Chlorophyll

Chlorophyll is any of several related green pigments found in cyanobacteria and in the chloroplasts of algae and plants. It gives many plants and algae their green color. Its name comes from the Greek words for "pale green" and "leaf".

Chlorophyll helps plants absorb energy from light. It plays a big role in a process called photosynthesis, where plants make their own food using sunlight. Unlike some similar molecules found only in bacteria, chlorophyll is important for making oxygen as part of this process.

Chlorophyll absorbs light best in the blue and red parts of the light spectrum. It does not absorb green light very well, which is why plants look green to our eyes. Two main types of chlorophyll, called chlorophyll a and b, work together in the tiny parts of plant cells where this important work happens.

History

Chlorophyll was first found and named by Joseph Bienaimé Caventou and Pierre Joseph Pelletier in 1817. Later, scientists discovered that magnesium is part of chlorophyll, which was the first time this element was found in living things.

More work on chlorophyll’s structure was done by Richard Willstätter from 1905 to 1915. Then, Hans Fischer figured out the basic shape of chlorophyll a in 1940. By 1960, most of how the parts of chlorophyll a fit together was known, and Robert Burns Woodward made the whole molecule in a lab. In 1967, Ian Fleming finished figuring out the last pieces, and in 1990, Woodward and others updated how to make it. In 2010, scientists found that chlorophyll f exists in cyanobacteria and other tiny organisms that build stromatolites. They learned its formula is C₅₅H₇₀O₆N₄Mg.

Photosynthesis

Chlorophyll is very important for photosynthesis. This is the process that helps plants take energy from light.

Chlorophyll is placed inside special parts of plant cells called photosystems. It helps in three main ways: it catches light, sends that light energy to a special spot, and helps make important things like energy for the plant and oxygen for us to breathe. This process uses tiny parts of the plant to create energy and oxygen from water and sunlight.

Chemical structure

Several types of chlorophyll exist, and they all come from a basic green ring structure. Most chlorophyll is similar to a group called porphyrins, which are found in things like hemoglobin. Instead of iron, chlorophyll usually holds magnesium. Plants often have a long chain attached to this structure. The most common type in land plants is chlorophyll a. Chlorophyll a differs slightly from chlorophyll b, which helps plants absorb more light.

Space-filling model of the chlorophyll a molecule

The different forms of chlorophyll include:

Structures of chlorophylls
chlorophyll a
chlorophyll b
chlorophyll c₁
chlorophyll c₂
chlorophyll d
chlorophyll f

Chlorophyll e was found in algae in 1966 but has not been fully described. There are also many small changes to chlorophyll structures found in nature. For example, a tiny blue-green organism called Prochlorococcus uses a special form of chlorophyll a and b.

	Chlorophyll a	Chlorophyll b	Chlorophyll c₁	Chlorophyll c₂	Chlorophyll d	Chlorophyll f
Molecular formula	C₅₅H₇₂O₅N₄Mg	C₅₅H₇₀O₆N₄Mg	C₃₅H₃₀O₅N₄Mg	C₃₅H₂₈O₅N₄Mg	C₅₄H₇₀O₆N₄Mg	C₅₅H₇₀O₆N₄Mg
C2 group	−CH₃	−CH₃	−CH₃	−CH₃	−CH₃	−CHO
C3 group	−CH=CH₂	−CH=CH₂	−CH=CH₂	−CH=CH₂	−CHO	−CH=CH₂
C7 group	−CH₃	−CHO	−CH₃	−CH₃	−CH₃	−CH₃
C8 group	−CH₂CH₃	−CH₂CH₃	−CH₂CH₃	−CH=CH₂	−CH₂CH₃	−CH₂CH₃
C17 group	−CH₂CH₂COO−Phytyl	−CH₂CH₂COO−Phytyl	−CH=CHCOOH	−CH=CHCOOH	−CH₂CH₂COO−Phytyl	−CH₂CH₂COO−Phytyl
C17−C18 bond	Single (chlorin)	Single (chlorin)	Double (porphyrin)	Double (porphyrin)	Single (chlorin)	Single (chlorin)
Occurrence	Universal	Mostly plants	Various algae	Various algae	Cyanobacteria	Cyanobacteria

Measurement of chlorophyll content

Chlorophyll forms deep green solutions in organic solvents.

Scientists can take chlorophyll out of plants and put it into special liquids to measure how much is in a leaf. They have ways to tell apart two types of chlorophyll, called chlorophyll a and chlorophyll b.

They can study how chlorophyll absorbs light using different liquids. For example, in one liquid, chlorophyll a absorbs light best at certain colors, and chlorophyll b absorbs it best at other colors. There are also ways to measure chlorophyll by looking at how it glows when light shines on it. These methods help scientists know just how much chlorophyll is in a leaf without harming the plant. Tools like Dualex and SPAD can quickly measure chlorophyll in real time, matching what lab tests show.

Biosynthesis

In some plants, chlorophyll is made from a special kind of building block and follows a path that is shared with other important plant parts. A special enzyme helps finish making chlorophyll a, turning one substance into another.

Plants that do not get enough light can stay pale. But some simpler plants and green algae can grow green even without light because they have an extra helper enzyme.

Chlorophyll attaches to special proteins in plants. One of the steps in making chlorophyll can create harmful substances if there is too much of it, so plants carefully control how much they make.

Senescence and the chlorophyll cycle

When plants age, they go through a process called senescence. During this time, chlorophyll—the green pigment that helps plants make food—breaks down. Special enzymes help change chlorophyll into other substances. This allows plants to reuse some parts of chlorophyll.

Eventually, chlorophyll turns into colorless compounds found in ripening fruits. These changes help the plant prepare for the end of its life cycle.

Distribution

Chlorophyll maps from 2002 to 2024, provided by NASA, show how much chlorophyll is in the ocean each month. Blue areas have very little chlorophyll, meaning few tiny ocean plants called phytoplankton. Yellow areas have lots of chlorophyll, meaning many phytoplankton are growing.

These maps come from a special tool on NASA's Aqua satellite. The darkest gray shows land, and light gray shows places where the satellite couldn't get data. The most chlorophyll is found in cold polar waters or where ocean currents bring cold, nutrient-rich water to the surface. These nutrients help the phytoplankton grow well when sunlight returns in spring and summer.

Uses

Chlorophyll is used as a natural green color in foods and drinks. Chefs add it to pasta, drinks, and even spirits to give them a pretty green look. For example, a special drink called absinthe gets its green color from the many herbs used to make it, which contain chlorophyll.

In the past, some companies used chlorophyll in products like toothpaste and soap, saying it could help get rid of bad smells. But later, people found out these claims were not true, so they stopped using it. Recently, some people on social media influencers have been talking about drinking "chlorophyll water," though these health claims are not proven either.