CBSE Class 10 Science Our Environment Assignment Set 04

Question. An ecosystem includes:
(a) All living organisms
(b) Non-Living objects
(c) Both Living and Non-living objects
(d) sometimes living and sometimes non-living

Answer: C

Question. 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

Answer: C

Question. Organisms which synthesise carbohydrates from inorganic compounds using radiant energy are called:
(a) Decomposers
(b) Producers
(c) Herbivores
(d) Carnivores

Answer: B

Assertion and Reason Type Questions

Directions: For questions given below, two statements are given – One labelled Assertion (A) and the other labelled Reason (R). select the correct answer from the codes (i), (ii), (iii) and (iv) as given below:
(i) Both (A) and (R) are true and (R) is the correct explanation of (A).
(ii) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(iii) (A) is true but (R) is false
(iv) (A) is false but (R) is true

Question. Assertion(A): Vegetables and fruit peels are biodegradable.
Reason (R): Decomposers have enzymes to break them down into simpler chemicals.

Answer: (i)

Question. Assertion(A): Herbivores are primary consumers.
Reason (R): They feed on small insects.

Answer: (iii)

Question. Assertion(A): In a pyramid of energy, maximum energy is contained in top carnivores.
Reason (R): Energy availability decreases with the rise in trophic level.

Answer: (iv)

Very Short Answer Type Question

Question. The flow of energy in the food chain is unidirectional. Why?
Answer: Energy flows from sun to plants (autotroph), plants to animals (consumer).

Question. In a food chain, 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: 10 J

Question. Producers always occupy the first trophic level in any food chain. Why?
Answer: Only producers have the ability to trap solar energy and manufacture organic food through the process of photosynthesis.

Question. Name any two abiotic components of an environment.
Answer:
(a) Climatic factors (light, temperature, rainfall)
(b) Edaphic factor (Soil)

Question. Give any two ways in which biodegradable substance would affect the environment.
Answer: They keep the environment clean as they are easily decomposed. They can easily go through the geochemical cycle with the help of decomposers.

Question. Draw a line diagram to show flow of solar energy in ecosystem
Answer:
Sun → Phytoplankton (\( 400 \text{ kJ} \)) → Zooplankton (\( 40 \text{ kJ} \)) → Smaller fishes (\( 4 \text{ kJ} \)) → Big fish (\( 0.4 \text{ kJ} \))

Question. What will happen if we kill all the organisms in one trophic level?
Answer:
i- The organisms in specific trophic level will not be able to get the food
ii-It will cause a disturbance in food chain and therefore ecological imbalance will take place.

Question. Why is a lake considered to be a natural ecosystem?
Answer: In Lake living organisms grow, reproduce and interact with other biotic and abiotic components. In lake different components carry out all activities in nature by themselves without any human interference; therefore it is referred to as a natural ecosystem.

Question. How can we help in reducing the problem of waste disposal? List two ways.
Answer:
i-Separation of biodegradable and non-biodegradable wastes
ii-Preparation of compost / vermicomposting from biodegradable waste
iii-Recycling of waste

Question. Which gas shield the surface of earth from harmful radiation of the sun. why these radiations are supposed to be harmful for us?
Answer: Ozone gas
Harmful radiation of the sun like UV radiation may causes skin cancer, cataract, fall in immunity in infants, decline in photosynthesis rate etc

Question. In a certain study conducted on the occurrence of DDT along food chains in an ecosystem, the concentration of DDT in grass was found to be 0.5 ppm. In sheep, it was 2 ppm and in man it was 10 ppm. Name the phenomenon and define?
Answer: Bio-magnification
Bio-magnification is the increase in the level of a toxic substance with each successive rise in the trophic level of a food chain.

Short Answer Type Questions

Question. What is the physical environment of an ecosystem called? Give one example.
Answer: Physical environment of an ecosystem is called the abiotic or non-living component of an ecosystem. This includes factors like air, water. Temperature etc.

Question. The first tropic level in a food chain is always a green plant. Why?
Answer: Because only plants can utilise the radiant energy of the sun and transform it to chemical form during photosynthesis.

Question. Write the mode of nutrition in fungi.
Answer: Saprophytic mode.

Question. Write any two consequences if decomposers are removed from the ecosystem?
Answer: (i) Dead organisms will pile up.(ii) There will be no replenishment of soil.

Question. Pesticides like DDT which are sprayed to kill pests on crops to kill pests on crops are found to be present in the soil, groundwater, water bodies etc. Explain. How do they reach these places?
Answer: Soil: Pesticides are used to protect plants from insects. They consequently get settled into soil particles, when used on plants.
Groundwater: Through irrigation in the fields, these pesticides present in soil pass into lower layers of soil and reach groundwater.
Water bodies: When the wastewater or other agricultural waste is thrown in water bodies like river, canals, ponds, etc. the pesticides affect water bodies.

Question. Food web increases the stability of an ecosystem. Justify.
Answer: Food web shows feeding connection in an ecological community. It consists if many food chains. Thus, if any one organism becomes endangered or extinct, the one dependent in it has an alternative option available to him for its survival. In this way food web increases stability in the ecosystem.

Question. List two causes of depletion of ozone layer. Mention any two harmful effects of depletion of this layer.
Answer: Two causes of depletion of ozone layer are as follows:
(a) Use of CFCs
(b) Use of Halons
Harmful effects of ozone depletion:
(i) Due to depletion of ozone UV radiation reaches the earth. This UV radiation causes skin cancer, damage to eyes and immune system.
(ii) Ozone depletion may also lead to variation in global rainfall, ecological disturbances and dwindling of global food supplies.

