10th Bio EM Gaseous Exchange PDF

CHAPTER 10 Gaseous Exchange Animation 10 : Gaseous Exchange Source & Credit: Wikispaces 10. Gaseous Exchange eLearn.Punjab In Grade IX, we have studied how cells generate ATPs from food. Cellular respiration is the process in which the C-H bonds in food are broken by oxidationreduction reactions and thenergy is transformed into ATP. In aerobic respiration, oxygen is used and there is complete oxidation of the food material. Carbon dioxide and water are also produced in this process. Organisms get the oxygen, needed for cellular respiration, from their environment and provide it to their cells. The carbon dioxide produced during cellular respiration is taken out of the cells and ultimately from the body. Taking inoxygen and giving out of carbon dioxide is termed as gaseous exchange. The term breathing is used for the process through which animals take air in their bodies to get oxygen from it and then give out the air for getting rid of carbon dioxide. Thus breathing and respiration are not synonymous. Respiration involves the mechanical and the bio-chemical processes whereas breathing is only the mechanical or physical process of exchange of gases. In this chapter we will go through the mechanisms of gaseous exchange in plants and in humans. 10.1 Gaseous Exchange In Plants Plants have no organs or systems for the exchange of gases with the environment. Every cell of the plant body exchanges gases with the environment by its own. The leaves and young stems have stomata in their epidermis. The gaseous exchange occurs through these stomata. The inner cells of leaves (mesophyll) and stems also have air spaces among them, which help in the exchange of gases (Fig:10.1). 2 10. Gaseous Exchange eLearn.Punjab Recalling Organisms need energy in the form of ATP for their activities. In young stems and leaves, some gaseous exchange also occurs through the cuticle which is present over their epidermis. Figure 10.1: Gaseous exchange in a leaf Leaf cells face two situations. During the daytime when the mesophyll cells of leaves are carrying out photosynthesis and respiration side by side, the oxygen produced in photosynthesis is utilized in cellular respiration. Similarly the carbon dioxide produced during cellular respiration is utilized in photosynthesis. However, during night when there is no photosynthesis occurring, the leaf cells get oxygen from the environment and release carbon dioxide through stomata. 3 10. Gaseous Exchange eLearn.Punjab Analyzing and Interpreting Draw diagram of stomata of a leaf indicating the movement of gases. In woody stems and mature roots, the entire surface is covered by bark which is impervious to gases or water. However, there are certain pores in the layer of bark. These are called the lenticels (Fig: 10.2). The lenticels allow air to pass through them. Gases diffuse in and out of the general surface of the young roots. The gases are found in the soil surrounding the roots. The aquatic plants get the oxygen dissolved in water and release carbon dioxide in the water. The lenticels are slightly more raised than the general surface of the stem Figure 10.2: Lenticels on a stem and the internal view of a lenticel 4 10. Gaseous Exchange eLearn.Punjab Practical Work: Investigate the effect of light on the net gaseous exchange from leaf Stomata are the microscopic pores in the epidermis of leaves. They are the passageways for gases and water vapours. Opening and closing of stomata controls the gaseous exchange. Problem: What is the net gaseous exchange from leaves during day and night times? Apparatus required: Petri dish, water, glass slides and cover slips, methylene blue, light microscope Background information: A stoma is an opening through which leaves exchange gases. The cells of leaves carry out photosynthesis during daytime only. The cells of leaves carry out respiration all the times. Procedure: 1. Take a thick leaf and peel off a thin layer (epidermis) from its surface. 2. Place the thin layer in water in a Petri dish. 3. Cut a piece of the peeled off epidermis and place it in a drop of water on a glass slide. 4. Pour a drop of methylene blue and place a cover slip on the material. 5. Observe under the low and high powers of the microscope. 6. Perform the same steps by taking the epidermis of leaf at night time. Observation: Observe both epidermis (upper and lower) and point out the stomata. Count the number of open stomata in both and compare their numbers. Draw your observation on the notebook. Evaluation: 1. How many stomata did you observe? 2. What is the structure of guard cells and how does it helps in the opening and closing of stomata? 10.2 Gaseous Exchange In Humans In humans and other higher animals the exchange of gases is carried out by the respiratory system. We can divide the respiratory system in two parts i.e. the air passageway and the lungs. 5 10. Gaseous Exchange eLearn.Punjab Analyzing and Interpreting Identify the structure of human air passageway in charts and models 10.2.1 The Air Passageway The air passageway consists of the parts through which the outside air comes in the lungs and after the exchange of gases it goes out. This passage of air consists of the following parts. The nose encloses the nasal cavity. It opens to the outside through the openings called the nostrils. The nasal cavity is divided into two portions by a wall. Each portion is lined by fine hairs and mucous which filter the dust particles from the air. The mucous also moistens and warms the incoming air and keeps its temperature nearly equal to that of the body. Figure 10.3: The air passageway and the lungs 6 10. Gaseous Exchange eLearn.Punjab Recalling The glottis is guarded by a flap of tissue called the epiglottis. The nasal cavity opens into the pharynx by means of two small openings called internal nostrils. Pharynx is a muscular passage and is common to both food and air. It extends to the opening of the oesophagus and the larynx. The air goes from the pharynx into the larynx. We know that glottis is a narrow opening at the floor of pharynx which leads into larynx. The larynx is a box, made of cartilage. It is present between pharynx and trachea. It is also called the voice box. Two pairs of fibrous bands called vocal cords are stretched across the larynx. The vocal cords vibrate when the air passes through them. This vibration produces sounds. Larynx continues to the trachea, which is also called the windpipe. It is about 12 cm long tube which lies in front of the oesophagus. There are C-shaped cartilagenous rings in the wall of trachea. The cartilages keep the trachea from collapsing even when there is no air in it. 7 10. Gaseous Exchange eLearn.Punjab On entering the chest cavity, the trachea divides into two smaller tubes called bronchi (Singular: bronchus). The bronchi also have cartilagenous plates in their walls. Each bronchus enters into the lung of its side and then divides into smaller branches. The bronchi continue dividing in the lungs until they make several fine tubes called bronchioles. The bronchioles progressively lose the cartilages as they become narrower. The bronchioles end as fine tubules called the alveolar ducts. Each alveolar duct opens into a cluster of pouches called alveoli. The alveoli form the respiratory surface in human body. Each alveolus is a sac-like structure lined by a single layer of epithelial cells. It is bound on the outside by a network of capillaries (Fig: 10.3). The pulmonary artery from the heart containing deoxygenated blood enters the lungs and branches into arterioles and then into capillaries which surround the alveoli. These then join together to form the venules which form pulmonary vein. The pulmonary vein carries the oxygenated blood back to the heart. The vibrations in vocal cords and the movements of lips, cheeks, tongue and jaws produce specific sounds which result in speech. Speech is an ability that only humans are gifted with and this is one of the characteristics which has put human beings superior to all. The trachea and the bronchi are also lined with ciliated and glandular cells. The glandular cells secrete mucus which moistens the air and also traps any fine particles of dust or bacteria that have escaped from the nasal cavity. The cilia beat with an upward motion so that the foreign particles along the mucus are sent to the oral cavity from where it may be either swallowed or coughed out. 10.2.2 The Lungs All the alveoli on one side constitute a lung. There is a pair of lungs in the thoracic cavity. The chest wall is made up of 12 pairs of ribs and the rib muscles called intercoastal muscles. A thick muscular structure, called diaphragm, is present below the lungs. 8 10. Gaseous Exchange eLearn.Punjab The left lung is slightly smaller and has two lobes and the right lung is bigger with three lobes. They are spongy and elastic organs. The lungs also have blood vessels that are the branches of the pulmonary arteries and veins. Each lung is enclosed by two membranes called the outer pleural membrane and the Figure 10.4: Lungs and Pleural membranes inner pleural membrane. The membranes enclose a fluid which provides lubrication for the free expanding and contracting of the lungs. 10.2.3 The Mechanism of Breathing The physical movements associated with the gaseous exchange are called breathing. There are two phases of breathing i.e. inhalation and exhalation. 9 10. Gaseous Exchange eLearn.Punjab 1. Inspiration or Inhalation During inspiration, the rib muscles contract and ribs are raised. At the same time the dome-shaped diaphragm contracts and is lowered. These movements increase the area of the thoracic cavity, which reduces the pressure on lungs. As a result, the lungs expand and the air pressure within them also decreases. The air from outside rushes into the lungs to equalize the pressure on both sides. The breathing movements are involuntary to a large extent. However, we can control the rate of breathing but not for a long time. 2. Expiration or Exhalation After the gaseous exchange in the lungs, the impure air is expelled out in exhalation. The rib muscles relax bringing the ribs back to the original position. The diaphragm muscles also relax and it gets its raised dome shape. This reduces the space in the chest cavity and increases the pressure on lungs. The lungs contract and the air is expelled out of them. Humans breathe 16 -20 times per minute in normal circumstances i.e. at rest. The rate of breathing is controlled by the respiratory centre in the brain. The respiratory centre is sensitive to the concentration of carbon dioxide in the blood. When we do exercise or some hard job our muscle cells carry out cellular respiration at a greater rate. It results in the production of more carbon dioxide which is released in the blood. This greater than normal concentration of carbon dioxide stimulates the respiratory centre of brain. The respiratory centre sends messages to the rib muscles and diaphragm to increase the rate of breathing so that the excess carbon dioxide present in blood can be removed out of body. During exercise or other hard physical works the breathing rate may increase up to 30-40 times per minute. 