Intext Questions

Q.1      Why are some substances biodegradable and some non-biodegradable?
Sol.

Biodegradable substances are those substances on which micro-organisms like bacteria or decomposers act and break down these substances into simpler compounds, example of Biodegradable substances are dead remains of plants and animals and their waste products, paper etc.
But on some compounds like plastics and metals, micro-organisms do not act to decompose them and these compounds are known as non-biodegradable compounds.

---

Q.2      Give any two ways in which biodegradable substances would affect the environment.
Sol.

Biodegradable substances would affect the environment in following two ways-
(i) These substances decomposed by the action of micro-organisms that cause foul smell.
(ii) The rotting biodegradable wastes act as breeding ground for insects which may cause diseases to living organisms.

---

Q.3      Give any two ways in which non-biodegradable substances would affect the environment.
Sol.

Non-biodegradable substances would affect the environment in following two ways-
(i) Non- biodegradable substances may cause soil pollution and water pollution.
(ii) If non-biodegradable substances remain in fertile soil or land than it becomes barren.

---

Page 261
Q.1      What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Sol.

Trophic levels – The flow of food or energy in an ecosystem is called food chain.
Those organisms which join the food chain are termed as trophic levels
There are four trophic levels:
(i) First trophic level – Producers (Plants)
(ii) Second trophic level – Primary consumers.
(iii) Third trophic level – Secondary consumers.
(iv) Fourth trophic level – Top consumers.
In the above food chain plants are producers and represents the first trophic level.
Rabbit is the primary consumer i.e. herbivorous animal and represent the second Trophic level.
Wolf is the secondary consumer and represents the third trophic level.
Tiger is the top consumer and represents the fourth trophic level.

---

Q.2      What is the role of decomposers in the ecosystem?
Sol.

Decomposers act as cleansing agents of environment as they decompose the dead bodies and dead parts of plants and animals and clean the environment.

---

Page 264
Q.1      What is ozone and how does it affect any ecosystem?
Sol.

Ozone is a gas made up of three atoms of oxygen joined together. i.e.O3.
Between 20 – 26 km above the sea level, ozone forms a layer known as ozone layer.
This ozone layer absorbs the harmful U.V. radiations of the sunlight and hence, protects the earth and living organisms from the harmful effects of U.V. rays.
So, this layer is very important for the survival and existence of life on earth. Thus, it protects the ecosystem.

---

Q.2      How can you help in reducing the problem of waste disposal? Give any two methods.
Sol.

(i) We should use more and more substances that leave biodegradable wastes.
(ii) We should reduce the use of non-biodegradable wastes like plastics or recycle them.

Exercise

Q.1      Which of the following groups contain only biodegradable items?
                    (a) Grass, flowers and leather     (b) Grass, wood and plastic
                    (c) Fruit peels, cake and lime      (d) Cake, wood and grass
Sol.         (a), (c) and (d)

---

Q.2      Which of the following constitute a food chain ?
                    (a) Grass, wheat and mango       (b) Grass, goat and human
                    (c) Goat, cow and elephant         (d) Grass, fish and goat
Sol.         (b) Grass, goat and human

---

Q.3      Which of the following are environment-friendly practices?
                    (a) Carrying cloth bags to put purchases in while shopping.
                    (b) Switching off unnecessary lights and fans.
                    (c) Walking to school instead of getting your mother to drop you on her scooter.
                    (d) All of the above.
Sol.         (d) All of the above.

---

Q.4      What will happen if we kill all the organisms in one trophic level?
Sol.        

If we kill all the organisms in one trophic level then transfer of food and energy to next level will stop.
For eg.
If,  in the above food chain, we kill the grasshoppers or Trophic level II organisms then transfer of energy from plants (Trophic level I) to snake (Trophic level III) will stop.

---

Q.5    Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem ?
Sol.

(a) Yes, the impact of removing all the organisms in a trophic level will be different for different trophic levels.
For eg : –  Grass → Rabbit → Tiger :
In the above food chain : –
(i) If we remove all the tigers at the third trophic level, then the number of rabbits will increase and these rabbits will eat up all the grass and plants  forest becomes desert.
(ii) If we remove all the rabbits at the second trophic level, then tigers will not get food and due to starvation they will die.
And, also the amount of grass and plants increase.
(b) No, all the organisms of any trophic level cannot be removed without causing any damage to the ecosystem.

---

Q.6      What is biological magnification? Will the level of this magnification be different at different levels of the ecosystem?
Sol.  

When any harmful chemical like DDT enters in a food chain, its concentration increases gradually at each trophic level. This phenomenon is known as Biological magnification. Yes, the level of biological magnification is different for different levels. In trophic level I concentration of harmful chemical is less than other trophic level and in last trophic level concentration of harmful chemical is high.
For eg :-  Plant →   Goat → Man
In the above food chain, plants have minimum concentration of chemicals (Pesticides) and in Man , Concentration of chemical is high.

---

Q.7      What are the problems caused by the non-biodegradable wastes that we generate?
Sol.

Non biodegradable wastes cause many problems like –
(i)Enter in food chain and damage the organisms of highest trophic level.
(ii)Cause toxic effects to living organisms and may cause pollution like soil pollution, water pollution and air pollution in the environment.
(iii)Reduced crop yield.
(iv)Increase Biological oxygen demand.

---

Q.8      If all the waste we generate is biodegradable, will this have no impact on the environment ?
Sol.

Even if all the waste we generate is biodegradable, it will have an impact on the environment. This is because too much biodegradable waste cannot be broken down into harmless simpler substances by the decomposers like micro-organisms at the right time. Due to this, the biodegradable wastes will go on accumulating in the environment and act as pollutants resulting in harmful effects on the environment. For example, the rotting biodegradable waste act as breeding grounds for flies and cockroaches, etc., which spread diseases. Moreover, the rotting biodegradable waste emit foul smell in the environment which makes the life of people miserable.

