1.

Importance of biology in engineering

Biology (Greek: Bios-life; Logos-study) plays an increasingly significant role in engineering,
contributing to the development of new technologies and solutions across various fields. Here
are some key areas where biology is important in engineering:
1. Biomedical Engineering:
o Medical Devices and Implants: Understanding biological processes is crucial
for designing biocompatible materials and devices such as artificial organs,
prosthetics, and pacemakers.
o Tissue Engineering: Biology helps in developing methods to grow tissues and
organs in the lab, which can be used for transplantation and regenerative
medicine.
o Drug Delivery Systems: Knowledge of cellular and molecular biology enables
the creation of targeted drug delivery systems that improve the efficacy and
reduce side effects of treatments.
2. Biotechnology:
o Genetic Engineering: Techniques like CRISPR-Cas9 are used to modify
organisms' genetic material for purposes such as improving crop yields,
developing disease-resistant plants, and creating biofuels.
o Industrial Biotechnology: Biological processes are harnessed for the
production of chemicals, materials, and energy. This includes using
microorganisms in fermentation processes to produce biofuels, bioplastics, and
pharmaceuticals.
3. Environmental Engineering:
o Bioremediation: Biological organisms, such as bacteria and plants, are used to
clean up contaminated environments, including soil and water.
o Sustainable Practices: Understanding ecosystems and biological cycles helps
in designing sustainable agricultural practices, waste management systems, and
conservation efforts.
4. Synthetic Biology:
o Creating New Biological Parts: Synthetic biology involves designing and
constructing new biological parts, devices, and systems that do not exist in
nature, which can be used for various applications, from biofuels to new
medicines.
o Biological Computing: Leveraging biological components to create computing
systems that can perform specific tasks, offering potential for advancements in
data storage and processing.
5. Materials Science:
 o Biomimicry: Studying natural biological materials and processes to inspire the
design of new materials and structures. Examples include creating adhesives
inspired by gecko feet or lightweight materials inspired by the structure of
bones.
o Smart Materials: Developing materials that respond to environmental stimuli,
such as temperature or pH, which can be used in various applications from
clothing to medical devices.
6. Agricultural Engineering:
o Precision Agriculture: Using biological data and insights to optimize farming
practices, improve crop yields, and reduce environmental impact.
o Genetically Modified Organisms (GMOs): Creating crops with desired traits,
such as pest resistance or improved nutritional content, to enhance food security
and sustainability.
Overall, the integration of biology in engineering drives innovation and leads to the
development of technologies that improve health, sustainability, and quality of life.

