SS2: WEEK 3. TRANSPORT SYSTEM

:TRANSPORT SYSTEM

The transport system is the movement of metabolic substances from various parts of the organism where they are produced or obtained to the parts where they are either used, stored, or removed from the body.

 NEED FOR TRANSPORTATION

i. It aids in the removal of metabolic waste, e.g., carbon dioxide, water and urea

ii. It helps to move hormones in plants and animals from where they are produced to areas of need.

iii. It helps transport essential materials in organisms for metabolic processes, e.g., nutrients, oxygen, and water.

iv. In plants, transport is necessary to move mineral salt and water from the root to the stems and leaves.

 

MATERIALS THAT ARE TRANSPORTED IN ANIMALS

 

The materials transported in animals include:

i. Water

ii. Digested foods (vitamins, amino acids, mineral salts, fatty acids, glycerol) iii. Gases (oxygen, carbon-dioxide)

iv. Excretory products (urea, carbon-dioxide, excess salt)

v. Hormones (adrenaline, insulin, estrogen, etc.) and other materials.

vi. Antibodies

 

MATERIALS THAT ARE TRANSPORTED IN PLANTS

These include:

i. Water II. Manufactured food iii. Excretory products iv. Hormones v. Mineral salts

vi. Oxygen

MEDIA OF TRANSPORTATION

In all organisms, a liquid or fluid is the medium of transportation of materials. It includes blood, lymph, and tissue fluid in most animals; latex or cell sap in many plants; and cytoplasmic fluid in small organisms such as protozoa, protists, and coelenterates.

Some of the media of transportation include

1. Blood and lymph in the vertebrates.

2. Cytoplasm in unicellular organisms.

3. Cell sap or latex in most plants.

4. Body fluid in vertebrates.

5. Closed and open circulations.

 FUNCTIONS OF THE BLOOD

There are several functions performed by the mammalian blood. These functions are grouped into three viz:

1. Transport:

(i). It carries oxygen from the lungs to the tissues and carbon (iv) oxide from the tissues to the

lungs for excretion.

(ii). It carries digested foods from the gut to the various parts of the body.

(iii).it carries nitrogenous waste products from the tissues to the kidneys, which get rid of them.

(iv). It carries hormones and antibodies from one part of the body to another.

 2. 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

3. Regulation:

(i) It helps to regulate the quantity of water in the tissues (osmoregulation).

(ii) It helps to regulate the quantities of the various chemical materials in the tissue (homeostasis).

(iii) 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 the 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 and 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 colors. For example, the latex of the rubber plant cassava (manihot) is white. A few plants have red or colorless latex.

 

STRUCTURE AND FUNCTION OF BLOOD

The mammalian blood comprises four main components:

I. Plasma II. Red corpuscles III. White corpuscles IV. Platelets.

I. Plasma: The plasma is a pale yellow liquid made 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 clotting of blood in damaged tissues.

II. Red corpuscles or erythrocytes: They are tiny, biconcave, disc-like cells 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 areas of high oxygen concentration (i.e., the alveoli of the lungs) to form oxyhemoglobin. 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 marrow of the sternum, ribs, and vertebrae. There are about 51/2 million of them in a cubic centimeter 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.

III. 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 the most common. 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, viruses, 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 millimeter of blood.

IV. 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. 

IV. Platelets: These are tiny, irregularly shaped particles formed in the red bone marrow. They lack a nucleus. In damaged tissues, they break down and liberate 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.

V. 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.

TRANSPORT TISSUES IN PLANTS AND ANIMALS

Tissues used for transportation are

i. Arteries,

ii. Capillaries,

iii. Veins, and

iv. Vascular bundles (in plants)

Structure of Arteries

i. All Arteries carry oxygenated blood from the heart to the body tissues, except pulmonary arteries

ii. These are wide vessels that generally transport blood from the heart to the limbs and organs.

iii. There is one artery to each of the organs of the body.

iv. They are muscular, thick-walled, and elastic and are able to withstand the high pressure caused by the heartbeat.

v. The arteries branch in the organs to form arterioles.

vi. The arterioles also branch repeatedly to form a network of blood capillaries, which permeate every living cell of the body.

 

Structure of Capillaries

i. These are tiny vessels with very thin walls, which are often one cell thick.

ii. Their walls allow water and dissolved substances, except proteins, to pass in and out of them.

iii. The capillaries branch within the tissues.

iv. Through their thin walls, dissolved food and excretory products are exchanged with the tissues around them.

v. The capillary network is so dense that no living cell is far from food and oxygen supplies.

vi. The capillaries rejoin to form veins.

vii. Through the capillary network, blood flows from the arterial end to the venous end.

Structure of Veins

i. All veins carry de-oxygenated blood from the body tissues to the heart, except the pulmonary vein.

ii. They are wider and have thinner walls than arteries.

iii. The veins branch from the organs to form venules.

iv. They have valves at intervals, which allow blood to flow in one direction from other organs towards the heart.

 Structure of Vascular Bundles

i. Vascular bundles consist mainly of xylem and phloem tissues. But in the root and stems of dicotyledons, a layer of cambium cells exists between the xylem and phloem tissue.

ii. Xylem transports water and mineral salts, while phloem translocates manufactured food from the leaves to where it is stored.

iii. Vascular bundles are found in the roots, stems, and leaves of flowering plants.

iv. Vascular tissues are grouped together in bundles within the plant body.

v. The vascular tissues of plants are made up of a network of long tubes called vascular bundles.

vi. They are called veins in the leaves.