CLASS 10 SCIENCE · CHAPTER 13 · STUDY NOTES
Our Environment
A comprehensive study of ecosystems, energy flow, biological magnification, and the human impact on the environment through ozone depletion and waste management.
EXPLORE
Explore a living system, not a list of animals
Connect organisms, surroundings and nutrient recycling.LOOK AT THE LIVING WORLD
Living things depend on a non-living world.
- Ecosystem
- Interacting organisms in an area together with their non-living surroundings.
| What to distinguish | Meaning |
|---|---|
| Living components | Organisms in the ecosystem |
| Physical surroundings | Water, light, temperature and minerals |
A pond includes living components—plants, animals and microorganisms—and physical surroundings such as water, light, temperature and minerals. Both belong to the ecosystem.
Producers make organic food from inorganic materials using light; consumers obtain food from organisms. Bacteria and fungi decompose remains, releasing simple substances that producers can use again.
Go deeper: Recycling matter does not recycle energy
Decomposers obtain energy from dead organic matter while breaking it down. The returned mineral nutrients can enter new plant growth; energy already dissipated as heat does not return as usable food energy.
Forests and ponds are natural ecosystems; crop fields, gardens and aquariums are human-made. Human-made does not mean lifeless, and natural does not mean immune to disturbance. An aquarium’s organisms and oxygen supply still need suitable conditions and care.
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Question
A learner labels only the fish and plants as “the pond ecosystem”. What important part of the system has been left out?
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EXPLORE
Follow food through a chain and a web
Read feeding arrows and pathway-dependent trophic positions.LOOK AT THE LIVING WORLD
Follow the food—and the direction of energy.
The arrow points from the food to the organism that eats it.
- Trophic level
- A feeding position along a particular food-chain pathway.
An arrow runs from food to the organism that eats it. In the illustrated grass → grasshopper → frog → snake pathway, the producer is level 1 and the three consumer positions are levels 2, 3 and 4.
A food web connects possible feeding pathways. Consumers include herbivores, carnivores, omnivores and parasites; an omnivore can occupy different trophic positions depending on what it eats.
Go deeper: A feeding link is not a guaranteed population outcome
A bird that eats plant material uses a shorter pathway than one that eats a plant-eating insect. The web therefore represents feeding relationships, not an identical route taken by every individual.
Removing a species can change both its consumers’ food and its prey’s exposure to predation. Alternative links can matter, but a diagram alone cannot guarantee stability or calculate population changes. Decomposers also receive dead material from many levels, not only the final consumer.
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Question
In the web, a bird eats plant material in one meal and a grasshopper in another. Must both meals place it at the same trophic level?
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EXPLORE
Compare energy before and after a transfer
Calculate the ten-percent model and distinguish energy from nutrients.LOOK AT THE LIVING WORLD
Less energy is available at every transfer.
10,000 J × 0.10 = 1,000 J for the next level.
- Ten-percent transfer model
- A simplified average in which about 10% of one trophic level’s available energy reaches the next.
Producers convert part of incoming sunlight into chemical energy. The source gives about 1% capture for light falling on leaves in a terrestrial example; this is different from the roughly 10% transfer between feeding levels.
Use the slider to change producer energy. Assuming 10% at each transfer, 10,000 J becomes 1,000 J, then 100 J, then 10 J. Energy flow is one-way, while nutrients can be recycled.
Go deeper: An average is not a universal efficiency or a population pyramid
Energy not passed to the next consumer includes respiration and heat, and material that is not eaten or assimilated. It is misleading to label the complete 90% as heat. Dead organic matter can support decomposers.
The pyramid widths are schematic; use the calculated numbers. The single-transfer view partitions a selected energy amount into 10% and 90% with proportional widths. Lower energy availability constrains higher levels; it does not prove that every real food chain has exactly four levels or a fixed number of individuals.
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Question
An original model starts with 8,000 J in producers. What energy reaches the third trophic level under two successive 10% transfers?
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