Transportation whether in plants or animals is the key to the efficient assimilation of the nutrients that the organisms synthesise, get from their environment or digest



Every living organism whether big or small, unicellular or multicellular, needs a regular supply of energy for its proper functioning. This energy is supplied to the body in the from of nutrients obtained from food. Moreover, the wastes generated are also to be removed from the body in order to maintain a proper equilibrium in the body. So, an arrangement is set up in every living orgainsm to carry out the process of transports substances from one part to other part is called transport system or circulatory system. 

Transportation in living beings is process through which nutrients (obtained during digestion), respiratory gases (obtained during respiration), excretory products, hormones, etc., are carried from one part to another part of the body. Transportation occurs in all organisms-microscopic to large ones. Depending upon the complexity of organisms, the method of transportantion varies. Diffusion is a major method of transportation in unicellular organisms like protozoans (Amoeba and Paramecium) and also in simple multicellular organisms like cnidarians and spongs.


Significance of transport system

(i) It transports food from the leaves in plants and small intestine (alimentary canal) in animals to each cell of the body.
(ii) It transports oxygen from lungs to all body cells and carbon dioxide from all body cells to the lungs.
(iii) It carries waste products to kidneys for elimination.
(iv) The water absorbed by the plants is circulated to all parts through the transport system.
(v) Hormones are formed in a particular area of the body. It is transported to the area of function via transport system.

Transportation in humans

The process of transporting the absorbed food, water and waste products from one place to another in the body is called circulation
In human beings,
circulatary (transport) system comprises two system


(A) Blood Vascular System

A system in which fluid is transported from one part of the body to the other through tubes is called vascular system. Blood vascular system or circulatory system is a system used for transportation of blood between various organs of the body and the heart. The system is a complex network of hollow tubes called blood vessels. Blood vessels carry blood and connect heart to all other organs of the body.

The circulatory system has three different parts –
(1) Pulmonary circulation (lungs)
(2) Coronary circulation (Heart)
(3) Systemic circulation (The rest of the systemics processes)

There are three major components of blood vascular system
(i) Blood (fluid)
(ii) Blood vessels (tubes)
(iii) Heart


(i) Blood
Blood is a fluid connective tissue. It is red, sticky and viscous fluid flowing in blood vessels. It forms 6-10% of total body weight. An adult human contains approximately 5-6 litres of blood. Blood is composed of two parts
(i) Blood plasma (fluid part)
(ii) Blood corpuscles (Solid or cellular part)

  • Properties of blood
    (i) In all chordates and in annelids amongst the non-chordates, blood is a bright red fluid of salty taste and peculiar smell.
    (ii) Blood flows in a continuous circuit of blood vessels.
  • Composition of blood Blood
    consists of four parts, each with its own job in the body.
    (i) Plasma
    (ii) Red Blood cells (erythrocytes)
    (iii) White Blood cells
    (iv) Platelets

 Different types of blood cells in man

(v) Regulation of Body Temperature
The blood flows in all parts of the body, so it equalises the body temperature. It carries heat produced from one place to another place of the body.

(vi) Maintenance of pH
The plasma proteins act as buffer system and maintain required pH of the body tissues.

(vii) Transport of Hormones 
The plasma of blood transports various hormones from one region to another and bring about the co-ordination in the working of the body.

(viii) Water Balance
The blood maintains water balance to constant level by distributing uniformly over the body.

(ix)  Protection from Diseases
The WBC (eosinophils, neutrophils, monocytes) engulf the bacteria and other disease causing organisms by phagocytosis. The lymphocytes produce antibodies against the invading antigens.

(x)  Clotting of Blood
Blood forms a clot at the site of injury, thus preventing further loss of blood. Blood helps in rapid healing of wounds.


Mechanism of blood clotting (Coagulation)

Sealing off a leaking blood vessel to stop bleeding is called blood clotting or haemostatic mechanism. A small leakage is sealed by blood platelets which adhere together to form a sticky plug called thrombus and the complete process is called the agglutination of the platelets. This process was discovered by physiologist Howell. He suggested that this mechanism is a complex process conststing of three steps which are as follows.

Step-1 Formation of enzyme thrombokinase (or thromboplastin) by the injured tissue cells and platelets Step-2 The enzyme deactivates heparin (natural anti-coagulant found in blood) in the presence of calcium ions (Ca2+). Heparin changes blood into ‘sol’. Thrombokinase converts plasma protein prothrombin (formed in liver) into thrombin.
Step-3 Thrombin acts as an enzyme and converts souble fibrinogen into insoluble fibrin which undergoes quick polymerisation and forms long fibrin threads. The fibrin threads form the clot which entraps RBCs.

