Question
What is the difference between autotrophs and heterotrophs? Give two examples of each.
This is a standard NCERT Class 7 question and a guaranteed 2-mark question in most school exams. The concept also links directly to food chains, so understanding it well pays off later.
Solution — Step by Step
The names themselves tell you the answer. Auto = self, trophe = nourishment. So autotrophs nourish themselves — they make their own food.
Hetero = other. Heterotrophs get nourishment from others — they depend on other organisms for food.
Autotrophs use sunlight, water, and carbon dioxide to prepare food through photosynthesis. The key here is the word prepare — they are the manufacturers of food in any ecosystem.
Examples: green plants (mango tree, wheat), algae, certain bacteria (like cyanobacteria).
Heterotrophs cannot make their own food. They consume plants, animals, or decomposed matter to get energy. Their energy ultimately traces back to autotrophs.
Examples: animals (cow, lion, humans), fungi, most bacteria.
| Feature | Autotrophs | Heterotrophs |
|---|---|---|
| Food source | Self-prepared (photosynthesis) | Obtained from other organisms |
| Chlorophyll | Present (in most) | Absent |
| Role in food chain | Producers | Consumers / Decomposers |
| Examples | Plants, algae | Animals, fungi |
Why This Works
Every food chain starts with an autotroph — the sun’s energy has to enter the biological world somehow. Autotrophs do this job by locking solar energy into glucose molecules during photosynthesis. Everything else in the ecosystem, from the grasshopper to the tiger, is simply passing that energy along.
Heterotrophs are further divided by what they eat: herbivores eat plants, carnivores eat animals, omnivores eat both. Decomposers like fungi and bacteria are also heterotrophs — they break down dead matter, completing the nutrient cycle.
The reason plants have chlorophyll and animals don’t comes directly from this difference. Chlorophyll is the molecule that captures sunlight — if you don’t need to photosynthesize, you simply don’t need it.
Alternative Method
If a board question asks you to “distinguish between” rather than just “define”, structure your answer using the keyword contrast method:
- Autotrophs → produce → sunlight + CO₂ + H₂O → food
- Heterotrophs → consume → ready-made food from other organisms
This framing is cleaner for 3-mark or 5-mark answers where examiners look for the contrast, not just definitions. Always write both sides — writing only about autotrophs and leaving heterotrophs thin is a very common reason students lose marks.
Common Mistake
Many students write “animals cannot make food because they don’t have leaves.” That’s wrong — the correct reason is that animals lack chlorophyll, the pigment needed for photosynthesis. Leaves are just the structure; chlorophyll is the actual player. The examiner wants the biochemical reason, not the physical one.
Fungi look like plants (they don’t move, they grow in soil) but they are heterotrophs — this is a classic trick question in Class 7 exams. Fungi have no chlorophyll and absorb nutrients from dead organic matter. Remember: looks like a plant ≠ autotroph.