The Class 9 is an important year in a student’s life and Maharashtra State Board Science is one of the subjects that require dedication, hard work, and practice. It’s a subject where you can score well if you are well-versed with the concepts, remember the important formulas and solving methods, and have done an ample amount of practice. Worry not! Home Revise is here to make your Class 9 journey even easier. It’s essential for students to have the right study material and notes to prepare for their board examinations, and through Home Revise, you can cover all the fundamental topics in the subject and the complete Maharashtra State Board Class 9 Science Book syllabus.
1. Carnivores occupy the second trophic level in the food chain. Is it correct? Justify your answer.
Answer: Carnivores occupy the second trophic level in the food chain- The statement is correct. Each level in the food chain is known as a trophic level. A trophic level is the step at which the organism obtains its food in the chain. These carnivores consumers use herbivores as their food and herbivores come at the first trophic level after producers.
2. The flow of nutrients in an ecosystem is considered to be a ‘one way’ transport. Is the statement correct? Justify.
Answer: Though the energy flow in an ecosystem is one way, the flow of nutrients is cyclical. Known as bio-geo-chemical cycle, the cyclical flow of nutrients required for the organisms to grow are continuously transmitted from abiotic to biotic factors and biotic to abiotic factors within an ecosystem. This cycle functions continuously via a medium of the biosphere that is made up of the lithosphere, atmosphere and hydrosphere.
3. Are plants in an ecosystem called primary consumers? Give reason.
Answer: Plants in an ecosystem are the autotrophs (producers) that produce their own food and other organisms depend on them to get their own food.
4. Energy flow through an ecosystem is ‘one way’. Give reasons.
Answers: One of the most significant sources of energy in any ecosystem is the sun. The green plants of the ecosystem store some of that solar energy in the form of food. Then, before reaching the decomposers, this energy is transferred from trophic level to the next one. Even if the decomposers may dissipate some of the energy in the form of heat, no part of it ever returns to the sun. For this reason, the passage of energy in an ecosystem is considered as ‘one way’ transport.
5. State a reason why equilibrium is necessary in the various bio-geo-chemical cycles.
Answer: Bio-geo-chemical cycle is the cyclical flow of nutrients within an ecosystem. Within an ecosystem, the nutrients are continuously transferred from abiotic to biotic factors and biotic to abiotic factors. The recycling of biological, geological and chemical sources of nutrients is a complex process and is dependent upon the level of energy transfer in the ecosystem. Any type of disturbance at any level of these cycles can affect ecosystems and the balance of nature. So, for this reason equilibrium is necessary in the various bio-geo-chemical cycles.
6. Flow of nutrients through an ecosystem is cyclic. Justify.
Answer: Energy transmission occurs at every trophic level. Herbivores, at the first trophic level feed on plants, which are known as the producers of food. Carnivores at the second trophic level then feed on herbivores, while omnivores or the apex consumers at the 3rd trophic level get their food from other herbivores or carnivores animals. Thus, the initial quantity of energy goes on decreasing at every level of energy exchange. Now, following the death of apex consumers, their energy is made available to the decomposers. During the process of getting food from the remaining organisms, the decomposers convert them to simple carbon compounds which can easily mix with air, water and soil. They are further absorbed by plants and then incorporated into the food chain.
7. Explain the carbon cycle.
Answer : Carbon cycle is circulating and recycling the carbon from the atmosphere to the living organisms and then back to the atmosphere following their death. The abiotic carbon atoms are circulated and recycled via photosynthesis and respiration into biotic form. Therefore, the carbon cycle is a significant bio-geo-chemical cycle.
Carbon is converted to carbohydrates by the plants using photosynthesis. They also form carbon compounds such as proteins and fats, as well. Herbivores feed on these plants and carnivores use herbivores as their food. Thus, biotic carbon is transmitted to the herbivores from the plants and to the carnivores from the herbivores. This is further transported to the apex consumers from the carnivores.
Main Process in the Carbon Cycle.
Finally, following its death, every type of consumer is decomposed with the help of decomposers such as bacteria and fungi. This results in the carbon dioxide to be released again into the atmosphere, which is used by living organisms. Hence, carbon is continuously transferred to one living organism from another. On the death of the organism, carbon is released in the atmosphere.
More details to be found at Carbon Cycle .
8. How is Carbon Dioxide released into the atmosphere?
Answer: Carbon dioxide is released into the atmosphere via abiotic processes such as burning of fossil fuels and wood, forest fires and volcanic activity. Oxygen is released into the atmosphere by the biotic process like photosynthesis, while CO2 via respiration.
9. How is the equilibrium of oxygen and carbon dioxide gases in the atmosphere maintained?
Answer: The equilibrium of oxygen and carbon dioxide gases in the atmosphere is maintained by plants.