This process takes 2 to 8 minutes and produces a ‘red clot’ at the wound site. After clot formation, bleeding stops. Now, the clot begins to contract and produces a pale-yellow fluid (serum) which is blood plasma without corpuscles and fibrinogen.

Mechanism of blood clotting


(ii) Blood Vessels
Blood vessels are the network of hollow muscular tubes that transport blood throughout the body. They are mainly of three types

The major differences between various blood vessels have been given in Table.

(iii) Heart

External View of Human Heart

Internal structure of the human heart


Size – 5 × 3.5 inches
Colour – Pink
Shape – Conical shape
Weight – 300 gm.

Structure of heart

The basic structure of the heart (illustrated below) may be described as follows:
The Heart is divided into separate right and left sections by the interventricular septum, or “septum” when the context is clearly that of the heart. Each of these (right and left) sections is also divided into upper and lower compartment known as atria and ventricles, respectively. The four main chambers of the heart are : Right Atrium
Right Ventricle
Left Atrium
Left Ventricle
It is essential that blood flows in the correct direction through the heart so the structure of the heart includes a series of valves The Tricuspid valve separates the right atrium from the right ventricle.

The Pulmonic/Pulmonary valve separates the right ventricle from the pulmonary artery.

The Mitral (also known as the Bicuspid) valve separates the left atrium from the left ventricle.

The Aortic valve separates the right ventricle from the ascending aorta.


Working of Heart/ Physiology of Heart

Heart does not work throughout the day. It rests double the time it works. It rests between every beat. The resting period is called diastole, its duration is twice as long as that of systole, which is the period of muscular contraction. The series of events which occur during one complete beat of the heart is known as cardiac cycle. Cardiac cycle mainly consists of three steps, i.e., Auricular systole, Ventricular systole and Joint diastole.
Contration of the two auricles is simultaneous and is called auricular systole, relaxation of the auricles is called auricular diastole. Similary ventricular systole is the simultaneous contration of two ventricles and ventricular diastole is their relaxation. Cardiac cycle occurs in the following steps:

1. In the beginning, both auricles and ventricles are in a joint diastole.

2. Blood flows into the left auricle from the pulmonary veins and from superior and inferior vena cavae in the right auricle.

3. Next step is of auricular systole in which both auricles contract simultaneously which drives most of their blood into their respective. At this stage ventricles are in diastole i.e., they are relaxed.

4. Ventricular systole follows immediately. Pressure of the blood in the ventricles forces to close the bicuspid and tricuspid valves.

Working of heart

5. The first sound “Lubb” is produced when the auriculo-ventricular valves get closed at the start of ventricular systole.

6. Pressure in the ventricles leads to the pressing of the semi-lunar valves of the great arteries  (i.e., aorta and pulmonary artery), and thus driving the blood into them. The second sound “Dupp” is produced when the semi-lunar values of aorta and pulmonary artery get closed.

7. After this ventricles get relaxed or there is ventricular diastole. The auricles are still undergoing diastole. Thus we can say, all chambers are in diastole or relaxed. One cardiac cycle is completed in 0.8 second.


Route of blood circulation

 Single Circulation· Single Circulation In fishes, the blood flows through the heart only once while completing the full circuit of the body. It is called single circulation. The heart receives and pumps only venous blood. It reaches to heart on deoxygenation.

Single circulation in fish

    • Double Circulation
      It is passage of the same blood twice through the heart first one the right side, then on the left side in order to complete one cycle. Double circulation has two components, pulmonary circulation and systemic circulation.

 Double circulation in mammals and birds


(i) Pulmonary circulation
It is movement of blood from heart to the lunge and back. Deoxygenated blood of the body enters the right auricle, passes into right ventricle which pumps it into pulmonary arch. With the help of two separate pulmonary arteries the blood passes into the lungs. Here, it is oxygenated. Oxygenated blood comes back to left auricle of heart through four pulmonary veins, two from each lung.

Double circulation of blood in man

(ii) Systemic Circulation
It is the circulation of blood between heart and different parts of the body except lungs. Oxygenated blood received by left auricle passes into left ventricle. The left ventricle pumps it into aorta for supply to different body part including walls of the heart by means of arteries. Inside the organs the blood loses oxygen and nutrients. It picks up carbon dioxide and waste products. This deoxygenated blood is drained by veins and sent to the right auricle of heart.


Differences between Pulmonary circulation and Systemic Circulation


Blood Pressure 

Measurement of Blood Pressure

Blood pressure is the pressure exerted by the blood on the walls of vessels (arteries). The blood pressure is always expressed in form of two values called systolic pressure and diastolic pressure. The temporary rise in blood pressure during contration of the heart is called systolic pressure. The temporary fall in blood pressure during relaxation of the heart is called diastolic pressure. The blood pressure inside the arteries is much more in comparison to that inside veins.