10 10. Gaseous Exchange eLearn.Punjab Figure 10.5: Steps of Inhalation Figure 10.6: Steps of Exhalation 11 10. Gaseous Exchange eLearn.Punjab Table 10.1 Comparison between the inspired and expired air Feature Inspired Air Expired Air Amount of oxygen 21% 16% Amount of carbon dioxide 0.04% 4% Amount of nitrogen 79% 79% Amount of water vapours Variable Saturated Amount of dust particles Variable Almost none Temperature Variable Almost equal to body temperature A model to show the action of diaphragm Apparatus: a bell jar, ‘Y’ shaped glass tube, two balloons, rubber sheet Procedure: Take a bell jar. Fix a ‘Y’ shaped glass tube towards its rounded end, as shown in the figure. Tie a balloon on the open ends of the two branches of glass tube. Tie a thin rubber sheet on the open end of the jar. The cavity of the bell jar acts as the thoracic cavity, the “Y” shaped tube as the trachea that branches into bronchi. The rubber sheet acts as the diaphragm and the balloon act as the lungs. To demonstrate inspiration, pull the rubber sheet down. The balloons get inflated. This shows how the lungs are filled with air when the diaphragm moves down. To demonstrate expiration, the rubber sheet is allowed to go back to its original position. The balloons get deflated. This shows how the lungs are deflated when the diaphragm comes back to its original position. Practical Work: Investigate the breathing rate at rest and after exercise The activity involves students exerting themselves in light exercise and monitoring their breathing rate for a period afterwards. Problem: What is the effect of exercise on the breathing rate? Apparatus required: Stopwatch or wristwatch Background information: The autonomic nervous system is specialized for controlling our automatic responses, for example breathing rate, heart rate and digestion. These are the processes that we do without conscious thought. The respiratory centre in the brain is sensitive for the blood carbon dioxide concentration. 12 10. Gaseous Exchange eLearn.Punjab Figure 10.7: Model of the Action of Diaphragm When we do exercise, our muscle cells increase the rate of cellular respiration so that the concentration of carbon dioxide increases in blood. To remove excess of carbon dioxide and to get more oxygen, respiratory centre sends messages to the respiratory system to increase the breathing rate. Procedure: SAFETY: Supervision of activity by teachers will ensure that the activity does not become competitive. The activity should be appropriate to footwear and clothing worn by students, for example, walking briskly up/ down stairs or steps up onto a low bench in the lab. Students with identified physical/ health problems should not be involved. Asthmatics may be able to take part if they use their inhalers prior to starting the exercise. The activity will be performed in groups (each consisting of 3 students). Each group will note down the readings in the form of table. 1. Each group will take the breathing rate, at rest, of its members and will get the average. 2. The group members will do some light exercise (e.g; running for 5 minutes). 3. The group will take the breathing rate of its members after exercise and will get the average. 13 10. Gaseous Exchange eLearn.Punjab 4. The members will do more hard exercise (running for 10 minutes). 5. The group will take the breathing rate of its members after hard exercise and will get the average. Evaluation: What was the average breathing rate at rest? What was the average breathing rate after light exercise? After which exercise, the breathing rate showed more increase? Why did the breathing rate increase during exercise? Practical Work: Find out how much air a person can take into his / her lungs Apparatus required: Water tub, plastic bottle (5 litres), rubber tube (0.5 metre long), plastic cover Background Information: Lungs have a limited capacity for taking and keeping air inside them. Procedure: 1. Take a 5 litre plastic bottle and graduate it externally with 100 ml distance. 2. Fill the bottle with water and cover it. 3. Fill 1/3 portion of the water tub and invert the plastic bottle in the tub in such a way that mouth of the bottle is dipped in water. 4. Remove the cover from the mouth of the bottle and insert one end of the rubber tube into the bottle. 5. Take a deep breath and exhale the air into the bottle through the rubber tube. 14 10. Gaseous Exchange eLearn.Punjab Observation: Note the lowering of the water level in the bottle. Result: The water level lowers when the exhaled air goes in the bottle. The volume of water that leaves the bottle is equal to the volume of the air exhaled from the lungs. Evaluation: What does the lowering of water level in the bottle indicate? Practical Work: Demonstrate through experiment that the exhaled air contains carbon dioxide Apparatus required: Conical flasks, glass tubing, double-hole stoppers, limewater Background Information: The exhaled air contains more carbon dioxide as compared to the inhaled air. Procedure: 1. Take two conical flasks (with limewater in each). Enclose the mouths of the flasks with double- hole stoppers. 2. Adjust the glass tubing as given in the picture. 3. Breathe in and out through the mouthpiece for 10 times. 15 10. Gaseous Exchange eLearn.Punjab Observation: Observe the colour of the limewater after a few minutes. Look for differences in the cloudiness of the limewater in the two flasks. Results: Conclude why the limewater in flask 2 turned more cloudy than in flask 1. 10.3 Respiratory Disorders There are a number of respiratory disorders which affect people. The percentage of such disorders is particularly high in Pakistan. It is due to the more concentration of air pollutants not only in the urban but also in the rural atmosphere. Some of the important respiratory disorders are described next. 1. Bronchitis Bronchitis is the inflammation of the bronchi or bronchioles. It results in excessive secretions of mucus into the tubes, leading to the swelling of tubular walls and narrowing of tubes (Fig. 10.8). It is caused by viruses, bacteria or exposure to chemical irritants (e.g. tobacco smoke). There are two major types of bronchitis i.e. acute and chronic. The acute bronchitis usually lasts about two weeks and patients recover with no permanent damage to the bronchi or bronchioles. In chronic bronchitis, the bronchi develop chronic inflammation. It usually lasts for three months to two years. Symptoms of bronchitis include a cough, mild wheezing, fever, chills and shortness of breath (especially when doing hard job). 16 10. Gaseous Exchange eLearn.Punjab 2. Emphysema Emphysema is the destruction of the walls of the alveoli. It results in larger sacs but with less surface area for gaseous exchange (Fig. 10.9). As lung tissue breaks down, the lungs do not come back to their original shape after exhalation. So air cannot be pushed out and is trapped in the lungs. The majority of people diagnosed with chronic bronchitis are 45 years of age or older. Figure 10.9: The Alveoli; normal (left) and emphysema (right) The symptoms of emphysema include shortness of breadth, fatigue, recurrent respiratory infections and weight loss. By the time the symptoms of emphysema appear, the patient has usually lost 50% to 70% of his / her lung tissue. The level of oxygen in blood may get so low that it causes serious complications. 3. Pneumonia Pneumonia is an infection of Figure 10.10: Pneumonia lungs. If this infection affects both lungs then, it is called double pneumonia. The most common cause of pneumonia is a bacterium, Streptococcus pneumoniae. 17 10. Gaseous Exchange eLearn.Punjab Some viral (influenza virus) and fungal infections may also lead to pneumonia. When the causative organisms enter the alveoli, they settle there and grow in number. They break the lung tissues and the area becomes filled with fluid and pus. The symptoms of pneumonia include a cold that is followed by a high fever, shivering, and a cough with sputum production. Patient may become short of breath. The patient’s skin colour may change and become dusky or purplish. It is due to poor oxygenation of blood. Vaccines are available to prevent pneumonia caused by S. pneumoniae. Antibiotics are used in the treatment of this type of pneumonia. Prior to the discovery of antibiotics, one-third of pneumonia patients died from the infection. 4. Asthma Asthma is a form of allergy, in which there is inflammation of the bronchi, more mucous production and narrowing of the airways (Fig. 10.11). In asthma patients, the bronchi and bronchioles become sensitive to different allergens (allergy causing factors) e.g. dust, smoke, perfumes, pollens etc. When exposed to any of such allergens, the sensitive airways show immediate and excessive response of constriction. In this condition, the patient feels difficulty in breathing. The symptoms of asthma vary from person to person. The major Figure 10.11: Asthma symptoms include shortness of breath (especially with exertion or at night), wheezing (whistling sound when breathing out), cough and chest tightness. The chemicals with ability to dilate the bronchi and bronchioles are used in the treatment of asthma. Such medicine is given in the form of inhalers. 