Author: Biology Junction Team

Earthworm Anatomy and Dissection Guide

Earthworm Dissection and Earthworm Anatomy

Pictures: Modern Biology, Holt

The following is a classification of a species in the earthworm family Lumbricidae. This common species is Lumbricus terrestris also known as the night crawler or dew worm. In this article, we will cover earthworm anatomy and an introduction on dissecting an earthworm. 

Phylum –
Class –
Family –
Genus –
Species –		 Annelida
Oligochaeta
Lumbricidae
Lumbricus
terrestris

Objectives:

In this earthworm dissection guide, you will learn to:


• Describe the appearance of various organs found in the earthworm.
• Name the organs that make up various systems of the earthworm.

Materials:
Safety goggles, dissecting pins, gloves, forceps, lab safety apron, scissors, paper towel, scalpel, water, dissecting probe, preserved earthworm, hand lens, dissection tray.

Purpose:
In this lab, you will dissect an earthworm in order to observe the external and internal structures of earthworm anatomy, whilst following the all-important lab safety procedures.

This guide is perfect for students in colleges or universities. 

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Background:


Among the most familiar invertebrate animals are the earthworms, members of the phylum Annelida. The word annelida means “ringed” and refers to a series of rings or segments that make up the bodies of the members of this phylum. Internally, septa, or dividing walls, are located between the segments. External segments are called metameres. There may be more than 100 segments in an adult worm. The clitellum is a swelling of the body found in sexually mature worms and is active in the formation of an egg capsule, or cocoon. This is the earthworm reproductive organ. Eggs are produced in the ovaries and pass out of the body through female genital pores. Sperm are produced in the testes and pass out through tiny male genital pores. During mating, sperm from one worm travel along the sperm grooves to the seminal receptacles of another worm. Fertilization of the eggs takes place outside the body as the cocoon moves forward over the body, picking up the eggs of one worm and the sperm of its mate. The pumping organs of the circulatory system are five aortic arches. Circulatory fluids travel from the arches through the ventral blood vessel to capillary beds in the body. The fluids then collect in the dorsal blood vessel and reenter the aortic arches. The earthworm takes in a mixture of soil and organic matter through its mouth, which is the beginning of the digestive tract. The mixture enters the pharynx, which is located in segments 1–6. The esophagus, in segments 6–13, acts as a passageway between the pharynx esophagus and the crop. The crop stores food temporarily. The mixture that the earthworm ingests is ground up in the gizzard. In the intestine, which extends over two-thirds of the body length, digestion and absorption take place. Soil particles and undigested organic matter pass out of the worm through the rectum and anus. The nervous system consists of the ventral nerve cord, which travels the length of the worm on the ventral side, and a series of ganglia, which are masses of tissue containing many nerve cells. The nerve collar surrounds the pharynx esophagus and consists of ganglia above and below the pharynx. Nervous impulses are responsible for movement and responses to stimuli. Each segment contains an enlargement, or ganglion, along the ventral nerve cord. Excretory functions are carried on by nephridia, which are found in pairs in each body segment. They appear as tiny white fibers on the dorsal body wall. The earthworm has no gills or lungs. Gases are exchanged between the circulatory system and the environment through the moist skin.

earthworm anatomy

External Earthworm Anatomy

What is the external anatomy of an earthworm?

The external body of an earthworm is well adapted for living in the soil, similar to the external structure of other insects. The front or head of the worm is called the anterior. The very first section of the anterior contains the mouth and prostomium. The prostomium is a kind of lip which is located on the front of the mouth. Earthworms lose moisture and breathe via their skin. They have light-sensitive cells across their external structure, which are scattered around the skin. These cells give earthworms the ability to detect changes in lighting, and these cells are also sensitive to chemicals and touch. The body is separated in segments which resemble rings. Each segment has a number of bristly hairs attached to it, which helps the earthworm to move around. On mature earthworms, you will find a saddle or glandular ring called a clitellum. When an earthworm has mated, the clitellum will secrete a sack of eggs. The final segment of an earthworm contains the anus which is where waste is secreted. 

