CBSE Class 10 Science HOTs Our Environment Set 02

Eco-System – What are its Components?

Question. In an ecosystem, herbivores represent
(a) producers
(b) primary consumers
(c) secondary consumers
(d) decomposers
Answer: (b) primary consumers

Question. Trophic level in an ecosystem represents
(a) oxygen level
(b) water level
(c) energy level
(d) salt level
Answer: (c) energy level

Question. A food chain comprises of birds, green plants, fish and man. The concentration of harmful chemical entering the food chain will be maximum in
(a) green plants
(b) man
(c) birds
(d) fish
Answer: (b) man

Question. First link in any food chain is usually green plants because
(a) they are widely distributed
(b) they are fixed at one place in the soil
(c) they alone have the capacity to synthesise food using sunlight
(d) there are more herbivores than carnivores
Answer: (c) they alone have the capacity to synthesise food using sunlight

Question. Which of the following statements about food chain and energy flow through ecosystem is false?
(a) Food webs include two or more food chains.
(b) All organisms that are not producers are consumers.
(c) A single organism can feed at several trophic levels.
(d) Detritivores feed at all trophic levels except the producer level.
Answer: (d) Detritivores feed at all trophic levels except the producer level.

Question. Which of the following is a logical sequence of food chain?
(a) Producer → consumer → decomposer
(b) Producer → decomposer → consumer
(c) Consumer → producer → decomposer
(d) Decomposer → producer → consumer
Answer: (a) Producer → consumer → decomposer

Question. Which of the following is an autotroph?
(a) Lion
(b) Insect
(c) Tree
(d) Mushroom
Answer: (c) Tree

Question. In the garden ecosystem, which of the following are producers?
(a) Insects
(b) Snakes
(c) Grasses
(d) Rabbits
Answer: (c) Grasses

Question. In an ecosystem 10% of energy available for transfer from one trophic level to the next is in the form of:
(a) heat energy
(b) chemical energy
(c) mechanical energy
(d) light energy
Answer: (b) chemical energy

Question. Soil fertility is determined by its ability to: 
(a) Decay organic matter
(b) Hold organic matter
(c) Hold water
(d) Support life
Answer: (d) Support life

Question. Which statement shows interaction of an abiotic component with a biotic component in an ecosystem? 
(a) A grasshopper feeding on a leaf.
(b) Rainwater running down into a lake.
(c) An earthworm making a burrow in the soil.
(d) A mouse fighting with another mouse for food.
Answer: (c) An earthworm making a burrow in the soil.

Question. What is an ecosystem? Give one example each of (i) natural, and (ii) man-made ecosystem. 
Answer: All organisms such as plants, animals, microorganisms and human beings as well as the physical surroundings interact with each other and maintain a balance in nature. All the interacting organisms together with the non-living constituents of the environment form as ecosystem.
Examples of–
(i) Natural ecosystem — Pond, forest
(ii) Artificial or man-made ecosystem — Crop field, aquarium.

Question. DDT was sprayed in a lake to regulate breeding of mosquitoes. How would it affect the trophic levels in the following food chain associated with a lake? Justify your answer. [CBSE Sample Paper 2022]
HAWK
LARGE FISH
SMALL FISH
PLANKTON
AQUATIC ENVIRONMENT
Answer:

• DDT being a non- biodegradable pesticide will enter the food chain from the first trophic level i.e Plankton.
• Non – biodegradable pesticides accumulate progressively at each trophic level. This phenomenon is known as biological magnification.
• HAWK will have the highest level of pesticide.

Question. With the help of an example explain that a garden is an ecosystem.
Answer: A garden comprises of different kind of flora and fauna such as grasses, flowering and non-flowering plants, trees, frogs, insects, birds, etc. All these living organisms depend and interact with each other and their growth, reproduction and other vital biological activities depend upon the abiotic component comprising of physical factors like temperature, rainfall, wind, soil and minerals. Therefore, we can say that a garden is an ecosystem.

