Science Ncert Exemplar Solutions for Class 10 Science Chapter 15 - Our Environment

Answer:

An artificial ecosystem is a man-made ecosystem e.g., crop field.

Hence, the correct answer is option (b).

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A food chains always starts with plants or producers so they occupy the first trophic level. The plants in turn, are consumed by herbivores which occupy the second trophic level. Primary carnivores eat the herbivores and occupy third trophic level.

Hence, the correct answer is option (a).

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An ecosystem consists of biotic components comprising living organisms and abiotic components (non-living constituents) comprising physical factors like temperature, rainfall, wind, soil and minerals.

Hence, the correct answer is option (c).

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In an ecosystem, only 10 percent of the energy available at each trophic level is passed on to the next trophic level of the food chain. Thus, if 5 kJ energy is available at the fourth trophic level, 10 percent more that is, 50 kJ energy will be available at the third trophic level, 500 kJ energy will be available at the second trophic level and 5000 kJ energy will be available at the first trophic level or producer level.

Hence, the correct answer is option (d).

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Biomagnification is the phenomenon through which certain pollutants such as non-biodegradable pesticides get accumulated in tissues in increasing concentration at successive trophic levels along the food chains.

Hence, the correct answer is option (c).

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Ozone depletion is due to ozone-depleting substances such as chlorofluorocarbon compounds.

Hence, the correct answer is option (a).

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All green plants and certain bacteria can make organic compounds like sugar and starch from inorganic substances using the radiant energy of the Sun. So, they are called producers.

Hence, the correct answer is option (b).

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According to Lindeman's 10% law of energy, the 10% energy refers to the average value for the amount of organic matter that is present at each step and reaches the next level of consumers. This organic matter is the source of chemical energy.

Hence, the correct answer is option (c).

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Different organisms of lower trophic levels are generally eaten by one organism of higher trophic level which in turn, are eaten by some other organism of higher trophic level of the same food chain or another food chain. So, instead of a straight line food chain, the relationship can be shown as a series of branching lines called a food web.

Hence, the correct answer is option (a).

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In an ecosystem, the autotrophs capture the energy present in sunlight and convert it into chemical energy. So, energy flows from Sun to the autotrophs. From autotrophs, the energy goes to the herbivores and decomposers. From, herbivores, the energy is passed on to the organisms of the next trophic level and so on but it never flows backwards. So, the flow of energy in an ecosystem is always unidirectional.

Hence, the correct answer is option (a).

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UV-rays cause damage to DNA causing damage to immune system and skin cancer.

Hence, the correct answer is option (c).

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Non-biodegradable substances are those man-made materials like plastics, detergent, PVC, Bakelite, DDT, etc. which cannot be broken down by the action of bacteria or other saprophytes. These materials will be acted upon by physical processes like heat and pressure, but under the ambient conditions found in our environment, these persist for a long time and harm the ecosystem.

Hence, the correct answer is option (d).

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Since only 10 percent of energy available at a trophic level is passed on to the next trophic level and rest energy is lost as heat, very little usable energy remains available after four trophic levels. So, decrease in energy at higher trophic levels limits the number of trophic levels in a food chain.

Hence, the correct answer is option (a).

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Green plants make their food in the form of organic compounds like sugar and starch from inorganic substances using the radiant energy of the Sun in the presence of chlorophyll. So, out of the given four statements, option (b) is incorrect.

Hence, the correct answer is option (b).

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The groups of organisms in listed in (i) and (iv) constitute food chains:
(i) Grass $\underset{}{\to }$  Rabbit $\underset{}{\to }$Wolf $\underset{}{\to }$ Lion
(iv) Grass $\underset{}{\to }$ Grasshopper $\underset{}{\to }$ Frog $\underset{}{\to }$ Snake $\underset{}{\to }$ Eagle

(ii) Three organisms (plankton, fish and man) constitute an aquatic food chain and grasshopper is a part of terrestrial food chain.
(iii) Three organisms (wolf, snake and tiger) are carnivores and grass is producer. Since there is no herbivore, a food chain cannot be constituted.

Hence, the correct answer is option (c).

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The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves and convert it into food energy through photosynthesis.

Hence, the correct answer is option (a).

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According to Lindeman's 10% law of energy, there is a progressive decrease in the available energy along a food chain, producers or organisms at the first trophic level (shown as T₁ in the given pyramid) have the maximum amount of available energy.

Hence, the correct answer is option (c).

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In the given food chain, the grass is eaten by deer which in turn, is eaten by tigers. If deer is missing in the food chain, grass will not be eaten by it so, the population of grass will increase whereas tigers will not get their food and its population will decrease.

Hence, the correct answer is option (d).

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Decomposers are the microorganisms such as bacteria and fungi, that break-down the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants.

Hence, the correct answer is option (b).

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A grasshopper consumes plants or producers, so it is a primary consumer. Frog eats grasshopper or primary consumer, so it is a secondary consumer. So, if a frog eats a grasshopper, the transfer of energy will be from primary consumer to secondary consumer.

Hence, the correct answer is option (c).

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Disposable plastic plates cannot be broken down by decomposers and remain in the environment for long. Since they are non-biodegradable, disposable plastic plates should not be used.

Hence, the correct answer is option (d).

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Improper disposal of waste is a curse to the environment because it not only pollutes the environment, soil, water and air but also has harmful effects on other living organisms including humans. For example, if waste is dumped onto the ground, it will be a breeding place for many disease-causing organisms such as bacteria, viruses, etc. and their vectors such as mosquitoes, house flies etc. It will also cause soil and water pollution. The atmosphere surrounding the dumping ground will also be polluted.

