Life Process | Transportation

Transportation in Plants

• ln plants, xylem transports minerals and water from roots to other parts of the plant while phloem transports food manufactured in leaves to other plant parts and storage organs.
• ln xylem tissue, vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water-conducting channels reaching all plant parts.

  

  

      
  

Transpiration :

It is defined as process by which plants lose water in the vapour form from the aerial parts of the plant.

Movement of water during transpiration in a tree

Importance of Transpiration

(a) Ascent of Sap : It is the upward movement of cell sap, i.e. water and minerals through the xylem and excess of water is then lost in the form of water vapours after preparation of food.

(b) Removal of Excess of Water : Transpiration helps to remove excess of water.

(c) Cooling effect : It helps to regulate the temperature of plant since evaporation reduces temperature.

(d) Absorption and Distribution of Salts : The continuous water current produced by transpiration helps to absorb and distribute the salts.

Translocation :

The transport of soluble products of photosynthesis, amino-acids and other substances through phloem is termed translocation. The translocation of food and other substances takes place in the sieve tubes with the help of adjacent companion cells both in upward and downward directions. The translocation in phloem is achieved by utilizing energy. Materials like sucrose is transferred into phloem tissue by using ATP.

Transportation in Human

In humans transportation of O₂, nutrients, hormones, and other substances to the tissues, CO₂ to the lungs and waste products to the kidney is carried out by a well-defined circulatory system.

Circulatory System :

It comprises of the heart, blood vessels, blood lymphatic vessels and lymph which together serve to transport materials throughout the body.

(i) Blood : Blood is a liquid (or fluid matrix) called plasma with red blood cells, white blood cells and platelets floating in it. It is bright red-coloured fluid connective tissue that circulates in the entire body by the muscular pumping organ – the heart. The volume of blood is about 6 l. in adult human body.

(a) Plasma : The liquid part of blood excluding blood cells.

·    Plasma consists of water, in which many substances are dissolved including plasma proteins (albumin, globulin, fibrinogen and anti-bodies) salts (sodium and potassium chlorides and bicarbonates) food substances (amino acids, glucose, fats) hormones, digested food and excretory waste products.

·    In the plasma, floats the RBC, WBC and blood platelets.

·    Plasma without fibrinogen is called serum.

        Plasma = Serum + fibrinogen

(b) Blood corpuscles

·    Red Blood Corpuscles (RBC) or Erythrocytes : These are minute, circular biconcave discs having no nucleus. They are red due to the presence of red coloured pigment – haemoglobin.

·    White Blood Corpuscles (WBC) or Leucocytes : These are large nucleated colourless cells, numerous than RBC’s. They are mainly of two types : Granulocytes and Agranulocytes.

·    Blood Platelets or Thrombocytes : Platelets are rounded, colourless, biconvex, non-nucleated blood cells, which help in the coagulation of blood. They are called thrombocytes.

·    Blood clotting : It is the mechanism that prevents the loss of blood during an injury. The blood has platelet cells which circulate around the body and plug these leaks by helping the blood to clot at these points of injury. The other name is ‘blood coagulation’. The major events are :

    Injured tissue + Blood platelets Release thromboplastin

    Prothrombin (inactive) Thrombin (Active)

    Fibrinogen (soluble) Fibrin (insoluble form)

    Fibrin + Red blood corpuscles Blood clot

(ii) Our Pump – The heart :     The heart is a pumping muscular organ that receives blood from the veins and pumps it into the arteries. It is situated in the thoracic cavity which lies above the diaphragm between two lungs. It is enclosed in double – walled membranous sac the pericardium. Heart is as big as our fist. Out heart has four chambers two auricles (left and right) and two ventricles (left and right).

Sectional view of the human heart

·    The oxygenated blood from lungs comes to thin walled left auricle through pulmonary veins.

·    The de-oxygenated blood comes to thin walled right auricle through two large veins superior and inferior vena cava.

·    When the left and the right atrium contracts, the oxygenated and deoxygenated blood reaches the respective ventricles.

