Types of RNA

Atomic RNA Dossier | BSI Style

The RNA World Dossier

Types, Enzymes & Cellular Secrets

The Division of Labour

In Eukaryotes, the task of transcription is split among three specialized RNA Polymerase enzymes. Below is the classified data on their production, structure, and unique functions.

rRNA

80%
Full Name
Ribosomal RNA
Primary Function
The structural and catalytic engine of the ribosome. It forms peptide bonds (Ribozyme activity).
Types (Svedberg Unit)
Prokaryotes (70S): 23S, 16S, 5S
Eukaryotes (80S): 28S, 18S, 5.8S, 5S
PRODUCED BY RNA POLYMERASE I
(Except 5S rRNA)

tRNA

15%
Full Name
Transfer RNA (Soluble RNA / sRNA)
Why “Soluble”?
Called sRNA because it is soluble in 1M NaCl solution. It is the smallest RNA.
The Numbers
Size: 73-93 Nucleotides.
Shape: Clover-leaf (2D) / Inverted L-shape (3D).
PRODUCED BY RNA POLYMERASE III
(+ 5S rRNA & snRNAs)

mRNA

2-5%
Full Name
Messenger RNA
Primary Function
Carries the genetic blueprint (codons) from DNA to the ribosome. It is the most unstable RNA.
Record Breaker
Largest Gene (Human): Dystrophin (2.4 million bases).
Structure: Linear, has Cap (5′) & Poly-A Tail (3′).
PRODUCED BY RNA POLYMERASE II
(Transcribes hnRNA precursor)

Classified Data Summary

RNA TYPE ENZYME (EUKARYOTES) KEY FUNCTION CELLULAR %
rRNA RNA Polymerase I Catalytic Core (Ribozyme) 80%
tRNA RNA Polymerase III Amino Acid Adapter 15%
mRNA RNA Polymerase II Genetic Messenger 2-5%
ATOMIC KNOWLEDGE DATABASE | BSISIR.COM

The Atomic History of DNA-A Chronological Dossier

The Atomic History of DNA | BSI Style

BSI SIR Presents

DNA HISTORY – A Chronological Dossier
DISCOVERY 1869

Friedrich Miescher

Identified DNA as an acidic substance present in the nucleus and named it ‘Nuclein’. However, isolating such a long polymer intact was technically limited at the time.

BIOCHEMISTRY 1889

Richard Altmann

A student of Miescher, Altmann purified ‘nuclein’ further, removing associated proteins. Recognizing its acidic properties, he coined the modern term “nucleic acid”.

THE BASES Late 1800s

Albrecht Kossel

Determined the chemical structure of the nitrogenous bases found in nucleic acids. He identified adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U).

THE NUCLEOTIDE 1920s

Phoebus Levene

Discovered the three major components of a single nucleotide unit: phosphate, pentose sugar (deoxyribose in DNA), and a nitrogenous base. He proposed that nucleic acids are polymers of these units.

TRANSFORMATION 1928

Frederick Griffith

Experimented with Streptococcus pneumoniae. He found that heat-killed virulent ‘S’ strain bacteria could somehow transform non-virulent ‘R’ strain bacteria into killers.

He called this the “Transforming Principle”.

BIOCHEMISTRY 1944

Avery, MacLeod & McCarty

They purified biochemicals from heat-killed S cells. Digestion with proteases and RNases did not stop transformation, but digestion with DNase did.

VERDICT: DNA is the hereditary material.

THE RULES 1950s

Erwin Chargaff

Observed that for double-stranded DNA, the ratios between Adenine and Thymine, and Guanine and Cytosine, are constant and equal to one.

THE PROOF 1952

Hershey & Chase

Worked with bacteriophages using radioactive Phosphorus (P32 for DNA) and Sulfur (S35 for protein). They proved that only DNA enters the bacteria upon infection.

This provided unequivocal proof that DNA is the genetic material.

X-RAY DATA 1953

Franklin & Wilkins

Maurice Wilkins and Rosalind Franklin produced critical X-ray diffraction data of DNA at King’s College. This visual data was the key to unlocking the helix structure.

THE DOUBLE HELIX 1953

Watson & Crick

Based on X-ray data and Chargaff’s rules, they proposed the famous Double Helix model.

Salient Features of the Model:

  • DNA is made of two polynucleotide chains, where the backbone is constituted by sugar-phosphate, and the bases project inside.
  • The two chains have anti-parallel polarity. (If one chain has polarity 5’→3′, the other has 3’→5′).
  • The bases in two strands are paired through hydrogen bonds (H-bonds) forming base pairs (bp).
  • Adenine forms two hydrogen bonds with Thymine (A=T) from opposite strand and vice-versa.
  • Guanine is bonded with Cytosine with three H-bonds (G≡C).
  • Consequently, a purine comes opposite to a pyrimidine. This generates approximately uniform distance between the two chains.
  • The two chains are coiled in a right-handed fashion.
  • The pitch of the helix is 3.4 nm.
  • There are roughly 10 bp in each turn. Therefore, the distance between base pairs in a helix is approximately 0.34 nm.
  • The plane of one base pair stacks over the other in the double helix, conferring stability to the structure.
PROKARYOTIC PROOF 1958

Meselson & Stahl

Used heavy Nitrogen isotope (N15) and CsCl density gradient centrifugation in E. coli to prove experimentally that DNA replicates semi-conservatively in prokaryotes.

EUKARYOTIC PROOF 1958

J. Herbert Taylor

Complementing Meselson & Stahl’s work on bacteria, Taylor used radioactive thymidine (H3) on the root tips of Vicia faba (broad bean).

Using autoradiography, he proved that DNA replication is also semi-conservative in eukaryotes.

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LIVING WORLD-TWO WORLDS STYLING

Living World Notes – Style 1

LIVING WORLD

Table of Contents

  1. Living World: Characteristics of Living Organisms
  2. Growth
  3. Reproduction
  4. Metabolism or Cellular Organization
  5. Consciousness
  6. Interaction
  7. Self-Evolution

1. Growth

Growth is defined as an increase in mass and an increase in the number of individuals.

Types of Growth:

  • Intrinsic Growth (Growth from inside):

    This type of growth is characteristic of living organisms. It is protoplasmic growth, meaning growth occurs from within the body.

    This is considered a defining character of living organisms.

  • Extrinsic Growth (Growth from outside):

    This occurs in non-living things due to the accumulation of material on their surface. Examples include mountains and boulders growing in size due to the deposition of sand or snow.

    Since non-living things can also grow by extrinsic means, growth cannot be considered a defining characteristic of living organisms if only extrinsic growth is considered.

Twin Characters of Growth:

  • Increase in Number (Cell Division):

    In Maize root tip cells, they divide to form 17,500 cells per hour.

  • Increase in Mass (Size):

    A cell of a watermelon increases 3,50,000 times its initial size during growth.

Indirect Ways to Measure Protoplasmic Growth:

Number (e.g., Maize: 17,500 cells per hour)
Mass (Size) (e.g., Watermelon cell)
Length (e.g., Pollen tube growth)
Area (e.g., Surface area of a leaf)

These are all measurable aspects of growth.

2. Reproduction

  • No non-living thing can reproduce.
  • When we talk about reproduction, we are generally referring to “Sexual Reproduction.”
  • However, a few organisms do not reproduce, such as mules, infertile human couples, or drones (male bees).
  • Despite not being able to reproduce, these organisms are still considered living.

Therefore, reproduction cannot be considered a defining property of living organisms, as there are exceptions.

Growth and Reproduction in Organisms:

  • In Unicellular Organisms (Prokaryotes): Growth and Reproduction are mutually inclusive.

    This means that in unicellular organisms, the terms ‘growth’ and ‘reproduction’ can be used synonymously or interchangeably because growth (increase in cell mass/size) directly leads to reproduction (cell division resulting in new individuals).

  • In Multicellular Organisms: Growth and Reproduction are mutually exclusive.

    This means that growth (increase in body mass/size) and reproduction (producing offspring) are distinct processes and do not necessarily occur simultaneously or depend on each other in the same way as in unicellular organisms.

  • In Eukaryotes (e.g., Plants): Growth and Reproduction are related but still exclusive.

    In plants, vegetative growth (increase in size, leaves, stems) leads to reproductive growth (flowering, seed formation). Reproduction is a step or part of growth, but they do not show the same meaning; both are “exclusive” in the sense that they are distinct biological processes.

Examples of Reproduction (Vegetative or Asexual Reproduction):

Generally, NCERT considers vegetative and asexual reproduction interchangeably, but they still have differences.

  1. Plant body breaks, detaches, and forms a new organism (e.g., Fragmentation in Spirogyra, an algae).
  2. Budding in yeast and Hydra.
  3. Asexual Spores in Fungi.
  4. High power of Regeneration in Planaria (Flatworms).