Answer:

The common food chain of a pond ecosystem is:
Phytoplanktons and aquatic plants → small aquatic animals (larvae, insects, shrimps, etc.) → small fish → large fish → bird (heron).

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Cloth bags are made up of plant-based fibres such as jute so, they are more advantageous over plastic bags during shopping for the following reasons:

• ​They are made of natural fibres which are biodegradable so they are environmental-friendly or do not pollute the environment.
• They can be reused multiple times and recycled.
• They are stronger and more durable than plastic bags.
• They can be used for multiple purposes and carry more things.

Answer:

Artificial ecosystems are ecosystems which are created or maintained by humans. Crop fields are an example of artificial ecosystems because  plants grown in fields are selected by humans. Also, humans add chemicals such as manure, pesticides or herbicides in the fields to increase soil nutrients or control the organisms. Since humans manipulate both biotic and abiotic components of the crop fields, these are known as artificial ecosystems.

Answer:

Biodegradable substances are those substances that can be broken down by biological processes, e.g., paper, wood, vegetable peels. etc.
Non-biodegradable substances are those substances that cannot be broken down by biological processes, e.g., plastic, DDT, bakelite, etc.

Answer:

(a)The physical and biological world where we live in-Environment/Biosphere.
(b) Each level of food chain where transfer of energy takes place-Trophic level.
(c) The physical factors like temperature, rainfall, wind and soil of an ecosystem-Abiotic factors.
(d) Organisms which depend on the producers either directly or indirectly for food-Consumers/Heterotrophs

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Decomposers are organisms that break down the dead remains and waste products of organisms into simple inorganic substances that they return to the soil. So, they help in cleaning the environment and constant re-cycling of the nutrients in the ecosystem.

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The mis-matched pair is (b) and correct pair is:
(b) Ecosystem - Biotic and abiotic components of environment

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An aquarium is an artificial and incomplete ecosystem i.e., it is a man-made ecosystem and it does not contain all the components of a natural ecosystem. For example, it does not contain soil and decomposers that break down the organic matter into simpler inorganic substances and act as cleaner. So, due to lack of cleaners, aquarium needs to be cleaned. In contrast, ponds or lakes are complete and natural ecosystem with all the components that keep them clean. So, they are self-sustaining ecosystems.

Answer:

The flow of energy in an ecosystem occurs in the following manner:

Sun $\underset{}{\to }$ Producers $\underset{}{\to }$ Primary consumers $\underset{}{\to }$Secondary consumers $\underset{}{\to }$ Tertiary consumers



The flow of energy is unidirectional for the following two reasons:

• Energy flows progressively through the various trophic levels and it is no longer available to the previous level because organisms are linked to each other through food relationships. 
• Only 10% of energy available at a trophic level is passed on to the next level and the energy available at each trophic level gets diminished progressively due to loss of energy as heat at each level.

Answer:

Decomposers are organisms that break down complex organic matter of dead animals and plants into simpler inorganic substances. These inorganic susbstances return to the soil and become available to producers for their use. If decomposers are not present in the ecosystem, dead organisms and waste will pile up and nutrient re-cycling will not occur. In the absence of nutrient re-cycling, soil will not be replenished and will lack most of the nutrients required by producers to synthesise their food. This, in turn, will affect the flow of energy along a food chain.

Answer:

Activities in daily life which are eco-friendly:
 

• Using paper/jute bags in place of plastic bags.
• Segregating bio-degradable and non-biodegradable wastes into separate bins.
• Using public transport for commuting, and walking or using cycle for short distances.
• Harvesting rain water.
• Switching off light/fans when not in use.
• Use of compost and vermi-compost in place of fertilisers.

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Suitable mechanisms for waste management in fertilizer industries:
Fertilizer industries generate solid waste, wastewater (contains organics, nitrates, alcohols, ammonia, phosphorous, heavy metals such as cadmium and suspended solids) and air pollutants (particulate matter, gaseous NH₃, oxides of nitrogen, sulphur and carbon dioxide). So, the waste management mechanisms in fertilizer industries are:

• Wastewater should be treated before its discharge into the surrounding water.
• Solid waste should be dumped in a safe place by following safety measures.
• Air pollution should be controlled e.g., by fitting certain adsorption equipment in chimneys to absorb harmful pollutants before the smoke is released into the atmosphere.

Answer:

The byproducts of fertiliser industries are oxides of nitrogen and sulphur, other liquid chemicals and some solid waste material.
The oxides of nitrogen and sulphur cause acid rain which is highly destructive to forests, crops, aquatic biota and historical buildings. Chemicals from liquid and solid wastes percolate through the soil causing soil pollution. It also causes a decrease in soil fertility. Liquid chemicals, if discharged directly into a water body, will cause the death of aquatic animals.

Answer:

Harmful effects of agricultural practices on the environment:

• Soil pollution - Excessive cropping causes robbing of nutrients from the soil leading to loss of soil fertility. Also, over time, it can lead to soil erosion and finally to desertification. Excessive use of fertilizers also changes soil chemistry and kills useful organisms.
• Water pollution - Agricultural runoff carries nutrients from fields to water and causes excessive growth of algae. This causes decreases in oxygen content in water leading to the death of many aquatic organisms.
• Lowering of the water table - Excess drainage of groundwater for irrigation purposes has lowered down the water table. This results in acute water shortages at many places.
• Biomagnification - The chemical pesticides are non-biodegradable thus, they accumulate in organisms in increasing amounts at each trophic level.
• Damage to natural ecosystem or habitat - The clearing of forests for agriculture has resulted in the loss of habitat to wildlife. Deforestation has also affected the water cycle and other nutrient recycling.