It is defined as a type of inheritance in which the expression of a gene is different from Mendelian Inheritance. The Mendelian inheritance expresses the trait of either dominant or recessive gene whereas the polygenic inheritance expresses the mixture or additive of traits displayed in parents. Therefore when the mixture of the traits present in parents is inherited into offspring, it is called a polygenic inheritance pattern.

What is Polygenic Inheritance?

A type of inheritance in which the trait is produced from the cumulative effects of many genes. Inheritance can be expressed mainly in two ways- monogenic inheritance and polygenic inheritance. When the traits result from the expression of only one trait, it is called monogenic inheritance.

The phenotypic ratio or Mendelian inheritance can predict the expression of monogenic inheritance but the polygenic inheritance is a non- Mendelian form. It is expressed together by multiple genes at different loci in the same trait.

For example- In monogenic expression, when heterozygotes having red and white progeny are crossed, the results will appear in the ratio of 3:1.

On the other hand in polygenic expression, the trait is controlled by two pairs of genes and the dominant allele of both loci are expressed in the flower. Here, the results produce red and white color in a ratio of 9:7.

The examples of polygenic inheritance inhuman include hair color, height, skin color, blood pressure, intelligence, and autism, etc. There are two types of alleles that control polygenic inheritance, namely:

1. Contributing alleles: These alleles contribute to continuous variation.

2. Non- contributing alleles: These alleles do not contribute to continuous variation.

They are also called effective and non-effective alleles.

Characteristics of Polygenic Inheritance

• A polygene is a gene that employs a minor effect on a phenotype.

• The effect of the gene remains undetected.

• An equal effect is exerted by numerous genes.

• The dominant gene does not mask the effect of the recessive gene.

• The genes may be either contributing and non-contributing, but there is not any dominant or recessive gene.

• Estimation of population parameters can be done by the statistical analysis of polygenic inheritance.

• The polygenic inheritance is different from multiple alleles. An example of multiple alleles is the human blood group system.

Analysis of Polygenic Traits

In 1918, Sir Ronald Aylmer Fisher describes the quantitative characters of Mendelian genetics. Polygenic inheritance is used to understand the differences between quantitative and qualitative inheritance.

1. The characters such as weight, length, width, height, duration are measured by polygenic traits.

2. The variations are expressed in terms of variance or co-variance.

3. The genetic interpretations of quantitative characters are studied in Quantitative genetics.

Polygenic Traits vs Oligogenic Traits

Segmentation of Polygenic Variability

Segregation of the polygenic variation present in a genetic population is done by variance. There are three types of polygenic inheritance, namely:

1. Phenotypic: The variability can be observed and also include environmental variations. It is often considered total variability.

2. Genotypic: It is genetically inherited variability. The genotypic variability is not influenced by environmental factors. The components of genotypic variability are dominant, additive, or epistatic. Plant breeders use this variability for hybridization and are considered the most commonly exploited variability. The additive variance is produced due to the average effects of genes that are present on different loci. In other words, there is not any dominant allele in additive variance. For example- The offspring produced by a cross between AA and aa alleles show intermediate expressions. It is the most common variance among self-pollinating crops.

3. Environmental: The non-inheritable variations that occur due to environmental factors are called environmental variance. The variance depends upon the environmental conditions and cannot be controlled. It is measured in terms of error mean-variance.

Polygenic Inheritance Examples

i. Polygenic Inheritance in Humans

I. Skin Color and Pigmentation: Skin color is an example of polygenic inheritance. About 60 loci control the skin color in humans. For example- three pairs of alleles present at a locus are responsible for skin color. The alleles are represented as A and a, B and b, C and c. here, the capital letters represent the incomplete dominant alleles that are responsible for the dark color of skin. So, in the offspring, the dark skin color is indicated by a capital letter and the small letter indicates the lighter color of the skin.

