Our Environment — Class 10 Science PYQs

(A) / Both assertion (A) and reason (R) are true and Reason (R) is the correct explanation of Assertion (A)

(B)/ Breakdown complex organic material into simple inorganic substances. (1 Mark)

(A)/ Convert simple substances into complex organic substances using radiant energy of the sun (1 Mark)

• Decomposers are organisms that break down dead and decaying organic matter into simpler inorganic substances. (1 Mark)
• Roles:
➢ Environment clean up (½ Mark)
➢ Nutrient recycling (½ Mark)
(or any other relevant point)

(C) / Decrease in energy at higher levels. (1 Mark)

(B) / Both Assertion (A) and Reason (R) are true but, Reason (R) is not the correct explanation of Assertion (A) (1 Mark)

(A) / Food Web

(B) / Grass and tree (1 Mark)

(A) / Producers (1)

(D) / They have the ability to make food using sunlight by photosynthesis (1 Mark)

Plant $\rightarrow$ Goat $\rightarrow$ Man
According to 10 % Law, only 10% of energy from a trophic level is transferred to the next trophic level.
So, if Man has 5 J energy
then Goat has $5 \times 10 = 50$ J
And plants (producers) have $50 \times 10 = 500$ Joule

As only 10% of the total amount of organic matter of the food eaten at one trophic level, is made available for the next trophic level of consumers. Since the loss of energy at each step is so great that little energy is available for the next level of consumers, food chains generally consist of only three to four steps. (2 Marks)

(B) / Human Beings

(A) / Both, Assertion (A) and Reason (R) are true and Reason (R) is
the correct explanation of the Assertion (A)
1
1

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

(i) To freeze the CFC production at 1986 levels.
(1)
(ii) Ozone shields the earth's surface from harmful UV radiations.
(1)

(a) $\ce{O2 ->[uv] O + O}$
$\ce{O + O2 -> O3}$ / (Ozone)
UV radiations split molecular oxygen into free oxygen and these atoms combine with oxygen to form ozone. (1 Mark)
(b) It can cause diseases like skin cancer in human beings. (or any other harmful effect) (1 Mark)

(C) / Polythene bag, rubber band, ball pen (1 Mark)

(B) / (iv) (1 Mark)

(B)/ DDT (1 Mark)

(C)/ 1, 2, 3 and 4 (1 Mark)

(i) Composting
(ii) recycle/reuse
(iii) recycle/reuse
(iv) Incineration
(or any other relevant answer)

• Kitchen wastes can be converted into manure/compost.
• Newspapers, magazines, etc. can be recycled.
• Metals/glass/plastic wastes can be recycled.
(Any two ways or any other)

(a) Sewage should not contain solid waste, so sieve should be installed at the opening of drain. (or any other valid point) (1 Mark)
(b) Chemical treatment of industrial waste should be done before disposing it off. (or any other valid point) (1 Mark)

(a) • Plastics being non - biodegradable persist in environment for a long time. (any other harmful effect) (½ Mark)
• Alternative - Jute or cloth bag (any other suitable alternative) (½ Mark)
(b) • Pesticides and chemical fertilizers are not biodegradable. They accumulate progressively at each trophic level. As human beings occupy the top level in any food chain the maximum concentration of these chemicals get accumulated in our bodies. (1 Mark)
• This Phenomenon is biological magnification. (1 Mark)