Dissection Guide:


1. Put on safety goggles, gloves, and a lab apron.

2. Place earthworm in the dissecting tray & rinse off the excess preservative. Identify the dorsal side, which is the worm’s rounded top, and the ventral side, which is its flattened bottom. Turn the worm ventral side up, as shown in the earthworm anatomy diagram below.

earthworm anatomy

3. Use a hand lens as you observe all parts of the worm, externally and internally. Locate the conspicuous clitellum, a saddle-like swelling on the dorsal surface.  The clitellum produces a mucus sheath used to surround the worms during mating and is responsible for making the cocoon within which fertilized eggs are deposited.  The anterior of the animal is more cylindrical than the flattened posterior and is the closest to the clitellum.  The ventral surface of the earthworm is usually a lighter colour than the dorsal surface.  The mouth is located on the ventral surface of the first segment while the anus is found at the end of the last segment. Find the anterior end by locating the prostomium (lip), which is a fleshy lobe that extends over the mouth. The other end of the worm’s body is the posterior end, where the anus is located.

earthworm anatomy

4. Locate the clitellum (the reproductive organ), which extends from segment 33 to segment 37. Look for the worm’s setae, which are the minute bristle-like spines located on every segment except the first and last one. Run your fingers over the ventral surface of the earthworm’s body.  You should be able to feel bristle-like setae used for locomotion

5. Refer again to the diagram of the ventral view of the worm to locate and identify the external parts of its reproductive system. Find the pair of sperm grooves that extend from the clitellum to about segment 15, where one pair of male genital pores is located. Look also for one pair of female genital pores on segment 14. There is another pair of male genital pores on about segment 26. Try to find the two pairs of openings of the seminal receptacles on segment 10.   Note: These openings are not easy to see.

Internal Earthworm Anatomy

What is the internal anatomy of an earthworm?

At the very front of an earthworm, you will find the pharynx. Earthworms push the pharynx from inside their mouths to grab hold of things. They pull food into their mouths and then soak it in saliva. As earthworms don’t have teeth, they have to use strong muscles called a gizzard, along with sand and soil, to grind up the food they are eating. Once the food has been fully ground up, it travels to the intestines where it is further broken down so that it can be absorbed. The majority of earthworms have five aortic arches which are like hearts and these move around their bodies. A large blood vessel runs across the top of the earthworm and this is called the dorsal blood vessel. This vessel contracts and pumps blood around to the aortic arches. There is a further blood vessel on the lower side of the earthworm which is called the ventral blood vessel. An earthworm has a very simple nervous system. A ventral nerve cord which runs the entire length of its body connects to the cerebral ganglion, which is an earthworm’s brain. Each segment is connected to the cord so that they can sense light and touch, and can move. Each segment is also wrapped in circular muscles, which contract to help the earthworm move. 

Continued: Dissection Procedure

Hint: Position your preserved earthworm dorsal side up and pin it down through the first segment and then again further back behind the clitellum.  Cut a slit in the dorsal surface near the posterior pin.  Using fine scissors extend the cut forward to the first segment.  Be careful not to cut too deep as to affect the internal organs.  Starting at the first segment, cut the septa (thin membranes) that internally divide the segments, so the skin can be laid flat.  Use additional pins to hold the integument open and expose the internal organs.  Continue to lay the skin back until you have uncovered a centimeter or so of the intestine.

6. Turn the worm dorsal side up. Using a scalpel and scissors, make a shallow incision in the dorsal side of the clitellum at segment 33. CAUTION: Scalpels and scissors are very sharp. Report any cuts to your teacher. Using the forceps and scalpel, spread the incision open, little by little. Separate each septum from the central tube using a dissecting needle, and pin down each loosened bit of skin. Continue the incision forward to segment 1.

7. Use the diagram below to locate and identify the five pairs of aortic arches, or hearts. Then find the dorsal blood vessel. Look for smaller blood vessels that branch from the dorsal blood vessel.

earthworm anatomy

earthworm anatomy

earthworm anatomy

earthworm anatomy

Digestive System

The earthworm is an example of a foraging herbivorous annelid, obtaining food by eating its way through the soil and extracting nutrients from the soil as it passes through the digestive tract.

