CBSE Class 10 Biology Our Environment Management Of Natural Resources Worksheet Set 07

This second printable worksheet for CBSE Class 10 Science (Biology) Chapter 13, Our Environment, has 19 questions with answers, including fill-ups, true or false, matching, analogies, naming questions and energy-flow numericals. It revises the producers and consumers of a forest and a pond, biomagnification, waste and its disposal and ozone depletion, and it is free of multiple-choice questions and diagrams.

Fill in the Blanks, True or False and Matching

Question 1. Fill in the blanks:
(1) All the interacting living organisms in an area together with the ________ components of the environment form an ________.
(2) All organisms depend on the ________ either directly or indirectly for their sustenance.
(3) The ________ or the producers are at the ________ trophic level.
(4) Consumers can be classified variously as ________, carnivores, ________ and ________.
(5) Since so little energy is available for the next level of consumers, food chains generally consist of only ________ or ________ steps.
(6) All living organisms in an ecosystem interact with each other and their growth, ________ and other activities are affected by the ________ components of the ecosystem.
(7) The microorganisms, comprising ________ and ________, break down the dead remains and waste products of organisms.
(8) Specific ________ are needed for the break down of a particular substance.
(9) Plastics will not be broken down by the action of ________ or other ________.
(10) Human-made materials will be acted upon by physical processes like ________ and ________ but under the ambient conditions found in our ________, these persist for a long time.
Answer:
(1) abiotic, ecosystem
(2) producers
(3) autotrophs, first
(4) herbivores, omnivores, parasites
(5) three, four
(6) reproduction, abiotic
(7) bacteria, fungi
(8) enzymes
(9) bacteria, saprophytes
(10) heat, pressure, environment
In simple words: These blanks restate the main facts of the chapter.

Teacher's Note:
1. Use the exact scientific terms.
2. Food chains usually have three or four steps.

Question 2. State true or false:
(1) Primary consumers form the second trophic level in food chain.
(2) The green plants in a terrestrial ecosystem capture about 10% of the energy of sunlight that falls on their leaves and convert it into food energy.
(3) Substances that are broken down by biological processes are said to be biodegradable.
(4) There are generally a greater number of individuals at the lower trophic levels of an ecosystem.
(5) The length and complexity of food chains remain mostly the same.
(6) The flow of energy in a food chain occurs in both directions.
(7) Ozone is a molecule formed by three atoms of oxygen.
(8) Harmful chemicals get accumulated into our body through biological magnification.
(9) The pesticide residue in food grains such as wheat and rice, vegetables and fruits and even meat cannot always be removed by washing or other means.
(10) Improvement in our life style have resulted in lesser amounts of waste material generation.
Answer:
(1) True
(2) False: green plants capture only about 1% of the sunlight.
(3) True
(4) True
(5) False: the length and complexity of food chains vary greatly.
(6) False: the flow of energy is unidirectional.
(7) True
(8) True
(9) True
(10) False: improvements in lifestyle have resulted in greater amounts of waste.
In simple words: Keep the facts about 1%, 10% and one-way flow in mind.

Teacher's Note:
1. Correct false statements in one line.
2. Only 1% of sunlight is trapped by plants, but 10% of the energy passes on at each step.

Question 3. Match the following (one to one).
(1) Column I: (A) Autotroph (B) Ozone (C) UNEP (D) CFC. Column II: (P) Chlorofluoro carbon (Q) United Nations environment programme (R) 1st trophic level (S) Three atoms of oxygen (O₃)
(2) Column I: (A) Abiotic factor (B) Natural ecosystem (C) Ozone protects us from (D) Trophic level. Column II: (P) Food chain (Q) Forest, ponds and lakes (R) Physical factors (S) Ultraviolet radiation
Answer:
(1) (A) → (R); (B) → (S); (C) → (Q); (D) → (P)
(2) (A) → (R); (B) → (Q); (C) → (S); (D) → (P)
In simple words: Match each term with its meaning.

Teacher's Note:
1. Autotrophs make the first trophic level.
2. A trophic level is a step of the food chain.

