Animal tissues

Animal tissues
Grouped in to four basic types: connective, muscle, nervous, and epithelial. Multiple tissue types
compose organs and body structures. While all animals can generally be considered to contain the
four tissue types, the manifestation of these tissues can differ depending on the type of organism. For
example, the origin of the cells comprising a particular tissue type may differ developmentally for
different classifications of animals.
The epithelium in all birds and animals is derived from the ectoderm and endoderm with a small
contribution from the mesoderm, forming the endothelium, a specialized type of epithelium that
composes the vasculature. By contrast, a true epithelial tissue is present only in a single layer of cells
held together via occluding junctions called tight junctions, to create a selectively permeable barrier.
This tissue covers all organismal surfaces that come in contact with the external environment such as
the skin, the airways, and the digestive tract. It serves functions of protection, secretion, and
absorption, and is separated from other tissues below by a basal lamina.
Connective tissue
Connective tissues are fibrous tissues. They are made up of cells separated by non-living material,
which is called an extracellular matrix. Connective tissue gives shape to organs and holds them in
place. Both blood and bone are examples of connective tissue.
Muscle tissue
Muscle cells form the active contractile (see contractility) tissue of the body known as muscle tissue
or muscular tissue. Muscle tissue functions are to produce force and cause motion, either locomotion
or movement within internal organs. Muscle tissue is separated into three distinct categories: visceral
or smooth muscle, which is found in the inner linings of organ (anatomy); skeletal muscle, which is
found attached to bone providing for gross movement; and cardiac muscle which is found in the
heart, allowing it to contract and pump blood throughout an organism. They are the longest group of
cells in the human body.
Nervous tissue
Cells comprising the central nervous system and peripheral nervous system are classified as neural
tissue. In the central nervous system, neural tissue forms the brain and spinal cord and, in the
peripheral nervous system forms the cranial nerves and spinal nerves, inclusive of the motor neurons.
Epithelial tissue
The epithelial tissues are formed by cells that cover the organ surfaces such as the surface of the skin,
the airways, the reproductive tract, and the inner lining of the digestive tract. The cells comprising an
epithelial layer are linked via semi-permeable, tight junctions; hence, this tissue provides a barrier
between the external environment and the organ it covers. In addition to this protective function,
epithelial tissue may also be specialized to function in secretion and absorption. Epithelial tissue
helps to protect organs from microorganisms, injury, and fluid loss. Functions:
 the cells of the body surface form the outer layer of skin.
 inside the body, epithelial cells form the lining of the mouth & alimentary canal & protect
these organs.
 epithelial tissues help in absorption of water & nutrients.

 epithelial tissues help in elimination of waste.
The different types of epithelial tissues are as follows:
 Simple squamous epithelium,
 Cuboidal epithelium,
 Columnar epithelium,
 Glandular epithelium,
 Ciliated columnar epithelium,
 Stratified squamous epithelium.
Plant tissues
Cross-section of a flax plant stem with several layers of different tissue types:
1. Pith,
2. Protoxylem,
3. Xylem I,
4. Phloem I,
5. Sclerenchyma (bast fibre),
6. Cortex,
7. Epidermis
Plant tissues are categorized broadly into three tissue systems: the epidermis, the ground tissue, and
the vascular tissue.
 Epidermis - Cells forming the outer surface of the leaves and of the young plant body.
 Vascular tissue - The primary components of vascular tissue are the xylem and phloem.
These transport fluid and nutrients internally.
 Ground tissue - Ground tissue is less differentiated than other tissues. Ground tissue
manufactures nutrients by photosynthesis and stores reserve nutrients.
Plant tissues can also be divided differently into two types:
1. Meristematic tissues
2. Permanent tissues.
Meristematic tissues
Meristematic tissue consists of actively dividing cells, and leads to increase in length and thickness of
the plant. The primary growth of a plant occurs only in certain, specific regions, such as in the tips of
stems or roots. It is in these regions that meristematic tissue is present. Cells in these tissues are
roughly spherical or polyhedral, to rectangular in shape, and have thin cell walls. New cells produced
by meristem are initially those of meristem itself, but as the new cells grow and mature, their
characteristics slowly change and they become differentiated as components of the region of
occurrence of meristimatic tissues, they are classified as:
a) Apical Meristem - It is present at the growing tips of stems and roots and increases the
length of the stem and root. They form growing parts at the apices of roots and stems and are
responsible for increase in length, also called primary growth. This meristem is responsible
for the linear growth of an organ.

