Sharing is caring!


Today we are going to discuss about plant and animal circulation in details.  So let’s start with the definition.

Definition:  The mode of transportation of various substances inside a multicellular living body via a liquid is known as circulation.

Objective of circulation:

  1. The digested or prepared food, oxygen, hormones etc are essentially needed by the various cells of a living body. It is through the process of circulation that these materials are transported inside the body.
  2. Nitrogenous and non-nitrogenous waste products (urea, carbondioxide, uric acid) are harmful metabolic byproducts. Circulation plays the key role in their elimination or transportation from the cells to the excretory organs.
  3. It maintains different types of homeostasis inside the animal body eg. temperature balance, water balance, acid-base balance.



It is the physical phenomenon in which, when liquids of different concentration are separated by a semipermeable membrane the solvents molecules move from the area of higher molecular concentration to the lower molecular concentration of the solvent via the membrane.

Osmosis in plants:  The capillary water that remains trapped among the soil particle finds entry into the root hairs by the process of osmosis.  A root hair is a single cell having the semipermeable cell membrane all around it.  There are two liquids having separated by this membrane.  One is the cell sap present within the root hair cells and is denser in composition or carries less water concentration than the other liquid the capillary water, which has more concentration of water or is diluted in composition to the former.  Hence osmosis takes place driving capillary water into the root hairs.  Minerals enter the root hair cells by the process of diffusion.


Plant circulation

It is the circulation of water inside a plant body.

This is achieved in an upward direction from the soil to the leaves via the xylem vessels.

 Ascent of Sap:  It is the process by which the water together with mineral salts is lifted up from the root to the leaves via the xylem vessels against the gravitational pull.  In some tall trees the ascent of sap is a rigorous process and the force needed for the purpose is realized from the following factors.


a)Cell to cell osmosis:  This is the process by which water or the sap absorbed by the root hair is led forward through the cells of the cortex towards the xylem vessels.  As water enters the epiblema cells, by the process of osmosis, the concentration of water in such a cell is more that that in the next cortical cell.  The water as a result leaves the epiblema cells and enters the cortical cells.  The process is repeated in all the cortical cells, driving all the water towards the xylem vessels. 

b)Root pressure:  The alternate turgidity and flaccidity of the cortical cells exert a good amount of pressure on the water circulating from the epiblema to xylem vessels.  This pressure generated during the process of cell to cell osmosis is known as root pressure.  This pressure pushes water up through the xylem vessels to a considerable height and the ascent of the water is also assisted by the capillary nature of the xylem vessel.  Hence the root pressure is the pressure exerted upon the circulating (materials water) by the cortical cells during the process of cell to cell osmosis is termed as root pressure.

c) Cohesive and adhesive forces: According to Dixon and Jolly the cohesive force occurring among the molecular water flowing through the xylem vessels, and the adhesive force between the water molecules and the cellulose molecules present on the wall of the xylem vessels support a continuous and uninterrupted water column inside the vessel extending from the root to the leaf.

d) Transpiration pull: A lot of water goes out of the leaf surface through evaporation by the process of transpiration.  This loss of water from the leaves creates a partial vacuum on the upper part of the water column supported inside the xylem vessels.  That initiates a pulling pressure on the water column lifting water up.  This is known as transpiration pull.

e) Capillary force:  It is the intermolecular forces between the liquid and surrounding solid surfaces which helps the liquid to flow in narrow spaces without any assistance


Conduction of prepared food:

This prepared food is transported through the medium of water, which also conducts other essential materials like hormones etc.  This way of conduction is carried out by the phloem.  The sieve tubes of the phloem play the principal role in this conduction.  The process is assisted by companion cells.  Generally, the mode of circulation through this path is directed in the downward direction.  So the liquid moves by its own inherent property to flow towards the pull of gravity.




1.       Composed of tracheid, trachea, xylem parenchyma and phloem fibre (wood).

2.       Except the xylem parenchyma, all the tissues are dead in nature.

3.       Xylem vessels run as continuous capillary tubes with highly lignified wall.

4.       Helps in the ascent of sap.

1.Composed of sieve tube, companion cells, phloem parenchyma and phloem fibre (bast).

