How Nature Works in HarmonyClass 8 Science NCERT Solutions
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Solution 1 of 17
Q1Discover, design, and debate
Plan a clean-up day at school or a nearby park. Wearing gloves and using bags, collect the litter you find. Discuss the kinds of waste you found. Which was the most common? How can we reduce such waste?
Solution
This is a plan for an activity. A possible outcome and discussion would be:
Plan:
- Organize a group of students and get permission from the school or local authorities.
- Arrange for safety gear (gloves) and materials (trash bags for different types of waste - recyclable and non-recyclable).
- Conduct the clean-up, carefully collecting and sorting the litter.
Discussion after Clean-up:
- Kinds of waste found: We would likely find plastic wrappers (chips, candy), plastic bottles, paper cups, straws, glass bottles, and food waste.
- Most common waste: The most common type of waste would probably be single-use plastics, such as food wrappers and beverage bottles, because they are widely used and do not decompose.
- How to reduce such waste:
- Reduce: The best way is to reduce the creation of waste in the first place. We can do this by using reusable water bottles, lunch boxes, and shopping bags instead of disposable ones.
- Reuse: Find new purposes for items instead of throwing them away.
- Recycle: Ensure proper waste segregation so that recyclable materials like plastic bottles, paper, and glass can be processed and made into new products.
- Awareness: Create posters or hold assemblies to educate other students and community members about the negative impact of littering and the importance of reducing single-use plastic consumption.
Q2Discover, design, and debate
In Arunachal Pradesh, the Nyishi and Mishmi tribes treat the Tiger as sacred. In Chhattisgarh, the Baiga tribe worships Bagheshwar or Bagesur Dev and believes the Tiger is the protector of the forest. Find out about another Indian tribe that has a special bond with any animal.
Solution
Another prominent example of an Indian community with a special bond with an animal is the Bishnoi community of Rajasthan.
- Community: The Bishnois.
- Animal: The Blackbuck (a type of antelope) and other wildlife, including the Chinkara and various birds.
- Special Bond: The Bishnoi faith, founded by Guru Jambheshwar, is based on 29 principles, many of which advocate for the protection of nature and compassion for all living beings. They consider the felling of green trees and the killing of animals to be a grave sin. The Blackbuck is held as particularly sacred. The Bishnois are renowned for their conservation efforts and have a long history of protecting wildlife from hunters, often at the risk of their own lives. This deep-rooted reverence makes them one of India's most dedicated conservationist communities.
Q3Discover, design, and debate
Pick a tree near your home or school. Observe it once a week for 4 weeks. Note any new leaves, flowers, fruits, or visiting birds and insects. Record your observations. You may even upload your findings to www.seasonwatch.in and become a young citizen scientist.
Solution
This is an observational activity. Here is a sample observation log for a Neem tree over four weeks.
Name of Tree: Neem Tree
Location: School Playground
Observation Log:
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Week 1: The tree has a full canopy of dark green, serrated leaves. There are no visible flowers or fruits. I observed several ants crawling up the trunk. A crow was perched on one of the higher branches for a few minutes.
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Week 2: I noticed some clusters of tiny, white, star-shaped flowers starting to bloom. They have a faint, sweet smell. There were a few bees buzzing around these new flowers. I also saw a squirrel running along a thick branch.
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Week 3: Many more flowers have opened up, and the sweet fragrance is stronger. The number of bees and other small flying insects around the flowers has increased significantly. Some of the older flowers seem to be wilting and falling off.
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Week 4: Most of the flowers have now fallen off. In their place, I can see tiny green, oval-shaped structures forming. These are the young, unripe Neem fruits (nimboli). The number of visiting insects has reduced. A pair of sparrows were chirping from within the leafy branches.
Q1Introductory Questions
How might the loss of forest cover and changes in rainfall patterns lead to elephants to enter human farms and villages?
Solution
Based on the provided text, the reasons are as follows:
- Scarcity of Food and Water: The loss of forest cover due to deforestation for roads and buildings, combined with changes in rainfall patterns, leads to a shortage of vegetation and the drying up of waterholes in the elephants' natural habitat.
