Green plants primarily carry out photosynthesis during the day when sunlight is available, as this process requires light energy, typically from the sun. Here's a breakdown of the different scenarios you mentioned:
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Only During the Day: This is the standard scenario for most green plants. They use sunlight to convert carbon dioxide and water into glucose and oxygen during daylight hours.
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Only at Night: Generally, green plants do not perform photosynthesis at night because they rely on sunlight. However, some plants, such as certain succulents (e.g., cacti), utilize a variation of photosynthesis known as Crassulacean Acid Metabolism (CAM). CAM plants capture carbon dioxide at night and store it for use during the day when the stomata are closed to conserve water.
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Continuously: While most plants do not continuously perform photosynthesis (as it is primarily a daytime process), certain conditions can lead to continuous or extended photosynthesis. For instance, in environments with artificial light (e.g., greenhouses or indoor grow lights), plants can photosynthesize both day and night. However, the energy and light quality for continuous photosynthesis need to be carefully managed.
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Never: Some plants do not carry out photosynthesis at all. For example, parasitic plants (like dodder) and mycoheterotrophic plants (like Indian pipe) do not have chlorophyll and rely on other plants or fungi for their nutrients. These plants cannot perform photosynthesis and therefore rely on other means to obtain energy.
In summary, typical green plants perform photosynthesis only during the day, while some special cases allow for night-time activity, and certain plants do not photosynthesize at all.