IL Read the passage and then complete the given diagram. Tobacco is a plant. Cigarettes are made of dried tobacco leaves. When a cigarette is lighted. produces smoke. This cigarette smoke contains more than 4000 substances. Som them are known to cause canner while many others are harmful to our health. These substances can be grouped into tar, nicotine, carbon monoxide and irritants. Tar ar is a thick brown liquid which is a mixture of substances. It sticks to the inside of the lungs. This tar is the same substance used to surface roads! Tar damages cells in the lungs. This makes it difficult for oxygen to enter the blood Tar causes breathing problems such as bronchitis. Tar can cause lung cancer. Nicotine Nicotine is a poison. It passes easily from the lungsinto the blood. Nicotine is a habit-forming drug. It causes a smoker to become addicted to smoking. Therefore, smokers need to smoke more and more cigarettes to get enough nicotine. Nicotine can damage brain tissues. Nicotine can cause heart disease. Carbon Monoxide This is a very poisonous gas. It also comes out from the exhaust pipes of cars. Carbon monoxide makes it more difficult for the blood to absorb oxygen from th lungs. Therefore, a person who smokes must breathe harder to get enough oxyg This extra effort can damage the heart and cause heart disease. Carbon monoxide can also pass from a mother to her unborn baby. This affects growth of the baby. The baby can be born prematurely, be underweight or ever dead. It is also less likely to survive its first year of life Irritants Irritants are substances which irritate the lungs and damages the small air tubes in the lungs. They can cause smoker's cough and lung cancer.