Do Plants Breathe? Gas Exchange Without Respiratory Organs
A tree weighing many tonnes lives for centuries without a lung, a gill, or any breathing apparatus at all. How? This quiz explores the elegant solution plants use: stomata and lenticels, short diffusion distances, and the loose packing of parenchyma cells that keeps every living cell close to air.
You will test your understanding of why plants require ##\ce{O2}## and give out ##\ce{CO2}##, why each plant part meets its own gas-exchange needs, and why roots, stems and leaves respire at rates far lower than animals.
- Gas exchange surfaces in plants
- Respiration versus photosynthesis
- Lenticels and the living layers beneath bark
- Air spaces and parenchyma packing
Answer carefully — the question “do plants breathe?” deserves more than a simple yes or no.
Q1. Which statement best describes the gas exchange of plants?
Plants require oxygen for respiration to occur and they also give out carbon dioxide as a product of respiration.
Q2. Unlike animals, plants possess no specialised organs for gaseous exchange. Which structures do they use instead?
Plants have no specialised organs for gaseous exchange but they have stomata and lenticels for this purpose.
Q3. Which of the following is a reason plants can get along without respiratory organs?
The first reason given is that each plant part takes care of its own gas-exchange needs, with very little transport of gases from one plant part to another.
Q4. How do the respiration rates of roots, stems and leaves compare with those of animals?
Plants do not present great demands for gas exchange; roots, stems and leaves respire at rates far lower than animals do.
Q5. When cells are actively photosynthesising, why is the availability of ##\ce{O2}## not a problem in those cells?
When cells photosynthesise, availability of ##\ce{O2}## is not a problem in these cells since ##\ce{O2}## is released within the cell.
Q6. In thick, woody stems, where are the living cells organised?
In stems, the living cells are organised in thin layers inside and beneath the bark, and they also have openings called lenticels.
Q7. What is the role of the dead cells in the interior of a thick woody stem?
The cells in the interior of the stem are dead and provide only mechanical support.
Q8. Which feature of parenchyma cells in leaves, stems and roots helps gas exchange?
The loose packing of parenchyma cells in leaves, stems and roots provides an interconnected network of air spaces that facilitates gas exchange.
Q9. Why is the diffusion distance for gases small even in large, bulky plants?
The distance that gases must diffuse even in large, bulky plants is not great because each living cell in a plant is located quite close to the surface of the plant.
Q10. Respiration continues in every living cell at all times. Which situation best illustrates why some plant cells must obtain ##\ce{O2}## from outside?
Respiration continues at all times, including at night and in tissues that never photosynthesise, such as roots and the living layers beneath bark, which must obtain oxygen from their surroundings.
Q11. Which statement about the relationship between photosynthesis and respiration is correct?
The relationship between photosynthesis and respiration is complementary rather than substitutive; photosynthesis produces carbohydrate substrates and releases oxygen, while respiration releases carbon dioxide that photosynthetic cells can fix.
Q12. Which of the following correctly describes the gas-exchange openings found in the bark of stems?
Plants have no specialised organs for gaseous exchange but use stomata and lenticels; in stems, the living layers beneath the bark have openings called lenticels.
Q13. What does the lesson say about the transport of gases from one plant part to another?
Each plant part takes care of its own gas-exchange needs, and there is very little transport of gases from one plant part to another.
Q14. According to the lesson, when are large volumes of gases exchanged in plants?
Only during photosynthesis are large volumes of gases exchanged, and each leaf is well adapted to take care of its own needs during these periods.
Q15. Which conclusion follows from the statement that most cells of a plant have at least a part of their surface in contact with air?
Because most cells of a plant have at least a part of their surface in contact with air, and diffusion distances are short, plants can get along without specialised respiratory organs.