18 10. Gaseous Exchange eLearn.Punjab 5. Lung Cancer Lung cancer is a disease of uncontrolled cell divisions in the tissues of the lung. The cells continue to divide without any control and form tumours. The cellular growth may also invade adjacent tissues beyond the lungs. The most common symptoms are shortness of breath, coughing (including coughing up blood) and weight loss. Lung cancer is the most common cause of cancer-related deaths and is responsible for more than 1.3 million deaths worldwide annually The main causes of any cancer include carcinogens (such as those in cigarette smoke), ionizing radiation and viral infection. Smoking is the main cause of lung cancer. This risk of lung cancer is significantly lower in non smokers. Cigarette smoke contains over 50 known carcinogens. Passive smoking (the inhalation of smoke from another’s smoking) is also a cause of lung cancer. The smoke from the burning end of a Figure 10.12: Lung Cancer cigarette is more dangerous than the smoke from the filter end. Eliminating tobacco smoking is a primary goal in the prevention of lung cancer. The World Health Organization has called for governments to stop tobacco advertising to prevent young people from taking up smoking. 19 10. Gaseous Exchange eLearn.Punjab 10.3.1 Bad Effects of Smoking Smoking is harmful due to the chemicals in cigarettes and smoke. Tobacco smoke contains over 4,000 different chemicals, out of which at least 50 are carcinogens and many are poisonous. Many people think that lung cancer is the only smoking-related disease and it is the number one cause of death among smokers. But it is not right. Cigarette smoke affects the body from head to toe. Smokers have a much higher risk of developing a number of life threatening diseases. If a person stops smoking, the chance to develop cancer decreases as damage to the lungs is repaired and contaminant particles are gradually removed. Nicotine is a powerful poison and was widely used as an insecticide in the past. When inhaled through tobacco smoking, it reaches our circulatory system and not only hardens the walls of the arteries but also damages the brain tissues. According to the WHO, the rates of smoking have declined in the developed world. In the developing world, however, it is rising by 3.4% per year as of 2002. Smoking may also lead to the cancers in kidneys, oral cavity, larynx, breast, bladder and pancreas etc. Many chemicals in tobacco smoke damage the air passageway, which leads to emphysema and other respiratory disorders. The World No Tobacco Day is celebrated on the 31st of May every year 20 10. Gaseous Exchange eLearn.Punjab Smoking also has effects on the circulatory system. The carbon monoxide present in tobacco smoke lessens the oxygen-carrying capacity of haemoglobin. Many other chemicals in smoke increase the production of blood platelets. When platelets are more than the normal numbers, they make the blood viscous and it can lead to arteriosclerosis. Smokers are at greater risk of developing infections, particularly in the lungs. For example, smoking increases the risk of tuberculosis by two to four times, and of pneumonia by four times. Smoking is also responsible for weakening and staining the teeth. Tooth loss is 2 to 3 times higher in smokers than in non-smokers. Non-smokers who are exposed to second-hand smoke (passive smoke) at home or work increase their heart disease risk by 25-30% and their lung cancer risk by 20-30% Smoking also affects the social life of a person. Smokers may face social un-acceptance because other people may not want to be exposed to other’s smoke. 21 10. Gaseous Exchange eLearn.Punjab UNDERSTANDING THE CONCEPT 1. How do the different parts of the plant body exchange gases with the environment? 2. Write down the steps of inhalation and exhalation. 3. State the signs and symptoms, causes and treatments of bronchitis, emphysema and pneumonia. 4. How does the tobacco smoke damage the respiratory system? SHORT QUESTIONS 1. Differentiate between breathing and cellular respiration. 2. Trace the path of air from the nasal cavity to the alveoli. 3. How will you differentiate between a stoma and a lenticel? THE TERMS TO KNOW Alveolar duct Diaphragm Alveolus Emphysema Nasal cavity Asthma Exhalation Nostril Breathing Gaseous exchange Pneumonia Bronchioles Inhalation Trachea Bronchus Larynx Vocal cords Bronchitis Lenticels ACTIVITIES 1. Investigate the effect of light on the net gaseous exchange from leaf, by using bicarbonate as the indicator. 2. Investigate the breathing rate at rest and after exercise. 3. Find out how much air a person can take into his lungs. 4. Demonstrate through experiment that carbon dioxide is exhaled during respiration. 22 10. Gaseous Exchange eLearn.Punjab SCIENCE, TECHNOLOGY AND SOCIETY 1. Evaluate the effects of tilling on roots for better exchange of gases with the soil air. 2. Outline the concept of Artificial Ventilator for artificial breathing in patients. 3. Interpret the dangers of breathing in exhausts of fossil fuels (Petrol and others) 4. Rationalize the importance of cross ventilation in homes. 5. Assess the adverse effects associated with smoking on health. 6. Point out bad social aspects of smoking. ON-LINE LEARNING 1. en.wikipedia.org/wiki/Respiratory_system 2. www.biotopics.co.uk/humans/resyst.html 3. www.who.int/respiratory/ 4. www.tutorvista.com › Science › Science II › Respiration 23 CHAPTER 11 Homeostasis Animation 11.1: Homeostasis Source & Credit: Lionden 11. Homeostasis eLearn.Punjab Homeostasis may be defined as the maintenance of the internal conditions of body at equilibrium, despite changes in the external environment. For example, the core temperature of human body remains at about 37°C despite fluctuations in the surrounding air temperature. Similarly, the blood glucose level remains about 1g per litre despite eating a meal rich in carbohydrates. Body cells need the internal environment in which conditions do not change much. Stable internal conditions are important for the efficient functioning of enzymes. The following are some process of homeostasis. Osmoregulation: It is maintenance of the amounts of water and salts in body fluids (i.e. blood and tissue fluids). We know that the relative amounts of water and salts in body fluids and inside cells control by the processes of diffusion and osmosis, which are essential for the functioning of cells (Recall “the concept of tonicity” from Grade IX Biology). Thermoregulation: The maintenance of internal body temperature is called thermoregulation. The enzymes of body work best at particular temperatures (optimum temperature). Any change in body temperature may affect the functioning of enzymes. Excretion is also a process of homeostasis. In this process, the metabolic wastes are eliminated from body to maintain the internal conditions at equilibrium. Metabolic waste means any material that is produced during body metabolism and that may harm the body. 11.1 Homeostasis In Plants Plants respond to environmental changes and keep their internal conditions constant i.e. homeostasis. They apply different mechanisms for the homeostasis of water and other chemicals (oxygen, carbon dioxide, nitrogenous materials etc). 2 11. Homeostasis eLearn.Punjab 11.1.1 Removal of Extra Carbon dioxide and Oxygen In daytime, the carbon dioxide produced during cellular respiration is utilized in photosynthesis and hence it is not a waste product. At night, it is surplus because there is no utilization of carbon dioxide. It is removed from the tissue cells by diffusion. In leaves and young stems, carbon dioxide escapes out through stomata. In young roots, carbon dioxide diffuses through the general root surface, especially through root hairs. Oxygen is produced in mesophyll cells only during daytime, as a by-product of photosynthesis. After its utilization in cellular respiration, the leaf cells remove the extra amount of oxygen through stomata. 11.1.2 Removal of Extra Water We know that plants obtain water from soil and it is also produced in the body during cellular respiration. Plants store large amount of water in their cells for turgidity. Extra water is removed from plant body by transpiration. At night, transpiration usually does not occur because most plants have their stomata closed. If there is a high water content in soil, water enters the roots and is accumulated in xylem vessels. Some plants such as grasses force this water through special pores, present at leaf tips or edges, and form drops. The appearance of drops of water on the tips or edges of leaves is called guttation (Fig 11.2). Figure 11.1: Guttation in different plants 3 11. Homeostasis eLearn.Punjab Recalling Transpiration is the loss of water from plant surface in the form of vapours. Guttation is not to be confused with dew, which condenses from the atmosphere onto the plant surface. 11.1.3 Removal of Other Metabolic Wastes Plants deposit many metabolic wastes in their bodies as harmless insoluble materials. For example, calcium oxalate is deposited in the form of crystals in the leaves and stems of many plants e.g. in tomato (Fig. 11.2). Figure 11.2: Calcium oxalate needles in a leaf cell The removal of excretory products is a secondary function of leaf fall. If the leaves are not shed, the calcium oxalate just remains as harmless crystals in the leaves In trees which shed their leaves yearly, the excretory products are removed from body during leaf fall. Other waste materials that are removed by some plants are resins (by coniferous trees), gums (by keekar), latex (by rubber plant) and mucilage (by carnivorous plants and ladyfinger) etc. (Fig. 11.3). 4 11. Homeostasis eLearn.Punjab Resin drops from Latex being extracted Mucilage drops on a a cut tree from a tree carnivorous plant Figure 11.3: Removal of some wastes in plants 11.1.4 Osmotic Adjustments in Plants On the basis of the available amount of water and salts, plants are divided into three groups. Hydrophytes are the plants which live completely or partially submerged in freshwater. Such plants do not face the problem of water shortage. They have developed mechanisms for the removal of extra water from their cells. Hydrophytes have broad leaves with a large number of stomata on their upper surfaces. This characteristic helps them to remove the extra amount of water. The most common example of such plants is water lily. Xerophytes live in dry environments. They possess thick, waxy cuticle over their epidermis to reduce water loss from internal tissues. They have less number of stomata to reduce the rate of transpiration. Such plants have deep roots to absorb maximum water from soil. Some xerophytes have special parenchyma cells in stems or roots in which they store large quantities of water. This makes their stems or roots wet and juicy, called succulent organs. Cacti (Singular Cactus) are the common examples of such plants. 