SCIENCE Ch 17. Forests: Our Lifeline WORKBOOK

 Ch 17. Forests: Our Lifeline 

1. Choose the correct option.  

(a) Afforestation refers to: (R) (i) cutting of trees  

(ii) soil erosion  

(iii) planting of trees 

(iv) disappearance of forests 

(b) Which layer of the forest receives very little sunlight? (U) (i) crown  

(ii) forest floor 

(iii) understorey 

(iv) canopy 

2. Give two examples for each of the following.  

(U) 

(a) Trees found in Deciduous forests - teak, sandalwood, mahua, sal, mango,  bamboo, banyan, jackfruit  

(b) Animals found in mountain vegetation - musk deer, wild goats, sheep,  wolves and the Indian snow leopard  

(Accept any two) 

3. In the following questions, two statements are given- one labelled Assertion (A)  and the other labelled Reason (R). Read the statements carefully and choose the  correct alternative (A), (B), (C) and (D) as given below. (An) 

(A) Both A and R are true and R is the correct explanation of the assertion. (B) Both A and R are true but R is not the correct explanation of the assertion. (C) A is true but R is false. 

(D) A is false but R is true. 

i. Assertion: In a food chain, the entire amount of energy is not transferred to the  next level. 

Reason: Some part of the energy is absorbed in the form of heat.  

(C) A is true but R is false.

ii. Assertion: Polluted soil is a cause of deforestation. 

Reason: Polluted soil causes maximum damage as the plants depend on soil  for anchoring, nutrients and water. 

(A) Both A and R are true and R is the correct explanation of the  assertion. 

4. Explain the following terms:  

(R)  

(a) Food web 

A food web is a complex feeding system of interlocking and interdependent food  chains.  

(b) Conservation 

Conservation means judicious use of resources without wasting them. 

5.Answer the following questions in brief:  

(R) 

i. What type of plants are found in the understorey layer of the forest?  Plants such as orchids, palms and ferns grow in this region. 

ii. Where are thorn forests found in India?  

These forests sprawl mostly over the Thar Desert of Rajasthan and the North  western region of India, from Saurashtra to Punjab. 

6. Answer the following questions in detail: 

(a) How is increased soil erosion a consequence of deforestation? (U) 

The roots of trees hold the soil particles together. This prevents the soil from  getting washed off. Without trees, the soil is free to blow away. Thus,  deforestation increases the rate of soil erosion.

(b) What are the characteristics of tropical rainforests? (R) 

∙ These forests are characterised by heavy rainfall and are also known as lowland  equatorial evergreen rain forests.  

∙ Typically, the tropical rainforests receive around 60 to 160 inches of rainfall  throughout the year.  

∙ The combination of warmth and moisture makes them a suitable place for  many plants and animals.  

∙ Rainforests are dominated by broad leaved evergreen trees which form a leafy  canopy over the forest floor. 

(c) How are plants and animals in a forest interdependent? (Give any four points)(U) 

∙ Herbivores depend directly on green plants for food. Omnivores depend both  on plants and other animals for food. Carnivores depend indirectly on plants  for their food. Thus ,all living organisms depend on green plants for their food. 

∙ Animal excreta and the bodies of dead animals are broken down by  decomposers and converted into humus. The humus provides minerals for the  growth of plants. Thus, plants too indirectly depend on animals.  

∙ The oxygen released by plants during photosynthesis is used by all the living  beings for respiration. 

∙ Plants also help in replenishing groundwater which is used by all living  organisms.  

• The carbon dioxide given out by animals during respiration is used by the plants  for photosynthesis. 

• Insects such as butterflies, honeybees and many birds help to pollinate flowers in  the forest. The continuity of plant species is not possible without pollination. 

• Dispersal of plant seeds takes place by means of birds, other animals and human  beings. 

• Many arboreal animals such as squirrels, monkeys etc. and birds live on trees.  Thus, plants also provide shelter to animals.

