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Transport System In Plants And Animals


The parts of the body can stay alive with a regular supply of oxygen and nutrients. The distribution of oxygen, nutrients and hormones to the different body parts is the function of the body’s internal transport system.

Transport in Plants

The transporting media in plants are the xylem and phloem tissues.

  1. Ascent of sap: The upward transport of water and minerals is called ascent of sap.
  • The tissue connected with transport of water in plants is the xylem, the most advanced conducting elements with angiosperms.
  • By keeping a freshly cut transparent plant-like balsam in a coloured (eosin) solution, it is possible to demonstrate the ascent of sap through the xylem.
  • Plants have no pumping organ like the heart in animals, to drive the sap upwards. Nevertheless, sap rises in tall trees hundreds of feet high by cohesion of water and transpiration pull.
  • Root pressure may contribute to ascent of sap in some herbaceous plants but cannot be the main mechanism of ascent of sap.
  1. Organic translocation: The transportation of food from the leaves to the stem and then to other parts of the plant and also to storage parts through phloem is called organic translocation.
  • Phloem consists of sieve tubes and companion cells. Carbohydrates synthesised in the leaves are transported through sieve tubes in the form of sucrose.
  1. Absorption in plants: Roots and leaves are the main absorbing organs of plants. Roots absorb water and minerals from the soil, while leaves take in oxygen and carbon dioxide from the atmosphere.
    Most land plants get their supply of water from the soil, while some epiphytes absorb it from the atmosphere. Root hairs of an individual root absorb water when the concentration of solutes in the cell sap is high.

A root has three primary functions:

  • To fix the plant to the soil
  • To absorb water and minerals from the soil
  • To conduct the absorbed substances through its tissues to the upper parts of the plant

Adaptations for Absorption

  • The root epidermis just behind the root tips is provided with a large number of unicellular root hairs through which water enters the root.
  • The thin, freely permeable cell wall of the root hair allows free movement of minerals in and out of the cells by the process of diffusion.
  • The semipermeable cell membrane permits entry of water and restricts the entry of salts by the process of osmosis.
  • The concentration of water in the cell sap of the root hair is lower than that of the surrounding soil. This makes absorption of water by osmosis.
  • Active transport: Root hairs absorb not only water but also nutrients from the soil. Dissolved minerals are absorbed by the root hair using energy (ATP), through a living cell membrane against the direction of flow, i.e. from lower concentration (minerals) to higher concentration (cell sap).

Transport in Unicellular Organisms

In organisms with a body composed of single cell, substances can be transported within the cell by cytoplasmic movement. Diffusion and active transport can carry nutrients, gases and wastes in and out of the cells in lower forms of animals.

Transport in Multicellular Organisms

Large animals require more elaborate system to carry substances throughout the body and out of it. This pick-up and delivery system is called transport or circulatory system. There are two major types of circulatory systems, namely open and closed.

  • In open circulatory system, the blood called haemolymph bathes the tissue. Most often, a muscular tube functions as the heart. It pumps the haemolymph through a network of channels and spaces. This type of circulatory system is seen in arthropods and molluscs.
  • In closed circulatory system, the blood moves through a system of tubes or vessels. In this system, blood is pumped by the heart and is brought back to the heart. This type of circulation is seen in annelids and all vertebrates.

Circulatory System in Humans


Blood Blood is a red-coloured, thick fluid tissue flowing in tubes called blood vessels. An average adult person contains 5–6 L of blood by volume in his body and about 8–10% of the body mass. The blood is slightly alkaline with a pH of 7.3–7.45.

