Chlorophyll: Definition, Function, Facts, Formula, Structure, Diagram

Edited By Irshad Anwar | Updated on Jul 02, 2025 07:03 PM IST

Definition Of Chlorophyll

Chlorophyll is the green pigment in plants, algae, and cyanobacteria; it is responsible for photosynthesis. The basic definition would be a pigment that can absorb light energy from the sun to create chemical energy. Light is absorbed in both the blue-violet and red areas of the spectrum; what is reflected is green in colour, which explains the green colour of plants.

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Definition Of Chlorophyll
Structure Of Chlorophyll
Function Of Chlorophyll
Chlorophyll In Different Organisms
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This pigment is a major player in the photosynthetic process, as it enables the transfer of absorbed light energy to the reaction centres that use this energy for the synthesis of glucose from carbon dioxide and water. Had it not been for the presence of chlorophyll, the solar energy-to-chemical energy conversion would not have taken place, and it is this energy conversion that sustains most life forms existing on Earth.

Structure Of Chlorophyll

The structure of chlorophyll is explained below:

Basic Structure

Porphyrin ring and its components

Chlorophyll molecules have a very complicated structure, with a porphyrin ring at its centre. This large, cyclic arrangement comprises carbon, hydrogen, and nitrogen atoms. Right at the centre of this ring is located a magnesium ion, an element central to the ability of the pigment to absorb light and undergo photosynthesis. Attached to the porphyrin ring is a phytol tail, which is a long hydrocarbon chain. This chain anchors the chlorophyll molecule within the thylakoid membrane of the chloroplast.

Central magnesium ion.

What makes chlorophyll capable of capturing light energy is the association of the porphyrin ring with a magnesium ion.

Types Of Chlorophyll

The types of chlorophyll are:

Chlorophyll a:

This is the major pigment responsible for the light-dependent reactions of photosynthesis. It is efficient in absorbing light at the blue-violet and red ends of the visible spectrum. It reflects green light, which means that it is the basis of green colouration in plants. Chlorophyll a is crucial in the primary conversion of light energy to chemical energy.

Chlorophyll b:

Chlorophyll b acts as an accessory pigment to the light-harvesting complex, picking out light in the parts of visible blue and red-orange areas of the spectrum. This helps to increase the ability of light that can be used in photosynthesis, feeding the collected energy into chlorophyll.

Chlorophyll c and d:

Chlorophyll c and d are found in some algae. Chlorophyll c has a slightly different structure than chlorophyll a and is adaptations to absorb light in different aquatic environments, and chlorophyll d is a modified form found in red algae, which captures light in the deeper or shadier water, while other types of chlorophyll cannot do as effectively.

Function Of Chlorophyll

The function of chlorophyll is described below:

Photosynthesis

Process of light absorption and energy conversion.

Chlorophyll plays a central role in the photosynthetic process by being responsible for light energy absorption, mainly within the blue-violet and red portions of the spectrum. The energy of this light that gets absorbed by the chlorophyll molecule excites electrons to begin a series of reactions involved in the light-dependent phase of photosynthesis

Role in the light-dependent reactions of photosynthesis.

In this process, the energy is transferred to electron carriers in the thylakoid membrane by the excited electrons, commonly known as the electron transport chain, which produces energy-rich molecules such as ATP and NADPH for the light-independent reaction.

Role In Energy Transfer

Chlorophyll participates in the production of ATP and NADPH for glucose production in the Calvin cycle. In light-dependent reactions, light is absorbed by the molecule of chlorophyll, which leads to the transfer of excited electrons through a series of proteins in the thylakoid membrane, thus ultimately leading to the production of ATP through photophosphorylation and reducing NADP+ to NADPH.

They then migrate into the stroma of the chloroplast and serve as both the energy and reducing power for carbon fixation and the synthesis of carbohydrates in light-independent reactions.

Chlorophyll In Different Organisms

Chlorophyll in different organisms is given below:

Chlorophyll In Plants

In plants, chlorophyll has a role in photosynthesis in various forms, from terrestrial to aquatic plants. The principal pigments capturing light energy to synthesise carbohydrates in the chloroplast of the leaf cells are chlorophyll a and b.

This arrangement of chlorophyll a and b in chloroplasts within the mesophyll cells of the leaves is quite common in terrestrial plants and enables them to capture optimal light from the sun. Aquatic plants also contain these chlorophylls but do so with adaptations to include additional pigments or different types of chlorophylls that allow the plants to survive underwater with low light intensities and different spectra.