2. Except the phloem fibre, all the tissues are living in nature.

3.Sieve tubes are interrupted by sieve plates and the wall made up of cellulose.

4.Helps in the translocation of prepared food to different parts of the plant body.


Circulation in animals

Circulation in animals is conducted through the media- the water and the blood, in the former the system is called water vascular system and in the latter it is called blood vascular system.

Water vascular system:  The materials needed to be transported from one place to another are conducted in this system through the medium of water.  In a hydra, the gastrovascular cavity is the main channel though which this system operates.  In echinodermata (star fish, sea urchin etc) there is a well developed canal system through which the water vascular system operates.

Blood vascular system:  Here the circulatory medium is the blood.  The components or units of this system are blood, heart, arteries, veins and capillaries.


The blood circulating system is of two types viz.

  1. Open circulation      and       2. Closed circulating.Open circulation: In this system the blood vessels open inside the body cavity, which thus comes in direct contact with the blood.  Such a type of body cavity is known as haemocoel.  The blood flowing through the haemocoel is also known as haemolymph. The blood coming through those open vessels is ultimately deposited inside the lacunae or sinuses scattered inside the haemocoel.  The blood from these spaces after proper purification in the respiratory organ is brought back to the heart.  Prawn, insects.Closed circulation: In this system blood flows through closed blood vessels through out the body as a result the blood never comes in direct contact with the body cavity.  Such a body cavity is called coelom.  In this system the heart is the central pumping station, which pumps out blood in to arteries, each of which breaks down into divergent capillaries.  The divergent capillaries of the arterioles then converge to form a venule.  A few such venules unite to form a vein that brings blood back to the heart.  all vertebrate, invertebrates-earthworm.


How does human blood differ from that of a) earthworm b) prawn, c) cockroach d) toad

  1. In human, blood respiratory pigment haemoglobin is present in the RBC but in earthworm it is present in the blood plasma.
  2. In human, the respiratory pigment is haemoglobin but in case of prawn the respiratory pigment is haemocyanin. The blood is colourless also in case of prawn.
  3. In human the respiratory pigment is haemoglobin but in case of cockroach the respiratory pigement is absent all together.
  4. In human the respiratory pigment haemoglobin is present inside the RBC but they are non-nucleated. In toad’s blood the RBC is nucleated.  The human RBC is biconcave but toad’s RBC is biconvex.



Blood is a fluid connective tissue that acts as a vehicle to transport various substances inside the body of an animal.

Composition of blood:  As it is a connective tissue it is made up of a liquid matrix, the blood plasma and the suspended cell- blood corpuscles.  Plasma and corpuscles constitute 55% and 45% respectively of the blood.

Blood plasma:  It is a straw yellow coloured, slightly alkaline liquid carrying about 90% of water in it.  The rest is composed of various organic and inorganic salts and special mention should be made about different types of plasma proteins.

Functions:  It bears the blood cells and mainly maintains the water balance of the body.

Blood corpuscles:

There are three main types of corpuscles found in blood.  They are erythrocytes (RBC), b) leucocytes (WBC) and thrombocytes (platelets).


They are present in most abundant number in comparison to other corpuscles.  In human blood about 4.5 – 5 million/c.c. of RBCs are present.  In man erythrocytes are biconcave in appearance and devoid of any nucleus in matured condition.  In toad, RBCs are biconvex and nucleated.

Site of formation:  In human RBC is produced within red bone marrow.

Destruction:  In human RBC is destroyed in spleen and liver.

Life span:  An average span of life of RBC is 120 days RBC carries respiratory pigment in it. Normally, they are of two types of pigments found in the animals, which are in the following.

  1. Haemocyanin: It is composed of copper and protein and is found in the blood of prawn.  Normally, haemocyanin is colourless, but when it is oxygenated it appears to be pale bluish in colour.
  2. Haemoglobin: It is composed of iron and protein and is present in RBC of the vertebrate blood.   Oxyhaemoglobin in red in colour.  In earthworm haemoglobin is found in plasma instead of RBC, hence its plasma is red in colour.