2. Development of technological subjects imitating nature’s biological entity

The development of technological subjects imitating nature's biological entities is commonly
referred to as biomimicry or bioinspiration. Biomimicry involves studying and replicating
natural systems, processes, and organisms to solve human problems and innovate in
technology. Here are some key areas and examples where biomimicry is applied:
1. Materials Science and Engineering:
o Gecko Adhesives: Inspired by the microscopic structures on gecko feet that
allow them to adhere to surfaces, scientists have developed synthetic adhesives
with similar properties.
o Spider Silk: Studying the properties of spider silk, which is lightweight and
extremely strong, researchers are developing new materials for use in
everything from medical sutures to bulletproof vests.
2. Robotics and Automation:
o Robotic Locomotion: Robots that mimic the movement of animals, such as the
Boston Dynamics' Spot robot that moves like a dog, or drones that fly like birds
or insects, enhance mobility and adaptability in various environments.
o Soft Robotics: Inspired by the flexibility and adaptability of octopus arms, soft
robots are being developed for applications in delicate surgeries and other tasks
requiring gentle handling.
3. Architecture and Design:
 o Energy-Efficient Buildings: The design of the Eastgate Centre in Zimbabwe
was inspired by termite mounds, which maintain a constant internal temperature
through natural ventilation, leading to energy-efficient cooling and heating.
o Self-Cleaning Surfaces: Inspired by the lotus leaf, which repels water and dirt,
researchers have developed self-cleaning materials for use in windows, paints,
and textiles.
4. Medical Devices and Health:
o Needle Design: Hypodermic needles inspired by the mosquito’s proboscis,
which allows painless insertion, are being developed to reduce discomfort
during injections.
o Drug Delivery Systems: Mimicking the targeted delivery mechanisms of
viruses, scientists are creating advanced drug delivery systems that can
precisely target diseased cells without affecting healthy ones.
5. Environmental and Sustainable Technologies:
o Water Harvesting: Inspired by the Namib Desert beetle, which collects water
from fog on its back, technologies are being developed to harvest water from
the air in arid regions.
o Solar Energy: The design of solar panels is being improved by studying the
way plants maximize light absorption for photosynthesis.
6. Transportation:
o High-Speed Trains: The nose of the Shinkansen Bullet Train in Japan was
redesigned to mimic the kingfisher’s beak, reducing noise and improving
aerodynamics.
o Aircraft Design: The wingtips of modern airplanes are often designed based on
the shape of bird wings, which reduces drag and increases fuel efficiency.
7. Information Technology:
o Neural Networks: Artificial neural networks are designed to mimic the way the
human brain processes information, leading to advancements in machine
learning and artificial intelligence.
o DNA Computing: Researchers are exploring how to use DNA for data storage
and computation, inspired by the complex information storage capabilities of
genetic material.
Biomimicry offers innovative solutions by leveraging millions of years of evolutionary
optimization found in nature, leading to sustainable and efficient technologies across various
fields.
Benefits:
 Innovation: Nature’s solutions provide inspiration for novel technologies.
  Sustainability: Biomimicry often leads to environmentally friendly and energy-
efficient solutions.
 Efficiency: Natural processes are typically optimized for performance, offering highly
efficient models.
In summary, biomimicry fosters innovation by translating nature’s time-tested strategies into
practical applications, resulting in sustainable and efficient technological advancements across
various fields.
Major Discoveries in Biology
1. Cell Theory (1839): All living organisms are composed of cells, the basic unit of life
(Matthias Schleiden and Theodor Schwann).
2. Theory of Evolution by Natural Selection (1859): Species evolve over time through
natural selection (Charles Darwin).
3. Mendelian Inheritance (1866): Traits are inherited according to specific laws (Gregor
Mendel).
4. DNA Structure (1953): Discovery of the double helix structure of DNA (James Watson
