How Chlorophyll Makes Plants Green and Supports Life
Green plants are also known as autotrophic plants because they are reported to contain a green-coloured photosynthetic pigment called chlorophyll, which is found in the chloroplast of plants. Plants are called photoautotrophs because they are capable of producing their own food through photosynthesis. The food synthesised by plants is stored in the form of starch. Green plants absorb carbon dioxide and release oxygen. Thus, plants help us to survive by providing oxygen to breathe in.
Why are Plants Green?
The integral part of a plant is the leaves, along with the other parts like the stem and root. Leaves are capable of performing photosynthesis with the aid of a primary pigment, chlorophyll which imparts green colour to the plants. The process of photosynthesis involves the conversion of light energy to chemical energy.
Plants have different pigments with different colours. The green pigment is known as chlorophyll which absorbs light. There are two types of chlorophyll, one is chlorophyll A which is the main pigment that takes part in the electron transport, and the other is chlorophyll B, which is the accessory pigment. They are reported to absorb light from 400-650nm.
Chlorophyll A can absorb blue light of wavelength 430 nm and red light of wavelength 662 nm. However, it is unable to absorb green light of wavelength 550 nm and thus reflects the green light. Due to the reflection of the green colour, the leaves on the plant come out green, and that is why the leaves are green.
Colourful Leaf Plants
The most colourful times of the year are spring and summer. Bright-coloured leaf plants blossom, and a sea of colour appears everywhere. There are different types of colourful leaf plants. The examples are discussed below.
The first is the hostas. This popular garden plant has large green leaves with thick white borders with numerous patterns and textures. The ‘Fire Island’ variety of hostas has luminous yellow leaves. The second is the Coleus which has interesting textures and colours ranging from reds, pinks, and yellows, to mixes of brilliant hues. They love the sun, and it appears bright during summer.
The Black Dragon variety has deep burgundy leaves with ruffled edges. Amaranthus Tricolour grows throughout the year; they appear in yellows, reds, and orange colours. It grows well during summer. The coral bells are low-growing shrubs that have purple to orange leaves.
Why are Green Plants Called Producers?
Green plants are called producers because they have the capability to produce their own food in the presence of sunlight through the process of photosynthesis. Green plants can prepare food from simple inorganic substances like carbon dioxide and water. During this process, energy in the form of glucose is released, which is used by the plants for survival, growth and reproduction.
Green plants are called autotrophs as they can manufacture their food from raw materials present in the surroundings like carbon dioxide and water. During the process of photosynthesis, plants consume carbon dioxide and release oxygen gas which is consumed by us. The steps of photosynthesis are discussed below.
Step 1: Absorption of light energy from the sun by chlorophyll.
Step 2: Conversion of light energy to chemical energy.
Step 3: The splitting of a water molecule into hydrogen and oxygen.
Step 4: Carbon dioxide is reduced to glucose.
Why are Leaves Green?
The green pigment present in leaves is chlorophyll which is contained in the thylakoid membranes of chloroplasts. There are five types of chlorophylls: chlorophylls a, b, c, and d, and a related molecule bacteriochlorophyll that is exclusively found in prokaryotes. It is present in the plasma membrane of bacteria.
The structure of chlorophyll molecules contains a hydrophobic tail that is inserted into the thylakoid membrane and a porphyrin ring head that is mainly responsible for absorbing light. Chlorophyll a is the main component, and the rest are accessory pigments. The accessory pigments help in absorbing a broader range of wavelengths so that more energy is captured from sunlight.
Interesting Facts
Green plants are called photoautotrophs because they can make their own food through the process of photosynthesis, which converts carbon dioxide and water in the presence of light to oxygen and energy. Chlorophyll assists this process by absorbing light energy.
Important Questions
1. What is the importance of green plants?
Ans: As the primary producers of the ecosystem, green plants are involved in producing food for consumers. Green plants are essential for maintaining the planet's carbon dioxide and oxygen equilibrium.
2. What are carotenoids?
Ans: Plants produce the yellow, orange, and red pigments known as carotenoids. The carotenoids alpha-carotene, beta-carotene, lutein, zeaxanthin, and lycopene are the most prevalent.
