INTRODUCTION TO BIOLOGY

Biology is a natural science concerned with the study of life and living organisms. Modern
biology is a vast and eclectic field composed of many specialized disciplines that study the
structure, function, growth, distribution, evolution, or other features of living organisms.
However, despite the broad scope of biology, there are certain general and unifying concepts
that govern all study and research:

• the cell is the basic unit of life

• genes (consisting of DNA or RNA) are the basic unit of heredity
• evolution accounts for the unity and diversity seen among living organisms
• all organisms survive by consuming and transforming energy
• all organisms maintain a stable internal environment

History of Biological Science

Natural philosophy was studied as early as the ancient civilizations of Mesopotamia,

Egypt, the Indian subcontinent, and China. However, the origins of modern biology and its
approach to the study of nature are most often traced back to ancient Greece. (Biology is
derived from the Greek word “bio” meaning “life” and the suffix “ology” meaning “study of.”).
In the early 19th century, several biologists pointed to the central importance of the cell
and in 1838, Schleiden and Schwann began promoting the now universal ideas of the cell
theory. Jean-Baptiste Lamarck was the first to present a coherent theory of evolution, although
it was the British naturalist Charles Darwin who spread the theory of natural selection
throughout the scientific community.

Biological classification
Biological classification is a scientific method for classifying organisms into hierarchical
groups and subgroups based on similarities and differences. The goal of biological
classification is to group together all of the known plants and animals into categories that can
be named, remembered, and studied.
According to biological classification history, Aristotle, a Greek philosopher, classified
various animals based on habitat, characteristics, and so on. Later, during the 18th century, a
Swedish botanist named Carolus Linnaeus introduced Taxonomic Hierarchy Categories,
which is still used today. Since he had introduced this system, he was known as the “father of
taxonomy.”
The major taxonomic hierarchies are;
• Domain - highest level of classification and broadest category,
• Kingdom - The highest level of classification, the kingdom, is broken down into
numerous degrees of subgroups,
• Phylum - The phylum is more specific than a kingdom,
• Classes: The organisms of a phylum are further sorted into more classes. It is one of
the most common ranks put forth by Linnaeus,
• Order: One or more families that are similar to one another make up the order,
• Family: Here, the living organisms share some resemblance among themselves,
• Genus: It consists of several species with similar characteristics but different from that
of species and another genus,
• Species: It describes a collection of organisms with comparable form, morphology, and
reproductive characteristics.
• Sub-species can be found within a species.
Five kingdom classification system
R.H. Whittaker (1969) proposed a Five Kingdom Classification. The kingdoms defined by
him were named Monera, Protista, Fungi, Plantae, and Animalia. This approach aided in the
differentiation of organisms based on their evolutionary relationships, mode of nourishment,
mode of reproduction, and cell structure.
CLASSIFICATION BASED ON CELLULARITY, STRUCTURE, MODE
OF NUTRITION AND EXCRETION
1. Cellularity
Cells are the building blocks of all life forms. Depending on the composition, distribution, and
number of cells present, organisms are classified as unicellular or multicellular
• Unicellular organisms can be defined as the living-organisms, which consist of only a
single cell. This single cell is capable to perform different life processes or cellular
activities. It consists of prokaryotic organisms like bacteria and archaea, and eukaryotic
organisms like protozoa, unicellular algae, and unicellular fungi.
• Multicellular organisms can be defined as living organisms, which consist of multiple
cells. With these distinct cell organelles, it is capable to perform different life processes or
separate cellular activities inside a body. It only consists of eukaryotic organisms like
insects, animals, birds, humans, etc.

2. Ultrastructure:
During the 1950s, all organisms were classified as prokaryotes and eukaryotes. The cells
of prokaryotes are simple than eukaryotes. The basic features of cells of prokaryotes and
eukaryotes are the plasma membrane and cytoplasm. Eukaryotes cells form large and complex
organisms. The characteristics of both types are mentioned below:
• Prokaryotic cells are single-celled organisms that include bacteria and archaea. The
nuclear membrane is absent and genetic material is present as a single chromosome.
The organelles such as mitochondria, Golgi bodies, chloroplast, and lysosomes are
absent. Flagella and pili are present for locomotion and attachment. The cell wall is
composed of carbohydrates and amino acids and reproduction occur asexually by
binary fission.
• Eukaryotic cells are multi-celled organisms that include protozoa, fungi, plants, and
animals. The nucleus is enclosed within the nuclear membrane and it contains single
 linear DNA which carries the genetic information. The organelle mitochondria are
present. The locomotion is usually carried out with flagella and cilia.

3. Energy and carbon utilization

All living organisms, including plants and animals, require food. Food provides energy
and nutrition for all living organisms on this planet. Nutrients are substances that provide
energy and biomolecules required for various body functions. To meet their nutritional needs,
some animals consume simple inorganic compounds, while others consume complex
compounds. The mode of nutrition differs between species.
• Autotrophs Organisms capable of producing their own food by utilizing the substance
from the surrounding environment are called autotrophs. Energy generation can be carried
out in either of two ways:
Photosynthesis: Photosynthesis occurs in the presence of light and chlorophyll. Water and
carbon dioxide are broken down into glucose and oxygen. E.g. Green plants, Cyanobacteria,
and green algae.
Chemosynthesis: Chemosynthesis utilizes the energy stored in inorganic compounds to
produce carbohydrates, sulfur, and water. Eg. Sulfur bacteria, Iron-oxidizing bacteria, and
nitrogen-fixing bacteria.
• Heterotrophs These organisms are unable to produce their own food and hence must
obtain it from plants and animals. For instance, heliobacteria, purple non-sulfur bacteria,
and green non-sulfur bacteria.
4. Excretion
The process of eliminating metabolic wastes (fluid, gaseous, organic, or inorganic)
from the body is called excretion. An organism gets rid of these excess substances through the
process of deamination. Toxic ammonia is either expelled in its original form or is first changed
into a less harmful form, such as urea or uric acid, before being eliminated. Generally, three
categories of animals can be distinguished depending on the nitrogenous wastes they create.
• Ammonotelism The process involves the removal of nitrogenous wastes in the form of
ammonia. Aquatic invertebrates, bony fishes, and aquatic/larval amphibians all exhibit
ammonotelism. Ammonotelic animals are those that lack an excretory system. E.g.,
Protozoa. Ammonotelic animals excrete ammonia through the skin, gills, and kidneys.
• Ureotelism The mode of excretion in which elimination of nitrogenous waste is in the
form of urea is called as Ureotelism. It requires less amount of water for getting eliminated.
The animals that follow this mode of excretion are known as ureotelic animals. Example -
Humans, turtles, frogs, sharks etc.
• Uricotelism The mode of excretion in which elimination of nitrogenous waste is in the
form of uric acid is called as uricotelism. The animals that follow this mode of excretion
are known as uricotelic animals. Most of these animals live in dry regions or do not
consume plenty of water (eg. birds), hence they must conserve water in their bodies.
Example - Birds (class Aves), Helix (commonly known as land snails), cockroach, lizard,
snakes etc.
 CELL: the basic unit of life
The body of all living organisms is made up of cells which carryout certain basic
functions. Hence the cells are called “Basic structural and functional units of living
organisms.” The classical branch of biology that deals with the study of structure, function and
life history of a cell is called “Cell Biology”
CELL SHAPE
• Cells are of variable shapes and sizes. Their shape is according to the function.
Generally, cells are spherical but they may be elongated (nerve cell), branched
(pigmented), discoidal (RBC), spindle shaped (muscle cell) etc.

CELL SIZE
• Size of cell is variable depending upon the type of organism. Some are microscopic
while some are visible with naked eyes. Their size may vary from 0.2 μm to18 cm.
• Size of a typical cell in a Multicellular organism range from 20-30 mn.
• The largest cell is ostrich egg (15 cm. in diameter with shell & 8 cm. in diameter
without shell)
• The longest cell is nerve cell. (up to 1m. or more)
• Smallest cells so far known are PPLOs e.g. mycoplasma (0.1 μm in dia.)
• CELL STRUCTURE AND FUNCTION: A typical cell has an outer non-living layer called
cell wall. The cell membrane is present below the cell wall. The cell membrane encloses
protoplasm. The protoplasm has a semi fluid matrix called cytoplasm and a large membrane
bound structure called Nucleus. The cytoplasm has many membrane bound structures like
endoplasmic reticulum, golgi bodies, mitochondria, plastids, micro bodies, vacuoles; and non-
membranous structures like Centrosome and ribosomes. These are called cell organelles. The
cytoplasm without these cell organelles is called cytosol.
1. CELL WALL: It is an outer non-living, rigid layer of cell. It is present in bacterial cells,
fungal cells, and plant cells. It is a permeable membrane chiefly composed of cellulose. It
gives rigidity, mechanical support, and protection to the cell. Cell wall possesses small pores
through which adjacent cells remain connected called Plasmodesmata.
Functions of cell wall:
• It provides definite shape to the cell.
• It provides strength to the cell.
• It is permeable and allows entry of molecules of different sizes.
• It has the characteristics of repair and regeneration.
2. CELL MEMBRANE OR PLASMA MEMBRANE: It is a semi permeable
membrane present in all cells. It is present below the cell wall in plant cell and outermost
membrane in animal cell. It is composed of phospholipids, proteins, carbohydrates and
cholesterol.
• It is made up of proteins and lipids where proteins are sandwiched between bilayer of
lipids.
• It is the limiting boundary of each cell which separates the cytoplasm from its
surroundings.
• It is flexible and can be folded, broken and reunited.

