man must reduce the amount of habitat destruction caused by reducing deforestation and promoting afforestation practices.
Question 5.Planting trees is known as afforestation and cutting down trees is deforestation.
Is there any permanent solution to the problem of deforestation?
Answer:To find a permanent solution of deforestation, we must follow two approaches:
a) Reducing cutting down of trees - There is a growing need for products that are derived from trees, which is the major cause of deforestation. Planning in advance, and not wasting material such as paper and wood by proper utilization of resources can help reduce deforestation.
b) Afforestation - Growing trees simultaneously will make sure that the next generation does not have to deal with devastating effects of deforestation.
To sum up, we must follow sustainable utilization of our resources and try to meet not only our needs, but also consider the needs of the next generation by cutting down less trees and and enthusiastically practicing afforestation.
Question 6.Deforestation leads to many changes in the following but they are not in the right order. Arrange them in proper sequence.
a) Earth b) cities (urban area) c) environment d) wild animals e) villages f) rural areas g) the next generation
Answer:a) Wild animals: The most immediate effect of deforestation is the destruction of the habitat of the animals living in the forest. The animals starve to death due to lack of shelter and food.
b) Environment: Plants are responsible for rainfall and reducing the carbon dioxide in the atmosphere. Deforestation will cause reduced rainfall and lead to global warming due to increased carbon dioxide.
c) Villages and rural areas: The major occupation in the villages, farming would no more be possible. This is because the top fertile layer of the soil will get eroded due to lack of plants which hold the soil together. The land will be infertile and deserted. Since plants also help the soil absorb excess water, there will also be an increased number of floods.
d) Cities (urban area): There may be shortage of food in the cities due to reduced supply from farmers. There may also be reduced rainfall and more flooding.
e) Earth: The levels of carbon dioxide in the environment will increase causing global warming. The groundwater level may be lowered due to decrease in rainfall, causing droughts. The risk of natural calamities will also be increased due to these effects.
f) Next generation: The next generation will have a harsh environment, reduced water supply, infertile lands, and reduced biodiversity.
Question 7.What will happen if:
a. we go on cutting down trees?
b. the habitat of an animal is disturbed?
c. the top layer of the soil is exposed?
Answer:a) If we go on cutting down trees, it will lead to the following effects:
1. Effect on soil:
- soil erosion: the trees hold on to the soil and prevent erosion
- eventually, all the soil will lose its fertility and resemble a desert. This is called desertification of soil.
2. Effect on environment:
- reduced rainfall as the trees help in cloud formation. This would also pose a problem for agriculture. There will also be increased floods.
- greenhouse effect: global warming will increase as the trees which absorb carbon dioxide are getting reduced
3. The natural habitat of many animals will be destroyed, leading to reduction in biodiversity.
b) If the habitat of animals is disturbed, the herbivores will get affected first, as they directly depend on their surrounding flora for nutrition. Their population will start decreasing. Meanwhile, the carnivores will have lack of herbivores to feed on. Their population will also decrease due to lack of food; they may also get killed due to wandering off from their territory due to disturbance of habitat and food shortage. They animals may become extinct.
c) Soil has three main layers: The top soil is the most fertile and has many essential nutrients. As we go towards the bottom, the soil keeps become less fertile and rockier. The bottom most layer consists solely of rocks.
Soil erosion involving removal of the top most layer of the soil, makes the soil infertile, making the growth of plants difficult. Slowly the fertile land gets converted to a desert. This process is called desertification.
Question 8.Indiscriminate cutting of trees will lead to deforestation. How does it reduce rainfall on the one hand and lead to floods on the other hand?
Answer:Plants absorb water from their roots which gets evaporated from leaves. This evaporated water forms the clouds, and lead to rainfall. Cutting down of trees leads to disturbance in this process of cloud formation, causing reduced rainfall.
On the other hand, the trees also help prevent flooding. The tree roots dig deep into the soil and help prevent washing away of soil in the presence of excess water. Also, the tree roots continuously absorb water from the soil, making the soil drier and able to store more rainwater.
