How Nature Works in Harmony — Class 8 Science
Curiosity · Chapter 12
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6- Mathematics
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- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
2- Mathematics
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
- Space weighted by chapter size
- Charts from the book's own data
- Traps corrected
Chapter summary
Key ideas & terms
- Habitat
- The place that provides an organism with the conditions it needs to live and grow.
- Ecosystem
- A unit formed by the interaction of biotic components with the abiotic components in an area.
- Producer
- An organism, such as a green plant, that makes its own food by photosynthesis; also called an autotroph.
- Decomposer
- An organism, such as fungi or bacteria, that breaks down dead matter and recycles nutrients; also called a saprotroph.
- Food web
- A network of interlinked food chains showing the many feeding relationships in an ecosystem.
- Mutualism
- A relationship in which both interacting organisms benefit, such as honeybees and flowers.
Extra questions & answers
What are the biotic and abiotic components of a habitat?
Biotic components are the living things such as plants, animals, and microbes; abiotic components are non-living things such as air, water, soil, sunlight, and temperature.
How are population, community, and ecosystem related?
A population is one kind of organism in a habitat, a community is several populations sharing a habitat, and an ecosystem is a community interacting with its abiotic surroundings.
What is the difference between producers and consumers?
Producers make their own food by photosynthesis, while consumers cannot make their own food and depend on other organisms for it.
Classify organisms by what they eat.
Herbivores eat only plants, carnivores eat only animals, and omnivores eat both plants and animals.
What is the role of decomposers in an ecosystem?
Decomposers break down dead plants and animals into simpler substances, returning important nutrients to the soil.
What is the difference between a food chain and a food web?
A food chain is a single sequence of who eats whom, while a food web is a network of many interlinked food chains.
What is a trophic level?
The specific feeding position an organism occupies in a food chain, such as producers at the first level and herbivores at the second.
Give one example each of mutualism, commensalism, and parasitism.
Mutualism: honeybees and flowers; commensalism: orchids on trees; parasitism: ticks on a dog.
How do human activities threaten ecosystems like the Sundarbans?
Activities such as cutting mangroves, illegal hunting, overuse of resources, and pollution damage habitats and endanger wildlife.
Why is sustainable farming important?
Overuse of synthetic fertilisers and pesticides and growing a single crop harm soil health and biodiversity, so eco-friendly methods are needed to protect them.
Probe and ponder
How might the loss of forest cover and changes in rainfall patterns lead to elephants to enter human farms and villages?
Loss of forest cover removes the elephants’ food, shelter and shade, and reduced or irregular rainfall dries up waterholes and reduces plant growth inside the forest. When their natural habitat cannot provide enough food and water, elephants follow scent and memory to nearby farms and villages where crops like banana and sugarcane and stored water are available, leading to crop raiding and human-elephant conflict.
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?
As a tree I would depend on abiotic components like sunlight for photosynthesis, water and nutrients from soil, and air for respiration. I would give shelter, food, nesting sites and oxygen to birds, insects, monkeys and squirrels, interact with pollinators and seed dispersers, provide shade and humid microclimate, hold soil with roots, and exchange nutrients with microbes and fungi in the soil.
Do you think the Earth can thrive without humans? Can humans survive without the Earth?
Yes, the Earth thrived for billions of years before humans and can maintain its ecosystems, water cycles and biodiversity without humans. Humans, however, cannot survive without the Earth because we depend completely on its air, water, soil, food, climate regulation and other ecosystem services for survival.
If two kinds of birds compete for the same fruit, how might their way of living change over time?
Competition for the same fruit creates pressure to use resources differently. Over time the two kinds of birds may adapt to eat fruits at different times, at different heights, in different parts of the forest, or shift to other foods or feeding techniques. This reduces direct competition and allows both to coexist, which is a form of resource partitioning.
Can human actions cause natural disasters?
Human actions do not directly create natural processes but can increase their frequency and intensity. Deforestation, wetland destruction, uncontrolled construction, over-extraction of groundwater and climate change from greenhouse gas emissions can worsen floods, droughts, landslides, soil erosion and storms, and make their impacts on people far more severe.
Share your questions
Student-generated questions could include: Why do elephant corridors need to be protected? How do trees help bring rainfall? What will happen if pollinators disappear from my neighbourhood?
Keep the curiosity alive
1. 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.
The wrong statement is (iii) An ecosystem is part of a community. In reality, a population is a group of one kind of organism at a place and time, a community comprises many interacting populations, and an ecosystem includes the community plus its abiotic components like air, water, soil and sunlight. As shown in Fig. 12.19 with nested circles of Population inside Community inside Ecosystem, the ecosystem is the largest level, not a part of the community. Statements (i) and (ii) are correct.
2. A population is part of a community. If all decomposers suddenly disappear from a forest ecosystem, what changes do you think would occur? Explain why decomposers are essential.
If decomposers like fungi and bacteria disappear, dead leaves, dead animals and animal droppings would pile up and not be broken down. Nutrients locked in dead matter would not return to the soil, so soil fertility and humus would fall, plant growth would weaken, and food for herbivores and carnivores would decline. Decomposers are essential because they recycle nutrients, clean the environment and keep the cycle of matter running, showing that nothing is wasted in nature.
3. 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?
Yes, mangroves protected Selvam’s village. Mangrove forests like those in the Sundarbans have dense stilt roots and trunks that act as a natural barrier. They absorb and break the energy of strong winds and waves, reduce flooding and erosion, and trap water and debris during storms and tsunamis. Villages behind intact mangroves therefore suffer less damage than exposed villages, which is why UNESCO values such ecosystems for protection and they must be conserved.