Functions:
• It allows the outward and inward movement of molecules across it. The movement of
molecules across the plasma membrane takes place by phagocytosis (cell eating) and
pinocytosis (cell drinking).
• It helps in maintaining the distinct composition of the cell.
• Transportation of molecules across the plasma membrane: This can be done by
following ways:
(A) Diffusion: Movement of solutes or ions from higher concentration to lower
concentration is called as diffusion. It does not require energy therefore it is called as
passive transport.
(B) Osmosis: The movement of solvent or water from higher concentration (solvent)
to lower concentration (solvent) through a semipermeable membrane is called as
osmosis.
• Endosmosis: Movement of solvent into the cell is called as Endosmosis.
• Endosmosis: Movement of solvent outside the cell is called as Endosmosis.
3. NUCLEUS: Nucleus is the most important cell organelle which directs and controls all
its cellular activities. It is called as “Headquarter of the cell.” It was discovered by “Robert
Brown in 1831”.

• In eukaryotes a well-defined nucleus is present while in prokaryotes a well-defined

nucleus is absent.
• Prokaryotes contain a primitive nucleus. It has double layered covering called as
nuclear membrane.
• Nuclear membrane has pores which regulate the movement of materials of materials in
& out of the cell.
• Besides nuclear membrane nucleus also contains nucleolus and chromatin material and
the substance filled inside the nucleus is nucleolus.
• Chromosomes or chromatin material consists of DNA which stores and transmits
hereditary information for the cell to function, grow and reproduce.

Function of the nucleus:

(A) It controls all the metabolic activities of the cell and regulates the cell cycle.

(B) It helps in transmission of hereditary characters from parents to off springs

4. CYTOPLASM: It is the jellylike, semi fluid matrix present between the cell membrane
and nuclear membrane. Cytoplasm was discovered by Kolliker in 1862. It is the site of both
biosynthetic and catabolic pathways. It can be divided into two parts:
(i) Cytosol: Aqueous soluble part contains various fibrous proteins forming cytoskeleton.
(ii) Cell organelles: Living part of the cells having definite shape, structure and function
bounded By Plasma membrane.
5. ENDOPLASMIC RETICULUM (ER):
• It is the network of membranes present in the cytoplasm.
• It was discovered by Porter, Claude and Fullam.
• These are present in all cells except prokaryotes and mammalian erythrocytes.
• They are made up of three components:
(i) Cisternae: These are long, flattened, parallely arranged, unbranched tubules. These

from Successive layers of nucleus. These are found in cells which are active in

protein synthesis and are 40-50 μm in diameter.

(ii) Vesicles: These are around or spherical they are founded in synthetically active
cells.

Types: Endoplasmic reticulum is of two types

Smooth ER Rough ER

• Made of tubules mainly. • Made of cisternae and vesicles.

• Helps in steroid, lipids and • helps in protein synthesis.
Polysaccharide synthesis. • Contains ribosomes on its surface.
• Ribosomes are absent.
• Helps in membrane biogenesis.

Function of ER:
(i) It is the only organelle which can move within a cell so it serves as a channel for the
transport of materials between various regions of cytoplasm and between cytoplasm and
nucleus.
(ii) It also function as a cytoplasmic framework to provide space for some of the biochemical
activities. It forms endoskeleton of cell.
(iii) It helps in synthesis of fats, steroids, cholesterol etc.

(iv) It contains secretory proteins.

(v) SER plays a crucial role in detoxification of drugs and poisonous by-products.

6. GOLGI APPARATUS:
• Golgi apparatus consists of a system of membrane bounded vesicles arranged parallel
to each other in stacks called Cisternae along with some large and spherical vacuoles.
• It was discovered by Camilo Golgi.
• In plants Golgi membrane bounded.
• It is single membrane bounded.
• It is absent in prokaryotes, mammalian RBC’s & sieve cells.

Functions:

(i) It helps in formation of lipids

(ii) It helps in formation of middle lamellae
(iii) It is secretary in nature.
(iv) It helps in melanin synthesis
(v) Lipids and proteins synthesized in endoplasmic reticulum are packed at Golgi complex.
They provide the site for assembly of new membrane material.

7. MITOCHONDRIA:
• It is a rod-shaped structure found in cytoplasm of all eukaryotic cells except mammalian
RBC’s.
 • These are also absent in prokaryotes.
• It was first seen by Kolliker in insect cells.
• Maximum mitochondria are found in metabolically active cells.
• It is also called as “Power House of the Cell” or the “Storage Battery”.
• It is double membranous structure where outer membrane has specific proteins
• While inner membrane is folded inside to from chambers called Cristae. “Cristae” are
the infoldings of inner mitochondrial membrane that possess enzymes for respiratory
cycles. ATP synthesizing units are called Oxysomes or F1 particles.
• Space between inner and outer mitochondrial membranes is called as Peri mitochondrial
space. The fluid present in mitochondrial is called as matrix.