In Algae And Cyanobacteria

In algae, there can be variations in chlorophyll types. For example, green algae contain chlorophylls a and b, typical for higher plants; red algae have chlorophyll a, but also chlorophyll d, which captures light better for photosynthesis in deeper or more turbid water.

Cyanobacteria, known simply as blue-green algae, are mostly chlorophyll a, but they also have several other pigments; many of them are phycobilins, such as phycocyanin and phycoerythrin, and they help to absorb more light. These pigments allow cyanobacteria to exist in shallow and more deep environments in water, where light conditions change gradually.

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Frequently Asked Questions (FAQs)

1. What is chlorophyll and why is it important?

Chlorophyll is a green pigment primarily present in plants, algae as well as Cyanobacteria. It plays a fundamental role in photosynthesis by capturing the energy from light to convert carbon dioxide and water into glucose and oxygen.

2. What are the different types of chlorophyll?

Types include chlorophyll a, chlorophyll b, chlorophyll c, and chlorophyll d. All of these types have different absorption spectra and photosynthetic functions.

3. How does chlorophyll contribute to photosynthesis?

It plays its part in the photosynthesis process by the absorption of light energy and then uses this energy to carry out the light-dependent reactions of photosynthesis to output ATP and NADPH. The two rich energy molecules will then drive the synthesis of glucose.

4. What factors affect the synthesis of chlorophyll in plants?

Factors involve the light intensity, temperature, and availability of nutrients like magnesium, nitrogen, and iron.

5. How can chlorophyll levels be used to assess plant health?

Chlorophyll content conveys health information about the plants. The lower the chlorophyll content of a plant, the more it may be under stress or suffering from a nutrient deficiency. There happens to be a device for measuring the same, which is called a chlorophyll meter.

6. How do accessory pigments work with chlorophyll in photosynthesis?

Accessory pigments, such as carotenoids and phycobilins, work alongside chlorophyll to expand the range of light wavelengths that can be used for photosynthesis. These pigments absorb light at different wavelengths than chlorophyll and transfer the energy to chlorophyll molecules. This allows plants to utilize more of the light spectrum for photosynthesis, increasing their efficiency in various light conditions.

7. How does chlorophyll content relate to a plant's shade tolerance?

Shade-tolerant plants often have higher chlorophyll content, especially chlorophyll b, compared to sun-loving plants. This adaptation allows them to efficiently capture the limited light available in shaded environments. The higher ratio of chlorophyll b to chlorophyll a in shade plants helps them absorb more efficiently in the blue-green spectrum, which is more prevalent in shaded conditions.

8. How does the presence of chlorophyll in algae affect aquatic ecosystems?

Chlorophyll in algae is crucial for aquatic ecosystems as it enables these organisms to photosynthesize, forming the base of many aquatic food chains. However, excessive algal growth, often due to nutrient pollution, can lead to algal blooms. These blooms can reduce water clarity, deplete oxygen levels, and potentially release toxins, negatively impacting aquatic life and water quality.

9. Why do some plants have variegated leaves with white or yellow patches?

Variegated leaves have areas that lack chlorophyll, resulting in white or yellow patches. This can be due to genetic mutations or viral infections that affect chlorophyll production in certain leaf areas. While these patches don't contribute to photosynthesis, they can serve other purposes like attracting pollinators or deterring herbivores. However, extensively variegated plants often grow more slowly due to reduced photosynthetic capacity.

10. How does chlorophyll degradation relate to leaf senescence?

Leaf senescence, the process of leaf aging and death, involves the breakdown of chlorophyll. As leaves age, chlorophyll is degraded faster than it's replaced. This reveals other pigments like carotenoids, causing the characteristic autumn colors. Chlorophyll degradation is a controlled process that allows the plant to recycle nutrients, particularly nitrogen, from the leaves before they fall.

11. What is chlorophyll fluorescence and how is it used in plant science?

Chlorophyll fluorescence is the re-emission of light by chlorophyll molecules after they absorb light energy. Not all absorbed light energy is used for photosynthesis; some is dissipated as heat or re-emitted as fluorescence. Scientists measure chlorophyll fluorescence to assess photosynthetic efficiency and plant stress. Changes in fluorescence can indicate various stresses like drought, nutrient deficiency, or disease before visible symptoms appear.