Hint: Starting at the anterior end, locate the muscular pharynx (food ingestion).  This is followed by a tube-like esophagus which terminates in a crop (the wider organ) which serves as a storage stomach.  Posterior to the crop you will find the gizzard.  Gently press on the crop and gizzard to test their firmness.  While the crop is soft and thin, the gizzard is muscular (soil is ground up and churned within the gizzard).  The gizzard is followed by a long intestine in which both digestion and absorption occur.  Undigested material is voided through the anus.

8. Locate the digestive tract, which lies below the dorsal blood vessel. Refer to the diagram above to locate the pharynx, esophagus, crop, gizzard, and intestine.

earthworm anatomy

9. To find organs of the nervous system, push aside the digestive and circulatory system organs. Use the diagram below to locate the ventral nerve cord. Trace the nerve cord forward to the nerve collar, which circles the pharynx. Find one pair of ganglia under the pharynx and another pair of ganglia above the pharynx. The ganglia above the pharynx serve as the brain of the earthworm.

earthworm anatomy

earthworm anatomy

10. The worm’s excretory organs are tiny nephridia. There are two in every segment. Use the preceding diagram to locate some nephridia.

earthworm anatomy

11. Use the diagram below to locate and identify a pair of ovaries in segment 13. Look for two pairs of tiny testes in segments 10 and 11. To find these organs, you will again have to push aside some parts already dissected.

earthworm anatomy

earthworm anatomy

earthworm anatomy

12. Dispose of your materials according to the directions from your teacher in your college or university.

13. Clean up your work area and wash your hands before leaving the lab.

Earthworm worksheet Earthworm facts

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Molecular Geometry Chart: Definition, Examples, and Study Guides

How much do you know about molecular geometry definition and the shapes of molecules in chemistry? Join us as we define this subject, go over some examples, and list the different structures you will find in an electron and molecular geometry chart. We have also included some study guides to help you go further.

 

Molecular Geometry Chart: Definition, Examples, and Study Guides

Molecular geometry is typically taught in college and advanced high school classes. This subject uses geometric models to represent the shape and structure of molecules. It allows scientists to get a precise idea of how the number of atoms and electrons are connected. There are also some rules that help scientists predict which shape a molecule will adopt. There are a huge number of molecules and sequences that can be analyzed. From looking at the number of atoms around a molecule to more difficult structures such as DNA sequence – there are many areas of molecular and electron geometry to explore.

 

What is a Molecular Geometry Chart?

molecular geometry 3d molecules, molecular geometry chart, molecular geometry definition

Molecular geometry is the science of representing molecules in a three-dimensional manner. A molecular geometry chart is a collection of rules on how molecules and electrons will connect and shape a molecule.

Students and scientists can use these charts to create three-dimensional diagrams that represent molecules. These visual representations are interesting because they help students and scientists predict the shape, polarity, and biological activities of a molecule.

These representations can also help with other concepts, such as:

  • Reactivity.
  • Phase of matter.
  • Color.
  • Magnetism.

Molecular geometry can be applied regardless of how complex a molecule is. Students will typically work with simple models at first before learning how to apply these concepts to create detailed models of more complex molecules.

 

Common Molecular Structures

Molecules obey certain laws when atoms and electrons connect with each other. Molecules will form specific shapes. It is crucial to familiarize yourself with these common shapes so you can determine the correct one.

These are the shapes and structures you will find in a molecular geometry chart:

  • Linear structures.
  • Bent or angular connections.
  • Pyramidal structures.
  • Tetrahedral molecules.

You are probably already familiar with these structures if you have been studying chemistry for a while. Most students have an understanding of these structures thanks to the visual representations of molecules shown in class or textbooks even though they might not know about the rules of molecular geometry.

 

Polar And Non-Polar Molecules

Certain molecules can be grouped as either polar or non-polar. Other molecules fall between the two.

 

The geometry of atoms in some molecules is arranged in such a way that one side has a negative charge and the other side has a positive electrical charge. In this case, this type of molecule is called a polar molecule. This means that it has electrical poles. Molecules that aren’t arranged in this way are called non-polar molecules.