Functions:
a. Its main function is to produce and store the energy in the form of ATP.
b. It is the site of Kreb cycle of respiration.
c. Oxysome contains enzymes for ATP production.
d. Matrix contains enzymes for Kreb cycle.

8. RIBOSOMES:
Ribosomes are the sites of protein synthesis.
All structural and functional proteins (enzymes) coded by the nuclear DNA, are
synthesized upon cytoplasmic ribosomes. The DNA codes are transcripted into messenger
RNA (mRNA) molecules in the chromosomes of the nucleus. mRNA molecules diffuse out
into the cytoplasm and each becomes attached to several ribosomes which thus from a group
 called polyribosome or polyribosomes. In this way each mRNA molecule brings about
polymerization of specific protein molecules, with the help of ribosomes from amino acid
molecules found in the Cytosol.

9. PLASTID:
• It is double membranous discoidal structure, found only in plant cells.

• Term plastid was given by Haeckel.

• Chloroplast was discount by A.V. Leeuwenhoek and named by Schimper.

• Besides being discoidal of rhombic in plant cells they occur in variable shapes like in
algae they can be ‘U’ shaped, spiral, coiled, ribbon shaped etc.
Depending upon the type of pigment present in them they are of following three types.

Leucoplast Chromoplast Chloroplast

• No pigments, white in • Coloured pigments other • Green pigment

color than green chlorophyll is found in
• Generally found in • Phaeoplast – Brown them.
Underground parts • Found in aerial parts of
• Important for food plant.
storage. • Rhodoplast – Red which
• e.g. Aleuronoplast, are green in colour
Elaioplast
 Chloroplast have Following Two Parts:
(i). Grana: It constitutes the lamellar system. These are found layered on top of each other,
these stacks are called as Grana. Each granum of the chloroplast is formed by superimposed
closed compartments called Thylakoids.
• Function: They are the sites of light reaction of photosynthesis as they contain
photosynthetic pigment chlorophyll.
(ii) Stroma: It is a granular transparent substance also called as matrix. Grana are embedded
in it. Besides Grana they also contain lipid droplets, starch grains, ribosomes etc.
• Function: This is the site of dark reaction of photosynthesis. Also helps in protein
synthesis due to presence of ribosomes.

10. VACUOLES
• These are membrane bounded regions in the cytoplasm containing water and other
substances.
• They are bounded by a single membrane called Tonoplast.

• In animal cells vacuoles are smaller in size and numerous while in plant cells a single large
vacuole Is found which occupies about 90% of the volume of cell.
Functions:
• It helps in maintaining osmotic pressure in a cell.

• It stores toxic metabolic products of plant cell.

• It contains various Coloured pigments like anthocyanins.

11. LYSOSMES
• These are tiny sac like granules containing enzymes of intracellular digestion.

• They are bounded by a single membrane.

• They occur in animal cells and a few plant cells.

• They do not have a definite shape or size.

• They contain hydrolyzing enzymes called acid hydrolyses.

FUNCTION:
• They are kind of waste disposal system.

• They help in digesting foreign materials.

• During disturbances in cellular metabolism i.e. in case of cell damage lysosomes burst
and their enzymes are released into the cytoplasm and they digest their own cell so they
are also called as “Suicidal Bags”.

DIFFERENCES BETWEEN A PLANT CELL AND AN ANIMAL CELL

CHARACTERS Plant Cell Animal Cell
Cell wall present absent
Plastids present absent
Number of Vacuole One Numerous
Size of Vacuole large small
Centriole absent present
Position of nucleus Side Centre
Nutrition autotroph Heterotroph
Aster in division present Absent
Cytoplasm division By Cell plate By cleavage
DIFFERENCES BETWEEN PROKARYOTIC CELL AND
EUKARYOTIC CELL
Characters Prokaryotic Cells Eukaryotic Cells
1. Nuclear body Incipient nucleus, True nucleus,
No nuclear membrane Nucleolus membrane
Nucleolus absent present
No mitosis Nucleolus present
Single closed loop, Mitosis found
(histones absent) Multiple chromosomes,
(histones in chromosome)
2. Mitosis No mitosis Mitosis found

3.DNA arrangement Single closed loop, Multiple chromosomes,

(histones absent) (histones present in
chromosome)
4. Respirator system In plasma a membrane, In mitochondria
(mitochondria)
5. Photosynthetic apparatus In intemal membranes, In chloroplasts
(chloroplasts absent)
6. Golgi bodies chloroplast Absent Present
ER
Mitochondria, Lysosomes
7. Ribosomes 70 S type 80 S type