5 11. Homeostasis eLearn.Punjab Halophytes live in sea waters and are adapted to salty environments. Salts enter in the bodies of such plants due to their higher concentration in sea water. On the other hand, water tends to move out of their cells into the hypertonic sea water. When salts enter into cells, plants carry out active transport to move and hold large amount of salts in vacuoles. Salts are not allowed to move out through the semi- permeable membranes of vacuoles. So the sap of vacuoles remains even more hypertonic than sea water. In this way, water does not move out of cells. Many sea grasses are included in this group of plants. Animation11.2: Osmosis Source & Credit: Leavingbio Recalling Osmosis is the movement of water from hypotonic solutions (less solute concentration) to hypertonic solutions (higher solute concentration), through semipermeable membrane. Hydrophytes Halophytes Xerophytes Figure 11.4: Three groups of plants 6 11. Homeostasis eLearn.Punjab 11.2 Homeostasis In Humans Like other complex animals, humans have highly developed systems for homeostasis. The following are the main organs which work for homeostasis: Lungs remove excess carbon dioxide and keep it in balance. Skin performs role in the maintenance of body temperature and also removes excess water and salts. The kidney filters excess water, salts, urea, uric acid etc. from the blood and forms urine. 11.2.1 Skin We know that our skin consists of two layers. Epidermis is the outer protective layer without blood vessels while dermis is the inner layer containing blood vessels, sensory nerve endings, sweat and oil glands, hairs and fat cells. Skin performs important role in the regulation of body temperature. The thin layer of fat cells in the dermis insulates the body. Contraction of small muscles attached to hairs forms ‘Goosebumps’. It creates an insulating blanket of warm air (Fig. 11.5). Initiating and Planning Hypothesize why the dogs hang their tongues out and pant Animation11.3: The Skin, Source & Credit: Leavingbio 7 11. Homeostasis eLearn.Punjab Figure 11.5: Goose bumps Similarly, skin helps in providing cooling effect when sweat is produced by sweat glands and excess body heat escapes through evaporation. Metabolic wastes such as excess water, salts, urea and uric acid are also removed in sweat. 11.2.2 Lungs In the previous chapter we have learned how lungs maintain the concentration of carbon dioxide in the blood. Our cells produce carbon dioxide when they perform cellular respiration. From cells, carbon dioxide diffuses into tissue fluid and from there into blood. Blood carries carbon dioxide to lungs from where it is removed in air. 11.3 The Urinary System Of Humans The excretory system of humans is also called the urinary system. It is formed of one pair of kidneys, a pair of ureters, a urinary bladder and a urethra. Kidneys filter blood to produce urine and the ureters carry urine from kidneys to urinary bladder. The bladder temporarily stores urine until it is released from body. Urethra is the tube that carries urine from urinary bladder to the outside of body. Figure 11.6: The urinary system of humans 8 11. Homeostasis eLearn.Punjab 11.3.1 Structure of Kidney Kidneys are dark-red, bean shaped organs. Each kidney is 10 cm long, 5 cm wide and 4 cm thick and weighs about 120 grams. They are placed against the back wall of abdominal cavity just below diaphragm, one on either side of vertebral column. They are protected by the last 2 ribs. The left kidney is a little higher than the right. The concave side of kidney faces vertebral column. There is a depression, called hilus, near the centre of the concave area of kidney. This is the area of kidney through which ureter leaves kidney and other structures including blood vessels, lymphatic vessels and nerves enter and leave kidney. 9 11. Homeostasis eLearn.Punjab The longitudinal section of the kidney shows two regions (Fig 11.7). Renal cortex is the outer part of kidney and it is dark red in colour. Renal medulla is the inner part of kidney and is pale red in colour. Renal medulla consists of several cone shaped areas called renal pyramids. Renal pyramids project into a funnel-shaped cavity called renal pelvis, which is the base of ureter. Figure 11.7: The anatomy of a kidney The functional unit of the kidneys is called nephron. There are over one million nephrons in each kidney. There are two parts of a nephron i.e. renal corpuscle and renal tubule (Fig. 11.8). The renal corpuscle is not tubular and has two parts i.e. glomerulus and Bowman’s capsule. Glomerulus is a network of capillaries while Bowman’s capsule is a cup-shaped structure that encloses glomerulus. The renal tubule is the part of nephron which starts after Bowman’s capsule. Its first portion is called the proximal convoluted tubule. Next portion is U-shaped and is called the Loop of Henle. The last portion of renal tubule is the distal convoluted tubule. The distal convoluted tubules of many nephrons open in a single collecting duct. Many collecting ducts join together to form several hundred papillary ducts which drain into renal pelvis. 10 11. Homeostasis eLearn.Punjab The capillaries of the glomerulus arise from the afferent arteriole and join to form the efferent arteriole Figure 11.8: The structure of a nephron (The capillaries surrounding the renal tubule are not shown for simplicity) 11 11. Homeostasis eLearn.Punjab 11.3.2 Functioning of Kidney The main function of kidney is urine formation, which takes place in three steps (Fig. 11.9).The first step is pressure filtration. When blood enters the kidney via the renal artery, it goes to many arterioles, and then to the glomerulus. The pressure of blood is very high and so most of the water, salts, glucose and urea of blood is forced out of glomerular capillaries. This material passes into the Bowman’s capsule and is now called glomerular filtrate. The second step is the selective re-absorption. In this step about 99% of the glomerular filtrate is reabsorbed into the blood capillaries surrounding renal tubule. It occurs through osmosis, diffusion and active transport. Some water and most of the glucose is reabsorbed from the proximal convoluted tubule. Here, salts are reabsorbed by active transport and then water follows by osmosis. The descending limb of loop of Henle allows the reabsorption of water while the ascending limb of Loop of Henle allows the reabsorption of salts. The distal convoluted tubule again allows the reabsorption of water into the blood. The third step is the tubular secretion. Different ions, creatinine, urea etc. are secreted from blood into the filtrate in renal tubule. This is done to maintain blood at a normal pH (7.35 to 7.45). Blood cells and proteins are not filtered through the glomerular capillaries because they are relatively larger in size. At the final stage urine is only 1% of the originally filtered volume. The typical volume of urine produced by an average adult is around 1.4 litres per day. Initiating and Planning Predict about the functioning of body without a kidney. Relate too much sugar intake by a diabetic with the functioning of kidney. 12 11. Homeostasis eLearn.Punjab Figure 11.9: Functioning of kidney (nephron) 13 11. Homeostasis eLearn.Punjab Table 11.1 Normal chemical composition of urine (Source: NASA Contractor Report) Water 95% Urea 9.3 g/I Chloride ions 1.87 g/I Sodium ions 1.17 g/I Potassium ions 0.750 g/I Other ions and compounds Variable amounts After the above mentioned steps, the filtrate present in renal tubules is known as urine. It moves into collecting ducts and then into pelvis. 11.3.3 Osmoregulatory Function of Kidney Osmoregulation is defined as the regulation of the concentration of water and salts in blood and other body fluids. Kidneys play important role in osmoregulation by regulating the water contents of blood. It is an important process as excessive loss of water concentrates the body fluids whereas excess intake of water dilutes them. 14 11. Homeostasis eLearn.Punjab When there is excess water in body fluids, kidneys form dilute (hypotonic) urine. For this purpose, kidneys filter more water from glomerular capillaries into Bowman’s capsule. Similarly less water is reabsorbed and abundant dilute urine is produced. It brings down the volume of body fluids to normal. When there is shortage of water in body fluids, kidneys filter less water from glomerular capillaries and the rate of reabsorption of water is increased. Less filtration and more reabsorption produce small amount of concentrated (hypertonic) urine. It increases the volume of body fluids to normal. This whole process is under hormonal control. Practical: Examination of the longitudinal section of a mammalian kidney Teacher will make a kidney of a sheep or goat available in the laboratory or classroom. Teacher will dissect the kidney longitudinally. Students will observe the cut halves with the help of hand lenses and will locate the renal cortex, medulla, pyramids and pelvis. Figure 11.10: Kidneys of goat (longitudinal sections) Students will draw the diagram of the longitudinal section of the kidney. 15 11. Homeostasis eLearn.Punjab What causes the material to move from glomerular capillaries to Bowman’s capsule? Activity: Trace the movement of a molecule of urea from blood to urethra using a flow chart Blood pressure diagram. 11.4 Disorders Of Kidney There are many different kidney disorders. 11.4.1 Kidney Stones When urine becomes concentrated, crystals of many salts e.g. calcium oxalate, calcium and ammonium phosphate, uric acid etc. are formed in it. Such large crystals cannot pass in urine and form hard deposits called kidney stones. Most stones start in kidney. Some may travel to ureter or urinary bladder. The major causes of kidney stones are age, diet (containing more green vegetables, salts, vitamins C and D), recurring urinary tract infections, less intake of water, and alcohol consumption. The symptoms of kidney stones include severe pain in kidney or in lower abdomen, vomiting, frequent urination and foul-smelling urine with blood and pus. About 90% of all kidney stones can pass through the urinary system by drinking plenty of water. In surgical treatment, the affected area is opened and stone(s) are removed. Lithotripsy is another method for the removal of kidney stones. In this method, non-electrical shock waves from outside are bombarded on the stones in the urinary system. Waves hit the dense stones and break them. Stones become sand-like and are passed through urine. 