 

Not every molecule that has polar bonds is a polar molecule. For example, carbon dioxide has two polar bonds (C O). However, the molecular geometry of carbon dioxide is linear. This means that the two bonds cancel each other out, resulting in the molecule being non-polar.

Electronegativity

What is electronegativity and why does it vary around a molecular geometry chart? Electronegativity is defined as the measure of the tendency of an atom to attract a bonding pair of electrons.

 

If two atoms are equally electronegative, then both of those atoms have the same tendency to attract a pair of bonding electrons, and therefore it will be found on average halfway between the two atoms. To get a bond such as this, both atoms would usually be the same atom.

 

If one of the atoms is slightly more electronegative than the other, this will mean that one of the atoms has a fair share of electron density, and this results in that atom becoming slightly negative. At the same time, the opposing atom will become slightly positive. This is a polar bond.

 

If one of the atoms is incredibly more electronegative than the other, this will result in the electron pair being dragged right over to that electronegative atom. This means that the other atom loses all control of its electron, and the electronegative atom has complete control over both electrons. This results in ions being formed and is called an ionic bond.

 

Lewis Theory And Valence-Shell Electron-Pair Repulsion Theory

You can’t gain a thorough understanding of molecular geometry without studying the Lewis theory and the Valence-shell electron-pair repulsion theory.

The Lewis theory is about how valence shell electrons bond with an atom. This approach represents atoms and electrons in a two-dimensional manner. You will often start with this simple visual representation called a Lewis structure to determine the correct three-dimensional structure for a molecule.

You can create a Lewis structure electron dot diagram by simply writing the symbol for the atom you want to represent. You would then add dots to represent the valence shell electrons connected to the atom.

A valence electron is an electron located in the outer shell of the atom. It is common to omit the electrons that aren’t connected to the outer shells of an atom since they won’t form bonds with other elements and would only make Lewis structure diagrams more complicated. If a shell is closed, the electrons that can be found in this shell won’t be shown on a Lewis electron dot diagram.

In a Lewis structure, you can place the dots on any side of the symbol. However, you can’t have more than two dots per side.

The Valence shell electron-pair repulsion theory states that electrons will naturally repel each other. This applies regardless of the type of pairs they form.

Electrons can form bonded pairs, lone pairs, double bonds, triple bonds, or exist as single unpaired electrons. They will position themselves around an atom so that there is as much space as possible between them. In molecular geometry, each pair or single unpaired electron counts as an electron group.

This natural behavior reduces repulsion between electrons and maximizes the space available to attract other elements the electrons can bond with.

The Valence-shell electron-pair repulsion theory is important vital in the context of molecular geometry because it will help you figure out the angle of the different bonds that exist around an atom. You can use this theory to deduce the structure of a molecule.

 

Molecular Geometry Structures And Atom Groups

You can determine the structure and shape of a molecule once you know about the atoms that make up this molecule, how many electrons are connected to these atoms, and which type of bond these electrons form.

These are the different structures molecules can adopt:

  • If you have an atom with two electron groups, the molecule will adopt take a linear structure.
  • If you have three electron groups, you will have a trigonal-planar structure.
  • The molecule will adopt a bent structure if there are three groups of electrons with a lone pair.
  • If there are four groups of electrons, the molecule will have a tetrahedral shape.
  • A molecule with four groups of electrons and a lone pair of electrons will take the shape of a trigonal pyramid.
  • If you have four groups of electrons and two lone pairs, the molecule will have a bent structure.
  • A molecule with five electron groups will adopt a trigonal-bipyramidal structure.
  • If there are five electron groups and a lone pair of electrons, the molecule will have a seesaw structure.
  • A molecule with five electron groups and two lone pairs, the molecule will be T-shape shaped.
  • If there are five electron groups and three lone pairs, you will have a linear structure.
  • A molecule with six electron groups will have an octahedral shape.
  • A molecule with six electron groups and a lone pair will be shaped like a square pyramid.
  • If you have six electron groups and two lone pairs, the molecule will adopt a square planar structure.

