Plants have complex biological processes that operate continuously to sustain themselves. This constant activity includes processes that are less visible than their daytime functions but are just as fundamental to their survival. Understanding what plants do in the absence of light reveals an important aspect of their biology and the continuous energy management required for life.
The Day and Night Cycle of Plants
During daylight hours, plants perform photosynthesis, using light energy to convert carbon dioxide and water into glucose, a sugar that serves as their food. A byproduct of this process is the release of oxygen into the atmosphere. This daytime activity is only one half of their metabolic story, however.
Plants, like animals, must break down the food they create to power their cells. This process is called cellular respiration, and it involves using oxygen to convert stored sugars like glucose into usable energy, releasing carbon dioxide and water. Unlike photosynthesis, which is dependent on light, respiration occurs continuously to meet the plant’s constant energy demands for growth and maintenance.
In the daytime, the rate of photosynthesis is significantly higher than the rate of respiration. This means plants take in much more carbon dioxide than they release and produce far more oxygen than they consume. When darkness falls and photosynthesis halts, only respiration occurs. The plant then takes in oxygen and releases carbon dioxide, a reversal of the net gas exchange seen during the day.
Environmental Factors Affecting Respiration
The rate at which a plant respires is not constant; it is influenced by several external conditions. These factors can cause the speed of this metabolic process to increase or decrease, affecting the plant’s energy consumption and growth.
Temperature is a primary driver of respiration rates. As the temperature rises, the chemical reactions of respiration speed up, causing the plant to consume more oxygen and release more carbon dioxide. However, this is only true up to an optimal temperature, which is between 18-40°C; beyond this point, extreme heat can damage plant tissues and cause respiration to decline.
Water availability also plays a part in regulating a plant’s respiration. When a plant is under drought stress, it may close the tiny pores on its leaves, called stomata, to conserve water. This closure reduces the intake of oxygen from the atmosphere, which can lower the rate of respiration. The plant’s age and type are also influential, as younger tissues have higher energy needs and respire more than older parts of the plant.
Plants in the Bedroom: A Scientific Perspective
A common concern is that having plants in a bedroom could be harmful because they release carbon dioxide at night. This idea stems from the fact that in the dark, plants switch to net carbon dioxide release. The fear is that this process could deplete the room’s oxygen or raise CO2 levels to a dangerous point while a person is sleeping.
While it is true that plants release carbon dioxide at night, the amount they produce is incredibly small. The quantity of CO2 emitted by a houseplant is negligible and poses no risk to human health. For perspective, a sleeping human exhales significantly more carbon dioxide than a plant in the same room. If sharing a room with another person is safe, then sleeping with a few houseplants is not a cause for concern.
The presence of houseplants is beneficial. NASA studies have shown that certain plants can help purify indoor air by removing common volatile organic compounds during the day. The minimal amount of carbon dioxide they release at night is far outweighed by their positive contributions to air quality and the psychological benefits they provide.