8. Cell wall Generally present, complex Present in some types,

chemical composition simple
Chemical composition
9. Flagella Submicroscopic, Microscopic size
no 9+2 fibrillar structure 9+2 Fibrillar structure
10. Cytoplasmic movements Cytoplasmic streaming rare Cytoplasmic streaming often
occurs
or absent
11. Vacuoles Absent Present
12. Lysosome Absent Present
13. Capsule May be present Always absent
14. Hereditary material DNA circular DNA (linear)
STEM CELLS AND THEIR APPLICATIONS
Stem cells are special human cells that can develop into many different types of cells,
from muscle cells to brain cells. Stem cells also have the ability to repair damaged cells. These
cells have strong healing power. They can evolve into any type of cell.
Types of cells
Stem cells are of the following different types:
• Embryonic Stem Cells: The fertilized egg begins to divide immediately. These cells form
a hollow structure within a few days. Cells in one region group together to form the inner
cell mass. This contains pluripotent cells that make up the developing foetus.
• Adult Stem Cells: These stem cells are obtained from developed organs and tissues. They
can repair and replace the damaged tissues in the region where they are located. These
stem cells are used in bone marrow transplants to treat specific types of cancers.
• Induced Stem Cells: These cells have been tested and arranged by converting tissue-
specific cells into embryonic cells in the lab. These cells are accepted as an important tool
to learn about the normal development, disease and are also helpful in testing various
drugs. These stem cells share the same characteristics as embryonic cells do.

• Mesenchymal stem cells: These cells are mainly formed from the connective tissues
surrounding other tissues and organs, known as the stroma. These mesenchymal stem cells
are accurately called stromal cells. There are different mesenchymal stem cells that are
used to treat various diseases as they have been developed from different tissues of the
human body.

Applications of Stem Cells:

• Tissue Regeneration: This is the most important application of stem cells. The stem cells
can be used to grow a specific type of tissue or organ. This can be helpful in kidney and
liver transplants.
• Treatment of Cardiovascular Disease: Within two weeks of implantation, the blood
vessels formed their network and were as efficient as the natural vessels.
• Treatment of Brain Diseases: Stem cells can also treat diseases such as Parkinson’s
disease and Alzheimer’s. These can help to replenish the damaged brain cells.
• Blood Disease Treatment: The adult hematopoietic stem cells are used to treat cancers,
sickle cell anaemia, and other immunodeficiency diseases. These stem cells can be used to
produce red blood cells and white blood cells in the body.
CARBOHYDRATES

• Carbohydrates are macronutrients and are one of the three main ways by which our body
obtains its energy.
• They are called carbohydrates as they comprise carbon, hydrogen, and oxygen at their
chemical level.
• Carbohydrates are essential nutrients which include sugars, fibers, and starches. They are
found in grains, vegetables, fruits and in milk and other dairy products. They are the basic
food groups which play an important role in a healthy life.
• The food containing carbohydrates are converted into glucose or blood sugar during the
process of digestion by the digestive system.
• The extra amount of energy or sugar is stored in our muscles and liver for further
requirement.
• The general formula of this class of organic compounds is Cn (H2O) n.

Classification of Carbohydrates (Types of Carbohydrates)

1. Simple Carbohydrates: Simple carbohydrates have one or two sugar molecules. In
simple carbohydrates, molecules are digested and converted quickly resulting in a rise in
the blood sugar levels. These carbohydrates are called empty calories, as they do not
possess fibres, vitamins and minerals.

a) Monosaccharides: Monosaccharides are the simplest carbohydrates. Made up of

single sugar molecule. Examples of monosaccharide: Erythrose, Ribose, Glucose,
Fructose.
b) Disaccharides: Two monosaccharides combine to form a disaccharide. Examples of
carbohydrates having two monomers include- Sucrose, Lactose, Maltose, etc.
c) Oligosaccharides: Carbohydrates formed by the condensation of 2-9 monomers are
called oligosaccharides. Example: Raffinose: a trisaccharide of galactose, glucose,
and fructose.
2. Complex Carbohydrates (Polysaccharides)
Complex carbohydrates have two or more sugar molecules; hence they are referred to
as starchy foods. In complex carbohydrates, molecules are digested and converted slowly
compared to simple carbohydrates. They are abundantly found in lentils, beans, peanuts,
potatoes, peas, corn, whole-grain bread, cereals, etc.
Polysaccharides are complex carbohydrates formed by the polymerization of many monomers.
Examples of polysaccharides include starch, glycogen, cellulose, etc.

