Transportation in Animals and Plants You have learnt earlier that all organisms need food, water and oxygen for survival. They need to transport all these to various parts of their body. Further, animals need to transport wastes to parts from where they can be removed. Have you wondered how all this is achieved? Look at Fig. 11.1. Do you see the heart and the blood vessels? They function to transport substances and together form the circulatory system. In this chapter you shall learn about transport of substances in plants and animals. 11.1 CIRCULATORY SYSTEM Blood What happens when you get a cut on your body? Blood flows out. But what is blood? Blood is the fluid which flows in blood vessels. It transports substances like digested food from the small intestine to the other parts of the body. It carries oxygen from the lungs to the cells of the body. It also transports waste for removal from the body. How does the blood carry various substances? Blood is a liquid, which has cells of various kinds suspended in it. Heart Vein Artery (Arteries are shown in red colour and vein in blue) The fluid part of the blood is called plasma. One type of cells are the red blood cells (RBC) which contain a red pigment called haemoglobin. 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. The presence of haemoglobin makes blood appear red. The blood also has white blood cells (WBC) which fight against germs that may enter our body. Boojho fell down while playing a game and his knee got injured. Blood was coming out from the cut. After some time, he noticed that bleeding had stopped and a dark red clot had plugged the cut. Boojho was puzzled about this. The clot is formed because of the presence of another type of cells in the blood, called platelets. Blood vessels There are different types of blood vessels in the body. You know that during inhalation a fresh supply of oxygen fills the lungs. Oxygen has to be transported to the rest of the body. Also, the blood picks up the waste materials including carbon dioxide from the cells. This blood has to go back to the heart for transport to the lungs for removal of carbon dioxide as you have learnt in Chapter 10. So, two types of blood vessels, arteries and veins are present in the body. (Fig. 11.1) Arteries 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. Let us perform an activity to study the flow of blood through arteries. Activity 11.1 Place the middle and index finger of your right hand on the inner side of your left wrist (Fig. 11.2). Can you feel some throbbing movements? Why do you think there is throbbing? This throbbing is called the pulse and it is due to the blood flowing in the arteries. Count the number of pulse beats in one minute. How many pulse beats could you count? The number of beats per minute is called the pulse rate. A resting person, usually has a pulse rate between 72 and 80 beats per minute. Find other places in your body where you can feel the pulse. Record your own pulse beats per minute and those of your classmates. SCIENCE Compare the values you obtained and insert them in Table 11.1. Table 11.1 Pulse rate S. No. 1. Name Pulse per minute 2. 3. 4. 5. Veins are the vessels which carry carbon dioxide-rich blood from all parts of the body back to the heart. The veins have thin walls. There are valves present in veins which allow blood to flow only towards the heart. Refer to Fig. 11.3. Do you see the arteries divide into smaller vessels. On reaching the tissues, they divide further into extremely thin tubes called capillaries. The capillaries join up to form veins which empty into the heart. Heart The heart is an organ which beats continuously to act as a pump for the transport of blood, which carries other substances with it. Imagine a pump working for years without stopping! Absolutely impossible. Yet our heart works like a pump non-stop. Let us now learn about the heart. The heart is located in the chest cavity with its lower tip slightly tilted towards the left (Fig. 11.1). Hold your fingers inwards on your palm. That 123TRANSPORTATION IN ANIMALS AND PLANTS makes your fist. Your heart is roughly chambers. The two upper chambers are called the atria (singular: atrium) and What will happen if the blood rich in the two lower chambers are called the oxygen and the blood rich in carbon ventricles (Fig. 11.4). The partition dioxide mix with each other? To avoid between the chambers helps to avoid this from happening, the heart has four Vena Cava Pulmonary artery Pulmonary vein Left atrium Left ventricle Fig. 11.4 Sections of human heart mixing up of blood rich in oxygen with the blood rich in carbon dioxide. To understand the functioning of the circulatory system, start from the right side of the heart in Fig. 11.3 and follow the arrows. These arrows show the direction of the blood flow from the heart SCIENCE to the lungs and back to the heart from where it is pumped to the rest of the body. Heartbeat The walls of the chambers of the heart are made up of muscles. These muscles contract and relax rhythmically. This rhythmic contraction followed by its relaxation constitute a heartbeat. Remember that heartbeats continue every moment of our life. If you place your hand on the left side of your chest, you can feel your heartbeat. The doctor feels your heartbeats with the help of an instrument called a stethoscope. A doctor uses the stethoscope as a device to amplify the sound of the heart. It consists of a chest piece that carries a sensitive diaphragm, two ear pieces and a tube joining the parts. Doctors can get clues about the condition of your Chest Piece heart by listening through stethoscope. Let us construct a model of a stethoscope with the materials that are available around us. Activity 11.2 Take a small funnel of 6ñ7 cm in diameter. Fix a rubber tube (50 cm long) tightly on the stem of the funnel. Stretch a rubber sheet (or a balloon) on the mouth of the funnel and fix it tightly with a rubber band. Put the open end of the tube on one of your ears. Place enters their bodies. The water carries away waste materials and carbon dioxide as it moves out. Thus, these animals do not need a circulatory fluid like the blood. Let us now learn about the removal of waste other than carbon dioxide. 11.2 EXCRETION IN ANIMALS Recall how carbon dioxide is removed as waste from the body through the lungs during exhalation. Also recall that the undigested food is removed during egestion. Let us now find out how the other waste materials are removed from the body. You may wonder where these unwanted materials come from! When our cells perform their 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 parts involved in excretion forms the excretory system. Excretory system in humans 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. From the kidneys, the urine goes into the urinary bladder through SCIENCE Kidney Ureter Urethra tube-like ureters. It is stored in the bladder and is passed out through the urinary opening at the end of a muscular tube called urethra (Fig. 11.6). The kindeys, ureters, bladder and urethra form the excretory system. An adult human being normally passes about 1ñ1.8 L of urine in 24 hours. The urine consists of 95% water, 2.5% urea and 2.5% other waste products. We have all experienced that we sweat on a hot summer day. The sweat TRANSPORTATION IN ANIMALS AND PLANTS Well, Boojho is right. Plants have pipe-like vessels to transport water and nutrients from the soil. The vessels are made of special cells, forming the vascular tissue. A tissue is a group of cells that perform specialised function in an organism. The vascular tissue for the transport of water and nutrients in the plant is called the xylem [Fig. 11.7 (a)]. The xylem forms a continuous network of channels that connects roots to the leaves through the stem and branches and thus transports water to the entire plant [Fig. 11.7 (b)]. You know that leaves synthesise food. The food has to be transported to all parts of the plant. This is done by the vascular tissue called the phloem. Thus, xylem and phloem transport substances in plants. Activity 11.3 Take a large potato and peel off its outer skin. Cut one of its ends to make the base flat. Now make a deep and hollow cavity on the opposite side. Fill half of the cavity with sugar solution and mark the level by inserting a pin in the wall of the potato (Fig. 11.8). Put the potato TRANSPORTATION IN ANIMALS AND PLANTS the process of transpiration. The water through a straw) which can evaporation of water from leaves pull water to great heights in the generates a suction pull (the same tall trees. Transpiration also cools that you produce when you suck the plant. Keywords Ammonia Artery Blood Blood vessels Capillary Circulatory system Dialysis Excretion Excretory system Haemoglobin What you have learntHeart beat Kidneys Phloem Plasma Platelets Pulse Red blood cell Root hair Stethoscope Sweat Tissue Urea Ureter Urethra Uric acid Urinary bladder Vein White blood cell Xylem SCIENCE SCIENCE

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