Here, the progeny shows intermediate color in the F1 generation and the genotype would be AaBbCc. The F2 generation produces different skin colors in the ratio of 1:6:15:20:15:6:1. The skin color depends upon the amount of melanin in the skin, thus the higher amount of melanin results in darker skin, and a low or negligible amount of melanin results in lighter skin color.

II. Human Heights: Three genes control the height in humans. So, a person having all dominant alleles has a tall phenotype and a short person will have recessive alleles. The polygenic inheritance pattern for height has represented by a curve where the middle portion represents the population with average height.

III. Polygenic Inheritance of Eye Color: The eye color has controlled by two prominent genes and 14 additional genes in humans. A variety of eye colors has been produced due to different combinations of alleles. The eye color depends upon the melanin present in the iris. A high amount of melanin results in black and brown eyes while a low amount of melanin produces hazel or green eye color. The dominant allele increases the amount of melanin and produces black eyes. The combination of these dominant and recessive alleles results in different intermediate eye colors, e.g. light brown eyes.

ii. Polygenic Inheritance in Plants

The common polygenic traits in plants include flower, stem, pollen, yield, oil content, time of flowering, etc.

I. Kernel Color of the Wheat: Three pairs of alleles control the kernel color of wheat. Here, all dominant alleles result in dark red wheat kernel, while the recessive allele produces the white kernel color. The F2 generation produces kernels with different shades of red.

II. Length of the Corolla in Tobacco: There are 5 genes express for the corolla of tobacco. The length of the corolla also shows polygenic inheritance.

Effect of Environment on Polygenic Inheritance

The environmental factors highly influence polygenes. The phenotypic variance is controlled by various environmental factors. The norm of reaction is defined as the variation in the phenotypic expression which can be classified as

• Narrow norms of reaction

• Broad norms of reaction

All the phenotypic variances such as intelligence, depression, skin color, height are affected by the environment. Hereditary disorder phenylketonuria is an example of a polygenic character that is caused due to lack of enzyme phenylalanine.

Importance of Polygenic Inheritance

Polygenes or polygenic variance has great significance in evolution. The polygenesis results in the evolution of species that is called the theory of polygeny of evolution. The specific requirements or needs of particular species result in different variations that are responsible for adaptive changes in the species. Plant breeders utilize polygenes to improve the crops. The polygenes work on the principle of segregation and recombination of polygenic genes after interbreeding.

Protein: Definition, Structure, and Examples

Polygenic Inheritance Citations

• Polygenic risk scores: from research tools to clinical instruments. Genome Med . 2020 May 18;12(1):44.
• The personal and clinical utility of polygenic risk scores. Nat Rev Genet . 2018 Sep;19(9):581-590.
• An Expanded View of Complex Traits: From Polygenic to Omnigenic. Cell . 2017 Jun 15;169(7):1177-1186.

The process of producing offspring by organized bodies is called reproduction.

What is Reproduction?

The process of producing offspring by different methods is called reproduction. Reproduction involves the production of a new individual organism from a single parent or may involve two parents. It is one of the fundamental processes of any living being that is demonstrated by the ability of an organism to produce a new organism.

It can be categorized into two types-

(1) Sexual Reproduction

(2) Asexual Reproduction

The mode of reproduction that involves the fusion of male and female gamete is called sexual reproduction. It requires two parent organisms, where the fusion results in the formation of the zygote that develops into genetically different offspring.

Meiosis and fertilization are the major processes of sexual reproduction. Meiosis is also known as reduction division that produces genetically different haploid gametes due to genetic recombination. Meiosis occurs to maintain the number of chromosomes in a zygote that has a different genome from either of the parents.

On the other hand, asexual reproduction is another mode of reproduction that involves only one parent. The offspring produced by asexual reproduction is a clone of its parent organism. The process of ploidy reduction, meiosis, and fertilization are absent in asexual reproduction.

