Tranportation in Plants and Animals

"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."

1.0Introduction

All living organisms need food and water for their survival. Green plants need carbon dioxide, water and sunlight. These substances need to be carried or transported to various parts of the body. In addition, waste materials produced within the body also need to be removed. In plants, there is a system (vascular system) of independent channels, while in animals, transportation is brought about by the circulatory system.

2.0Transportation in animals

In unicellular animals such as Amoeba and Paramecium, no special transport system is required. Every part of the organism gets nutrients and oxygen directly through cell diffusion. In multicellular organisms, the transportation is done by a specialized system known as the circulatory system.

3.0Human circulatory system

Circulatory system is a transport system moving substances throughout our body with the help of blood. It consists of the heart, arteries, veins and capillaries. It forms a broad network which carries blood to all parts of the body. Blood is the medium for transport of all the necessary materials to different parts of the body.

• The English physician, William Harvey (A.D.1578-1657), discovered the circulation of blood.
• The current opinion in those days was that blood oscillates in the vessels of the body. For his views, Harvey was ridiculed and was called "circulator". He lost most of his patients. However, before he died, Harvey's idea about circulation was generally accepted as a biological fact.
  

In an adult human body, there is about 5.5 litres of blood, forming the most amazing transportation system in the body. Humans have a very well-developed and efficient circulatory system. It consists of - (a) Blood (b) Blood vessels (c) Heart

Blood

Blood is a bright red-coloured fluid flowing inside blood vessels. It consists of plasma which is the liquid part of blood and the three types of cells or corpuscles : (i) red blood cells (RBCs), (ii) white blood cells (WBCs), and (iii) platelets.

(i) Red blood cells (Erythrocytes): Red blood cells (RBC) are disc shaped cells with a depression in the centre and contain a red pigment called haemoglobin. The presence of haemoglobin makes blood appear red. Haemoglobin binds with oxygen and transports it to all the parts of the body and ultimately to all the cells. It will be difficult to provide oxygen efficiently to all the cells of the body without haemoglobin.

(ii) White blood cells (Leucocytes) : White blood cells (WBC) are colourless cells and do not have a definite shape. Their function is to protect the body against germs or infection.

(iii) Platelets (Thrombocytes) : Blood platelets are colourless, small, irregularly shaped, and much smaller than the RBCs. The platelets help in clotting of blood, whenever there is a blood flow due to some injury.

Functions of blood

(i) It transports substances like digested food from the small intestine to the other parts of the body. (ii) It carries oxygen from the lungs to the cells of the body. (iii) It also transports waste for removal from the body. (iv) Protect the body against germs or infection. (v) It regulates the body temperature.

Blood Vessels

Blood flows through our body in a complex system of tubes called blood vessels. There are three different types of blood vessels in the body. (i) Arteries: Arteries generally carry oxygen-rich blood from the heart to all parts of the body. Since the blood flow is rapid and at a high pressure, the arteries have thick elastic walls and are deep seated. (ii) Veins : Veins are the vessels which generally carry carbon dioxide-rich blood from all parts of the body to the heart. The veins have thin walls. There are valves present in veins which allow blood to flow only towards the heart.

Differences between arteries and veins

Heart

The heart is a muscular organ which is located in the chest cavity between the lungs with its lower tip slightly tilted towards the left and beats continuously to act as a pump for the transport of blood. The adult human heart is about the size of a clenched fist. The heart has four chambers. The two upper chambers are called the atria and the two lower chambers are called the ventricles. The partition between the chambers helps to avoid mixing up of blood rich in oxygen with the blood rich in carbon dioxide

4.0Blood Circulation

Blood circulates throughout the body by the pumping action of the heart. The impure blood (deoxygenated blood, rich in carbon dioxide) is collected from different organs of the body through two major veins (vena cava). The two veins empty blood into the right auricle. This blood enter into the right ventricle and is pumped into the pulmonary artery. Through this artery, blood is carried to the lungs. Exchange of gases (between carbon dioxide and oxygen) takes place in the lungs. The pure blood (oxygenated blood) is carried by the pulmonary vein to the left auricle. From here, it enters the left ventricle and is then carried by an artery called aorta to all parts of the body.

5.0Heartbeat and Pulse

The heart shows regular contraction and relaxation. This rhythmic contraction of muscles followed by expansion constitutes a heartbeat. Heart beat increases when you do some extra work, such as running, cycling or when you are excited or under stress. This can be felt as an increase in the thumping or throbbing of the heart. The rhythmic beating of the various chambers of the heart maintain circulation of blood and transport of substances to the different parts of the body.

The rythmic contraction and dilation of the arteries resulting from the beating of the heart, is called as pulse. Normal pulse rate (In adult) ranges from 72-80 beats/minute.

Arteries lie deep in the tissues, except at the wrist and along the side of the neck. The pulse can be felt at any of these places. Veins lie closer to the surface to the skin and can be seen as greenish blue lines in our hands and legs. You have often seen that a physician holds your wrist and counts your heart beat. In fact, he is noting the pulse, by feeling the pressure of movement of blood through the artery at your wrist. The heartbeat can also be measured by using an instrument called stethoscope. A stethoscope is a device that amplifies the sound of a heart beat and is used to hear heart beats in the chest, by placing the chest piece of the stethoscope at the appropriate place.