16 11. Homeostasis eLearn.Punjab Abu Nasr al-Farabi (872-951) was a prominent scientist who wrote many books that contained information about kidney diseases. The genius Abu al-Qasim Al-Zahrawi (known as Albucasis: 936- 1013), is considered to be Islam’s greatest surgeon who invented many surgical procedures including the surgical removal of stones from the urinary bladder. His encyclopedia, Al-Tasrif (“The Method”), contained over 200 surgical medical instruments he personally designed. 11.4.2 Kidney (Renal) failure Kidney failure means a complete or partial failure of kidneys to function. Diabetes mellitus and hypertension are the leading causes of kidney failure. In certain cases, sudden interruption in the blood supply to kidney and drug overdoses may also result in kidney failure. The main symptom of kidney failure is the high level of urea and other wastes in blood, which can result in vomiting, nausea, weight loss, frequent urination and blood in urine. Excess fluids in body may also cause swelling of legs, feet face and shortness of breath. The kidney failure is treated with dialysis and kidney transplant. a. Dialysis Dialysis means the cleaning of blood by artificial ways. There are two methods of dialysis. Animation 11.4: Stone Kidney, Source & Credit: Renux.dmed 17 11. Homeostasis eLearn.Punjab 1. Peritoneal Dialysis In this type of dialysis, the dialysis fluid is pumped for a time into the peritoneal cavity which is the space around gut (Fig. 11.11). This cavity is lined by peritoneum. Peritoneum contains blood vessels. When we place dialysis fluid in peritoneal cavity, waste materials from peritoneal blood vessels diffuse into the dialysis fluid, which is then drained out. This type of dialysis can be performed at home, but must be done every day. Figure 11.11: Peritoneal dialysis 18 11. Homeostasis eLearn.Punjab 2. Haemodialysis In haemodialysis, patient’s blood is pumped through an apparatus called dialyzer. The dialyzer contains long tubes, the walls of which act as semi-permeable membranes (Fig. 11.12). Blood flows through the tubes while the dialysis fluid flows around the tubes. Extra water and wastes move from blood into the dialysis fluid. The cleansed blood is then returned back to body. The haemodialysis treatments are typically given in dialysis centres. Figure 11.12: Haemodialysis b. Kidney Transplant We know that dialysis needs to be repeated after every few days and is unpleasant for patients and attendants. Another treatment for the end-stage kidney failure is kidney transplantation. It is the replacement of patient’s damaged kidney with a donor healthy kidney. Kidney may be donated by a deceased-donor or living-donor. The donor may or may not be a relative of the patient. Before transplant, the tissue proteins of donor and patient are matched. The donor’s kidney is transplanted in patient’s body and is connected to the patient’s blood and urinary system. The average lifetime for a donated kidney is ten to fifteen years. When a transplant fails, the patient may be given a second kidney transplant. In this situation, the patient is treated through dialysis for some intermediary time. Problems after a transplant may include transplant rejection, infections, imbalances in body salts which can lead to bone problems and ulcers. Analyzing and Interpreting Rationalize why dialysis machine is considered as artificial kidney. Design dialysis apparatus by cellophane paper and empty photographic film case. 19 11. Homeostasis eLearn.Punjab UNDERSTANDING THE CONCEPT 1. Describe the process of selective re-absorption in the kidneys. 2. How do the plants excrete extra water and salts from their bodies? 3. What is the functional unit of the kidney? Describe its structure and draw labelled diagram. 4. What steps are involved in the formation of urine in the kidneys? 5. “Along with excretion, kidneys also play role in Osmoregulation.” Comment on this statement. SHORT QUESTIONS 1. What are the major organs involved in homeostasis in human body? State the roles of each of these organs. 2. Identify and label the following: diagram. 20 11. Homeostasis eLearn.Punjab THE TERMS TO KNOW Bowman’s capsule Homeostasis Renal pyramid Collecting duct Lithotripsy Renal tubule Dialysis Loop of Henle Selective reabsorption Dialyzer Nephron Tubular secretion Distal convoluted tubule Osmoregulation Ureter Excretion Papillary ducts Urethra Glomerular filtrate Peritoneal dialysis Urinary bladder Glomerulus Pressure filtration Urinary system Guttation Proximal convoluted tubule Hemodialysis Renal corpuscle Hilus Renal pelvis ACTIVITIES 1. Examine the structure of kidney (sheep or goat kidney / model). 2. Trace the movement of a molecule of urea from blood to urethra using a flow chart diagram. SCIENCE, TECHNOLOGY AND SOCIETY 1. Realize the importance of drinking plentiful water daily. 2. Predict how the kidney helps to overcome the problem of dehydration. 3. Recognize the right treatments of kidney problems. ON-LINE LEARNING 1. biology-animations.blogspot.com/.../nephron-animation.html 2. highered.mcgraw-hill.com/sites 3. leavingbio.net/EXCRETION/EXCRETION.html 4. www.tutorvista.com/.../excretion/excretory-system-animation.php 21 CHAPTER 12 Coordination and Control Animation 12.1: Neuron Source & Credit: nichd.nih 12. Coordination and Control eLearn.Punjab The tissues and organs in the bodies of multicellular organisms do not work independently of each other. They work together performing their many tasks as the needs of the whole body. This means that these activities are coordinated. Coordination also enables the organism to respond to happenings in the world around it. One familiar example of coordination is the way in which muscles work together during movement. When a boy runs to catch a ball, he uses hundreds of muscles to move his arms, legs and back. His nervous system uses information from his sense organs and coordinates these muscles. Due to this coordination, the muscles contract in the correct sequence, power and length of time. But that is not all. Such activities involve many other kinds of coordination. For example breathing and heartbeat rates are increased blood pressure is adjusted, and extra heat is removed fast from the body. How does it happen? Life activities are controlled and coordinated i.e. body works as one unit, in which its different organs and systems cooperate and work in harmony with each other. When we are writing something, our hands and fingers work in collaboration with our muscles, eyes, thoughts etc. and then very intricate movements result. Animation 12.2: HumanAnatomy Source & Credit: soundtells 2 12. Coordination and Control eLearn.Punjab 12.1 Types Of Coordination There are two types of coordination in organisms: i. Nervous coordination brought about by nervous system and ii. Chemical coordination brought about by endocrine system. Animals have both the nervous and chemical coordination systems in their bodies while plants and other organisms have only chemical coordination. 12.1.1 Coordinated Action A coordinated action has five components; i- Stimuli What happens when we touch a snail? We might have seen the flowers of sunflower plant moving towards the sun. What could be the reason for all this? Touch, light etc. are factors that can bring about certain responses in living organisms. These factors are called stimuli. We can define a stimulus as any change in environment (external and internal), which can provoke a response in organism. More examples of stimuli are heat, cold, pressure, sound waves, presence of chemicals, microbial infections etc. Coordination also takes place in unicellular organisms. The response to stimuli is brought about through chemicals 3 12. Coordination and Control eLearn.Punjab ii- Receptors Stimuli are detected by special organs, tissues or cells of body. For example sound waves are detected by ears, light is detected by eyes, chemicals in air are detected by nose and so on. The organs, tissues or cells which are specifically built to detect particular type of stimuli are called receptors. iii- Coordinators These are the organs that receive information from receptors and send messages to particular organs for proper action. In nervous coordination, brain and spinal cord are coordinators. They receive information and send messages through neurons in the form of nerve impulses. On the other hand, in chemical coordination, various endocrine glands play the role of coordinators. They receive information in the form of various chemicals and send messages by secreting particular hormones in blood. iv- Effectors These are the parts of body which receive messages from coordinators and produce particular responses. In nervous coordination, neurons carry messages from coordinators (brain and spinal cord) to muscles and glands, which act as effectors. In chemical coordination, particular hormones carry messages from coordinators (endocrine glands) to particular target tissues, which act as effectors. For some hormones, nephrons act as effectors. Similarly, bones and liver act as effectors for many hormones. v- Response On receiving the message from coordinators, the effector performs action. This action is called response. For example, pulling our hand away from something very hot and the movement of the flower of sunflower towards light are responses. Usually, nervous coordination produces immediate but short-living responses while chemical coordination produces slow but long-living responses. 4 12. Coordination and Control eLearn.Punjab Figure 12.1: Nervous and chemical coordination Recording Skills: Using the knowledge gained from the above topic, draw a table that can show the differences between the two types of coordination i.e. nervous coordination and chemical coordination. 