Functions
• The main function of carbohydrates is to provide energy and food to the body and to
the nervous system.
• Carbohydrates are known as one of the basic components of food, including sugars,
starch, and fibre which are abundantly found in grains, fruits and milk products.
• Carbohydrates are also known as starch, simple sugars, complex carbohydrates and so
on.
• It is also involved in fat metabolism and prevents ketosis.
• Inhibits the breakdown of proteins for energy as they are the primary source of energy.
• An enzyme by name amylase assists in the breakdown of starch into glucose, finally to
produce energy for metabolism.

NUCLEIC ACIDS
• Nucleic acids are long-chain polymeric molecules. The monomer or the repeating unit is
known as the nucleotides and hence sometimes nucleic acids are referred to as
polynucleotides.
• Nucleic acids can be defined as organic molecules present in living cells. It plays a key
factor in transferring genetic information from one generation to the next.
• In the nucleus, nucleotide monomers are linked together comprising of distinct
components namely a Phosphate Group, Nitrogenous Bases or Ribose and Deoxyribose.

• Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are two major types of nucleic
acids.
• DNA and RNA are responsible for the inheritance and transmission of specific
characteristics from one generation to the other.

DIFFERENCE BETWEEN DNA AND RNA

DNA RNA

• it is a double stranded. • it is a single stranded.

• The sugar moiety present in DNA • RNA has ribose in it as the sugar
molecules is deoxyribose. moiety.
 • The cyclic bases that have nitrogen in • The heterocyclic bases present in
them are adenine (A), guanine (G), RNA are adenine (A), guanine (G),
cytosine(C) and thymine (T). cytosine(C) and uracil (U).

• Present inside the nucleus. • Present inside the cytoplasm

• Transfer genetic information from • Helps in protein synthesis.

parent to daughter cells.

Functions of Nucleic Acids

• Nucleic Acid is responsible for the synthesis of protein in our body

• RNA is a vital component of protein synthesis.

• Loss of DNA content is linked to many diseases.

• DNA is an essential component required for transferring genes from parents to offspring.

• All the information of a cell is stored in DNA.

• DNA fingerprinting is a method used by forensic experts to determine paternity. It is also

used for the identification of criminals. It has also played a major role in studies regarding
biological evolution and genetics.

PROTEINS
Proteins are composed of amino acids, arranged into different groups. These
fundamental amino acids sequences are specific and its arrangements are controlled by the
DNA. Since our body cannot synthesize these essential amino acids by its own, we should have
plenty of protein foods in our everyday diet to keep our body metabolisms stable.

Protein Structure:

a) Primary Structure: It is a specific sequence of amino acids. The order of amino acids
bonded together is detected by information stored in genes.
b) Secondary Structure: It is a three-dimensional form of a local segment of proteins.
They are formed by hydrogen bonds between the atoms along the backbone of the
polypeptide chain. Forms into alpha and beta sheets.
c) Tertiary Structure: It is a three-dimensional shape of a protein. Many numbers of
tertiary structure fold to form Quaternary Structure.
 d) Quaternary Structure: It is the arrangement of multiple folded protein subunits in a
multi-subunit complex.

Protein Synthesis
Protein synthesis takes place through a process called translation. This process occurs
in the cytoplasm. It involves the rendering of genetic codes. Ribosomes of a cell help in
translating genetic codes into a polypeptide chain. These polypeptide chains become
functioning proteins only after undergoing certain modifications.

Classification of Proteins:

Depending upon their chemical compositions, proteins may be categorized into the
following types:

a) Simple proteins: Sometimes also called homoproteins, these proteins consist of only amino
acids e.g. albumin, collagen, keratin, globulin etc.
b) Conjugated proteins: Are also known as heteroproteins; upon hydrolysis, they yield amino
acids and non-protein components called prosthetic groups. Prosthetic groups could be
metal ions, phosphate groups, pigments, lipids, nucleic acids and flavins e.g. Metalloprotein,
lipoprotein etc.
c) Derived proteins These are proteins derived from simple or conjugated proteins by the action
of heat, enzyme, or chemical reagents e.g, peptone, peptides

Functions of Proteins
1. Enzymes: Enzymes mostly carry out all numerous chemical reactions which take place
within a cell. They also help in regenerating and creating DNA molecules and carry out
complex processes.
2. Hormones: Proteins are involved in the creation of various types of hormones which help
in balancing the components of the body. For example hormones like insulin, which helps
 in regulating blood sugar and secretin. It is also involved in the digestion process and
formation of digestive juices.
3. Antibody: Antibody also known as an immunoglobulin. It is a type of protein which is
majorly used by the immune system to repair and heal the body from foreign bacteria. They
often work together with other immune cells to identify and separate the antigens from
increasing until the white blood cells destroy them completely.
4. Energy: Proteins are the major source of energy that helps in the movements of our body.
It is important to have the right amount of protein in order to convert it into energy. Protein,
when consumed in excess amounts, gets used to create fat and becomes part of the fat cells.