Choose the best answer:
a. Species with low population numbers that are in considerable danger of elimination are termed as ––––––––––(endangered species / extinct)
b. All non-domesticated and non-cultivated biota in the natural environment are termed –––––––––––––(wildlife / ordinary life)
c. The natural vegetation in a particular area is termed as –––––––––– (flora / forest)
d. All the organisms of the animal kingdom are termed as ––––––––––– (fauna / protozoans)
e. The word ‘dinosaur’ means –––––––––––––– (terrible lizard / dragon lizard)
Answer:
a. Species with low population numbers that are in considerable danger of elimination are termed as endangered species
When the population of a species continues becoming less in number, with danger of elimination, they are referred to as ‘endangered species’.
When no more individuals of that species is alive anywhere in the world, the species is defined as ‘extinct species’.
b. All non-domesticated and non-cultivated biota in the natural environment are termed wildlife
We often say that, “we are going to the zoo to look at wildlife.” The definition of wildlife is also structured in the same context. Wildlife refers to non-domesticated (when referring to animals) and non-cultivated (plants) biota in the natural environment.
For example: Lions, birds, deer, etc. are largely non-domesticated and present in the natural environment (i.e forests). Hence, they would come under the definition of wildlife. Similarly, plants such as sunflower, thyme, etc. are also considered wildlife.
Note: Biota refers to a grouping of animals, plants, or other organisms that share the same geographical region on Earth.
c. The natural vegetation in a particular area is termed as flora.
Flora is a term used to collectively refer to all the plants occurring in a particular region. For example, the flora of India will refer to all the species of plants in India.
A forest mostly refers to a large area covered chiefly with trees.
The diagram below shows an example of flora on an island: (the flora of this island has four species of plants)
d. All the organisms of the animal kingdom are termed as fauna.
All Life on this planet has been divided into broad categories or “kingdoms” according to the cell structure, nutrition requirements and body organisation of different organisms. The animal kingdom includes all animals.
Protozoans are unicellular organisms belonging to the animal kingdom.
Hence, protozoans refer to only few organisms of animal kingdom; and all organism of animal kingdom are called as fauna.
e. The word ‘dinosaur’ means terrible lizard
The term dinosaur is derived from Greek; ‘dienos’ meaning terrible, and ‘sauros’ meaning lizard. Hence, the literal meaning of the word dinosaur becomes “terrible lizard”.
Question 2.
In India, Social Forestry was started in 1976. Its aim is to promote natural forests and create man made forests on unused lands. Suggest some steps to convert a sterile land into a cultivable one.
Answer:
a) Use organic compost to nourish the sterile land by adding materials like leaves, wood chips, bark, hay or even discarded fruits and vegetables. This will add nutrient content to the superficial layers of the soil, making it more suitable for cultivation.
b) Add animals such as earthworms, ants, or other arthropods to the soil. These animals break down organic matter in the soil into small particles readily absorbed by plants, making the soil more fertile
c) Water the soil regularly
d) Start growing plants. Even if the plants die, continue efforts to grow new plants, as the old dead plants will nourish the soil and make it more fertile for the subsequent crops.
Question 3.
Wildlife is essential for ecological balance and is a big attraction to tourism. Support the statement with your suggestions.
Answer:
Ecology deals with the relations of organisms to one another and to their physical surroundings. The ecosystem of earth is a very complex one, with many species directly and indirectly depending upon each other for survival.
For example, the lion eats the sheep, the sheep eats grass, and the grass eats the decomposed lion and sheep which ultimately become part of the soil. (the interactions among thousands of species are much more complex)
While considering the prosperity of one species, we must not ignore the health of other species, as we all depend on each other indirectly. These complex interactions form the basis of our ecosystem.
The huge biodiversity in particular regions, such as that of the ‘Big Cats in India’ like Lion, Tiger, Leopard, etc. make it a great tourist attraction and is of great value to people.
Question 4.
People tried several methods to keep wild animals away from the fields and villages. Power fences were erected around the fields against animals.
Is it a healthy practice? Do you have any alternative that would help both animals and man?
Answer:
No, it is not a healthy practice. Man must be empathetic to other species on earth. The wild animals attempt to enter fields and villages as their natural habitat was destroyed due to deforestation by man. These animals wander around searching for food, water and new places to inhabit to avoid starvation and death.