3. Metabolism

Metabolism is the sum of all chemical reactions occurring in the cells/body of an organism.

This is a Defining Character of Living organisms.

Chemical Reactions in Cell-Free Systems (in vitro):

  • Chemical reactions may occur in cell-free systems or in vitro (e.g., in a test tube).
  • Are these chemical reactions in a test tube living? No, they are neither living nor non-living.
  • They are considered “living reactions” but not “living beings.”
  • For a reaction to be considered a living reaction within a living being, it must occur within a cellular boundary.

Therefore, Cellular Organization is a Defining Property of living organisms because metabolic reactions, to be considered part of a living system, must occur within the organized structure of a cell.

4. Consciousness

Consciousness is the ability of an organism to sense and respond to external stimuli.

An External Stimulus leads to a Response by the living organism. This interaction between the external environment and the organism results in consciousness.

All living creatures are conscious.

Self-Consciousness:

  • Humans are also “Self-Conscious.”
  • This means humans are conscious of themselves and know that “we are conscious.”
  • A patient in a coma, lying on a bed, is conscious (their organs are interacting with each other and responding to some stimuli, albeit minimally) but not self-conscious.

Consciousness is a defining property of living organisms, and self-consciousness is a unique defining property of humans.

5. Interaction

Cells interact with each other and show “emergent properties” as a Tissue.

Emergent properties are characteristics that arise from the interaction of simpler components and are not present in the individual components themselves. For example, a tissue has properties that individual cells do not possess.

6. Self-Evolution

Living organisms are self-replicating, evolving, and growing systems that interact and respond to external stimuli.

Mind Mapping: Diversity of Living World (Biodiversity)

  • Biodiversity refers to the number and variety of life forms on Earth.
  • There are approximately 1.7 to 1.8 million described species.
  • To study organisms, we need:
    1. Characterization
    2. Identification
    3. Nomenclature
    4. Classification

    These are the prerequisites for studying the diversity of life.

↓
Characterization
→
Identification
→
Nomenclature

Taxonomy

Taxonomy is the classification of organisms based on their external structure, internal structure, cell structure, ecological role, and developmental process.

Basic of Taxonomy:

Characterization, Identification, Classification, and Nomenclature are the fundamental basis of Taxonomy.

Systematics

  • The word “Systematics” originated from “Systema.”
  • It means the systematic arrangement of organisms.
  • Systematics includes everything from Taxonomy (Characterization, Identification, Classification, and Nomenclature) along with evolutionary relationships of organisms.

Taxonomical Categories

There are 7 basic taxonomical categories in ascending order:

  1. Species
  2. Genus
  3. Family
  4. Order
  5. Class
  6. Phylum/Division (Phylum for animals, Division for plants)
  7. Kingdom

As we move towards the upper rank of the category (from species to kingdom), the common characters among the discussed members are going to decrease.

Binomial Nomenclature

Binomial Nomenclature is a system of naming organisms with two parts.

Proposed by:

Carl von Linné (Carolus Linnaeus)

His Works (Books):

  1. Systema Naturae
  2. Species Plantarum (Publishing date: May 1, 1753) – Considered as the starting point of Botanical Nomenclature.
  3. Genera Plantarum

The publishing year of the 10th edition of Systema Naturae (1758) is considered the starting point of Zoological Nomenclature.

Rules of Binomial Nomenclature:

  1. Species name is Binomial: It is made up of two words:
    • [A] Generic Name (Genus)
    • [B] Specific Epithet (Species)

    Example: Mango’s botanical name is Mangifera indica.
    Generic Name: Mangifera
    Specific Epithet: indica

  2. Name should be in Latin: Latin is a dead language, or it should be Latinized.

    For example, Sandalwood is white. So in Latin, “white” is “album.” The botanical name is Santalum album.

  3. First letter of Generic name should be Capital.
  4. Specific epithet should be in small letters.
  5. Both names should be underlined separately when handwritten.
  6. When printed, they should be in Italics to show their Latin origin.
  7. Name of the Scientist who described that organism is written at the end.

    Example: Mangifera indica Linn, Rosa indica Linn.

Nomenclature Systems:

  • Presently, the Botanical Nomenclature System is governed by the Rules of ICBN (International Code of Botanical Nomenclature).
  • Zoological Nomenclature is governed by ICZN (International Code of Zoological Nomenclature).

Trinomial System:

  • In Botanical Nomenclature, the Trinomial System (three parts: genus, species, sub-species/variety) should be avoided.
  • In Zoological Nomenclature, the Trinomial System can be accepted.

    Example: Homo sapiens sapiens (Cabbage – Sub Species, acceptable in Zoology).

  • Botanical examples like Brassica oleracea var. capitata (Cabbage) and Brassica oleracea var. botrytis (Cauliflower) are generally not acceptable in Botany for formal binomial naming conventions, though they are used to denote varieties.

Tautonyms:

Tautonyms are names where the generic name and specific epithet are the same.
  • Tautonyms are not acceptable in Botany.
  • Tautonyms are agreed upon in Zoological Nomenclature.

    Examples: Naja naja naja (Indian Cobra), Gorilla gorilla gorilla.

What is Classification?

Classification is a process to group organisms on the basis of observable characters.
  • The unit of classification is “Category.” It’s an abstract positioning.
  • Category is generally a layman term used by common man.
  • When we create grouping on the basis of rules, it’s called a “Taxon.”
  • Taxon is the unit of Classification. It is an actual organism that belongs to a particular category.

Examples of Taxonomical Hierarchy for Plants and Animals

Plant Example (Mango – Mangifera indica):

  • Domain – Eukarya
  • Kingdom – Plantae
  • Division – Angiospermae
  • Class – Dicotyledonae
  • Order – Sapindales
  • Family – Anacardiaceae
  • Genus – Mangifera
  • Species – Mangifera indica

Animal Example (Human – Homo sapiens):

  • Kingdom – Animalia
  • Phylum – Chordata
  • Class – Mammalia
  • Order – Primates
  • Family – Hominidae
  • Genus – Homo
  • Species – Homo sapiens
Living World Notes – Style 2

LIVING WORLD

Table of Contents

  1. Living World: Characteristics of Living Organisms
  2. Growth
  3. Reproduction
  4. Metabolism or Cellular Organization
  5. Consciousness
  6. Interaction
  7. Self-Evolution

1. Growth

Growth is defined as an increase in mass and an increase in the number of individuals.

Types of Growth:

  • Intrinsic Growth (Growth from inside):

    This type of growth is characteristic of living organisms. It is protoplasmic growth, meaning growth occurs from within the body.

    This is considered a defining character of living organisms.

  • Extrinsic Growth (Growth from outside):

    This occurs in non-living things due to the accumulation of material on their surface. Examples include mountains and boulders growing in size due to the deposition of sand or snow.

    Since non-living things can also grow by extrinsic means, growth cannot be considered a defining characteristic of living organisms if only extrinsic growth is considered.

Twin Characters of Growth:

  • Increase in Number (Cell Division):

    In Maize root tip cells, they divide to form 17,500 cells per hour.

  • Increase in Mass (Size):

    A cell of a watermelon increases 3,50,000 times its initial size during growth.

Indirect Ways to Measure Protoplasmic Growth:

Number (e.g., Maize: 17,500 cells per hour)
Mass (Size) (e.g., Watermelon cell)
Length (e.g., Pollen tube growth)
Area (e.g., Surface area of a leaf)

These are all measurable aspects of growth.

2. Reproduction

  • No non-living thing can reproduce.
  • When we talk about reproduction, we are generally referring to “Sexual Reproduction.”
  • However, a few organisms do not reproduce, such as mules, infertile human couples, or drones (male bees).
  • Despite not being able to reproduce, these organisms are still considered living.

Therefore, reproduction cannot be considered a defining property of living organisms, as there are exceptions.

Growth and Reproduction in Organisms:

  • In Unicellular Organisms (Prokaryotes): Growth and Reproduction are mutually inclusive.

    This means that in unicellular organisms, the terms ‘growth’ and ‘reproduction’ can be used synonymously or interchangeably because growth (increase in cell mass/size) directly leads to reproduction (cell division resulting in new individuals).

  • In Multicellular Organisms: Growth and Reproduction are mutually exclusive.

    This means that growth (increase in body mass/size) and reproduction (producing offspring) are distinct processes and do not necessarily occur simultaneously or depend on each other in the same way as in unicellular organisms.

  • In Eukaryotes (e.g., Plants): Growth and Reproduction are related but still exclusive.

    In plants, vegetative growth (increase in size, leaves, stems) leads to reproductive growth (flowering, seed formation). Reproduction is a step or part of growth, but they do not show the same meaning; both are “exclusive” in the sense that they are distinct biological processes.

Examples of Reproduction (Vegetative or Asexual Reproduction):

Generally, NCERT considers vegetative and asexual reproduction interchangeably, but they still have differences.