These thirteen different scenarios cover all the different structures you will encounter in molecular geometry. You don’t need to learn them by heart since you can easily deduct the structure that makes the most sense by applying the Valence-shell electron-pair repulsion theory.

 

Molecules With More Than One Atom

blue and red molecules, molecular geometry chart, molecular geometry definition

The molecular geometry chart still applies if you have a molecule with more than one atom. The structure will be more complex and will probably combine different geometric shapes.

If you have a complex molecule, break it down into smaller section and look at each atom individually. Determine how the electrons will connect to this atom in function of the type of bond they form and of the number of electron groups.

You can use molecular geometry rules to determine the shape and structure of each atom and its electrons. You can then apply the Valence-shell electron-pair repulsion theory to determine how these different small structures will connect to each other to form a more complex molecule.

 

Ions

An ion is defined as a molecule or atom which has acquired an electrical charge due to gaining or losing electrons. Polyatomic ion charges are ones which are composed of two or more atoms. When a polyatomic ion is involved in a chemical reaction, the oxidation number of it plays a significant role. This is a number which is either negative, positive, or zero. This oxidation number is an indication of the number of electrons in which an ion can share, lose, or gain when chemically reacting which an atom, compound, molecule, or with another ion. The oxidation number of a polyatomic ion is worked out at the sum of the oxidation numbers that belong to its constituent atoms. This is equal to the positive charge, negative charge or neutral charge that exists on the ion.

 

Diatomic Molecules

A diatomic molecule consists of two atoms. The majority of diatomic molecules are ones of the same element, however, a few combine different elements. Most diatomic molecules are gases at room temperature.

 

Octahedral Molecular Geometry

Octahedral molecular geometry refers to the shape of the compounds that have six atoms or ligands symmetrically arranged around a central atom. This defines the vertices of an octahedral shape. The octahedron is platonic solid, even though octahedral molecules tend to have a central atom and no bonds. The term “octahedral” is a loosely used term amongst scientists, as it focuses purely on the geometry of bonds to the central atom, rather than looking at the differences in the ligands.

 

Bond Angles And Three-Dimensional Geometry

Students often make the mistake of thinking in two dimensions when determining bond angles. Electrons will position themselves to be as far away from each other as possible, but keep in mind that they will do this on a three-dimensional plane. A molecular geometry chart with bond angles will help to clarify these structures.

Working with three-dimensional models is a great way to get used to thinking about geometry in a three-dimensional plane. There are also apps and software you can use to create virtual models and get used to these concepts.

What is the Difference Between Electron-Pair Geometry and Molecular Structure?

Electron Geometry

Electron geometry is the term used for the geometry of the electron pair located on the central atom. This applies whether they are bonding electrons or non-bonding electrons. The definitions of an electron pair is electrons that are in pairs or multiple bonds, lone pairs and sometimes even just one single electron that is unpaired. Electrons are always in constant motion and it can be difficult to determine the path that they are going to take. With this in mind, the arrangement of electrons within a molecule is defined by electron density distribution.

 

An Example of Electron Geometry

We will use CH4 as an example.

 

The central atom in this example is C, plus there are also four valence shell electrons. The hydrogen atoms give four electrons, so that means that there are a total of eight electrons around C. In this example, the single number of bonds are four, and the number of lone pairs here is zero. So with this in mind, we can determine here that the electron geometry of CH4 is tetrahedral.

 

Molecular Geometry

Molecular geometry is the term used when determining the shape of a molecule. This refers to the three-dimensional structure or arrangement of the atoms within a molecule. There is usually a central atom which is surrounded by electrons. When we understand the molecular geometry of a compound, this makes it much easier to determine the magnetism, phase of matter, polarity, color, and reactivity of that compound. The geometry of molecules is often described using bond lengths, bond angles, and torsional angles. With smaller molecules, simply the molecular formula, along with a table of angles and standard bond lengths may be all that is needed to determine the geometry of that particular molecule. It is predicted by looking at only the electron pairs, which is what makes molecular geometry different from electron geometry.

 

An Example of Molecular Geometry

We will use H2O as an example.

