How Does A Cactus Do Photosynthesis?

How Does A Cactus Do Photosynthesis

Cacti differ from other plants, in that they do not have the typical leaf structure that one might deem necessary for photosynthesis to take place. With no leaves, you may wonder how cacti carry out photosynthesis, which is a crucial process by which plants produce food for their survival.

As it happens, cacti actually perform a different type of photosynthesis, known as crassulacean acid metabolism, or CAM. In CAM, the cactus’ stems and branches are where the photosynthesis takes place.

At night, the plant absorbs carbon dioxide and releases oxygen, while in the daytime it continues to release oxygen while also turning the carbon dioxide it has absorbed into sugar.

This type of photosynthesis is tailor-made for plants like cacti, because it allows them to do it without drying out under the intense heat of their natural habitat.

In this article we will discuss more about how cacti photosynthesize, and how this process differs from that of regular plants. To learn more about the process, just keep reading.

How do regular plants perform photosynthesis?

Chloroplasts are organelles inside a plant’s cells that store the energy the plant harnesses from the sun. They contain chlorophyll, which is the light-absorbing pigment that gives plants their green color, and this pigment gets energy from the sun’s light waves.

Photosynthesis happens in two stages. The first is the light-dependent stage, during which the chlorophyll absorbs light waves from the sun, and the light energy is converted into chemical energy. This process results in the formation of nicotinamide adenine dinucleotide phosphate enzyme, or NADPH, and adenosine triphosphate molecules, or ATP.

Oxygen is then released at the end of the light-dependent stage as a by-product of the process.

Due to the production of NADPH and ATP during the light-dependent stage, the second stage of photosynthesis, or the Calvin cycle, can begin. This stage is not dependent on light. The plant absorbs water and carbon dioxide from the atmosphere and from the soil. Once inside the plant’s cells, the water molecules lose their electrons as they are oxidized, while the carbon dioxide molecules gain these electrons as they are reduced. This results in the production of oxygen, which the plant releases, and sugars from the carbon dioxide.

The sugars, specifically glucose, are then used to store energy.

How does crassulacean acid metabolism photosynthesis work?

Knowing how regular photosynthesis works is important in order to properly understand the difference between this and crassulacean acid metabolism photosynthesis, or CAM.

With one significant exception, CAM functions almost identically to regular photosynthesis. During the day, the stomata, or plant pores, remain closed in order to prevent the rapid evaporation of water from the plant. Consequently, carbon dioxide is absorbed and stored during the night, because this is the only time the stomata are open. Photosynthesis occurs during the day, and oxygen is released during the night.

What is the difference between regular photosynthesis and CAM?

Stomata are normally open during the day in order for plants to absorb carbon dioxide and release oxygen while performing photosynthesis, but this is not always the case.

Succulents have stomata as well, but they are found on the stems of the plants rather than on the leaves. They open their stomata at night in order to perform photosynthesis, because they would lose too much water if their stomata were open during the day. The environments in which cacti and other succulents thrive are simply too hot for them to survive if they were to keep their stomata open during the day. Their stored water would simply evaporate and the plant would dry out and die.

Cacti and other succulents had to adapt their basic survival processes to their harsh living conditions, hence they have their own way of photosynthesizing – CAM.

During the course of the night, a cactus opens its stomata and absorbs as much carbon dioxide as it can. Thanks to a complex chemical reaction, this carbon dioxide is stored in the form of malic acid.

During the day, the stomata will close and the cactus will continue to perform regular photosynthesis using the stored carbon dioxide, water, and sunlight. However, because its stomata are still closed, it is unable to release the oxygen that is produced as a byproduct of photosynthesis.

The cactus will therefore store the oxygen during the day and release it at night, once the sun has set and the stomata have reopened.

Why do cacti not have leaves?

It is possible that the absence of leaves from the physiological structure of cacti is due to evolution or adaptation.

Because cacti are native to some of the driest places on earth, with some of the most intense sunlight possible, any kind of regular leaves would end up sun damaged. Even if regular plants could shut their stomata and perform CAM, it still would not help them in the desert, because the hot sun would destroy their leaves in a matter of hours.

This is why the stomata of cacti are located on their thick stems and branches instead; they have evolved to handle the extreme temperatures of the desert while preventing most of the moisture stored in their bodies from evaporating.

The spines present on these plants, even if they do not look like much, also provide shade to the body of the cactus, especially when they are grouped in bundles. They also protect the cactus from animals, such as rodents and birds, that feed on its juicy flesh.


Cacti are succulents that do not have traditional-looking leaves, as one might expect from a plant that is able to perform photosynthesis.

Photosynthesis is the process by which plants turn light energy from the sun into chemical energy that they use for survival.

Plants, including cacti, use sunlight to convert water and carbon dioxide into energy-rich glucose and oxygen. The oxygen is then released into the atmosphere.

Cacti have a different method of photosynthesis, called crassulacean acid metabolism. This type of photosynthesis shares many similarities with regular photosynthesis, but the stomata, present on the stems and branches of the cactus, remain closed during the daytime so that the water stored in the plant does not evaporate under the intense heat and light of the desert.

The stomata open at night instead, so this is when cacti absorb carbon dioxide. They store it during the night and, when daylight comes, use it for photosynthesis. The oxygen produced during this photosynthesis will then be released at night, when the stomata open again.

Image: / Techa Tungateja