b) Lateral Meristem - This meristem consist of cells which mainly divide in one plane and
cause the organ to increase in diameter and growth. Lateral Meristem usually occurs beneath
the bark of the tree in the form of Cork Cambium and in vascular bundles of dicots in the form
of vascular cambium. The activity of this cambium results in the formation of secondary
growth.
c) Intercalary Meristem - This meristem is located in between permanent tissues. It is
usually present at the base of node, inter node and on leaf base. They are responsible for
growth in length of the plant and increasing the size of the internode, They result in branch
formation and growth.
The cells of meristematic tissues are similar in structure and have thin and elastic primary cell wall
made up of cellulose. They are compactly arranged without inter-cellular spaces between them. Each
cell contains a dense cytoplasm and a prominent nucleus. Dense protoplasm of meristematic cells
contains very few vacuoles. Normally the meristematic cells are oval, polygonal or rectangular in
shape.
Meristemetic tissue cells have a large nucleus with small or no vacuoles, they have no inter cellular
spaces.
Permanent tissues
The meristematic tissues that take up a specific role lose the ability to divide. This process of taking
up a permanent shape, size and a function is called cellular differentiation. Cells of meristematic
tissue differentiate to form different types of permanent tissue. There are 3 types of permanent
tissues:
1. simple permanent tissues
2. complex permanent tissues
3. special or secretory tissues (glandular).
Simple tissues
A group of cells which are similar in origin; similar in structure and similar in function are called
simple permanent tissue. They are of four types:
1. Parenchyma
2. Collenchyma
3. Sclerenchyma
4. Epidermis
Parenchyma
Parenchyma (para - 'beside'; chyma - 'in filling, loose, unpacked') is the bulk of a substance. In plants,
it consists of relatively unspecialised living cells with thin cell walls that are usually loosely packed
so that large spaces between cells (intercellular spaces) are found in this tissue. This tissue provides
support to plants and also stores food. In some situations, a parenchyma contains chlorophyll and
performs photosynthesis, in which case it is called a chlorenchyma. In aquatic plants, large air
cavities are present in parenchyma to give support to them to float on water. Such a parenchyma type
is called aerenchyma.
Collenchyma

Collenchyma is Greek word where "Collen" means gum and "enchyma" means infusion. It is a living
tissue of primary body like Parenchyma. Cells are thin-walled but possess thickening of cellulose,
water and pectin substances (pectocellulose) at the corners where number of cells join together. This
tissue gives a tensile strength to the plant and the cells are compactly arranged and have very little
inter-cellular spaces. It occurs chiefly in hypodermis of stems and leaves. It is absent in monocots and
in roots.
Collenchymatous tissue acts as a supporting tissue in stems of young plants. It provides mechanical
support, elasticity, and tensile strength to the plant body. It helps in manufacturing sugar and storing
it as starch. It is present in the margin of leaves and resist tearing effect of the wind.
Sclerenchyma
Sclerenchyma is Greek word where "Sclrenes" means hard and "enchyma" means infusion. This
tissue consists of thick-walled, dead cells. These cells have hard and extremely thick secondary walls
due to uniform distribution of lignin. Lignin deposition is so thick that the cell walls become strong,
rigid and impermeable to water. Sclerenchymatous cells are closely packed without inter-cellular
spaces between them. Thus, they appear as hexagonal net in transverse section. The cells are
cemented with the help of lamella. The middle lamella is a wall that lies between adjacent cells.
Sclerenchymatous cells mainly occur in hypodermis, pericycle, secondary xylem and phloem. They
also occur in endocarp of almond and coconut. It is made of pectin, lignin, protein. The cells of
sclerenchymatous cells can be classified as :
1. Fibres- Fibres are long, elongated sclerenchymatous cells with pointed ends.
2. Sclereids- Sclerenchymatous cells which are short and possess extremely thick, lamellated,
lignified walls with long singular piths. They are called sclereids.
Complex permanent tissue
The complex tissue consists of more than one type of cells which work together as a unit. Complex
tissues help in the transportation of organic material, water and minerals up and down the plants. That
is why it is also known as conducting and vascular tissue. The common types of complex permanent
tissue are:
 Xylem or wood
 Phloem or bast.
Xylem and phloem together form vascular bundles.
Xylem
Xylem consists of:
 Tracheid
 Vessel Members
 Xylem fibers
 Xylem parenchyma.
Xylem is a chief, conducting tissue of vascular plants. It is responsible for conduction of water and
mineral ions/salt.