In humans, the systolic pressure is about 120 mm of Hg whereas diastolic pressure is about 80 mm of Hg. The blood pressure under normal conditions is thus 120/80 mm of Hg. It varies from person to person and from time to time. It also varies with age.

A persistent increase in blood pressure is called hypertension or high blood pressure. It is caused by narrowing of arteries which results in increased resistance to blood flow. A lower systolic or diastolic pressure is known as hypotension (low blood pressure). Blood pressure is measured by using an instrument called sphygmomanometer.

  •  Pulse
    Due to beating of heart, the blood enters into the arteries forcefully due to which artery expands a little. Pulse is the expansion of an artery each time the blood enters into it. Each heartbeat produces one pulse. Thus, the pulse rate is similar to heartbeats/minute, i.e., the pulse rate of a person in 70-72 per minute while resting.  During exercise or any physical activity the pulse rate increases. Due to deeply-seated arteries, pulse cannot be felt everywhere except certain places like wrists, temple and neck where they are close to skin.


The Lymphatic System

Lymphatic system is another circulatory system in human body which transports materials through circulating fluid called lymph. The lymphatic system consists of the following parts.

(i) Lymph
(ii) Lymph capillaries
(iii) Lymph vessels
(iv) Lymph nodes (or glands)

(i) Lymph 
Lymph is a straw-coloured or light yellow coloured fluid connective tissue. It is translucent alkaline fluid present in the lymph vessels. It is formed of two parts, i.e., plasma and lymphocytes.

(ii) Lymph capillaries
Lymph drains into lymphatic capillaries (or lymph capillaries) which are thin-walled, highly permeable tubes that form a network in every organ except nervous system.

(iii) Lymph vessels
The lymphatic capillaries unite to form lymph vessels which are small vessels with numerous values. The lymph vessels are like veins but they have comparatively thin wall and numerous valves.

(iv) Lymph nodes
At places, lymph vessels bear swellings called lymph nodes or lymph glands. They are the site where lymphocytes accumulate and produce antibodies. As lymph nodes are rich in lymphocytes, they filter out germs and foreign particles from lymph. Lymph nodes are abundant in the regions of neck, armpit and groin. Tonsils and adenoides are masses of lymphatic tissues.

Lymphatic System in human

  • Functions of lymphatic system
    (i) The volume of blood decreases due to filtration of blood plasma from blood capillaries. Lymph collects this excess fluid and drains it back into the blood, thus, maintains the volume of blood.
    (ii) It acts as a connecting link between blood and the body cells and helps in exchange of materials between them.
    (iii) Lymph capillaries (lacteals) of intestinal villi help in absorption of fat and transport of the same to the blood.
    (iv) It protects the body by killing the germs with the help of lymphocytes. Thus, develops immunity of the body.
    (v) Various tissue secretions like hormones, macromolecules, plasma proteins are first added to lymph which passes it to the blood.
    (vi) It collects carbon dioxide, waste products and metabolites from tissues via tissue fluid and passes to blood.


Differences between blood and lymph


Transportation in Plants

Unlike animals, some materials pass in and out of plants through diffusion. For gaseous diffusion to occur, the plants possess stomata and lenticels. During the daytime the photosynthetic organs obtain carbon dioxide from outside by diffusion. The same is used for synthesis of food. Oxygen is released as a by-product. It passes out of me plant by diffusion. Simultaneously, a lot of water vapours pass out.
Other materials required for building plant body are obtained from soil, e.g., nitrogen, phosphorus, other minerals, water .They are sent to chlorophyll containing organs where food is manufactured. The manufactured food is passed to all parts for utilisation and storage. If the distance between the two is small, the materials reach there by diffusion.  If the distance is large, as in most plants, they have to be transported through a proper system of transportation. However, plants have a large proportion of dead cells. They do not move. Therefore, they have low energy needs. The transport systems are slow. Further, there are two independent pathways having conducting tubes.  One is xylem that moves water and minerals from soil to aerial parts. The other is phloem which carries food and hormones from the region of availability (e.g., leaves, storage organs) to the areas of utilisation (all living cells, growing points, storage organs, developing fruits).

  •  XYLEM It is a complex tissue which transports sap (water and minerals). Xylem has four types of cells.1. Xylem fibres
    2. Xylem parenchyma
    3. Tracheids
    4. Vessels
    Only xylem parenchyma are living cells. Others are dead, empty and lignified. Vessels and tracheids are called tracheary elements because they take part in transport of sap (water + minerals). Vessels are long multicellular tubes which are formed by end to end union of several cells in which cross walls have broken down. Tracheids are elongated cells with pointed ends. Both the tracheary elements have pits or other thin unlignified areas for element to element movement of water. Xylem parenchyma takes part in lateral flow of water.

