How do plants breathe without lungs?
Written by
Paul Reynolds
Reviewed by
Prof. Martin Thorne, Ph.D.Plants do not have lungs, but they can still breathe using special structures for gas exchange. Oxygen enters the plant, and carbon dioxide leaves the plant, through a process known as passive diffusion. The stomata on leaves are tiny pores. The lenticels on the bark of woody stems permit air to flow into the stems. The root hairs absorb oxygen directly from spaces in the soil that contain gas. This entire system operates continuously, 24 hours a day, in all parts of the plant.
Stomata
- Microscopic pores on leaf surfaces controlled by guard cells
- Open during daylight to allow gas exchange and photosynthesis
- Close at night or during drought to prevent water loss
- Account for 90% of oxygen intake in most plants
Lenticels
- Raised corky spots on tree bark and woody stems
- Permit limited gas exchange for internal tissues
- Remain open permanently unlike stomata
- Essential for oxygen supply in dormant winter trees
Root Hairs
- Thin extensions on roots absorbing soil oxygen
- Require well-aerated soil for optimal function
- Sensitive to waterlogging which causes suffocation
- Develop air channels (aerenchyma) in flood-tolerant species
Gas movement follows the principles of diffusion mechanics. Gases move from areas of high concentration to areas of low concentration. The oxygen moves into plant cells, which are low in oxygen. The carbon dioxide flows out of plant cells, where the concentration is high. The diffusion of gases is changed by humidity and temperature. The flow of gases is increased inarily because of the loss of water by the plant through open stomata.
External conditions have a crucial effect on plant respiration. The stomata, therefore, remain open longer at high humidity. Root oxygen is minimized by soil packing. Waterlogged conditions induce aerobic fermentation. The use of organic material, such as organic matter, improves soil aeration. Working the soil well also ensures the right planting depth for good gas exchange.
Specialized plants have devised unique methods of breathing. Mangroves produce aerial roots (pneumatophores) to breathe. Rice develops internal air passages that come into play under flooded field conditions. Cacti open their stomata only at night to conserve water loss. Each adaptation answers specific environmental problems.
Read the full article: Respiration in Plants: The Complete Process Guide
