Movement is a phenomenon which distinguishes living organisms. The living organism has self-movement and can respond to external stimuli
Types of movement in livings:
1. A continuous movement inside each cell for its biotic activities such as cytoplasmic streaming.
2. A positional movement of some organs such as peristalsis in vertebrate intestines, and the movement of insectivorous plant leaves.
3. Movement of the organism from place to place in search of food, or for mate. This type of movement is restricted to animals.
The importance of the skeleton for the occurrence of movement:
An animal cannot attain balance or move unless it possesses a solid support to which muscles are attached. Such kind of support may be external, as in the arthropods or internal, as in vertebrates. This is the skeleton. The internal skeleton may be cartilaginous as in cartilaginous fish or bony as in bony fish. Whatever the kind of skeleton, it consists of segments attached to each other by joints to facilitate movement.
First: Movement in Plants:
Leaves of some plants are affected by touch; when the leaflets of Mimosa are touched, they collapse in successive order followed by the petiole. This movement is a response to touch. The leaves of this plant, and some leguminous plants partially close during darkness and return back to their original position in the light. Thus, through the succession of light and dark, movement of the leaves, which is similar to awakening and sleeping, occurs and so this movement is known as sleeping movement. We also studied tropism, which is the response of different parts of the plant to light, humidity, and gravity due to the difference in growth rates resulting from the effect of Auxins.
A) Haptotropism: (Pulling movement):
1. Tendrils in Pea:
One special type of movement is Haptotropism, which is seen in tendrils of pea. The tendril raises itself into the air and is likely to make contact with a solid object. It immediately twines closely around the object for few turns in a spiral form. Its length decreases, and so the plant stem approaches the support, and grows vertically. The tendril becomes thickened and lays down a considerable amount of mechanical tissue. If the tendril doesn’t meet a support during its twining movement, it wilts and dies. The twining of the tendril around the support is due to slow growth in the side in contact with the support, and accelerated growth in the far side. This leads to elongation of the far side, and so the tendril twines around the support.
2. Pulling roots:
Corms and bulbs have pulling roots below them, by contracting of these roots, the corm or bulb is pulled downwards to a suitable level in the soil. Subterranean storing stems remain at a suitable distance from the soil surface by the help of these pulling roots which support the aerial parts against wind effects.
B) Cytoplasmic streaming:
One of the main characteristic of the living cytoplasm is its continuous rotation inside the cell. This is shown when examining Elodea leaf cell, which is an aquatic plant under the high power of the microscope. We can see the cytoplasm forming a thin layer lining the cell wall and streaming in a rotational movement in one direction. This movement is indicated by the movement of the chloroplasts embedded in the cytoplasm.
Second: Movement in Man:
Looking for your hand while turning over these pages, or your leg while walking on your way to school, you will find that the movement depends on three systems which are: The skeletal system which supports the movement of limbs, the muscular system for contraction and relaxation of the muscles that move the limbs, and the nervous system which gives the order to muscles to contract and relax.
The muscular system:
The muscular system is a group of body muscles by which different parts of the body can move. The unit of structure of the muscular system is the muscle. The muscle consists of a muscular tissue, and usually known as flesh. The number of muscles in man is about 620 muscles or more.
Functions of muscles:
The muscles are characterized generally by being filamentous and have the ability of contraction and relaxation. Muscle contraction is important to perform the following functions: