LIVINGS
In
BIOLOGY
FOR
GENERAL SECONDARY CERTIFICATE
Unit (I)
Chapter (7)
Support & movement in Livings
Support in Plants.
The plant possesses different methods and systems for support so as to maintain its shape and for protection. These methods may be physiological, concerning the cell as a whole, or may be structural, as the deposition of hard substance such as cellulose and lignin or the support depends on the position and distribution of these systems.
1. The physiological support:
If you soak dried fruit in water, you will notice that it absorbs water, enlarges in size, and swells due to the turgidity of its cells.
On the contrary, if you leave fresh seeds such as peas or beans for a time, you will notice that the seeds become wrinkled and wilt due to loss of water from their cells.
The cell becomes turgid, when water passes by osmosis into its vacuoles. As a result, the size and pressure of vacuoles increase, affecting the shape of the cell wall.
This phenomenon has been noticed in the turgidity of the guard cells, as well as the wilting of leaves and stems of herbaceous plants that face drought. The wilting plant will attain its turgidity by soil irrigation.
2. The structural support:
The plant has many other methods for support such as the deposition of substances on or in the cell wall. The external plant cells cannot prevent loss of water from the inner cells and so the epidermal cell walls become thick and impermeable due to cutin being deposited. The plant may become surrounded with an impermeable cork layer containing suberin in its cells. Cellulose or lignin may be deposited in the cell walls or in some of its parts, so these cells become stronger, such as: Collenchyma cells and Sclerenchyma cells (Fibers and stone cells)
The Skeletal System in Man.
The skeleton of Man consists of an axis called the vertebral column attached at its upper end with the skull. The vertebral column is also connected to the thoracic cage and the fore limbs through the shoulder bones and to the lower limbs through the pelvis bones. The skeleton can be divided into axial and appendicular skeleton:
1. The axial skeleton:
Includes the skull, the vertebral column, and the thoracic cage.
2. The appendicular skeleton:
Includes pectoral girdle, fore (upper) limbs, pelvic girdle, and hind (lower limbs).
First - The axial skeleton:
1. The vertebral column:
Consists of 33 vertebrae in the form of:
Seven cervical vertebrae. (Of moderate size)
Twelve thoracic vertebrae. (Larger than the cervical)
Five lumbar vertebrae. (The largest and present in the abdominal region)