Xylem and phloem elements


  • Phloem
    It is complex tissue which takes part in transport of food. Phloem has four types of cells —
    1. Sieve tubes
    2. Companion cells
    3. Phloem parenchyma
    4. Phloem fibres.
    Only phloem fibres are dead cells. Others are living cells. Sieve tubes are conducting channels of phloem. They are elongated multicellular tubular channels formed by end to end union of numerous sieve tube elements. The end walls or septa between adjacent sieve tube elements are bulged out and have pores. They are calied sieve plates. Sieve tube elements do not have a nucleus. Their functioning is controlled by adjacent nucleated companion cells.




(L. trans-across, spirate-to breathe) Transptiration is loss of water in vapour form from the exposed parts of a plant. Aerial parts of the  plants are always losing water through transpiration.


  • Functions of transpiration
    (i) Cooling
    Evaporation of water from the aerial parts results in lowering of their temperature which will otherwise rise due to exposure to sun.
    (ii) Concentration of Minerals
    Transpiration helps in increasing concentration of minerals present in rising water.
    (iii) Transport
    It helps in transport of water and minerals.

Transport of Water and Minerals


There is a continuous system of dead conducting channels (vessels and tracheids) from near the root tips to leaves and shoot tips. It transports water and minerals. The two are obtained from soil by the roots. The various steps involved in transport of water and minerals are as follows :

1. Mineral absorption
It occurs in the growing parts of the root. Both the surface or epiblema cells as well as root hairs take part in mineral absorption. Mineral absorption is an active process which involves expenditure of energy. Active absorption creates a higher concentration of minerals in the root as compared to soil solution.

2. Absorption of water
Root hair zone is the region of water absorption. The inside of the root has higher osmotic concentration than the soil solution. Root hairs are in contact with soil interspaces having capillary water. The root hairs pick up water which is ransferred inwardly due to still higher osmotic concentration. It reaches the cells surrounding the xylem channel. Salts accumulated in the basal part of xylem channel cause osmotic entry of water into xylem and form column of water. It also creates a positive pressure known as root pressure. This is, however, unable to push water to any great height. Root pressure is often absent, atleast during the day time. Its effect becomes important at night.

3. Ascent of sap
It is upward movement of absorbed water or sap from root to the top of the plant. The mechanism of ascent of sap was given by Dixon and Joly (1894). It is called transpiration pull or cohesion-tension theory of ascent of sap. The force for ascent of sap lies in the aerial parts. Here mesophyll and other cells lose water to outside air through transpiration which produces a negative pressure.

diagrammatic representation of ascent of sap

Development of Negative Pressure
Loss of water by mesophyll cells increases their suction pressure. They withdraw water from the xylem channels. As there are billions of mesophyll cells withdrawing water from xylem channels, water column present in the xylem comes under tension or negative pressure.  Its value is 10-20 atmospheres. Water column does not break due to two forces:

(a) Cohesion force among the water molecules.
(b) Adhesion force between water molecules and wall of the xylem channels.

Rise of Water
Tension or negative pressure of the water column results in its upward pull just as cold drink is sucked with the help of a straw pire. Since it develops due to transpiration, it is called transpiration pull.


Translocation or Transport of Food and Other Substances
Food materials are translocated from the region of their manufacture or storage to the region of their utilisation.

Transpiration or evaporation of water from aerial
surface causing absorption and ascent of sap


The region of supply of food is called source while the area of utilisation is called sink The direction of translocation can be downward, upward or both. The food manufactured by leaves passes into the storage region and other sinks in the downward direction as well as towards growing points and developing fruits in the upward direction. In spring season, the stored food present in root and stem is translocated upwardly to buds for their growth.
The translocating nutrients consist of soluble carbohydrates (mostly sucrose), amino acids, organic acids, hormones and other organic solutes.
Translocation occurs through phloem. The channels of transport are sieve tubes (sieve cells in non-flowering plants). Sieve tubes are specialised for this purpose. They are devoid of nuclei and internal membranes. The cytoplasm of one tube cell is continuous with that of adjacent sieve tube cells through sieve plates. The translocation activity of sieve tubes is controlled by companion cells which lie adjacent to sieve tube cells.


Mechanism of Pholem Transport

Translocation of organic solutes as per mass flow hypostesis

The transport of organic solutes or nutrients occurs through a physical process but entry and exit of nutrients from the phloem can occur only through an active process which utilises energy from ATP. With the help of energy, food materials pass into the phloem from the region of manufacture or srorage (source end) . After entering the sieve tubes the nutrients being in high concentration, exert an osmotic pressure which causes entry of water into this region. A high turgor pressure develops. It forces the nutrients to pass towards the regions which have low turgor pressure. The movement is like a mass flow (Munch 1930). Low turgor pressure is maintained in the area where being withdrawn for consumption (growing points) or storage (root, stem, fruits) by an active process.




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