  1. Plant body breaks, detaches, and forms a new organism (e.g., Fragmentation in Spirogyra, an algae).
  2. Budding in yeast and Hydra.
  3. Asexual Spores in Fungi.
  4. High power of Regeneration in Planaria (Flatworms).

3. Metabolism

Metabolism is the sum of all chemical reactions occurring in the cells/body of an organism.

This is a Defining Character of Living organisms.

Chemical Reactions in Cell-Free Systems (in vitro):

  • Chemical reactions may occur in cell-free systems or in vitro (e.g., in a test tube).
  • Are these chemical reactions in a test tube living? No, they are neither living nor non-living.
  • They are considered “living reactions” but not “living beings.”
  • For a reaction to be considered a living reaction within a living being, it must occur within a cellular boundary.

Therefore, Cellular Organization is a Defining Property of living organisms because metabolic reactions, to be considered part of a living system, must occur within the organized structure of a cell.

4. Consciousness

Consciousness is the ability of an organism to sense and respond to external stimuli.

An External Stimulus leads to a Response by the living organism. This interaction between the external environment and the organism results in consciousness.

All living creatures are conscious.

Self-Consciousness:

  • Humans are also “Self-Conscious.”
  • This means humans are conscious of themselves and know that “we are conscious.”
  • A patient in a coma, lying on a bed, is conscious (their organs are interacting with each other and responding to some stimuli, albeit minimally) but not self-conscious.

Consciousness is a defining property of living organisms, and self-consciousness is a unique defining property of humans.

5. Interaction

Cells interact with each other and show “emergent properties” as a Tissue.

Emergent properties are characteristics that arise from the interaction of simpler components and are not present in the individual components themselves. For example, a tissue has properties that individual cells do not possess.

6. Self-Evolution

Living organisms are self-replicating, evolving, and growing systems that interact and respond to external stimuli.

Mind Mapping: Diversity of Living World (Biodiversity)

  • Biodiversity refers to the number and variety of life forms on Earth.
  • There are approximately 1.7 to 1.8 million described species.
  • To study organisms, we need:
    1. Characterization
    2. Identification
    3. Nomenclature
    4. Classification

    These are the prerequisites for studying the diversity of life.

↓
Characterization
→
Identification
→
Nomenclature

Taxonomy

Taxonomy is the classification of organisms based on their external structure, internal structure, cell structure, ecological role, and developmental process.

Basic of Taxonomy:

Characterization, Identification, Classification, and Nomenclature are the fundamental basis of Taxonomy.

Systematics

  • The word “Systematics” originated from “Systema.”
  • It means the systematic arrangement of organisms.
  • Systematics includes everything from Taxonomy (Characterization, Identification, Classification, and Nomenclature) along with evolutionary relationships of organisms.

Taxonomical Categories

There are 7 basic taxonomical categories in ascending order:

  1. Species
  2. Genus
  3. Family
  4. Order
  5. Class
  6. Phylum/Division (Phylum for animals, Division for plants)
  7. Kingdom

As we move towards the upper rank of the category (from species to kingdom), the common characters among the discussed members are going to decrease.

Binomial Nomenclature

Binomial Nomenclature is a system of naming organisms with two parts.

Proposed by:

Carl von Linné (Carolus Linnaeus)

His Works (Books):

  1. Systema Naturae
  2. Species Plantarum (Publishing date: May 1, 1753) – Considered as the starting point of Botanical Nomenclature.
  3. Genera Plantarum

The publishing year of the 10th edition of Systema Naturae (1758) is considered the starting point of Zoological Nomenclature.

Rules of Binomial Nomenclature:

  1. Species name is Binomial: It is made up of two words:
    • [A] Generic Name (Genus)
    • [B] Specific Epithet (Species)

    Example: Mango’s botanical name is Mangifera indica.
    Generic Name: Mangifera
    Specific Epithet: indica

  2. Name should be in Latin: Latin is a dead language, or it should be Latinized.

    For example, Sandalwood is white. So in Latin, “white” is “album.” The botanical name is Santalum album.

  3. First letter of Generic name should be Capital.
  4. Specific epithet should be in small letters.
  5. Both names should be underlined separately when handwritten.
  6. When printed, they should be in Italics to show their Latin origin.
  7. Name of the Scientist who described that organism is written at the end.

    Example: Mangifera indica Linn, Rosa indica Linn.

Nomenclature Systems:

  • Presently, the Botanical Nomenclature System is governed by the Rules of ICBN (International Code of Botanical Nomenclature).
  • Zoological Nomenclature is governed by ICZN (International Code of Zoological Nomenclature).

Trinomial System:

  • In Botanical Nomenclature, the Trinomial System (three parts: genus, species, sub-species/variety) should be avoided.
  • In Zoological Nomenclature, the Trinomial System can be accepted.

    Example: Homo sapiens sapiens (Cabbage – Sub Species, acceptable in Zoology).

  • Botanical examples like Brassica oleracea var. capitata (Cabbage) and Brassica oleracea var. botrytis (Cauliflower) are generally not acceptable in Botany for formal binomial naming conventions, though they are used to denote varieties.

Tautonyms:

Tautonyms are names where the generic name and specific epithet are the same.
  • Tautonyms are not acceptable in Botany.
  • Tautonyms are agreed upon in Zoological Nomenclature.

    Examples: Naja naja naja (Indian Cobra), Gorilla gorilla gorilla.

What is Classification?

Classification is a process to group organisms on the basis of observable characters.
  • The unit of classification is “Category.” It’s an abstract positioning.
  • Category is generally a layman term used by common man.
  • When we create grouping on the basis of rules, it’s called a “Taxon.”
  • Taxon is the unit of Classification. It is an actual organism that belongs to a particular category.

Examples of Taxonomical Hierarchy for Plants and Animals

Plant Example (Mango – Mangifera indica):

  • Domain – Eukarya
  • Kingdom – Plantae
  • Division – Angiospermae
  • Class – Dicotyledonae
  • Order – Sapindales
  • Family – Anacardiaceae
  • Genus – Mangifera
  • Species – Mangifera indica

Animal Example (Human – Homo sapiens):

  • Kingdom – Animalia
  • Phylum – Chordata
  • Class – Mammalia
  • Order – Primates
  • Family – Hominidae
  • Genus – Homo
  • Species – Homo sapiens

Living World-NCERT -PRE CLASS CONTENT for NEET by Sidd Sir

The Living World – Notes Style 6

The Living World

Table of Contents: Key Concepts
  1. Characteristics of Living Organisms
    • Growth
    • Reproduction
    • Metabolism & Cellular Organization
    • Consciousness
    • Interaction & Emergence
    • Self-Evolution
  2. Diversity in the Living World
  3. Nomenclature & Identification
    • Binomial Nomenclature
    • Rules of Nomenclature
    • Trinomial System & Tautonyms
  4. Classification & Taxonomy
  5. Systematics
  6. Taxonomic Categories & Hierarchy
    • Species
    • Genus
    • Family
    • Order
    • Class
    • Phylum / Division
    • Kingdom
  7. Taxonomical Aids
    • Herbarium
    • Botanical Gardens
    • Museum
    • Zoological Parks
    • Key
    • Other Recording Means (Flora, Manuals, Monographs, Catalogues)

1. Characteristics of Living Organisms

Biology is the scientific study of life forms and their processes. The Earth’s living world showcases an astonishing variety of organisms. Historically, humans easily distinguished between inanimate matter and living organisms. Early humans often revered inanimate objects like wind, sea, and fire, as well as certain animals and plants, due to the awe or fear they inspired. The systematic description of living organisms, including humans, developed much later in history. Societies that indulged in an anthropocentric (human-centered) view of biology registered limited progress in biological knowledge. The necessity to describe life forms systematically led to the development of detailed systems for identification, nomenclature (naming), and classification. The most significant outcome of these studies was the recognition of shared similarities among living organisms, both horizontally (among contemporary species) and vertically (across generations and evolutionary lineages). The revelation that all present-day living organisms are related to each other, and also to all organisms that ever lived on this Earth, humbled humanity and led to cultural movements advocating for the conservation of biodiversity. In the following sections, we will delve into a description, including classification, of animals and plants from a taxonomist’s perspective.

Ernst Mayr (1904-2004): The Darwin of the 20th Century
  • Born: July 5, 1904, Kempten, Germany.
  • Harvard University evolutionary biologist.
  • Recognized as one of the 100 greatest scientists of all time.
  • Joined Harvard’s Faculty of Arts and Sciences in 1953; retired in 1975 as Alexander Agassiz Professor of Zoology Emeritus.
  • Nearly 80-year career research spanned: ornithology, taxonomy, zoogeography, evolution, systematics, and the history & philosophy of biology.
  • Pioneered the currently accepted definition of a biological species.
  • Awarded the “triple crown of biology”:
    • Balzan Prize (1983)
    • International Prize for Biology (1994)
    • Crafoord Prize (1999)
  • Died: 2004, at the age of 100.