·    Contraction of ventricles results in transfer of blood from them into lungs and various body parts.

·    Left ventricle on contraction sends oxygenated blood to body through the largest artery aorta. While the right ventricle pumps the blood into lungs for oxygenation through pulmonary artery.

·    The walls of ventricle are thicker than auricle as they have to pump the blood to various body organs.

·    Valves present in between auricle and ventricle as well as at the opening of major arteries in ventricles, check the back flow of blood and allow its unidirectional flow.

·    ln mammals and birds separation of the right side and left side of the heart is useful as it does not allow oxygenated and deoxygenated blood to mix. Hence the heart is four chambered in birds and mammals.

·    Amphibians and reptiles have three-chambered heart two auricles and one ventricle.

·    Fishes have two-chambered heart – one ventricle and one auricle.

·    In fishes the blood is pumped into gills where it is oxygenated and supplied directly to body parts from gills. Thus blood goes only once through the heart.

·    In other vertebrates, the blood passes twice through the heart. This is known as double circulation.

Blood circulation in human body

Mechanism of Double Circulation :

As the blood passes twice through the heart in one complete cycle in man, it is called double circulation.

1. Pulmonary circulation :

·    It begins in the right ventricle which sends the blood into the pulmonary trunk (lungs) by pulmonary artery. Pulmonary artery is the only artery carrying deoxygenated blood.

·    The blood flowing to the lungs, becomes oxygenated and returns to the heart (left atrium) through pulmonary vein. Pulmonary vein is the only vein carrying pure blood.

2. Systemic Circulation :

·    Left ventricle pumps the blood through aorta into the body.

·     The aorta divides into arteries, arterioles finally to capillaries and thereby supplies oxygenated blood to various parts of the body.

·     From there deoxygenated blood is collected by veinules which join to form veins and finally vena cava and pour blood back into the heart.

·    Arteries are the blood vessels which carry blood away from the heart to various organs of the body.

·    Since the blood emerges from the heart under high pressure, the arteries have thick, elastic walls.

·    Veins collect the blood from various organ and bring it back to the heart. They do not need thick walls, instead they have valves that ensure that the blood flows only in one direction i.e. from organs to heart.

Schematic representation of transport and exchange of oxygen and carbon dioxide

·    Usually arteries carry oxygenated blood away from the heart except pulmonary artery which carries deoxygenated blood from right ventricle to lungs for oxygenation.

·    On the contrary, veins carry deoxygenated blood from body organs to heart except pulmonary vein which carries oxygenated blood from lungs to heart.

·    On reaching organ or tissue, the artery divide into smaller and smaller vessels to bring the blood in contact with all the individual cells. The smallest vessels are known as capillaries.

BLOOD VESSELS

·    Capillaries have walls which are one-cell thick to allow exchange of material between the blood and surrounding cells.

·    The capillaries then join together to form veins that carry the blood away from the organs or tissue back to heart.

(iii) Lymph is another type of fluid which also helps in transportation. This is formed by passage of some fluid from blood capillaries into intercellular spaces in the tissue through the pores present in the walls of capillaries.

·    It is similar to the plasma of blood but colourless and contains very less proteins.

·    Lymph drains into lymphatic capillaries from the intercellular spaces, these capillaries join to form large lymph vessels that finally open into larger veins.

The major functions of lymph are:

1.    It carries digested and absorbed fat from intestine into blood.

2.    Drains excess fluid from extra cellular space back into the blood.

3.    Provides immunity to the body.

(iv) Blood pressure :     It is the force that blood exerts against the wall of a vessel. This pressure is much greater in arteries than in veins.

·    The presence of blood inside artery during contraction or ventricular systole is called systolic blood pressure. Pressure in artery during relaxation or ventricular diastole is called diastolic blood pressure.

·    The normal systolic blood pressure is about 120 mm of Hg and diastolic blood pressure is 80 mm of Hg.

Blood Pressure

·    Blood pressure is measured using an instrument called sphygmomanometer.

·    Abnormally high blood pressure is called hypertension and it can lead to rupture of an artery.