30. Organisms like yeast do not use oxygen and incomplete break-down of glucose into ethanol, carbon dioxide and energy takes place. Such kind of respiration is referred to as anaerobic respiration.
31. Similarly, during vigorous exercise in our body muscles, anaerobic respiration takes place resulting in formation of lactic acid and energy. Accumulation of lactic acid causes muscle cramps.
32. Glycolysis - the first step in the break-down of glucose - a six-carbon molecule, into a three-carbon molecule called pyruvate. It is a common step for both aerobic and anaerobic respiration which takes place in the cytoplasm of cell.
33. However, the break-down of pyruvate in presence of oxygen takes place in mitochondria resulting in release of energy. Hence, mitochondria are also known as power-house of the cell.
34. The energy released during cellular respiration is used to synthesise, a molecule called ATP (Adenosine triphosphate) which is the energy currency of living organism.
35. Plants exchange gases through stomata by the process of diffusion. In plants, during night CO2 is released while during day time the CO2 released is used in photosynthesis, hence only O2 is released.
36. Animals have evolved different organs for the uptake of O2 and release of CO2. The organisms that live in water use the oxygen dissolved in water. Since the amount of oxygen in the water is fairly low compared to the amount of oxygen in the air, the rate of breathing in aquatic organisms is much faster than that seen in terrestrial organisms.
37. The respiratory system of all organisms have following features :
(Large, fine, delicate and thin surface area.
(ii) Respiratory surface should be richly supplied with blood capillaries.
(iii) There should be a provision for carrying oxygen to respiratory surface and carrying away CO2 from the respiratory surface. So respiratory surface m ust be permeable to respiratory gases.
38. In human beings, the air is taken into the body by nostrils. The air while passing through the nostrils is filtered by fine hairs that line the passage so that the air going into the body is free of dust and other impurities. The passage is also lined with mucus which helps in cleansing the air by trapping microbes.
39. From nostril, the air passes through pharynx into lungs via trachea. Incomplete C-shaped rings of cartilage are present in the trachea which ensure that the air-passage does not collapse when there is no air in it.
40. The trachea branches into bronchi and bronchioles in lungs which finally terminate in thin-walled, balloon-like structures called alveoli, where exchange of gases takes place as they have extensive network of blood-vessels.
41. When we breathe in air our chest cavity becomes larger. Contraction of external intercostal muscles pushes the rib cage outward and upward Diaphragm flattens. The volume chest cavity increases and pressure decreases. So the air rushes into the lungs through external nostrils. This process is referred as inspiration or inhalation.
42. During expiration or exhalation expulsion of foul air rich in carbon dioxide takes place. It is caused due to relaxation of inspiratory muscles. It pulls the rib cage inward. Diaphragm relaxes taking dome shape. Reduction in size of thoracic cavity causes compression of lungs.
43. In humans, a respiratory pigment haemoglobin is present in the RBC (Red Blood Corpuscles) which has a very high affinity for O2 and CO2. The upper respiratory tract i.e., trachea, bronchi and bronchioles have small hair-like cilia. These cilia help remove germs, dust etc. from inhaled air. Cigarette smoking destroys these cilia due to which all harmful substances enter into our lungs causing infections, cough and lung cancer.
44. Blood transports many substances like salts, vitamins, hormones, waste products. We thus need a pumping organ to push blood around the body. The transport system in human beings consist of heart, blood vessels (arteries, veins and capillaries) and circulatory fluid (blood and lymph).
45. The heart is a muscular organ which is as big as our fist. Amammalian heart is four-chambered. The upper chambers are called auricles or atria and lower chambers are referred as ventricles.
46. Double circulation occurs in humans. It refers to the passage of same blood twice through the heart to complete one cycle. The right side receives deoxygenated blood whereas the left chambers of the heart pump oxygenated blood. There is no intermixing of oxygenated and deoxygenated blood.
47. The oxygenated blood from lungs comes to left auricle through pulmonary veins.
48. Simultaneously, the deoxygenated blood comes to right auricle through two large veins, superior and inferior vena cava.
49. When the left and right atria contract, the oxygenated and deoxygenated blood reaches the respective ventricles.
50. Contraction of ventricles results in transfer of blood from them into lungs and various body parts. Left ventricle on contraction sends oxygenated blood to body through the largest artery Aorta. While the right ventricle pumps the blood into lungs for oxygenation through pulmonary artery
51. The walls of ventricle are thicker than auricle as they have to pump the blood into various body organs.
52. Valves present in between auricle and ventricle as well as at the opening of major arteries, and veins to check the backflow of blood.