The living world is truly wonderful and encompasses an amazing wide range of living types. The extraordinary habitats in which we find living organisms, such as cold mountains, deciduous forests, oceans, freshwater lakes, deserts, or hot springs, leave us speechless. The beauty of a galloping horse, the sight of migrating birds, a valley of flowers, or an attacking shark evokes awe and a deep sense of wonder. The ecological conflict and cooperation among members of a population, and among populations of a community, or even the molecular traffic inside a cell, prompt us to deeply reflect on what life truly is. This fundamental question contains two implicit aspects: a technical one seeking to define ‘living’ versus ‘non-living’, and a philosophical one concerning the purpose of life. As scientists, we will focus on the technical aspect and try to understand what constitutes ‘living’.

1.1. Growth

All living organisms exhibit growth. Growth is characterized by two fundamental aspects, often called the “twin characters of growth”:

  • Increase in Mass
  • Increase in Number of Individuals (or Cells)

Types of Growth:

  • Intrinsic Growth (Growth From Inside):
    • Also known as Protoplasmic Growth.
    • Occurs due to the increase in protoplasmic material within the organism.
    • This is a Defining Character of Living organisms.
    • Example: A watermelon cell increases its initial size by 3,50,000 times during growth.
  • Extrinsic Growth (Growth From Outside):
    • Occurs due to the accumulation of material on the surface.
    • Observed in non-living objects like mountains, boulders, and sand mounds.
    • This is NOT a Defining Character of Living, as non-living things can also grow extrinsically.

Measuring Growth:

  • In Multicellular Organisms: Growth primarily occurs through cell division.
    • Plants: Continuous growth by cell division throughout their lifespan (e.g., Maize root tip cells form 17,500 cells per hour).
    • Animals: Growth seen only up to a certain age, though cell division continues for tissue replacement.
  • In Unicellular Organisms: Grow by cell division. Easily observed in in vitro cultures by counting cell numbers.
  • Indirect Ways to Measure Protoplasmic Growth:
    • Length (e.g., Pollen tube growth)
    • Mass / Size (e.g., Watermelon cell increase)
    • Area (e.g., Surface area of a leaf)

Key Takeaway: Growth as a Defining Property

While increase in body mass is a characteristic of growth, it is only a defining property when it occurs intrinsically (from inside). A dead organism does not grow.

1.2. Reproduction

Reproduction is a characteristic feature of living organisms, involving the production of progeny similar to parents. Critically, No non-living thing reproduces.

Forms of Reproduction:

  • Primarily refers to Sexual Reproduction.
  • Organisms also reproduce by Asexual Means (often interchangeably called Vegetative Reproduction in plants).

Examples of Asexual/Vegetative Reproduction:

  • Fragmentation: Seen in Spirogyra (algae), fungi, filamentous algae, and the protonema of mosses. Plant body breaks, detaches, and forms new organisms.
  • Budding: Observed in lower organisms like yeast and Hydra.
  • Asexual Spores: Fungi multiply easily by producing millions of asexual spores.
  • Regeneration: High power of true regeneration in Planaria (flatworms), where a fragmented organism regenerates lost parts into a new organism.

Relationship between Growth and Reproduction:

  • In Unicellular Organisms (Prokaryotes & some Eukaryotes): Growth and Reproduction are mutually inclusive.
    • Increase in cell number is considered both growth and reproduction.
    • Terms can be used synonymously (interchangeably).
  • In Multicellular Organisms: Growth and Reproduction are mutually exclusive.
    • Growth (increase in mass/size) and reproduction (producing offspring) are distinct processes.
    • In Eukaryotes, they are related (e.g., reproductive growth in plants), but do not have the same meaning.

Key Takeaway: Reproduction as a Defining Property

Reproduction cannot be considered a defining property of living organisms because it is not universally true for all living beings. Examples include:

  • Mules
  • Sterile Worker Bees
  • Infertile Human Couples (or Drones)
Despite their inability to reproduce, these organisms are still living. However, no non-living object is capable of reproducing or replicating by itself.

1.3. Metabolism and Cellular Organization

Metabolism is a Defining Character of Living organisms.

  • Definition: It is the sum total of all chemical reactions occurring in the cell/body of an organism.
  • All living organisms are composed of chemicals that are constantly being formed and converted into other biomolecules through thousands of metabolic reactions.
  • Exhibited by all plants, animals, fungi, and microbes.
  • No non-living object exhibits metabolism.

Metabolic Reactions in Test Tubes (In Vitro):

  • Chemical reactions can occur in cell-free systems or in vitro (in a test tube).
  • An isolated metabolic reaction in a test tube is:
    1. Neither a Living Being.
    2. Nor Non-Living.
    3. It is a Living Reaction, but not a Living Being.
  • This is because for a reaction to be considered “living,” it must occur within a cellular boundary.

Key Takeaway: Cellular Organization as a Defining Property

Therefore, Cellular Organization of the body is the Defining Property and Feature of Living organisms.

1.4. Consciousness

Consciousness is the most obvious and technically complex feature of all living organisms.

  • Definition: It is the ability to sense their surroundings or environment and respond to external stimuli (physical, chemical, or biological).
  • Organisms sense their environment through sense organs or other mechanisms.
  • Examples: Plants respond to light, water, temperature, other organisms, pollutants. All organisms, from prokaryotes to complex eukaryotes, respond to environmental cues.
  • Photoperiod affects reproduction in seasonal breeders.
  • All organisms are ‘aware’ of their surroundings.
  • Therefore, all living creatures are conscious.

Self-Consciousness:

  • Human beings are unique in having Self-Consciousness (awareness of themselves).
  • Comatose Patients:
    • Considered conscious (organs interact).
    • But not self-conscious (brain-dead).
    • This poses a complex dilemma in defining the living state.

Key Takeaway: Consciousness as a Defining Property

Consciousness, including self-consciousness in humans, is a Defining Property of Living Organisms.

1.5. Interaction and Emergence

  • All living phenomena result from underlying interactions within the biological system.
  • Emergent Properties: Properties at a higher level of organization arise from interactions among components at a lower level.
    • Example: Properties of tissues are not present in individual cells but emerge from interactions among cells.
    • Example: Properties of cellular organelles emerge from interactions among their molecular components.
  • This phenomenon is true across all levels of organizational complexity.

1.6. Self-Evolution

Living organisms are:

  • Self-replicating
  • Evolving
  • Self-regulating interactive systems
  • Capable of responding to external stimuli.

Biology is the story of life’s evolution on Earth. All living organisms (past, present, future) are linked by shared genetic material to varying degrees.

2. Diversity in the Living World

  • Earth harbors a vast diversity of living organisms (visible and microscopic).
  • Each distinct kind of plant, animal, or organism represents a species.
  • Number of known and described species: 1.7 to 1.8 million.
  • This vast array is called Biodiversity (number and types of organisms).
  • New organisms are continuously being identified as new/old areas are explored.

3. Nomenclature and Identification

Local names for organisms vary widely, causing confusion. Hence, a standardized naming system is essential.

  • Nomenclature: The process of standardizing the naming of living organisms so a particular organism is known by the same name globally.
  • Identification: The process of correctly describing an organism and knowing its identity before naming.

International Codes for Nomenclature:

  • For Plants: International Code for Botanical Nomenclature (ICBN).
  • For Animals: International Code of Zoological Nomenclature (ICZN).
  • These codes ensure:
    • Each organism has only one scientific name.
    • A name is not used for any other known organism.
    • Description allows universal identification to the same name.

3.1. Binomial Nomenclature

  • System of using two components for scientific naming.
  • Proposed and popularized by Carolus Linnaeus.
  • Components:
    1. Generic Name (Genus)
    2. Specific Epithet (Species)
  • Example: Mango → Mangifera indica
    • Mangifera: Genus
    • indica: Specific Epithet (Species)

Key Contributions of Carolus Linnaeus:

  • Proposed the Binomial Nomenclature system.
  • Authored seminal works:
    • Systema Naturae: 10th Edition (1758) is the starting point of Zoological Nomenclature.
    • Species Plantarum: Publication date (May 1) is the starting point of Botanical Nomenclature.
    • Genera Plantarum

Universal Rules of Binomial Nomenclature:

  1. Latin Origin: Biological names are in Latin and italicized (or Latinized). Latin is a “dead language,” ensuring stability. (e.g., Santalum album for white sandalwood).
  2. Two Components: First word is Genus, second is Specific Epithet.
  3. Formatting:
    • Handwritten: Separately underlined.
    • Printed: Italicized.
  4. Capitalization:
    • Genus name: Starts with a capital letter.
    • Specific epithet: Starts with a small letter.
  5. Author Citation: Abbreviated author name appears after the specific epithet (e.g., Mangifera indica Linn.).