A stethoscope consists of three parts - (i) A chest piece, that carries a sensitive diaphragm. (ii) Two earpieces and (iii) A tube joining the chest piece and the ear-pieces.

6.0Blood donation

Hundreds of people die due to unavailability of blood. Voluntary blood donation is harmless and painless and can save precious lives. Blood can be donated to hospitals and other places authorized by the government. Donated blood is stored with special care in Blood Banks.

7.0Transport of substances in plants

Water required for food manufactured by the plants is absorbed from the soil, through the root

The water absorbed from the soil through the root system has to be moved upwards to other plant parts and the food synthesised in the leaves has to be carried to other plant parts. In plants, there are special tubes called xylem and phloem, which comprise the conducting tissues or vascular tissues.

Transport of water and minerals

Upward movement of water and minerals occurs through pipe-like structures or channels, called xylem elements, present in roots, stem and leaves of plants. Water is thus carried to the entire plant. Plants absorb water and minerals by the roots.

Transport of water and minerals in (a) section of root, (b) a tree The roots have root hairs. These root hairs increase the surface area for absorbing water and minerals. The root hair absorbs water present between the soil particles and from there it reaches the xylem elements.

Translocation of food

The prepared food material is carried in a soluble form through another channel, constituted by phloem, from the leaves to all other parts of the plant body.

Transpiration

Transpiration is the process of loss of water in a vapour form from the leaves in plants. It occurs through stomata present on the leaves by the process of diffusion. Water absorbed through the roots is moved upwards within the plant body. A part of it is used in the process of photosynthesis and some of it is also used to keep the plant erect and stop it from wilting (drooping).

The rest is lost as water vapour into the atmosphere from the leaves. The evaporation of water from leaves produces a suction pull which helps to pull the water upwards to great heights.

8.0Importance of transpiration

(i) It results in the transport of water and minerals from the soil to the leaves. In the leaves, water forms the raw material for photosynthesis. (ii) It produces a cooling effect which helps in preventing hot sunlight from damaging delicate cells.

9.0Excretion in animal

When the cells perform metabolic functions, certain waste products are released. These are toxic and hence need to be removed from the body. The process of removal of wastes produced in the cells of the living organisms is called excretion. The various parts involved in excretion forms the excretory system.

The way in which waste chemicals are removed from the body of the animal depends on the availability of water. Aquatic animals like fishes, excrete cell waste as ammonia which directly dissolves in water.

Some land animals like birds, lizards, snakes excrete a semi-solid, white coloured compound (uric acid). The major excretory product in humans is urea.

Note : We all sweat on a hot summer day. Sweating is the production of a watery fluid from sweat glands in the skin. The watery fluid contains dissolved salts. In summer, you may have seen white patches on your clothes. These patches are produced by the salt present in the sweat. Sweating produces a cooling effect.

Human excretory system

The waste which is present in the blood has to be removed from the body. How can this be done? A mechanism to filter the blood is required. This is done by the blood capillaries in the kidneys. When the blood reaches the two kidneys, it contains both useful and harmful substances. The useful substances are absorbed back into the blood. The wastes dissolved in water are removed as urine.

Human excretory system consists of the following organs :

• A pair of kidneys
• Ureters
• Urinary bladder
• Urethra
  
  (1) Two pairs of kidney present in the humans. They are bean shaped organs which help in filtering blood to remove waste. (2) A narrow tube called the ureter runs from the inner side of each kidney. (3) The ureters, in turn, are connected to a large sac called the urinary bladder. Urine passes from the kidney through two ureters into the urinary bladder. Urine is collected and stored here. (4) Leading from the bladder there is another tube called the urethra. Urethra works as the outlet passage for urine.

• About 1.0-1.8 litres of urine are passed out by an adult human being in 24 hours. The urine consists of $95\%$ water, $2.5\%$ urea and $2.5\%$ other waste products.

Sometimes a person's kidneys may stop working due to infection or injury. As a result of kidney failure, waste products start accumulating in the blood. Such persons cannot survive unless their blood is filtered periodically through an artificial kidney. This process is called dialysis.

10.0Building Concepts

Which side of the heart will have oxygen-rich blood and which side will have carbon dioxide-rich blood?

• Left side of the heart will have oxygen-rich blood and right side will have carbon dioxide-rich blood.

Why does the water kept in an earthen pot is cooled?

• The water kept in an earthen pot is cooled because the water evaporates from the pores of the pot, which causes cooling.

11.0Biology Diagrams made Easy

12.0Chapter At a Glance

13.0SOME BASIC TERMS

• Blood: It is a fluid connective tissue that consists of plasma and blood cells.
• Blood clot: It is a sticky lump that forms when blood dries up or becomes thick, it prevents excessive bleeding.
• Heartbeat: It is the rhythmic contraction and relaxation of heart muscles.
• Xylem: The vascular tissue for the transport of water and minerals in the plant is called xylem.
• Phloem: The vascular tissue for the transport of food (product of photosynthesis) in the plant is called phloem.