TISSUES movement is essential for locating food, escaping predators,


is one of the essential features of living things. Cellular movement is
observed in one-celled amoebas, ciliates, and flagellates. Flagella whip about
to produce cellular motion, while cilia beat synchronously to propel a cell. In
animals, movement is essential for locating food, escaping predators, and
seeking mates. In many animals, the
movement process is centered in the muscle cell, which contracts and relaxes.
The contraction yields great force, which is applied against a surface by means
of a skeleton.

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Skeleton is the bony
framework of the body which provides support, shape and protection of the soft
tissues and organs in animals. It enables animals to move from place to place.

Forms and Component
of Skeleton:
The three forms of skeleton are:-

Cuticles: The cuticle is composed of a
protein called chitin. Chitin is a non-living substance, hence, arthropods
which are insects, crabs, scorpions, prawns etc with this type of skeletal material
can only grow by “moulting” or “ecdysis” (process in which an organism
sheds off its old skeleton and put on a new one).

Bones: It is the major component of the
skeleton. It consists of the living bone cells (osteocytes), protein fibres
(collagen) and minerals (inorganic salts) which are mainly calcium phosphate
and calcium carbonate. The inorganic makes the bone stronger and more rigid
than the cartilage. Examples of organisms which have bones are mainly
vertebrates which are the bony fishes, toads, crocodile, snakes, birds and

Cartilages: Cartilage is a tissue found in
the skeleton of complex vertebrae. It consists of living cells (chondroblasts),
carbohydrates and protein fibres. It is a firm, flexible material which can
support great weight. It also acts as a shock absorber, cushioning the effect
of bones moving against bones during movement. Examples of organisms which
possess cartilages are cartilaginous fishes like sharks, rays and mammals.                                          There are three types of cartilages
which are hyaline cartilage, fibro-cartilage and elastic cartilage.

Types of Skeleton: The three main types of skeleton

(Fluid) Skeleton:
Many animals have a water-based skeleton, or hydrostatic skeleton.
Hydrostatic skeletons do not contain hard structures, such as bone, for muscles
to pull against. Rather, the muscles surround a fluid-filled body cavity. In a
worm, for example, movement occurs when muscle cells contract, and the
contractions squeeze internal fluid (the hydrostatic skeleton) against the
skin, causing the worm to stiffen and the body to shorten and widen. The
squirming motion of a worm also depends on a hydrostatic skeleton. Examples of
organisms with hydrostatic skeleton are worms, sea anemone, slug, earthworm

Exoskeleton: This is the hard cuticle found
in arthropods (millipedes, insects, crabs) and other organisms. It performs the
function of skeleton which as it lies outside the muscles is called
exoskeleton. The exoskeleton is made up of non-living substance called chitin. Organisms with this type of
skeleton can only grow by a process called moulting
or ecdysis (a process an organism
sheds off its old skeleton, grow and later covered with a new one). Examples of
organisms with exoskeleton are the arthropods, hydra, snail, e.t.c.

Endoskeleton: The skeletons are found inside
the body of organisms. Muscles are attached to these skeletons inside the body
of organisms. Endoskeletal animals grow by continuous increase in size and not
by ecdysis. Examples of organisms with this type of skeleton are mammals, aves,
cartilaginous fishes, bony fishes, reptiles, amphibian e.t.c.

and the Appendicular Skeleton

Fig 13.1 The human skeleton showing the major bones of the


Axial skeleton is made up of the
skull, vertebral column (backbone), the ribs and the breastbone (sternum).

The skull: The mammalian skull is made up of
several flat bones which are joined together by means of joints called sutures. The three (3) major parts of
the skull are the brain box or cranium which contains and enclose the brain the facial
skeleton which supports the nose, eyes, e.t.c. and the jaws
which are made up of the upper jaw (maxilla)
and lower jaw (mandible) which
contains the teeth. The skull gives the head its shape. It protects vital organs
in the head e.g. eyes, nose & ears. It bears the teeth which aids grinding
of food.