Question. In the following food chain, only 2 J of energy was available to the peacocks. How much energy would have been present in grass? Justify your answer. GRASS → GRASS HOPPER → FROG → SNAKE → PEACOCK 
Answer: In the given food chain GRASS → GRASS HOPPER → FROG →SNAKE → PEACOCK, 2 J of energy was available. In a food chain, there is a loss of energy and only 10 percent of the energy available at each trophic level is passed on to the next trophic level.
Let energy present in Grass (first trophic level) = \( A \text{ J} \)
Energy present in Grasshopper (second trophic level) = \( A \times \frac{10}{100} = \frac{A}{10} \text{ J} \)
Energy present in Frog (third trophic level) = \( \frac{A}{10} \times \frac{10}{100} = \frac{A}{100} \text{ J} \)
Energy present in Snake (fourth trophic level) = \( \frac{A}{100} \times \frac{10}{100} = \frac{A}{1000} \text{ J} \)
Energy present in Peacock (fifth trophic level) = \( \frac{A}{1000} \times \frac{10}{100} = \frac{A}{10,000} \text{ J} \)
\( 2 \text{ J} = \frac{A}{10,000} \)
\( \implies \) \( A = 20,000 \text{ J} \)
Energy present in grass is 20,000 J.

Question. (a) List two natural ecosystems. (b) List two biotic components of a biosphere. 
Answer: (a) Two natural ecosystems are forest and river. (b) Two biotic components of a biosphere are plants and animals.

Question. (a) When plants are eaten by primary consumers, a great deal of energy is lost as heat to the environment and some amount goes in carrying out various life processes. State the average percentage of energy lost in this manner. [HOTS] (b) What happens to Sun’s energy that fall on green plants?
Answer: (a) The average percentage of energy lost when plants are eaten by primary consumers is 90 %. (b) Green plants absorb 1% of Sun’s energy that falls on their leaves.

Question. (a) What will be the amount of energy available to the organism of the 2nd trophic level of a food chain, if the energy available at the first trophic level is 10,000 Joules? (b) The first trophic level in a food chain is always a green plant. Why? 
Answer: (a) 1,000 Joules of energy will be available to the organism of the 2nd trophic level. (b) Only green plants can make their own food from sunlight. Green plants therefore, always occupy the 1st trophic level in a food chain.

Question. (a) Which of the following are always at the second trophic level of the food chains? [AI 2015] Carnivores, Autotrophs, Herbivores (b) The following organisms form a food chain. Which of these will have the highest concentration of non-biodegradable chemicals? Name the phenomenon associated with it.Insects, Hawk, Grass, Snake, Frog.
Answer: (a) Herbivores are always at the 2nd trophic level. (b) Hawk will have highest concentration of non-biodegradable chemicals. The phenomenon is called biological magnification.

Question. What are consumers? Name the four categories under which the consumers are further classified. 
Answer: The organisms which cannot manufacture their own food and depend on plants and other animals for their food. There are four categories under which the consumers are further classified are: (i) Herbivores (ii) Carnivores (iii) Omnivores (iv) Decomposers

Question. What is an ecosystem? List its two main components. We do not clean natural ponds or lakes but an aquarium needs to be cleaned regularly. Why is it so? Explain. 
Answer: Ecosystem: It is the structural and functional unit of biosphere, comprising of all the interacting organisms in an area together with the non-living constituents of the environment. Thus, an ecosystem is a self sustaining system where energy and matter are exchanged between living and non-living components.
Main components of ecosystem:
Biotic Component: It means the living organisms of the environment–plants, animals, human beings and microorganisms like bacteria and fungi, which are distinguished on the basis of their nutritional relationship.
Abiotic Component: It means the non-living part of the environment–air, water, soil and minerals. The climatic or physical factors such as sunlight, temperature, rainfall, humidity, pressure and wind are a part of the abiotic environment.
An aquarium is an artificial and incomplete ecosystem compared to ponds or lakes which are natural, self-sustaining and complete ecosystems where there is a perfect recycling of materials. An aquarium therefore needs regular cleaning.

Question. “Energy flow in food chains is always unidirectional.” Justify this statement. Explain how the pesticides enter a food chain and subsequently get into our body. 
Answer: The energy flow through different steps in the food chain is unidirectional. The energy captured by autotrophs does not revert back to the solar input and it passes to the herbivores, i.e. it moves progressively through various trophic levels. Thus energy flow from sun through producers to omnivores is in single direction only. Pesticides are sprayed to kill pests on food plants. The food plants are eaten by herbivores and alongwith the food, pesticides are also eaten by the herbivores. Herbivores are eaten by carnivores and alongwith the herbivore animal, pesticide also enters the body of the carnivore. Man eat both plants and animals and pesticide alongwith food enters the body of human. Concentration of pesticides increases as we move upward in the food chain and the process is called biological magnification.