However, in asexual reproduction, the offspring results in low genetic variation in the species and is considered a clone of the parent. Etymology- The word reproduction is derived from the Latin word re meaning “again” and production meaning “production”. It is also known as breeding or procreation.

Protein: Definition, Structure, and Examples

Reproduction Citations

• Thyroid hormones and female reproduction. Biol Reprod . 2018 Nov 1;99(5):907-921.
• Sleep and female reproduction. Curr Opin Obstet Gynecol . 2019 Aug;31(4):222-227.

In biology and biochemistry, Proteins are defined as a chain of amino acids joined together by peptide bonds. They are nutrient-rich macromolecules that provide 4cal/gram food energy.

Etymology: The word protein has derived from the French word “protein” and Greek word “protos”, meaning “first”.

What is Protein?

Proteins are a type of biomolecules made up of amino acid chains. Amino acids are considered a monomeric unit of proteins that join together by peptide bonds to form a polypeptide chain or protein. All living organisms produce different biomolecules such as carbohydrates, lipids, and nucleic acids.

Proteins are considered as one of the major biomolecules that are made up of carbon, hydrogen, oxygen, sulfur, nitrogen, and sometimes phosphorus.

They have a different composition, sequence, function, and spatial configuration than other biomolecules. The protein folding and its particular 3D configuration is determined by the amino acid sequence. The specific protein configuration further determines the activity and function of the protein.

Proteins have various important functions in a biological system, for example- some proteins are structural material whereas others help in transport, immunity, and act catalysts (enzymes).

Protein vs Peptide

The amino acid consists of a compound called a peptide, which is connected by a peptide bond. The bond is formed between the carboxyl group of one amino acid and the amino group of another amino acid. When a peptide is composed of two amino acids, it is considered a dipeptide.

Similarly, peptides are made up of several amino acid residues from an unbranched linear chain that is called a polypeptide. The polypeptide may have as many as 4,000 amino acid residues or sometimes contain only 20 to 30 amino acid residues. A complex of polypeptides or 3D structure of a polypeptide is called a protein.

Protein Structure

The amino acid residues are the monomeric unit of protein. These amino acids are joined together by peptide bonds. All polypeptide chains are composed of different amino acids where the DNA specifies the sequence of amino acids in the protein.

There are usually 20 standard amino acids that define the genetic code however the genetic code of some Archaea and other organisms specifies more amino acids. The structure and function of a particular protein are determined by the sequence of amino acids.

The proteins can form a complex either with another protein or with any other biomolecule. The co-factors or prosthetic groups are also a type of non-peptide group in a protein.

Based on the structural proteins are divided into four types-

(1) Primary Structure

(2) Secondary Structure

(3) Tertiary Structure

(4) Quaternary Structure

The unbranched sequence of amino acids in a polypeptide chain is concerned as the primary structure. The secondary structure is stabilized by hydrogen bonds that include α-helix, β-sheet, and turns and loops.

The tertiary structures are also called folds that are stabilized by various nonlocal interactions such as disulfide bonds, salt bridges, etc. The protein complexes are often found in the quaternary structure.

The tertiary and quaternary structure is also known as conformations and the transition between these two structures are called conformational change. The binding of substrate to the protein induces conformational changes in the structure of the substrate.

Types of Protein

Based on the forms and functions of proteins, they are categorized into different types, such as globular proteins, fibrous proteins, or membrane proteins. Most of the enzymes are globular proteins whereas fibrous proteins have structural roles such as collagen, keratin, etc.

The membrane receptors or channel proteins are a type of membrane proteins that helps in the transportation of polar molecules.

Biosynthesis of Proteins

Proteins are synthesized inside the cell in most living organisms. In eukaryotes, the process starts from the nucleus, where the transcription completes and results in the formation of an mRNA script.

Later, the mRNA script moves into the cytoplasm, and the ribosomes along with tRNA use this script for translation into an amino acid sequence. In the case of prokaryotes, the nucleus is absent therefore the transcription also completes in the cytoplasm of a prokaryotic cell.