12. What is the significance of the "red edge" in remote sensing of vegetation?

The "red edge" refers to the sharp change in reflectance of vegetation between red and near-infrared wavelengths. This is due to chlorophyll strongly absorbing red light but reflecting near-infrared light. Remote sensing techniques use this characteristic to assess vegetation health and density. A stronger "red edge" typically indicates healthier vegetation with more chlorophyll.

13. How does chlorophyll content relate to a plant's nitrogen status?

Chlorophyll content is closely related to a plant's nitrogen status because nitrogen is a key component of chlorophyll molecules. Plants with adequate nitrogen typically have higher chlorophyll content and appear darker green. As nitrogen becomes deficient, chlorophyll production decreases, leading to yellowing of leaves (chlorosis). Farmers and researchers often use leaf color or chlorophyll content as an indicator of a plant's nitrogen status to guide fertilization practices.

14. What is the significance of chlorophyll in the food industry?

Chlorophyll has several applications in the food industry. It's used as a natural food coloring (E140) to give a green color to various products. Chlorophyll and its derivatives are also used as food supplements due to their potential health benefits, including antioxidant properties. In food science, chlorophyll content is often used as a quality indicator for vegetables and herbs. Additionally, the breakdown of chlorophyll during food processing and storage is an important consideration in maintaining the visual appeal of green foods.

15. What is chlorophyll and why is it important for plants?

Chlorophyll is a green pigment found in plants that is crucial for photosynthesis. It absorbs light energy, primarily from the red and blue parts of the visible spectrum, and converts it into chemical energy that plants use to produce glucose from carbon dioxide and water. Without chlorophyll, plants would not be able to carry out photosynthesis and produce their own food.

16. How does chlorophyll's structure contribute to its function?

Chlorophyll's structure consists of a porphyrin ring with a magnesium ion at its center. This structure allows it to absorb light energy efficiently. The long hydrocarbon tail helps anchor the molecule within the thylakoid membrane of chloroplasts. The specific arrangement of atoms in chlorophyll enables it to become excited by light energy and transfer that energy to other molecules in the photosynthetic process.

17. Why do plants appear green if chlorophyll absorbs red and blue light?

Plants appear green because chlorophyll reflects green light while absorbing red and blue light. The reflected green light is what we see when we look at plants. This is why leaves change color in autumn as chlorophyll breaks down, revealing other pigments like carotenoids that were present but masked by the green chlorophyll.

18. What role does chlorophyll play in the light-dependent reactions of photosynthesis?

In the light-dependent reactions, chlorophyll molecules in photosystems I and II absorb light energy. This energy excites electrons in the chlorophyll molecules, which are then passed through an electron transport chain. This process drives the production of ATP and NADPH, which are used in the light-independent reactions (Calvin cycle) to produce glucose.

19. How does the chemical formula of chlorophyll relate to its function?

The chemical formula for chlorophyll a is C55H72O5N4Mg. This formula reflects its complex structure, which includes a porphyrin ring (containing nitrogen atoms) with a magnesium ion at the center, and a long hydrocarbon tail. The magnesium ion is crucial for light absorption, while the porphyrin ring structure allows for electron excitation and energy transfer. The hydrocarbon tail helps anchor chlorophyll in the thylakoid membrane.

20. How does the molecular structure of chlorophyll compare to that of hemoglobin?

Chlorophyll and hemoglobin have similar ring-like structures called porphyrins, but with key differences. Chlorophyll has a magnesium ion at its center and a long hydrocarbon tail, while hemoglobin has an iron ion at its center and is attached to a protein. These structural differences reflect their different functions: chlorophyll for light absorption in photosynthesis, and hemoglobin for oxygen transport in blood.

21. What is the difference between chlorophyll a and chlorophyll b?

Chlorophyll a and b are two main types of chlorophyll found in plants. They differ slightly in their chemical structure and absorption spectra. Chlorophyll a has a methyl group (-CH3) where chlorophyll b has an aldehyde group (-CHO). Chlorophyll a absorbs light most strongly at 430 nm and 662 nm, while chlorophyll b absorbs most strongly at 453 nm and 642 nm. This difference allows plants to capture a wider range of light wavelengths for photosynthesis.