---

Q.9     Why is the damage to the ozone layer a cause for concern?What steps are being taken to limit this damage?
Sol.

Ozone layer protects life on our earth from harmful rays (U.V. rays) of sun by absorbing these rays. Damage of Ozone layer leads to decrease in absorption of harmful rays of sun due to which these harmful rays reaches to earth’s surface and cause harmful effects, so it is necessary to control this damage.
Steps being taken to limit this damage are –
(i)To protect ozone layer, the United Nations environment program forged an agreement to freeze CFC production at 1986 levels.
(ii)Chlorofluoro carbons are now being replaced by hydro-fluorocarbons which do not damage the ozone layer.

Exemplar

Multiple Choice Question :

Q.1 Which one of the following is an artificial ecosystem?

(a) Pond

(b) Crop field

(c) Lake

(d) Forest

Sol. (b)

---

Q.2 In a food chain, the third trophic level is always occupied by

(a) Carnivores

(b) Herbivores

(c) Decomposers

(d) Producers

Sol. (a)

---

Q.3 An ecosystem includes

(a)All living organisms

(b)Non-living objects

(c)Both living organisms and non-living objects

(d)Sometimes living organisms and sometimes non-living objects

Sol. (c)

---

Q.4 In the given food chain, suppose the amount of energy at fourth trophic level is 5 kJ, what will be the energy available at the producer level?
Grass → Grasshopper → Frog → Snake → Hawk

(a)5 k J

(b)50 k J

(c)500 k J

(d)5000 k J

Sol. (d)

---

Q.5 Accumulation of non-biodegradable pesticides in the food chain in increasing amount at each higher trophic level is known as

(a)Eutrophication

(b)Pollution

(c)Biomagnification

(d)Accumulation

Sol. (c)

---

Q.6 Depletion of ozone is mainly due to

(a)Chlorofluorocarbon compounds

(b)Carbon monoxide

(c)Methane

(d)Pesticides

Sol. (a)

---

Q.7 Organisms which synthesise carbohydrates from inorganic compounds using radiant energy are called

(a) Decomposers

(b) Producers

(c) Herbivores

(d) Carnivores

Sol. (b)

---

Q.8 In an ecosystem, the 10% of 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

Sol. (c)

---

Q.9 Organisms of a higher trophic level which feed on several types of organisms belonging to a lower trophic level constitute the

(a) Food web

(b) Ecological pyramid

(c) Ecosystem

(d) Food chain

Sol. (b)

---

Q.10 Flow of energy in an ecosystem is always

(a)Unidirectional

(b)Bidirectional

(c)Multi directional

(d)No specific direction

Sol. (a)

---

Q.11 Excessive exposure of humans to U V-rays results in

(a) damage to immune system

(b) damage to lungs

(c) skin cancer

(d) peptic ulcers

(i) and (ii)

(ii) and (iv)

(i) and (iii)

(iii) and (iv)

Sol. (c)

---

Q.12 In the following groups of materials, which group (s) contains only non-biodegradable items?

(i) Wood, paper, leather

(ii) Polythene, detergent, PVC

(iii) Plastic, detergent, grass

(iv) Plastic, bakelite, DDT

(a)(iii)

(b)(iv)

(c)(i) and (iii)

(d)(ii) and (iv)

Sol. (d)

---

Q.13 Which of the following limits the number of trophic levels in a food chain?

(a) Decrease in energy at higher trophic levels

(b) Defficient food supply

(c) Polluted air

(d) Water

Sol. (a)

---

Q.14 Which of the statement is incorrect?

(a) All green plants and blue green algae are producers

(b) Green plants get their food from organic compounds

(c) Producers prepare their own food from inorganic compounds

(d) Plants convert solar energy into chemical energy

Sol. (b)

---

Q.15 Which group of organisms are not constituents of a food chain?

(i) Grass, lion, rabbit, wolf

(ii) Plankton, man, fish, grasshopper

(iii) Wolf, grass, snake, tiger

(iv) Frog, snake, eagle, grass, grasshopper

(a) (i) and (iii)

(b) (iii) and (iv)

(c) (ii) and (iii)

(d) (i) and (iv)

Sol. (c)

---

Q.16 The percentage of solar radiation absorbed by all the green plants for the process of photosynthesis is about

(a) 1%

(b) 5%

(c) 8%

(d) 10%

Sol. (a)

---

Q.17 In the given Figure 15.1 the various trophic levels are shown in a pyramid. At which trophic level is maximum energy available?

(a) T₄

(b) T₂

(c) T₁

(d) T₃

Sol. (c)

---

Q.18 What will happen if deer is missing in the food chain given below?

Grass → Deer → Tiger

(a) The population of tiger increases

(b) The population of grass decreases

(c) Tiger will start eating grass

(d) The population of tiger decreases and the population of grass increases

Sol. (d)

---

Q.19 The decomposers in an ecosystem

(a) Convert inorganic material, to simpler forms

(b) Convert organic material to inorganic forms

(c) Convert inorganic materials into organic compounds

(d) Do not breakdown organic compounds

Sol. (b)

---

Q.20 If a grass hopper is eaten by a frog, then the energy transfer will be from

(a) producer to decomposer

(b) Producer to primary consumer

(c) Primary consumer to secondary consumer

(d) Secondary consumer to primary consumer

Sol. (c)

---

Q.21 Disposable plastic plates should not be used because

(a) they are made of materials with light weight

(b) they are made of toxic materials

(c) they are made of biodegradable materials

(d) they are made of non-biodegradable materials

Sol. (d)