LIPIDS
“Lipids are organic compounds that contain hydrogen, carbon, and oxygen atoms,
which form the framework for the structure and function of living cells.” These organic
compounds are nonpolar molecules, which are soluble only in nonpolar solvents and insoluble
in water because water is a polar molecule. In the human body, these molecules can
be synthesized in the liver and are found in oil, butter, whole milk, cheese, fried foods and also
in some red meats.

Properties of Lipids
Lipids are a family of organic compounds, composed of fats and oils.

1. Lipids are oily or greasy nonpolar molecules, stored in the adipose tissue of the body.

2. Lipids are a heterogeneous group of compounds, mainly composed of hydrocarbon

chains.

3. Lipids are energy-rich organic molecules, which provide energy for different life
processes.

4. Lipids are a class of compounds characterised by their solubility in nonpolar solvents

and insolubility in water.

5. Lipids are significant in biological systems as they form a mechanical barrier dividing
a cell from the external environment known as the cell membrane.
Types of Lipids

(a) Simple Lipids: Esters of fatty acids with various alcohols.

1. Fats: Esters of fatty acids with glycerol. Oils are fats in the liquid state

2. Waxes: Esters of fatty acids with higher molecular weight monohydric alcohols

(b) Complex Lipids: Esters of fatty acids containing groups in addition to alcohol and fatty
acid.
1. Phospholipids: These are lipids containing, in addition to fatty acids and alcohol,
phosphate group.

2. Glycolipids (glycosphingolipids): Lipids containing a fatty acid, sphingosine and

carbohydrate.

(c) Derived Lipids: These include fatty acids, glycerol, steroids, other alcohols, fatty
aldehydes, and ketone bodies, hydrocarbons, lipid-soluble vitamins, and hormones.
Because they are uncharged, acylglycerols (glycerides), cholesterol, and cholesteryl esters
are termed neutral lipids. These compounds are produced by the hydrolysis of simple and
complex lipids.

Fatty Acids

Fatty acids are carboxylic acids (or organic acid), usually with long aliphatic tails (long
chains), either unsaturated or saturated.

• Saturated fatty acids: Lack of carbon-carbon double bonds indicate that the fatty acid
is saturated. The saturated fatty acids have higher melting points compared to
unsaturated acids of the corresponding size due to their ability to pack their molecules
together thus leading to a straight rod-like shape.

• Unsaturated fatty acids: Unsaturated fatty acid is indicated when a fatty acid has more
than one double bond. On the other hand, unsaturated fatty acids contain a cis-double
bond(s) which create a structural kink that disables them to group their molecules in
straight rod-like shape.

Role of Fats
• Fats in the correct amounts are necessary for the proper functioning of our body.
 • Many fat-soluble vitamins need to be associated with fats in order to be effectively
absorbed by the body.

• They also provide insulation to the body.

• They are an efficient way to store energy for longer periods.

ENZYMES

The human body is composed of different types of cells, tissues, and other complex
organs. For efficient functioning, our body releases some chemicals to accelerate biological
processes such as respiration, digestion, excretion to sustain a healthy life. Hence, enzymes are
pivotal in all living entities which govern all the biological processes. “Enzymes can be
defined as biological polymers that catalyze biochemical reactions.”

The initial stage of metabolic process depends upon the enzymes, which react with a
molecule and is called the substrate. Enzymes convert the substrates into other distinct
molecules, which are known as products.

Enzymes Classification

Types Biochemical Property

Oxidoreductases The enzyme Oxidoreductase catalyzes the oxidation reaction where the electrons
tend to travel from one form of a molecule to the other. e.g. pyruvate
dehydrogenase
 Transferases These catalyze transferring of the chemical group from one to another compound.
An example is a transaminase, which transfers an amino group from one molecule
to another.

Hydrolases Hydrolases are hydrolytic enzymes, which catalyze the hydrolysis reaction by
adding water to cleave the bond and hydrolyze it. For example, the enzyme pepsin
hydrolyzes peptide bonds in proteins.

Lyases With addition of water, they catalyze the breakage of bonds without catalysis, e.g.
aldolase

Isomerases The Isomerases enzymes catalyze the structural shifts present in a molecule, thus
causing the change in the shape of the molecule. Example: phosphoglucomutase

Ligases Ligases catalyze the association of two molecules. For example, DNA ligase

Mechanism of action:
LOCK AND KEY MODEL: Enzymes are very specific and it was suggested by Fischer in
1890 that this was because the enzyme had a particular shape into which the substrate or
substrates fit exactly. This is often referred as Lock and Key hypothesis.