- Search for Resources: When their natural resources become scarce, elephants are forced to wander into nearby human-inhabited areas, such as farms and plantations, in search of alternative food sources like bananas and sugarcane, and water.
- Habitat Shrinkage: The overall shrinking and drying of forests means there is not enough space or resources to support the wildlife population, compelling animals like elephants to move into human habitats to survive.
Q2Introductory Questions
Imagine you are a tree in a dense forest. What kind of relationships would you have with water, sunlight, other animals, and other components of the forest?
Solution
If I were a tree in a dense forest, my relationships would be:
- With Water: I would absorb water from the soil through my roots. Water is essential for me to perform photosynthesis and transport nutrients. My roots would also help hold the soil together and retain moisture in the ground, benefiting the entire ecosystem.
- With Sunlight: I would use sunlight as an energy source to make my own food through photosynthesis. In a dense forest, I would compete with other trees to grow tall and reach the sunlight.
- With Other Animals: I would be a habitat and a source of food for many animals. Birds and squirrels might build nests in my branches. Insects, bees, and butterflies would visit my flowers for nectar, helping in pollination. Herbivores like deer might eat my leaves or bark. In return, animals would help disperse my seeds to new areas.
- With Other Components of the Forest:
- Soil: I would be anchored in the soil and draw essential nutrients from it. My fallen leaves and branches would be broken down by decomposers, enriching the soil.
- Air: I would take in carbon dioxide from the air for photosynthesis and release oxygen, which is vital for almost all other living beings.
- Other Plants: I would compete with other trees and plants for sunlight, water, and soil nutrients. My presence would also create shade, influencing which smaller plants can grow beneath me.
- Fungi and Microbes: I would have a relationship with microorganisms in the soil. Some fungi (mycorrhizae) might live on my roots, helping me absorb more nutrients, while decomposers would break down my dead parts, recycling nutrients back into the ecosystem.
Q3Introductory Questions
Do you think the Earth can thrive without humans? Can humans survive without the earth?
Solution
Based on the principles discussed in the text:
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Can the Earth thrive without humans? Yes, the Earth could likely thrive, and in many ways, recover without humans. The text highlights that human activities such as deforestation, pollution, and overuse of resources disrupt the natural balance of ecosystems (e.g., the Sundarbans). Without these pressures, ecosystems would have the chance to restore their balance, biodiversity would likely increase, and natural cycles would function without interference.
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Can humans survive without the Earth? No, humans absolutely cannot survive without the Earth. The text explicitly states that humans benefit from ecosystems in countless ways. We depend on the Earth for essential resources such as:
- Clean air and water
- Food and medicines
- Fertile soil for agriculture
- Raw materials like timber and fibres
- Climate regulation Our survival is fundamentally linked to the health and resources of the planet's ecosystems.
Q4Introductory Questions
If two kinds of birds compete for the same fruit, how might their way of living change over time?
Solution
When two kinds of birds compete for the same fruit, their ways of living might change over time to reduce this competition. This is a key aspect of how ecosystems maintain balance. Possible changes include:
- Niche Partitioning: The birds might adapt their behaviors. For example, one species might start feeding in the morning while the other feeds in the afternoon. Or, one might feed on fruits at the top of the tree, and the other on fruits on lower branches.
- Dietary Shift: One of the bird species might gradually shift its diet to include other food sources, such as different types of fruits, seeds, or insects, reducing its dependence on the fruit they are competing for.
- Competitive Exclusion: If one species is much better at getting the fruit, it might outcompete the other species. The less successful species could see its population decline in that area or be forced to migrate to a different habitat where the fruit is more accessible or there is less competition.
- Character Displacement: Over many generations, the two species might evolve physical differences. For example, they could develop slightly different beak sizes or shapes, allowing each to specialize in eating fruits of a particular size or hardness, thereby reducing direct competition.
Q5Introductory Questions
Can human actions cause natural disasters?