Function of RBC

  1. The haemoglobin of RBC transports the respiratory gases in the animal body.
  2. Haemoglobin acts as a buffer to maintain the acid-base balance in the body.

In normal healthy adult human being about 14 gm of haemoglobin is present per 100 ml of blood.  Deficiency of haemoglobin content in the blood is caused due to the deficiency of iron result in the disease called anaemia.


Leucocytes:  These are the blood cells with irregular shape and are always nucleated.  About 8000 WBC are found per cubic mm of blood.  They are of following types:


Granulocytes (having grains in cytoplasm)                  Agranulocytes (without grains in cytoplasm)

  1. Eosinophil (secretes histamin)                                              1.  Lymphocytes (secretes anitbody)
  2. Basophil (secretes heparin)                                                    2.  Monocytes (does phagocytosis)
  3. Neutrophil (Does phagocytosis)


Life span:  The average life span varies between 8-15 days.

Formation:  Produced in the bone marrow and lymph nodes.


  1. It secretes anti-allergic substances like histamin (eosinophil).
  2. It secretes anti-coagulant like substance like heparin (basophil).
  3. It produces antibody to build up immunity in the body (lymphocytes).
  4. It prevents the body from different infections by destroying pathogens through the process of phagocytosis (monocytes and neutrophil).



They are non-nucleated cell-like structure about 3 lac/c.c. of blood are present.

Life span:  Its average life span is 2-3 days.

Function:  It is responsible for the process of blood clotting, preventing a person from bleeding to death.

Blood Clotting:

It is a process by which a thrombus or a clot made up of a fine mesh is formed on a cut surface to arrest further loss of blood.

Process:  Thrombocyte or platelets while coming out through the cut surface with the blood get ruptured with the contact to the rough surface of the cut area.  As they rupture an enzyme called thrombokinase/thromboplastin is liberated in the blood.  This enzyme then converts the plasma protein prothrombin into thrombin then reacts with another plasma protein the fibrinogen to convert it into fibrin, which is made up of very fine delicate threads.  These threads then form a mesh on the cut surface preventing any further blood loss.



Thrombocytes                           thrombokinase

Prothrombin + Ca+ +                                                 thrombin

Fibrinogen                                                                     Fibrin




The blood when flowing through the blood vessel normally does not clot because of the presence of an anti-coagulant called heparin in the blood.

Under some abnormal condition the thrombus may form inside the blood vessels, which in acute cases results in the thrombosis.  Eg. coronary thrombosis.


There is a disease in man in which the blood does not get clot.  The disease is known as haemophilia.  It is a hereditary disease.

The whole process of blood clotting is controlled by vitamin K, the deficiency of which cause defective blood clotting.

When the blood clots, at a first part of the blood plasma tickles out through the clot.  The blood plasma devoid of any fibrinogen in it is called the blood serum.  Sodium citrate is an anticoagulant used for the storing blood in the blood banks.


Blood groups

Blood is classified into different groups to determine the compatibility between the blood groups of the donor and the recipient.  So as to prevent agglutination of blood in the recipient’s body.

Landsteiner classified blood in the ABO system.  In this system of classification blood is grouped into four classes depending on the presence or absence of the agglutinogen in the blood.

In the blood there are two types of agglutinogen (antigen), agglutinogen A and agglutinogen B.  There are also two types of agglutinin (antibody) in the blood, agglutinin a and agglutinin b results in the process of agglutination (clumping) of blood.  Thus according to the ABO system.  The composition of blood in different groups can be tabulated in the following manner.


Blood group



A A b
B B a
O x ab


During the blood transfusion donor’s agglutinogen and recipient’s agglutinin are taken in consideration.


Why blood group O is considered to be a universal donor?

While blood transfusion donor’s agglutinogen and recipient’s agglutinin are taken into consideration. Thus in case of people belonging to blood group ‘O’ having no agglutinogen in his blood and therefore he can donate blood to anybody belonging to any group.  That is why blood group ‘O’ is considered to be a universal donor.