  1. Composition of blood: It consists of two parts, namely plasma and formed elements.
  • Plasma is a complex fluid made up of 90–92 % water and a variety of proteins, sugars, gases, hormones, mineral and wastes dissolved in it. More volume (about 55 percent) of blood is formed of plasma.
  • Formed elements include erythrocytes (RBC), leucocytes (WBC) and blood platelets.
  1. RBC (erythrocytes): The mature red blood cells are circular or disc-shaped and without nucleus. The main function of RBC is to transport O2 and CO2 in combination with the iron containing pigment haemoglobin which acts as the oxygen carrier.
    The natural haemoglobin content of an adult man is about 14.5 g/100 mL of blood. Around 5,000,000 RBCs occur per cubic millimetre of blood in a normal healthy man. Both erythrocytes and leucocytes are formed in the bone marrow. The life span of human RBC is 120 days.
    The number of RBC increases when one lives at higher altitude because of less oxygen content in the atmosphere. Abnormal increase in the total RBC count is referred to as polycythemia.
  2. WBC (leucocytes): The white blood cells are larger with distinct nucleus. These are much less in number, about 5000–8000 WBC per cubic millimetre of blood.
    Types of WBC: WBCs are classified into two types, namely agranulocytes and granulocytes.
  • Agranulocytes have no granules in the cytoplasm and are produced in the bone marrow. These are of two kinds: (i) lymphocytes, having round nucleus and (ii) monocytes, having kidney-shaped nucleus.
  • Granulocytes have larger granules in the cytoplasm and have lobed nucleus. These are of three types: (i) neutrophils, having more than two lobes of the nucleus, (ii) basophils, having bilobed or irregular nucleus and (iii) eosinophils, having bilobed nucleus.
    WBCs help in developing immunity (resistance against diseases) in the body. These protect the body from disease causing germs by either devouring them or by producing antibodies against the germs. Excessive production of WBC causes leukaemia or blood cancer.
  1. Platelets (thrombocytes): Platelets are smallest in size and are about 2–3 lakhs per cubic millimetre of blood. Platelets help in the clotting of blood.
  2. Functions of the blood:
  • It transports oxygen, nutrients, hormones and vitamins to all parts of the body
  • It brings waste products to organs such as kidney and lungs from where they are passed out of the body
  • It maintains water balance in the tissues
  • It regulates body temperature by distributing heat equally in the different parts of the body
  • It protects against diseases by destroying the disease causing germs
  • It prevents excessive bleeding by blood clotting

V.S. of Human Heart


Blood Vessels Based on the size, structure and function, three types of blood vessels can be distinguished. They are arteries, capillaries and veins.

  • Arteries: Arteries are efferent vessels which transport blood away from the heart. Arteries which are nearer to heart are large, strong and thick-walled. They branch into smaller vessels called arterioles which in turn branch into capillaries.
  • Capillaries: Capillaries are very narrow, thin-walled microscopic tubes. Through the thin walls of the capillaries exchange of gases, nutrients and wastes occur between the blood and body cells.
  • Veins: Veins are afferent vessels, which take the blood to the heart. Blood that leaves the capillaries flows into small vessels called venules which join to form larger veins. They increase in size as they approach the heart.

Heart: The Pumping Organ The study of heart and its diseases is called cardiology.

Heart is a muscular organ. It is situated between the two lungs and above the diaphragm. Heart is protected by a double-walled membrane called pericardium. It contains lubricating pericardial fluid which reduces friction during heart beat and protects it from mechanical injuries (Figure 6.4).

  1. Chambers of the heart: Heart of a man consists of four chambers.
  • The upper or superior chambers are the right and left atria or auricles and lower or inferior chambers called right and left ventricles.
  • Interatrial septum separates right and left atria whereas interventricular septum separates right and left ventricles.
  • The left ventricle of the heart has the thickest muscular wall. Chordae tendinae are found in the ventricle of heart. The right ventricle pumps blood only up to the lungs for oxygenation. But the left ventricle pumps it up to the farthest points in the body, such as up to the toes in the feet and up to the brain against gravity, and hence its walls are thicker.
  • The auricles have thinner walls because their major function is to receive blood from the body and pump it into the very next ventricles.
  1. Blood vessels entering the heart: The right auricle receives two large vessels, namely anterior (superior) vena cava and posterior (inferior) vena cava.
  • Anterior vena cava brings deoxygenated blood from the anterior or upper part of the body including head, chest and arms.
  • Posterior vena cava brings blood from the posterior or the lower region of the body including abdomen and lungs.
  • The pulmonary veins bring oxygenated blood from the lungs to the left auricle.
  1. Blood vessels leaving the heart: Arising from the ventricles are two large blood vessels.
  • The pulmonary artery arises from the right ventricle and carries deoxygenated blood to the lungs for oxygenation.
  • The aorta arises from the left ventricle and carries oxygenated blood to supply it to all parts of the body.
  1. Valves of the heart: Valves are muscular flaps which prevent the blood which has once passed through it, to flow back through it. Two types of heart valves are distinguished.
  • The atrio-ventricular valves: These valves separate the atria from the ventricles and allow blood to flow from the atria to the ventricles.

Examples: Tricuspid valve and bicuspid valve (mitral).

Semilunar valves: These valves have three half-moon-shaped folds and are located in the arteries leaving the heart. They prevent the blood from flowing back into the heart when the ventricles relax. Examples include pulmonary semilunar valve and aortic semilunar valve.