12.2 Human Nervous System We have understood the basic model of the working of nervous system. The nervous system in man and in other higher animals is composed of two major components i.e. central nervous system and peripheral nervous system. 5 12. Coordination and Control eLearn.Punjab Central nervous system comprises of coordinators i.e. brain and spinal cord while peripheral nervous system consists of nerves that arise from central nervous system and spread in different parts of body. All these components are made of neurons. Now we will first examine the structure and types of neuron and then we will go to the divisions of nervous system. 12.2.1 Nerve cell or Neuron Nerve cell or neuron is the unit of the nervous system. The human nervous system consists of billions of neurons plus supporting (neuroglial) cells. Neurons are specialized cells that are able to conduct nerve impulses from receptors to coordinators and from coordinators to effectors. In this way they communicate with each other and with other types of body cells. The nucleus and most of the cytoplasm of a neuron is located in its cell body. Different processes extend out from cell body. These are called dendrites and axons. Dendrites conduct impulses toward cell body and axons conduct impulses away from cell body (Fig 12.2). Animation 12.3: Nerve impulse Source & Credit: spiritualgarden Unlike ordinary cells, mature neurons never divide. But a protein called nerve-growth-factor promotes the regeneration of broken nerve cells. The degenerating brain cells could be repaired, by using embryonic stem cells. 6 12. Coordination and Control eLearn.Punjab Figure 12.2: Neurons Schwann cells are special neuroglial cells located at regular intervals along axons. In some neurons, Schwann cells secrete a fatty layer called myelin sheath, over axons. Between the areas of myelin on an axon, there are non- myelinated points, called the nodes of Ranvier. Myelin sheath is an insulator so the membrane coated with this sheath does not conduct nerve impulse. In such impulses are called saltatory (‘jumping’) impulses. This increases the speed of nerve impulse. Animation 12.4: bp120 Source & Credit: clc.uc 7 12. Coordination and Control eLearn.Punjab On the basis of their functions, neurons are of three types; 1. Sensory neurons conduct sensory information (nerve impulse) from receptors towards the CNS. Sensory neurons have one dendrite and one axon. Animation 12.5: Nerve impulse 2. Interneurons form brain and spinal cord. They receive Source & Credit: wikibooks information, interpret them and stimulate motor neurons. They have many dendrites and axons. 3. Motor neurons carry information from interneurons to muscle or glands (effectors). They have many dendrites but only one axon. Practical: Observe the contraction of shin muscle of a frog, using a DC current of 12 volt. Apparatus: Dissected frog, Petri dish, methylene blue solution, 12 volt battery with wires. Procedure: Get the shin muscle of a dissected frog (dissection would be done by teacher). Put the shin muscles in a Petri dish filled with methylene blue. Place a battery of 12 volt power near the Petri dish and touch its two wires with the opposite ends of the muscle. Observation: The muscle would contract when a current is applied to it. 8 12. Coordination and Control eLearn.Punjab Animation 12.8: Deporepol Source & Credit: cybercuba In certain parts of body, the cell bodies of many neurons form a group enveloped by a membrane. This is called ganglion. Nerve A nerve means the union of several axons that are enveloped by a covering made of lipid. Based on the property of axons, the nerves are classified into three types. 1. Sensory nerves contain the axons of sensory neurons only. 2. Motor nerves contain the axons of motor neurons only. 3. Mixed nerves contain the axons of both i.e sensory and motor neurons. 12.2.2 Divisions of the Nervous System The details of the central and peripheral nervous systems are given below. Central nervous system The central nervous system consists of brain and spinal cord. A- Brain In animals, all life activities are under the control of brain. The structure of brain is suitable to perform this function. Brain is situated inside a bony cranium (part of skull). Inside cranium, brain is covered by three layers called meninges. Meninges protect brain and also provide nutrients and oxygen to brain tissue through their capillaries. The brain contains fluid-filled ventricles that are continuous with the central canal of spinal cord. Fluid within ventricles and central canal is called cerebrospinal fluid (CSF). 9 12. Coordination and Control eLearn.Punjab The Divisions of Brain There are three major regions in the brain of human and other vertebrates. These are forebrain, midbrain and hindbrain. Important parts of each of these regions are described below: Forebrain Forebrain is the largest area of brain. It is most highly developed in humans. Following are the important parts of this region. (i) Thalamus lies just below cerebrum. It serves as a relay centre between various parts of brain and spinal cord. It also receives and modifies sensory impulses (except from nose) before they travel to cerebrum. Thalamus is also involved in pain perception and consciousness (sleep and awakening). (ii) Hypothalamus lies above midbrain and just below thalamus. In humans, it is roughly the size of an almond. One of the most important functions of hypothalamus is to link nervous system and endocrine system. It controls the secretions of pituitary gland. It Animation 12.7: Nervous System also controls feelings such as rage, pain, pleasure and Source & Credit: hermes sorrow. (iii) Cerebrum is the largest part of forebrain. It controls skeletal muscles, thinking, intelligence and emotions. It is divided into two cerebral hemispheres. The anterior parts of cerebral hemispheres are called olfactory bulbs which receive impulses from olfactory nerves and create the sensation of smell. The upper layer of cerebral hemispheres i.e. cerebral cortex consists of grey matter. The grey matter of nervous system consists of cell bodies and non-myelinated axons. Beneath this layer is present the white matter. The white matter of Animation 12.8: Brainlobes nervous system consists of myelinated axons. Cerebral Source & Credit: people.eku cortex has a large surface area and is folded in order to fit in skull. It is divided into four lobes. 10 12. Coordination and Control eLearn.Punjab Hippocampus is a structure that is deep in the cerebrum. It functions for the formation of new memories. People with a damaged hippocampus cannot remember things that occurred after the damage but can remember things that had occurred before damage. Lobe Function Control motor functions, permits conscious Frontal control of skeletal muscles and coordinates movements involves in speech Contains sensory areas that receive impulses Parietal from skin. Occipital Receives and analyzes visual information Temporal Concerned with hearing and smell 11 12. Coordination and Control eLearn.Punjab Midbrain Midbrain lies between hindbrain and forebrain and connects the two. It receives sensory information and sends it to the appropriate part of forebrain. Midbrain also controls some auditory reflexes and posture. Figure 12.3: Structure of human brain The medulla oblongata, pons, and midbrain connect the rest of brain to spinal cord. They are collectively referred to as brain stem. 12 12. Coordination and Control eLearn.Punjab Hindbrain Hindbrain consists of three major parts. (i) Medulla oblongata lies on the top of spinal cord. It controls breathing, heart rate and blood pressure. It also controls many reflexes such as vomiting, coughing, sneezing etc. Information that passes between spinal cord and the rest of brain pass through medulla. (ii) Cerebellum is behind medulla. It coordinates muscle movements. (iii) Pons is present on top of medulla. It assists medulla in controlling breathing. It also serves as a connection between cerebellum and spinal cord. Animation 12.9: Rotating brain colored Source & Credit: wikipedia B- Spinal Cord The spinal cord is in fact a tubular bundle of nerves. It starts from brain stem and extends to lower back. Like brain, spinal cord is also covered by meninges. The vertebral column surrounds and protects spinal cord. The outer region of spinal cord is made of white matter (containing myelinated axons). The central region is butterfly shaped that surrounds the central canal. It is made of grey matter (containing neuron cell bodies). 31 pairs of spinal nerves arise along spinal cord. These are “mixed” nerves because each contains axons of both sensory and motor neurons. 13 12. Coordination and Control eLearn.Punjab At the point where a spinal nerve arises from spinal cord, there are two roots of spinal nerve. Both roots unite and form one mixed spinal nerve (Fig. 12.4). The dorsal root contains sensory axons and a ganglion where cell bodies are located. The ventral root contains axons of motor neurons. Spinal cord is the continuation of medulla oblongata. Figure 12.4: Spinal Cord and Spinal Nerves Spinal cord performs two main functions: 1. It serves as a link between body parts and brain. Spinal cord transmits nerve impulses from body parts to brain and from brain to body parts. 2. Spinal cord also acts as a coordinator, responsible for some simple reflexes. Peripheral Nervous System The peripheral nervous system (PNS) is composed of nerves and ganglia. Ganglia are the clusters of neuron cell bodies outside CNS. Nerves arise or lead to brain and spinal cord. So they are named as cranial and spinal nerves. 