What is photosynthesis?
Photosynthesis is the process by which plants convert light energy into chemical energy. Plants use sunlight to build energy-rich sugar compounds from carbon dioxide and water – releasing oxygen into the air as a "by-product" in the process. They use these energy-rich substances for their own growth. Photosynthesis is not only vital for the plant's own survival, but it is also one of the central foundations of all life on Earth.
Photosynthesis explained simply
The process takes place in the chloroplasts within leaf cells, specifically the green pigment chlorophyll, which captures light energy and makes it usable. Almost all green plant parts can perform photosynthesis, but the leaves do the largest share, as their large surface area allows them to capture a great deal of light.Fast all green parts of the plant can carry out photosynthesis, but the leaves take on the largest share, as they can capture a particularly large amount of light with their large surface area.
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Light absorption: The plant absorbs light via chlorophyll. In this process, the chlorophyll captures the energy of the sunlight, similar to a small solar cell, and makes it usable for the plant.
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Gas absorption: Carbon dioxide from the air also enters the plant through small stomata (pores) in the leaves. These openings are usually located on the underside of the leaf and open or close as needed. For most houseplants, they are open during the day when there is enough light for photosynthesis so that sufficient carbon dioxide can be absorbed.
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Water absorption: Water is absorbed from the soil through the roots and transported to the leaves. This transport takes place via fine vessels in the stem that carry the water to the leaf cells, where it is needed for the subsequent steps of photosynthesis. Along with the water, the plant also takes up nutrients dissolved in the soil, which it also needs for its growth.
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Energy conversion: The plant uses light energy to chemically convert water and carbon dioxide. This does not happen in a single step, but in a series of consecutive reactions in which new, more energy-rich compounds are gradually created from the two starting materials.
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Product formation: This process produces sugar, which the plant uses as an energy source and building material for its growth, as well as oxygen, which is released back into the air as a by-product. The sugar is either used by the plant immediately as energy or incorporated into solid components such as new leaves, stems, and roots. The oxygen leaves the plant through the same stomata through which the carbon dioxide was previously absorbed.
Chemical background
The short formula for photosynthesis is: 6 CO₂ + 6 H₂O + light → C₆H₁₂O₆ + 6 O₂
It is a redox reaction, i.e., a coupled reduction and oxidation. The light is not consumed, but rather provides the energy for the reaction. During photosynthesis, sugar (glucose) and oxygen are thus produced from carbon dioxide and water.
Factors that influence photosynthesis
For plants to be able to perform photosynthesis, various conditions must be met. Influencing factors are:
- Light (quantity & quality): The more sunlight a plant receives, the more actively it can perform photosynthesis.
- Water supply: Without sufficient water, the plant closes its stomata under drought stress to save water, which simultaneously results in less carbon dioxide entering.
- CO₂ concentration: If more carbon dioxide is available, the plant can use it more efficiently up to a certain point.
- Temperature: The reactions involved only run optimally within a certain temperature range. If it becomes too cold or too hot, photosynthesis slows down noticeably.
- Humidity: The humidity of the air influences how wide the stomata open and how much water the plant loses in the process.
- Chlorophyll content: How much leaf surface area with chlorophyll is available determines how much light can be captured at all. This is particularly evident in variegated plant species. Their white or cream-colored leaf areas contain no chlorophyll and therefore cannot perform photosynthesis. Consequently, they effectively have less leaf surface area available for energy production, which is why they usually grow more slowly than fully green plants and often benefit from a little more light.
C3, C4, and CAM plants
Not all plants perform photosynthesis in the same way. Depending on their location and climate, three different strategies for absorbing and processing carbon dioxide have evolved: C3, C4, and CAM.
C3 plants – the most common type
Approximately 85% of all plant species operate according to the C3 type, including most classic houseplants such as Monstera, Philodendron, and Pilea. They fix carbon dioxide directly into a three-carbon compound. In heat and drought, they close their stomata to save water. This simultaneously reduces CO₂ uptake and makes photosynthesis less efficient.
C4 plants – efficient in heat and full sun
C4 plants initially fix carbon dioxide in special cells, with the first product being a molecule with four carbon atoms – hence the name C4. Only then is the carbon dioxide passed on for the actual sugar production. This additional intermediate step makes C4 plants efficient even in extreme heat and lower CO₂ availability and allows them to lose less water.
CAM plants – nocturnal CO₂ uptake
CAM plants are adapted to particularly dry locations and are therefore much more prevalent in the houseplant assortment: succulents, cacti, and many orchids belong to this group. To lose as little water as possible, they do not open their stomata during the day, but at night, when it is cooler and the humidity is higher. The absorbed carbon dioxide is stored and used for photosynthesis the following day with closed stomata. As a result, CAM plants can survive in very dry, hot environments and generally get by with significantly less water than C3 or C4 plants.
Photosynthesis in houseplants
For you as a houseplant owner, this is more than just dry theory: how well your plant can perform photosynthesis directly determines how vigorously it grows, how intense its leaf color is, and how resistant it is to stress. If a plant is kept in too dark a place, the amount of light is often not sufficient to produce enough energy. The consequences are weak growth, pale or dropping leaves, and a higher susceptibility to pests.
Therefore, it is important to pay attention to the right location. Some houseplants require a lot of light, while others are suitable as plants for darker rooms. If the natural light at the chosen location is not sufficient, a grow light can be a useful addition. It provides additional light in a spectrum that can be used for photosynthesis and helps to keep growth stable, especially in the darker winter months. The amount of water and nutrients are also crucial, as they are needed as raw materials and auxiliary factors. In addition, the carbon dioxide content of the air influences the process; without CO₂, photosynthesis cannot take place. Finally, temperature and humidity also play a role, as many plants can only work optimally within a certain range.