Key Features
The leaves of the plants appear green because of the presence of the green pigment Chlorophyll.
Chlorophyll plays a significant role in photosynthesis by absorbing light energy from the sun. Chlorophyll A mainly absorbs light strongly within the blue and red portions of the spectrum.
The green leaves can absorb light of all wavelengths except the wavelength of green light, i.e. the wavelength of 550nm. This green wavelength of light is reflected by the plant.
FAQs on Why Are Plants Green: The Science Behind Their Color
1. Why do most plants appear green to our eyes?
Plants appear green because their leaves contain a pigment called chlorophyll. This molecule is essential for photosynthesis. When sunlight, which contains all colours of the spectrum, shines on a leaf, chlorophyll primarily absorbs the red and blue wavelengths of light but reflects the green wavelengths. Our eyes detect this reflected green light, making the plant look green.
2. What is chlorophyll and where is it located inside a plant cell?
Chlorophyll is the primary pigment used in photosynthesis, the process plants use to convert light energy into chemical energy. It is not spread randomly throughout the cell but is contained within specific organelles called chloroplasts. Inside the chloroplasts, chlorophyll is embedded in the membranes of disc-like structures known as thylakoids.
3. Besides chlorophyll, what other types of pigments are found in plants?
While chlorophyll is the most dominant, plants contain several other pigments that serve various functions. The main groups include:
- Carotenoids: These produce yellow, orange, and red colours. They assist in photosynthesis and protect the plant from sun damage.
- Anthocyanins: These create red, purple, and blue hues, often seen in flowers, fruits, and autumn leaves. Their production is often triggered by environmental factors like light and temperature.
- Betalains: These are responsible for the deep red and yellow colours in some plants like beets and bougainvillea.
4. How do other pigments, like carotenoids, contribute to a plant's colour if chlorophyll is dominant?
Carotenoids (yellow and orange pigments) are present in leaves throughout the spring and summer, but their colours are masked by the much larger amount of green chlorophyll. During autumn, as days get shorter and temperatures drop, plants stop producing chlorophyll. The existing chlorophyll breaks down, and its green colour fades, revealing the underlying yellow and orange carotenoid pigments that were there all along.
5. If absorbing light is key, why aren't plants black to absorb all colours and maximise energy?
This is a fascinating question of evolutionary trade-offs. While a black plant would absorb more total light, it could also lead to overheating and damage to the plant's sensitive photosynthetic machinery. Furthermore, the sun's peak energy output is in the green part of the spectrum. Reflecting this intense light might be a protective mechanism to avoid absorbing too much energy at once, a phenomenon called photo-oxidation. Evolution has thus favoured the chlorophyll system, which is highly efficient at absorbing the abundant red and blue light without the risk of absorbing excessive energy.
6. Can a plant survive if its leaves are not green?
Yes, a plant can survive without appearing green, for a few reasons. Some plants, like the Coleus or Caladium, have such a high concentration of other pigments (like red anthocyanins) that they overpower and mask the green chlorophyll, even though chlorophyll is still present and working. Other plants, known as parasitic plants (e.g., Dodder), have evolved to have little or no chlorophyll at all. They survive by attaching to a host plant and stealing nutrients from it, so they do not need to perform photosynthesis.
7. What causes the vibrant red and purple colours in autumn leaves?
Unlike the yellow and orange colours that are revealed when chlorophyll fades, the bright reds and purples in autumn leaves are actively produced. They come from pigments called anthocyanins. As sugars produced during the day get trapped in the leaves at night due to cool temperatures, the combination of bright light and excess sugar triggers the synthesis of these red pigments. They are thought to act as a sunscreen, protecting the leaf as it retrieves valuable nutrients before falling.
8. What is the primary function of chlorophyll in the life of a plant?
The primary function of chlorophyll is to power life on Earth through photosynthesis. Its main job is to capture energy from sunlight. This captured light energy is then used to convert carbon dioxide from the air and water from the soil into glucose (sugar). This glucose serves as the plant's food, providing the energy it needs for growth, repair, and reproduction.