and Francis Crick, with key contributions from Rosalind Franklin and Maurice
Wilkins).
5. Germ Theory of Disease (1860s): Microorganisms cause many diseases (Louis
Pasteur and Robert Koch).
6. Antibiotics (1928): Discovery of penicillin, the first true antibiotic (Alexander
Fleming).
7. Genetic Code (1960s): Deciphering the code that translates DNA sequences into
proteins (Marshall Nirenberg, Har Gobind Khorana, and Robert Holley).
8. PCR (1983): Technique to amplify small DNA segments (Kary Mullis).
9. Human Genome Project (2003): Sequencing the entire human genome (International
collaboration).
10. CRISPR-Cas9 Gene Editing (2012): Precise method for editing genes (Jennifer
Doudna and Emmanuelle Charpentier).
11. Pluripotent Stem Cells (2006): Inducing adult cells to become pluripotent stem cells
(Shinya Yamanaka).
12. Role of Microbiome (2000s): Significant impact of the microbiome on health and
disease (Various researchers).
13. Endosymbiotic Theory (1967): Mitochondria and chloroplasts originated from
bacteria (Lynn Margulis).
14. RNA Interference (1998): Process where RNA molecules inhibit gene expression
(Andrew Fire and Craig Mello).
 Concept of scientific classification of living entity
The scientific classification of living entities is a system used to organize and categorize
organisms based on various characteristics. This system helps in understanding the
relationships between different organisms and provides a structured way to study the
diversity of life. Below is a discussion of classification based on cellularity,
ultrastructure, and energy and carbon utilization.
(a) Cellularity: Unicellular and Multicellular
Unicellular Organisms
 Definition: Organisms consisting of a single cell that performs all the functions
necessary for life.
 Examples:
o Bacteria: Escherichia coli (E. coli) - Commonly found in the intestines of
humans and animals.
o Protozoa: Amoeba proteus - A free-living protozoan found in freshwater
environments.
o Algae: Chlamydomonas - A single-celled green alga that swims using two
flagella.
Multicellular Organisms
 Definition: Organisms consisting of multiple cells that are specialized to perform
specific functions, working together as a single entity.
 Examples:
o Plants: Arabidopsis thaliana - A model organism in plant biology.
o Animals: Homo sapiens - Humans, complex organisms with specialized cells
and tissues.
o Fungi: Agaricus bisporus - Common mushroom, which has a multicellular
structure.
(b) Ultrastructure: Prokaryotes and Eukaryotes
Prokaryotes
 Definition: Organisms whose cells lack a true nucleus and membrane-bound
organelles. Their DNA is located in a region called the nucleoid.
 Characteristics:
o Simple cell structure
o No nucleus
o Circular DNA
o Lack of membrane-bound organelles
 o Examples:
 Bacteria: Staphylococcus aureus - Causes skin infections and other
diseases.
 Archaea: Methanobrevibacter smithii - Found in the human gut,
involved in methane production.
Eukaryotes
 Definition: Organisms whose cells contain a true nucleus enclosed by a nuclear
membrane and possess membrane-bound organelles.
 Characteristics:
o Complex cell structure
o True nucleus containing linear DNA
o Membrane-bound organelles (e.g., mitochondria, chloroplasts)
o Examples:
 Protists: Paramecium caudatum - A ciliated protozoan found in
freshwater.
 Fungi: Saccharomyces cerevisiae - Yeast used in baking and brewing.
 Plants: Zea mays - Corn, a major agricultural crop.
 Animals: Panthera leo - Lion, a large carnivorous mammal.
 (c) Energy and Carbon Utilization: Autotrophs, Heterotrophs, and Lithotrophs
Autotrophs
 Definition: Organisms that produce their own food using light (photosynthesis) or
chemical energy (chemosynthesis).
 Types:
1. Photoautotrophs: Use light energy to synthesize organic compounds from
carbon dioxide.
Photosynthesis, the process by which green plants and certain other organisms
transform light energy into chemical energy. During photosynthesis in green plants,
light energy is captured and used to convert water, carbon dioxide, and minerals into
oxygen and energy-rich organic compounds. Carbohydrates are the most-important
direct organic product of photosynthesis in the majority of green plants. The formation
of a simple carbohydrate, glucose, is indicated by a chemical equation,