Question 4. Write one word answer for the following statements or definitions ?
(i) Decline in the thickness of ozone layer over a restricted area.
(ii) The substances which react with the ozone layer in the stratosphere and destroy it.
(iii) The useless left over or discarded materials.
Answer:
(i) Ozone hole
(ii) Ozone depleting substances
(iii) Wastes
In simple words: One word for each definition.

Teacher's Note:
1. CFCs are the main ozone depleting substances.
2. The ozone hole is largest over Antarctica.

Question 5. Complete the following analogy.
(i) Sewage : Biodegradable : : Mercury : __________
(ii) Automobile exhaust : Gaseous waste : : Trash and rubbish : ___________
(iii) Paper and plastic : Recycling : : Hospital waste : _________
(iv) Global warming : Troposphere : : Ozone depletion : __________
(v) Household waste : Compost : : Incineration : __________
Answer:
(i) Non-biodegradable
(ii) Solid waste
(iii) Incineration
(iv) Stratosphere
(v) Chemical waste
In simple words: Find the relation in the first pair and apply it to the second.

Teacher's Note:
1. Mercury is not broken down by microbes.
2. Hospital waste is burnt in incinerators.

Question 6. Name the following:
(i) Organisms feeding on animal and plant food.
(ii) Organisms breaking down wastes of living beings.
(iii) The organisms occupying the first trophic level of any food chain.
(iv) A complex network of many interconnected food chains and feeding relationships.
(v) The cumulative increase in the concentrations of a persistent substance in successively higher levels of the food chain.
Answer:
(i) Omnivores
(ii) Decomposers
(iii) Producers
(iv) Food web
(v) Biological magnification (biomagnification)
In simple words: Five definitions, five terms.

Teacher's Note:
1. Learn the definitions together with the terms.
2. Humans and bears are omnivores.

Food Chains and Energy Numericals

Question 7. Give examples of the following:
(i) Two step food chain in a forest ecosystem.
(ii) Three step food chain in a forest ecosystem.
(iii) Four step food chain in a pond ecosystem.
Answer:
(i) Grass → Deer.
(ii) Grass → Deer → Tiger.
(iii) Phytoplankton → Zooplankton → Small fish → Large fish.
In simple words: A step is one organism of the chain.

Teacher's Note:
1. Count organisms to find the number of steps.
2. Arrows point from the food to the eater.

Question 8. 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.
Answer:
(a) Green plants → Rabbit → Fox → Lion
(b) (i) Herbivore: rabbit. (ii) Carnivores: fox and lion.
(c) The fox is a predator of the rabbit and also the prey of the lion.
(d) (i) Second trophic level: rabbit. (ii) Third trophic level: fox.
In simple words: Plants are first, then the herbivore, then two carnivores.

Teacher's Note:
1. The top predator, the lion, has no predator here.
2. The producer is the first level.

Question 9. 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) Algae (phytoplankton).
(b) Algae → Tadpole → Water beetle → Fish.
(c) Aquatic food chain.
(d) (i) Water beetle (ii) Algae (iii) Fish (iv) Tadpole.
(e) Secondary consumer has 0.2 ÷ 0.1 = 2 J, primary consumer 20 J, producer 200 J. Producers trap only about 1% of the sunlight, so the energy radiated by the Sun = 200 ÷ 0.01 = 20,000 J.
In simple words: Work back one step at a time, then use the 1% rule for sunlight.

Teacher's Note:
1. The producer traps about 1% of the Sun’s energy.
2. Each upward step is a division by 10%.

Question 10. Write the common food chain of a pond ecosystem.
Answer:
Phytoplankton → Zooplankton → Fish → Bird
In simple words: Tiny plants, tiny animals, fish and then a fish-eating bird.

Teacher's Note:
1. Producers of a pond are phytoplankton.
2. This is an aquatic food chain.

Question 11. In the following food chain plants provide 500 J of energy to rats. How much energy will be available to hawks from snakes? Plants → Rats → Snakes → Hawks
Answer:
Rats receive 500 J.
Snakes receive 10% of 500 J = 50 J.
Hawks receive 10% of 50 J = 5 J.
In simple words: 500 J → 50 J → 5 J.