Solution
Yes, while human actions may not create the natural event itself (like a cyclone or an earthquake), they can significantly increase the severity and impact of these events, effectively turning them into major disasters. The text provides examples:
- Increased Flood and Storm Damage: The text mentions that the Sundarbans mangrove forests protect coastal areas by slowing down strong winds and waves. Deforestation of these mangroves, a human action, removes this natural barrier. This makes coastal communities much more vulnerable to the destructive power of storms and tsunamis, increasing loss of life and property.
- Landslides: Cutting down trees on hillsides (deforestation) weakens the soil. The roots of trees help hold the soil in place. Without them, heavy rainfall can easily wash the soil away, leading to devastating landslides.
Therefore, human activities that disrupt ecosystems can greatly worsen the impact of natural phenomena, causing what are often referred to as 'human-induced natural disasters'.
Q1Keep the curiosity alive
Refer to the given diagram (Fig. 12.19) and select the wrong statement.
(i)
A community is larger than a population.
(ii)
A community is smaller than an ecosystem.
(iii)
An ecosystem is part of a community. 2. A population is part of a community.
Solution
Analysis of Ecological Levels:
The text and the standard ecological hierarchy describe the levels of organization as follows:
- Population: A group of organisms of the same species living in the same area (e.g., all the fish of one kind in a pond).
- Community: All the different populations of different species living and interacting in the same area (e.g., all the fish, frogs, plants, and insects in a pond).
- Ecosystem: The community of living organisms (biotic components) interacting with their non-living environment (abiotic components like water, soil, sunlight).
Evaluating the Statements:
- (i) A community is larger than a population. This is correct. A community consists of many different populations.
- (ii) A community is smaller than an ecosystem. This is correct. An ecosystem includes the community plus all the non-living factors.
- (iii) An ecosystem is part of a community. This is incorrect. The community is a part of the ecosystem, not the other way around.
- The text for this option seems to have a typo and likely meant to list (iv). Assuming the fourth statement is "A population is part of a community." This is correct. A community is made up of various populations.
Final Answer: The wrong statement is (iii) An ecosystem is part of a community.
Q2Keep the curiosity alive
If all decomposers suddenly disappear from a forest ecosystem, what changes do you think would occur? Explain why decomposers are essential.
Solution
Changes that would occur if decomposers disappeared:
- Accumulation of Dead Organic Matter: Dead plants, animals, and waste products would not rot or decay. The forest floor would become covered in a thick layer of dead leaves, fallen trees, and animal carcasses.
- Nutrient Depletion: The nutrients (like nitrogen, phosphorus, etc.) contained within this dead organic matter would remain locked up and would not be returned to the soil.
- Loss of Soil Fertility: Without the recycling of nutrients, the soil would quickly become infertile. Plants would not be able to get the essential nutrients they need to grow.
- Collapse of the Food Web: As plants struggle to grow and die off due to nutrient shortages, the herbivores that depend on them for food would starve. This would be followed by the starvation of carnivores that feed on herbivores. The entire ecosystem would eventually collapse.
Why Decomposers are Essential:
Decomposers, such as bacteria and fungi, are essential because they are nature's recyclers. As the text states, they "break down complex substances in dead plants and animals into simpler ones. This process returns important nutrients to the soil." This process of decomposition is vital for:
- Nutrient Cycling: They ensure that essential nutrients are continuously made available for producers (plants) to use, thus sustaining the entire ecosystem.
- Cleaning the Environment: They prevent the build-up of dead organic waste, keeping the habitat clean.
Q3Keep the curiosity alive
Selvam from Cuddalore district, Tamil Nadu, shared that his village was less affected by the 2004 Tsunami compared to nearby villages due to the presence of mangrove forests. This surprised Sarita, Shabnam, and Shijo. They wondered if mangroves were protecting the village. Can you help them understand this?
Solution
Yes, the mangrove forests were indeed protecting Selvam's village. Here is an explanation based on the information in the text:
- Natural Barriers: Mangrove forests grow along coastlines and have a very dense and complex network of roots and trees. This structure acts as a natural shield or barrier.
- Energy Absorption: When a large wave, like a tsunami, approaches the coast, the mangrove forest absorbs a significant amount of its energy. The trunks, branches, and roots slow the water down and reduce the height and force of the waves before they can reach the land behind them.