The vertebral
column: It
is the central supporting structure of the skeleton. It protects the spinal
cord. In humans, there are 33 vertebrae. The vertebrae are held one to the
other with strong ligaments called inter-vertebral

In mammals, the
five (5) different vertebrae are:

vertebrae- Found in the neck region.

vertebrae- Found in the chest region.

vertebrae- Found in the upper abdomen.

vertebrae- Found in the lower abdomen.

vertebrae- Found in the tail region.

of a Typical Vertebra

A typical vertebrae possess the
following features, these are:

canal: This
is the passage of the spinal cord.

spine: This
projects upwards and dorsally for the attachment of muscles.

processes: –
They project from the sides of each vertebrae for the attachment of muscles and

– It is a
solid piece of bone below the neural canal.

Facet: – This is a small, smooth, flat
or slight depressed area on a bone that is usually a point of contact with
another bone.

Zygapophysis: – These are articular surfaces
for the articulation of successive vertebrae. They are grouped into two parts;

Pre-zygapophyses facing inwards and upwards and

Post-zygapophyses facing outward and downward.

Cervical Vertebrae

The cervical
vertebrae are found in the neck region. The first cervical vertebrae is called
the atlas,
the second is called axis. The 3rd to 7th
bones are the normal cervical bones.

Characteristics of

atlas vertebra has a large neural canal.

has a flat and broad transverse process.

neural spine is very short -or absent.

centrum is absent.

has a vertebraterial canal for the passage of blood vessels.

Function: Atlas allows the head to nod on
it, as it fits into the occipital condyles of the skull.

Characteristics of
the Axis

axis has a broad and flat centrum.

articulates with the atlas through the odontoid process.

has a large, flattened neural spine.

transverse process is reduced to a pin-like structure.

has a vertebraterial canal.

Function: It allows the head to be turned
easily i.e. twisting of the head.

Thoracic Vertebrae

Thoracic vertebrae are found in
the chest region. They are 12 in number in man.

Characteristics of Thoracic

has a long prominent neural spine which projects upwards and backwards.

has a pair of short transverse process.

is a presence of demifacets and articular surfaces for attachment of ribs.

has a large neural canal and neural arch.

has a large cylindrical centrum.


Functions: It aids the attachment of the
ribs, muscles of the shoulder and back are attached to neural spines. It also
assists in breathing alongside with the ribs.

Lumber Vertebrae

The lumbar
vertebrae are found in the upper abdominal region. In man, they are five (5) in

Characteristics of
Lumber Vertebrae

possess a large, flattened transverse process.

has broad and flat neural spine.

has large and thick centrum.

has well developed pre and post zygapophyses.

also has two (2) extra paired projections for attachment of abdominal muscles.

Functions: They provide attachment for
abdominal muscles and they bear considerable weight of the body.

Sacral Vertebrae

The sacral vertebrae are found in
the lower abdominal region. In man, they are five (5) in number. They fuse to
form a structure called sacrum.

Characteristics of Sacral

has a narrow neural canal.

has a neural spine that is highly reduced.

has a large centrum.

Function: They are joined to the pelvic
girdles to provide support, rigidity and strength.

Caudal Vertebrae

The last vertebrae are the caudal
vertebrae. It is found in the tail region. They are four (4) in number in man.
They fuse together to form a structure called coccyx. They have no neural spine, neural canal and transverse
process. They support the tail and provide attachment for tail muscles.

The Ribs: The ribs are long semi-circular
rods connecting the thoracic vertebrae to the breastbone (sternum). There are
12 pairs of ribs in humans. The first 7 pairs of ribs are called the true ribs
because they are connected directly with the sternum in front by coastal
cartilages. The next five pairs are called the false ribs because the 8th
to 10th have a common connection with the sternum; each being
attached to the coastal cartilage of the rib above. The 11th and 12th
pair is called floating ribs because they have no connection at all with the
breast bone.



The appendicular skeleton is made
up of the pectoral girdle, pelvic girdle, fore limbs and the hind limbs.

The Pectoral Girdle: The pectoral girdle is found
around the shoulder in man. The bones of the pectoral girdle are the scapula
(shoulder blade), the clavicle (collar bone) and coracoids.     The scapula is a flat triangular bone. It
is also called the shoulder blade. At the apex is a hollow or cavity called glenoid cavity into which the head of
the humerus fits into from the shoulder joints. Above the glenoid cavity is a
small hook-shaped bone called coracoid


The Pelvic Girdle: The pelvic girdle is found around
the waist of man. It consists of two halves which are joined to each other
ventrally and to the sacrum dorsally (top).
The line of fusion of the two (2) halves is called pubis symphysis. Each half is called innominate bone. Each half is made up of three (3) bones which are;




They are fused together. At the
top is the ilium which is the largest and longest of the three (3) bones. The
ischium and pubis are fused together at the lower end. The ischium and pubis
enclose an opening called “obturator foramen”. It is through this hole that
nerves, blood vessels and muscles pass. On the other surface of each half of
girdle where the three (3) bones meet, there is a deep hollow or depression
called acetabulum where the head of the femur of the hind limb fits to form the
hip joint.

