Protection:
(i). It protects the body from the attacks of germs, which cause diseases, by killing germs.
(ii). It protect the body from excessive bleeding, by clotting when a body tissue is cut or wounded
Regulation:
It helps to regulate the quantity of water in the tissues (osmoregulation).
It helps to regulate the quantities of the various chemical materials in the tissue (homoeostasis).
It helps to keep the body temperature fairly constant by distributing heat evenly around the body.
In small organisms like Amoeba, and paramecium, cytoplasm which is fluid part of the organism is used
for transportation of food and other materials in and out of the organisms.
In many plants, the medium of transportation of materials is the latex or cell sap. The cell sap is made up
primarily of water, dissolved materials like synthesised foods, growth substances and inorganic salts.
The sap is transported to all the parts of a plant through the phloem tissue. Different plants have latex
(cell sap) of different colours. For example, the latex of rubber plant cassava (manihot) is white. A few
plants have red or colourless latex.
STRUCTURE AND FUNCTION OF BLOOD
The mammalian blood comprises four main components;
Plasma
Red corpuscles
White corpuscles
Platelets.
Plasma: The plasma is a pale yellow liquid made of mainly of water (about 90%), with many substances
dissolved in it. These include digested food, mineral salts, vitamins, hormones, dissolved oxygen and
excretory products such as urea and carbon (iv) oxide. The plasma also contains large molecules, the
plasma proteins, such as fibrinogen, which assist in the clothing of blood in damaged tissues.
Red corpuscles or erythrocytes: They are tiny, biconcave, disc-like cell without any nucleus in adult
mammals. They contain a red pigment-haemoglobin, a protein that contains iron. This enables the red
blood corpuscles to readily combine with oxygen in area of high oxygen concentration (i.e., the alveoli of
lungs) to form oxyhaemoglobin. This is the form in which oxygen is carried to all body tissues. They also
readily give oxygen in places where the oxygen concentration is low (e.g., all the tissues except those
near the alveoli). Erythrocytes are synthesised in the red bone marrows of sternum, ribs and vertebrae.
There are about 51/2 million of them in a cubic centimetre of blood. They live for about 120 days and
are destroyed in the liver or spleen.
Erythrocytes
Erythrocytes, or red blood cells, are the primary carriers of oxygen to the cells and tissues of the body.
The biconcave shape of the erythrocyte is an adaptation for maximizing the surface area across which
oxygen is exchanged for carbon dioxide. Its shape and flexible plasma membrane allow the erythrocyte
to penetrate the smallest of capillaries.
White corpuscles or leucocytes: There are many types of white corpuscles all of which have nuclei. They
are made in the red bone marrow, the lymph node or the spleen. They live for many months. Those that
are irregular in shape, i.e., the phagocytes, are commonest. They are large with lobed nuclei. Like the
Amoeba, they have pseudopodia and are able to pass through the walls of the capillaries into the tissue
fluid. In the lymphatic system, they ingest bacteria, virus and dead cells, and help in preventing diseases.
The ingestion of materials is called phagocytosis and hence such white corpuscles are called phagocytes.
Those that produce antibodies are called lymphocytes and are produced in the lymph glands. They
produce chemicals called antibodies, which stick to the surface of germs and kill them. White corpuscles
are fewer than the red corpuscles. There are about 5000 of them in a cubic millimetre of blood.
Lymphocyte
Scanning electron micrograph of a normal T lymphocyte. Lymphocytes are specialized white blood cells
whose function is to identify and destroy invading organisms such as bacteria and viruses. Some T
lymphocytes directly destroy invading organisms, whereas other T lymphocytes regulate the immune
system by directing immune responses.
Platelets: These are tiny, irregularly-shaped particles formed in the red bone marrow. They lack nucleus.
In damaged tissues, they break down and librate an enzyme, which catalyses the first of a series of
reactions, fibrinogen, a blood protein, is converted to threads of fibrin, which form a mesh that plugs the
wound. This stops the bleeding.
Thrombocytes and Clotting
Thrombocytes, or platelets, are the smallest cellular component of blood. They circulate inactivated,
about 250,000 per cubic mm of blood, until they come into contact with a damaged blood vessel. At this
point, the platelets form a clump, adhering to each other and to the blood vessel wall. They secrete
chemicals that alter a blood-borne protein, fibrinogen, so that it forms a mesh of fibers at the damage
site. A clot forms when platelets and red and white blood cells become trapped in the fibers. Blood
clotting begins within seconds of injury. The same process can produce unwelcome clots in undamaged
blood vessels.
EVALUATION
List three media of transportation.
Describe the four components of the blood.
TRANSPORT TISSUES IN PLANTS AND ANIMALS
Tissues used for transportation are
Arteries,
Capillaries,
Veins, and
Vascular bundles (in plants)
Structure of Arteries
All Arteries carry oxygenated blood from the heart to the body tissues, except pulmonary arteries
These are wide vessels that generally transport blood from the heart to the limbs and organs.
