Food Chain and Food Web
NCERT Class 10 • Science • Chapter "Our Environment" | NCERT Class 12 • Biology • Chapter "Ecosystem"
Food Chain and Food Web
A food chain is the sequence through which food energy passes from one organism to the next. Each step in that sequence is a trophic level, and understanding how energy moves through these levels explains almost every rule in ecology.
Trophic Levels and Energy Flow
- The first trophic level is the producer, which captures solar energy through photosynthesis.
- The second is the herbivore or primary consumer, the third the secondary consumer and the fourth the tertiary consumer.
- Energy flow in an ecosystem is unidirectional: it enters as sunlight and is finally lost as heat, never returning.
- The ten per cent law states that only about ten per cent of the energy at one trophic level passes to the next.
- The rest is lost in respiration, movement and heat, which is why food chains rarely have more than four or five levels.
- Because each level loses so much, a shorter food chain supports more organisms at the top.
- A food web is the network formed when many food chains interlink, which makes the ecosystem more stable than a single chain would be.
Ecological Pyramids and Biomagnification
- An ecological pyramid shows the relationship between trophic levels in terms of number, biomass or energy.
- The pyramid of energy is always upright, because energy always decreases at each higher level.
- The pyramid of number can be inverted, as in a single large tree supporting many insects.
- The pyramid of biomass can also be inverted, as in an ocean where small phytoplankton support larger fish.
- Biomagnification is the increase in concentration of a harmful chemical at each higher trophic level.
- Pesticides sprayed on crops enter the food chain and reach their highest concentration in top consumers, including humans.
- This is why chemicals that appear harmless in the soil can become dangerous by the time they reach the end of the chain.
| Pyramid Type | Shape | Reason |
|---|---|---|
| Energy | Always upright | Energy always falls at each level |
| Number | Can be inverted | One tree supports many insects |
| Biomass | Can be inverted | Small plankton support large fish |
Biomagnification — the increase in the concentration of a harmful chemical at each successive trophic level of a food chain.
Exam me kaise aata hai
- Energy transfer between trophic levels is about — ten per cent
- Which ecological pyramid is always upright — the pyramid of energy
- Increase of a chemical along the food chain is called — biomagnification
- Energy flow in an ecosystem is — unidirectional
UPSC/State PSC ke liye
- The ten per cent law explains why the number of top carnivores in any ecosystem is always small; there is simply not enough energy left to support more.
- Biomagnification is most severe in aquatic food chains because they tend to be longer, giving the chemical more steps in which to concentrate.
Yahan confuse hote hain
✗ Energy cycles through an ecosystem | Energy flows one way; only matter cycles | ✓
✗ All ecological pyramids are upright | Only the pyramid of energy is always upright | ✓
✗ A food web is simpler than a food chain | A food web is many interlinked chains and is more complex | ✓
Ek nazar me
- A food chain moves energy through trophic levels in one direction.
- Only about ten per cent of energy passes to the next level.
- The pyramid of energy is always upright; number and biomass pyramids can invert.
- Biomagnification concentrates harmful chemicals in top consumers.