The Fore limb: The fore limb is made up of the
humerus, the ulna, the radius, carpals, metacarpals and phalanges.

The Hind limb: The hind limb is made up of the
femur, tibia, fibula, tarsals, metatarsals and phalanges.



A joint is a point or place where
two or more bones meet or articulate. Joints are held together firmly by
ligaments. Ligaments join bones to bones.

Types of joints: The two types of joints are the
immovable (i.e. movement of bones of this joint is impossible e.g. skull) and
movable joints (i.e. bones that make up this joint move over each other making
movement possible).

of Movable Joints

and socket joints: It
allows movement in all directions (even up to 360o). This joint is
found in the shoulder and hip joints.

joints: It
allows movement in one direction only (i.e. up to 360o). This joint
is found in the elbow and knee joints.

or sliding joints: This
joint allows the sliding of bones over one another. Examples of these joints
are found in the wrist and ankle.

joints: This
allows nodding or rotation of one part of the body on another. It is found
between the atlas and axis vertebrae.

Structure of a

Ligaments: These are tough partly elastic
bands of tissue. They hold two (2) bones together at a joint. They join one
bone to another.

Tendons: They are extensions of
connective tissues which surround the muscles. They are non-elastic in nature.
They connect muscles to bones.

These are found at the surface of bones at joint. They cushion bones by
protecting them from wear and tear during movement. They prevent the
articulating surface from being worn out due to friction.

Membrane: It
is responsible for the secretion of synovial fluid.

Fluid: This
is the fluid secreted by the synovial membrane which lubricates the joints and
reduces shock as well as friction between two (2) bones.

Capsule: Capsule is the space which
contains the synovial fluid.

How Muscles Act
on Bones to Cause Movement

are bundles of long thin cells enclosed in sheaths of connective tissues.
Muscle tissue consists of long cells called muscle fibres which have the
remarkable ability to change their length and produce tension (pull). This is
the basis of the main function of muscle: to move the whole body or parts of
it. Muscles are attached to the bones by means of non-elastic, tough, whitish
cord of fibrous materials called TENDONS.                  Muscles can contract and relax. When a muscle
contracts, it becomes shorter and thicker. Thus a pulling force is exerted on
the bone in which it is attached. When a muscle relaxes, it lengthens and
becomes thinner. Most muscles act in pairs called ANTAGONISTIC PAIRS, so that while one member is
contracting, the other is relaxing i.e. the muscles acts in opposite direction.
One member is called extensor and
this tends to extend or straighten a limb by its contraction; the other member
is called flexor, this bends or
flexes the limb.                                    Thus,
muscles act in opposite directions in order to cause a bone to move. This aids
movement of the body. Muscles are attached to the bones at two points. One of
the points of attachment is called the origin of the muscles. This is where the
muscles are attached to an immovable or rigid bone e.g. shoulder blade. The
other point of attachment is called insertion. This is where the muscles are
attached to a movable bone e.g. radius.

of Forelimbs at the Elbow Joint

muscles of the upper arm on humerus are referred to as biceps and triceps.
Bicep muscles are attached to the front of the humerus and are attached to the
scapula by means of two (2) tendons. The triceps muscles are attached at the
back of the humerus. The contraction and relaxation of these muscles bring
about bending and straightening of the limb. The muscles are antagonistic
muscles, that is, they work together in pairs in opposite ways.            When an impulse is received from the
central nervous system, the biceps called the flexors contract by becoming shorter and thicker, and at the same
time, the triceps (extensors) relax.
Since the tendons do not stretch, the shortening of the biceps result in a pull
of the radius and as a result, the arm is bent.                On
the other hand, when the triceps muscle (extensor muscles) contract, becoming
shorter and thicker at the same time, the biceps muscle (flexors) relax, a
force is exerted on the ulna and the arm is straightened as a result.

Functions of Skeleton in Man

The functions of skeleton in man

Support: The rigid skeleton supports the
body. It also supports some vital organs and it maintains shape of the body.