The process of creating protein is called the biosynthesis of protein synthesis. The process involves transcription, amino acid synthesis, and translation. The set of biochemical reactions that produce amino acids from carbon sources is called amino acid synthesis.

The process includes two major processes named transcription and translation. The conversion of DNA into mRNA is called transcription, this mRNA molecule act as a template for translation.

The process of translating a nucleotide sequence into an amino acid sequence is called translation. The process completes in the cytoplasm of the cell where the ribosomes are located.

The translation completes in the following steps-

(1) The binding of mRNA to a ribosome

(2) The ribosome begins matching tRNA anticodon sequences to the mRNA codon

(3) The amino acid carried by the tRNA gets added to the elongating chain

(4) A stop codon releases the polypeptide chain and the mRNA. The process also includes proteolysis, post-translational modification, and protein folding.

Protein Degradation

Different kinds of proteins have a different lifespans. Some proteins remain for years while some proteins degrade within few minutes of production. The misfolded proteins can cause instability and dysfunctions in the body thus they are degraded to prevent the causes.

Proteins may be degraded in proteasomes or in eukaryotes the proteins are degraded in lysosomes of the cell. The lysosome is a membrane-bound organelle that contains digestive enzymes such as proteases that helps in the digestion of endocytosed proteins.

Biological Functions of Protein

Proteins are considered one of the major biomolecules. They have various significant roles in the biological system. Structural proteins such as keratins are the structural components of hairs, and actin and myosin are the components of muscles.

Most of the enzymes are proteins that catalyze various biochemical reactions. Some other important functions of protein include transportation, antibodies, and as regulators of gene expression. Some of the proteins are acquired through diet whereas others are biosynthesized in the cell. Thus the dietary proteins serve as a food source.

Plant Cell: Definition, Labeled Diagram, and Examples

Protein Citations

• Immunogenicity of Protein Pharmaceuticals. J Pharm Sci . 2019 May;108(5):1637-1654.
• The physiology of protein S-acylation. Physiol Rev . 2015 Apr;95(2):341-76.
• Proteins: molecules defined by their trade-offs. Curr Opin Struct Biol . 2020 Feb;60:50-56.

Tertiary consumers are those organisms that get their nutrition from primary and secondary consumers. They are also called top carnivores. In ecology, a shape pyramid is used to show the feeding relationships of organisms, it is called an ecological pyramid.

The flow of energy through different trophic levels in an ecosystem is also represented by the ecological pyramid. Based on the mode of nutrition, the organisms are categorized into different groups, these groups are called trophic levels. A specific position in the ecological pyramid based on the mode by which an organism obtains its nutrition is called a trophic level.

The base of the pyramid is occupied by producers or autotrophs. Autotrophs can produce their food by the process of photosynthesis, they convert inorganic molecules such as CO2 and water into organic sugars in the presence of sunlight.

Other trophic levels of the pyramid are occupied by consumers. The consumers can be divided into primary consumers, secondary consumers, and tertiary consumers. They cannot perform photosynthesis and get their nutrition from other organisms. Decomposers or detritivores are found at the top of the pyramid and feed upon the dead organic matter.

Consumers depend upon the producers of other heterotrophs for their nutrition. They adopt different methods such as parasitism, predation, hunting, etc. to obtain food. Tertiary consumers are found at the fourth trophic level in the pyramid. These organisms are mainly carnivores and feed upon the primary consumers and secondary consumers.

In other words, the carnivores that get their nutrition from other carnivores are called tertiary consumers. They are also called third-level consumers.

Diffusion: Definition, Mechanism, and Examples

Tertiary Consumers Citations

• Consumer involvement in the tertiary-level education of mental health professionals: a systematic review. Int J Ment Health Nurs . 2014 Feb;23(1):3-16. 