10. Explain Oxygen cycle.
Answer: Nearly 21% of the atmosphere is made up of Oxygen. Oxygen can also be found in the hydrosphere and lithosphere. Oxygen cycle means to circulate and recycle oxygen within the biosphere including both the biotic and abiotic components. Oxygen that is continuously generated is also utilised in the atmosphere. It is also very reactive and it reacts quickly with the other compounds and elements. Meanwhile, for the reason that oxygen is available in several forms such as molecular oxygen (O2), water (H2O), carbon dioxide (CO2), inorganic compounds, and so on, the oxygen cycle of the biosphere is extremely complex. Now, during the process of photosynthesis, oxygen is released and then used up in processes such as combustion, corrosion, respiration, decomposition, rusting and more.
To find more about Oxygen cycle with diagram.
11. What are aerobes and anaerobes?
Answer: Aerobes are the microorganisms that use oxygen for respiration, while anaerobes are the microbes that do not need oxygen.
12. What is Oxygen used for?
Answer: Oxygen is used for the synthesis of fats, carbohydrates and proteins and also in several chemical reactions. Meanwhile, Ozone (O3) is formed from oxygen by using several atmospheric processes, Some microorganisms even use it for respiration.
13. Explain the nitrogen cycle.
Answer: Maximum portion, that is almost 78% of the atmosphere is made up of Nitrogen, which is required for the maintenance of the cycle of nature. Nitrogen cycle is the circulation and the recycling of the nitrogen gas into different compounds via several biotic and abiotic processes. Every organism takes part in the nitrogen cycle. It is a very significant component of the nucleic acids and the proteins, but in comparison to other elements, it is inactive and does not combine easily with other elements. Free form of nitrogen cannot be used by most of the microorganisms. Given below are some of the important processes of the nitrogen cycle:
1. Nitrogen fixation: Converting nitrogen into nitrates and nitrites using processes that are biological, atmospheric and industrial.
2. Ammonification: Releasing ammonia via excretory wastes of organisms and decomposition of dead bodies.
3. Nitrification: Converting ammonia into a nitrite and further to nitrate.
4. Denitrification: Converting nitrogen compounds into nitrogen that is gaseous.
Details with the image about the Nitrogen cycle are here.
14. How is nitrogen present in the atmosphere?
Answer: It is seen that nitrogen is found in the form of a gas in the atmosphere, while it is present in the form of compounds such as nitrogen oxide in the soil and sediments.
15. Explain the presence of carbon.
Answer: Carbon is present in the earth’s crust in the abiotic form, chiefly in granite, limestone, diamond, coal and more, while in the atmosphere it is present as carbon dioxide gas. Carbon occurs in plants and animals for a shorter duration than in coal.
16. What are the types of bio-geo-chemical cycles?
Answer: There are two types of bio-geo-chemical cycles such as gaseous cycle and sedimentary cycle. Gaseous cycle is faster than the sedimentary cycle.
| Gaseous cycle | Sedimentary cycle |
| On the atmosphere of the earth the main abiotic gaseous nutrient materials have accumulated | On the soil, sediment and sedimentary rocks and more of the earth the main abiotic nutrient materials is found |
| I t consists of carbon dioxide, nitrogen, water vapour, oxygen and so on | It includes soil components such as phosphorus, iron, calcium and more |
17. What is The Indian Institute of Ecology and Environment, Delhi?
Answer: Set up in 1980, in Delhi, The Indian Institute of Ecology and Environment, is responsible for training, conducting workshops and seminars, research and so on. The International Encyclopaedia of Ecology and Environment has also been published by the institute.
18. Illustrate the pyramid of energy in an aquatic ecosystem.
Answer:
19. What is a pyramid of energy?
Answer: Energy transfer occurs at each trophic level. In the food chain, various levels of energy exchange are taking place. At every level of energy transfer, the original quantity of energy decreases. Likewise, the number of organisms also reduces from the lowest level to the highest level. This pattern of energy exchange is termed a ‘Pyramid of energy’.
20 Who are the primary consumers in an ecosystem?
Answer: The primary consumers of the ecosystem are the herbivores, which are directly dependent on the autotrophs (producers) like plants for food. Examples are Grasshopper, Squirrel, Elephant and more.
21. Who are apex or top consumers?
Answers: Apex consumers or top consumers are those who feed on the herbivores and carnivores as their food. No animals will feed on these top consumers. Examples are Tiger, Lion and so on.
22. Who are Omnivores?
Answer: Omnivores are mixed consumers who feed on both the herbivores and carnivores. Examples are Human, Bear and more.
23. What is the food web?
Answer: An organism can be food for many organisms. Take the example of an insect that feeds on leaves of various plants, but is in fact the food for various animals such as wall lizard, frogs, birds and so on. Now, the image illustrating this would represent an intricate web as an alternative to a liner food chain. This intricate network is known as a ‘Food Web’. Food Webs are seen everywhere in nature.
24. Who proposed the concept of the Ecological Pyramid in 1927? Why is it called Eltonian Pyramid?
Answer: A British Scientist, Charles Elton in 1927 first put forward the concept of the Ecological Pyramid, after studying the Tundra Ecosystem of the Beer islands in England. So, the pyramid came to be called the Eltonian Pyramid.
25. Each level in the food chain is a trophic level. Who is found at the third trophic level?
Answers: The omnivores are found at the topmost level, that is the third trophic level in the food chain. Omnivores feed on both herbivores and carnivores.