History of Biology and Key Contributions

History of Biology

Lamarck and Treviranus coined the term 'Biology'
Aristotle is known as the Father of Biology and Zoology
Theophrastus is known as the Father of Botany

Botany and Zoology

Botany is the study of plants
Zoology is the study of animals

Key Biologists and Their Contributions

Robert Hooke coined the term 'cell'
Carolus Linnaeus developed binomial nomenclature
Beadle and Tatum proposed the one gene-one enzyme hypothesis
Jacob and Monod developed the operon concept
Dr. McClintock discovered jumping genes
Karl Landsteiner discovered human blood groups
Singer and Nicholson proposed the Fluid Mosaic Model

Classification of Organisms

Organisms are categorized into different groups
Monera: Includes prokaryotic organisms like bacteria, cyanobacteria, and archaebacteria
- True bacteria (Eubacteriales), fungus-like bacteria (Actinomycetales), and blue-green algae (cyanobacteriae) are included
Protista: Includes unicellular organisms often found in parasitic and saprophytic forms
- Euglenophyta, Pyrrophyta, Chrysophyta, and Xarthophytes are included
- Euglena has both heterotrophic and autotrophic modes of nutrition
Fungi: Includes non-green plants, generally multinucleate organisms with eukaryotic nuclei
- Saprophytic nutrition, growing on dead and decaying organic matter
- Examples: Mushroom, Mucor, Albugo
Plantae: Includes all plants except some algae, diatoms, fungi, and members of the monera and protista kingdoms
Animalia: Multicellular eukaryotic organisms with cells lacking a rigid cell wall and photosynthetic apparatus
- Almost all animals belong to this kingdom, except protozoan

Study of the Cell

The cell is the basic structural and functional unit of all known living organisms
The smallest unit of life, often called the building block of life
The largest known cells are unfertilized ostrich egg cells
The smallest cell is of PPLO (Mycoplasma gallisepticum)
Human nerve cells are the longest animal cells
The largest unicellular plant is Acetabularia (10 cm) and animal is Amoeba (1 mm)
The largest human cell is the female ovum and the smallest human cell is the red blood cell
Robert Hooke coined the term "cell"
Leeuwenhoek discovered the first living cell
The longest cell is a neuron
The biggest cell is the egg of an ostrich

Types of Cells

Prokaryotic Cells:
- Primitive cells lacking a nucleus and most other cell organelles
Eukaryotic Cells:
- These cells have a nucleus and membrane-bound cell organelles

Differences Between Eukaryotic Cells and Prokaryotic Cells

Cell Organelle	Eukaryotic	Prokaryotic
Nucleus	Present	Absent
Number of chromosomes	More than one	One (but not a true chromosome, Plasmids)
Cell type	Usually multicellular	Usually unicellular (some cyanobacteria may be multicellular)
True Membrane-bound Nucleus	Present	Absent
Examples	Animals and plants	Bacteria and archaea
Genetic Recombination	Meiosis and fusion of gametes	Partial, undirectional transfers, DNA
Lysosomes and peroxisomes	Present	Absent
Microtubules	Present	Absent or rare
Endoplasmic reticulum	Present	Absent
Mitochondria	Present	Absent
Cytoskeleton	Present	May be absent
DNA wrapping on proteins	Eukaryotes wrap their DNA around proteins called histones	Multiple proteins act together to fold and condense prokaryotic DNA. Folded DNA is then organized into a variety of conformations that are supercoiled and wound around tetramers of the HU protein.
Ribosomes	Larger	Smaller
Vesicles	Present	Present
Golgi apparatus	Present	Absent
Chloroplasts	Present (in plants)	Absent; chlorophyll scattered in the cytoplasm
Flagella	Microscopic in size, membrane-bound, usually arranged as nine doublets surrounding two singlets	Submicroscopic in size, composed of only one fiber
Permeability of nuclear membrane	Selective	Not present
Plasma membrane with steroid	Yes	Usually no
Cell wall	Only in plant cells and fungi (chemically simpler)	Usually chemically complexed
Vacuoles	Present	Present
Cell size	10–100 μm	1–10 μm

Main Features of the Cell Theory

All organisms are composed of cells
Each cell arises from a pre-existing cell
Every organism starts its life from a single cell

Parts of the Cell and their Functions

Cell wall:
- Present in plant cells, rigid, non-living, freely permeable
- Made up of cellulose and chitin
- Provides shape and rigidity to the cell
Cell membrane:
- Also known as the plasma membrane
- Forms the outer covering of animal cells
- Found within the cell wall in plant cells
- Regulates the movement of molecules inside and outside the cell
Protoplasm:
- The entire fluid present inside the plasma membrane
- (A) Cytoplasm: The fluid found outside the nuclear membrane
- (B) Nucleoplasm: The fluid found inside the nucleus
- Cytoplasm:
Contains various cell organelles like mitochondria, Golgi bodies, endoplasmic reticulum, ribosomes, lysosomes, etc.
Site for various metabolic activities
Provides a medium for the transport of substances within the cell
Nucleus:
- Called the control center of the cell as it contains genetic material (DNA)
- Directs all cellular activities
- Contains one or more nucleoli responsible for the production of ribosomes
- Nucleolus:
Spherical body found inside the nucleus
Contains RNA and proteins
Involved in the synthesis of ribosomes
Mitochondria:
- The powerhouse of the cell
- Site of ATP production (cellular respiration)
- Contains its own DNA and ribosomes
- Number of mitochondria vary depending on the cell's energy needs
Golgi apparatus:
- Stacked membrane-bound sacs called cisternae
- Modifies, sorts, and packages proteins and lipids
- Produces lysosomes
Endoplasmic Reticulum (ER):
- A network of interconnected membrane-bound sacs and tubules
- Two types: rough ER (with ribosomes) and smooth ER (without ribosomes)
- Rough ER is involved in protein synthesis and transport; smooth ER is involved in lipid synthesis, detoxification, and calcium storage
Ribosomes:
- Small organelles composed of RNA and proteins
- Sites of protein synthesis
- Found in the cytoplasm or attached to the rough ER
Lysosomes:
- Membrane-bound sacs containing hydrolytic enzymes
- Involved in digestion of cellular waste, worn-out organelles, and engulfed materials
- Important for defense against pathogens and cellular repair
Vacuoles:
- Fluid-filled sacs enclosed by a membrane
- Store water, nutrients, and waste products
- Larger in plant cells, smaller in animal cells
- Central vacuole:
Occupies a large portion of a plant cell
Stores water, maintains turgor pressure, and plays a role in cell expansion
Plastids:
- Found only in plant cells
- Types: Chloroplasts, chromoplasts, leucoplasts
- Chloroplasts:
Site of photosynthesis
Contain chlorophyll
Contain their own DNA and ribosomes
- Chromoplasts:
Responsible for the color of fruits, flowers, and leaves (contain pigments like carotenoids)
- Leucoplasts:
Store starch, lipids, and proteins
Colorless
Centrioles:
- Found in animal cells and some plant cells
- Involved in cell division
- Organize microtubules and spindle fibers