Question. Why bacteria and fungi are called decomposers? List any two advantages of decomposers to the environment.
Answer: Decomposers degrade breakdown the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants.
Advantages:
i- Clean environment by decomposing dead bodies of plants/ animals
ii- Replenish nutrients (Inorganic substance) into soil
iii- Helps in Nutrient recycling

Question. Answer the followings-
i- What is ozone? How is it formed in the atmosphere?
ii- How ozone layer is useful
iii- Name the substances responsible for the depletion of ozone layer.
Answer:
i- Ozone is triatomic form of oxygen, \( \text{O}_3 \). Ozone is formed in the upper atmosphere by the action of ultraviolet (UV) radiations over oxygen (\( \text{O}_2 \))
ii- It protects us from harmful UV radiation of sun.
iii- The important ozone depleting substances chlorofluorocarbons (CFC), methane, \( \text{N}_2\text{O} \), chlorine.

Question. (a) Write two harmful effects of using plastic bags on the environment. Suggest alternatives to the usage of plastic bags.
(b) List any two practices that can be followed to dispose of the waste produced in our homes.
Answer: (a) Harmful effects of using plastic bags :
(i) These are non-biodegradable substances. They cannot be decomposed and therefore remains as pollutants in nature for many years.
(ii) The plastic bags choke drains and causes waterlogging.
(iii)The pastic release harmful chemicals in soil, water slowly over to years.
Jute bags and cloth bags are the alternatives to the polyethene bags.
(b) Practices to dispose off the waste produced in our homes:
(i) Separation of biodegradable and non- biodegradable wastes.
(ii)The biodegradable waste can be converted to manure.
(iii) Non-biodegradable waste should be disposed off at suitable places from where municipal authorities can pick them up and dispose properly and scientifically.
(iv) Reuse the waste

Question. In the following food chain, 100 J of energy is available to the lion. How much energy was available to the producer?
Answer: simple food chain
Plants → Deer → Lion.
As per \( 10\% \) law only \( 10\% \) of energy is transferred to next trophic level
Energy available to deer = \( 100 \text{ J} \times 10 = 1000 \text{ J} \)
Energy available to plants = \( 1000 \text{ J} \times 10 = 10,000 \text{ J} \).

Long Answer Type Questions

Question. (a) “Energy flow in a chain is unidirectional”. Justify this statement. Explain how the pesticides enter a food chain and subsequently get into our body.
(b) What is an ecosystem? List two main components.
Answer: (a) Because the energy moves progressively through the various trophic levels and is no longer available to the previous trophic level. The energy captured by autotrophs does not revert back to the solar input.
* Pesticides, used for crop protection when washed down into the soil/water body, are absorbed by the plant along with water and minerals
* Being non-biodegradable, these chemicals get accumulated progressively in the food chain and into our body
(b)A self-sustaining functional unit consisting of living and non-living component is called an ecosystem.

Question. Explain the flow of energy between various components of the environment.
Answer: (i) Green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves.
(ii) The loss of energy at each step is so great that very little usable energy remains after four trophic levels.
(iii) In a food chain, the greatest number of individuals are at lower trophic level of an ecosystem, the greatest number is of the producers.

CCT Based Question

Question. Producers are autotrophs. They manufacture organic food from inorganic raw material. For this they pick up energy from sun and raw materials from the environment. Solar energy is absorbed by chlorophyll and changed into chemical energy. The chemical energy is stored in organic food formed by photosynthesis. Photosynthesis is performed by plants, algae, phytoplankton, blue green algae and some bacteria. Producers are also called transducers or converts as they change solar energy to chemical energy. Food manufactured by producers is used by all organisms including themselves. Producers have also a global impact of keeping the balance of CO₂—→ O₂ constant. They absorb CO₂ and release O₂.
(a) Why are photoautotrophs called producers?
(b) Why are environmentalist stressing for growing more trees?
(c) What is the source of energy in the biosphere?
(d) Why are heterotrophs called consumers?
Answer: (a) Photoautotrophs are chlorophyll containing organisms which manufacture organic food that is made available to all other organisms.
(b) Plantation of more trees will reduce the rising concentration of CO2 being produced because of higher combustion of fossil fuels.
(c) Sunlight
(d) Heterotrophs are organisms which obtain readymade food from outside sources. They are therefore called Consumers.

Question. Good quantity of ozone occurs in upper atmosphere or stratosphere at a height of 11-16 Km over poles reaching 23-25 km above equator. This region is called ozone layer or Ozonosphere. It is highly protective to life on earth as it destroys very harmful short waves ultraviolet radiations of 100-320 nm wavelength. Longer wave ultraviolet radiations (320-390 nm) are allowed to pass through and reach the earth. It was found in 1980s that thickness of ozone layer is decreasing rapidly. On searching for the reason, it was noted that certain man-made chemicals like chlorofluorocarbons and halons are bringing about destruction of ozone. They are called ozone depleting substances (ODS). With great international efforts starting from Montreal Protocol (1987) to Kigali conference (2016), it was decided to eliminate the use of ODS and replace them with safer chemicals.
(a) Where is ozone found in plenty in the atmosphere?
(b) What is the function of stratospheric ozone?
(c) Name an ozone depleting substance?
(d) Name an international effort to check damage to ozone layer.
Answer: (a) Ozonosphere/Ozone layer in upper atmosphere.
(b) Ozone destroys harmful ultraviolet radiations so that they do not reach the earth.
(c) chlorofluorocarbons
(d) Montreal Protocol (1987) for limiting chlorofluorocarbons production level.