Xylem is a very important plant tissue as it is part of the ‘plumbing system' of a plant. Think of
bundles of pipes running along the main axis of stems and roots. It carries water and dissolved
substances throughout and consists of a combination of parenchyma cells, fibers, vessels, tracheids
and ray cells. Long tubes made up of individual cells are the vessels Tracheae, while vessel members
are open at each end. Internally, there may be bars of wall material extending across the open space.
These cells are joined end to end to form long tubes. Vessel members and tracheids are dead at
maturity. Tracheids have thick secondary cell walls and are tapered at the ends. They do not have end
openings such as the vessels. The tracheids ends overlap with each other, with pairs of pits present.
The pit pairs allow water to pass from cell to cell. While most conduction in the xylem is up and
down, there are some side-to-side or lateral conduction via rays. Rays are horizontal rows of long-
living parenchyma cells that arise out of the vascular cambium. In trees, and other woody plants, ray
will radiate out from the center of stems and roots and in cross-section will look like the spokes of a
wheel.
Phloem
Phloem consists of:
 Sieve tube
 Sieve cell
 Companion cell
 Phloem fiber
 Phloem parenchyma.
Phloem is an equally important plant tissue as it also is part of the ‘plumbing system’ of a plant.
Primarily, phloem carries dissolved food substances throughout the plant. This conduction system is
composed of sieve-tube member and companion cells, that are without secondary walls. The parent
cells of the vascular cambium produce both xylem and phloem. This usually also includes fibers,
parenchyma and ray cells. Sieve tubes are formed from sieve-tube members laid end to end. The end
walls, unlike vessel members in xylem, do not have openings. The end walls, however, are full of
small pores where cytoplasm extends from cell to cell. These porous connections are called sieve
plates. In spite of the fact that their cytoplasm is actively involved in the conduction of food
materials, sieve-tube members do not have nuclei at maturity. It is the companion cells that are
nestled between sieve-tube members that function in some manner bringing about the conduction of
food. Sieve-tube members that are alive contain a polymer called callose, a carbohydrate polymer,
forming the callus pad/callus, the colourless substance that covers the sieve plate. Callose stays in
solution as long at the cell contents are under pressure. As a repair mechanism, if an insect injures a
cell and the pressure drops, the callose will precipitate. However, the callose and a phloem protein
will be moved through the nearest sieve plate where they will form a plug. This prevents further
leakage of sieve tube contents and the injury is not necessarily fatal to overall plant turgor pressure.
Phloem transports food and materials in plants upwards and downwards as required.
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Some of the main physiographic divisions of India are as follows:
On the basis of the tectonic history, stratigraphy and relief features, India may be divided into the
following four physiographic divisions
The Northern Mountains:
It stretches across northern India from Jammu and Kashmir to Arunachal Pradesh (about 2500 km)
with a varying width of 240 to 320 km forming Himalaya in the East-West direction and its offshoots
run in North-South direction along the India-Myanmar boundary traversing through Nagaland,
Manipur and Mizoram known as eastern hills. They represent the youngest and highest folded
mountains of the earth formed by the tectonic collision of the Indian plateau with the Eurasian
plateau.
Longitudinally the Himalaya consist of four parallel range from South to North
i. The outer Himalayas (Shiwalik) It is almost continuous range of low hills, composed of
unconsolidated tertiary sediments emerged as most recent phase in Himalaya orogeny.
ii. The lesser Himalayas (The Himachal) It generally consists of unfossiferous sediments or
metamorphosed crystalline. Important range include the Dhauladhar, Pirpanjal, Nag Tiba,
Mahabharat and Mussoorie range.
iii. The Greater Himalaya (The Himadri) This is the most continuous loftiest and northern most range
of Himalayas. It has a core of Archaean granites, gneisses and schist’s rocks. This range contains one
of the highest mountain peaks of the world.
iv. The Trans Himalaya It is also called the Tibetan Himalaya. This range consisting of mainly
Karakoram, Ladakh and Kailash range.
Purvanchal:
This is the North-Eastern Himalayas that run north to South through Arunachal Pradesh, Nagaland,
Manipur, Mizoram, Tripura and eastern Assam.
The Great Plains:
The Great Plains of India consists largely of alluvial deposits brought down by the rivers originating
in the Himalayan and the peninsular region. They are mainly formed by the alluvial deposits of the
Indus, Ganga, Brahmaputra and their tributaries.
Northern plains is divided into four main divisions
i. The Bhabar:
The Bhabar belt is adjacent to the foothills of the Himalayas and consists of boulders and pebbles
which have been carried down by streams. As the porosity of this belt is very high, the streams flow
underground.
ii. The Tarai:

The Tarai belt lies south of the adjacent Bhabar region and is composed of newer alluvium. The
underground streams reappear in this region.
iii. The Bhangar:
The Bhangar belt consists of older alluvium and forms the alluvial terrace of the flood plains.
iv. The Khadar:
It is made up of fresh newer alluvium which is deposited by the rivers flowing down the plain.
The Peninsular Plateau:
It covering an area of about 16 lakh sq km forms the largest and oldest physiographic division of
India. It is bounded by the Aravallis in the North-West, Maikal range in the North, Hazaribagh and
Rajmahal Hills in the North-East, the Western Ghats in the West and the Eastern Ghats in the East.
The peninsular plateau is divided into
i. Central High lands which include Aravalli Range, Malwa Plateau, Vidhya Range, Bundelkhand
Plateau, Baghelkhand Plateau.
ii. Eastern Plateau-Chhota Nagpur plateau and Meghalaya Plateau
iii. The Deccan Plateau which include Mahadev Hills, Kaimur Hills, Maikal Range, Western Ghats,
Nilgiri, Anaimalai Hills, Palani Hills and Cardamom Hills, Eastern Ghats (Shevaroy Hills, Javadi
Hills, Palkonda Range Nallamala Hills) Mahendragiri. Maharashtra Plateau, Mahanadi Basin, Garhjat
Hills, Karnataka Plateau, Telangana Plateau and Tamil Nadu Upland.
The Coastal Plains the West Coast Plain:
This is a narrow coastal strip in the West facing Arabian Sea. The plain area between the Western
Ghats and the Arabian Sea from the gulf of Kuchchh and Gulf of Khambat located on either side of
Kathiawar Peninsula is called Gujarat Plains.
To the South the coastline is more rugged. It is called the Konkan Coast up to Goa and from there
onwards in Karnataka, it is the Kanara Coast, further South the part that lies in Kerala is called
Malabar Coast till Kanyakumari, the southern tip of the Indian mainland.
The East coastal plain is broader and more continuous than the West coastal plain and lies between
the Eastern Ghats and the Bay of Bengal. A major part of the eastern Coastal Plains is covered by the
deltaic deposits of rivers Mahanadi, Godavari, Krishna and Cauvery. It is called northern Circars
between Mahanadi and Krishna rivers and Coromandel Coast South of the Cauveri up to the
southernmost tip of the Indian mainland.
The Islands:
There are a number of small and large islands some of which are of volcanic origin while some are of
coral origin.
i. Lakshadweep islands in the Arabian Sea are a group of 36 coral islands. They are located off the
coast of Kerala. These islands are mostly flat and hardly a few metres above sea level.