INDUCED FIT MODEL: In 1959, Koshland suggested a modification to the ‘Lock and Key’
hypothesis which is known as ‘Induced fit’ hypothesis. Working from evidence that suggested
that some enzymes and their active site are more flexible. To this, he proposed that the active
site can modify its shape as the substrate interact with the enzyme.
Functions of Enzymes
1. Enzymes help in signal transduction. The most common enzyme used in the process
includes protein kinase that catalyzes the phosphorylation of proteins.

2. They break down large molecules into smaller substances that can be easily absorbed
by the body.

3. They help in generating energy in the body. ATP synthase is the enzyme involved in
the synthesis of energy.

4. Enzymes are responsible for the movement of ions across the plasma membrane.

5. Enzymes perform a number of biochemical reactions, including oxidation, reduction,

hydrolysis, etc. to eliminate the non-nutritive substances from the body.

6. They function to reorganize the internal structure of the cell to regulate cellular
activities.

VITAMINS
Vitamins are organic molecules that are essential to an organism in small quantities for
proper metabolic function, for protection, for maintenance of health and proper growth.
Essential nutrients cannot be synthesized in the organism in sufficient quantities for survival,
and therefore must be obtained through the diet.
Vitamins are of widespread occurrence in nature, both plant and animal. All common food
stuff contains more than one vitamin. Vitamins are effective when taken orally.

Classification of Vitamins
Vitamins are generally classified as water-soluble vitamins and fat-soluble vitamins.
1. Fat-Soluble Vitamins: Vitamin A, D, E and K are fat-soluble. These are stored in adipose
tissues and hence are called fat-soluble vitamins.

2. Water-Soluble Vitamins: Vitamins in B-group and vitamin C are water-soluble and cannot
be stored in our bodies as they pass with the water in urine. These vitamins must be supplied
to our bodies with regular diets.

Functions of Vitamins
1. Vitamin A – Hardening of the cornea in the eye, night blindness.

2. Vitamin B1 – Deficiency may cause beriberi and dwarfism.

3. Vitamin B2 – Deficiency can cause disorders in the digestive system, skin burning
sensations, and cheilosis.

4. Vitamin B6 – Deficiency of B6 causes convulsions, conjunctivitis, and sometimes

neurological disorders.

5. Vitamin B12 – Its deficiency can cause pernicious anaemia and a decrease in red blood
cells in haemoglobin.

6. Vitamin C – It is a water-soluble vitamin; its deficiency causes bleeding in gums and

scurvy.

7. Vitamin D – It is obtained by our body when exposed to sunlight. Its deficiency causes
improper growth of bones, soft bones in kids, and rickets.

8. Vitamin E – Deficiency of vitamin E leads to weakness in muscles and increases the

fragility of red blood cells.

9. Vitamin K – It plays an important role in blood clotting. The deficiency of vitamin K

increases the time taken by the blood to clot. Severe deficiency may cause death due to
excessive blood loss in case of a cut or an injury.

HORMONES
“Hormones are chemicals synthesized and produced by the specialized glands to
control and regulate the activity of certain cells and organs. These specialized glands are
known as endocrine glands.” These endocrine glands are distributed throughout the body.
These messengers control many physiological functions as well as psychological health. They
are also quite important in maintaining homeostasis in the body.
Types of Hormones:
To regulate various functions, different types of hormones are produced in the body. They are
classified as follows:
• Peptide Hormones

• Steroid Hormones

Peptide Hormones: Peptide hormones are composed of amino acids and are soluble in water.
Peptide hormones are unable to pass through the cell membrane as it contains a phospholipid
bilayer that stops any fat-insoluble molecules from diffusing into the cell. Insulin is an
important peptide hormone produced by the pancreas.

Steroid Hormones: Unlike peptide hormones, steroid hormones are fat-soluble and are able
to pass through a cell membrane. Sex hormones such as testosterone, estrogen and progesterone
are examples of steroid hormones.

Functions of Hormones
• Food metabolism.

• Growth and development.

• Controlling thirst and hunger.

• Maintaining body temperature.

• Regulating mood and cognitive functions.

• Initiating and maintaining sexual development and reproduction.

IMPORTANT QUESTIONS:
1. What is the difference between diffusion and osmosis?
2. Draw a neat and labeled diagram of nucleus. State its main function.

3. Describe the types of endoplasmic reticulum and draw necessary figure. Give it’s main
functions also.
4. Draw a neat and labeled diagram of mitochondria.
5. Differentiate between plant and animal cell with suitable figures.
6. Differentiate between prokaryotic and eukaryotic cell with suitable figures.
7. Write a note on stem cell and its application.
8. Explain about carbohydrates and its types.
9. Write a note on protein and its structure.
10. Differentiate between DNA and RNA.
11. Explain about vitamins.
12. What are hormones? Explain their function.
13. Explain in detail about classification of proteins.