Little free glucose is produced in plants; instead, glucose units are linked to
form starch or are joined with fructose, another sugar, to form sucrose.

 Examples:
 Plants: Uses photosynthesis to convert light energy into
chemical energy.
 Algae: Single-celled green alga that performs photosynthesis.
2. Heterotrophs
 Definition: Organisms that obtain their energy and carbon by consuming organic
matter produced by other organisms.
 Examples:
o Animals: Homo sapiens - Humans consume plants and animals for energy and
nutrients.
o Fungi: Agaricus bisporus - Common mushroom that decomposes organic
matter.
o Protozoa: Amoeba proteus - Feeds on smaller organisms and organic particles.
3. Chemotrophs
Chemo: Because they obtain energy through the chemical breakdown of
organic molecules;
 Chemotrophs are a class of organisms that obtain their energy through the
oxidation of chemical molecules. The most common type of chemotrophic organisms
is prokaryotic and include both bacteria and fungi. All of these organisms require
carbon to survive and reproduce. The ability of chemotrophs to produce their own
organic or carbon-containing molecules differentiates these organisms into two
different classifications–chemoautotrophs and chemoheterotrophs.
3.1 Chemoautotrophs
Chemoautotrophs are able to synthesize their own organic molecules from the
fixation of carbon dioxide. These organisms are able to produce their own source of
food, or energy. The energy required for this process comes from the oxidation of
inorganic molecules such as iron, sulphur or magnesium. Chemoautotrophs are able to
thrive in very harsh environments, such as deep-sea vents, due to their lack of
dependence on outside sources of carbon other than carbon dioxide. Chemoautotrophs
include nitrogen fixing bacteria located in the soil, iron oxidizing bacteria located in the
lava beds, and sulphur oxidizing bacteria located in deep sea thermal vents. E.g.
Nitrobacter, Nitrosomonas and Sulphur bacteria
3.2 Chemoheterotrophs
Chemoheterotrophs, unlike chemoautotrophs, are unable to synthesize their
own organic molecules. Instead, these organisms must ingest preformed carbon
molecules, such as carbohydrates and lipids, synthesized by other organisms. They do,
however, still obtain energy from the oxidation of inorganic molecules like the
chemoautotrophs. Chemoheterotrophs are only able to thrive in environments that are
capable of sustaining other forms of life due to their dependence on these organisms for
carbon sources. Chemoheterotrophs are the most abundant type of chemotrophic
organisms and include most bacteria, fungi, protozoa and animals.
3. Lithotrophs
 Definition: Organisms that obtain energy from inorganic compounds (e.g., minerals).
 Types:
o Chemoautotrophic Lithotrophs: Use inorganic compounds as an energy
source and carbon dioxide as a carbon source.
 Examples:
 Bacteria: Thiobacillus ferrooxidans - Oxidizes iron or sulfur
compounds for energy.
o Chemoheterotrophic Lithotrophs: Use inorganic compounds as an energy
source but require organic carbon for growth.
 Examples:
 Bacteria: Pseudomonas stutzeri - Uses nitrate as an electron
acceptor and inorganic compounds for energy.
 Classification of living entity based on ammonia excretion- aminotelic, uricotelic
and ureotelic
The classification of living organisms based on how they excrete nitrogenous waste—
specifically ammonia—includes three main categories: aminotelic, uricotelic, and
ureotelic. These categories are defined by the form in which the nitrogen is excreted.
1. Aminotelic
 Definition: Organisms that excrete nitrogenous waste primarily as ammonia.
 Characteristics: Ammonia is highly toxic and soluble in water, so it needs to be excreted
quickly and efficiently. Aminotelic organisms typically live in aquatic environments
where water is abundant to dilute the ammonia.
 Examples: Aquatic animals: Many fish, amphibians (in their larval stages), and aquatic
invertebrates like sponges and jellyfish are aminotelic.
2. Uricotelic
 Definition: Organisms that excrete nitrogenous waste primarily as uric acid.
 Characteristics: Uric acid is less toxic and insoluble in water, which allows it to be
excreted as a paste or solid. This conserves water, making it an adaptation for organisms
in arid environments or those that need to conserve water.
 Examples: Birds: Most birds excrete nitrogenous waste as uric acid, Reptiles: Many
reptiles, including lizards and snakes, are uricotelic, Insects: Many insects also excrete
uric acid.
3. Ureotelic
 Definition: Organisms that excrete nitrogenous waste primarily as urea.
 Characteristics: Urea is less toxic than ammonia and more soluble in water, allowing it
to be stored and excreted with less water than ammonia but more than uric acid. This is
a common adaptation in terrestrial animals that live in environments where water is
available but needs to be conserved.
 Examples:
o Mammals: Humans and most other mammals are ureotelic, excreting
nitrogenous waste primarily in the form of urea.
o Amphibians: Many adult amphibians, such as frogs, are ureotelic.
o Some fish: Certain species of cartilaginous fish, like sharks, are ureotelic.
Summary:
 Aminotelic: Excrete ammonia (common in aquatic environments).
 Uricotelic: Excrete uric acid (adapted to conserve water).
 Ureotelic: Excrete urea (balanced water conservation).
 Three Kingdom classification
The configuration of organisms into taxonomic groups known as taxa based on
similarities or relationships is known as classification. Closely related organisms (those
with similar characteristics) are classified as belonging to the same taxon. The
similarities and differences between organisms are used to classify them into larger
groups. Because the categorization of living organisms is a complex and contentious
subject, various taxonomic classification schemes have existed at various times.
Linnaeus recognized only two kingdoms of living things in his classification scheme:
Animalia and Plantae. Microscopic organisms had not been thoroughly studied at the
time. They were either classified as a separate section titled Chaos or, in some cases, as
plants or animals.
In 1866, Ernst Haeckel proposed a three-kingdom classification system for organisms
based on their characteristics, functions, and other factors:
 Animalia: Includes all animals, both with and without backbones, such as sponges,
insects, birds, and mammals
 Plantae: Includes all plants, such as mosses, ferns, and flowering plants
 Protista: Includes unicellular and multicellular organisms such as protozoa, algae, and
slime Molds