- Protection for Coastal Communities: As the text mentions in the context of the Sundarbans, mangroves "protect us by slowing down strong winds and waves during storms and floods." By acting as a buffer zone, they significantly reduce the potential for destruction, flooding, and loss of life in coastal villages like Selvam's. Villages without this natural protection would have faced the full, devastating force of the tsunami waves.
Q4Keep the curiosity alive
Look at this food chain: Grass ⟶ Grasshopper ⟶ Frog ⟶ Snake If frogs disappear from this ecosystem, what will happen to the population of grasshoppers and snakes? Why?
Solution
If frogs disappear from this food chain, it will disrupt the balance and affect the populations of both grasshoppers and snakes.
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Effect on the Grasshopper Population:
- What will happen: The population of grasshoppers will likely increase significantly.
- Why: In this food chain, frogs are the primary predators of grasshoppers. Without frogs to eat them, there would be fewer threats to the grasshoppers, allowing them to reproduce and multiply with less control.
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Effect on the Snake Population:
- What will happen: The population of snakes will likely decrease.
- Why: Frogs are the main source of food for snakes in this particular food chain. With the disappearance of frogs, the snakes will lose their food supply. This would lead to starvation and a decline in the snake population. Some snakes might migrate to other areas in search of food, but the local population would suffer.
Q5Keep the curiosity alive
In a school garden, students noticed fewer butterflies the previous season. What could be the possible reasons? What steps can students take to have more butterflies on campus?
Solution
Possible Reasons for Fewer Butterflies:
- Lack of Food Source: There might have been fewer flowering plants that produce the nectar butterflies feed on.
- Use of Pesticides: The use of chemical pesticides in the garden to control pests could have unintentionally harmed or killed the butterflies, their caterpillars, or their eggs.
- Absence of Host Plants: Butterflies lay their eggs on specific types of plants called host plants, which the caterpillars eat after hatching. If these plants were removed, butterflies would not be able to reproduce in the garden.
- Increase in Predators: An increase in the population of butterfly predators, such as birds or dragonflies, could have led to a decline in their numbers.
- Habitat Loss: Changes in the garden, such as removing patches of native plants or weeds that butterflies use for shelter and breeding, could reduce their population.
Steps to Attract More Butterflies:
- Plant Nectar-Rich Flowers: Students can plant a variety of native, colorful flowers that are known to attract butterflies. Planting them in sunny spots is ideal.
- Avoid Pesticides: Use natural and organic methods for pest control to ensure the garden is a safe environment for butterflies and other pollinators.
- Include Host Plants: Research and plant the specific host plants for local butterfly species to encourage them to lay their eggs and complete their life cycle in the garden.
- Provide Water: Create a "butterfly puddler" by filling a shallow dish with sand or soil and keeping it moist. Butterflies land on these spots to drink water and absorb minerals.
- Create Shelter: Leave some areas of the garden a bit wild with native grasses or shrubs to provide shelter for butterflies from wind and predators.
Q6Keep the curiosity alive
Why is it not possible to have an ecosystem with only producers and no consumers or decomposers?
Solution
An ecosystem cannot be sustained with only producers (like plants) for two critical reasons related to the roles of consumers and decomposers:
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Role of Decomposers (Nutrient Cycling): This is the most critical reason. Producers obtain nutrients from the soil to grow. When these producers die, if there were no decomposers (like bacteria and fungi), their bodies would not break down. All the essential nutrients they absorbed during their life would remain locked within their dead matter. The soil would not be replenished with these nutrients, would become infertile, and eventually, no new producers could grow. The ecosystem would collapse due to a lack of nutrient recycling.
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Role of Consumers (Energy Transfer and Population Control): While less critical than decomposers for nutrient cycling, consumers play important roles. They help transfer energy through the ecosystem. Herbivores control the population of producers, preventing them from overgrowing and exhausting resources like water and space. Carnivores, in turn, control the populations of herbivores. This system of checks and balances helps maintain the stability of the ecosystem.
