chapter 7

• All organisms need food, water, and oxygen for survival
• Animals need to transport wastes to parts from where they can be removed
• The heart and blood vessels function to transport substances and form the circulatory system
• Transport of substances in animals and plants

  Learn about the transport of substances in animals and plants
• Circulatory system

  Blood is the fluid that flows in blood vessels, transporting substances like digested food, oxygen, and waste for removal from the body
• Blood


  The fluid that flows in blood vessels, composed of plasma and different types of cells including red blood cells (RBC) containing haemoglobin, and white blood cells (WBC) which fight against germs
• Haemoglobin

  A red pigment in red blood cells (RBC) that binds with oxygen and transports it to all parts of the body
• The presence of haemoglobin makes blood appear red
• Platelets


  Another type of cells in the blood that help in clot formation
• Arteries


  Blood vessels that carry oxygen-rich blood from the heart to all parts of the body, with thick elastic walls due to rapid and high-pressure blood flow
• Activity 7.1

  Study the flow of blood through arteries by feeling the pulse, which is the throbbing movements due to blood flowing in the arteries
• A resting person usually has a pulse rate between 72 and 80 beats per minute
• The pulmonary artery carries blood from the heart, so it is called an artery and not a vein. It carries carbon dioxide-rich blood
• Table 7.1 and compare them
• Rationalised 2023-24 SCIENCE
• Paheli explained that the pulmonary artery carries blood from the heart, so it is called an artery and not a vein. It carries carbon dioxide-rich blood to the lungs. Pulmonary vein carries oxygen-rich blood from the lungs to the heart.
• 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. 7.3. 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 to form veins which empty into the 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. 7.1). Hold your fingers inwards on your palm. That makes your fist. Your heart is roughly the size of your fist.
• What will happen if the blood rich in oxygen and the blood rich in carbon dioxide mix with each other? To avoid this from happening, the heart has four chambers. The two upper chambers are called the atria (singular: atrium) and the two lower chambers are called the ventricles (Fig. 7.4). The partition between the chambers helps to avoid 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. 7.3 and follow the arrows. These arrows show the direction of the blood flow from the heart to the lungs and back to the heart from where it is pumped to the rest of the body.
• 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 heart by listening through a stethoscope.
• Let us construct a model of a stethoscope with the materials that are available around us.
• Listening to the condition of the heart through a stethoscope

  Doctors can get clues about the condition of your heart by listening through a stethoscope
• Constructing a model of a stethoscope


  Take a small funnel of 6–7 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 the mouth of the funnel on your chest near the heart. Listen carefully to hear the heartbeats
• Each heart beat generates one pulse in the arteries and the pulse rate per minute indicates the rate of heart beat
• 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
• Animals such as sponges and Hydra do not possess any circulatory system. They rely on water to bring food, oxygen, and carry away waste materials and carbon dioxide
• Excretion is the process of removal of wastes produced in the cells of living organisms
• The excretory system is involved in excretion
• In humans, the waste present in the blood is filtered by the blood capillaries in the kidneys. Useful substances are absorbed back into the blood, while wastes dissolved in water are removed as urine
• William Harvey discovered the circulation of blood. He was initially ridiculed for his views but they were later accepted as a biological fact
• Before he died, Harvey’s idea about circulation was generally accepted as a biological fact
• 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
• Excretory system


  Kidneys, ureters, bladder, and urethra form the excretory system
• An adult human being normally passes about 1–1.8 L of urine in 24 hours. The urine consists of 95% water, 2.5% urea, and 2.5% other waste products