Classification of microorganisms based on: (a) temperature (b) salt concentration (c)
oxygen requirement
Microorganisms can be classified based on various environmental factors, including
temperature, salt concentration, and oxygen requirements. Here's a breakdown of these
classifications:
(a) Classification Based on Temperature
1. Psychrophiles
o Definition: Microorganisms that thrive at low temperatures, typically between
-20°C and 10°C.
o Examples: Microbes found in Arctic and Antarctic regions, such as
Psychrobacter.
2. Mesophiles
o Definition: Microorganisms that grow best at moderate temperatures, usually
between 20°C and 45°C. Most human pathogens are mesophiles.
o Examples: Escherichia coli, Staphylococcus aureus.
3. Thermophiles
o Definition: Microorganisms that thrive at higher temperatures, usually between
45°C and 80°C.
 o Examples: Thermus aquaticus, used in PCR (polymerase chain reaction)
processes.
4. Hyperthermophiles
o Definition: Microorganisms that thrive at extremely high temperatures,
typically above 80°C, often found in hot springs and hydrothermal vents.
o Examples: Pyrolobus fumarii, which can survive in temperatures up to 113°C.
(b) Classification Based on Salt Concentration
1. Non-halophiles
o Definition: Microorganisms that do not require high salt concentrations and
typically grow in environments with low salt levels (less than 1% NaCl).
o Examples: Most freshwater bacteria, such as Escherichia coli.
2. Halotolerant
o Definition: Microorganisms that can tolerate some salt concentration but do not
require it for growth, typically thriving in environments with up to 7.5% NaCl.
o Examples: Staphylococcus aureus, which can survive on human skin.
3. Halophiles
o Definition: Microorganisms that require moderate salt concentrations (between
3% and 15% NaCl) for growth.
o Examples: Halobacterium, found in salt lakes.
4. Extreme Halophiles
o Definition: Microorganisms that require very high salt concentrations (15% to
30% NaCl) to survive.
o Examples: Halobacterium salinarum, found in extremely salty environments
like the Dead Sea.
(c) Classification Based on Oxygen Requirement
1. Obligate Aerobes
o Definition: Microorganisms that require oxygen for growth and cannot survive
without it.
o Examples: Mycobacterium tuberculosis, which causes tuberculosis.
2. Facultative Anaerobes
o Definition: Microorganisms that can grow in the presence or absence of
oxygen, though they grow better with oxygen.
o Examples: Escherichia coli, found in the human gut.
3. Obligate Anaerobes
 o Definition: Microorganisms that cannot survive in the presence of oxygen and
are harmed by it.
o Examples: Clostridium botulinum, which causes botulism.
4. Aerotolerant Anaerobes
o Definition: Microorganisms that do not use oxygen for growth but can tolerate
its presence without being harmed.
o Examples: Lactobacillus, used in yogurt production.
5. Microaerophiles
o Definition: Microorganisms that require oxygen for growth but at lower
concentrations than is present in the atmosphere (typically 2-10% oxygen).
o Examples: Helicobacter pylori, associated with stomach ulcers.
Summary:
 Temperature: Psychrophiles, Mesophiles, Thermophiles, Hyperthermophiles.
 Salt Concentration: Non-halophiles, Halotolerant, Halophiles, Extreme Halophiles.
 Oxygen Requirement: Obligate Aerobes, Facultative Anaerobes, Obligate Anaerobes,
Aerotolerant Anaerobes, Microaerophiles.
These classifications help in understanding the ecological niches and physiological adaptations
of microorganisms.
Microorganisms, classification of microorganisms
All organisms that are very small or microscopic in size, and cannot be seen with the
naked eye are referred to as microorganisms. Microorganisms are visible under the microscope.
Anton van Leeuwenhoek first observed microorganisms under the microscope.
Microorganisms include bacteria, archaea, algae, fungi, protozoa, etc.