53. In mammals and birds separation of the right side and left side of the heart is useful as it does not allow oxygenated and deoxygenated blood to mix. Hence, the heart is four-chambered in birds and mammals.
54. Amphibians and reptiles (except crocodiles, turtles) have three-chambered heart, two auricles and one ventricle.
55. Fishes have the two-chambered heart - one ventricle and one auricle. The blood is pumped into gills where it is oxygenated and supplied directly to body parts from gills. Thus blood goes only once through the heart.
56. Arteries are the vessels which carry oxygenated blood from the heart to the various organs of the body except pulmonary artery. Since the blood emerges from the heart under high pressure, the arteries have thick, elastic walls.
57. Veins collect deoxygenated blood from various organs and bring it back to the heart. They do not need thick walls, instead-they have valves that ensure the blood flows only in one direction i.e., from organs to heart except pulmonary vein.
58. On reaching an organ or tissue, the artery divides into small fine vessels to bring the blood in contact with all the individual cells. The smallest vessels are known as capillaries. Capillaries have walls which are one-cell thick, to allow the exchange of material between the blood and surrounding cells.
59. The capillaries then join together to form veins that convey the blood away from the organs or tissues back to the heart.
60. Blood pressure is the force that the blood exerts against the wall of a vessel. This pressure is much greater in arteries than in veins. Contraction of heart is termed as systole and relaxation of heart is called diastole. Blood pressure during systole is termed systolic pressure and during diastole, it is called diastolic pressure. The normal systolic pressure is 120 mm of Hg and diastolic pressure is 80 mm of Hg. The instrument used to measure blood pressure is called sphygmomanometer.
61. Lymph is a light yellow viscous fluid which is formed by passage of some fluid from blood capillaries into intercellular spaces in the tissues through the pores present in the walls of capillaries. Lymph is similar to the plasma of blood but contains very less protein.
62. Lymph is specialised to collect tissue secretions which cannot pass directly into blood e.g., hormones, plasma, proteins from liver, fats from intestine. It also carries waste products and drains excess fluid from extra cellular space back into the blood.
63. In plants, xylem transports minerals and water from roots to other parts of the plant while phloem transports food manufactured in leaves to other plant parts and storage organs.
64. Xylem tissue consists of four components : xylem vessels, xylem tracheids, xylem fibres and xylem parenchyma. Water and minerals are conducted from roots to other parts due to root pressure, transpirational pull and cohesion-adhesion forces.
65. The transport of soluble products of photosynthesis, amino acids and other substances through phloem is termed as translocation. Phloem is a complex tissue which has four types of elements - sieve tubes, companion cells, phloem parenchyma and phloem fibres. The translocation of food and other substances take place in the sieve tubes with the help of adjacent companion cells both in upward and downward directions. Material like sucrose is transferred into phloem tissue by using ATP.
66. The biological process involved in the removal of harmful metabolic wastes from the body is called excretion. Human excretory system includes a pair of kidneys, ureters, a urinary bladder and a urethera. Urine produced in the kidneys passes through the ureters into the urinary bladder where it is stored until it is released through the urethra.
67. Each kidney has a large number of filtering units called nephrons which are packed close to each other. Each nephron consists of a cup-shaped structure called Bowman’s capsule (containing a bunch of capillaries called glomerulus) convoluted tube and a collecting duct.
68. As the glomerular filtrate passes through the tubular part of nephron, useful substances like glucose, amino acids, mineral ions, water etc., are reabsorbed by blood capillaries surrounding the nephron. Kidney filters 180 L of blood everyday. However, the volume of urine excreted is only a litre or two a day because the remaining filtrate is reabsorbed by kidney tubules.
69. Kidneys perform two main vital functions :
(i) filtering the nitrogenous waste from the blood,
(ii) osmoregulation i.e., maintaining the right amount of water and ionic balance in the body.
70. Artificial kidney is used to filter the blood of a patient. The process of purifying the blood by the artificial kidney is called as haemodialysis.
71. Plants get rid of excess water by transpiration. Waste products in plants maybe stored in leaves, bark or any other plant part which can be shed off. In some plants the metabolic endproducts are stored in the form of crystals. Several plant products like resins and tannins are also planted wastes.