Q7Keep the curiosity alive
Observe two different places near your home or school (e.g., a park and a roadside). List the living and non-living components you see. How are the two ecosystems different?
Solution
Here is a comparison of two common ecosystems: a park and a roadside.
Ecosystem 1: A Park
- Living (Biotic) Components: Trees, grass, shrubs, flowering plants, birds, squirrels, butterflies, bees, ants, earthworms, microorganisms in the soil.
- Non-living (Abiotic) Components: Soil, sunlight, air, water (from rain or irrigation), rocks, benches, pathways.
Ecosystem 2: A Roadside
- Living (Biotic) Components: Hardy weeds, some patches of grass, ants, flies, perhaps some bacteria adapted to polluted conditions.
- Non-living (Abiotic) Components: Asphalt/concrete, gravel, compacted and often polluted soil, air containing vehicle exhaust fumes, sunlight, rainwater runoff.
How the Two Ecosystems are Different:
- Biodiversity: The park has a much higher biodiversity, meaning a greater variety of living organisms. The roadside has very low biodiversity, with only a few resilient species able to survive the harsh conditions.
- Health of Abiotic Components: The park's abiotic components (soil, air, water) are generally healthier and cleaner. The roadside's components are heavily impacted by human activity, with polluted air and soil, and less water retention.
- Complexity of Interactions: The park is a complex ecosystem with many interactions between its biotic and abiotic parts (e.g., pollination, seed dispersal, decomposition). The roadside is a much simpler, highly disturbed ecosystem with fewer and less stable interactions.
- Stability: The park ecosystem is more stable and balanced. The roadside ecosystem is unstable and constantly disturbed by traffic and pollution.
Q8Keep the curiosity alive
'Human-made ecosystems like agricultural fields are necessary, but they must be made sustainable.' Comment on the statement
Solution
This statement is accurate. Here's a comment based on the information in the text:
Why Agricultural Fields are Necessary:
Human-made ecosystems like farms are essential for human survival. As the global population has grown, we have become heavily dependent on agriculture to produce the vast quantities of food needed to feed everyone. They are the foundation of our food security.
Why They Must be Made Sustainable:
However, the text points out that modern farming methods, while increasing food production (the Green Revolution), are often unsustainable. Practices like:
- Overuse of synthetic fertilizers and pesticides: These can degrade soil health by killing beneficial microorganisms, reduce organic matter, and pollute water. Pests can also develop resistance.
- Excessive groundwater extraction: This can deplete water resources.
- Monoculture (growing only one crop): This reduces biodiversity, affects pollinators crucial for food production, and makes crops more vulnerable to pests and diseases.
To be sustainable means meeting our present needs without compromising the ability of future generations to meet their own. Sustainable farming practices, such as organic and natural farming, aim to work in harmony with nature. They focus on:
- Improving soil health using organic manure (like the Vrikshayurveda example of Kunapa Jala).
- Using natural predators to control pests.
- Conserving water and preventing soil erosion.
By adopting these methods, we can ensure that our farms remain productive for generations to come without causing long-term damage to the environment.
Q9Keep the curiosity alive
If the Indian hare population (Fig. 12.20) drops because of a disease, how would it affect the number of other organisms?
Solution
A food web shows that organisms are interconnected, and a change in one population can affect many others. Although the specific food web is not shown, based on the principles in the text, a drop in the Indian hare population would have the following effects:
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Effect on Predators: The Indian hare is a herbivore (primary consumer). The predators that feed on the hare (secondary consumers like foxes, eagles, or snakes) would be directly affected.
- Their primary food source would become scarce.
- This could lead to a decrease in the predator populations due to starvation or reduced reproduction.
- Alternatively, these predators might increase their hunting of other prey (like mice or squirrels), which would put more pressure on those populations.
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Effect on Plants (Producers): The Indian hare eats plants like grass.
- With fewer hares to eat them, the population of the specific plants that hares feed on might increase due to reduced grazing pressure.
This chain reaction demonstrates the interconnectedness of a food web. The decline of a single species like the hare can cause ripple effects, leading to population changes in both the trophic levels above (predators) and below (plants) it.