Question
Compare aerobic and anaerobic respiration. How does respiration in plants differ from respiration in animals? Give examples of organisms that use anaerobic respiration.
(NCERT Class 7 — Respiration in Organisms)
Solution — Step by Step
Aerobic respiration uses oxygen to break down glucose completely:
Anaerobic respiration happens without oxygen. Glucose is only partially broken down:
- In yeast:
- In muscles:
| Feature | Aerobic | Anaerobic |
|---|---|---|
| Oxygen needed? | Yes | No |
| End products | + | Ethanol + (yeast) OR Lactic acid (muscles) |
| Energy released | High (38 ATP) | Low (2 ATP) |
| Where it happens | Mitochondria | Cytoplasm |
| Complete breakdown? | Yes | No |
| Feature | Plants | Animals |
|---|---|---|
| Gas exchange organs | Stomata, lenticels | Lungs, gills, skin |
| Movement of gases | Diffusion (no blood) | Blood carries and |
| Rate of respiration | Slower (no locomotion) | Faster (energy for movement) |
| All cells respire? | Yes | Yes |
| Also do photosynthesis? | Yes (in green parts, during day) | No |
Both plants and animals perform aerobic respiration 24 hours a day. Plants also do photosynthesis during the day, but respiration never stops.
Why This Works
Every living cell needs energy to survive. Respiration is the process that releases this energy from food (glucose). The fundamental chemistry is the same in plants and animals — glucose gets oxidised.
The difference is in the delivery system. Animals have specialised organs (lungs, gills) and a circulatory system to transport gases. Plants rely on diffusion through stomata and lenticels because their energy needs are lower and their cells are closer to the surface.
A common misconception: “plants breathe in .” That is photosynthesis, not respiration. During respiration, plants take in and release — just like animals.
Alternative Method
You can also remember this through the energy comparison: aerobic gives 19 times more energy than anaerobic (38 vs 2 ATP). That is why most complex organisms are aerobic — they need more energy for body functions.
CBSE loves asking: “Do plants respire at night?” The answer is yes — plants respire 24/7. Photosynthesis only happens during the day, but respiration is continuous. This is a scoring point in 1-mark questions.
Common Mistake
The most common error: writing that “plants take in CO₂ and give out O₂” as respiration. That is photosynthesis, not respiration. During respiration, plants (like all organisms) take in O₂ and release CO₂. During the day, photosynthesis is faster, so the NET exchange appears to be CO₂ in and O₂ out — but respiration is still happening underneath.