The passive movement of molecules or particles from higher concentration to lower concentration region is called diffusion. A concentration gradient is needed for the diffusion. The molecules can only move when there is dissimilar amount of solutes or molecules between two regions that form a concentration gradient.

In biology, diffusion is the passive movement of ions or other particles such as glucose, respiratory gases that move from higher concentration to lower concentration of these solutes. The concentration gradient generated by unequal amount of the particles incite them to equalize the concentrations among both the regions.

During diffusion, the solutes move in bidirectional route. It is defined as net movement of particles along their concentration gradient. For example- carbon dioxide and oxygen move across the alveolar-capillary membrane of mammalian lungs, similarly the movement of glucose is also an example of diffusion.

Diffusion Etymology

The solutes or particles move from their higher concentration to lower concentration region by the process of diffusion. It is a type of passive transport. In diffusion, the particles move along their concentration gradient therefore it is an energy independent process.

The word diffusion is derived from the Latin word “diffusionem” that means “a pouring forth”.

What is Diffusion?

In physics, diffusion is defined as movement of particles from their higher concentration to their lower concentration that is driven by thermal energy.

Diffusion is defined in chemistry as motion of the particles suspended in any liquid or gas due to the collision of particles. The collision is called pedesis or the Brownian movement. The Brownian movement of particles decreases when the particles increase in number.

It can be easily observed in a concentrated solution. The movement again starts with decrease in concentration and follows fick’s Law. The rate of diffusion is affected by some factors like temperature, concentration, distance, and material. The rate of diffusion increases when the temperature is higher and decreases at a lower temperature.

The rate of diffusion get faster with increasing concentration of particles in a solution. Distance also affect the rate of diffusion, shorter distance increases the rate of diffusion. Similarly, small and lighter particles diffuse faster than large molecules.

The example of diffusion in chemistry includes food dye dropped in an aqueous solution. Diffusion is also defined as spreading out of the particles.

In biology, the diffusion occur within a biological system. For example cell membrane that is a semipermeable membrane. The diffusion is defined in biology as a type of passive transport used for the movement of particles or molecules.

Transport is of two types- Active transport and passive transport. When the particles move down to the concentration gradient it is called passive transport that is energy-independent process. In active transport the particles move from lower concentration region to higher concentration region or against the concentration gradient therefore it requires chemical energy.

Types of Diffusion

Diffusion is classified into two types- simple diffusion, and facilitated diffusion. In simple diffusion, the movement does not require assistance whereas the facilitated diffusion requires any assistance to complete the process.

The assistance is provided by transport proteins found in the cell membrane. Thus, the facilitated diffusion can only occur in presence of any transport proteins when the molecule binds to the protein transporter.

Diffusion vs Active Transport

Diffusion is a type of passive transport where the particles move from their higher concentration region to the lower concentration region, whereas active transport facilitates the movement of particles from lower concentration to higher concentration region.

The passive transport does not require chemical energy but active transport requires energy. The energy used in the form of ATP.

Plant Cell: Definition, Labeled Diagram, and Examples

Diffusion and Osmosis

The passive transport can occur by different types. For example- diffusion and osmosis. Both facilitates the movement of particles in a downhill manner and do not require energy. The main difference between both the methods is the diffusing molecules.

Solutes of a solution are diffused by the process of diffusion, whereas, osmosis diffuse the particles of solvent of the solution. In osmosis, the solvent molecules diffuse through a biological membrane.

Importance of Diffusion

Diffusion plays a significant role in a cell. The cell has an outer covering that regulates the transport of substance. It is called cell membrane or plasma membrane that is selectively permeable membrane. Plasma membrane is composed of lipid bilayer, transport proteins, and carbohydrates.

Due to its structure, only small nonpolar molecules and ions can pass directly through the lipid bilayer. The cell membrane does not allow large polar molecules to diffuse easily therefore they cross the membrane via transport proteins. Based on the polarity and size, different molecules cross the membrane by different mechanisms.