Special Cases: Trinomial System & Tautonyms

  • Trinomial System (e.g., Homo sapiens sapiens for subspecies):
    • Generally acceptable in Zoology.
    • Avoided in Botany (e.g., Brassica oleracea var. Capitata not generally accepted).
  • Tautonyms (Generic name and specific epithet are identical, e.g., Naja naja, Gorilla gorilla):
    • Not acceptable in Botany.
    • Accepted in Zoological nomenclature.

4. Classification and Taxonomy

Studying all organisms individually is impossible, necessitating grouping.

  • Classification: Process of grouping organisms into convenient categories based on easily observable characteristics.
  • Taxa (singular: Taxon): The scientific term for these convenient categories.
    • Can represent categories at different levels (e.g., ‘Plants’, ‘Wheat’, ‘Animals’, ‘Mammals’, ‘Dogs’ are all taxa at varying levels).
    • A taxon is an actual group of organisms belonging to a particular category, defined by rules.
    • Unit of classification is a Taxon (not merely an abstract ‘Category’).

The process of classification is called Taxonomy.

Basis of Modern Taxonomy:

Classification of organisms based on:

  • External Structure
  • Internal Structure
  • Cellular Structure
  • Ecological Role
  • Developmental Processes
Fundamental Processes of Taxonomy:
  1. Characterization
  2. Identification
  3. Classification
  4. Nomenclature

Historically, early classifications were based on the ‘uses’ of various organisms (food, clothing, shelter).

5. Systematics

Beyond classification, humans have been interested in the relationships among organisms.

  • Systematics: The branch of study dealing with the systematic arrangement of organisms and their relationships.
  • Word origin: Latin ‘systema’.
  • Carolus Linnaeus’s publication title: “Systema Naturae”.
Scope of Systematics:

Systematics includes:

  1. Characterization
  2. Identification
  3. Classification
  4. Nomenclature
  5. PLUS Evolutionary Relationships between organisms.

6. Taxonomic Categories and Hierarchy

Classification is a multi-step process involving a hierarchy of steps.

  • Each step represents a Rank or Category.
  • Taxonomic Category: Each category is part of an overall taxonomic arrangement.
  • Taxonomic Hierarchy: All categories together form this arrangement.
  • Each category is a unit of classification, commonly called a Taxon.

Seven Basic Taxonomic Categories (in Ascending Order):

  1. Species
  2. Genus
  3. Family
  4. Order
  5. Class
  6. Phylum (for animals) / Division (for plants)
  7. Kingdom
  • Species is the lowest category for all organisms.
  • As we move towards upper ranks (species → kingdom), the number of common characteristics shared by members decreases.
  • Conversely, lower the taxa, more shared characteristics.
  • Higher the category, more complex the classification problem.
  • Species name is binomial; all other categories have uninominal names.

6.1. Species

  • Group of individual organisms with fundamental similarities.
  • Distinguishable from closely related species based on distinct morphological differences.
  • Specific epithet represents the species.
  • Examples:
    • Mangifera indica
    • Solanum tuberosum (potato)
    • Panthera leo (lion)
    • Homo sapiens (human)

6.2. Genus

  • Comprises a group of related species.
  • More characters in common compared to species of other genera.
  • Aggregates of closely related species.
  • Examples:
    • Solanum: includes potato, tomato, brinjal.
    • Panthera: includes lion (P. leo), leopard (P. pardus), tiger (P. tigris).
    • Felis: includes cats; differs from Panthera.

6.3. Family

  • Group of related genera.
  • Fewer similarities compared to genus and species.
  • Characterized by both vegetative and reproductive features (for plants).
  • Examples:
    • Plants: Solanum, Petunia, Datura → Family Solanaceae.
    • Animals: Genus Panthera + Genus Felis → Family Felidae.
    • Cat (Felidae) and Dog (Canidae) are in different families.

6.4. Order

  • Assemblage of families.
  • Identified based on aggregates of characters.
  • Fewer similar characters compared to genera in a family.
  • Examples:
    • Plants: Convolvulaceae, Solanaceae → Order Polymoniales (based on floral characters).
    • Animals: Felidae, Canidae → Order Carnivora.

6.5. Class

  • Includes related orders.
  • Example: Order Primata (monkey, gorilla, gibbon) + Order Carnivora (tiger, cat, dog) → Class Mammalia.

6.6. Phylum (for animals) / Division (for plants)

  • Next higher category after Class.
  • Animals: Classes (fishes, amphibians, reptiles, birds, mammals) → Phylum.
    • Example: Presence of notochord & dorsal hollow neural system → Phylum Chordata.
  • Plants: Classes with few similar characters → Division (e.g., Angiospermae).

6.7. Kingdom

  • Highest category in classification.
  • Kingdom Animalia: All animals belonging to various phyla.
  • Kingdom Plantae: All plants from various divisions.

Taxonomic Classification Examples:

Common Name Biological Name Genus Family Order Class Phylum/Division Kingdom
Man Homo sapiens Homo Hominidae Primata Mammalia Chordata Animalia
Housefly Musca domestica Musca Muscidae Diptera Insecta Arthropoda Animalia
Mango Mangifera indica Mangifera Anacardiaceae Sapindales Dicotyledonae Angiospermae Plantae
Wheat Triticum aestivum Triticum Poaceae Poales Monocotyledonae Angiospermae Plantae
Visual Representation of Plant Hierarchy (Simplified):

Kingdom Plantae → Divisions (e.g., Angiospermae)

Angiospermae → Classes (e.g., Monocotyledonae, Dicotyledonae)

Dicotyledonae → Orders (e.g., Sapindales, Polymoniales)

  • Sapindales → Family Anacardiaceae → Genus Mangifera → Species Mangifera indica (Mango)
  • Polymoniales → Family Solanaceae → Genus Solanum (S. tuberosum – potato, S. nigrum, S. melongena – brinjal), Datura, Petunia

Monocotyledonae → Order Poales → Family Poaceae → Genus Triticum → Species Triticum aestivum (Wheat)

Visual Representation of Animal Hierarchy (Simplified):

Kingdom Animalia → Phyla (e.g., Chordata, Arthropoda)

Chordata → Classes (e.g., Mammalia, Aves, Reptilia, Amphibia, Pisces)

Mammalia → Orders (e.g., Primata, Carnivora)

  • Primata → Family Hominidae → Genus Homo → Species Homo sapiens (Human)
  • Carnivora → Family Felidae (Genus Panthera: P. leo, P. tigris, P. pardus; Genus Felis: F. catus)
  • Carnivora → Family Canidae (Genus Canis: C. lupus – Dog)

Arthropoda → Class Insecta → Order Diptera → Family Muscidae → Genus Musca → Species Musca domestica (Housefly)

7. Taxonomical Aids

These are essential tools for correct classification and identification of organisms, crucial for agriculture, forestry, industry, and understanding bio-resources.

  • Requires intensive laboratory and field studies.
  • Actual specimens (plant/animal) are prime sources.
  • Information gathered is stored with specimens for future studies.
  • Biologists use specific procedures/techniques for storage and preservation.

7.1. Herbarium

  • Definition: Storehouse of collected plant specimens that are dried, pressed, and preserved on sheets.
  • Arranged according to a universally accepted classification system.
  • Repository for future use.
  • Label information: Date & place of collection, English name, local name, botanical/scientific name, family, collector’s name.
  • Serves as a quick referral system.

7.2. Botanical Gardens

  • Definition: Specialized gardens with collections of living plants for reference.
  • Plants grown for identification purposes.
  • Each plant labeled with botanical/scientific name and family.
  • Famous examples: Kew (England), Indian Botanical Garden (Howrah, India), National Botanical Research Institute (Lucknow, India).

7.3. Museum

  • Definition: Generally set up in educational institutes (schools, colleges).
  • Collections of preserved plant and animal specimens for study and reference.
  • Specimens preserved in containers/jars in preservative solutions.
  • Dry specimens also used (e.g., insects in insect boxes after collecting, killing, pinning).
  • Larger animals (birds, mammals) usually stuffed and preserved.
  • Often contain animal skeletons.

7.4. Zoological Parks (Zoos)

  • Definition: Places where wild animals are kept in protected environments under human care.
  • Purpose: Learn about their food habits and behavior.
  • Conditions provided are as similar as possible to natural habitats.
  • Popular for children’s visits.

7.5. Key

  • Definition: Taxonomical aid for identification based on similarities and dissimilarities.
  • Based on contrasting characters in a pair called a couplet.
  • Couplet: Choice between two opposite options (acceptance of one, rejection of other).
  • Each statement in the key is called a lead.
  • Separate keys required for each taxonomic category (family, genus, species).
  • Generally analytical in nature.

