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A student claims that 'Plants only perform photosynthesis and animals only perform cellular respiration! Evaluate this statement. Is it true or false? Explain your reasoning scientifically.
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False.
Why: both plants and animals carry out cellular respiration, and photosynthesis is not limited strictly to "plants" — the two processes are distinct, often coupled, and occur in different sets of organisms and organelles.
Key points
- What photosynthesis and cellular respiration are:
- Photosynthesis (in photoautotrophs) uses light energy to build organic molecules:
6 CO2 + 6 H2O + light → C6H12O6 + 6 O2
(occurs in chloroplasts of plants and algae, and in cyanobacteria)
- Cellular respiration breaks down organic molecules to release energy (ATP):
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP
(glycolysis in the cytosol, Krebs cycle and oxidative phosphorylation in mitochondria for aerobic respiration)
- Plants do both:
- Plants perform photosynthesis in chloroplast-containing green tissues when light is available.
- Plants also respire continuously (day and night). They use mitochondria to oxidize sugars (some made by photosynthesis) to produce ATP for growth, maintenance, active transport, etc.
- Animals primarily respire:
- Animals cannot carry out photosynthesis because they lack chloroplasts and the pigments/photosystems required.
- Animals perform cellular respiration (aerobic in mitochondria; anaerobic fermentation in some tissues under low oxygen), extracting ATP from food.
- Exceptions and complications:
- Some non-plant organisms photosynthesize (algae, cyanobacteria). Some animals host photosynthetic symbionts (corals with zooxanthellae) or, rarely, keep functional chloroplasts from their food (kleptoplasty in some sea slugs), leading to limited photosynthetic activity in the animal’s body — but these are exceptions, not the rule.
- Many microbes have diverse metabolisms (aerobic respiration, anaerobic respiration, fermentation, chemoautotrophy, photoheterotrophy, etc.), so the simple dichotomy in the student’s statement is biologically inaccurate.
Simple experimental evidence you could observe
- A green leaf in light produces O2 (photosynthesis) and consumes CO2; the same leaf in darkness consumes O2 and releases CO2 (respiration continues).
- Measuring O2 consumption in plant tissues at night shows ongoing respiration.
Conclusion: The statement is false. Plants perform both photosynthesis (when light is available) and cellular respiration; animals perform cellular respiration and generally do not photosynthesize (with rare, special cases).
Why: both plants and animals carry out cellular respiration, and photosynthesis is not limited strictly to "plants" — the two processes are distinct, often coupled, and occur in different sets of organisms and organelles.
Key points
- What photosynthesis and cellular respiration are:
- Photosynthesis (in photoautotrophs) uses light energy to build organic molecules:
6 CO2 + 6 H2O + light → C6H12O6 + 6 O2
(occurs in chloroplasts of plants and algae, and in cyanobacteria)
- Cellular respiration breaks down organic molecules to release energy (ATP):
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP
(glycolysis in the cytosol, Krebs cycle and oxidative phosphorylation in mitochondria for aerobic respiration)
- Plants do both:
- Plants perform photosynthesis in chloroplast-containing green tissues when light is available.
- Plants also respire continuously (day and night). They use mitochondria to oxidize sugars (some made by photosynthesis) to produce ATP for growth, maintenance, active transport, etc.
- Animals primarily respire:
- Animals cannot carry out photosynthesis because they lack chloroplasts and the pigments/photosystems required.
- Animals perform cellular respiration (aerobic in mitochondria; anaerobic fermentation in some tissues under low oxygen), extracting ATP from food.
- Exceptions and complications:
- Some non-plant organisms photosynthesize (algae, cyanobacteria). Some animals host photosynthetic symbionts (corals with zooxanthellae) or, rarely, keep functional chloroplasts from their food (kleptoplasty in some sea slugs), leading to limited photosynthetic activity in the animal’s body — but these are exceptions, not the rule.
- Many microbes have diverse metabolisms (aerobic respiration, anaerobic respiration, fermentation, chemoautotrophy, photoheterotrophy, etc.), so the simple dichotomy in the student’s statement is biologically inaccurate.
Simple experimental evidence you could observe
- A green leaf in light produces O2 (photosynthesis) and consumes CO2; the same leaf in darkness consumes O2 and releases CO2 (respiration continues).
- Measuring O2 consumption in plant tissues at night shows ongoing respiration.
Conclusion: The statement is false. Plants perform both photosynthesis (when light is available) and cellular respiration; animals perform cellular respiration and generally do not photosynthesize (with rare, special cases).
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