Bacteria
Bacteria are unicellular organisms. The cells are described as prokaryotic because they
lack a nucleus. They exist in four major shapes: bacillus (rod shape), coccus (spherical shape),
spirilla (spiral shape), and vibrio (curved shape). Most bacteria have a peptidoglycan cell wall;
they divide by binary fission; and they may possess flagella for motility. The difference in their
cell wall structure is a major feature used in classifying these organisms.
Archaea
Archaea or Archaebacteria differ from true bacteria in their cell wall structure and lack
peptidoglycans. They are prokaryotic cells with avidity to extreme environmental conditions.
Based on their habitat, all Archaeans can be divided into the following groups: methanogens
(methane-producing organisms), halophiles (archaeans that live in salty environments),
thermophiles (archaeans that live at extremely hot temperatures), and psychrophiles (cold-
temperature Archaeans). Archaeans use different energy sources like hydrogen gas, carbon
dioxide, and sulphur. Some of them use sunlight to make energy, but not the same way plants
do.
Fungi
Fungi (mushroom, molds, and yeasts) are eukaryotic cells (with a true nucleus). Most
fungi are multicellular and their cell wall is composed of chitin. They obtain nutrients by
absorbing organic material from their environment (decomposers), through symbiotic
relationships with plants (symbionts), or harmful relationships with a host (parasites). They
form characteristic filamentous tubes called hyphae that help absorb material. The collection
of hyphae is called mycelium. Fungi reproduce by releasing spores.
Protozoa
Protozoa are unicellular aerobic eukaryotes. They have a nucleus, complex organelles,
and obtain nourishment by absorption or ingestion through specialized structures. They make
up the largest group of organisms in the world in terms of numbers, biomass, and diversity.
Algae
Algae, also called cyanobacteria or blue-green algae, are unicellular or multicellular
eukaryotes that obtain nourishment by photosynthesis. They live in water, damp soil, and rocks
and produce oxygen and carbohydrates used by other organisms. It is believed that
cyanobacteria are the origins of green land plants.
Viruses
Viruses are noncellular entities that consist of a nucleic acid core (DNA or RNA)
surrounded by a protein coat. Although viruses are classified as microorganisms, they are not
considered living organisms. Viruses cannot reproduce outside a host cell and cannot
metabolize on their own. Viruses often infest prokaryotic and eukaryotic cells causing diseases.
Taxonomy
Taxonomy is the science of classifying organisms, while a taxon is a group of organisms that
are classified together.
or
Taxonomy referred only to the classification of organisms on the basis of shared
characteristics.
or
The process of organizing and categorizing organisms based on shared characteristics.
Taxonomy can also refer to the classification of other things, like concepts or documents.
Carl Linnaeus (1707-1758) is known as the "father of taxonomy" for his work in developing a
system for classifying and naming organisms.
Taxon
A group of organisms that are classified together as a unit. The term "taxon" comes from the
Greek words taxis and nomos. Note: Taxa is the plural form of the word taxon
The taxonomic ranks used in the classification of bacteria are (example in parentheses):
Kingdom - broadest classification and groups together all forms of life that share the most
general characteristics.
Division/ phylum - groups together organisms that share a general body plan or organization.
Class - The class rank narrows down the organisms within a phylum by grouping those that
share more specific characteristics.
Order - The order groups organisms within a class that share even more specific traits and
evolutionary history.
Family - groups together closely related genera (plural of genus) that share more specific
common characteristics.
Genus - The genus groups species that are very closely related and share a common ancestor.
Species - The species is the most specific rank and refers to a group of individuals that can
interbreed and produce fertile offspring. It is often defined by the presence of specific, shared
characteristics.
E.g Kingdom: Animalia (Animals); Phylum: Chordata (Animals with a spinal cord); Class:
Mammalia (Mammals); Order: Primates (Primates); Family: Hominidae (Great apes and
humans); Genus: Homo (Humans and close relatives); Species: Homo sapiens (Modern
humans)

