Topmost Famous Scientists and Their Contribution | NEET 2023 Biology Exam Preparation

Table of Contents:

• The Living World
• Biological Classification
• Plant Kingdom
• Cell – The Unit of Life
• Mineral Nutrition
• Photosynthesis in Higher Plants
• Respiration in Plants
• Plant Growth and Development
• Principle of Inheritance and Variation
• Molecular Basis of Inheritance
• Evolution
• Human Health and Diseases
• Microbes in Human Welfare
• Biotechnology – Principles and Processes
• Organisms and Populations

The Living World

The 1st chapter of Class 11, ‘The Living World’ deals with the various multicellular and unicellular organisms in this diverse living world. It also briefs about the taxonomic categories. Some of the notable scientists covered in this chapter are –

• Ernst Mayr – He was born on 5th July 1904 in Kempten, Germany. He joined Harvard’s faculty of Arts and Sciences in 1953 and retired in 1975, assuming the title – Alexander Agassiz Professor of Zoology Emeritus.
• Carolus Linnaeus – The binomial nomenclature was proposed by Carolus Linnaeus in his books Systema Naturae and Species Plantarum. Binomial nomenclature is nothing but the use of two terms to name a living organism – generic name and species epithet.

Biological Classification

Chapter 2: ‘Biological Classification’ deals with the classification of living organisms using certain criteria. The scientists who contributed to this biological classification are –

• Aristotle – He was the first to propose the biological classification of plants and animals. He is also called the father of biology. His work was the earliest scientific classification that was based on simple morphological characters.
• Carolus Linnaeus – He is known as the father of systematic botany. He gave the two kingdom classification in 1758 – Plantae and Animalia. Linnaeus wrote Species Plantarum and Systema Naturae.
• Ernst Haeckel – Haeckel proposed the three kingdom classification – Protista, Plantae and Animalia. He was the one to establish the kingdom Protista. The demerit of this classification was that he placed both prokaryotic and eukaryotic organisms containing chlorophyll in a single group.
• Herbert Copeland – He proposed the four kingdom classification by establishing the kingdom Monera. Thus the 4 kingdoms were – Monera, Protista, Plantae and Animalia. The demerit here is that the algae, fungi and protozoans were all included under the kingdom Protista.
• R. H. Whittaker – He proposed the five kingdom classification by establishing the kingdom Fungi. This classification was based on the cell structure, body organisation, mode of nutrition, reproduction and phylogenetic relationship.
• Carl Woese – He proposed the 6 kingdom or 3 domain classification. He separated monera into eubacteria and archaebacteria. Thus cellular life forms were divided into the domains – bacteria, archaebacteria and eubacteria.
• Dmitri Ivanovsky – He worked on tobacco mosaic virus (TMV) and found that viruses were smaller than bacteria.
• M. W. Beijerinck – He coined the term ‘virus’. Beijerinck demonstrated that an extract from infected tobacco plants caused disease in healthy plants. He called the extract ‘contagium vivum fluidum’ (infectious living fluid).
• W. M. Stanley – He crystallised TMV (tobacco mosaic virus) and the crystals mostly consisted of proteins.

Plant Kingdom

Chapter 3 deals with the classification of plant kingdom given by George Bentham and JosephDalton Hooker – ‘Bentham: Hooker’s System of Classification’

It is a natural classification system that classifies flowering plants based on –

• Ultrastructure
• Anatomy
• Embryology
• Phytochemistry

Bentham and Hooker are British botanists who were closely associated with the Royal Botanic Gardens of Kew in England.

Cell – The Unit of Life

All organisms are made up of cells or aggregate of cells. Chapter 8 of Class 11 deals with the concept of cell and cell theory. The scientists who contributed to this field are –

• Robert Hooke – He was the first to observe cells (dead cork cells) and coined the term ‘cell’.
• Antonie van Leeuwenhoek – He was the first to observe live cells (animal cells) and called them ‘animalcules’.
• Robert Brown – He was the first to discover plant nucleus and coined the term ‘nucleus’.
• Mathias Schleiden – He was a German botanist who examined a large number of plants. He observed that all plants are composed of different kinds of cells which form tissues.
• Theodor Schwann – He studied different types of animal cells and reported that they had a thin outer layer (plasma membrane). He also concluded that plants have a cell wall. He hypothesised that the bodies of animals and plants are composed of cells and products of cells.
• Rudolf Virchow – He was the first to explain that cells are formed from pre-existing cells (omnis cellula-e cellula).
• Singer and Nicholson – They proposed the ‘Fluid mosaic model’ in 1972 which is also known as the Singer-Nicolson Fluid Mosaic Model. This explains the structure of the cell membrane.
• George Palade – He discovered ribosomes using an electron microscope.

The cell theory was first proposed based on the observations of Mathias Schleiden (1838) and Theodor Schwann (1839). It stated that all plants and animals are composed of cells and cell products. Later came the modern cell theory which also included Rudolf Virchow’s (1855) work. It stated that all organisms are composed of cells and cell products and all these cells arise from pre-existing cells.