14 12. Coordination and Control eLearn.Punjab Spinal cord is roughly 40cm long and about as wide as your thumb for most of its length. Humans have 12 pairs of cranial nerves and 31 pairs of spinal nerves. Some cranial nerves are sensory, some are motor and some are mixed. On the other hand, all spinal nerves are mixed nerves. The cranial and spinal nerves make two pathways i.e. sensory pathway (conducting impulses from receptors to CNS) and motor pathway (conducting impulses from CNS to effectors). Motor pathway makes two systems. Somatic Nervous System It is responsible for the conscious and voluntary actions. It includes all of the motor neurons that conduct impulses from CNS to skeletal muscles. Figure 12.5: Divisions of the nervous system 15 12. Coordination and Control eLearn.Punjab Autonomic Nervous System It is responsible for the activities, which are not under conscious control. It consists of motor neurons that send impulses to cardiac muscles, smooth muscle and glands. Autonomic nervous system comprises of sympathetic system and parasympathetic system. Sympathetic nervous system prepares body to deal with emergency situations. This is often called the “fight or flight” response. During an emergency situation, this system takes necessary actions. For example; it dilates pupils, accelerates heartbeat, increases breathing rate and inhibits digestion. When stress ends, the parasympathetic nervous system takes action and normalizes all the functions. It causes pupils to contract, promotes digestion, and slows the rate of heartbeat and breathing rate. 12.2.3 Reflex Action When central nervous system sends impulses to muscles and glands, two types of actions (responses) result. 1. The higher centres of brain control the conscious action or voluntary actions. 2. When impulses are not passed to the higher centres of brain, it results in responses which are not under conscious control. Such responses are called involuntary actions. Sometimes, the involuntary response produced by the CNS is very quick. Such a response is called reflex action. The pathway followed by the nerve impulses for producing a reflex action, is called reflex arc. The most common example of reflex action is the withdrawal of hand after touching a hot object. In this reflex action, spinal cord acts as coordinator. Heat stimulates temperature and pain receptors in skin. A nerve impulse is generated which is carried by sensory neurons to the interneurons of spinal cord. It doesn't matter how clever we are we will always pull our hand away from a flame without thinking about it. Animation 12.10: Reflexrotulien Source & Credit: Corpshumain 16 12. Coordination and Control eLearn.Punjab From interneurons, the impulse is passed to motor neurons, which carry it to the muscles of arm. As a result, the muscles contract to withdraw hand. During it, other interneurons transmit nerve impulses up to brain so that the person becomes aware of pain and what happened. Figure 12.6: Reflex arc in a reflex action See animation of Reflex Arc at: http://bio.rutgers.edu/~gb102/lab_5/103ar.html 12.3 Receptors In Humans We know that the organs or parts which are specifically built to detect particular type of stimuli are called sense organs or receptors. Main receptors in man are eyes, ears, nose, taste buds, receptors of touch, heat and cold etc. 17 12. Coordination and Control eLearn.Punjab 12.3.1 Eye Our eyes are located in small portions of skull known as the orbits or eye sockets. Eyelids wipe eyes and prevent dehydration. They spread tears on eyes, which contains substances for fighting bacterial infections. Eyelashes prevent fine particles from entering eye. The structure of eye can be divided into three main layers (Fig. 12.7). Figure 12.7: Structure of human eye The outer layer of eyeball consists of sclera and cornea. Sclera gives eye most of its white colour. It consists of dense connective tissue and protects the inner components of eye and maintains its shape. In the front, sclera forms the transparent cornea. Cornea admits light to the interior of eye and bends light rays so that they can be brought to a focus. 18 12. Coordination and Control eLearn.Punjab The middle layer is called choroid. It contains blood vessels and gives the inner eye a dark colour. The dark colour prevents disruptive reflections within eye. Behind cornea, choroid bends to form a muscular ring, called iris. There is round hole, called pupil, in the centre of iris. After striking the cornea, light passes through the pupil. The size of pupil is adjusted by the muscles of iris. Pupil constricts in bright light when the circular muscles of iris contract. Similarly, pupil dilates in dim light when the radial muscles of iris contract (Fig. 12.8). Figure 12.8: Contraction and dilation of pupil Practical: Perform an experiment in which a student will flash a spotlight in the eyes of another student and the third student would calculate the time taken for the eye to contract its pupil. Behind iris, there is a convex lens, which focuses light on retina. Lens is attached to ciliary muscles of eye via a ring of suspensory ligament. To clearly see an object far away, ciliary muscles are relaxed and lens becomes less convex. When ciliary muscles contract, lens becomes more convex and round. The inner layer is sensory and is called as retina. It contains the photosensitive cells called rods and cones and associated neurons. 19 12. Coordination and Control eLearn.Punjab Too much light being let in could damage the retina; too little light makes sight difficult. Rods are sensitive to dim light while cones are sensitive to bright light and so distinguish different colours. Retina has two points i.e. fovea and optic disc. Fovea is a dip in retina, directly opposite to lens and is densely packed with cone cells. It is largely responsible for colour vision and sharpness. Optic disc is a point on retina where the optic nerve Have you seen the eyes of cat and dog enters retina. There are no rods and cones at this shining in the night? The reason for this is point, that is why it is also referred to as the blind the presence of tapetum behind the eye spot. which is a layer capable of reflecting light. In a human eye there are about 125 lakhs rods and 7 lakhs cones. The iris divides the cavity of eye into two chambers. The anterior chamber is in front of iris i.e. between cornea and iris; whereas the posterior chamber is between iris and retina. The anterior chamber contains a clear fluid known as aqueous humour while the posterior chamber contains a jelly-like fluid known as vitreous humour. It helps maintain the shape of eye and suspends the delicate lens. Light from objects enters eye and is refracted when it passes through cornea, aqueous humour, lens and vitreous humour. Lens also focuses light on retina. As a result, the image falls on retina. Rods and cones generate nerve impulses in the optic nerve. These impulses are carried to the brain, which makes the sensation of vision. Rods contain a pigment called rhodopsin. When light falls on rhodopsin, it breaks for generating a nerve impulse. In the absence of light, the breakdown products are again converted into rhodopsin. Body synthesizes rhodopsin from vitamin A and that is why the deficiency of vitamin A causes poor night vision. This problem is called night blindness. 20 12. Coordination and Control eLearn.Punjab Cones also contain a pigment, known as iodopsin. There are three main types of cones and each type has a specific iodopsin. Each type of cones recognizes one of the three primary colours i.e. blue, green and red. If any type of cones is not working well, it becomes difficult to recognize that colour. Such person is also not able to distinguish different colours. This disease is called colour blindness and it is a genetic problem. Disorders of the Eye The working of eye is affected by the changes in the shape of eyeball. Myopia (Short sight) The elongation of eyeball results in myopia. Such persons are not able to see distant objects clearly. The image of a distant object is formed in front of retina (Fig. 12.9). This problem can be rectified by using concave lens. Hypermetropia (Long sight): It happens when eyeball shortens. Such persons are For a pilot, colour vision is essential so not able to see near objects clearly. The image is that he/she can recognize aircraft position formed behind retina (Fig. 12.9). Convex lens is used lights, light-gun signals, airport beacon, to rectify this problem. approach-slope indicators, and chart symbols, especially at night. A pilot must have the ability to perceive these colours necessary for the safe performance of his/her duties. 21 12. Coordination and Control eLearn.Punjab Figure 12.9: Myopia and hypermetropia Contributions of Muslim Scientists Ali ibn Isa (950 - 1012) was a famous Arab scientist. He wrote three books on ophthalmology (study of the diseases and surgery of eyes). He described 130 eye diseases and prescribed 143 drugs to treat these diseases. Ibn al-Haytham’s “Book of Ibn al-Haytham (965 - 1039), an Arab scientist, made Optics” has been ranked significant contributions to the principles of eye and vision. He alongside a book of Isaac is regarded as the father of optics (study of the behaviour of Newton. It is one of the most light). His “Book of Optics” correctly explained and proved the influential books ever written inmodern theory of vision. He discussed the topics of medicine the history of physics. and eye surgery in his book. He made several improvements to eye surgery and accurately described the process of sight, the structure of eye, image formation in eye and visual system. Ibn al-Haytham also described the principles of pinhole camera. 