H2O is a common polar molecule. The central atom in this case is the oxygen atom which has six valence electrons. Hydrogen, in this case, gives a total of two electrons, which makes the total overall amount of electrons eight. In this example, there are two lone electron pairs, and four electron groups, as well as two single bond pairs. Therefore, the molecular geometry in this example is bent.

 

Why Do Most Atoms Form Chemical Bonds?

 

Most elements contain atoms that form chemical bonds. This is because those atoms become more stable when they are bonded together. Neighbouring atoms are attracted to each other by electrical forces which make them stick together. Atoms that are strongly attractive rarely spend much time on their own – other atoms will usually bond to them quite quickly. The arrangement of electrons around a central atom is what determines the strength in which it seeks out other atoms to bond with.  

 

Chemical Bonds

A chemical bond is formed by the joining of two or more atoms. A stable compound occurs when the total energy of the combined atoms has lower energy than if the atoms were separate. The combined state of these atoms implies there is an attractive force between these atoms – a chemical bond. There are two extreme cases of chemical bonds. These are covalent formula bonds and ionic formula bonds.

 

Covalent Bonding

A covalent formula bond is one which involves sharing of valence electrons by two atoms. These types of covalent bonding can create stable molecules, as long as they share electrons in a way that creates noble gas electron configuration for each atom.

 

Ionic Bonds

During chemical bonds, atoms can either share or transfer their valence electrons. In some extreme cases, one or more atoms may lose electrons and then other atoms gain them which produces noble gas electron configuration. The bond in this case is called an ionic bond.

 

What Is The Difference Between Atomic Orbitals And Molecular Orbitals?

 

The orbital is a region in which the probability of finding an electron is relatively higher than usual. Atoms have a nucleus and within this nucleus they have their own electrons rotating around. When orbitals are overlapped to create molecules via bonding, these types of orbitals are named molecular orbitals. Molecular orbital theory and valence bond theory both explain the properties of molecular and atomic orbitals. Orbitals can hold two electrons within them maximum. The main difference between molecular orbital calculation and atomic orbital calculation is that electrons within a molecular orbital are influenced by two or more nuclei. This depends on the number of atoms in the molecule. Atomic orbitals are different as they are only influenced by one positive nucleus.

 

Organic Chemistry

 

Organic chemistry refers to the study of the composition, structure, properties, preparation, and reactions of compounds which contain carbon. This includes compounds that are not only hydrocarbons, but also compounds which contains a number of other elements such as hydrogen, oxygen, halogens, nitrogen, phosphorus, sulfur, and silicon. This type of chemistry used to only refer to compounds that were produced by living beings. However, it has now been broadened to focus on other substances such as plastics. There is a huge range of organic compounds and these include things such as food, explosives, paints, cosmetics, and pharmaceuticals. Organic chemistry is the best way of creating new compounds. Scientists will develop new and better ways of synthesizing existing compounds with organic chemistry.

 

 

Study Guides

There are several study guides on molecular geometry chart information which you can use to go further and practice molecular geometry. This subject gets easier once you start applying it and become familiar with all the different structures molecules can adopt.

You should start by modeling simple molecules or look at three-dimensional models of different molecules to identify their shape and ask yourself what kind of atom groups and bond types caused the molecule to adopt this structure.

Here are a few study guides to help you go further:

  • This study guide from NYU covers the basics and includes some helpful diagrams of the most common shapes you encounter. We like that the angles are indicated for each diagram.
  • This study guide from Angelo University goes over the Lewis structures, the types of bonds you will encounter, and talks about exceptions and resonance structures. There are plenty of examples, and this material will help you explore additional concepts.
  • This molecular geometry guide from Oklahoma State University sums up all the different structures with a detailed table. This is a great resource if you need help with understanding how angles are determined.
  • This comprehensive guide explores the Lewis dot structures and shows you how to place the dots around the atom symbols.
  • You can test your molecular geometry knowledge with these flashcards and quiz questions.

Interactive 3D Tool

The University of Colorado has an online interactive tool that lets you create 3D models of different molecules. You can select different types of electron groups and see how they will connect to an atom.

This tool will show you the angle of the bonds and show models for different molecules if you don’t want to create one from scratch.