Mineral Nutrition

Chapter 12 of Class 11, Mineral Nutrition focuses on inorganic plant nutrition and the methods to identify the elements essential for plant growth and development. The chapter also briefs on the concept of hydroponics. Julius von Sachs demonstrated a method for growing plants without soil, known as hydroponics. Here, the plants are grown in a nutrient solution.

Photosynthesis in Higher Plants

Chapter 13 deals mainly with the structure of photosynthetic machinery and various reactions that transform light energy into chemical energy. The following are some top scientists who contributed to the concept of photosynthesis.

• Joseph Priestly – He performed a series of experiments that revealed the essential role of air in the growth of green plants.
• Jan Ingenhousz – He conducted the aquatic plant experiment and proved that green parts of plants release oxygen, and sunlight is required for it.
• Julius von Sachs – He found that the green parts in plants are where glucose is made and glucose is usually stored as starch.
• T. W. Engelmann – He demonstrated the importance of red and blue light in photosynthesis. The material that was used in his experiment was Cladophora.
• Cornelius van Niel – He demonstrated that photosynthesis is essentially a light-dependent reaction in which hydrogen from a suitable oxidisable compound reduces carbon dioxide to carbohydrates.

Respiration in Plants

Plants perform photosynthesis to produce sugars (glucose). The reverse process of photosynthesis is respiration. Here, the breaking of complex compounds through oxidation happens within the cells, leading to the release of energy.

Glycolysis is a metabolic pathway where glucose undergoes partial oxidation to form two molecules of pyruvic acid. The scheme of glycolysis was given by Gustav Embden, Otto Meyerhof and Jakub Parnas and is often referred to as the EMP pathway.

Plant Growth and Development

Chapter 15 deals with the intrinsic and extrinsic factors that govern and control the plant developmental process. Plants require a periodic exposure of light to induce flowering. The response of plants to periods of light or dark (day/night) is referred to as photoperiodism. This concept was discovered by Garner and Allard in 1920. They worked on the ‘Maryland mammoth’ variety of tobacco plants.

Principle of Inheritance and Variation

Gregor Mendel conducted hybridisation experiments on garden peas for seven years (1856 to 1863) and is also known as ‘the father of genetics’. He proposed the following laws of inheritance in living organisms – law of dominance, law of segregation and law of incomplete dominance.

He also investigated the characters in the garden pea plant that were manifested as two opposite traits. He conducted artificial pollination or cross-pollination experiments using several true-breeding pea lines.

Seven pairs of contrasting traits in pea plants studied by Mendel

Hugo de Vries, Carl Correns and Erin von Tschermak independently rediscovered Mendel’s results on the inheritance of characters. Thus Mendel’s work resurfaced and got the appropriate recognition.

Chromosomal Theory of Inheritance

Every chromosome has an almost identical partner and occurs in pairs. The chromosomal theory of inheritance was given by Theodor Boveri and Walter Sutton in the early 1900s. It states that:

• Chromosomes come in pairs.
• Chromosomes segregate during gamete formation.
• Chromosomes segregate independently of each other.

The experimental verification of chromosomal theory of inheritance was given by Thomas Hunt Morgan, who used Drosophila melanogaster with different eye colours. The experiment concluded that –

• Eye colour was sex-linked.
• Specific genes are carried on specific chromosomes.
• Genes located on the sex chromosomes exhibit unique inheritance patterns.

Alfred Sturtevant was a geneticist who constructed the first-ever genetic map. He used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes and ‘mapped’ their position on the chromosome.

Molecular Basis of Inheritance

This Class 12 chapter deals with the structure and properties of nucleic acids and the molecular basis of inheritance. The top scientists who contributed to this field are:

• Friedrich Miescher – He identified DNA as an acidic substance present in the nucleus in 1869. Miescher named it as nuclein.
• Erwin Chargaff – He found that, for a double-stranded DNA, the ratios between adenine and thymine, and guanine and cytosine are constant and equal to one.
• Rosalind Franklin and Maurice Wilkins used X-ray photos of DNA to investigate its structure.
• In 1953, James Watson and Francis Crick worked on the molecular structure of DNA and proposed the ‘double helix’ structure of DNA which is also known as the Watson and Crick model.
• Frederick Griffith – The bacterial transformation was shown by him in his experiments on Streptococcus pneumoniae. He showed that the bacteria could transform from one strain to another. The two strains of pneumococci are – the virulent smooth (S) strain that has a polysaccharide coat and the non-virulent rough (R) strain that has no polysaccharide coat.
• Oswald Avery, Colin MacLeod and Maclyn McCarty performed biochemical characterisation of the above-mentioned transforming principle.
• Alfred Hershey and Martha Chase – They performed the transduction experiment and worked with T₂ bacteriophage and E.coli bacteria. They gave unequivocal proof that DNA is genetic material.

