Plant Respiration and Gas Exchange

Plant Respiration and Gas Exchange

• Plants respire 24 hours a day, unlike animals which may only respire during daylight
• Respiration is the process of releasing energy from organic molecules like carbohydrates. This energy is used by the organism for different life processes.
• Cellular respiration occurs in the cells and involves the chemical breakdown of carbohydrates.
• The equation for cellular respiration is: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + about 38 ATP
• Respiration is the opposite of photosynthesis
• The main respiratory gases are oxygen (O2) and carbon dioxide (CO2)
• Plants obtain oxygen from the air spaces between the soil particles by diffusion through root hairs.
• Carbon dioxide produced during respiration diffuses out through the root hairs.
• If the soil is waterlogged, the roots cannot get enough oxygen and metabolic processes will be affected.

Gas Exchange in Plants

• Plants exchange gases to respire and photosynthesize
• Gas exchange in plants primarily takes place through the leaves
• Stomata are tiny pores on the leaf surface that facilitate gas exchange.
• Stomata open and close to regulate water loss and gas exchange
• When water is abundant, stomata are wide open for efficient gas exchange.
• When water is scarce, stomata close to conserve water
• The stoma consists of two guard cells positioned around a small opening (stoma).
• Photosynthesis takes place mostly in the daytime, which is why oxygen is primarily produced and carbon dioxide is absorbed during the day.
• Cellular respiration occurs all day which is why there is also a gas exchange happening all the time.
• Woody stems of plants (trees) employ lenticels for gas exchange, which are small pores for gas exchange
• Bryophytes (like mosses, liverworts, and hornworts): gas exchange occurs through thin leaves

Cellular Respiration in Plants

• Cellular respiration happens in specialized organelles, called mitochondria. Mitochondria is where the breakdown of carbohydrates occurs.
• The overall process releases energy for the plant's activity.
• There are three stages in cellular respiration (Glycolysis -> Krebs Cycle -> Electron Transport System):
• Glycolysis breaks down glucose into a compound called pyruvic acid
• The Krebs Cycle breaks down the pyruvic acid
• Electron transport system uses the energy from the Krebs Cycle to produce ATP (adenosine triphosphate), the main energy source in most cells

Additional Structures Involved in Gas Exchange

• Root hairs: small extensions of root cells that help plants absorb oxygen dissolved in the soil.
• Lenticels: pores in the stems and outer layers of woody structures, allowing for gaseous exchange

Key Structures Involved

• Chloroplasts: organelles where photosynthesis occurs
• Mitochondria: organelles where cellular respiration takes place
• Stomata: openings on leaves used for gas exchange
• Guard cells: cells around the stomata controlling their opening and closing
• Lenticels: pores in woody stems and roots
• Root hairs: projections on roots for absorption and gas exchange