Protection: The skeleton protects important
and delicate organs of the body. The skull protects the brain and houses the
inner structures of the ear and eyeball. The vertebral column protects the
spinal cord and the ribcage protect the heart and lungs. The pelvic girdle
protects the abdominal organs e.g. urinary bladder and female reproductive

Movement: The several pieces of bones
making up the skeleton allow free movement of the body and limbs. The skeleton
provides a base for the attachment of muscles which bring about movement of the
body and limbs and it gives them the ability to bend and twist in any desired

Respiration: The ribcage together with the
muscles attached to them assist in respiration (both inspiration and

of Blood Cells:
The white and red blood cells are manufactured in the marrow of long bones.

Skeleton provides places for the attachment of muscles. Muscles are attached to
bones by tendons.

Shape: Skeleton gives shape to the
body. Thus controlling growth rate in animals is not the function of the


possess supporting tissues which give them definite shape, strength, rigidity etc.

The supporting
tissues in plant and mechanisms of support in plants are:

Tissues: –
They are found in the cortex of stem, phloem, root, leaf, xylem e.t.c. They are
packing tissues made up of thinned walled cells with a central vacuole each.
The cells have intercellular air spaces. They provide flexibility, firmness and
turgidity to the stems of herbciceous (dicotyledonous) plants.

Tissues: –
They are usually located in the cortex of stems, roots and in the hypodermis
just beneath the epidermis. The cells have thick walls that are pronounced at
the corners. They provide strength and support in young growing plants. They
also give flexibility and resilience to plants i.e. enable plants to bend
without breaking.

Tissues: –
They are made up of cells which have very thick walls containing lignin,
cellulose and other substances. There are two types of sclenrenchyma, these are
sclereids and fibres. Hence, they provide rigidity, resilience, hardness and
support to plants. It also provides flexibility to plants.

Tissues: –
It is found mainly in the vascular tissues of stems, roots and leaves. Xylem is
made up of cells like tracheids (It aids the passage of water and dissolved
mineral salts), vessels, fibres and xylem parenchyma. It has a rigid thick
wall. Xylem provides support, strength and shape to the plant. It also conducts
water and dissolved mineral salts from the roots to the leaves (i.e. it is a
conducting tissue).

Tissues: –
It is also located within the vascular bundles of all plants in roots, stems
and leaves. It is made up of four (4) cells. These are;

Sieve tubes: These are living elongated cells
that conduct mainly food.

Phloem parenchyma: They provide strength and
support to the plant. It also helps in food storage.

Phloem fibres: They also provide strength.

Companion cells: They are small and short cells
which also assist in the conduction of food substances.

The function of phloem is to
conduct manufactured food from their area of synthesis to areas where they are
needed. It also provides support.

or piliferous layer: –
Epidermis is the outer covering of the leaves and stem while that of the root
is piliferous layer. They are one cell thick. They help in protection. They
prevent the inner cells from injury, infection and loss of water.

Cortex: – It is found between the
epidermis and vascular bundles (xylem & phloem) of a dicotyledonous stem.
The cortex is made up of three (3) tissues which are the (i) collenchyma (on
the outside), (ii) the middle parenchyma and (iii) the inner epidermis (it is
also called starch sheet). It stores starch; hence, when stained with iodine
solution, it will turn blue black.

– It is
found between the phloem and xylem. This increase the size of cells (which is
called secondary thickening or growth). It is responsible for the increase in
size of the trunks of many trees. It makes the trees get wider.

Pith: – This is the central part of
the stem. It is large and made of parenchyma and extends between the vascular


Functions of
Supporting Tissues in Plants

The functions of
supporting tissues in plants are;

Strengthening: Sclerenchyma and collenchyma provide
the necessary strength required by plants.

Rigidity: Collenchyma, sclenrenchyma and
wood fibres provide necessary materials to make the plant strong against
external forces.

and Flexibility:
The supporting tissues also provide the necessary materials which make the
plant resilient and flexible thereby preventing the plants from being broken by
the bending and twisting movements caused by strong winds.

Protection: Some supporting tissues protect
the delicate parts of plant body e.g. cambium.

Supporting tissues generally give shapes to plants.

Conduction: Some supporting tissues,
especially xylem and phloem tissues are known to conduct water and manufactured
food respectively within the plant.