Molecular taxonomy
It is the classification of organisms based on the structure and sequence of molecules, such as
DNA, RNA, and proteins. This approach allows scientists to analyze the genetic and molecular
differences and similarities among organisms, providing a more precise understanding of
evolutionary relationships.
In molecular taxonomy, life is broadly categorized into three major domains, often referred
to as kingdoms in older classifications. These domains represent the three fundamental
branches of life:
1. Bacteria (Eubacteria)
 Characteristics:
o Bacteria are single-celled prokaryotic organisms, meaning they lack a true
nucleus and membrane-bound organelles.
o They have a simple cell structure with a cell wall made of peptidoglycan.
o Bacteria are incredibly diverse, occupying nearly every habitat on Earth, from
soil to water to the human gut.
o They reproduce asexually through binary fission and can exchange genetic
material through processes like conjugation, transformation, and transduction.
 Examples:
o Escherichia coli (E. coli), a common bacterium in the human intestine.
o Staphylococcus aureus, a bacterium associated with skin infections.
2. Archaea
 Characteristics:
o Archaea are also prokaryotic, single-celled organisms, but they differ
significantly from bacteria in terms of genetics, biochemistry, and membrane
structure.
o They have unique lipids in their cell membranes and lack peptidoglycan in their
cell walls.
o Archaea are often found in extreme environments, such as hot springs, salt
lakes, and deep-sea hydrothermal vents, but they can also be found in more
moderate environments.
o Like bacteria, archaea reproduce asexually by binary fission, budding, or
fragmentation.
 Examples:
o Methanogens, which produce methane and are found in anaerobic environments
like wetlands and the guts of ruminants.
o Halophiles, which thrive in extremely salty environments.
3. Eukarya (Eukaryota)
 Characteristics:
 o Eukarya are organisms with complex cells that have a true nucleus enclosed by
a membrane, along with other membrane-bound organelles such as
mitochondria and the endoplasmic reticulum.
o This domain includes a wide variety of life forms, including plants, animals,
fungi, and protists (unicellular or simple multicellular organisms).
o Eukaryotes can reproduce sexually or asexually and exhibit a high degree of
cellular complexity and organization.
 Examples: Homo sapiens (humans), Zea mays (corn), and Saccharomyces cerevisiae
(yeast).
Summary of the Three Major Domains (Kingdoms):
 Bacteria: Prokaryotic, simple cells with peptidoglycan cell walls.
 Archaea: Prokaryotic, distinct from bacteria with unique membrane lipids and often
living in extreme environments.
 Eukarya: Eukaryotic, complex cells with a nucleus and organelles, including all
multicellular life forms.