This visual tool would be very useful in a classroom when teaching molecular geometry chart information, but you can use it to try and recreate the thirteen different structures that exist in molecular geometry or to try recreating different specific molecules.

Molecular geometry is a fascinating subject. Studying molecular geometry can seem complex at first, but things become easier once you become familiar with the different structures that exist and understand which factors will influence how a molecule is shaped. Make good use of the study guides listed above, and take the time to play with the interactive 3D tool to try different things.

 

Everything You Need to Know About the Calvin Cycle

The Calvin Cycle occurs during photosynthesis and consists of light independent redox reactions that convert carbon dioxide into glucose. This conversion happens in the chloroplast, or more specifically the stroma of the chloroplast. The chloroplast region is an area between the thylakoid membrane and the inner membrane of the organelle which is typically located in the leaves of plants.

This cycle used to create carbon sugars, mostly, was discovered by Melvin Calvin, Andrew Benson, and James Bassham in 1950 at the University of California. The used radioactive material to trace the pathways carbon atoms took during the carbon fixation step in plant life.

You’ve probably heard the Calvin Cycle called a few other names including the CBB Cycle, C3 Cycle, and dark reactions to name a few.

This process of carbon fixing by plants is essential to all life on the planet. Most new organic growth stems from plants converting carbon to sugars either directly or indirectly. Other plants, or animals, can use these sugars to forms more complex sugars and amino acids when they consume them. It all stems from little plants working day and night to capture light and water.

A Technical Take on the Calvin Cycle

The Calvin Cycle

The Calvin Cycle occurs during photosynthesis and is repeated until it forms a glucose molecule. Photosynthesis goes through two stages to create food and building materials for plants to grow. During the first stage, chemical reactions from light produce ATP and NADPH. The second stage is when the Calvin Cycle takes place. In this stage, carbon dioxide and water get converted to organic materials like glucose. These reactions are called dark reactions which confuses people, but they do not take place at night.

The short explanation of the Calvin Cycle is that it begins with carbon fixation. Carbon dioxide molecules are plucked out of the air to produce glyceraldehyde 3-phosphate. RuBisCO, an enzyme found abundantly around the planet, brings on the carboxylation of a 5-carbon compound and provides a 6-carbon compound that halves itself form two 3-phosphoglycerate. The enzyme phosphoglycerate kinase uses the phosphorylation to create biphosphoglycerate.

Next, the enzyme glyceraldehyde 3-phosphate dehydrogenase uses the reduction of biphosphoglycerate by NADPH. This is called the reduction reactions. Eventually, when the cycle ends, the reactions and reductions produce one glyceraldehyde 3-phosphate molecule per every three carbon dioxide molecules.

That’s a lot of massive words. What that means is the plant uses light and water to convert carbon dioxide into nutrients and oxygen. It takes six turns on the Calvin Cycle for the plant to produce a single glucose molecule. Now that we simplified the process, let’s look at the chemical equation for the Calvin Cycle:

3 CO2 + 6 NADPH + 5 H2O + 9 ATP → glyceraldehyde-3-phosphate (G3P) + 2 H+ + 6 NADP+ + 9 ADP + 8 Pi (Pi = inorganic phosphate)

The Simplified Function of the Calvin Cycle

Simplified-Calvin-Cycle-diagram

How plants create sugar from sunlight, water, and carbon dioxide is complicated as you probably noted from the previous section. However, plants toil away day and night creating glucose, starch, and cellulose so they can grow. The Calvin Cycle plucks carbon molecules right out of the air and creates new plant growth.

The Calvin Cycle is vital to every ecosystem, and it reaches far beyond the plants using it. Plants are the building blocks of all the food in any ecosystem. Herbivores eat plants for energy and growth while carnivores eat herbivores for the same reasons. In the end, everything goes back into the ground and plants start the process all over again.

If plants stopped all their hard work tomorrow, it would only take a few days for animals to start feeling the effects and starving. Herbivores lose their food right away. Carnivores would follow behind the herbivores. Plants make most of the basic building blocks we all need to continue life as we know it. Without their hard work, we’d all be doomed.