22. What is the role of protochlorophyllide in chlorophyll synthesis?

Protochlorophyllide is a precursor molecule in chlorophyll synthesis. In the final step of chlorophyll a production, protochlorophyllide is converted to chlorophyllide by the enzyme protochlorophyllide oxidoreductase. This step requires light in angiosperms (flowering plants), which is why seedlings grown in darkness appear yellow until exposed to light. Understanding this process is crucial for comprehending how plants regulate chlorophyll production in response to light conditions.

23. How do environmental factors affect chlorophyll synthesis in plants?

Chlorophyll synthesis is influenced by various environmental factors. Light is crucial, as plants grown in darkness do not produce chlorophyll (etiolation). Nutrient availability, especially nitrogen and magnesium, is essential for chlorophyll production. Temperature also plays a role, with extreme temperatures inhibiting chlorophyll synthesis. Stress factors like drought or salt stress can reduce chlorophyll production. Understanding these factors is important for optimizing plant growth in agriculture and horticulture.

24. What is the relationship between chlorophyll and photosystems?

Chlorophyll molecules are organized into complexes called photosystems within the thylakoid membranes of chloroplasts. There are two main photosystems: Photosystem I and Photosystem II. Each photosystem contains hundreds of chlorophyll molecules along with other pigments and proteins. These photosystems work together to capture light energy and initiate the electron transport chain in the light-dependent reactions of photosynthesis.

25. How does chlorophyll concentration affect the rate of photosynthesis?

Generally, higher chlorophyll concentration leads to increased photosynthetic rate, as more light can be absorbed. However, this relationship is not linear. After a certain point, increasing chlorophyll concentration does not significantly increase photosynthesis rate due to factors like light saturation and limitations in other parts of the photosynthetic process, such as carbon dioxide availability or enzyme activity.

26. What is the relationship between chlorophyll and cytochromes in the electron transport chain?

Chlorophyll and cytochromes work together in the electron transport chain of photosynthesis. Chlorophyll in photosystems absorbs light energy and becomes excited, releasing high-energy electrons. These electrons are then passed through a series of cytochromes and other electron carriers. Cytochromes, which contain iron, accept and donate electrons, helping to create a proton gradient that ultimately drives ATP synthesis.

27. What is the evolutionary significance of chlorophyll in plants?

The evolution of chlorophyll was a crucial step in the development of photosynthetic organisms. It allowed early plants to efficiently capture light energy, enabling them to produce their own food. This autotrophic ability gave plants a significant advantage, allowing them to colonize land and diversify into numerous species. The evolution of chlorophyll-based photosynthesis also dramatically changed Earth's atmosphere by producing oxygen, paving the way for the evolution of complex life forms.

28. What is the significance of chlorophyll in global carbon cycling?

Chlorophyll plays a crucial role in global carbon cycling through its function in photosynthesis. By enabling plants to fix atmospheric carbon dioxide into organic compounds, chlorophyll-driven photosynthesis is a major pathway for carbon to enter ecosystems. This process not only provides the basis for most food chains but also helps regulate atmospheric CO2 levels, playing a significant role in global climate regulation.

29. How do herbicides that target chlorophyll biosynthesis work?

Some herbicides work by inhibiting enzymes involved in chlorophyll biosynthesis. For example, some target the enzyme protoporphyrinogen oxidase, which is involved in one of the final steps of chlorophyll synthesis. When this enzyme is inhibited, it leads to the accumulation of protoporphyrin IX, which generates reactive oxygen species in the presence of light, causing cell death. Understanding these mechanisms is crucial for developing effective and environmentally safe weed control strategies.

30. What is the relationship between chlorophyll and plant productivity in agriculture?

Chlorophyll content is often used as an indicator of plant health and potential productivity in agriculture. Higher chlorophyll content generally correlates with greater photosynthetic capacity and, therefore, higher potential yield. However, other factors like nutrient availability, water status, and overall plant health also play crucial roles. Farmers and researchers use chlorophyll measurements (often through remote sensing) to assess crop health, guide fertilization, and predict yields.

31. How does chlorophyll contribute to the vertical distribution of algae in aquatic ecosystems?

The vertical distribution of algae in water bodies is largely influenced by their chlorophyll content and light availability. Algae need to balance their need for light (for photosynthesis) with the risk of photodamage from excessive light exposure. Different species have varying amounts and types of chlorophyll, allowing them to occupy different depths. This results in a stratified distribution of algal species in the water column, with some adapted to high light conditions near the surface and others adapted to lower light conditions at greater depths.

