Chlorophyll is the name of the substance that gives a plant’s leaves their green appearance. Chlorophyll is contained within chloroplasts in a plant’s leaves. Chlorophyll plays a crucial part in photosynthesis by catching the energy from the sun, which is then turned into energy.
Chlorophyll and Photosynthesis
In this article, we delve into the intriguing and fascinating world of photosynthesis. We focus on the pigment chlorophyll and it is crucial in sustaining life on planet earth.
The Fundamentals of Chlorophyll
Cholophyl mainly resides in chloroplasts within plant cells. Chlorophyll is a green pigment, integral to photosynthesis. The term chlorophyll originates from the Greek words ‘chloros’, meaning green, and ‘phyllon’, meaning leaf.
The Structure of Chlorophyll
Chlorophyll is a complex molecule comprising a porphyrin ring coordinated to a central magnesium ion. This is fundamental to light absorption. Chlorophyll has a hydrocarbon tail, which helps to ensure that chlorophyll remains embedded within the thylakoid membrane of chloroplasts.
Chloroplasts
Chloroplasts are key to photosynthesis. They are very intricate and complex structures. Some people compare the structure of chloroplasts to mitochondria in animal cells. There is a striking similarity in structure even though they do different things.
Each chloroplast contains an outer membrane and an inner membrane, sheltering a stroma, which is a fluid-filled space that hosts enzymes and ribosomes for protein synthesis. Within the stroma, thylakoids, which are flattened sac-like structures store chlorophyll and other pigments. Chloroplasts also contain DNA, reminiscent of their evolutionary origin from cyanobacteria through endosymbiosis.
Chlorophyll and Light Absorption
When sunlight strikes chlorophyll, it absorbs light energy, prompting a cascade of reactions. The light energy is transferred through chlorophyll molecules until it reaches the thylakoid space where reactions occur, leading to photosynthesis.
Photosynthesis Basics
At the reaction centre within the thylakoid space, the absorbed energy from light is harnessed to combine water and carbon dioxide to produce glucose and oxygen. This is photosynthesis. The photosynthesis equation/reaction can be summarised as:
6CO2 + 6H2O + light energy > C6H12O6 + 6O2
- CO2 = carbon dioxide (each carbon dioxide molecule contains one carbon atom attached to two oxygen atoms, connected by covalent bonds)
- H2O = water (each water molecule contains two hydrogen atoms connected to one oxygen atom by covalent bonds)
- C6H12O6 = glucose (each glucose molecule contains six carbon atoms, 12 hydrogen atoms, and six oxygen atoms, all connected by covalent bonds). Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis. Glucose is used to make cellulose in cell walls, the most abundant carbohydrate in the world. Ref. Wikipedia – see https://en.wikipedia.org/wiki/Glucose for more information.
- O2 = oxygen (each oxygen molecule contains two oxygen atoms).
Chlorophyll’s Role in Light Spectrum Absorption
Chlorophyll absorbs light predominantly in the red and blue regions of the spectrum but reflects green. This is a contributing factor to the characteristic green colour of plants.
Leaf Structure
A leaf of a plant is the primary location where photosynthesis takes place. Leaves are much more complex structures than you may think. Leaves contain multiple layers and have several active structures that are utilized during photosynthesis.
The cuticle is the outer layer. This protects the leaf and prevents water loss. The cuticle is the top part of the leaf. This often has a waxy texture, which aids in the prevention of water loss and helps protect the leaf.
The epidermis is under the cuticle. This allows light to pass into the leaf. Beneath the epidermis are two types of mesophyll, these are palisade (the upper part of the mesophyll) and spongy (the lower part of the mesophyll).
The palisade mesophyll contains many chloroplasts and is the part of the leaf where most photosynthesis takes place.
The spongy mesophyll has air spaces to allow gas (oxygen and carbon dioxide) exchange.
The veins in the leaf contain xylem and phloem. The xylem and phloem are vascular (vein-like) structures allowing for water distribution, the transport of nutrients, and sugars to be diffused throughout the necessary parts of the leaf and to the main parts of the plant. The xylem is mainly responsible for the transport of water and nutrients and the phloem is mainly responsible for the transport of the soluble organic compounds (photosynthates) made during photosynthesis. This includes sugars (primarily sucrose), which are transported to the necessary parts of the leaf and to the rest of the plant for its energy needs.
Chlorophyll, Photosynthesis and the Environment
Photosynthesis, utilising chlorophyll, produces oxygen, which is vital for aerobic respiration (breathing) in most life forms. Simultaneously, plants absorb vast amounts of atmospheric carbon dioxide, acting as effective ‘carbon sinks’. Of course, photosynthesis and carbon dioxide/oxygen exchange has happened since the earliest lifeforms and is needed to sustain life on Earth. However, plants are playing an increasingly essential role in mitigating climate change.
Photosynthesis and the Carbon Cycle
The absorption of carbon dioxide during photosynthesis helps balance the global carbon cycle, ensuring that our atmosphere remains habitable and that oxygen is produced. This is essential to maintaining life on Earth.
Read more about chlorophyll here.