Microbiological techniques and their mechanism: serial dilution, pour plating, streak
plating, spread plating, nutrient agar and broth
1. Serial dilution
Mechanism: Serial dilution is a technique used to decrease the concentration of a sample, often
to isolate individual colonies of microorganisms. The process involves diluting a concentrated
sample in a stepwise manner, usually by transferring a small volume of the sample into a larger
volume of a diluent (like sterile water or saline). Each subsequent dilution decreases the
concentration of the original sample exponentially (e.g., 10-fold, 100-fold). These diluted
samples can then be plated to estimate the concentration of microorganisms in the original
sample.
Purpose: Serial dilution is commonly used to obtain countable colonies when the original
sample concentration is too high. This technique is essential for accurate colony-forming unit
(CFU) estimation.
2. Pour plate method-
Mechanism: Pour plating involves mixing a small volume of a microbial sample with molten
agar (cooled to about 45-50°C to avoid killing the microorganisms) and then pouring this
mixture into a sterile Petri dish. Once the agar solidifies, microorganisms are trapped within
the agar matrix as well as on the surface. As the plate incubates, colonies form both on the
surface and within the agar. Prior to performing the pour plate technique, the sample must be
serially diluted to make the microbial load in the sample between 20 – 300 CFU/mL (suitable
colony counting range is 20 – 200, some consider it to 30 – 300, and in average it is taken as
25 – 250).
Purpose: Pour plating is used to estimate the number of viable microorganisms in a sample and
is particularly useful for isolating anaerobic or facultative organisms that might grow within
the agar.
Number of CFU per ml = # of Colonies * Dilution factor *1/ Aliquot

3. Spread plate technique -The spread plate technique is used for enumeration, enrichment,
screening and selection of microorganism. In this the culture is uniformly spread over the
surface of an agar plate, resulting in the formation of isolated colonies distributed evenly across
the agar surface if the appropriate concentration of cells is plated. Materials required Sample,
sterilized petri plates, sterilized nutrient media, flame, glass marker, glass rod (alternatively
sterile plastic rod also can be used), beaker with alcohol.
4. Agar overlay method- This technique can be used for isolation bacteriophage. Phages are
viruses affecting bacterial cell and they cannot live outside the cell as like other viruses.
Quantification of phage as phage forming unit also can be done using this method. First
Bacterial mat called lawn formed in the plate. Then the phages mixed infect the bacterial cells.
So the bacterial lawn disappears. The resultant zone of clearance is called plaque. As like
bacterial colonies, single plaque also formed by single phage and it is expressed as plaque
forming unit.
Procedure
1. First the agar plate is prepared as like streaking or spread plate technique
2. Bacterial culture usually108 bacteria and phage suspension (50-200μl) is uniformlyl) is
uniformly mixed with soft agar (0.5-0.7%) of 2-3 ml.
3. Pour it on top of pre-settled agar plate and shake it vigorously for uniform spreading 4. Allow
it to settle and incubate 24-48 hrs.
5. Nutrient Broth-
Mechanism:
Nutrient broth is a liquid medium composed of peptones, beef extract, and sometimes sodium
chloride. Like nutrient agar, it provides a rich environment for microbial growth but in liquid
form. When microorganisms are introduced into the broth, they grow throughout the medium,
causing it to become turbid (cloudy).
Purpose:
Nutrient broth is used to grow bacteria and other microorganisms in large quantities. It is
especially useful for growing bacteria that do not form distinct colonies on solid media, or for
experiments requiring a liquid culture.
6. Streak plate method

Separate Notes
 Structure of proteins
1. Primary Structure:
o The primary structure of a protein is the sequence of amino acids in the
polypeptide chain. Each amino acid is linked to the next via peptide bonds,
forming a linear chain. It is the most basic level of protein structure.
o Example: Glycine-Valine-Alanine-Leucine…………….so on

or

2. Secondary Structure:
o The secondary structure is formed by hydrogen bonds between the backbone
atoms in the polypeptide chain.
o The two most common forms are:
  α-helix: A coiled structure stabilized by hydrogen bonds between every
fourth amino acid.
 β sheet: A folded structure where strands lie side by side, forming
hydrogen bonds between them.

3. Tertiary Structure:
o The tertiary structure is the overall 3D shape of a single polypeptide chain. It is
formed by interactions between the side chains (R-groups) of the amino acids.
o Types of interactions include:
 Hydrogen bonds
 Ionic bonds
 Hydrophobic interactions
 Disulfide bridges (covalent bonds between cysteine residues)
4. Quaternary Structure:
o The quaternary structure is the arrangement of multiple polypeptide chains
(subunits) in a multi-subunit protein.
o These subunits are held together by non-covalent interactions, and sometimes
covalent bonds like disulfide bridges.
o Example: Haemoglobin (composed of 4 subunits).