Animals - Form And Structure


There are various animals, each one with different forms and function. Each organism has a distinct body plan with a different size and shape. Animals’ bodies are also designed to interact with their environment; whether in the deep sea, a rainforest canopy, or the desert. Therefore, a large amount of information about the structure of an organism's body (anatomy) and the function of its cells, tissues and organs (physiology) can be learned by studying that organism's environment.

In order to survive, animals must be able to perform functions of their many specialized cells, like, take in and digest food, pull oxygen from the air, circulate nutrients and oxygen to their cells, eliminate waste, move, maintain body temperature and reproduce. Animals have also developed various behaviors that help them to survive.


A change in the position of any object is called movement. Many movements take place in our body and also in other organisms’ body.


When movement results in change of position of the whole organism, it is called locomotion.

Examples of movements in the human body:

  1. Movement of eyelids.
  2. Movement of the heart muscles.
  3. Movement of teeth and jaw.
  4. Movement of arms and legs.
  5. Movements of head.
  6. Movements of neck.

Movement of some organs happens because of the combined efforts of bones and muscles. In such cases, movement is possible along a point where two or more bones meet.


The location where two or more bones meet is called a joint. Ligaments bind a bone to another bone. Tendons bind a bone to a muscle.

Types of Joints

  1. Fixed joints: The joints where no movement of bones are possible is called a fixed joint. The joints in the skull bone (cranium) are examples of fixed or immovable joints.
  2. Moveable joint: Movement is possible in these joints.

The framework of bones and cartilage which gives shape and support to the body in an animal is called the skeleton. The human skeleton is made up of 206 bones. While the bones are hard, cartilages are soft. Cartilage is found between joints and in some elastic organs; like the ear lobe and nose. Cartilage reduces friction between a joint.

Various organs of the skeletal system:

Chest Bone or Rib Cage:  The bones of the rib cage are called ribs. There are 12 pairs of ribs. The rib-cage protects the lungs and the heart.

Backbone or Vertebral Column: The vertebral column extends from the base of the skull to the hip. It consists of 33 small rings; called vertebrae which are joined from end-to-end.

Shoulder Bone or Pectoral Girdle: The shoulder bone is formed by the collar bone and the shoulder blade. It is attached to the upper part of the rib-cage and to the upper arm bone.

Hip Bone or Pelvic Girdle: It is formed by the fusion of three bones, the hip bones and the tail parts of the backbone; to from a large bony bowl. The thigh bones are attached to the hip bone.

Skull: The skull is at the top of the vertebral column. It is composed of two main parts.

  1. Cranium: The cranium gives protection to the brain.
  2. Facial bones: These bones make the front and the lower part of the skull. The lower jaw bone is the only movable bone; which helps us chew, eat and talk.

Gait of Animals

Gait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate.

  • Earthworm: Earthworm has a body with a number of segments. The surface which is close to the base is called the ventral surface. These bristles are connected with muscles at their bases.

    The earthworm moves by contracting and expanding portions of its body alternatively.

  • Snail: The snail has a muscular foot which helps in locomotion. The muscular foot is made up of strong muscles.
  • Cockroach: A cockroach has three pairs of jointed legs, which help it to walk, run and climb. It also has two pairs of wings for flying. Large and strong muscles help in the movement of legs.
  • Birds: Birds can walk on the ground and fly as well. Some birds can also swim in the water. Their bones are light and strong to support movement. Birds have special flight muscles and the forelimbs are modified as wings. The wings and tail have long feathers, which help in flying.
  • Snake: The body of a snake consists of a large number of vertebrae. The adjoining vertebrae, ribs and skin are interconnected with slender body muscles. The movement of a snake is called slithering.

  • Fish: Fish swim with the help of fins. They have two paired fins and an unpaired fin. When a fish swims; its front part turns to one side and the tail part stays in the opposite direction. In the next move, the front part turns to the opposite side and the tail part also changes its position to another side. The tail fin helps in changing direction.

Control Systems

Animals have two major systems for coordinating and synchronizing the functions of their millions of individual cells.

A) The nervous system works rapidly by transmitting electrochemical impulses.

B) The endocrine system is a slower system of control; it works by releasing chemical signals into the circulation. These control systems allow the animal to react to both its external and internal environments appropriately.

The Nervous System

The nervous system functions by the transmission of electrochemical signals. The transmission is done through highly specialized cells known as neurons, which are the functional unit of the nervous system.

The neuron is an elongated cell that usually consists of three main parts:

  • The dendrites,
  • The cell body,
  • The axon.

The Endocrine System

The endocrine system works along with the nervous system to control and coordinate the functions of the other organs in our body. The organs that make up the endocrine system are called the endocrine glands, and they communicate with the body by releasing chemical messengers into our bloodstream known as hormones.

A hormone affects a targeted cell cluster for a specific amount of time; such as the regulation of blood sugar.