7.6. Other Means of Recording Descriptions

These also help in correct identification and disseminating information:

  • Flora: Contains actual account of habitat and distribution of plants of a given area. Provides an index to plant species.
  • Manuals: Useful for providing information for identification of names of species found in an area.
  • Monographs: Contain comprehensive information on any one taxon.
  • Catalogues: Provide a list of species found in a particular area with brief descriptions.

Understanding Polymorphic & Pleomorphic Nature of Lysosomes and Golgi Apparatus

Polymorphic Lysosomes

Poly = many, morphic = forms

Exist in different forms within the same cell.

Hover to see types

  • Primary lysosome: Inactive enzymes
  • Secondary lysosome: Active digestion
  • Residual body: Waste-filled
  • Autophagic vacuole: Self-organelle digestion

Example: Macrophages show all types simultaneously.

Pleomorphic Lysosomes

Pleo = varied, morphic = forms

Shape varies by activity and cell type.

  • Granular in neutrophils (granulocytes)
  • Irregular in hepatocytes
  • Large or tubular in macrophages

Key: Shape variability = pleomorphism.

Polymorphic vs Pleomorphic

Hover to view table

TermMeaningFocus
PolymorphicMany forms by function/stageWithin one cell
PleomorphicVariable shapes and sizesAcross or within cells

Pleomorphic Golgi

Adapt shape by function and stress.

  • Secretory cells: Large stacks
  • Neurons: Fragmented Golgi
  • Plant cells: Multiple scattered stacks
  • Mitosis: Vesiculated Golgi
  • Stress: Swollen or misoriented
“FROM NCERT – The Golgi cisternae (in animals) are concentrically arranged near the nucleus.”

Dictyosome (Plant Golgi)

Pleomorphic version in plant cells

  • Small, multiple stacks in plant cells
  • Shape & number depend on activity
  • Produce pectin & hemicellulose
Polymorphic Lysosomes

Poly = many, morphic = forms → having many forms

Exist in several forms within the same cell based on function:

  • Primary lysosome: Inactive enzymes
  • Secondary lysosome: Active digestion
  • Residual body: Waste-filled
  • Autophagic vacuole: Self-organelle digestion

Example: Macrophages show all types simultaneously.

Pleomorphic Lysosomes

Pleo = varied, morphic = forms → variable shapes

Shape/size differ based on activity, type of cell, or digestive load.

  • Granular in neutrophils (granulocytes)
  • Irregular in hepatocytes
  • Large or tubular in macrophages

Key: Shape variability = pleomorphism.

Difference Table: Polymorphic vs Pleomorphic
TermMeaningFocus
PolymorphicMany forms based on function/stageWithin one cell
PleomorphicVariable shapes and sizesAcross or within cells
Pleomorphic Golgi Apparatus
  • Secretory cells: Large stacks
  • Neurons: Fragmented Golgi
  • Plant cells: Multiple scattered stacks
  • Mitosis: Vesiculated Golgi
  • Stress: Swollen or misoriented

Key: Golgi shape changes to suit function.

“FROM NCERT-The Golgi cisternae (in animals) are concentrically arranged near the nucleus.”
Dictyosome (Plant Golgi)
  • Small, multiple stacks in plant cells
  • Variable shape and number depending on activity
  • Produce pectin & hemicellulose for the cell wall

Key: Dictyosome is a pleomorphic version of Golgi in plants.

Understanding Polymorphic & Pleomorphic Nature of Lysosomes and Golgi Apparatus

Polymorphic Lysosomes

Poly = many, morphic = forms → having many forms

Lysosomes are polymorphic because they exist in several forms within the same cell, depending on their function:

  • Primary lysosome: Inactive enzymes
  • Secondary lysosome: Active digestion
  • Residual body: Waste-filled
  • Autophagic vacuole: Self-organelle digestion

Example: Macrophages show all types simultaneously.

Pleomorphic Lysosomes

Pleo = varied, morphic = forms → variable shapes

Lysosome shape and size differ based on activity, type of cell, or digestive load.

  • Granular in neutrophils (granulocytes)
  • Irregular in hepatocytes
  • Large or tubular in macrophages

Key: Shape variability = pleomorphism.

Difference Table: Polymorphic vs Pleomorphic

Term Meaning Focus
Polymorphic Many forms based on function/stage Within one cell
Pleomorphic Variable shapes and sizes Across or within cells

Pleomorphic Golgi Apparatus

  • Secretory cells: Large stacks
  • Neurons: Fragmented Golgi
  • Plant cells: Multiple scattered stacks
  • Mitosis: Vesiculated Golgi
  • Stress: Swollen or misoriented

Key: Golgi shape changes to suit function.

“FROM NCERT-The Golgi cisternae (in animals) are concentrically arranged near the nucleus.”

Dictyosome (Plant Golgi)

  • Small, multiple stacks in plant cells
  • Variable shape and number depending on activity
  • Produce pectin & hemicellulose for the cell wall

Key: Dictyosome is a pleomorphic version of Golgi in plants.

The force of buoyancy exerted by the atmosphere on a balloon is B in the upward direction and remains constant. The force of air resistance on the balloon acts opposite to the direction of velocity and is proportional to it. The balloon carries a mass M and is found to fall down near the earth’s surface with a constant velocity . How much mass should be removed from the balloon so that it may rise with a constant velocity u?

Balloon Mass Calculation

Solving Problem Q.5.19: Balloon Motion Analysis

Problem Statement

The force of buoyancy exerted by the atmosphere on a balloon is $B$ in the upward direction and remains constant. The force of air resistance on the balloon acts opposite to the direction of velocity and is proportional to it. The balloon carries a mass $M$ and is found to fall down near the earth’s surface with a constant velocity $v$. How much mass should be removed from the balloon so that it may rise with a constant velocity $u$?

Step 1: Understand the Forces Involved and Principle of Constant Velocity

Before writing equations, let’s identify all the forces acting on the balloon and their directions:

  • Gravitational Force (Weight): This acts vertically downwards. If the total mass of the balloon (including its contents) is $m_{total}$, then the weight is $m_{total}g$.
  • Buoyant Force ($B$): This acts vertically upwards and is given as constant ($B$). This force is due to the displacement of air by the balloon.
  • Air Resistance Force ($F_r$): This force opposes the direction of velocity and is proportional to the velocity. We can write it as $F_r = k \times \text{velocity}$, where $k$ is the constant of proportionality.

The crucial part of the problem statement is “constant velocity”. This implies that the net force on the balloon is zero in both scenarios, according to Newton’s First Law of Motion ($\Sigma F = 0$). This is because if velocity is constant, acceleration is zero.

Step 2: Analyze the Initial Scenario – Falling Down with Constant Velocity $v$

In this initial scenario, the balloon has a total mass $M$ and is falling downwards with a constant velocity $v$. Since the net force is zero, the sum of upward forces must equal the sum of downward forces.

Let’s define our positive direction. For falling motion, it’s often convenient to take the downward direction as positive.

  • Weight ($Mg$): Acts downwards (positive).
  • Buoyant Force ($B$): Acts upwards (negative).
  • Air Resistance ($F_r$): Since the balloon is moving downwards, the air resistance acts upwards (opposite to velocity). Its magnitude is $kv$ (negative).

Applying Newton’s Second Law ($\Sigma F = ma$, where $a=0$):

$$\Sigma F_{\text{vertical}} = 0$$

$$Mg – B – kv = 0$$

Rearranging this equation, we get a fundamental relationship for the initial state:

$$Mg = B + kv \quad \text{(Equation 1)}$$

This equation will be crucial for determining the constant $k$ in terms of known initial conditions.

Step 3: Analyze the Final Scenario – Rising Up with Constant Velocity $u$

Now, some mass has been removed from the balloon. Let the new, reduced total mass of the balloon be $m’$. The balloon is now rising upwards with a constant velocity $u$. Again, the net force on the balloon is zero.

For rising motion, it’s convenient to take the upward direction as positive.

  • Weight ($m’g$): Acts downwards (negative).
  • Buoyant Force ($B$): Acts upwards (positive). This force remains constant as given.
  • Air Resistance ($F_r$): Since the balloon is moving upwards, the air resistance acts downwards (opposite to velocity). Its magnitude is $ku$ (negative).

Applying Newton’s Second Law ($\Sigma F = ma$, where $a=0$):

$$\Sigma F_{\text{vertical}} = 0$$

$$B – m’g – ku = 0$$

Rearranging this equation, we get a relationship for the final state:

$$B = m’g + ku \quad \text{(Equation 2)}$$

From Equation 2, we can express the new mass $m’$ that the balloon must have to rise with constant velocity $u$:

$$m’g = B – ku \implies m’ = \frac{B – ku}{g}$$

Step 4: Determine the Constant of Proportionality ($k$)

The constant $k$ for air resistance is a property of the balloon’s shape and the medium (air), which are assumed to remain constant. We can determine $k$ from the initial scenario using Equation 1:

From Equation 1 ($Mg = B + kv$):

$$kv = Mg – B$$

Solving for $k$:

$$k = \frac{Mg – B}{v}$$

This expression for $k$ connects the initial known conditions to the property of air resistance.