As an alternative, we can attempt to restore the habitat of the wildlife by transporting them to natural parks or wildlife sanctuaries and attempt to provide basic food, water, and shelter for the wildlife.
Also, in the long run, man must reduce the amount of habitat destruction caused by reducing deforestation and promoting afforestation practices.
Question 5.
Planting trees is known as afforestation and cutting down trees is deforestation.
Is there any permanent solution to the problem of deforestation?
Answer:
To find a permanent solution of deforestation, we must follow two approaches:
a) Reducing cutting down of trees - There is a growing need for products that are derived from trees, which is the major cause of deforestation. Planning in advance, and not wasting material such as paper and wood by proper utilization of resources can help reduce deforestation.
b) Afforestation - Growing trees simultaneously will make sure that the next generation does not have to deal with devastating effects of deforestation.
To sum up, we must follow sustainable utilization of our resources and try to meet not only our needs, but also consider the needs of the next generation by cutting down less trees and and enthusiastically practicing afforestation.
Question 6.
Deforestation leads to many changes in the following but they are not in the right order. Arrange them in proper sequence.
a) Earth b) cities (urban area) c) environment d) wild animals e) villages f) rural areas g) the next generation
Answer:
a) Wild animals: The most immediate effect of deforestation is the destruction of the habitat of the animals living in the forest. The animals starve to death due to lack of shelter and food.
b) Environment: Plants are responsible for rainfall and reducing the carbon dioxide in the atmosphere. Deforestation will cause reduced rainfall and lead to global warming due to increased carbon dioxide.
c) Villages and rural areas: The major occupation in the villages, farming would no more be possible. This is because the top fertile layer of the soil will get eroded due to lack of plants which hold the soil together. The land will be infertile and deserted. Since plants also help the soil absorb excess water, there will also be an increased number of floods.
d) Cities (urban area): There may be shortage of food in the cities due to reduced supply from farmers. There may also be reduced rainfall and more flooding.
e) Earth: The levels of carbon dioxide in the environment will increase causing global warming. The groundwater level may be lowered due to decrease in rainfall, causing droughts. The risk of natural calamities will also be increased due to these effects.
f) Next generation: The next generation will have a harsh environment, reduced water supply, infertile lands, and reduced biodiversity.
Question 7.
What will happen if:
a. we go on cutting down trees?
b. the habitat of an animal is disturbed?
c. the top layer of the soil is exposed?
Answer:
a) If we go on cutting down trees, it will lead to the following effects:
1. Effect on soil:
- soil erosion: the trees hold on to the soil and prevent erosion
- eventually, all the soil will lose its fertility and resemble a desert. This is called desertification of soil.
2. Effect on environment:
- reduced rainfall as the trees help in cloud formation. This would also pose a problem for agriculture. There will also be increased floods.
- greenhouse effect: global warming will increase as the trees which absorb carbon dioxide are getting reduced
3. The natural habitat of many animals will be destroyed, leading to reduction in biodiversity.
b) If the habitat of animals is disturbed, the herbivores will get affected first, as they directly depend on their surrounding flora for nutrition. Their population will start decreasing. Meanwhile, the carnivores will have lack of herbivores to feed on. Their population will also decrease due to lack of food; they may also get killed due to wandering off from their territory due to disturbance of habitat and food shortage. They animals may become extinct.
c) Soil has three main layers: The top soil is the most fertile and has many essential nutrients. As we go towards the bottom, the soil keeps become less fertile and rockier. The bottom most layer consists solely of rocks.
Soil erosion involving removal of the top most layer of the soil, makes the soil infertile, making the growth of plants difficult. Slowly the fertile land gets converted to a desert. This process is called desertification.
Question 8.
Indiscriminate cutting of trees will lead to deforestation. How does it reduce rainfall on the one hand and lead to floods on the other hand?
Answer:
Plants absorb water from their roots which gets evaporated from leaves. This evaporated water forms the clouds, and lead to rainfall. Cutting down of trees leads to disturbance in this process of cloud formation, causing reduced rainfall.
On the other hand, the trees also help prevent flooding. The tree roots dig deep into the soil and help prevent washing away of soil in the presence of excess water. Also, the tree roots continuously absorb water from the soil, making the soil drier and able to store more rainwater.