32. What is the connection between chlorophyll and the production of oxygen during photosynthesis?

Chlorophyll is essential for oxygen production during photosynthesis. In Photosystem II, chlorophyll molecules absorb light energy, which is used to split water molecules into hydrogen ions, electrons, and oxygen. The oxygen released as a byproduct of this process is what we breathe. This light-dependent reaction, driven by chlorophyll, is the source of nearly all the oxygen in Earth's atmosphere, highlighting chlorophyll's crucial role in supporting life on Earth.

33. How does the absorption spectrum of chlorophyll relate to the action spectrum of photosynthesis?

The absorption spectrum of chlorophyll shows which wavelengths of light it absorbs most effectively, with peaks in the blue and red regions. The action spectrum of photosynthesis shows the effectiveness of different wavelengths of light in driving photosynthesis. While these spectra are similar, they're not identical due to the presence of accessory pigments. The action spectrum is broader than chlorophyll's absorption spectrum alone, reflecting the contribution of these accessory pigments in capturing a wider range of light wavelengths for photosynthesis.

34. What is the role of chlorophyll in non-photosynthetic plants like parasitic plants?

Many parasitic plants, such as dodder (Cuscuta) or Indian pipe (Monotropa uniflora), have reduced or no chlorophyll. These plants obtain their nutrients from host plants rather than through photosynthesis. The absence or reduction of chlorophyll in these plants reflects their alternative nutritional strategies. Some may retain small amounts of chlorophyll for reasons other than photosynthesis, such as light sensing or defensive functions. This adaptation showcases the diversity of plant survival strategies and the plasticity of chlorophyll's role in plant biology.

35. How does chlorophyll content change during leaf development and why?

Chlorophyll content changes throughout a leaf's lifecycle. In young leaves, chlorophyll content increases rapidly as the leaf expands and develops its photosynthetic capacity. Mature leaves maintain a relatively stable chlorophyll content. As leaves age, chlorophyll content decreases due to breakdown and reduced synthesis. This decrease is particularly noticeable in deciduous trees in autumn. The changes in chlorophyll content reflect the leaf's changing roles, from rapid growth and development to peak photosynthetic activity, and finally to nutrient recycling before leaf fall.

36. What is the relationship between chlorophyll and photoprotection in plants?

While chlorophyll is essential for capturing light energy, excess light can damage the photosynthetic apparatus. Plants have evolved several photoprotective mechanisms involving chlorophyll. One key mechanism is non-photochemical quenching (NPQ), where excess energy absorbed by chlorophyll is dissipated as heat. Additionally, plants can adjust their chlorophyll content and the ratio of chlorophyll a to b in response to light conditions. Understanding these mechanisms is crucial for improving crop resilience to varying light conditions and climate change.

37. How does chlorophyll degradation contribute to fruit ripening?

Chlorophyll degradation is an important aspect of fruit ripening in many species. As fruits ripen, chlorophyll breaks down, revealing other pigments like carotenoids or anthocyanins. This process not only changes the fruit's color but also affects its flavor and nutritional content. The breakdown of chlorophyll is often used as an indicator of ripeness in fruits like bananas or tomatoes. Understanding this process is crucial for post-harvest management and determining optimal harvest times in agriculture.

38. How does chlorophyll content relate to a plant's ability to tolerate high light stress?

Plants exposed to high light stress often adjust their chlorophyll content as part of their adaptive response. While chlorophyll is necessary for photosynthesis, too much chlorophyll under high light conditions can lead to photodamage. Plants may reduce their overall chlorophyll content or change the ratio of chlorophyll a to b to mitigate this risk. They also employ other protective mechanisms like increasing carotenoid content or enhancing non-photochemical quenching. Understanding these adaptations is crucial for developing crops with improved tolerance to high light conditions.

39. What is the role of chlorophyll in photoacclimation?

Photoacclimation is the process by which plants adjust their photosynthetic apparatus in response to changes in light conditions. Chlorophyll plays a central role in this process. Plants can adjust their chlorophyll content, the ratio of chlorophyll a to b, and the organization of chlorophyll-protein complexes in response to changing light environments. For example, shade leaves typically have higher chlorophyll content, especially chlorophyll b, compared to sun leaves. These adjustments help plants optimize their light