Step 5: Calculate the New Mass ($m’$) by Substituting $k$

Now that we have an expression for $k$, we can substitute it into the equation for the new mass $m’$ (from Step 3). This will allow us to express $m’$ solely in terms of the given parameters ($M, B, v, u, g$).

We had: $$m’ = \frac{B – ku}{g}$$

Substitute $k = \frac{Mg – B}{v}$ into this equation:

$$m’ = \frac{B – \left(\frac{Mg – B}{v}\right)u}{g}$$

To simplify this complex fraction, multiply the numerator and denominator by $v$:

$$m’ = \frac{v \left(B – \frac{(Mg – B)u}{v}\right)}{gv}$$

$$m’ = \frac{Bv – (Mg – B)u}{gv}$$

Distribute the negative sign and $u$ in the numerator:

$$m’ = \frac{Bv – Mgu + Bu}{gv} \quad \text{(New mass of the balloon)}$$

Step 6: Calculate the Mass That Should Be Removed ($\Delta M$)

The problem asks for the amount of mass that must be removed from the balloon. This is the difference between the initial mass $M$ and the new mass $m’$ required for rising with velocity $u$.

$$\Delta M = M – m’$$

Substitute the expression for $m’$ we just derived:

$$\Delta M = M – \left(\frac{Bv – Mgu + Bu}{gv}\right)$$

To combine these terms, find a common denominator ($gv$) for $M$:

$$\Delta M = \frac{M(gv)}{gv} – \frac{Bv – Mgu + Bu}{gv}$$

Combine the numerators, being very careful with the signs when subtracting the second term:

$$\Delta M = \frac{Mgv – (Bv – Mgu + Bu)}{gv}$$

$$\Delta M = \frac{Mgv – Bv + Mgu – Bu}{gv}$$

Now, let’s group terms that contain $M$ and terms that contain $B$ in the numerator:

$$\Delta M = \frac{(Mgv + Mgu) – (Bv + Bu)}{gv}$$

Factor out common terms from each grouped pair:

$$\Delta M = \frac{Mg(v + u) – B(v + u)}{gv}$$

Notice that $(v + u)$ is a common factor in both terms in the numerator. Factor it out completely:

$$\Delta M = \frac{(Mg – B)(v + u)}{gv}$$

This is the final expression for the amount of mass that needs to be removed, stated in terms of the given parameters ($M, B, v, u, g$).

An equivalent form can be obtained by substituting $Mg – B = kv$ (from Equation 1) into the numerator:

$$\Delta M = \frac{(kv)(v + u)}{gv} = \frac{k(v+u)}{g}$$

Both forms are mathematically equivalent and correct. The first form uses only the initially given parameters, which is usually preferred as a final answer.

Final Answer

The amount of mass that should be removed from the balloon so that it may rise with a constant velocity $u$ is given by:

$$\boxed{\Delta M = \frac{(Mg – B)(v + u)}{gv}}$$

Find the reading of the spring balance shown in figure(5-E6). The elevator is going up with an acceleration of g/10, the pulley and the string are light and the pulley is smooth.

Spring Balance Reading Calculation

Calculating the Reading of the Spring Balance in an Accelerating Elevator

Problem Statement

Find the reading of the spring balance shown in figure (5-E6). The elevator is going up with an acceleration of $g/10$, the pulley and the string are light, and the pulley is smooth. Take $g = 9.8 \text{ m/s}^2$.

The figure shows two masses, $1.5 \text{ kg}$ and $3.0 \text{ kg}$, connected by a string over a pulley. The entire system is inside an elevator accelerating upwards.

Step 1: Understand the Concept of Apparent Weight in an Accelerating Frame

When an object is in an accelerating frame of reference (like an elevator), the forces acting on it appear differently compared to an inertial frame (a non-accelerating frame). This difference is often described using the concept of apparent weight or by considering an effective gravitational acceleration.

Let’s consider an object of mass $m$ inside an elevator, and analyze the forces using Newton’s Second Law, $\Sigma F = ma$.

  • Case 1: Elevator is stationary or moving with constant velocity ($a_e = 0$).

    The net force on the object is zero. If the object is resting on a scale, the normal force ($N$) exerted by the scale on the object is equal to the object’s gravitational force (weight) $mg$.

    $$N – mg = 0 \implies N = mg$$

  • Case 2: Elevator accelerates upwards with acceleration $a_e$.

    When the elevator accelerates upwards, the object inside it also accelerates upwards with the same acceleration $a_e$. According to Newton’s Second Law, there must be a net upward force on the object equal to $ma_e$.

    The forces acting on the object are:

    • Normal force $N$ (or tension for a hanging mass) acting upwards.
    • Gravitational force $mg$ acting downwards.

    Applying Newton’s Second Law (taking upward as positive):

    $$N – mg = ma_e$$

    Now, let’s solve for the normal force $N$, which represents the apparent weight:

    $$N = mg + ma_e$$

    We can factor out $m$ from the right side:

    $$N = m(g + a_e)$$

    Comparing this to the stationary case ($N = mg$), it looks as if the gravitational acceleration has effectively increased. We define this new effective gravitational acceleration as $g’$.

    $$\text{Therefore, we get the relation: } g’ = g + a_e$$

    This means any object inside the upward accelerating elevator will behave as if gravity is stronger by an amount $a_e$.

  • Case 3: Elevator accelerates downwards with acceleration $a_e$.

    If the elevator accelerates downwards, the net force on the object is $ma_e$ downwards.

    Applying Newton’s Second Law (taking downward as positive in this case, or upward as negative):

    $$mg – N = ma_e$$

    Solving for $N$:

    $$N = mg – ma_e$$

    $$N = m(g – a_e)$$

    Here, $g’ = g – a_e$, meaning objects inside a downward accelerating elevator behave as if gravity is weaker.

In this specific problem, the elevator is accelerating upwards with $a_e = g/10$. So, the effective gravitational acceleration ($g’$) experienced by the masses relative to the elevator’s frame will be:

$$g’ = g + a_e = g + \frac{g}{10} = \frac{10g}{10} + \frac{g}{10} = \frac{11g}{10}$$

Now, we can substitute the value of $g = 9.8 \text{ m/s}^2$:

$$g’ = \frac{11 \times 9.8}{10} = 11 \times 0.98 = 10.78 \text{ m/s}^2$$

We will use this effective $g’$ in our calculations for the tension in the string connecting the masses, treating the elevator’s frame as our non-inertial reference frame.

Step 2: Define Variables and Draw Free Body Diagrams (Relative to the Elevator’s Accelerating Frame)

Let $m_1 = 1.5 \text{ kg}$ and $m_2 = 3.0 \text{ kg}$. Let $T$ be the tension in the string connecting the two masses. The pulley and string are light and smooth, so the tension is uniform throughout the string.

We will analyze the motion of each mass relative to the elevator’s accelerating frame, using the effective gravitational acceleration $g’$. This approach simplifies the problem as we don’t need to consider pseudo forces explicitly if we use $g’$.

  • For mass $m_1$ ($1.5 \text{ kg}$):

    The forces acting on $m_1$ are the tension $T$ pulling upwards and its effective weight $m_1 g’$ pulling downwards. Since $m_2 > m_1$, $m_1$ will accelerate upwards relative to the elevator. Let its acceleration relative to the elevator be $a$.

    Equation of motion (net force in the direction of acceleration): $$T – m_1 g’ = m_1 a \quad \text{(1)}$$

  • For mass $m_2$ ($3.0 \text{ kg}$):

    The forces acting on $m_2$ are its effective weight $m_2 g’$ pulling downwards and the tension $T$ pulling upwards. Since $m_2 > m_1$, $m_2$ will accelerate downwards relative to the elevator. Let its acceleration relative to the elevator be $a$ (same magnitude as $m_1$ due to the string and pulley).