ii. Andaman and Nicobar Islands lie in the Bay of Bengal. They are a group of 324 islands which are
volcanic in nature. Andaman Islands are separated from the Nicobar Islands by the ten degree
channel. They are mostly rugged mountainous hills and considered submerged part of Arakanyoma
fold belt.
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0 (zero; BrE: /ˈzɪərəʊ/ or AmE: /ˈziːroʊ/) is both a number[1] and the numerical digit used to
represent that number in numerals. It fulfills a central role in mathematics as the additive identity of
the integers, real numbers, and many other algebraic structures. As a digit, 0 is used as a placeholder
in place value systems. Names for the number 0 in English include zero, nought or (US) naught
(/ˈnɔːt/), nil, or — in contexts where at least one adjacent digit distinguishes it from the letter "O" —
oh or o (/ˈoʊ/). Informal or slang terms for zero include zilch and zip.[2] Ought and aught (/ˈɔːt/), as
well as cipher, have also been used historically.[3]
History
Egypt
Ancient Egyptian numerals were base 10. They used hieroglyphs for the digits and were not
positional. By 1740 BC, the Egyptians had a symbol for zero in accounting texts. The symbol nfr,
meaning beautiful, was also used to indicate the base level in drawings of tombs and pyramids and
distances were measured relative to the base line as being above or below this line.[10]
Mesopotamia
By the middle of the 2nd millennium BC, the Babylonian mathematics had a sophisticated
sexagesimal positional numeral system. The lack of a positional value (or zero) was indicated by a
space between sexagesimal numerals. By 300 BC, a punctuation symbol (two slanted wedges) was
co-opted as a placeholder in the same Babylonian system. In a tablet unearthed at Kish (dating from
about 700 BC), the scribe Bêl-bân-aplu wrote his zeros with three hooks, rather than two slanted
wedges.[11]
The Babylonian placeholder was not a true zero because it was not used alone. Nor was it used at the
end of a number. Thus numbers like 2 and 120 (2×60), 3 and 180 (3×60), 4 and 240 (4×60), looked
the same because the larger numbers lacked a final sexagesimal placeholder. Only context could
differentiate them.
India
The concept of zero as a number and not merely a symbol or an empty space for separation is
attributed to India, where, by the 9th century AD, practical calculations were carried out using zero,
which was treated like any other number, even in case of division.[12][13]
The Indian scholar Pingala, of 2nd century BC or earlier, used binary numbers in the form of short
and long syllables (the latter equal in length to two short syllables), a notation similar to Morse
code.[14] In his Chandah-sutras (prosody sutras), dated to 3rd or 2nd century BC, Pingala used the
Sanskrit word śūnya explicitly to refer to zero. This is so far the oldest known use of śūnya to mean
zero in India.[15] The fourth Pingala sutra offers a way to accurately calculate large metric
exponentiation, of the type (2)n, efficiently with less number of steps.[15]

The earliest text to use a decimal place-value system, including a zero, is the Jain text from India
entitled the Lokavibhāga, dated 458 AD, where śūnya ("void" or "empty") was employed for this
purpose.[16] The first known use of special glyphs for the decimal digits that includes the indubitable
appearance of a symbol for the digit zero, a small circle, appears on a stone inscription found at the
Chaturbhuja Temple at Gwalior in India, dated 876 AD.[17][18] There are many documents on copper
plates, with the same small o in them, dated back as far as the sixth century AD, but their authenticity
may be doubted.[11]
In 498 AD, Indian mathematician and astronomer Aryabhata stated that "sthānāt sthānaṁ daśaguṇaṁ
syāt;"[19] i.e., "from place to place each is ten times the preceding,"[19][20] which is the origin of the
modern decimal-based place value notation.[21][22]
Rules of Brahmagupta
The rules governing the use of zero appeared for the first time in Brahmagupta's book Brahmasputha
Siddhanta (The Opening of the Universe),[23] written in 628 AD. Here Brahmagupta considers not
only zero, but negative numbers, and the algebraic rules for the elementary operations of arithmetic
with such numbers. In some instances, his rules differ from the modern standard. Here are the rules of
Brahmagupta:[23]
 The sum of zero and a negative number is negative.
 The sum of zero and a positive number is positive.
 The sum of zero and zero is zero.
 The sum of a positive and a negative is their difference; or, if their absolute values are equal,
zero.
 A positive or negative number when divided by zero is a fraction with the zero as
denominator.
 Zero divided by a negative or positive number is either zero or is expressed as a fraction with
zero as numerator and the finite quantity as denominator.
 Zero divided by zero is zero.
In saying zero divided by zero is zero, Brahmagupta differs from the modern position.
Mathematicians normally do not assign a value to this, whereas computers and calculators sometimes
assign NaN, which means "not a number." Moreover, non-zero positive or negative numbers when
divided by zero are either assigned no value, or a value of unsigned infinity, positive infinity, or
negative infinity.
Elementary algebra
The number 0 is the smallest non-negative integer. The natural number following 0 is 1 and no
natural number precedes 0. The number 0 may or may not be considered a natural number, but it is a
whole number and hence a rational number and a real number (as well as an algebraic number and a
complex number).
The number 0 is neither positive nor negative and appears in the middle of a number line. It is neither
a prime number nor a composite number. It cannot be prime because it has an infinite number of
factors and cannot be composite because it cannot be expressed by multiplying prime numbers (0
must always be one of the factors).[40] Zero is, however, even.
The following are some basic (elementary) rules for dealing with the number 0. These rules apply for
any real or complex number x, unless otherwise stated.

 Addition: x + 0 = 0 + x = x. That is, 0 is an identity element (or neutral element) with respect
to addition.
 Subtraction: x − 0 = x and 0 − x = −x.
 Multiplication: x · 0 = 0 · x = 0.
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