For example- Small non-polar molecules diffuse by simple diffusion, Polar molecules such as glucose and larger ions use facilitated diffusion, and large non-polar ions such as retinol are diffused by facilitated diffusion and require membrane proteins (e.g. retinol-binding protein).

Diffusion in Plants and Animals

The common example of diffusion in plants is diffusion of gases. For example – The transport of carbon dioxide and oxygen in leaves of the plant. Plant take carbon dioxide to perform photosynthesis and release oxygen into the environment through stomata.

Similarly in animals the transport of respiratory gases also occur by diffusion. In humans, the respiratory gases diffuse through the capillary beds that separate blood from the tissue fluid.

The alveoli of the lungs diffuse carbon dioxide from the blood and oxygen into the blood respectively. The oxygen then diffuses from the blood to the cells and tissues of the body.

Diffusion Citations

• Enhanced Diffusion and Chemotaxis at the Nanoscale. Acc Chem Res . 2018 Oct 16;51(10):2365-2372.
• Complex Diffusion in Bacteria. Adv Exp Med Biol . 2020;1267:15-43.

An element is a substance made of atoms having an identical number of protons. The element cannot be decomposed by any chemical method into simpler substances. In general, the element act as a fundamental component of any entity, for example, the phloem in plants are made up of sieve element.

Etymology: The word element is derived from the Latin word “elementum” meaning “rudiment”.

Chemical Element

A pure substance that consists of only one type of atom is called an element. All the chemical elements have the fundamental building block or the smallest unit, called the “atom”.

An atom has the same number of protons in its nuclei therefore the elements made by the atoms also have a particular number of protons in their atomic nuclei. For example- An element named Carbon is made up of atoms that have the same number of protons, i.e. 6.

Examples of some common elements are iron, copper, silver, gold, copper, hydrogen, nitrogen, and oxygen. At present, there are 118 elements have been identified by scientists among which 94 are natural and 24 are synthetic elements.

The natural elements have an atomic number below or equal to 94 whereas the synthetic elements have atomic numbers beyond 94.

Element of Human Body

Living beings are mainly made up of organic molecules that include carbon, hydrogen, oxygen, and nitrogen. The human body is also made of these elements in the ratio of as follows: oxygen (65%), carbon (18.5%), hydrogen (9.5%), nitrogen (3.2%), calcium (1.5%), and phosphorus (1%).

Almost 99% of the total mass of the human body is comprised of these elements and 0.85% is comprised of other elements such as potassium (0.4%), sulfur (0.3%), sodium (0.2%), chlorine (0.2%), and magnesium (0.1%).

Substances

A substance is defined as a matter which has a definite chemical composition and distinct properties. The substance can be made of the same type of elements or maybe different types of elements in combination.

A compound is formed by elements, for example, Table salt of sodium chloride is formed by the combination of sodium and chloride atoms. These compounds include atoms that are held together by chemical bonds.

Phosphodiester Bond: Definition, Structure, and Examples

The combination of various elements results in the formation of some important compounds that are crucial to living beings such as water, salt, carbon dioxide, etc. An element can also exist in different physical forms or multiple substances can be formed by only one type of element, which is called allotropes.

Allotropes are made of similar elements however they can differ in their physical structure. For example- Carbon can form various structures such as coal, graphite, and diamond. All these compounds are made up of a similar element- carbon but they have different physical structures.

Another type of substance is alloy. A mixture of metal or non-metallic elements is called an alloy. For example- brass is the mixture of copper and zinc, similarly, bronze is also formed by mixing copper and tin.

Minerals

It is an abiogenic chemical compound that is usually found in crystalline form. A pure mineral is usually made up of an uncombined form of a mineral that has a distinct mineral structure.

For example- Gold, silver, carbon, aluminum, cobalt, copper, lead, iron, etc Minerals are also important for living organisms and act as an essential nutrient needed by our bodies.