Question. Your mother always thought that fruit juices are very healthy for everyone. One day she read in the newspaper that some brands of fruit juices in the market have been found to contain certain level of pesticides in them. She got worried as pesticides are injurious to our health. (a) How would you explain to your mother about fruit juices getting contaminated with pesticides? (b) It is said that when these harmful pesticides enter our body as well as in the bodies of other organisms they get accumulated and beyond a limit cause harm and damage to our organs. Name the phenomenon and write about it. 
Answer: (a)

• Pesticides are the chemicals used to protect our crops from diseases and pests.
• Pesticides stick to the surface of the fruit and if juices are made without proper washing, pesticide will also go into the juice.
• These pesticides also get washed down to underground water and are absorbed by plants. The pesticides then enter into the system of the plants including the fruits.

(b)

• The phenomenon is called biological magnification. It is the phenomenon in which certain harmful chemicals enter the food chain and get accumulated and increase in concentration at successive trophic levels.
• It is because they are not degradable.
• The maximum concentration of these chemicals is found in the top level consumers.

Question. Why are bacteria and fungi called decomposers? List any two advantages of decomposers to the environment.
Answer: Bacteria and fungi breakdown the dead remains and waste products of organisms. These microorganisms are called the decomposers as they breakdown the complex organic substances into simple inorganic substances that go into the soil and are used up again by the plants.
Two advantages of decomposers to the environment are as follows :
(i) Decomposers feed on the dead bodies of plants and animals. They return the simple components to soil and help in maintaining the steady state of ecosystem by cycling of nutrients. They therefore, create a balance in the environment.
(ii) They also act as scavengers or cleansing agents of the atmosphere.

Question. What is food web? Explain with example. 
Answer: Food Web: It is the network of various food chains which are interconnected at various trophic levels. Since an organism can occupy position in more than one food chain, in a food web it occupies more than one trophic level. Example: Grass may be eaten by grasshopper as well as rabbit or cattle and each of these herbivores may be eaten by many carnivores such as frog, bird or tiger depending on their food habits.

Question. Explain how harmful chemicals enter our body. 
Answer: Harmful and toxic chemicals enter our bodies when they are added to the soil and water. Pesticides are used to protect the food crops from diseases, and pests. Chemical wastes of factories are dumped in open or disposed off into rivers. These chemicals are washed down into the soil and ultimately to the water table or get absorbed or taken up from the soil by the plants along with water and minerals. In this way harmful chemicals enter the food chain. The quantity of these chemicals increase with increase in trophic levels of the food chain because these substances are not degradable and man is at the top of the food chain, so concentration is maximum in human beings. Thus, accumulation of DDT has been maximum in man as DDT is used to destroy pests. DDT is accumulated in the following way in the given food chain –
Water (0.02 ppm) → Phytoplankton (5.0 ppm) → Fish (240 ppm) → Bird (1600 ppm)
This is the reason why our food grains such as wheat and rice, vegetable and fruits and even meat contain varying amounts of pesticides residues. So, the highest trophic level at the extreme right of food chain has the maximum concentration of harmful chemicals in a food chain.

Question. (a) What is biodiversity? What will happen if biodiversity of an area is not preserved? Mention one effect of it. [AI 2015] (b) With the help of an example explain that a garden is an ecosystem. (c) Why only 10% energy is transferred to the next trophic level? 
Answer: (a) Biodiversity is the existence of a wide variety of species of plants, animals and microorganisms in a natural habitat within a particular environment or existence of genetic variation within a species. Biodiversity of an area is the number of species or range of different life forms found there. Forests are ‘biodiversity hotspots’. Every living being is dependent on another living being. It is a chain. If biodiversity is not maintained, the links of the chain go missing. If one organism goes missing, this will affect all the living beings who are dependent on it.
(b) A garden comprises of different kind of flora and fauna such as grasses, flowering and non-flowering plants, trees, frogs, insects, birds, etc. All these living organisms depend and interact with each other and their growth, reproduction and other vital biological activities depend upon the abiotic component comprising of physical factors like temperature, rainfall, wind, soil and minerals. Therefore, we can say that a garden is an ecosystem.
(c) Only 10% energy is transferred to the next trophic level because other 90 per cent is used for things like respiration, digestion, running away from predators.