While plants are supplying us with the building blocks, we need to continue living, and they help out the environment in other ways. Because the Calvin Cycle depends on carbon dioxide, plants indirectly play a role in regulating carbon dioxide and other gases proven to be harmful to the atmosphere. Plants perform an essential role in helping us clean the air we breathe.

The Calvin Cycle Step by Step

Calvin Cycle step by step

Carbon fixation is the first step. We explained it in brutal technical detail above, but let’s look at it in simpler terms in this section. A carbon dioxide molecule is plucked from the air and combined with a five-carbon acceptor molecule called ribulose-1,5-bisphosphate, or RuBP for short. The result is a six-carbon molecule.

The six-carbon molecule is split in half to form a set of new carbon molecules called 3-phosphoglyceric acid, or 3-PGA for short. The new three-carbon molecules are catalyzed by an enzyme called RuBisCo. This creates the simple sugar molecules the Calvin Cycle needs for stage two. On a side note, because it is used by every plant during photosynthesis, the RuBisCo enzyme if the most common catalyst on Earth. The result of this step is passed on to the next phase.

Step two of the Calvin Cycle is called the reduction step. The 3-PGA molecules created in the carbon fixation step are used in phase two to develop glyceraldehyde-3 phosphate or G3P for short. G3P is a simple sugar. This process uses energy and reactions captured during light-dependent stages of photosynthesis.

This step is called the reduction step because electrons are stolen from molecules created during photosynthesis and given to our new sugars. In chemistry, when you take electrons from a molecule, it’s called a reduction hence the name of this stage. Technically, the electrons are donated and not taken. Taking electrons by force is called oxidation, and that’s not what happens in this stage.

At this point, our plant has created sugar it can store for a long time and use for energy. Anything that eats this plant gets to take advantage of these sugars as well including humans. The plant may choose to use these stored molecules to form new plant materials or repair itself, but that’s not part of the Calvin Cycle so we won’t get into it. This is the end of the sugar-producing phase of the Calvin Cycle.

The final stage of the Calvin Cycle is called the regeneration step. Some of the G3P are held back and not used to make sugars. Instead, they are used to revitalize the five – carbon compound the Calvin Cycle needs to start the process over again. It takes six carbon molecules to make glucose, so plants have to go through the Calvin Cycle six times to make one glucose molecule.

Once the plant has completed this cycle six times, the Calvin Cycle ends and begins again. So, technically, the Calvin Cycle is all three steps done six times each. Plants repeat this process over and over during daylight hours. At night they continue to work making various compounds that don’t require light. This makes plants the most efficient lifeforms on the planet.

Bonus Information About Plants and Their Internal Food Factories

plants

We usually consider waste products bad or at least not edible. However, we need the waste materials plants to produce to survive. An essential waste, or by-product, plants produce is oxygen. While plants are using water and carbon dioxide to make sugars, they release oxygen into the air around them as a waste product.

The delicious fruits and vegetables we all enjoy get most of their flavor from the carbon sugars plants store for energy. From the crunchy stalk of the celery plant to the succulent meat of the peach, plants developed all using just carbon dioxide, water, sunlight, and a few minerals leeched from the soil. I think we can assume these tasty treats are little gifts from the plant kingdom.

The tiny organelles called chloroplasts on the surface of a plant’s leaves can move. Ok, they can’t move individually, but in many plants, they can turn the leaf, so it gets better exposure to sunlight. These plant-based solar cells help capture sunlight so being able to point yourself in the sun makes sense. Some plants take it to another level and bend their stalk or branches to help reach the sunlight.

Some Final Notes

photosynthesis diagram

The fantastic plants we ignore all around us are vital to our survival. They use energy from the Sun in little energy reactors called chloroplasts to do all sorts of cool things. If you glance at the bigger picture and oversimplify it, plants take light from the Sun and turn it into carbon sugars they can store for long periods of time. We could call them solar powered batteries if we want to be humorous about the process.

Plants pitch in and help everywhere they can from cleaning the air to enriching the soil they grow in for the next plants. Plants give us so many things from apples to steak. Without plants toiling away at the bottom of the food chain, nothing in the top of the food chain could survive. Every food we consume comes from plants either directly or indirectly.