    Equation of motion (net force in the direction of acceleration): $$m_2 g’ – T = m_2 a \quad \text{(2)}$$

Step 3: Calculate the Acceleration of the Masses Relative to the Elevator ($a$)

We have a system of two linear equations:

(1) $T – m_1 g’ = m_1 a$

(2) $m_2 g’ – T = m_2 a$

To find the acceleration $a$, we can add equation (1) and equation (2) to eliminate the tension $T$:

$$(T – m_1 g’) + (m_2 g’ – T) = m_1 a + m_2 a$$

$$T – m_1 g’ + m_2 g’ – T = (m_1 + m_2) a$$

$$(m_2 – m_1) g’ = (m_1 + m_2) a$$

Now, we can solve for $a$:

$$a = \frac{(m_2 – m_1) g’}{(m_1 + m_2)}$$

Substitute the known values:

  • $m_1 = 1.5 \text{ kg}$
  • $m_2 = 3.0 \text{ kg}$
  • $g’ = 10.78 \text{ m/s}^2$ (calculated in Step 1)

$$a = \frac{(3.0 \text{ kg} – 1.5 \text{ kg}) \times 10.78 \text{ m/s}^2}{(1.5 \text{ kg} + 3.0 \text{ kg})}$$

$$a = \frac{1.5 \times 10.78}{4.5}$$

$$a = \frac{16.17}{4.5}$$

$$a \approx 3.593 \text{ m/s}^2$$ (This matches the approximation in the provided solution of $3.59 \text{ m/s}^2$)

Step 4: Calculate the Tension in the String ($T$)

Now that we have the acceleration $a$, we can substitute its value back into either equation (1) or (2) to find the tension $T$. Let’s use equation (1):

$$T – m_1 g’ = m_1 a$$

Rearrange to solve for $T$:

$$T = m_1 a + m_1 g’$$

Factor out $m_1$:

$$T = m_1 (a + g’)$$

Substitute the values:

  • $m_1 = 1.5 \text{ kg}$
  • $a = 3.593 \text{ m/s}^2$
  • $g’ = 10.78 \text{ m/s}^2$

$$T = 1.5 \text{ kg} \times (3.593 \text{ m/s}^2 + 10.78 \text{ m/s}^2)$$

$$T = 1.5 \times 14.373$$

$$T \approx 21.5595 \text{ N}$$ (This matches the approximation in the provided solution of $21.55 \text{ N}$)

Step 5: Determine the Reading of the Spring Balance

The spring balance is attached to the ceiling of the elevator and supports the pulley system. The tension in the string passing over the pulley exerts a downward force on the pulley from both sides. Since the tension in the string is $T$ everywhere, the total downward force exerted on the pulley by the string is $2T$.

The spring balance measures the total force exerted on it. Assuming the pulley’s mass is negligible (it’s “light”), the reading of the spring balance will be equal to this total downward force.

$$\text{Reading of Spring Balance (Force)} = 2T$$

Substitute the calculated value of $T$:

$$\text{Reading (Force)} = 2 \times 21.5595 \text{ N}$$

$$\text{Reading (Force)} = 43.119 \text{ N}$$

Spring balances are often calibrated to show readings in kilograms (mass units) by effectively dividing the measured force by the standard gravitational acceleration ($g = 9.8 \text{ m/s}^2$). It’s important to use the standard $g$ here, not $g’$, because the balance itself is giving a reading that corresponds to a mass under Earth’s standard gravity.

$$\text{Reading in kg (Mass Equivalent)} = \frac{\text{Force}}{g}$$

$$\text{Reading in kg} = \frac{43.119 \text{ N}}{9.8 \text{ m/s}^2}$$

$$\text{Reading in kg} \approx 4.399 \text{ kg}$$ (This matches the approximation in the provided solution of $4.39 \text{ kg}$)

Final Answer

The reading of the spring balance is approximately $\boxed{4.39 \text{ kg}}$.

Hakuna Matata –no worries-A Message for NEET Aspirants

🦁 Hakuna Matata – A Message for NEET Aspirants

Hakuna Matata is a Swahili phrase that means “no worries”. It gained popularity from the movie The Lion King, but its message is timeless — especially for students preparing for something as challenging as NEET.

NEET preparation can feel overwhelming — mock tests, ranks, competition, pressure from society — but worrying never solves anything. What solves it is focused action, daily improvement, and a peaceful mind.

Don’t carry the burden of yesterday’s failures or tomorrow’s uncertainty. As the phrase says:

Hakuna Matata! Live in the present, work hard, and trust the journey.

It doesn’t mean being careless — it means being care-free with full effort. Be disciplined, but not anxious. Be passionate, but not panicked.

Your NEET journey is not just about a college seat. It’s about becoming the kind of person who can earn it — with peace, perseverance, and patience.

– Prof. Siddharth Sanghvi
27 Years of Mentorship

🦁 हाकुना मटाटा – NEET विद्यार्थियों के लिए प्रेरणा

Hakuna Matata एक स्वाहिली वाक्य है, जिसका अर्थ होता है — “कोई चिंता नहीं।”

NEET जैसी परीक्षा की तैयारी में चिंता और तनाव आम हैं। लेकिन चिंता से समाधान नहीं आता — समाधान आता है शांति से किए गए निरंतर प्रयास से।

जो बीत गया, उसे छोड़ दो। जो आना है, उसका डर मत रखो। बस आज पर ध्यान दो — पूरी मेहनत और पूरे विश्वास से।

Hakuna Matata का मतलब यह नहीं है कि आप लापरवाह बन जाएँ, बल्कि यह है कि आप निश्चिंत होकर संकल्प के साथ आगे बढ़ें।

आपका लक्ष्य सिर्फ मेडिकल कॉलेज नहीं है, बल्कि वह व्यक्ति बनना है जो उस सीट का हकदार है — मेहनती, शांत और धैर्यवान।

– प्रो. सिद्धार्थ संघवी
27 वर्षों की मार्गदर्शना
#HakunaMatata #NEETMotivation #NoWorriesJustEffort

G0 Stage – Some cells in the adult animals do not appear to exhibit division (e.g., heart cells) and many other cells divide only occasionally, as needed to replace cells that have been lost because of injury or cell death. These cells that do not divide further exit G1 phase to enter an inactive stage called quiescent stage (G0) of the cell cycle. Cells in this stage remain metabolically active but no longer proliferate unless called on to do so depending on the requirement of the organism

🧬 G₀ Phase – Quiescence in the Cell Cycle

In adult animals, not all cells keep dividing. Some cells, like neurons and heart muscle cells, stop dividing after development and enter a state called the G₀ phase, also known as the quiescent phase.

This phase is reached from the G1 phase — not directly from M phase. Once in G₀, cells remain metabolically active but stop dividing.

There are two categories of G₀ entry:

  • Permanently in G₀ – e.g., neurons and heart muscle cells. They divide during development and permanently exit the cycle early in G1.
  • Temporarily in G₀ (quiescent) – e.g., liver cells and lymphocytes. These cells can re-enter the cycle when needed, such as during tissue repair or immune response.

Important checkpoint: Cells exit into G₀ only if they do not cross the restriction point (R-point) in late G1. If they cross it, they are committed to completing the cycle and cannot go to G₀ from there.

🧠 Why do heart or neuron cells enter G₁ if they won’t divide?

This is a common question — and here’s the key reason:

  • All post-mitotic daughter cells must enter G1 phase after mitosis. That’s how the cell cycle is structured in eukaryotes.
  • From there, cells evaluate whether to continue to divide or exit into G₀.
  • The G₀ pathway is a branch from G1, not from M or S phase.
  • Heart cells and neurons, after their final division during development, enter early G1 — and then permanently exit into G₀ before the R-point.

Why not directly exit from M phase?
Because G₀ is molecularly defined as a branch off G1 — not from M. The decision-making molecules (e.g., Cyclin D, Rb-E2F pathway) are active only in G1.

🚉 Analogy – Cell Cycle Train Station

Imagine the cell cycle as a train journey. After mitosis (M phase), every new cell lands on the platform (G1). At G1, the cell chooses whether to:

  • Board the next train (S phase, replication)
  • Exit the station into a peaceful rest area (G₀)

But no one can exit the station directly from the train (M phase). You must step onto the platform (G1) first. This is exactly how cells behave.

Q1. Neurons enter G₀ phase from:

  • A) End of M phase
  • B) S phase
  • C) Early G1 phase
  • D) G2 phase
Answer: C) Early G1 phase
Neurons briefly enter G1 after final division, then permanently exit into G₀.

Q2. The restriction point in G1 is located at:

  • A) Start of G1
  • B) Middle of G1
  • C) End of G1
  • D) G1/S border
Answer: C) End of G1
Restriction point lies in late G1. After crossing it, the cell is committed to divide.

Q3. Which of these cells can re-enter the cell cycle from G₀?

  • A) Neurons
  • B) Cardiomyocytes
  • C) Liver cells
  • D) RBCs
Answer: C) Liver cells
They are quiescent but can divide during regeneration or injury.

Q4. G₀ cells are:

  • A) Dividing actively
  • B) Metabolically inactive
  • C) Dead cells
  • D) Metabolically active but non-dividing
Answer: D)
They are alive and functioning, but not dividing.

🔬 Summary

  • 🌀 G₀ phase is a non-dividing but active state.
  • 🧠 Permanent G₀: Neurons, heart muscle cells
  • 🧪 Reversible G₀: Liver cells, lymphocytes
  • ⛔ G₀ exit occurs before R-point in late G1
  • ⚙️ Decision to divide or pause happens only in G1

G₀ is not an end — it’s a wise biological pause. And it starts only after stepping into G1.

– Concept Clarified by Prof. Siddharth Sanghvi