7. Give reasons for the following: (An) (a) Forests play an important role in maintaining the water cycle. 

Trees present in the forest absorb the water from soil and give it out through the  leaves. The process of transpiration contributes to the formation of rain clouds,  thus also helping in rainfall. 

(d) In evergreen forests, almost no air pollution seen. 

∙ Trees have the unique ability to absorb carbon dioxide from the atmosphere  and release oxygen during the process of photosynthesis. 

∙ Trees bind soil particles together thus reducing the amount of dust getting  into the air. 

(b) All living organisms depend on green plants for their food.  

Green plants are the only living organisms that can manufacture their own food by  the process of photosynthesis. Herbivores feed only on plants and hence depend  directly on green plants for food. Omnivores feed both on plants and other  animals for food. Carnivores feed on animals and hence depend indirectly on  plants for their food. 

8. Observe the picture given below and answer the questions that follow.  (In) A D E B C

a) Identify the secondary consumer in the above food chain.  

C- frog  

b) Identify the herbivore in the given diagram.  

B- grasshopper  

c) In a food chain every organism represents a level or a link. What will be the  consequences in the following situations?  

(i) If any organism in this link is missing? 

It will affect the feeding and survival of all the organisms linked with  the food chain /the entire food chain will be adversely affected 

(ii) If there is a great increase or decrease in the number of a particular  organism. 

An increase or decrease in the number of a particular organism (link)  affects the number of all other the organisms linked in in the food  chain. 

9. Read the paragraph and answer the questions that follow. (U) 

Forests cover about 30 percent of the world’s land area, but they are disappearing at an  alarming rate. Between 1990 and 2016, the world lost 502,000 square miles of forest,  according to the World Bank an area larger than South Africa. Since humans started  cutting down forests, 46 percent of trees have been felled, according to a 2015 study in  the journal Nature. About 17 percent of the Amazonian rainforest has been destroyed  over the past 50 years, and in recent years the loss is increased.  

Causes of deforestation 

∙ Farming, grazing of livestock, mining, and drilling combined account for more  than half of all deforestation.  

∙ Forestry practices, wildfires and, in small part, urbanization account for the rest.  

∙ In Malaysia and Indonesia, forests are cut down to make way for producing palm  oil, which can be found in everything from shampoo to saltines. 

∙ In the Amazon, cattle ranching and farms (particularly soy plantations) are key  culprits. 

1. State the causes which account for more than half of all deforestation.  • Farming, grazing of livestock, mining and drilling  

2. What is the percentage of the Amazon rainforest that has been destroyed over the  past 50 years? State the key culprits for the same. 

∙ about 17 percent 

∙ Cattle ranching and farms (particularly soy plantations) are key culprits.

3. How much of the forest area has the world lost from1990 and 2016? The world has lost 502,000 square miles of forest. 

10. WORD SEARCH (An) Find the words given in the box in the word search given below.  

 HUMUS ECOSYSTEM BIOTIC  

 FOOD WEB PRODUCER MANGROVE 

A	X	J	P	Z	T	Q	K	D	T	K	B
H	O	P	A	S	J	D	S	S	J	Q	T
S	C	N	E	C	O	S	Y	S	T	E	M
A	E	R	C	X	K	P	B	K	F	X	Z
V	O	H	U	M	U	S	D	G	O	T	D
F	B	Q	J	A	J	K	Z	I	O	Z	S
C	I	Z	F	N	S	Q	J	G	D	Z	J
Z	O	F	D	G	T	G	X	J	W	I	D
B	T	B	P	R	O	D	U	C	E	R	Q
W	I	Q	L	O	T	Z	J	I	B	K	D
C	C	F	Q	V	D	N	K	D	L	Z	J
V	X	J	D	E	N	T	S	Q	S	B	T

11. Higher Order Thinking Skills (HOTS) An  

Seema wrote a food chain in an incorrect order. Help her to write the food chain correctly. Birds snakes Leaves caterpillars  

Leaves caterpillars birds snakes