Essential nutrients are classified into four groups: (1) vitamins (2) essential fatty acids (3) essential amino acids and (4) essential minerals. There are three types of essential elements that are macrominerals, bulk elements, and trace elements.

Bulk elements include carbon, hydrogen, oxygen, and nitrogen that have a large proportion of the human diet. As compared to bulk elements, the macrominerals are needed in lower amounts, such as calcium, phosphorous, potassium, and chlorine, etc.

The trace elements are required in a very small amount for the survival of the organism. The example of trace elements includes copper, zinc, manganese, iodine, and sulfur, etc.

Isotopes

An element can have different forms based upon the different number of neutrons within its nuclei, these forms are called isotopes. Isotopes have the same number of protons and a different number of neutrons therefore they have the same atomic number but different mass numbers.

For example, carbon can exist in three isotope forms: carbon-12, carbon-13, and carbon-14. Radioactive isotopes are known as radioisotopes. The radioisotope loses energy and emits radiation due to an unstable atomic nucleus that is called radioactive decay. The radioisotopes are used to monitor DNA replication, and also to monitor pollutants and water runoffs.

Biological Definitions

The fundamental unit or component of an entity is defined as an “element”. Sieve element in angiosperms is an example of this term. The sieve elements are the main conductive cells in the phloem.

Element Citations

• The Long-Standing Paradox of Seed Dormancy Unfolded? Trends Plant Sci . 2019 Nov;24(11):989-998.
• The role of light in regulating seed dormancy and germination. J Integr Plant Biol . 2020 Sep;62(9):1310-1326.

The word homologous describes any sort of similarity in some ways. For example, if a pair of the chromosome have similar gene sequence and centromere location, they are called homologous chromosomes.

The homologous structures are exemplified in biology by the same anatomical composition or structural features of the body parts. According to evolutionary biology, the organisms having similarities indicate a common ancestor or the same developmental origin.

Homologous Structures Examples

i. Limbs: Humans and other animals contain similar bone parts in the upper limbs. The arms of humans and other animals contain the same set of bones, i.e. humerus, radius, and ulna. The arms of different animals are the example of homologous structures.

The forelimbs have the same anatomical structure but are used differently. They have the same embryonic origin, therefore, have a similar basic structure. The basic bone component of lower limbs is also similar among humans and other animals that composed of femur, tibia, and fibula.

ii. Vestigial Structures: Another example of homologous structures is vestigial structures that are remnants of the ancestral form. These structures alter their original function and remain in the body as remnants but they are used to study the evolutionary history of the species.

The common example of the remnant is the pelvis in snakes which is structurally similar to the pelvis of humans, dogs, and cats. The vestigial structures or remnants are also found in humans. For example- In the embryonic stage, the appearance of human tailbone show shreds of evidence that human and other mammals share a common ancestor.

Homologous Structures vs Analogous Structures

The structures having the same functions but differ in their anatomical structure are called analogous structures. The organisms having analogous structures represent dissimilar ancestors and do not show any evidence of common evolutionary lines.

They also may live in different locations but they use the body parts for similar functions. The example of analogous structures include wings of a bird, bat, and insect.

Autotrophs: Definition, Types, and Examples

The wings of birds and bats perform the same function of flying but they differ in their composition, the anatomical features of these organisms are unrelated. Another example is the flippers of a whale and the fins of a fish.

The structures having similar functions but differ in their anatomy are called analogous structures whereas structures having the same anatomical features but different functions are known as homologous structures. Homologous structures show similar developmental patterns on the other hand analogous structures do not.

Homologous Structures Citations

• The Search for Common Origin: Homology Revisited. Syst Biol. 2019 Sep; 68(5): 767–780.
• Genetic and developmental bases of serial homology in vertebrate limb evolution. Development . 2000 Dec;127(24):5233-44.

Autotrophs are organisms that can convert inorganic materials into nutritive organic molecules. They use two different methods including photosynthesis (which involves light energy) and chemosynthesis (which involves chemical energy) to produce organic molecules.