4. 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?
If frogs disappear, grasshoppers which are eaten by frogs will increase because their predator is gone. Snakes which feed on frogs will decrease or be forced to find alternative prey or move away because their food source is lost. This shows how a change at one trophic level creates cascading effects through the food chain.
5. 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?
Possible reasons are loss of nectar flowering plants, use of pesticides that kill caterpillars and butterflies, mowing or clearing of host plants, air pollution and loss of sunlight or water, and fewer places for egg-laying. Students can plant diverse native flowering plants that bloom in different seasons, avoid pesticides, grow caterpillar host plants, provide shallow water and sunny sheltered corners, and maintain a pesticide-free butterfly patch.
6. Why is it not possible to have an ecosystem with only producers and no consumers or decomposers?
An ecosystem needs all roles to cycle matter and energy. Producers make food and oxygen, but without consumers the food would not flow to higher levels and populations would not be controlled. Without decomposers, dead producer material would accumulate and nutrients would remain locked, so soil would lose fertility and producers could not continue to grow. The recycling of nutrients by consumers and decomposers is necessary to sustain the ecosystem.
7. 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?
Example park: biotic - grass, neem or peepal trees, squirrels, sparrows, bees, earthworms; abiotic - soil, sunlight, air, watered soil, leaf litter. Roadside: biotic - few weeds, pigeons, stray dogs, microbes; abiotic - concrete, dust, polluted air, more heat, less water, hard soil. The park is more biodiverse, cooler, moist and fertile with many interactions, while the roadside is disturbed, polluted and supports fewer species.
8. ‘Human-made ecosystems like agricultural fields are necessary, but they must be made sustainable.’ Comment on the statement
Human-made ecosystems like farms, ponds and parks are needed to grow food and support livelihoods for a large population. However, intensive unsustainable practices such as monoculture, overuse of synthetic fertilisers and pesticides, excessive groundwater extraction and repeated ploughing degrade soil, kill friendly microbes and natural predators, reduce biodiversity and harm health. Sustainable practices like crop rotation, organic manure such as Kunapa Jala and compost, natural pest control, conserving soil moisture and protecting pollinators keep productivity while protecting soil, water and ecosystems for the future.
9. If the Indian hare population (Fig. 12.20) drops because of a disease, how would it affect the number of other organisms? Fig. 12.20: Parts of a food web Sun Grass and plants Hare Fox Deer Eagle
In the food web (Fig. 12.20) the hare is a herbivore eaten by the fox; the eagle preys on the deer, not the hare. If hares decline sharply, the foxes that depend on them lose a food source and may decline or shift to other prey. With fewer hares grazing, the grass/plants they ate may increase. The change ripples through the web — predators of the hare are most affected, while organisms not linked to the hare are affected only indirectly.
Discover, 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?
On a clean-up we commonly find plastic wrappers, chips packets, plastic bottles, paper and polythene bags, with plastic wrappers usually the most common. We can reduce this waste by refusing single-use plastic, using cloth bags and steel bottles, segregating waste, reusing paper, composting organic litter and creating awareness posters to encourage everyone to put waste in bins.
In Arunachal Pradesh, the Nyishi and Mishmi tribes treat the Tiger as sacred. In Chhattisgarh, the Baiga tribe worships the Bagesur Dev and believes the Tiger is the protector of the forest. Find out about other Indian tribes that have a special connection with animals.
Many tribes live in harmony with animals. The Bishnoi of Rajasthan protect blackbuck and peafowl, the Warli of Maharashtra respect the tiger and forest spirits, the Toda of Nilgiris revere the buffalo, and the Soliga of Karnataka protect elephants and tigers of Biligiri Rangana Hills. Such cultural beliefs help conserve wildlife and habitats.
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.
Choose a neem or mango tree and prepare a table with date, new leaves, buds, flowers, fruits and visitors. For example Week 1: young light-green leaves and bees visiting; Week 2: small flower buds and butterflies; Week 3: open flowers and sparrows; Week 4: tiny fruits and caterpillars. Regular recording shows seasonal changes and helps in citizen science on www.seasonwatch.in.
Interact with farmers and record indigenous practices followed by them for sustainable farming. Create a sustainable herbal garden/natural farm at home or at school. It could be a group activity with students from different grades.
Farmers often use crop rotation, intercropping, compost and Kunapa Jala, neem-based organic pest repellents, mulching and rainwater harvesting. Students can create a small herbal garden with tulsi, mint, coriander and aloe using compost from kitchen waste, avoiding synthetic chemicals, watering carefully and involving different grades to maintain and observe biodiversity.
Look at Fig. 12.21 to understand the different farming practices adopted by farmers or you may also visit a nearby farm with an elderly person to observe the same. List a few suggestions in your notebook to improve farming practices by adopting eco-friendly and sustainable techniques. You can also make posters or model and display while participating in school functions, science fairs or Krishi Mela. The school may also invite agricultural scientists, farmers, and experts to discuss the prevalent farming practices with the students.
Suggestions include: use organic manure and compost instead of only synthetic fertilisers, practise crop rotation and mixed cropping to maintain soil health, use biological pest control with natural predators like ladybird beetles, conserve water with drip irrigation and rainwater harvesting, avoid monoculture and protect field borders with trees. These can be shown on posters or models and discussed with invited farmers and scientists at a Krishi Mela.