QUESTIONS

Question. What will happen if deer is missing in the given food chain? [KVS] Grass → Deer → Tiger
(a) The population of tiger decreases and the population of grass increases.
(b) The population of grass decreases.
(c) Tiger will start eating grass.
(d) The population of tiger increases.
Answer: (a) The population of tiger decreases and the population of grass increases.

Question. The percentage of solar radiation absorbed by all the green plants for the process of photosynthesis is about: 
(a) 1 %
(b) 8 %
(c) 5 %
(d) 10 %
Answer: (a) 1 %

Question. An ecosystem comprising of producers, herbivores and carnivores is an incomplete ecosystem if it does not include:
(a) secondary consumers
(b) decomposers
(c) top carnivores
(d) secondary and tertiary consumers
Answer: (b) decomposers

Question. A correct food chain is:
(a) Producers → Carnivores → Herbivores
(b) Producers → Herbivores → Carnivores
(c) Herbivores → Producers → Carnivores
(d) Herbivores → Carnivores → Producers
Answer: (b) Producers → Herbivores → Carnivores

Question. The transfer of energy through a terrestrial ecosystem is depicted by energy pyramids. Which of the following statements is true?
(a) About 10% of the energy from one trophic level is incorporated into biomass of the next level.
(b) Only 25% of the energy in one trophic level is passed onto the next level.
(c) The energy lost as heat or in cellular respiration is 10% of the available energy of each trophic level.
(d) Ecological efficiency is highest for top consumers.
Answer: (a) About 10% of the energy from one trophic level is incorporated into biomass of the next level.

Question. DDT was accidently added to the water of a lake. All the organisms in it would be affected by DDT. Which of the organisms would be affected the most?
(a) Man
(b) Birds living near the lake
(c) Fish living in the lake
(d) Aquatic plants living in the lake
Answer: (a) Man

Question. Write the aquatic organisms in order of who eats whom starting from producer and form a chain of at least three steps. What name is given to such a chain in an ecosystem and what name is given to each stage? 
Answer: Aquatic plants (Phytoplankton) → Small aquatic animals (Zooplankton) → Small fish → Large fish. This is called an aquatic food chain. Each stage is called a trophic level.

How do Our Activities Affect the Environment?

Question. Which of the following is biodegradable?
(a) Plastic mugs
(b) Leather belts
(c) Silver foil
(d) Iron nails
Answer: (b) Leather belts are made from animal skin. They are biodegradable.

Question. Which of the following is non-biodegradable?
(a) Wool
(b) Nylon
(c) Animal bones
(d) Tea leaves
Answer: (b) Nylon is synthetic polymer. It is non-biodegradable.

Question. Which one of the following will undergo fastest bio-degradation?
(a) Mango seed
(b) Wood
(c) Mango peel
(d) Mango pulp
Answer: (d) Mango pulp

Question. Which rays strike on earth due to depletion of ozone layer?
(a) Visible light
(b) Microwaves
(c) Infrared
(d) Ultraviolet
Answer: (d) Ultraviolet. Ozone layer protects us from harmful ultraviolet radiations.

Question. Nowadays, which type of cups are being generally used in trains for serving tea, coffee, soup, etc. on daily basis?
(a) Disposable cups made of clay
(b) Washable plastic cups
(c) Washable glass cups
(d) Disposable paper cups
Answer: (d) Disposable paper cups

Question. The manufacturing of chlorofluorocarbons free refrigerators is mandatory throughout the world. How does this help prevent ozone depletion? 
(a) This will help convert oxygen molecules into ozone.
(b) This will help convert the CFCs into ozone molecules.
(c) This will reduce the production CFCs from oxygen molecules.
(d) This will reduce the release of CFCs that reacts with ozone molecules.
Answer: (d) This will reduce the release of CFCs that reacts with ozone molecules.

Question. The table lists some waste products: • Grass cutting • Polythene bags • Plastic toys • Used tea bags • Paper straw • Old clothes. Which group of waste materials can be classified as non-biodegradable? 
(a) Plant waste, tea bags
(b) Polythene bags, plastic toys
(c) Used tea bags, paper straw
(d) Old clothes, broken footwear
Answer: (b) Polythene bags, plastic toys