22 12. Coordination and Control eLearn.Punjab Practical: Study of the Bull Eye Get a real bull eye and study its longitudinal section (cut by the teacher) or study the model of bull eye. Identify different parts of the eye and draw a labelled diagram that would clearly show the sclera, choroid, retina, iris and lens. 12.3.2 Ear Hearing is as important as vision. Our ear helps us in hearing and also to maintain the balance or equilibrium of our body. Ear has three main parts i.e. external ear, middle ear, and internal ear. A- External Ear External ear consists of pinna, auditory canal and ear drum (tympanum). Pinna is the broad Owl is not able to see during day time. The external part, made of cartilage and covered reason for this is the deficiency of cones with skin. It helps to direct sound waves into which receive and sense the bright light. auditory canal. There are special glands in the But the presence of more rods gives it walls of auditory canal, which produce wax. The greater power of vision during night. All wax and the hairs in auditory canal protect ear animals that search for prey during night from small insects, germs and dust. In additions have this characteristic. to this, they help to maintain the temperature and dampness of auditory canal. Auditory canal ends in ear drum. This thin membrane separates external ear from middle ear. 23 12. Coordination and Control eLearn.Punjab Animation 12.11: Human Ear Source & Credit: leavingbio B- Middle Ear Middle ear is a chamber after external ear. Three small bones, called middle ear ossicles, are present in a chain in middle ear. These movable bones include malleus, incus and stapes. Malleus is attached with ear drum, then comes incus and finally stapes that is connected with a membrane called oval window. Oval window separates middle ear from inner ear. Middle ear also communicates with the nasal cavity through Eustachian tube. This tube regulates the air pressure on both sides of ear drum. Stapes is the smallest bone of the human body. 24 12. Coordination and Control eLearn.Punjab Figure 12.10: Structure of human ear C- Inner Ear Inner ear consists of three parts i.e. vestibule, semicircular canals and cochlea. Vestibule is present in the centre of inner ear. Three canals called semicircular canals are posterior to the vestibule. The cochlea is made of three ducts and wraps itself into a coiled tube. Sound receptor cells are present within the middle duct of cochlea. Figure 12.11: Structure of Inner ear To which part of ear the tympanum belongs? External Ear 25 12. Coordination and Control eLearn.Punjab The Process of Hearing The pinna of the external ear focuses and directs sound waves into auditory canal. The sound waves strike ear drum and produce vibrations in it. From ear drum, the vibrations strike middle ear and produce further vibrations in malleus, incus and then stapes. From stapes, the vibrations strike the oval window and then Image 12.1: Smallest bone reach the fluid-filled middle duct of cochlea. The fluid Source & Credit: lachicchattenoir.wordpress of cochlea is moved and receptor cells are stimulated. Hold the fingers of your palm close to The receptor cells generate a nerve impulse, which each other and place it behind the pinna. travels to brain and is interpreted as sound. Then concentrate on a particular sound continuously having the same frequency. Remove the palm and concentrate on the same sound again. Soundless world Deafness is a state in which hearing is not possible. The defect of ear drum, cochlea, middle ear ossicles, or auditory nerve may cause deafness. Infection in Eustachian tube may spread to middle ear too. Ear drum may be damaged by an infection in auditory A thunderstorm is characterized by the canal. Excessive noise, strong blows on cheek, presence of lightning and a thunder. pointed objects entering auditory canal and attack The lightning is caused by an electrical from insects may also affect hearing. charge due to the movement of water droplets or crystals carried by the wind. The sudden increase in pressure Ears maintain the Balance of Body and temperature from lightning Semicircular canals and vestibule help to maintain the produces rapid expansion of the air. balance of body. Semicircular canals contain sensory This expansion of air produces a sound nerves which can detect any movement of head. of thunder. The flash of lightening is Vestibule can detect any changes in the posture of followed after some seconds by a roar body. The neurons coming from these two receptors of thunder. This time difference is due to reach cerebellum through the auditory nerve. the fact that sound travels slower than light. 26 12. Coordination and Control eLearn.Punjab 12.4 Endocrine System The activities such as growth, reproduction, maintenance of glucose concentration in blood, reabsorption of water in kidneys etc. need to be regulated. Endocrine system performs this job. This system uses chemicals to “communicate” with its effectors. These chemicals are known as hormones. A hormone is a specific messenger molecule synthesized and secreted by an endocrine gland. These glands are ductless and release their secretions (hormones) directly into bloodstream. Blood carries the hormones to target organs or tissues, upon which they act. Many glands in our body are exocine. Such glands have ducts for releasing their secretions e.g. digestive glands, skin glands etc. 12.4.1 Important Endocrine Glands 1. Pituitary Gland It is a pea-shaped gland attached to the hypothalamus of brain. Many hormones (trophic hormones) of pituitary gland influence the secretions of other endocrine glands. However some hormones of this gland act directly on various tissues of body. There are two lobes of pituitary gland i.e. anterior lobe and posterior lobe. a. Anterior Lobe: It produces many hormones. One of its important hormones is somatotrophin (growth hormone). It promotes the growth of body. If the production of this hormone is diminished during growing age, the rate of growth decreases. This condition is called dwarfism. If this hormone is excessively produced during growing age, it leads to gigantism (very tall and overweight). If somatotrophin is excessively produced after growing age, internal organs and body extremities alone grow large. This condition is known as acromegaly. Such persons will have large hands, feet and jawbones. 27 12. Coordination and Control eLearn.Punjab Another important hormone secreted by the anterior lobe of pituitary gland is thyroid-stimulating- hormone (TSH). It stimulates thyroid gland to secrete its hormones. The remaining hormones of anterior lobe influence reproductive organs and also control adrenal glands. b. Posterior Lobe: The posterior lobe of pituitary gland stores and secretes two hormones i.e. oxytocin and vasopressin (antidiuretic hormone: ADH). These hormones are produced by hypothalamus (a part of brain). Vasopressin increases the rate of reabsorption of water from nephrons. When we have low amount of water in body fluids, pituitary gland secretes vasopressin and so more reabsorption of water occurs from nephrons into blood. In this way, body retains water and less amount of urine is produced. On the other hand, when body fluids have more than normal water, there is a decline in the secretion of this hormone. If pituitary gland does not secrete this hormone in the required amount, less water is reabsorbed from nephrons and there is excessive loss of water through urine. This condition is known as diabetes insipidus. The hormone, oxytocin stimulates the contraction of uterus walls in mothers for child birth. Moreover, this hormone is necessary for the ejection of milk from breast. The stepwise process of metamorphosis in many animals is controlled by hormones. Life activities such as cell division in invertebrates are also regulated by hormones. Hormones also control activities like migration in birds. Hormones have been identified even in unicellular organisms. 2. Thyroid gland This is the largest endocrine gland in human body. It is present in neck region, below larynx, and produces a hormone thyroxin. Iodine is required for the production of this hormone. If a person lacks iodine in diet, thyroid gland cannot make its hormone. In this condition, thyroid gland enlarges. This disorder is called goitre. Have you noticed that during summer, the urine output is low? Due to increased sweating, the water level of blood is lowered. As a result, pituitary gland releases more ADH into blood. 28 12. Coordination and Control eLearn.Punjab Our government encourages salt refiners to add iodine to salt. It also encourages people to choose this iodized salt. Thyroxin increases the break down of food (oxidation) and release of energy in body. It is also responsible for the growth of body. Hypothyroidism is caused by the under-production of thyroxin. It is characterized by low energy production in body and slowing down of heart-beat. Hyperthyroidism is caused by over-production of thyroxin. Its symptoms are increase in energy production, increased heart-beat, frequent sweating and shivering of hands. The thyroid gland produces another hormone called calcitonin. It decreases the level of calcium ions in blood and promotes the absorption of calcium from blood into bones. Calcitonin and parathormone complement each other and regulate the level of calcium ions in the blood. 3. Parathyroid glands These are four glands situated on the posterior side of thyroid gland. They produce a hormone known as parathormone. It increases the level of calcium ions in blood. When there is increased production of parathormone, more than normal calcium salts are absorbed from the bones and added to blood. Consequently the bones become brittle. If there is deficiency in the production of parathormone, blood calcium level falls. It leads to tetany, which affects the functioning of muscles. Tetany is marked by sharp flexion of the wrist and ankle joints, muscle twitching, cramps and convulsions. It is due to decreased blood calcium level which makes the nerves and muscles more excitable. 29 12. Coordination and Control eLearn.Punjab 4. Adrenal glands Two adrenal glands are situated above kidneys. Each adrenal gland consists of two parts. The outer part is cortex and the inner part is medulla. Adrenal medulla secretes a hormone called epinephrine or adrenaline in response to stress. It prepares our body to overcome emergency situations. Therefore, adrenaline is also termed as ‘emergency hormone’. The adrenal cortex secretes many hormones called corticosteroids which maintain the balance of salts and water in blood. When a person experiences fear, anger or anxiety, the rate and intensity of heartbeat increases, blood pressure increases, blood flow to the limbs increases, blood flow to the alimentary canal and skin is reduced. Such changes prepare the body to face any emergency situation. 5. Pancreas This organ has two functions. The major part of pancreas is a ducted (exocrine) gland. This portion secretes digestive enzymes, through a duct, into the small intestine. Some portions of pancreas serve as ductless (endocrine) gland. Activity: Write a paper on “The changes in the body while performing an exercise like running a 100 meter race This portion contains groups of endocrine cells referred to as islets of Langerhans. These islets secrete two hormones i.e. insulin and glucagon. Glucagon influences the liver to release glucose in blood and so the blood glucose concentration rises. Insulin influences the liver to take excess glucose from blood and so the blood glucose concentration falls.

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