Why blood group AB is considered to be a universal recipient?
While blood transfusion donor’s agglutinogen and recipient’s agglutinin are taken into consideration. People having blood group AB carrying no agglutinin in their blood, so he can receive blood from any person of any group.  That is why blood group AB is considered as universal recipient.


Blood pressure:  It is measured by sphygmomanometer.  It is the lateral pressure exerted by the blood while flowing through the blood vessels.  The cause of this pressure is the contraction (systole) and relaxation (diastole) of the heart.

Systolic pressure:  It is the maximum lateral pressure of the flowing blood during systole of the heart.  In normal healthy adult the systolic pressure = 110-130 mm of Hg.

(average = 120 mm Hg.)

Diastolic pressure:  It is the minimum pressure of the flowing blood during diastole of the heart.  In normal adult the DP is 70 – 80 mm of Hg. (average = 80 mm of Hg.)


Function of blood:

  • Transport:
  1. It transports respiratory gases like carbondioxide and oxygen.
  2. Transport of nutrients from intestine to the tissue.
  3. Transport of waste products from tissue to the kidney.
  4. It acts as a transport medium for hormone, vitamin, and enzymes.
  • The WBC of the blood defends the body against various infections by destroying pathogens through the process of phagocytosis.
  • The WBC builds up immunity to combat various diseases through the process of antibody formation.
  • Thrombocytes protect a person from bleeding to death through the process of blood clotting.
  • Blood maintains body temperature.
  • Blood maintains the water balance and acid-base balance.



This is a special type of liquid connective tissue that flows through the lymph vessels.

A part of the blood plasma while flowing through the arteriole capillaries leaks out and comes in the intercellular spaces where it gets mixed up with the tissue fluid, to form what is called lymph.  It flows through the lymph vessels, which are very delicate vessels ramifying through out the body.


  1. It acts as a ‘go-between’ between the blood and the cells in transporting essential and excretory materials, and thus supplements the functions of the blood.
  2. It acts as the medium of circulation of the digested fat from the lacteals to all the living cells.
  3. It defends the body against various infections by forming the lymphocytes.



Heart is the central pumping station of blood in the blood vascular system.  According to the nature of flow of blood through the heart it can be divided into two types.

  • Single circuit heart: Through this heart blood flows in a unidirectional manner.  It is composed of two chambers.  Blood is received form the body into the auricle and is pumped out into the body through the ventricle.  Only deoxygenated blood flows through it.  The heart of the fish is single circuit heart, and as only deoxygenated blood flows through a fish’s heart, so it is known as venous heart.  This type of circulation is called single circuit circulation.


  1. Double circuit heart: Here blood flows through two different circuits.  In one circuit, called pulmonary circuit, only deoxygenated blood is sent to the lungs from the right ventricle via the pulmonary artery and oxygenated blood is received by the left auricle through the pulmonary veins.  This circuit is called the small circuit. In another circuit called the systemic circuit, the deoxygenated blood is received by the right auricle and the oxygenated blood is pumped to the body from the left ventricle.  This circuit is called the long circuit.

Thus through this type of heart both oxygenated and deoxygenated blood flow. Eg. man.  This type of circulation is also called double circulation.


Artery:  Artery is the type of blood vessel that carries blood away from the heart.  It generally carries oxygenate blood (exception pulmonary artery).  Its wall is composed of three layers and is thicker that the wall of a vein.  It does not carry any valves in it.  Blood flows through it with alternate jerks.  Producing then pulse beat.

Three layers are a) Tunica intima, b) Tunical media and c) Tunica adventitia.

Functions:  It helps to transport essential materials like oxygen, food, hormones etc to different parts of the body.


Vein:  A vein is a blood vessel, which carries blood towards the heart.  It generally carries deoxygenated blood (exception-pulmonary vein).  Its wall is thinner than an artery.  It has rows of valves placed inside the lumen.  Blood does not provide any pulsatile movement while flowing through it.