Teacher's Note:
1. Apply 10% at each step.
2. Write the energy under each organism.

Question 12. What will be the amount of energy available to the organisms of the second trophic level of a food chain, if the energy available at the first trophic level is 10,000 J?
Answer:
Second trophic level = 10% of 10,000 J = 1000 J.
In simple words: One tenth of 10,000 J.

Teacher's Note:
1. Only one transfer is needed.
2. 1000 J is available to the herbivores.

Question 13. In the following food chain, 10 J is energy available to the hawks. How much energy would have been present for the rats? Plants → Rats → Snakes → Hawks
Answer:
Hawks have 10 J, so snakes had 10 ÷ 0.1 = 100 J.
Rats had 100 ÷ 0.1 = 1000 J.
In simple words: Going back, multiply by 10 each time.

Teacher's Note:
1. Work from the top of the chain downward.
2. Two steps back mean multiplying by 100.

Question 14. In a food chain, if 10,000 joules of energy is available to the producer, how much energy will be available to the secondary consumer to transfer it to the tertiary consumer?
Answer:
Primary consumer: 10% of 10,000 J = 1000 J.
Secondary consumer: 10% of 1000 J = 100 J, which it can pass on to the tertiary consumer (10 J of this reaches the tertiary level).
In simple words: 10,000 J → 1000 J → 100 J.

Teacher's Note:
1. The secondary consumer is on the third trophic level.
2. A tertiary consumer would receive 10 J.

Question 15. What is the difference between the food habits of organisms belonging to the first and third trophic levels? Give one example each of the organisms belonging to these two trophic levels.
Answer:
Organisms of the first trophic level (producers) make their own food from inorganic substances by photosynthesis, e.g. grass.
Organisms of the third trophic level (secondary consumers) cannot make food; they feed on herbivores, e.g. frog or snake.
In simple words: Producers make food; third-level animals eat other animals.

Teacher's Note:
1. Name the mode of nutrition for each.
2. Give one named example each.

Question 16. Give reasons:
(i) Forest ecosystem is more stable than a cropland ecosystem.
(ii) Available energy goes on decreasing at each trophic level in a food chain.
Answer:
(i) A forest is a natural ecosystem with a large number of species and many interlinked food chains (a food web), so if one organism is lost others can replace it. A cropland has one or a few crop species and depends on human care, so it is less stable.
(ii) At each trophic level most of the energy (about 90%) is used for life processes and lost as heat, and only about 10% passes to the next level.
In simple words: Many species make a forest stable; energy is used up at each step.

Teacher's Note:
1. Mention the food web for part (i).
2. Use the 10% law in part (ii).

Question 17. State a way to prevent accumulation of harmful chemicals in our bodies.
Answer:
Reduce the use of pesticides and chemical fertilisers (use organic manure and biopesticides), and wash fruits and vegetables well before eating.
In simple words: Use fewer chemicals on crops and wash food.

Teacher's Note:
1. Fewer pesticides means less biomagnification.
2. Check the final answer against the chapter.

Question 18. Very briefly explain the phenomenon of ozone layer depletion.
Answer:
Ozone in the stratosphere is formed from oxygen by UV radiation. CFCs used in refrigerators, air conditioners and aerosols rise to the stratosphere, where UV rays split them and release chlorine atoms. Chlorine breaks ozone down into oxygen, so the ozone layer becomes thin and more UV reaches the Earth.
In simple words: CFCs release chlorine, which destroys ozone and lets in more UV.

Teacher's Note:
1. Name CFCs and the stratosphere.
2. The effects are skin cancer and cataract.

Question 19. The amount of ozone in the atmosphere began to drop sharply in the 1980s. This decrease has been linked to synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers. In 1987, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels. It is now mandatory for all the manufacturing companies to make CFC-free refrigerators throughout the world. Suggest an alternative coolant that can be used.
Answer:
Hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) are used in place of CFCs, because they break down more quickly and do not harm the ozone layer to the same extent.
In simple words: HFCs replace CFCs in refrigerators.

Teacher's Note:
1. Name the compound class.
2. CFC-free refrigerators are now compulsory.