Bacteriophage is nothing but a virus that infects bacteria. The phage coat is made of protein and the phage genome is DNA. Transduction is the process by which a foreign DNA is introduced into a cell by a virus vector.

• Mathew Meselson and Franklin Stahl gave the semi-conservative replication model of the DNA.
• Dr. Herbert Taylor – He did experiments on Vicia faba (faba beans) involving the use of radioactive thymidine to detect the distribution of newly synthesised DNA in the chromosomes.
• Francis Jacob (Geneticist) and Jacque Monod (Biochemist) won the Nobel Prize for their work on Lac Operon.

Evolution

Evolutionary biology is the study of the history of life forms on earth. Scientists who contributed to evolutionary studies are –

• Louis Pasteur – He proved that life emerges from pre-existing life forms and thus disproved the doctrine of spontaneous generation.
• Alexander Oparin and J. B. S. Haldane – Their hypothesis states that life emerges from pre-existing non-living organic molecules like fatty acids, nucleotides and amino acids. Also, Haldane used the term ‘soup’ to describe the accumulation of water and organic molecules on earth. Amino acid accumulation gave rise to proteins and fatty acids gave rise to lipids. Likewise, nucleotides polymerise to form RNA and DNA. Thus the theory of the origin of life was proposed.
• The above-mentioned hypothesis was supported by Harlod C. Urey and Stanley Miller through their Urey-Miller experiment. The experiment tested the chemical origin of life under prebiotic atmospheric conditions.
• Jean Baptiste de Lamarck – He proposed Lamarckism (first theory of evolution-Inheritance of acquired characteristics). He stated that the evolution of life forms had occurred but was driven by the use and disuse of organs. Example – Giraffes, in an attempt to forage leaves on tall trees, had to adapt by elongation of their necks. They passed on this acquired character of elongated neck to succeeding generations.
• Charles Robert Darwin – He was born in Shrewsbury, England (1809-1882). He proposed the theory of natural selection. Natural selection is a process in which organisms better adapt to their environment to survive and produce more offspring.
• Alfred Russel Wallace – Wallace studied the flora and fauna of the Malay Archipelago (present-day Indonesia and Malaysia).
• Hugo Marie de Vries – According to him, new species are not formed by continuous variations but by the sudden appearance of variations (mutations). He stated that mutations are heritable and persist in successive generations. The mutation-caused speciation is termed saltation (single-step large mutation).

Here is a brief comparison between Darwin’s theory and Hugo de Vries’s theory

• Ernst Haeckel – Biogenetic law is expressed using Haeckel’s phrase “ontogeny recapitulates phylogeny”. This means the stages of development for an animal embryo are the same as other animals’ adult stages.
• Karl Ernst von Baer – He disproved the biogenetic law. He noted that embryos never pass through the adult stages of other animals.
• Thomas Malthus – He was an economist who gave the theory of Human Population Growth. He said that food supply increases in arithmetic progression whereas population increases in geometric progression.

When the population crosses a certain limit, some factors called limiting factors become operational and limit the size of the population.

• The Hardy-Weinberg principle was given by Godfrey Harold Hardy and Wilhelm Weinberg. They stated that allele frequencies in a population are stable and are constant from generation to generation. The gene pool remains constant and is called genetic equilibrium. Also, the sum total of all allelic frequencies is 1.

(p+q)² = p² + 2pq + q² = 1

Where p = frequency of allele A

q = frequency of allele a

p² = frequency of individual AA

q² = frequency of individual aa

2pq = frequency of individual Aa

Also Check:Hardy Weinberg Law

Human Health and Diseases

Willian Harvey was an English physician who discovered and described the blood circulatory system.

Microbes in Human Welfare

Microbes are a major life component on earth. They are used to produce several products like lactic acid, acetic acid, vaccines and antibiotics.

Antibiotics like penicillin are produced from useful microbes and are used to kill disease-causing harmful microbes. Sir Alexander Fleming discovered penicillin from the moulds of Penicillium notatum. Alexander Fleming, Ernst Boris Chain and Sir Howard Walter Florey won the Nobel prize in 1945 for their work on antibiotics. Antibiotics have played a major role in controlling infectious diseases like whooping cough, diphtheria and pneumonia.

Biotechnology – Principles and Processes

Biotechnology is an advancing field that deals with techniques of using live organisms or their enzymes to produce useful products. Scientists who contributed to this field are –

• Stanley N. Cohen and Herbert Boyer – They were the first to demonstrate rDNA technology in 1972. These scientists came up with the idea of combining the DNA of two different organisms.
• Kary Mullis – He invented the polymerase chain reaction (PCR) technique in 1985. This allowed scientists to make millions of copies of a scarce sample of DNA.
• Francisco Bolivar and Raymond Rodriguez were the scientists who first constructed the pBR322 cloning vector.

Organisms and Populations

G.F. Gause gave the competitive exclusion principle (Gause’s Exclusion Principle). It states that two closely related species competing for the same resources cannot coexist indefinitely and the competitively inferior one will be eliminated eventually. Also, it is only when the resources are limited.

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