Circulation of Blood in the Heart 
The heart is made up of strong cardiac muscles. The chambers of the heart by their rhythmic contraction and relaxation create pressure required to maintain the flow of blood throughout the body.

Circulation of blood in the heart starts with the contraction of the two auricles. The ventricles at this time are relaxing and are empty. Therefore, the blood from the auricles passes into the ventricles easily.

When the ventricles contract, the auricles relax. The blood from the ventricles under pressure tends to return to the auricles, but the flaps of the two cuspid valves get tightened and puffed up, thus closing the passage and preventing the return of blood. Chordae tendinae hold the flaps of the valves in a position and prevent their overturning into the auricles. The only course left for the ventricular blood is to enter the pulmonary artery from the right ventricle and the aorta from the left ventricle.

When ventricles dilate, the blood from the pulmonary artery and the aorta tends to return, and the blood fills the pocket of the valves and closes the passage.

  1. Heart beat: The repeated contraction and relaxation of the chambers of the heart is called cardiac cycle. One cardiac cycle is one heart beat which lasts on an average 0.8 seconds.
  • The contraction is called systole and the relaxation is called diastole.
  • Diastole brings about the entry of blood into heart. The diastolic pressure in a healthy person is 80 mm of Hg.
  • Systole brings about the exit of blood from the ventricles. The systolic pressure in a healthy person is 120 mm of Hg.
  • Blood enters the heart because of the auricular diastole.
  • In a normal person at rest, the cardiac output, i.e. the amount of blood pumped per minute by the left ventricle, is approximately 5 L.
  • Pulse beat is measured in the artery.
  • The pulse rate is the same as the heart beat rate and it is 72 per minute in a healthy man.
  • The typical lub-dub sounds heard in heart beat are due to the closure of bicuspid–tricuspid valves followed by semilunar valves.
  • The heart murmur indicates a defective heart valve.
  • Blood pressure is the pressure of blood exerted on the walls of arteries.
  • The normal blood pressure for the adults is 100–140 mm of Hg (systolic) and 60–80 mm of Hg (diastolic).
  • A rise in blood pressure above 140/90 is known as hypertension.
  • The instrument used to measure blood pressure is called sphygmomanometer.
  1. Blood circulation: A circulatory system in which blood flows through two separate circuits is called double circulation. They are (i) pulmonary circulation and (2) systemic circulation.
  • Pulmonary circulation pertains to the lungs. It starts in the pulmonary artery arising from the right ventricle which soon divides into two branches that enter the respective lungs. Pulmonary veins collect the oxygenated blood from the lungs and carry it back to the left auricle of the heart.
  • The systemic circulation pertains to the major circulation of the body. It starts with the aorta that arises from the dorsal aorta. The aorta sends the arteries to various body parts and their tissues. From there, the blood is collected by veins and sent back into the heart. Sino atrial node (SAN) is called the pacemaker of heart because beating of the heart starts from here.
  1. Portal system:
  • A portal system is one in which a vein breaks in an organ into capillaries and restart by their union as a new vein in the same organ.
  • The hepatic portal system runs from the digestive system to the liver, and the renal portal system runs from the limbs to the kidney.
  • Circulatory system of rabbit differs from that of a frog, in that there is no renal portal system in rabbit.
Blood Groups In human beings, four different types of blood groups are found, namely A, B, AB and O. They may be Rh+ or Rh-.
  • Blood groups in man and Rh factor were discovered by Landsteiner. Rh factor is named after rhesus monkey.
  • Blood groups are inherited from parents.
  • Blood group ‘O’ can be given to all groups because the RBC of ‘O’ blood group does not have any antigens. Therefore, ‘O’ group individuals are called universal donors.
  • Person having AB group can receive blood from A, B, AB and O. Therefore, AB group individuals are called universal recipients.
  • Marriage between Rh+ boy and Rh- girl is biologically incompatible and results in erythroblastosis foetalis.

Blood Clotting Bleeding occurs when the wall of a blood vessel breaks or is injured.

  • The blood clotting mechanism involves many substances such as blood platelets, prothrombin, thromboplastin, Ca++, fibrinogen, vitamin K, etc.
  • Thromboplastin for blood clotting is secreted by platelets. In vertebrates, thrombin occurs in the blood and is important for clotting.
  • In human, the prothrombin required for blood clotting is produced inside the liver.
  • Blood clot inside a blood vessel is called thrombus.
  • Blood is stored in spleen.
  • Heparin is an anticoagulant in the blood.
  • The requirement of dietary iron is more in females than males because they lose iron during menstruation.

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