What Makes a Plant Green?

Plants are green because they contain chlorophyll, which is used in the photosynthesis process for plants' food production. Chlorophyll's unique molecular structure allows it to capture and store the energy of sunlight. It also absorbs all colors on the spectrum except for green, which is reflected back to the person looking at the plant. Chlorophyll doesn't just make plants green; it has a critical role in plants' and human existence.

Significance

Chlorophyll gives plants its green color, and that particular shade is actually critical to the plants' life processes. The fact that chlorophyll is green makes it ideal for capturing the portion of the spectrum of sunlight that is needed for the plants to make their food and survive.

Types

There are actually multiple types of chlorophyll present in different types of plants. All plants, cyanobacteria (aquatic organisms) and algae that make their own food via photosynthesis contain chlorophyll "a." Chlorophyll "b" is present in algae and plants, and chlorophyll "c" is used by Chromista, such as diatoms and mildew.

Function

Chlorophyll's structure contains free electrons and can gain and lose electrons easily, thus making it able to retain the energy of sunlight. This chemical structure is what enables the process of photosynthesis, allowing plants to grow and the entire food cycle to begin.

Non-Green Plants

The green color of chlorophyll makes many plants green, but some plants are colors other than green. For example, plants with leaves that are nearly black are often used in landscaping. These plants often have very dark red or purple leaves, and still have a green or coppery look due to the presence of chlorophyll. Without some chlorophyll, these plants would be unable to manufacture their own food through photosynthesis. Other plants--like carrots and tomatoes--have colors other than green because they contain pigments called carotenoids. These carotenoids, such as beta-carotene and lycopene, may have health benefits; more information on these is available at the Micronutrient Information Center link in the Resources below.

Benefits

Some people choose to take chlorophyll as a nutritional supplement, believing it to have anti-carcinogenic and other healthful properties. Though there isn't extensive research on chlorophyll yet, some studies have suggested it may help prevent gastrointestinal cancers. However, the benefits of taking a chlorophyll supplement as compared to eating a diet high in green plants content haven't been conclusively studied. Generally, eating whole foods has been suggested as the best way to obtain these plant-based chemical compounds for good health. For example, a 1995 study published in the Journal of the National Cancer Institute found that people who consumed higher amounts of the carotenoid lycopene through their diets---as in tomatoes, among other foods---had a 21 percent lower risk of prostate cancer than those who consumed lower levels of lycopene.

References

• Photosynthetic Pigments
• Black Plants for Green Thumbs
• Intake of Carotenoids and Retinol in Relation to Risk of Prostate Cancer

Resources

• Micronutrient Information Center at Oregon State University
• Green Vegetables, Red Meat and Colon Cancer