Veins are of two types  a) Systemic veins and b) Portal vein

  1. Systemic veins: This type of vein capillarises once only ie. it begins with capillaries and ends in the heart.  It carries blood from an organ directly to the heart.
  2. Portal veins: This type of vein capillarises twice ie. it begins with capillaries in an organ and ends in capillaries in an intermediate organ (kidney or liver).  This vein cannot return blood directly to the heart.


Portal system:  It is a system that is composed of portal vein and transport blood from an organ to an intermediate organ.  According to the nature of intermediate organ the portal system is divided into two types a) hepatic portal system and b) renal portal system.

  1. The hepatic portal system brings digested food from the intestine to the liver, where only a regulated amount of glucose, amino acids etc is allowed to enter the blood flow it is present in man and toad.
  2. The renal portal system the excretory materials are isolated by the kidney from the blood brought from hind limbs through the renal portal system. It is only present in the toad but absent in human.


Human heart

Location:  It is situated inside the thoracic cavity between the two lungs, tilted towards the left lung.

Structure:  It remains externally covered by the pericardium.  The heart is tetra chambered with two auricles and two ventricles.  The ventricular wall is thicker and more muscular that the auricle wall.

  1. Right auricle / Right atrium:

The precaval and postcaval veins (anterior venacava and the posterior venacava) are carrying blood respectively from the anterior and posterior part of the body open inside the chamber.  The right auricle opens into the right ventricle through the auriculoventricular opening, which is guarded by tricuspid valve.  It allows blood to flow from the right auricle to the right ventricle and arrests the backflow.

  1. Right ventricle:

It receives the deoxygenated blood from the right auricle.  It opens to a blood vessel called the pulmonary artery that goes to the lungs.  The opening of the pulmonary artery carries semilunar valves, which allow blood to flow from the ventricle to the artery arrests the backflow of the blood.

  1. Left auricle or left atrium:

Four pulmonary veins carrying oxygenated blood from the lungs open into this chamber.  It opens into the left ventricle through the auriculoventricular opening that remains guarded by the Bicuspid valve / mitral valve.  This valve opens into the ventricle allowing blood to flow from the auricle to the ventricle but prevents the backflow.

  1. Left ventricle:

It receives oxygenated blood from the left auricle and drains the same into the aorta that originates from this chamber.  The opening of the aorta is guarded by the semilunar valve.



The auricles and the ventricles undergo alternately the process of systole and diastole.  During the auricular systole deoxygenated blood is led from the right auricle to the right ventricle forcing open the tricuspid valves.  The oxygenated blood at the same time is led from the left auricle to the left ventricle forcing open the bicuspid valves.  With the ventricular systole, the deoxygenated blood is pumped out from the right ventricle to the pulmonary artery forcing open the semilunar valves.  The oxygenated flood is simultaneously pumped out from the left ventricle into the aorta, then throughout the body by forcing open the semilunar valves.

Right from the time of the auricular systole up to the ventricular systole – the time period is known as a heart beat.  In a normal healthy adult man the heart beats about 72 times per minute.  This rhythm of heart is known as rhythmicity of the heart.

It is maintained by special nodal muscles of the heart.  The stimulus necessary for the heart is provided by SA node called the pacemaker of the heart.

At the onset of ventricular systole the tricuspid and bicuspid valve close with a sudden jerk and that produces the first heart sound called LUBB.  With the ventricular diastole, the semilunar valves close producing the second heart sound, called DUPP.     

If you have enjoyed reading this post I would be very grateful if you would help it to spread by sharing on social media like Facebook, Twitter, Google+, by clicking on the share buttons below.If you have any questions or comments, feel free to ask them in the comment section below.

See you in my next blog post.


Also Read on Science Reckoner:


Sharing is caring!

The following two tabs change content below.
Hi viewers My name is Partha Pratim Goswami, (PpG) I am a teacher by profession. I have been teaching biology, chemistry and physics, sometimes mathematics also for last sixteen years. I would like to share my entire experience with all the viewers across the world through YouTube, which I think is an amazing platform to share all my experiences.

Latest posts by Partha Pratim Goswami (see all)

Leave a Reply