Even though Cacti don´t look like it they are still plants and therefore need to perform some kind of photosynthesis in order to stay alive.
But unlike other Plants, Cacti don’t have any leaves that are usually necessary to perform photosynthesis so how can cacti survive even though they don´t have any leaves to help them carry out photosynthesis?
Cacti can carry out Photosynthesis but they do it a little differently than other plants. Cacti utilize Crassulacean Acid Metabolism (CAM) Photosynthesis. Basically, their stems are doing the photosynthesis work but in two steps. During the night oxygen is released and carbon dioxide is stored. During the Day the carbon dioxide is being transformed into sugar and oxygen with the help of the sun.
So, as you can see, cacti have a slightly different approach to photosynthesis.
The reason for that is the environment that cacti grow in. If they would perform photosynthesis the same way as regular plants would then they would dry out after a few hours.
So they had to adapt and use a different method of photosynthesis called Crassulacean Acid Metabolism (CAD) Photosynthesis in order to survive the harsh environments of the dessert.
How Crassulacean Acid Metabolism (CAM) Works
To properly understand the difference between regular Photosynthesis and Crassulacean Acid Metabolism Photosynthesis I will take a quick look at how regular photosynthesis works.
But for all of you who already know exactly how photosynthesis works here is (in short) how CAM works.
Crassulacean Acid Metabolism works almost like regular photosynthesis with one major difference. The Stomata (pores of the plant) are shut during the day to avoid rapid evaporation of the water inside the plant. So CO2 is stored during the night, photosynthesis is being done during the day, and the oxygen is released at night.
But that is only a quick explanation. Don´t worry if it is not fully clear to you yet what CAM actually is because I will explain it in great detail in a second
But before I do I will quickly go over how photosynthesis works, as I already stated above.
How Does Photosynthesis Work
I won´t go into great detail here but if you want a very detailed explanation of how photosynthesis works then check out the National Geographics article about it right here.
Almost every plant on the planet does photosynthesis in one way or another.
Plants only need water, CO2, and sunlight in order to perform it.
Water is taken in through the soil and the leaves.
Carbon Dioxide (CO2) is being taken in through Stomata in the leaves of the plants.
Stomata are comparable with pores that help the plant to take in CO2 and to release Oxygen.
Sunlight is necessary for the plant in order to perform the chemical process of transforming water and CO2 into Oxigen and Glucose.
Glucose is the main „food“ for the plant. It is basically sugar that gives the plant enough energy to grow and live.
Oxygen is a byproduct of photosynthesis and the plant doesn´t need it for anything.
So it simply releases it into the air.
We Humans then inhale the Oxygen and exhale CO2 (among other things).
That is, very simplified, the way photosynthesis works.
Now that you know that let´s take a look at how Crassulacean Acid Metabolism works and how it is different.
How is Crassulacean Acid Metabolism Different to Regular Photosynthesis
While regular photosynthesis is almost completely done during the day CAM is done in parts during the night and during the day.
Normally plants will have their Stomata (plant pores) open during the day in order to absorb CO2 and to release Oxygen while doing photosynthesis.
Succulents have Stomata as well but they are located on their stems instead of on leaves.
While plants have their Stomata open during the day in order to perform Photosynthesis, succulents have them open during the night.
This is because succulents would lose too much water if they would open their Stomata during the day. The environments where cacti and succulents grow are just too hot.
If the Stomata of the Cactus were open during the day then the water inside it would simply evaporate and the Cactus would dry out and die.
So succulents had to adapt to the harsh conditions of the desert in order to survive.
This is why succulents use Crassulacean Acid Metabolism (CAM).
During the night Succulents will open their Stomata and absorb as much CO2 as they can.
They will store that CO2 through a complex chemical process as malic acid.
During the day the Stomata will shut and the Cactus will do regular photosynthesis with the stored CO2, water, and the help of the sun.
But because the stomata are still shut the Cactus can´t release the Oxygen that is being created as a byproduct of Photosynthesis.
So succulents will store the Oxygen and release it during the night as soon as the sun is gone and the Stomata open up again.
I explained it overly simply here so if you want an in-depth explanation that also goes into detail on how the chemical processes work that make it possible for succulents to store CO2 and Oxygen then check the Wikipedia page about Crassulacean Acid Metabolism out where everything is explained in great detail.
Why Cacti Don’t Have Leaves
Now that you know how Crassulacean Acid Metabolism Photosynthesis works you might wonder why cacti don’t have leaves.
After all the Stomata can also open and close in plants so CAM Photosynthesis should also be possible with leaves, right?
Well, you would be right. CAM is also possible when the plant has leaves but the harsh desert sun would burn right through the thin leaves of any plant even if it has its Stomata shut.
Cacti don´t have leaves because the desert sun would simply burn them. This is why Cacti instead have a very sturdy and large stem that can take the heat of the desert without losing too much water during the day through evaporation.
Cacti have expertly adapted to one of the harshest environments on the planet.
Their leaves have turned into needles overtime to keep predators like rodents away from their juicy insides.
Their stems have become thick and strong to withstand the heat during the day and they perform Crassulacean Acid Metabolism photosynthesis to avoid wasting any water during the day.