Photoautotrophs are those organisms that synthesize food through the process of photosynthesis whereas chemoautotrophs synthesize food through chemosynthesis. Autotrophs are also known as autophytes. They produce their food hence they are called producers.

Etymology: The word autotroph is made of the Greek word autos, meaning “self” and trophe, meaning “nutrition.” Synonyms: autotrophic organism, primary producer

Types of Autotrophs

Autotrophs are classified into two major types:

i. Photoautotrophs

ii. Chemoautotrophs

i. Photoautotrophs

The organisms that perform photosynthesis in the presence of sunlight are called photoautotrophs. They produce organic compounds, such as carbohydrates, fats, and proteins, from inorganic substances. The equation for photosynthesis is as follows:

6CO₂ + 12H₂O + energy ⇒ C₆H₁₂O₆ + 6O₂ + 6H₂O

Photoautotrophs consist high amount of chlorophyll pigments that capture sunlight. The chlorophyll has found in specific organelles called the chloroplast. Chlorophyll is also responsible for the green color of leaves. Some other pigments are also used in the process of photosynthesis such as accessory pigments.

Accessory pigments include carotenoids and phycobilins help in absorbing light. The process needs inorganic substances such as carbon dioxide, inorganic salts, and water to perform photosynthesis in the presence of sunlight.

In the present scenario, several artificial light resources are also developed and proven useful in inciting photosynthesis. The research in lighting plays an important role in crop improvement and horticulture.

ii.Chemoautotrophs

Several organisms produce their food by the process of chemosynthesis and do not require sunlight. These organisms are called chemoautotrophs. Instead of photoautotrophs, chemoautotrophs use chemical energy to produce organic molecules such as carbohydrates. They convert the inorganic compounds such as hydrogen sulfide, sulfur, ammonium into sugar molecules.

Autotrophs Examples

All the Green land plants, algae, and lichens are common examples of autotrophs. The land plants include grasses, dicots, gymnosperms, bryophytes, and ferns and photosynthetic algae such as charophytes, chlorophytes, dinoflagellates, and diatoms are examples of autotrophs.

They all contain chlorophyll that absorbs sunlight. Due to the high amount of chlorophyll plants have a distinctively green color especially in photosynthetic organs (e.g. leaves). They produce organic molecules and store food in form of starch.

Cellular Respiration: Definition, Equation, and Examples

Plants also produce oxygen as a by-product and release it into the air that is used by other organisms in the process of aerobic respiration. Examples of chemoautotrophs include methanogens, halophiles, nitrifiers, thermoacidophiles, and sulfur oxidizers.

The Role of Autotrophs in an Ecosystem

Autotrophs play many important roles in an ecosystem. They act as primary producers in a food chain and are found at the base of the ecological pyramid. They are autotrophic organisms that mean they produce their food and do not depend on other organisms whereas the heterotrophic organisms cannot make their food and rely on primary producers for nutrition.

Autotrophs store food in the form of starch that is an energy source for heterotrophic organisms. Autotrophs also perform in nutrient cycles of the ecosystem.

They can convert complex molecules into simpler substances, For example, carbon dioxide is used by plants to produce organic molecules through photosynthesis. They also produce oxygen as a by-product and release it into the environment through transpiration.

The oxygen is used by other aerobic organisms for aerobic respiration. All living organisms, especially animals use oxygen in the redox reaction during ATP synthesis. ATP is an energy currency for all animals that are used to perform metabolic activities or other cellular functions properly.

Autotrophs Citations

• Conservation and dissipation of light energy as complementary processes: homoiohydric and poikilohydric autotrophs. J Exp Bot . 2006;57(6):1211-23.
• Carbohydrate movement from autotrophs to heterotrophs in parasitic and mutualistic symbiosis. Biol Rev Camb Philos Soc . 1969 Feb;44(1):17-90.