Living organisms need to move food, oxygen, water and other substances from one part of the body to another. In complex organisms like humans, there are many cells far away from the source of food and oxygen, and it is impossible for every cell to be in direct contact with these substances. Therefore, organisms have developed transport systems. In this chapter we study the circulatory system in animals and the transport of water and food in plants.
Transport in animals is carried out by the circulatory system, which consists of blood, blood vessels and the heart. Blood carries oxygen, digested food, hormones and waste materials to and from different parts of the body. In plants, water and minerals are transported through the xylem, while food is transported through the phloem. The transport system is essential for the survival of all complex organisms.
The transport system in animals is called the circulatory system. Its main components are the blood, the heart and blood vessels. Blood is a red-coloured fluid that flows through blood vessels and carries substances like oxygen, digested food, carbon dioxide and nitrogenous wastes. Blood also helps in fighting infections and maintaining body temperature. The liquid part of blood is called plasma, in which the blood cells - red blood cells, white blood cells and platelets - are suspended.
The heart is a muscular organ that pumps blood to all parts of the body. Blood vessels are of three types: arteries carry oxygenated blood away from the heart, veins carry deoxygenated blood back to the heart, and capillaries are the tiny vessels that connect arteries to veins. Arteries are thick-walled because the blood flows under high pressure, while veins have valves that prevent the backflow of blood. The blood circulation in the human body is called double circulation because the blood passes through the heart twice in one complete circuit.
The removal of waste products from the body is called excretion. The wastes produced in the cells must be removed because their accumulation is harmful to the body. The main nitrogenous waste in humans is urea, which is formed when excess proteins and amino acids are broken down in the liver. This urea is carried by the blood to the kidneys.
The kidneys are a pair of bean-shaped organs that filter waste from the blood and form urine. Each kidney contains millions of tiny filtering units called nephrons. The urine formed contains water and dissolved nitrogenous wastes, and it is stored in the urinary bladder before being passed out of the body through the urethra. In this way, harmful wastes are removed and the body's internal environment is kept stable. The removal of carbon dioxide occurs through the lungs during breathing, and excess water and salts are removed through sweat and urine.
Plants do not have a heart or blood, but they have a transport system made of special tissues called vascular tissues. There are two types of vascular tissues: xylem and phloem. Xylem transports water and minerals from the roots to the leaves, while phloem transports food prepared in the leaves to all other parts of the plant.
Water is absorbed by the roots through root hairs by a process called osmosis. From the roots, water and minerals are transported upward through the xylem to the leaves. This movement of water is continuous; water is lost from the leaves as water vapour through the process of transpiration, which occurs through the stomata. Transpiration helps in the upward movement of water, keeps the plant cool, and also helps in the absorption of minerals. The food made in the leaves by photosynthesis is transported to all parts of the plant through the phloem, in a process called translocation. In autumn, some trees lose water rapidly; transpiration explains many such natural processes.
The heart beats continuously to pump blood around the body, and this rhythmic contraction and relaxation is called the heartbeat. With each heartbeat, blood is pushed into the arteries, causing a wave of expansion and contraction in the artery walls. This is called the pulse, and it can be felt at places where arteries lie close to the skin, such as the wrist. The pulse rate is usually counted for a minute and gives the number of heartbeats per minute. In a healthy adult, the pulse rate is about 72 times per minute, and it increases during exercise or excitement because the body needs more oxygen.
The heartbeat can be heard with a stethoscope. The doctor listens to the sounds 'lub' and 'dub', which are produced by the closing of the heart valves. The pulse and heartbeat rates are important indicators of health and are used by doctors to assess the condition of a patient. In this way, the circulatory system keeps working continuously from before birth until death, delivering essential substances to every cell of the body.
| Component | Function |
|---|---|
| Blood | Transports oxygen, food, CO2 and wastes |
| Heart | Pumps blood to all parts of the body |
| Arteries | Carry oxygenated blood away from the heart |
| Veins | Carry deoxygenated blood back to the heart |
| Capillaries | Connect arteries and veins, exchange substances |
| Plant Tissue | Substance Transported | Direction |
|---|---|---|
| Xylem | Water and minerals | Roots to leaves |
| Phloem | Food (sugars) | Leaves to all parts |
Transport systems are essential for all complex organisms because every cell needs food, oxygen and removal of waste. In animals, the circulatory system with blood, the heart and blood vessels carries out this transport, while the kidneys filter out harmful nitrogenous wastes through urine. In plants, xylem transports water and minerals upward and phloem transports food to all parts, with transpiration helping in the process. The heartbeat and pulse are reliable indicators of health. Understanding transportation helps us appreciate how our bodies and plants function efficiently and stay alive.